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Disentangling the effects of competition and climate on individual tree growth: A retrospective and dynamic approach in Scots pine

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... For instance, increasing tree size and density in a population imply an increase in space filling that may intensify competitive interactions among neighbouring individuals (Yoda et al. 1963;Jump et al. 2017). Furthermore, temporal fluctuations in the environment can modify the interactions between neighbouring tree individuals (Biondi 1996;Travis et al. 2005), thereby affecting their competitive ability (Weber et al. 2008;Sánchez-Salguero et al. 2015;Aakala et al. 2018). Understanding how competition evolves over time is therefore essential to evaluate how forest functioning might be compromised under changing environmental conditions. ...
... Intraspecific competition has been particularly observed when the abiotic stress gradient is driven by water resources (Maestre et al. 2009). Increased aridity may promote more intense tree-to-tree competitive interactions than in other, non-water limited areas (Zavala and Bravo de la Parra 2005), particularly in tree populations subjected to xeric conditions (Hampe and Petit 2005;Sánchez-Salguero et al. 2015). One of the most drought-vulnerable species in Mediterranean forests is Scots pine (Pinus sylvestris L.) (Martínez-Vilalta et al. 2008;Camarero et al. 2015a, b). ...
... Scots pine was found to be subject to higher competition in dry years by Weber et al. (2008) when studying competitive dynamics of pines and oaks over time in Valais (Switzerland). Other studies also found tree growth and competition effects to be highly dependent on local climatic conditions (Gómez-Aparicio et al. 2011;Sánchez-Salguero et al. 2015;Madrigal-González et al. 2016). In that sense, drought constraints on growth are particularly important in the southernmost dry limits of the tree species distribution (Hampe and Petit 2005;Sánchez-Salguero et al. 2016). ...
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Key message Competitive interactions change over time and their influence on tree growth is intensified during drought events in marginal Scots pine populations. Abstract Competition is a key factor driving forest dynamics and stand structure during the course of stand development. Although the role neighbourhood competition on stand dynamics has received increasing attention, the response of competition to environmental fluctuations and stand development remains poorly explored. We evaluated changes in competition during stand development in a dry-edge Scots pine relict population located in Central Spain. Typically, tree-to-tree interactions have been investigated through static competition measurements, which usually lack the temporal variation associated to natural forest development and environmental conditions. Here, we assessed how individual and neighbourhood components of competition evolved along a 35-year period, and we related competition dynamics to population structure and drought levels. On six plots, 508 trees were mapped and diameters at breast height (DBH) were measured. Two increment cores were taken from target trees to derive basal area increment (BAI), and neighbourhood was reconstructed back to 1980. Results provide insights into inter-annual variability in competition effects and their role on tree radial growth depending on climatic conditions. From the year 2005 onwards, both individual and neighbourhood components of competition showed a decoupled pattern over time. This effect was particularly pronounced during the extreme drought in 2012, in which the individual component decreased, whereas the neighbourhood component increased. In addition, climatic variability modulated the competition effects during stand development. This approach of evaluating competition dynamics proves to be promising for studying forest stand development and the influence of climate impacts on tree populations subjected to xeric conditions.
... The impact of climate-induced oak dieback can be also modulated by other extrinsic (e.g., soil conditions, microclimate) and intrinsic (e.g., tree height, competition) factors (McDowell et al., 2008;Colangelo et al., 2017aColangelo et al., , 2017b. However, it remains to be answered to what degree past uses legacies, which determine recent tree-to-tree competition (e.g., Sánchez-Salguero et al., 2015), trigger long-term climate sensitivity and contrasting vulnerability to climate warming trends in cooccurring oak trees showing different canopy dieback after droughts. Recent research has provided evidence that drought sensitivity of temperate forests depends partly on how selective cutting or coppicing treatments changed the natural structure of the stands (e.g., Buckley, 1992;Mausolf et al., 2018;Sangüesa-Barreda et al., 2015). ...
... The threshold radius above which neighbors were regarded as not competing was estimated to be 5 m following Petritan et al. (2017). This competition index has been previously used in tree-ring studies focused on growth-management associations (see Sánchez-Salguero et al., 2015). ...
... The divergent growth pattern after 1980s of living and dead trees in both forests, as well the weaker sensitivity of the dead and living trees of old-growth forest compared with those from managed forests suggest that the management legacies, but probably also the regeneration type (generative or vegetative), are important factors driving the climate sensitivity of sessile oak. It was already shown that past management practices could influence the tree growth response to climate trough legacy effects on the stand structure and changes in stand microsite conditions (Camarero et al., 2011;Latif and BlackBurn, 2010;Rozas, 2015;Sánchez-Salguero et al., 2015). Stojanović et al. (2017) found also that coppiced sessile oak trees have a higher sensitivity to summer temperature and water balance of the current year that high forest trees, originated from seed, and came to the conclusion than coppice forest will be highly vulnerable to further warmer and drier conditions. ...
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Climate warming-related drought could become a major driver of large-scale forest dieback. However, little is known about how past management legacies modulate the climate-growth responses during recent dieback episodes in central European oak forests. Here, we examine the role played by past management –unmanaged old-growth vs. managed forests– in recent tree mortality events occurring in Quercus petraea (Matt.) Liebl. stands across large areas of western Romania. We analyze how stand structure (tree size, competition) and climatic factors (drought, temperature and precipitation) drive tree radial growth patterns in neighboring standing dead and living trees. We analyzed basal area increments (BAI) trends, past management legacies and climate- and drought-growth relationships during the 20th century to distinguish the roles and interactions on recent warming-induced dieback. We observed that temperature rises and changes in atmospheric water demand during growing season let to increasing drought stress during the late 20th century affecting both managed and unmanaged forests. Dead trees from old-growth and managed forests showed lower growth than living trees after dieback onset. In both forests, dead and living trees displayed divergent growth patterns after dry 1980s, indicating that dieback was triggered by severe extreme conditions. Dead trees from managed stands experienced significant stronger growth reductions after 1980s though they experienced less tree-to-tree competition than dead trees in old-growth forest. High stand density negatively drove growth and enhanced climate sensitivity in old-growth stands. Competition acted synergistically with climate warming and drought causing tree mortality regardless of the management legacies in of Q. petraea forests. Our retrospective assessment of growth rates in relation with climate and structure changes offers valuable information for further forest conservation and management decisions of Q. petraea forests. These findings highlight the importance of past uses legacies driving recent forest dieback in temperate oak forests, making them more vulnerable under forecasted climate-warming related droughts in central Europe.
... Different access of individual trees to the available resources (e.g., light, moisture, nutrients) leads to the formation of forest stands with a gradient in their structure, from dominant to suppressed trees (Linares et al., 2010;Peet and Christensen, 1987), affecting tree growth rate (Liu et al., 2018;Martin-Benito et al., 2011) and climate sensitivity (Johnson et al., 2017;Rozas and Olano, 2013;Sánchez-Salguero et al., 2015). Inter-tree competition results in growth decline and high mortality rates of suppressed individuals (Castagneri et al., 2008;Linares et al., 2010), but at the same time, suppressed trees can reach the canopy after dominant trees decease. ...
... Dominant and suppressed trees usually differ in their climate response (Castagneri et al., 2008;Cherubini et al., 1998;Liu et al., 2018;Sánchez-Salguero et al., 2015;Zang et al., 2012). This discrepancy reflects differences in microclimate conditions as well as in the access to light and resources establishing a gradient between trees (Laskurain et al., 2018;Rozas, 2014;Rozas and Olano, 2013). ...
... For example, tree size and canopy structure determine a gradient in sunlight availability within the forest stand (Thomas and Winner, 2002). In contrast, competition for water and nutrients between neighboring trees is more complex (Sánchez-Salguero et al., 2015), albeit dominant trees might benefit from their higher carbohydrate production to expand their root system and maintain a broader mycorrhizal community (Nehls, 2008). Literature (e.g., Kirdyanov et al., 2018;Laskurain et al., 2018;Rozas and Olano, 2013) suggests a stronger climate sensitivity in dominant trees with higher growth rates, which has been explained as the capacity of dominant trees to sustain higher rates of growth during favorable climatic windows thanks to their higher carbohydrates reserves (von Arx et al., 2017). ...
Article
Climate change affects forest dynamics with potential consequences for essential ecosystem services. The retrospective analysis of secondary growth unveils the effect of climate on forests. However, most tree-ring studies focus on dominant trees, and less is known about the climatic response of their neighbor suppressed trees. We evaluated the influence of tree social status (dominant/suppressed) on climate response in Pinus sylvestris L. trees from two sites with contrasting water availability conditions in the forest-steppe ecotone in southern Siberia. Tree-ring width and intra-annual density fluctuations (IADFs) were used as proxies. Late spring to early summer conditions were the main climate drivers in both tree social status, but the climate response of suppressed trees was stronger and had a longer time window (May-June). IADFs’ occurrence was controlled by temperature and its frequency was modulated by local conditions, being more common at the dry site, with tree status just marginally significant. Our results suggest that under the projected warmer and drier climate, suppressed trees in southern Siberia will be prone to increased water shortage, leading to possible higher mortality of more sensitive suppressed trees, with potential consequences for carbon sequestration in the forest-steppe ecosystems in southern Siberia.
... On the other hand, tree ring chronologies used to assess the climate forcing of tree growth generally exclude tree competition or species interaction (Büntgen et al., 2007). Some studies have shown tree growth sensitivity to climate, increasing with decreasing competition intensity (Sánchez-Salguero et al., 2015), so studies based only on a dendrochronological approach may not be adequate to estimate tree-level growth. Processbased models are generally considered powerful tools to improve understanding of the processes that regulate forest ecosystems, as they are based on the description of cause-effect relationships. ...
... However, their predictions may be not necessarily accurate or biased (Larocque, 2018) at typical management scales in comparison to traditional empirical approaches (Calama et al., 2019). Therefore, competition and tree-level climate-growth sensitivity should be explicitly taken into account (Sánchez-Salguero et al., 2015). However, the combination of climate and competition structures in tree-growth models remains scarce (Calama et al., 2019;Sánchez-Salguero et al., 2015), and is rarer still in studies of mixed stands (González de Andrés et al., 2018;Houtmeyers and Brunner, 2020;Manso et al., 2014a;Mina et al., 2018;Navarro-Cerrillo et al., 2020;Schwarz and Bauhus, 2019). ...
... Therefore, competition and tree-level climate-growth sensitivity should be explicitly taken into account (Sánchez-Salguero et al., 2015). However, the combination of climate and competition structures in tree-growth models remains scarce (Calama et al., 2019;Sánchez-Salguero et al., 2015), and is rarer still in studies of mixed stands (González de Andrés et al., 2018;Houtmeyers and Brunner, 2020;Manso et al., 2014a;Mina et al., 2018;Navarro-Cerrillo et al., 2020;Schwarz and Bauhus, 2019). In this study, we go one step further and use annual weather information and spatial competition structures to model species-specific growth. ...
Article
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Mixed forests are suggested as a strategic adaptation of forest management to climate change. Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) are tree species of high economic and ecological value for European forestry. Both species coexist naturally in a large part of their distributions but there is a lack of knowledge on the ecological functioning of mixtures of these species and how to manage such stands. This paper analyses these species' intra-and inter-specific competition, including size-symmetric vs. size-asymmetric competition, and explore the effect of weather conditions on tree growth and competition. We studied basal area growth at tree level for Scots pine and Norway spruce in mixed versus pure stands in 22 triplets of fully-stocked plots along a broad range of ecological conditions across Europe. Stand inventory and increment cores provided insights into how species mixing modifies tree growth compared with neighbouring pure stands. Five different competition indices, weather variables and their interactions were included and checked in basal area growth models using a linear mixed model approach. Interspecific size-asymmetric competition strongly influenced growth for both tree species, and was modulated by weather conditions. However, species height stratification in mixed stands resulted in a greater tree basal area growth of Scots pine (10.5 cm 2 year − 1) than in pure stands (9.3 cm 2 year − 1), as this species occupies the upper canopy layer. Scots pine growth depended on temperature and drought, whereas Norway spruce growth was influenced only by drought. Interspecific site-asymmetric competition increased in cold winters for Scots pine, and decreased after a drought year for Nor-way spruce. Although mixtures of these species may reduce tree size for Norway spruce, our results suggest that this could be offset by faster growth in Scots pine. How inter-specific competition and weather conditions alter tree growth may have strong implications for the management of Scots pine-Norway spruce mixtures along the rotation period into the ongoing climate change scenario.
... 10]. Previous studies have also reported increasing diameter growth with thinning and reduced inter-individual competition in Scots pine [51,52,[95][96][97][98], sessile oak [18,99,100], and ponderosa pine [16,51,56,[101][102][103][104][105][106]. Stand density reductions can improve the growth of remaining trees by release from inter-individual competition for above and belowground resources, such as light, water, and nutrients [19,26,40], and are therefore often used as a silvicultural measure to maximize diameter growth and tree value on relatively short rotation [10]. ...
... Mean tree growth sensitivity, measured here as the coefficient of variation of the detrended index series, was estimated to be 23% greater for Scots pine trees in low stand density environments as compared with fully stocked stands ( Figure 2). This general response of growth sensitivity to reduced stand density was also observed by Sánchez-Salguero et al. [98], who reported a higher growth responsiveness to climate under low competition levels for Scots pine along an altitudinal gradient in Spain. Correspondingly, Guillemot et al. [11] found higher inter-annual growth sensitivity with increasing thinning intensity of Atlas cedar (Cedrus atlantica (Endl.) ...
... In the case of ponderosa pine, growing under chronically water stressed conditions with a more irregular seasonal water supply and a higher frequency of drought events, water can be seen as the principle limiting factor for tree growth. Here, larger trees in the more heavily thinned stands may suffer more from hydraulic constraints and water/nutrient limitations may become more important [98,112]; competition for below-ground resources might be higher due to larger average tree size and associated root systems. Growth sensitivity of sessile oak was not significantly influenced by stand density, which might indicate that inter-individual competition for resources was comparatively low under average growing conditions. ...
Article
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A higher frequency of increasingly severe droughts highlights the need for short-term measures to adapt existing forests to climate change. The maintenance of reduced stand densities has been proposed as a promising silvicultural tool for mitigating drought stress. However, the relationship between stand density and tree drought susceptibility remains poorly understood, especially across ecological gradients. Here, we analysed the effect of reduced stand density on tree growth and growth sensitivity, as well as on short-term drought responses (resistance, recovery, and resilience) of Scots pine (Pinus sylvestris L.), sessile oak (Quercus petraea (Matt.) Liebl.), and ponderosa pine (Pinus ponderosa Douglas ex C. Lawson). Tree ring series from 409 trees, growing in stands of varying stand density, were analysed at sites with different water availability. For all species, mean tree growth was significantly higher under low compared with maximum stand density. Mean tree growth sensitivity of Scots pine was significantly higher under low compared with moderate and maximum stand density, while growth sensitivity of ponderosa pine peaked under maximum stand density. Recovery and resilience of Scots pine, as well as recovery of sessile oak and ponderosa pine, decreased with increasing stand density. In contrast, resistance and resilience of ponderosa pine significantly increased with increasing stand density. Higher site water availability was associated with significantly reduced drought response indices of Scots pine and sessile oak in general, except for resistance of oak. In ponderosa pine, higher site water availability significantly lessened recovery. Higher site water availability significantly moderated the positive effect of reduced stand density on drought responses. Stand age had a significantly positive effect on the resistance of Scots pine and a negative effect on recovery of sessile oak. We discuss potential causes for the observed response patterns, derive implications for adaptive forest management, and make recommendations for further research in this field.
... Further, droughtinduced growth declines may trigger mortality (Allen et al., , 2010Bigler et al., 2007;Cailleret et al., 2017;DeSoto et al., 2020;Pedersen, 1998), especially when resources are already limited by competition (Bradford and Bell, 2017;Young et al., 2017). The effects of competition and climate on tree growth may interact dynamically and depend, in part, on species interactions (Gómez-Aparicio et al., 2011;Marqués et al., 2021;Pretzsch et al., 2013;Sánchez-Salguero et al., 2015). Few studies have directly examined the effects of competition on tree growth under prolonged and severe drought conditions (except see Vernon et al. 2018). ...
... For each subject tree, the Hegyi index was calculated separately using Douglas-fir competition and oak competition. We evaluated the optimality of various competition radii lengths and found that Hegyi indices using the full radius of 15 m correlated best with BAI for both species (Pearson correlation coefficient; Sánchez-Salguero et al., 2015). As a comparison to species-specific competition indices, we also summed competition for each subject tree ("total competition") and calculated the percent of total competition from Douglas-fir (see Appendix B for supplementary analyses). ...
... Interestingly, the best drought resistance models for Oregon white oak included a positive relationship with oak competition. High competition may reduce, cancel out, or mask climate effects (Sánchez-Salguero et al., 2015) and can induce phenotypic structural changes (such as increased proportion of latewood) that aid in drought resistance (Carnwath et al., 2016). In our study system, the beneficial effect of oak competition on drought resistance could relate to subsurface resource sharing by neighboring trees, as some oaks grow in a multistem habit with a shared root system. ...
Article
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Oregon white oak (Quercus garryana Douglas ex Hook.) is experiencing increasing competition from Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) across much of its range at the same time as climate variability is increasing, including more frequent and extreme droughts. These combined factors suggest that Douglas-fir encroachment is not only leading to range reduction from competition, but also likely exacerbating drought stress for a keystone oak species in the Pacific West of North America. Our research examines this by evaluating radial tree growth and drought response in Oregon white oak (n = 104 trees) and Douglas-fir (n = 104 trees) along a gradient of encroachment in an oak woodland in the North Coast region of California. Linear mixed-effects models were used to evaluate the effects of tree diameter, Douglas-fir competition, oak competition, and climate on drought resistance (2013–2015) and recent tree growth (2002–2016). Oregon white oak growth was more resistant to prolonged drought than Douglas-fir. However, Oregon white oak drought resistance declined with increasing Douglas-fir competition and increased with increasing oak competition. Oregon white oak and Douglas-fir growth related to different seasonal climate factors, but both species were more strongly limited by Douglas-fir competition than climate. Oregon white oak may be better suited to future climate conditions than Douglas-fir, although Douglas-fir encroachment will likely continue to reduce Oregon white oak resistance to future drought. These results present a strong case for the need to release Oregon white oak by controlling Douglas-fir in areas that were historically oak woodlands with diverse understory species, wildlife, and important traditional ecological values and services.
... Our results are in line with the greater sensitivity to drought of gymnosperms, also in terms of lasting drought legacies (Anderegg et al. 2015, which is also supported by their greater drought vulnerability (Appendix S1 : Fig. S4). However, the spatial gradient in water availability can induce strong changes in growth responses to climate (Lebourgeois et al. 2012) and drought (Gazol et al. 2017a, 2017b, Sánchez-Salguero et al. 2015. The relatively frequent presence of drought-tolerant gymnosperms in the driest south-eastern Spanish Iberian regions (where droughts are more common and intense as e.g., Pinus halepensis) and the prevalence of productive angiosperms in the wettest regions (less impacted by drought, Gazol et al. 2018 and see Fig. 1 and Fig. 2) might be determining the greater drought vulnerability in gymnosperms than angiosperms. ...
... At smaller scales, local factors influencing tree growth might play a more relevant role masking the regional drought signal (Tardif et al. 2003, Caminero et al. 2018. Thus, part of the relationship between tree and forest growth might be due to local variations in key drivers of tree responses to drought such as microsite, topography or soil conditions that can differ across species (Camarero et al. 2017, Sánchez-Salguero et al. 2015, Gazol et al. 2017a, b, 2018, and between populations within the same species (Linares and Tiscar 2011, Gazol et al. 2017a, Sánchez-Salguero et al. 2018, Sangüesa-Barreda et al. 2019, Serra-Maluquer et al. 2019). ...
... evaluating tree and growth relationships with data derived from complete samplings of tree populations along altitudinal gradients (e.g. Sánchez-Salguero et al. 2015), are required to further understand the scalability from individual trees to forest stands. The dendrochronological sampling of trees in NFI plots along environmental gradients may provide complementary information on forest dynamics and tree growth and allow testing if tree-ring records are related to other stand characteristics such as changes in density or regeneration. ...
Article
Tree‐ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes in forest dynamics. Here, we related tree‐ring growth chronologies and stand‐level forest changes in basal area from two independent datasets to test if tree‐ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree‐ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981‐2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index (SPEI), and their impacts on tree growth by quantifying tree‐ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought‐prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought‐induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought‐prone gymnosperm forests we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought‐induced growth reductions and their cumulative impacts have strong potential to be used as early‐warning indicators of regional forest vulnerability.
... Zhang et al. (2015) found that competition rather than climate was the primary factor causing boreal forest trees mortality and recruitment in western Canada. Sánchez-Salguero et al. (2015) revealed that competition rather than climate affected the tree growth of intensively managed scots pine (P. sylvestris) along an altitudinal gradient in central Spain. ...
... The R-squares of full linear models with both competition and climate (0.55 and 0.44 for SEG and NG respectively) were higher than the marginal R-squares (0.45 and 0.26) but lower than the conditional R-squares (0.69 and 0.49), indicating that the climates partly explained the random effects. The higher relative contributions of competition than that of climate for both SEG and NG indicated that competition was the major factor in affecting trees radial growth, which also have been found in other areas (Gómez-Aparicio et al., 2011;Sánchez-Salguero et al., 2015). From southeastern region to northern region, the relative effect of competition decreased while the effect of climate increased. ...
... While in northern region, trees were more sensitive to climate factors (October sunshine duration) than in southeastern region (September precipitation), which makes the relative importance of climate increase from southeast region to north region. This has been confirmed that different competition levels changed the sensitivity of trees to climate (Linares et al., 2010;Martinbenito et al., 2011;Sánchez-Salguero et al., 2015). ...
Article
It is critical to investigate the effects of competition and climate on forest growth as they are main forces affecting forest dynamics. However, in subtropics of China such a study has never been conducted. Here we conducted a pioneer study to evaluate the effects of competition and climate on growth of Chinese red pine (Pinus massoniana) in mixed forests of subtropical China along a broad latitudinal gradient (23°N∼32°N). Twenty-three plots (20m × 20m) were randomly selected from 11 sites and competition and tree radial growth data were collected. Principal component analysis (PCA) was used to detect the potential spatial pattern in site-specific standard tree-ring chronologies during the common period (1990-2015). The linear mixed-effect models (LMMs) were employed to quantify the relationships between cumulated basal area increment (5, 10, 15, 20 and 25 years) of subject trees and six distance-independent competition indices. The relationships between tree radial growth and climate were evaluated by response analyses. Finally the best predicted competition index and climate factor were employed in a full model and their relative importance were calculated. The PCA results allowed classifying the mixed forests into southeastern and northern groups along the Nanling Mountains and Wuyi Mountains. LMMs results revealed that competition pressures mainly come from density and size of larger individuals. Response coefficients demonstrated that precipitation in September and sunshine duration in October influenced trees radial growth of southeastern group and northern group respectively. Our results clearly showed that effects of competition on tree radial growth decreased from southeast to north while effects of climates increasing over this large spatial scale. This is the first attempt to clarify the effects of competition, and further quantify the contributions of competition and climate on tree radial growth in China subtropics. Our finds will certainly contribute to a better policy-making for sustainable forest management.
... For example, North American pine trees with a history of strong competition were predisposed to growth decline, and sometimes death, with the addition of short-term climatic stress, such as an unusually hot summer [17,18]. Tree species [19], crown-class [12], size [20], and exposure to tree-to-tree competition [21] may all influence the growth response of trees when they are exposed to changes in climate [22]. Tree-to-tree competition influences the growth rate of trees by modifying access to resources, such as water, nutrients and sunlight [23,24]. ...
... Evidence from a southern temperate eucalypt forest indicated that competition had a much greater explanatory effect than climate on diameter growth, and that competition effects were strongest at the most productive sites [46]. This suggests that in temperate eucalypt forests, competition could be most important when other factors do not limit growth, as quantified in other forest types [21]. ...
... The negative competition effect on stem growth was most evident when growth rates were greatest and climate conditions were favourable for growth. This is in accordance with studies from other forest types, where tree stem growth was more responsive to competition when other factors, such as climate, were not limiting [21,79]. ...
Article
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Insights on tree species and competition effects on seasonal stem growth is critical to understanding the impacts of changing climates on tree productivity, particularly for eucalypts species that occur in narrow climatic niches and have unreliable tree rings. To improve our understanding of climate effects on forest productivity, we examined the relative importance of species, competition and climate to the seasonal stem growth of co-occurring temperate eucalypts on the tree productivity of temperate eucalypts. We measured monthly stem growth of three eucalypts (Eucalyptus obliqua, E. radiata, and E. rubida) over four years in a natural mixed-species forest in south-eastern Australia, examining the relative influences of species, competition index (CI) and climate variables on the seasonal basal area increment (BAI). Seasonal BAI varied with species and CI, and was greatest in spring and/or autumn, and lowest in summer. Our study highlights the interactive effects of species and competition on the seasonal stem growth of temperate eucalypts, clearly indicating that competitive effects are strongest when conditions are favourable to growth (spring and autumn), and least pronounced in summer, when reduced BAI was associated with less rainfall. Thus, our study indicates that management to reduce inter-tree competition would have minimal influence on stem growth during less favourable (i.e., drier) periods.
... According to our BAI models (Table 4), the increase in competition following the cessation of forest management is the most important factor related with the negative growth trend of Q. petraea and Q. pyrenaica, although climate also explained some of the Q. petraea growth decline (Figs. 3 and 8b). These results are concordant with previous works, where highfrequency growth changes are related to climate, while radial growth is explained by the size and competition (Sánchez-Salguero et al. 2015;Liang et al. 2019). Indeed, competition among trees may cause much larger reductions in forest growth and carbon uptake than climate stress (Vayreda et al. 2012;Rozas 2014). ...
... Changes in tree-to-tree competition must be considered in order to understand long-term changes in growth and forest dynamics since they may be more relevant than climate to forecast changes in forest composition and dynamics (Sánchez-Salguero et al. 2015). In addition, changes in competition can drive or modulate the responses of tree growth and functioning (e.g., water-use efficiency) to climate (Linares et al. 2010;Martín-Benito et al. 2011;Fernández-de-Uña et al. 2015;González de Andrés et al. 2018). ...
Article
Context: In recent decades, two major factors have influenced tree growth in many forests: climate warming, which is associated with aridification and negative growth trends in many Mediterranean forests, and abandonment of forest management, resulting from forest policy in conjunction with rural depopulation in Europe, often leading to an increase in competition and a decrease in growth. Aims: Here we study growth trends in a mixed forest of Fagus sylvatica, Quercus petraea and Quercus pyrenaica, where the abandonment of traditional uses in the 1960s has been followed by an increase in tree density. In this forest, both F. sylvatica and Q. petraea reach their south-westernmost limits of distribution. Methods: Using dendrochronological methods and growth modeling, we assess the importance of climate warming on the shifts in competitive growth advantage of these three coexisting tree species and the relative importance of climate and competition on growth trends. Results and conclusions: Q. petraea and especially F. sylvatica, showed favorable evolution of their competitive capacity, despite the increase in temperatures that has occurred in the area in recent decades. F. sylvatica presented the lowest sensitivity to climate. Under the current climate and forest structure conditions, competition is the most limiting factor on tree growth for the two oak species.
... Tree growth and stand structure are affected by numerous exogenous and endogenous factors, including disturbances of various types, frequencies, durations, spatial extents, and intensities. Many authors consider climate and tree-to-tree competition to be major factors driving tree growth and, thus, forest dynamics (Coomes and Allen, 2007;Kunstler et al., 2011;Lebourgeois et al., 2014;Sánchez-Salguero et al., 2015;Luo et al., 2017). Tree growth is generally limited by intense competition for resources such as light, water, and nutrients (Peet and Christensen, 1987;Das et al., 2011;Sánchez-Salguero et al., 2015). ...
... Many authors consider climate and tree-to-tree competition to be major factors driving tree growth and, thus, forest dynamics (Coomes and Allen, 2007;Kunstler et al., 2011;Lebourgeois et al., 2014;Sánchez-Salguero et al., 2015;Luo et al., 2017). Tree growth is generally limited by intense competition for resources such as light, water, and nutrients (Peet and Christensen, 1987;Das et al., 2011;Sánchez-Salguero et al., 2015). Trees of different sizes, species, and canopy status compete differently for resources within forest stands (Peet and Christensen, 1987;Orwig and Abrams, 1997;Das et al., 2011). ...
Article
Our study analyzes the growth response (release or suppression) of Norway spruce trees growing along a landslide zone in eastern Czech Republic. A total of one hundred and eighty-six increment cores were extracted from Norway spruce (Picea abies (L.) Karst.) individuals, which were affected by two different disturbances, the Girová landslide in May 2010 and an anthropogenic cut-off in the neighborhood of the landslide later the same year. Growth changes were analysed in three zones that were defined according to the type of effect the disturbance had on the surrounding vegetation. The aims of our study are to (i) detect growth changes in trees that survived the disturbances in 2010, (ii) evaluate the delay time of the growth reaction to the disturbances, (iii) compare how growth changes differed in response to the two different disturbance types (natural landslide vs. anthropogenic harvesting and deforestation), and (iv) investigate spatio-temporal differences in the growth changes. Our results indicate that tree growth changed in response to the altered environmental conditions following the 2010 disturbances. The changes vary depending on the intensity of the disturbance and its effect on the forest stand. Trees in Zone 1 responded with a slight growth release (14.6 % of responding trees), which was strongest after 2013. However, growth suppression (85.4 %) was the dominant reaction in Zone 1; with the majority of trees showing growth suppression in 2014, four years after the events. The strongest and most abrupt growth release (66.1 %) occurred in Zone 2 in 2011, after a one-year delay. Since 2010, we have observed a trend of growth suppression (33.9 %) in this zone. In Zone 3, following a one-year delay, growth release has occurred gradually in about a third of the trees (37.0 %). The majority of trees in this zone have responded with growth suppression (63.0 %) in 2010 and with a three-year delay after 2013. We also found differences in how tree growth responds to anthropogenic and landslide disturbances, as well as spatio-temporal differences related to the extent of post-disturbance changes.
... They have a low ability to acquire extra resources and low growth potential (Bréda et al. 1995), decreasing their capacity to respond to water availability (weak climate response) ). On the other hand, dominant trees (i.e., trees with a higher relative tree size) are seldom limited by light availability (Sánchez-Salgueroa et al. 2015) and have faster growth rates but may also be more vulnerable to variation in climatic conditions than suppressed individuals. ...
... On the other hand, the study of Gea-Izquierdo et al. (2009) led in Quercus ilex showed that highdensity stands responded to similar climatic factors as lowdensity stands, but their response was generally weaker. Concerning the social status, results appeared also highly contrasted with a stronger climatic effect on dominant trees (Olivar et al. 2012;Sánchez-Salgueroa et al. 2015), no clear difference between social classes (Meyer and Bräker 2001) or differences depending on stand basal area . Similar various results have been observed for studies dealing with tree size (i.e., raw diameter classes) (Castagneri et al. 2012;Mérian and Lebourgeois 2011a, b;Zang et al. 2012). ...
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Key message Decreasing stand density increases resistance, resilience, and recovery of Quercus petraea trees to severe drought (2003), particularly on dry sites, and the effect was independent of tree social status. ContextControlling competition is an advocated strategy to modulate the response of trees to predicted changes in climate.AimsWe investigated the effects of stand density (low, medium, high; relative density index 0.20, 0.53, 1.04), social status (dominant, codominant, suppressed), and water balance (dry, mesic, wet; summer water balance − 182, − 126, − 96 mm) on the climate-growth relationships (1997–2012) and resistance (Rt), resilience (Rs), and recovery (Rc) following the 2003 drought.Methods Basal area increments were collected by coring (269 trees) in young stands (28 ± 7.5 years in 2012) of sessile oak (Quercus petraea) in a French permanent network of silvicultural plots.ResultsWe showed that the climate-growth relationships depend on average site-level water balance with trees highly dependent on spring and summer droughts on dry and mesic sites and not at all on wet sites. Neither stand density nor social status modulated mean response to climate. Decreasing stand density increased Rt, Rs, and Rc particularly on dry sites. The effect was independent of tree social position within the stand.Conclusion Reducing stand density mitigates more the effect of extreme drought events on drier sites than on wet sites.
... Competition may be high in old-growth forests because available space may become utilized more completely than in younger stands where trees may not have grown large enough to exploit all available resources [2,3]. Competition may suppress or alter climatic response [4,5], creating the potential for a different relationship between competition and climate in old-growth forests than in early and mid-successional forests. ...
... As an example, European beech (Fagus sylvatica L.) is sensitive to water balance when under strong competition, but it is most sensitive to temperature at low competition [8]. Several studies indicated that climate sensitivity is low under strong competition [4,5]. Nevertheless, utilization of consumable resources such as soil water may be high under conditions of high competition and, therefore, higher sensitivity to annual precipitation might be anticipated [9]. ...
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Research Highlights: We applied neighborhood and dendro-ecological methods in a stand with a 33-year record of forest dynamics, finding that growth will decrease for several species under predicted climate trends. Background and Objectives: Conventional tree-ring analysis removes the influence of competition and size on growth, precluding assessment of the relative influence of these factors. An old-growth eastern hemlock forest in east–central New York was mapped in 1978 and was measured at eight-year intervals since then. Our objective was to use these data to examine the influence of climate, neighborhood, and tree size on radial growth. Materials and Methods: We evaluated an array of climatic indices to find which ones had the strongest influence on radial growth from increment cores of eastern hemlock (Tsuga canadensis L.), yellow birch (Betula alleghaniensis Britton), and sugar maple (Acer saccharum Marsh.). We used the strongest climatic indices in combination with neighborhood and target-tree size information to create growth models for the three tree species. Results: Size accounted for 2% to 21% of observed growth; the shade-tolerant sugar maple and eastern hemlock grew fastest when large, but the mid-tolerant yellow birch grew fastest when small. Competition accounted for 9% to 21% of growth; conifers had a weaker competitive effect than deciduous trees, and eastern hemlock was less sensitive to competition than sugar maple and yellow birch. Climate accounted for only 2% of growth variation; eastern hemlock showed a positive response to warming climate trends, but yellow birch and sugar maple showed negative responses. Conclusions: Predicted climate trends are likely to result in decreased growth of sugar maple and yellow birch, and the sensitivity of these species to competition suggests the effect will be exacerbated when they grow in crowded conditions.
... P. pinaster growth was less synchronous when growing mixed with P. pinea (Table 4, B), which implies that species mixing reduces its dependence on climate variation. This fact highlights the importance of competition-facilitation processes to mitigate climate effect (Sánchez-Salguero et al. 2015), which is particularly relevant in a restrictive habitat, such as the Mediterranean pinewoods studied. However, this effect was not identified during extreme events, possibly because growth in those extreme years was more limited by climate conditions than by competition. ...
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Over recent decades, climate change has been particularly severe in the Mediterranean basin, where the intensity and frequency of drought events have had a significant effect on tree growth and mortality. In this context, differences in structural and physiological strategies between tree species could help to mitigate the damage inflicted by climate variability and drought events. Here, we used dendroecological approaches to observe common associations (synchrony) between indexed ring width in Pinus pinea and P. pinaster, as a measure of degree of dependence on climate variation or growth sensitivity to climate, as well as to analyze species growth responses to drought events through the Lloret’s indices of resistance, recovery and resilience. Based on data from 75 mixed and pure plots installed in the Northern Plateau of Spain, we used modeling tools to detect the effect of the mixture, along with climate and stand-related variables, on the short-term responses and long-term growth sensitivity to climate. Our results showed a trade-off between resistance and recovery after the drought episodes. In addition, different attributes of tree species, such as age and size as well as stand density seemed to act synergistically and compensate drought stress in different ways. The presence of age and quadratic mean diameter as covariates in the final synchrony model for P. pinaster reflected the influence of other variables as modulators of growth response to climate. Furthermore, differences in growth synchrony in mixed and monospecific composition suggested the existence of interactions between the two species and some degree of temporal niche complementarity. In mixed stands, P. pinaster exhibited a lower sensitivity to climate than in monospecific composition, whereas P. pinea enhanced its resistance to extreme droughts. These results allowed us to identify the species-specific behavior of P. pinea and P. pinaster to mitigate vulnerability to climate-related extremes.
... Spatial distribution and resource availability change dramatically over time, resulting in altered tree growing space conditions (Li et al. 2013;Aakala et al. 2013). As a result, growth rate is affected by inter-tree competition and also influenced by tree size (diameter, height and crown area), age, site, stand density, thinning, diseases, pests, natural disturbances and genetic characteristics, among others (Sánchez-Salguero et al. 2015;Ou et al. 2019). Trees are in constant competition for limited resources, such as water, minerals and light to maintain physiological functions to survive and to grow. ...
Article
The Weibull function, a continuous probability distribution, is widely used for diameter distribution modelling, in which parameter estimation performance is affected by stand attributes and fitting methods. The Weibull cumulative distribution function is nonlinear, and classical fitting methods may provide a not optimal solution. Invoking the use of artificial intelligence by metaheuristics is reasonable for this optimisation task. Therefore, aimed and compared (1) the metaheuristics genetic algorithm and simulated annealing performance over the moment and percentile methods; (2) the hybrid strategy merging the metaheuristics tested and the percentile method and, (3) the metaheuristics fitness functions under basal area and density errors. A long-term experiment in a Pinus taeda stand subjected to crown thinning was used. According to our findings, all methods have a similar performance, independent of the thinning regimes and age. The pattern of the estimated parameters tends to be acceptable, as b increases over time and c increases after thinning. Overall, our findings suggest that methods based on metaheuristics have a higher precision than classical methods for estimating Weibull parameters. According to the classification test, the methods that involved simulated annealing stood out. The hybrid method involving this metaheuristic also stood out, with accurate estimates. Classical methods showed the poorest performance, and we therefore suggest the use of simulated annealing due to its faster processing time and high-quality solution.
... The spatial composition of tree species is essential for forest inventory and analysis, which benefits the conservation and exploitation policies of the forests. A great deal of forest management requires the information at tree species level [1][2][3][4]. Both governments and companies have spent a lot of money on forest surveys. ...
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Explicit information of tree species composition provides valuable materials for the management of forests and urban greenness. In recent years, scholars have employed multiple features in tree species classification, so as to identify them from different perspectives. Most studies use different features to classify the target tree species in a specific growth environment and evaluate the classification results. However, the data matching problems have not been discussed; besides, the contributions of different features and the performance of different classifiers have not been systematically compared. Remote sensing technology of the integrated sensors helps to realize the purpose with high time efficiency and low cost. Benefiting from an integrated system which simultaneously acquired the hyperspectral images, LiDAR waveform, and point clouds, this study made a systematic research on different features and classifiers in pixel-wised tree species classification. We extracted the crown height model (CHM) from the airborne LiDAR device and multiple features from the hyperspectral images, including Gabor textural features, gray-level co-occurrence matrix (GLCM) textural features, and vegetation indices. Different experimental schemes were tested at two study areas with different numbers and configurations of tree species. The experimental results demonstrated the effectiveness of Gabor textural features in specific tree species classification in both homogeneous and heterogeneous growing environments. The GLCM textural features did not improve the classification accuracy of tree species when being combined with spectral features. The CHM feature made more contributions to discriminating tree species than vegetation indices. Different classifiers exhibited similar performances, and support vector machine (SVM) produced the highest overall accuracy among all the classifiers.
... In S2700, tree growth rate and its response to warming was more strongly inhibited than in S2900 (Figure 4), even if the SDI in S2700 is lower than S2900 (Table 1). It is noted that competition intensity tends to increase with decreasing resource availability [12,45]. This may result in stronger competition amongst stand-grown trees at lower elevation, where there is lower soil moisture (Table 1). ...
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Dryland montane forests conserve water for people living in the fluvial plains. The fate of these forests under climate warming is strongly affected by local environmental factors. The question remains of how internal factors contribute to climate change impacts on forest growth in these regions. Here, we investigated tree ring records for similar-aged stand-grown trees and their neighboring open-grown trees at elevation in a dryland montane forest (Picea crassifolia Kom.) in northwestern China. The growth rate of open-grown trees is much higher than their neighboring stand-grown trees across the entire elevation gradient, and the lower the altitude, the greater the difference. Open-grown trees at different elevations showed similar growth patterns, as tree growth at all sites was accelerated over time. In contrast, growth patterns of stand-grown trees were divergent at different altitudes, as growth at high elevations (3100–3300 m a.s.l.) was accelerated, whereas growth at low elevations (2700–2900 m a.s.l.) became stable after the year 1990. Analysis of growth–climate relationships indicated that warming promoted open-grown tree growth across the entire altitude gradient, and also stand-grown tree growth at high elevations, but negatively affected the growth of stand-grown trees at low elevations. Water scarcity can be exacerbated by competition within forests, inhibiting the warming-induced benefits on tree growth. Moving window correlation analysis suggested the negative effect of warming on tree growth at low elevations was diminished after the late 1990s, as the drought stress was alleviated. Our research shows the divergent growth responses to warming of stand-grown and open-grown trees along elevation. It reveals effects of internal factors in determining tree growth response to warming and holds the potential to aid forest management and ecosystem models in responding to climate change.
... processo de simulação o índice de competição é utilizado para determinar o crescimento e mortalidade das árvores, além de quantificar o estresse competitivo ou a habilidade competitiva da árvore ou mesmo seu vigor individual(SEIFERT et al., 2014;WEIGELT;JOLLIFFE, 2003). Na maioria dos casos o índice é considerado para representar o efeito total da competição por recursos escassos como luz, água, nutrientes e espaço físico (CORDONNIER;KUNSTLER, 2015;DANIELS;BURKHART, 1988).Índices que utilizam como suporte as características das árvores são propostos e utilizados para inferir sobre o nível de concorrência sofrida pelas árvores que destacam com maior incremento volumétrico ou diamétrico dentro da floresta(SÁNCHEZ-SALGUERO et al., 2015;WEBER et al., 2008). De acordo com Vanclay(2002) o índice de competição permite quantificar, em equações simples, o efeito de árvores vizinhas sobre o crescimento de uma árvore individual. ...
... It is important to note that seed traps were placed always in the middle section of each stand density, and particularly in the case of clear-cut, higher seed numbers can be expected with decreasing distance to adjacent mature stands. als in the understory (Wiedemann 1925;Valkonen et al. 2002;Sánchez-Salguero et al. 2015). This negative effect may not be apparent immediately after the seed fall, but will increase with the growth of juvenile trees (Belend et al. 2000). ...
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In the context of climate change, the crucial question is how silvicultural treatments should be modified, in order to reach favourable conditions for initiating natural regeneration of forest stands. The aim of the study was to evaluate the influence of clear-cutting, basal area reduction (0.4, 0.6 and 0.8) and soil preparation (milling cutter, forestry mulcher, brush rake and control variant without soil preparation) on the regeneration of Scots pine (Pinus sylves-tris L.) in the conditions of natural pine sites (Northern Bohemia). Seedling numbers, heights and crown widths were recorded on transects representing all combinations of stand densities treatments and soil preparations variants three years after the silvicultural operations. Seed traps were installed to determine the numbers of seeds from 2016 to 2018. Soil water potential (Delmhorst Instrument Company) and soil temperature (sensor Pt1000 A-class sensors, EMS Brno) were measured. All variants of soil preparation had higher numbers of seedlings compared to control variant. When comparing stand densities, total numbers of seedlings were the highest in stand density 0.4 (cutter 32,402 ± 34,208 S.D. ind.ha −1 ; mulcher 26,832 ± 24,088 S.D. ind.ha −1 ; rake 24,496 ± 22,913 S.D. ind.ha −1). This stand density was also beneficial with respect to seed numbers, seedling characteristics and soil moisture and temperature characteristics. We conclude that shelterwood regeneration on natural Scots pine sites is promising silvicultural approach and may become an important tool in mitigating negative effects of climate change in the future.
... sylvestris populations located at high altitudes, mainly associated with moisture conditions [55], suggesting that in Mediterranean mountains Scots Pine populations at high elevations may in fact be more vulnerable to drought stress than lower populations (however see [27]). Second, water availability rather than low temperature is the main limiting factor for tree growth at low-and mid-altitude sites in Mediterranean mountains [34,56]. Pinus sylvestris populations at low altitudes may be locally adapted and more drought tolerant than high altitude populations. ...
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Research Highlights. This research highlights the importance of environmental gradients in shaping tree growth responses to global change drivers and the difficulty of attributing impacts to a single directional driver. Background and Objectives: Temperature increase associated with climate change might strongly influence tree growth and forest productivity in temperate forest species. However, the direction and intensity of these effects at the dry edge of species range are still unclear, particularly given the interaction between local factors and other global change drivers such as land use change, atmospheric CO2 increase and nitrogen deposition. While recent studies suggest that tree growth in cool temperate forests has accelerated during the last decades of the 20th century, other studies suggest a prevalence of declining growth especially in dry-edge populations. Materials and Methods: Using historical forest inventories, we analyzed last century tree growth trends (1930-2010) along an elevation gradient (1350-1900 m a.s.l.) in a dry edge scots pine (Pinus sylvestris L.) forest in Central Iberian Peninsula. Growth was estimated as decadal volume increments in harvested trees of different size classes from 1930 to 2010 (1930-1940, 1939-1949, 1949-1959, 1959-1968, 1989-1999, 2000-2010). Results: Our results showed opposite growth trends over time depending on elevation. While tree growth has accelerated in the low end of the altitudinal gradient, tree growth slowed down at higher elevations (1624-1895 m a.s.l.). Moreover, the magnitude of growth reduction along the altitudinal gradient increased with tree age. Conclusions: Throughout the last 80 years growth trends in a rear-edge P. sylvestris forest has shown divergent patterns along an altitudinal gradient. Specifically, environmental conditions have become more adverse for growth at high altitudes and have improved at low altitudes. This suggest that local factors such as topography can modulate the impact of climate change on forest ecosystems.
... Some studies have suggested that trees subjected to low levels of competitive stress are more sensitive to climate variability [19][20][21]. However, other studies support that trees subjected to high level of competitive stress have a more sensitive response to climate variability [22][23][24]. ...
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Climate variability can exert a powerful impact on biotic competition, but past studies have focused largely on short-lived species, with a lack of attention to long-lived species such as trees. Therefore, there is a need to evaluate how competition regulates the climate-growth relationship in mature trees. We sampled the dominant tree species, Picea wilsonii Mast., on Xinglong Mountain, China, and studied the above issues by analyzing the relationship between tree radial growth, precipitation, and competition. In relatively wet years (precipitation > average), there was no significant difference in climate sensitivity between different competition classes. However, trees suffering from highly competitive stress were more sensitive to climate variability in all years, and particularly in the subset of years that was relatively drought (precipitation < average). These results suggest that competition enhances its ability to regulate tree growth response to climate variability in adverse weather conditions. Competition for resources between trees was asymmetrical, and an increase in height could give trees a disproportionate benefit. Thus, at trunk-level, both basal area incremental growth and intrinsic water-use efficiency of trees subjected to low competitive stress were significantly higher than trees that are subjected to highly competitive stress. Although the intrinsic water-use efficiency of trees under highly competitive stress increased more rapidly as the drought level increases, this did not change the fact that the radial growth of them declined more. Our research is valuable for the development of individual-tree growth models and advances our understanding for forest management under global climate change.
... In contrast, the higher-elevation site FW was less impacted despite the predominance of more drought-sensitive conifers. Our study thus supports the findings of context-specific climate change impacts, which depend strongly on the specific abiotic and biotic conditions (Condes and del Rio 2015;Sanchez-Salguero et al. 2015;Etzold et al. 2019). ...
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Mountain forest managers face the challenge to anticipate climate change (CC) impacts across large elevational ranges. For management planning, information on site-specific long-term responses to CC as well as the consequences for protection functions is particularly crucial. We used the process-based model ForClim to provide projections of forest development and their protective function as decision support for a large forest enterprise in the Northern Pre-Alps. Specifically, we investigated the impact of three climate scenarios (present climate, low- and high-impact CC) at five representative sites along an elevational gradient (700–1450 m a.s.l.). Relatively small changes to current forest structure and composition were evident under present climate, but divergent trajectories occurred under CC: while the low-elevation sites (≤ 1000 m) were affected by drought-related mortality, high-elevation sites benefited from the warming. Changes at low-elevation sites were accompanied by shifts in species composition, favouring in particular Tilia (‘low-impact’ CC) and Pinus sylvestris (‘high-impact’ CC). Forest management accelerated the shift towards climate-adapted tree species, thereby reducing detrimental effects of the ‘low-impact’ CC scenario. Under the ‘high-impact’ scenario, however, drastic decreases in protective function occurred for the late twenty-first century at low elevations. A set of exemplary disturbance scenarios (windthrow and bark beetle) demonstrated the importance of forest management and low browsing for the resilience of mountain forests. Overall, our results underline the potential of process-based forest models as decision support tools for forest enterprises, providing local projections of CC impacts across large elevational ranges at the site-specific resolution required by forest managers.
... Forest Ecology and Management 459 (2020) 117848 competition used, because we used the basal area in the tree neighborhood at the end of the study period to infer their effect on drought events in past years. Further studies should consider past stand structure, for example by using a retrospective analysis of radial growth at stand level (Sánchez-Salguero et al., 2015). The evaluation of living and dead saplings supports P. pinaster as the dominant tree species in this relict forest. ...
Article
Understanding species' tolerance to recurrent extreme droughts is key to predict species' performance and forest dynamics under ongoing climate change. Inter-specific differences in juvenile responses can largely shape forest composition and structure. However, the vulnerability of tree species is typically evaluated in adult canopy dominant individuals. The question of whether inter-specific differences in drought tolerance vary between adult and young trees remains largely unexplored. We sampled canopy dominant trees and saplings of three co-occurring pine species with different drought tolerance (Pinus pinaster, P. nigra and P. sylvestris) in a relict forest in the Northern Iberian plateau. Using basal area increment in canopy dominant trees and shoot elongation in saplings, we reconstructed annual growth for the period 2000-2015 and calculated resilience and resistance indices to two consecutive extreme droughts (2005 and 2012). We used generalized least square models to analyze species-specific differences in resistance and resilience in adults and saplings, respectively after accounting for tree size and stand basal area effects. In addition, we recorded living and dead saplings to assess inter-specific dissimilarities after the drought events. Drought events strongly reduced the growth of both adults and saplings (40% on average), but they were more resilient to the 2005 than to the 2012 drought. Increased magnitude and frequency of drought events led to inter-specific differences in drought responses, which were revealed in saplings rather than adults after the 2012 drought. P. pinaster saplings were more resilient than P. nigra and P. sylvestris, consistently to the drought stress experienced by each species in the dry-edge of their natural ranges. Moreover, a greater recruitment and similar sapling mortality confirm P. pinaster as the most successful pine species from a demographic perspective. In addition, tree size reduced resilience whereas basal area in the tree neighborhood did not show any significant effect on pine tolerance to drought. In conclusion, we showed that increased the magnitude and frequency of drought events uncovers species-specific differences in drought resilience in saplings rather than adults. Our results suggest potential shifts in the dominance of P. pinaster as the expense of P. nigra and P. sylvestris under climate change in this relict forest. This highlights the need to include juveniles and demographic rates in models aiming to describe and predict species responses to climate change in dry-edge forests.
... Future studies expanding the range of observed environmental conditions should also analyze the role of climatic and edaphic variables on tree growth, allowing to integrate the role of climatic or soil limitations on tree growth predictions (e.g., [16,17,58,79,80]) for improving our decision making capacity under climatic or management scenarios. ...
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Lack of knowledge of individual tree growth in species-rich, mixed forest ecosystems impedes their sustainable management. In this study, species-specific models for predicting individual diameter at breast height (dbh) and total tree height (h) growth were developed for 30 tree species growing in mixed and uneven-aged forest stands in Durango, Mexico. Growth models were also developed for all pine, all oaks, and all other species of the genus Arbutus (strawberry trees). A database of 55,158 trees with remeasurements of dbh and h of a 5-year growth period was used to develop the models. The data were collected from 217 stem-mapped plots located in the Sierra Madre Occidental (Mexico). Weighted regression was used to remove heteroscedasticity from the species-specific dbh and h growth models using a power function of the tree size independent variables. The final models developed in the present study to predict dbh and total tree height growth included size variables, site factors, and competition variables in their formulation. The developed models fitted the data well and explained between 98 and 99% and of the observed variation of dbh, and between 77 and 98% of the observed variation of total tree height for the studied species and groups of species. The developed models can be used for estimating the individual dbh and h growth for the analyzed species and can be integrated in decision support tools for management planning in these mixed forest ecosystems.
... Competition affects the diameter growth, height, width, and shape of tree canopy (Kunstler et al. 2011;Potvin and Dutilleul 2009;Thorpe et al. 2010). Therefore, competition is an essential factor driving forest dynamics (Sanchez-Salguero et al. 2015;Coomes and Allen 2007;Kunstler et al. 2011). ...
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Distance-based competition between merbau (Intsia bijuga (Colebr.) Kuntze) and neighboring trees could be applied to determine the planting space between merbau trees and shade trees in plantations. This research was conducted to identify the characteristics of merbau competition with neighboring trees and determine the ideal spacing of merbau trees. The sampling design using was the systematic line technique with hypothetical plot and sample tree as the quadrant center. The competitors were determined using a virtual high approach and header contact. Distance-based competitions were identified using the Hegyi index. Sixteen species had the highest competition index because of their dominance in the tree structure, namely Pometia coriacea, Intsia bijuga, Pimelodendron amboinicum, Horsfieldia laevigata, Palaquium amboinense, Pometia pinnata, Garcinia sp., Spathiostemon javensis, Prunus costata, Sterculia macrophylla, Terminalia complanata, Lepiniopsis ternatensis, Horsfieldia irya, Dysoxylum octandrum, Buchanania arborescens, and Ficus similis. Merbau responded to the high intensity of competition by tilting its canopy in the opposite direction to the position of the competitors’ canopy, making an irregular canopy shape, and growing the first branch at the lowest point on the stem. The ideal planting space for merbau trees in the plantations was 3-7 m. © 2018, Society for Indonesian Biodiversity. All rights reserved.
... Drought induced decline in tree growth and forest dieback have been reported in many Pinus nigra forests [62], as well as in other coniferous forest ecosystems in the Mediterranean region [83,84]. The lack of forest management can increase tree-to-tree competition by increasing stand density, and this increasing stand density can potentially aggravate the anticipated effects of the increasing frequency and severity of extreme droughts in coming years [85]. Our study showed that younger Pinus nigra stands are more resilient, as well as resistant, to drought events; therefore, promoting a greater presence of young Pinus nigra stands in the forested landscape through forest management [66,82] can enhance the resilience of Mediterranean conifer forests to extreme droughts. ...
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The magnitude of drought impact in forest ecosystems depends on which group of trees are more severely affected; greater mortality of smaller trees can modulate the trajectories of succession, while the mortality of larger trees can disproportionately offset the ecosystem’s carbon balance. Several studies have documented a greater vulnerability of large trees to extreme droughts while some other studies reported a greater growth reduction in smaller trees during droughts. We tested these hypotheses by comparing tree basal area increment (BAI), drought resistance (i.e., magnitude of growth decline during drought), and resilience (i.e., magnitude of growth recovery after drought) across five different age-classes in black pine (Pinus nigra Arn. Ssp salzmannii) forests in Spain. Our results showed that the BAI patterns, drought resistance, and resilience were strongly influenced by tree age-classes. In addition, the effect of climatic water balance (precipitation minus potential evapotranspiration) on BAI significantly varied among age-classes. The effect of water balance on BAI was lower for younger age-classes (1–39 years of age) compared to older age-classes. We observed a greater growth reduction (i.e., lower resistance) in older trees (>40 years of age) during droughts compared to younger trees (<40 years of age). However, all trees, irrespective of their ages, were able to recover the growth rates after the drought. In general, younger trees showed a greater capacity in recovering the growth rate (i.e., more resilient) than older trees. We detected no significant effects of stand basal area and stand density on BAI, drought resistance, and resilience. Overall, our results indicated that growth of older trees was more negatively affected during drought. Therefore, these older/larger trees can be selected for commercial thinning, or can be released from competition, which can minimize the potential impacts of future droughts in black pine forests in Spain.
... As such, our results agree with the general pattern that trees growing under low competitive stress have higher growth rates, greater WUE and a better response in growth to high water availability (e.g. Linares et al. 2009;Sánchez-Salguero et al. 2015). Rozas et al. (2009) showed that growth-climate sensitivity in Spanish junipers is higher in earlier life stages. ...
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Key messageThe dioecious tree species Juniperus thurifera L. is undergoing a spontaneous process of forest expansion in southwest Europe. We investigated how growth, climate sensitivity, and wood density varied simultaneously between sexes and among stages of expansion while accounting for the variability of forest structure. We found few sex-based differences but detected lower wood density, greater growth rates, and higher sensitivity to drought in expanding fronts compared to long-existing forests.ContextJuniperus thurifera L. (Spanish juniper) is a dioecious tree species undergoing a natural process of forest expansion in southwest Europe.AimsTo assess how radial growth and wood density are simultaneously shaped by sex-based differences, the stage of forest expansion (long-existing forests, transition zones, and expanding fronts), variability in forest structure, and climate (in the case of radial growth).Methods We measured forest structure characteristics, tree rings, and wood density in 17 plots dominated by Spanish juniper in three stages of forest expansion in central Spain. We used linear mixed models (LMMs) to explore the main drivers of variability in radial growth and wood density and sex- and stage-based differences in climate-growth sensitivity.ResultsRather than by sex, growth and wood density were mainly shaped by the stage of forest expansion, forest structure variables that characterize these stages, and climate variables (in the case of growth).Conclusion Sexual dimorphism had a minimal effect in growth and wood density in expanding Spanish juniper woodlands. Expanding fronts could be benefiting from land-use legacies in the abandoned fields they are colonizing, as reflected in higher growth rates and lower wood density, especially during years with less summer drought stress. However, this pattern could be reversed in the event of an increase in drought episodes.
... Generally, the increasing trend in A t , which is age-related, exhibits an exponential-like function due to fast increasing growth in juvenile individuals and slower growths for older trees, becoming steady over time ( Sanchez-Salguero et al., 2015 ). Since our sampling tree growth curves fit this pattern, we applied a negative exponential or linear function to estimate A t . ...
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At the local scale, artificial impounded reservoirs in dry regions exert influence on the surrounding local climate. Impounded reservoirs have been found to alter precipitation patterns and increase temperature, specific humidity and surface evaporation. The consequences of impoundment or its related climatic changes on the surrounding vegetation are still not well understood. We here examined the potential effect on surrounding tree growth from the impoundment of the Ertan Reservoir, China, in 1998. We measured Yunnan pine tree rings at three sites on a slope close to the reservoir and two control sites far away from the reservoir. We compared the annual radial growth of tree rings at all sites with air temperature, precipitation and air humidity in the region. We also used cumulative distribution functions to quantify the probability of attributing radial growth changes to background climate variability. We find an enhancement of tree growth from 2000 to 2002, right after the reservoir's impounding in experimental and control sites. The tree growth can initially be explained by favourable conditions benefiting tree growth. However, we cannot entirely attribute such enhancement to the background climate variability when studying the relationship between tree growth and climatic variables over the 36 years and their probability of occurrence. Hence, we infer that the tree growth in the three years following impoundment can only be attributed to the simultaneous effect of favourable regional climate conditions and the reservoir's impoundment in itself. These conditions decrease vegetation stress by decreasing air temperature and increasing air relative humidity. Although the findings of this study shed more light on the environmental and climatic changes induced by the impoundment of reservoirs, they also call for the need of monitoring climatic variables in the vicinity of the reservoirs.
... This fire regime primarily depended on human burning and secondarily on climate variability since warm spring conditions occurred during those decades [13]. Scots pine growth in the study area is enhanced by wet spring and summer conditions [29,45], and reconstructed summer precipitation in the 1890s showed the smallest range of variability since 1800 [46]. Surface fires of different intensity usually affect Scots pine forests, albeit lethal crown fires could occur in dense stands under drought conditions [20]. ...
Article
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Mountain forests are subjected to several pressures including historical land-use changes and climate warming which may lead to shifts in wildfire severity negatively impacting tree species with low post-fire growth resilience. This is the case of relict Mediterranean Scots pine (Pinus sylvestris) forests in the Sierra de Gredos mountains (central Spain). We reconstructed the historical fire regime of these forests since 1700 by using paleoecology, historical ecology and dendroecology. We detected an increase in charcoal accumulation rate and coprophilous fungi in peat bogs during the late 19th century when the pine pollen percentage sharply decreased, historical records of fire peaked and many trees showed growth suppressions. We inferred an increased wildfire incidence during the late 19th century, which could have shaped the current distribution of Scots pine forests. This shift in fire-forest interactions can be explained by the uncontrolled use of mountain forests and grasslands due to the dissolution of “Mesta”, one of the major and lasting transhumance livestock associations in Europe. Integrating historical human and climate influences on fire regimes allows decomposing the resilience and conservation components of relict forests.
... Tree age and size can noticeably influence tree-ring width (Sanchez-Salguero et al., 2015). Therefore, to remove interference due to the growth trends of trees, we needed to detrend the original tree-ring width data before assessing the effects of climate on tree growth. ...
Article
Carbon allocation in tree stems critically affects how trees respond to climate variability and extreme weather. However, it is difficult to directly measure nonstructural carbohydrates in tree stems, and monitoring them over time is expensive and usually lasts only a few years at most. Hence, we utilized a method substituting nonstructural carbohydrates with the basal area increment (BAI) and intrinsic water-use efficiency (iWUE) to study tree stem carbon allocation. The results indicated that the values of the RAW (BAI-based tree-ring width index) and iWUEres (iWUE residual serial) in the current year could reveal information about early growing season climatic conditions. Thus, coniferous species might utilize carbon produced by photosynthesis during the early growing season to support tree growth. Wet years caused the RAW in the next year to significantly increase, and the RAW in drought years showed a significant correlation with the iWUEres in the previous year, while the RAW in the next year showed little correlation with the iWUEres in the current year. These results suggested that favourable climatic conditions could stimulate the accumulation of carbon, which promoted radial growth in the following year. In addition, drought in semiarid areas has a 1–3-year legacy effect on tree growth, suppressing the growth rate below the normal rate. The decline in tree growth was most noticeable in the year after drought, suggesting that inter-annual allocation of carbon reserves is a long-term process, yet trees prioritize using the newest carbon source for growth during adjacent years. This study broadens the understanding of nonstructural carbohydrates and their supply in evergreen coniferous species and has important implications for forest climate–carbon cycle models under changing climates.
... On the one hand, the process of tree growth response to increased competition was nonlinear. Some researchers showed that the competition effect on restricting trees' radial growth faded under intensive competition (Gómez-Aparicio et al., 2011;Sánchez-Salguero et al., 2015;Dorman et al., 2015;González de Andrés et al., 2017). The calculation of response indices (Rt, Rc, Rs) was based on radial growth. ...
Article
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As climate changes, understanding tree responses to climate is important to predict tree growth, and plant competition as a nonnegligible biotic factor plays a key role in such responses. However, few studies have investigated how competition affects the response of Pinus tabulaeformis plantations to climate. In our study, we investigated nine 29-year-old P. tabulaeformis plantation plots (three density gradients: 1208 N/ha, 2275 N/ha, 2989 N/ha). The dendroecological method was used to analyze the impact of competition on tree responses to drought and interannual climate variation. The stand density index was used to indicate the intensity of competition. The results showed that competition modified the climate–growth relationship. Competition increased tree sensitivity to drought but the relationship between competition and sensitivity to drought was nonlinear, which suggested that the competition effect slightly increased under intense competition conditions. Additionally, competition reduced trees growth sensitivity to interannual climate variation. After 1999, the effect of competition was obvious. The sensitivity of small-diameter trees, especially those in middle- and high-density stands, declined. Thus, in future, these trees presumably may exhibit a reduced sensitivity to interannual climate variation and a greater sensitivity to drought.
... An increase in temperature implies higher water demand, causing greater drought stress, and ultimately, mortality of the water-demanding pine species [41]. Under low competition levels, tree growth is usually enhanced [42]. Conversely, tree growth is already close to the lower limit for survival under higher competition levels [43]. ...
Article
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Background Projections of climate change impacts upon forests are likely inaccurate if based on the premise that only climate controls tree growth. Species interactions control growth, but most research has ignored these effects on how trees respond to climate change. Climate change is inducing natural species selection. However, this selection does not occur at the community level. Species selection starts with competition amongst individual trees. Competition is an individual-to-individual antagonistic interaction that, if severe, can constrain the presence of trees within a particular environment. Thus, climate change impacts individual tree selection within forests. Projecting climate change impacts on forests should account for the effects of climate on tree growth and the effects of competition. The inclusion of competition can increase the predictive power of simulations. Methods We propose a protocol to systematically map the available literature on climate change impacts on forests and produce a comprehensive list of methods applied to measure competition and model the competition effects on tree growth responses to climate change. This systematic map is not limited to any country or continent or specific tree species or forest type. The scope of the search focuses on time (when the evidence was published), location (geographic location of the evidence) and research design (competition indices and modelling methods). We will evaluate articles at three levels: title, abstract and full text. We will conduct a full-text assessment on all articles that pass a screening at the title and abstract stages. We will report the extracted evidence in a narrative synthesis to summarize the evidence’s trends and report knowledge gaps.
... Another factor that might have affected the Rbar values in our study was the relatively small distance between trees, possibly leading to competition and affecting tree growth (e.g. Chi et al., 2015;Ford et al., 2017;Luo et al., 2020;Sánchez-Salguero et al., 2015;Zalloni et al., 2019;Zhang et al., 2016). ...
Article
Tree-ring inter-annual pattern variation is crucial in dendrochronology, allowing the identification of possible limiting factors on growth. Thus, trees exposed to subtropical or tropical climates without a marked seasonality may show a low degree of interannual variation, impeding a straightforward dendroclimatological approach. Meanwhile, subtropical regions, and areas in transitional climates such as the Azores archipelago, are widely unexplored in terms of dendroclimatology, providing opportunities to work with endemic trees, including the dominant Azorean tree Juniperus brevifolia (Seub.) Antoine. To evaluate the dendrochronological potential of J. brevifolia, we analyzed tree-ring patterns, crossdating capabilities, and correlation with climate parameters. We sampled 48 individual trees from two natural populations (São Miguel and Terceira islands) using an increment borer. Besides, a Trephor tool was used to obtain wood microcores for micro-anatomical analysis. Although the transition between early and latewood was evident, partially indistinct ring boundaries and wedging rings were present in some cases, affecting the crossdating process, but not impeding the establishment of reliable ring-width chronologies. Following detrending, master chronologies were built and correlated with monthly temperature and precipitation data using the treeclim R package. The climate-growth relationships indicated negative correlations with late summer temperature in both populations. Considering our results and the importance of J. brevifolia as a dominant tree in the Azores natural forests, we conclude that it shows an acceptable potential for dendrochronological research. Thus, this study provides baseline information to help fill the knowledge gap regarding the climate-growth relationship of Azorean trees.
... As stand structure can vary between plots, we include its effect on tree growth through total plot basal area. Plot basal area (m² ha −1 ) was calculated at each census, with expectations that increasing basal area would have a general negative effect on tree growth (Muledi et al., 2020;Sánchez-Salguero et al., 2015). ...
Article
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A better understanding of how climate affects growth in tree species is essential for improved predictions of forest dynamics under climate change. Long-term climate averages (mean climate) drives spatial variations in species’ baseline growth rates, whereas deviations from these averages over time (anomalies) can create growth variation around the local baseline. However, the rarity of long-term tree census data spanning climatic gradients has so far limited our understanding of their respective role, especially in tropical systems. Furthermore, tree growth sensitivity to climate is likely to vary widely among species, and the ecological strategies underlying these differences remain poorly understood. Here, we utilise an exceptional dataset of 49 years of growth data for 509 tree species across 23 tropical rainforest plots along a climatic gradient to examine how multiannual tree growth responds to both climate means and anomalies, and how species’ functional traits mediate these growth responses to climate. We show that anomalous increases in atmospheric evaporative demand and solar radiation consistently reduced tree growth. Drier forests and fast-growing species were more sensitive to water stress anomalies. In addition, species traits related to water use and photosynthesis partly explained differences in growth sensitivity to both climate means and anomalies. Our study demonstrates that both climate means and anomalies shape tree growth in tropical forests, and that species traits can provide insights into understanding these demographic responses to climate change, offering a promising way forward to forecast tropical forest dynamics under different climate trajectories.
... Some studies have reported dieback in Mediterranean tree species, generally viewed as drought-tolerant, such as Holm oak (Quercus ilex) [4]. The rise in mortality in some pine forests has also been observed in plantations, and this has been connected not only to increased drought but also to lack of silvicultural intervention (i.e., absence of thinning), which may increase competition between trees for water and light in structurally homogeneous planted stands [3,5]. ...
Article
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In Mediterranean seasonally dry regions, the rise in dieback and mortality episodes observed in pine afforestations has been related to higher drought intensity and lack of appropriate management, which enhance competition between trees for water and light. However, there is little understanding of the benefits of silviculture for plantations under seasonal drought stress. A combination of dendrochronology and wood C and O isotope analyses was used in three Black pine (Pinus nigra) plantations to work out the responses of radial growth (BAI, basal area increment) and water-use efficiency (WUEi) to thinning treatments (removal of 40% of the stand basal area). Thinning had a positive effect on BAI and WUEi, reduced drought sensitivity, and reduced the temporal dependence on the previous year’s growth. These results were significant even 13–14 years after thinning and coherent for the three study sites. Differences were found between the sites regarding the physiological mechanisms of adaptation. In two sites, we inferred the enhanced WUEi was due to increased photosynthetic rates (A) at constant stomatal conductance (gs). In the third site, which had higher tree density and therefore competition, we inferred increases in both A and gs, with the former being proportionally larger than the latter.
... While invaluable for applications such as reconstructing past climates (e.g., Buntgen et al., 2011), accurately representing the climate sensitivity of forest productivity requires an analysis of sensitivity to multiple climatic variables and how this varies across trees in a forest stand (Babst et al., 2018). Precipitation and temperature can have additive or interactive effects on growth (Foster et al., 2016;Meko et al., 2011;Sánchez-Salguero et al., 2015;Vlam et al., 2014;Zuidema et al., 2020), and we hypothesize that both influence the growth of most species, often over different seasonal windows (Table 1). In addition, we hypothesize that nonlinear climate responses, already known to be widespread within forest settings Wilmking et al., 2020;Woodhouse, 1999), are in fact the predominant form of response in forests around the world (Table 1). ...
Article
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Tree rings provide an invaluable long‐term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree‐ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologically relevant hypotheses on tree growth sensitivity to environmental drivers and their interactions with tree size. Here, we develop and apply a new method to simultaneously model nonlinear effects of primary climate drivers, reconstructed tree diameter at breast height (DBH), and calendar year in generalized least squares models that account for the temporal autocorrelation inherent to each individual tree’s growth. We analyze data from 3811 trees representing 40 species at 10 globally distributed sites, showing that precipitation, temperature, DBH, and calendar year have additively, and often interactively, influenced annual growth over the past 120 years. Growth responses were predominantly positive to precipitation (usually over ≥ 3‐month seasonal windows) and negative to temperature (usually maximum temperature, over ≤ 3‐month seasonal windows), with concave‐down responses in 63% of relationships. Climate sensitivity commonly varied with DBH (44% of cases tested), with larger trees usually more sensitive. Trends in ring width at small DBH were linked to the light environment under which trees established, but basal area or biomass increments consistently reached maxima at intermediate DBH. Accounting for climate and DBH, growth rate declined over time for 92% of species in secondary or disturbed stands, whereas growth trends were mixed in older forests. These trends were largely attributable to stand dynamics as cohorts and stands age, which remain challenging to disentangle from global change drivers. By providing a parsimonious approach for characterizing multiple interacting drivers of tree growth, our method reveals a more complete picture of the factors influencing growth than has previously been possible.
... Tree-ring widths usually show variation over the life of a tree; therefore, such age/size trends need to be estimated and removed from time series in order to detect the evidence of climatically-driven tree growth. Regarding the interdependence of increasing temperatures and decreasing water availability, Sánchez- Salguero et al. (2015) showed that growth is more sensitive to drought than to temperature in several Mediterranean species, which is in accordance with the findings by Calama et al. (2019). Understanding the effects of climate change on the ecology of Pinus pinea forests can help to assess the adaptive capacity of the species, and develop management programs aimed to ensure the conservation of its populations (Natalini et al. 2016). ...
... In the subsequent stage, however, the growth of mediumor high-CI stands decelerated and became significantly lower than low-CI ones over several decades, indicating a competitionrestrained growth (Figure S3). Other studies observed that high competition negatively affected tree growth as BAI and CI followed negative exponential functions (Sánchez-Salguero et al., 2015b). Moreover, the responsiveness to climate increased with decreasing competition, indicating a loss of growth sensitivity to climate with increasing competition. ...
Article
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Understanding the response of tree growth and drought vulnerability to climate and competition is critical for managing plantation forests. We analyzed the growth of Mongolian pines in six forests planted by the Three-North Shelter Forest Program with tree-ring data and stand structures. A retroactive reconstruction method was used to depict the growth-competition relationships of Mongolian pines during the growth period and their climatic responses under different competition levels. Drought vulnerability was analyzed by measuring the basal area increment (BAI) of different competition indices (CIs). In young trees, differences in BAIs in stands with different CIs were not statistically significant. After 15–20 years, medium- and high-CI stands had significantly lower tree-ring widths (TWs) and BAIs than the low-CI stands ( p < 0.05). The standardized precipitation evapotranspiration index (SPEI), precipitation, relative humidity, and vapor pressure deficit were major factors affecting tree growth. On a regional scale, climate outweighed competition in determining radial growth. The relative contribution of climatic factors increased with the gap in SPEI between plantation sites and the native range, while the reverse pattern of the competition-growth relationship was observed. Drought reduced TWs and BAIs at all sites. Stands of different CIs exhibited similar resistance, but, compared with low-CI stands, high- and medium-CI stands had significantly lower recovery, resilience, and relative resilience, indicating they were more susceptible to drought stresses. Modeled CI was significantly negatively related to resistance, resilience, and relative resilience, indicating a density-dependence of tree response to drought. After exposure to multiple sequential drought events, the relative resilience of high-CI stands decreased to almost zero; this failure to fully recover to pre-drought growth rates suggests increased mortality in the future. In contrast, low-CI stands are more likely to survive in hotter, more arid climates. These results provide a better understanding of the roles of competition and climate on the growth of Mongolian pines and offer a new perspective for investigating the density-dependent recovery and resilience of these forests.
Article
Forests are an important global carbon sink but their responses to climate change are uncertain. Tree stems, as the predominant carbon pool, represent net productivity in temperate eucalypt forests but the drivers of growth in these evergreen forests remain poorly understood partly because the dominant tree species lack distinct growth rings. Disentangling eucalypt species’ growth responses to climate from other factors, such as competition and disturbances like fire, remains challenging due to a lack of long-term growth data. We measured monthly stem-diameter changes (as basal area increment, BAI) of two co-occurring dominant eucalypts from different sub-genera (Eucalytpus obliqua and E. rubida) over nearly four years. Our study included seven sites in a natural temperate forest of south-eastern Australia, and we used linear mixed-effects models to examine the relative importance to monthly BAI of species, monthly climate variables (temperature and rainfall), inter-tree competition, and recent fire history (long-unburnt, prescribed fire, wildfire). Monthly BAI peaked in spring and autumn and was significantly different between species during spring and summer. BAI variation was most clearly associated with temperature, increasing in hyperbolic response curves up to maximum mean temperatures of ~ 15 – 17 °C and thereafter decreasing. Temperature optima for maximum monthly BAI were 1 to 2 °C warmer for E. rubida than E. obliqua. While less important than temperature, rainfall, particularly autumn rainfall, also helped explain patterns in monthly BAI, with inter-tree competition and recent fire history of comparatively minor importance. Our study provides the first comprehensive field-based evidence of different growth niches for eucalypts from different subgenera in natural temperate mixed forests. It highlights the importance of intra-annual climate to understanding productivity variation in temperate evergreen forests and provides insights into the mechanisms underpinning the successful co-existence of different tree species as well as their relative vulnerabilities to changing climates.
Article
A machine learning method called the random forest approach was used to explore the relationship between forest productivity and stand and climate factors. Data was sampled from the long-term spacing trails of Chinese fir plantations in southern China. Results showed that the productivity of Chinese fir plantations increased with increasing value of the Gini coefficient and dominant height (Hd), while it decreased with increasing age (A) and stand basal area (BA). Furthermore, forest productivity was positively correlated with annual precipitation (AP) and summer mean maximum temperature (SMMT); in contrast, it was negatively associated with winter mean minimum temperature (WMMT) and annual heat-moisture index (AHM). Age had the greatest influence on forest productivity compared to a more secondary influence of climate factors. We found that older forests were more vulnerable to climatic stress and the productivity of forests with middle-and high-levels of competition behaved similarly, and was lower than forests with low level of competition intensity. Higher SMMT, AP and lower AHM would enlarge the gap of forest productivity under different levels of stand structure, competition intensity and site quality. Changes in site conditions had little effect on productivity when AP was lower than 1250 mm. Our findings will provide a good framework for Chinese fir plantation management under future climate change.
Conference Paper
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This article deals with individual tree diameter increment of mature Scots pine (Pinus sylvestris L.) trees after release cut. The study is focused mainly on individual seed trees. Measurement was done altogether in 22 forest stands at three different forest administrations (State Forest of the Czech Republic: LS Choceň, LS Nasavrky a LS Plasy). By Pressler auger 104 trees were sampled in total. Increment cores were further analyzed in dendrochronological laboratory. By comparing tree ring widths 10 years before and 10 years after release cut, there mature trees of Scots pine were found responding to that partial logging in stem diameter increment for more than half of the trees. Nevertheless, the Student´s t-test confirmed statistically significant increment only in one third of tree individuals. The study proved, that mature trees of Scots pine reacted to release cut very quickly; i.e. during one or two years after the partial logging. The period with an elevated stem diameter increment last for 18 years on average. The reaction of stem diameter increment of individual Scots pine trees can be expected on the natural pine habitats at lowlands (Target management unit-CHS 13) and on the acidic soils at lowlands and also uplands (CHS 23 and 43). At these sites, 50 % probability for elevated stem diameter increment could be expected. Abstrakt Tento článek se zabývá vlivem uvolnění na tloušťkový přírůst dospělých jedinců borovice lesní (Pinus sylvestris L.). Studie byla zaměřena především na jedince ve formě semenných výstavků. Sběr dat proběhl v rámci tří lesních správ, LČR, s. p.: LS Choceň, LS Nasavrky a LS Plasy, celkem ve 22 porostech. Pomocí Presslerova přírůstového nebozezu byly odebrány vývrty ze 104 stromů. Tyto vývrty byly dále analyzovány s ohledem na tloušťky jednotlivých letokruhů v dendrochronologické laboratoři. Dle porovnání tlouštěk letokruhů 10 let před uvolněním a 10 let po uvolnění bylo zjištěno, že dospělí jedinci borovice reagovali na uvolnění hospodářsky významným navýšením na tloušťkovém přírůstu ve více než polovině případů, dle Studentova t-testu statisticky významného navýšení přírůstu dosáhla třetina stromů. Výzkum odhaluje, že dospělé borovice reagují na uvolnění velmi rychle, a to takřka bezprostředně či do dvou let po momentu uvolnění. Průměrná doba reakce zvýšeného tloušťkového přírůstu byla vyčíslena na 18 let. Přírůstovou reakci dospělých jedinců lze očekávat na přirozených borových stanovištích (CHS 13) a na kyselých stanovištích nižších a středních poloh (CHS 23 a 43). Na těchto stanovištích je možné počítat s minimálně 50 % pravděpodobností výrazného světlostního přírůstu.
Article
The frequency, duration, and severity of drought events are expected to increase in the Mediterranean area as a result of climate change, with strong impacts on forest ecosystems and in particular individual tree growth. Tree growth response to drought is strongly influenced by local site and stand characteristics that can be quantified using competition indices (CIs) and water stress indices (WSIs). These indices have been widely used to predict tree growth; however, they are numerous, and few studies have investigated them jointly. In this context, we investigated the potential of using CIs and WSIs to investigate tree behaviour under drought. The main objective of this study was to quantify P. halepensis Mill. annual radial growth using tree size from the previous year, CIs and WSIs. We studied twelve 50-year-old Pinus halepensis plots located in the SouthEast of France distributed in different density treatments (light, medium and dense). At each plot, all trees were measured (height, circumference), spatialized and the ring-widths were measured for ~15 trees. We also developed a two-strata (over-and understorey) forest water balance model to simulate soil water content at a daily resolution based on stand characteristics (LAI values in particular) and soil properties. A mixed modelling approach was eventually used to investigate the drivers of P. halepensis annual radial growth and to test the performance of five CIs and four WSIs. The best growth model included tree size, the sum of Basal Area of Larger trees in a 5 m-radius (BAL; as CI), and the number of days that trees experienced water stress in a year (as WSI) as predictors. This model explained up to 56% of the variance in observed pine tree growth, which increased up to 77% when the individual tree was included as a random effect on the intercept. We found that distance-independent CIs can perform as well as distance-dependent CIs in our study site. The duration of drought alone appeared to better predict tree growth than drought intensity and duration, or drought timing. The selected model led us to reaffirm the positive effect of thinning on tree secondary growth when facing long and intense drought.
Article
In Mediterranean areas where drought-induced forest dieback and tree mortality have been widely reported, it is still under debate how the likely risks of climate change will affect tree growth and consequently forest productivity. Increasing tree mortality has been associated not only to increased drought, but also to a lack of management in many dense pine forests and plantations, where warming may intensify tree-to-tree competition for soil water. This emphasizes the need of using silviculture to adapt dense stands of Mediterranean pine reforestations to warmer and drier conditions. Here we combined dendrochronology and C and O isotope analyses of wood in two Aleppo pine (Pinus halepensis) plantations, growing under semiarid conditions and experimentally thinned at high and moderate intensities along with control. The main aim was to understand the responses of radial growth and water use efficiency (WUEi) to different thinning intensities, and to analyze the effectiveness of thinning to enhance post-drought growth resilience. Thinning had a positive effect on growth, produced an increase of δ¹⁸O, reduced growth sensitivity to drought and decreased WUEi, suggesting a reduction of drought stress. These results were consistent across sites, and were significant even 20 years after the intervention took place. Considering the climate effects on growth through the SPEI drought index to calculate resistance and recovery indices, an increase of resistance after thinning was observed. We conclude that high thinning intensity (50% of basal area removed) is a useful silviculture intervention on Mediterranean Aleppo pine plantations that enhances their growth, and makes them less dependent on harsh climatic conditions, improving their resilience against drought and consequently making them better adapted to more unfavourable conditions.
Article
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National Forest Inventories (NFIs) perform systematic forest surveys across space and time. They are hence powerful tools to understand climate controls on forest growth at wide geographical scales and account for the effects of local abiotic and biotic interactions. To investigate the effects of climate change upon growth dynamics of four major European conifer species along elevation and continentality gradients, we herein provide an original harmonization of the French and Austrian NFI datasets. The growth of Norway spruce, Scots pine, silver fir and European larch over the 1996–2016 period was studied in pure and even-aged plots across different ecological regions. We derived climate-driven growth trends from > 65, 000 radial increment series filtered out from major biotic and abiotic influences using statistical modeling. We further identified primary environmental drivers of conifer growth by regressing growth trends against regionally aggregated biotic and abiotic forest attributes. Negative growth trends were observed in continental regions undergoing the most rapid warming and thermal amplitude contraction over the study period. Negative trends were also associated with lower forest structural heterogeneity and, surprisingly, with greater available water capacity. Remarkably, we observed these associations both at the inter- and intra-species levels, suggesting the universality of these primary growth determinants. Our study shows that harmonized NFI data at the transnational level provide reliable information on climate–growth interactions. Here, greater forest structural complexity and greater water resource limitation were highlighted as drivers of greater forest resilience to climate change at large-scale. This result forms crucial bases to implementing climate-smart forest management.
Preprint
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With climate change, understanding tree responses to climate is important for predicting trees’ growth, and plant competition as a nonnegligible biotic factor plays a key role in such response. However, few studies have investigated how competition affects the response of Pinus tabulaeformis plantations to climate . In our study, we investigated nine 29-year-old P. tabulaeformis plantation plots (three density gradients). The dendroecological method was used to analyze the impact of competition on tree s response to drought and interannual climate variation. Stand density index was used to indicate the intensity of competition. The results showed that competition modified the climate-growth relationship. Competition increased trees’ sensitivity to drought but the relationship between competition and sensitivity to drought was nonlinear. The competition effect slightly increased under intense competition conditions. Additionally, competition reduced trees’ sensitivity to interannual climate variation. After 1999, the effect of competition was obvious. The sensitivity of small-diameter trees, especially those in middle- and high-density stands, declined. Thus, in the future these trees presumably may exhibit a reduced sensitivity to interannual climate variation and a greater sensitivity to drought.
Article
Under the current climate change conjuncture, understanding the forest plantations capacity of acclimation to warming and increased drought stress is crucial for forest managers. To get some understanding of their adaptability, plantations of similar provenance but located in climatically contrasting sites can be compared. Here we study the growth dynamics and their relationship with climate and drought in two Scots pine (Pinus sylvestris L.) plantations located in the center (Sierra de Guadarrama, wetter site) and south (Sierra Nevada, drier site) of Spain, the latter situated at the southernmost distribution limit of the species. Our objectives are to quantify the trends in radial growth of these plantations, to quantify the influence of climate on growth, and to project the plantations growth as a function of forecasted climate. Results reveal that the plantations from the drier site show lower, and less responsive to climate, growth and greater resilience than those from the wetter site. Furthermore, if the current climate-growth relationships continue in the future, these plantations would maintain the current limited growth rate during the 21st century. On the contrary, plantations from the wetter site show higher growth rate and more resistance to drought, and they are projected to increase growth under the warmer conditions forecasted for the 21st century. Our study shows that plantations in drier sites may have a great capacity to acclimate to local climate conditions and would not be negatively impacted by the projected climate warming.
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Coastal sand dunes near the Baltic Sea are a dynamic environment marking the boundary between land and sea and oftentimes covered by Scots pine (Pinus sylvestris L.) forests. Complex climate-environmental interactions characterize these ecosystems and largely determine the productivity and state of these coastal forests. In the face of future climate change, understanding interactions between coastal tree growth and climate variability is important to promote sustainable coastal forests. In this study, we assessed the effect of microsite conditions on tree growth and the temporal and spatial variability of the relationship between climate and Scots pine growth at nine coastal sand dune sites located around the south Baltic Sea. At each site, we studied the growth of Scots pine growing at microsites located at the ridge and bottom of a dune and built a network of 18 ring-width and 18 latewood blue intensity chronologies. Across this network, we found that microsite has a minor influence on ring-width variability, basal area increment, latewood blue intensity, and climate sensitivity. However, at the local scale, microsite effects turned out to be important for growth and climate sensitivity at some sites. Correlation analysis indicated that the strength and direction of climate-growth responses for the ring-width and blue intensity chronologies were similar for climate variables over the 1903-2016 period. A strong and positive relationship between ring-width and latewood blue intensity chronologies with winter-spring temperature was detected at local and regional scales. We identified a relatively strong, positive influence of winter-spring/summer moisture availability on both tree-ring proxies. When climate-growth responses between two intervals (1903-1959, 1960-2016) were compared, the strength of growth responses to temperature and moisture availability for both proxies varied. More specifically, for the ring-width network, we identified decreasing temperature-growth responses, which is in contrast to the latewood blue intensity network, where we documented decreasing and increasing Frontiers in Forests and Global Change | www.frontiersin.org 1 September 2020 | Volume 3 | Article 578912 Janecka et al. Climate Sensitivity of Scots Pine temperature-growth relationships in the north and south respectively. We conclude that coastal Scots pine forests are primarily limited by winter-spring temperature and winter-spring/summer drought despite differing microsite conditions. We detected some spatial and temporal variability in climate-growth relationships that warrant further investigation.
Thesis
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The frequency, duration, and severity of drought events are expected to increase in the Mediterranean area as a result of climate change, with strong impacts predicted for forest ecosystems. In particular, individual tree growth and plant recruitment are expected to decrease, leading to a decline in forest resilience. In this context, understanding the processes that underlie the response of trees and juvenile trees to drought is of great interest for forest management. In this thesis, we quantified the interactions for resources along a pine cover gradient between adult Aleppo pines (Pinus halepensis), saplings of strawberry trees (Arbutus unedo), manna ashes (Fraxinus ornus), service trees (Sorbus domestica) and a competitive shrubby understorey composed mainly of kermes oaks (Quercus coccifera). Water stress was found to be the key limiting factor controlling the stands’ dynamics. Dense pine cover increased competition for water, inducing reduced growth for Aleppo pines, strawberry trees and service trees as well as reducing survival for strawberry trees and service trees. However, this dense pine cover was beneficial for manna ash, which is known to be a shade-tolerant species. On the other hand, light pine cover decreased competition for water, inducing a growth increase for the Aleppo pines, tree saplings and the competitive vegetation cover. These results further highlighted the positive effects of thinning pine cover, while maintaining the shrubby understorey, especially in terms of alleviating drought-related stress and maximizing sapling survival and growth. Finally, all results were integrated into a functional-structural model named RReShar (Resource and Regeneration Sharing) that was adapted for Mediterranean pine stands.
Conference Paper
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The suitability of wild cherry for reforestation of clear-cuts and gaps in two types of planting stock was tested under the conditions of nutrient-rich forest clear-cut site in Doupovské hory Mts. region. Semi-saplings and standard-sized trees were compared. Initial growth and vitality were evaluated – mortality, total height, height increment, and root collar diameter. Vitality (dry terminal and stem deformation) was visually assessed during the vegetation season. The evaluation of the plantations after first vegetation period showed that the mortality was negligible for both planting stock (zero in case of semi-saplings) and height increment slightly higher in the case of semi-saplings in comparison to standard-sized planting stock (21 vs. 17 cm). Overall, the plantations were highly resistant against weed with the ability to grow through tough weed, which seems to be an advantage in this particular tree species. Keywords: Prunus avium, planting stock, reforestation, drought, seedlings
Book
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El libro se centra en el estudio de las masas de pino silvestre de la Sierra de Guadarrama, concretamente en los montes de Valsaín, Cercedilla y Navacerrada. La obra se ha dividido en varias partes, con el fin de analizar independientemente la estructura productiva de estos pinares y los factores (sociales, ecológicos y selvícolas) que la han condicionado, así como elaborar unas tablas de producción que permitan programar y planificar una selvicultura racional. En primer lugar, se han abordado aspectos generales relacionados con el pino silvestre, la Sierra de Guadarrama y los montes de Valsaín, Cercedilla y Navacerrada. A continuación, y dadas las evidentes implicaciones que tiene en el estado actual de cualquier masa forestal la forma en que se haya gestionado y aprovechado durante siglos, se ha realizado un análisis de la evolución histórica de estos montes, tanto desde el punto de vista de su propiedad, como de su gestión y aprovechamiento antes y después de ser ordenados. Se han estudiado todos los factores que han influido en el devenir histórico de estos pinares, así como las dificultades encontradas para la aplicación de criterios técnicos y los logros obtenidos después de un siglo de ordenación. Esta parte del trabajo se ha llevado a cabo de forma independiente para los montes de Cercedilla y Navacerrada, por un lado, y para el pinar de Valsaín por otro, debido a sus notables diferencias. Además, se ha precedido de una serie de consideraciones acerca de la existencia y extensión histórica de las masas naturales de pino silvestre en esta zona del Sistema Central. La regeneración natural tiene también una enorme trascendencia en la estructura de las masas que se tratan por aclareos sucesivos, como es el caso de estos pinares. Por ese motivo, se ha abordado el análisis de la regeneración natural de los montes de Pinus sylvestris, con especial atención a los condicionantes existentes en la Sierra de Guadarrama. Para ello, se ha realizado una síntesis de la escasa y desordenada información que se ha podido recopilar sobre el tema, estudiando la influencia de los diversos factores implicados en este proceso natural. En la última parte se estudian las leyes y procesos que regulan el crecimiento y la producción de las masas de Pinus sylvestris en la Sierra de Guadarrama, a través de los siguientes aspectos: - Definición de las calidades de estación en función de la edad y la altura dominante. - Ajuste de tarifas de cubicación, de crecimiento corriente y de porcentaje de corteza, para las distintas calidades de estación. - Caracterización de la selvicultura encontrada, mediante las variables de masa. - Elaboración de unas tablas de producción de selvicultura de referencia por calidades de estación y para dos diferentes tratamientos de claras, uno moderado y otro fuerte, dotando de esta manera a los gestores de dichas masas de un instrumento que permita la planificación de diferentes alternativas selvícolas. Estas tablas de producción se han construido siguiendo un proceso híbrido entre la metodología utilizada en anteriores trabajos en nuestro país, y la propuesta por DECOURT (1964, 1972) y por BARTET y BOLLIET (1976), basadas en el inventario único de una red de parcelas experimentales.
Article
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Tree growth and competition play central roles in forest dynamics. Yet models of competition often neglect important variation in species-specific responses. Furthermore, functions used to model changes in growth rate with size do not always allow for potential complexity. Using a large data set from old-growth forests in California, models were parameterized relating growth rate to tree size and competition for four common species. Several functions relating growth rate to size were tested. Competition models included parameters for tree size, competitor size, and competitor distance. Competitive strength was allowed to vary by species. The best ranked models (using Akaike's information criterion) explained between 18% and 40% of the variance in growth rate, with each species showing a strong response to competition. Models indicated that relationships between competition and growth varied substantially among species. The results also suggested that the relationship between growth rate and tree size can be complex and that how we model it can affect not only our ability to detect that complexity but also whether we obtain misleading results. In this case, for three of four species, the best model captured an apparent and unexpected decline in potential growth rate for the smallest trees in the data set.
Article
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Plant-plant interactions influence how forests cope with climate and contribute to modulate species response to future climate scenarios. We analysed the functional relationships between growth, climate and competition for Pinus sylvestris, Quercus pyrenaica and Quercus faginea to investigate how stand competition modifies forest sensitivity to climate and simulated how annual growth rates of these species with different drought tolerance would change throughout the 21st century. Dendroecological data from stands subjected to thinning were modelled using a novel multiplicative nonlinear approach to overcome biases related to the general assumption of a linear relationship between covariates and to better mimic the biological relationships involved. Growth always decreased exponentially with increasing competition, which explained more growth variability than climate in Q. faginea and P. sylvestris. The effect of precipitation was asymptotic in all cases, while the relationship between growth and temperature reached an optimum after which growth declined with warmer temperatures. Our growth projections indicate that the less drought-tolerant P. sylvestris would be more negatively affected by climate change than the studied sub-Medi-terranean oaks. Q. faginea and P. sylvestris mean growth would decrease under all the climate change scenarios assessed. However, P. sylvestris growth would decline regardless of the competition level, whereas this decrease would be offset by reduced competition in Q. faginea. Conversely, Q. pyrenaica growth would remain similar to current rates, except for the warmest scenario. Our models shed light on the nature of the species-specific interaction between climate and competition and yield important implications for management. Assuming that individual growth is directly related to tree performance, trees under low competition would better withstand the warmer conditions predicted under climate change scenarios but in a variable manner depending on the species. Thinning following an exponential rule may be desirable to ensure long-term conservation of high-density Mediter-ranean woodlands, particularly in drought-limited sites.
Article
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Plant-plant interactions influence how forests cope with climate and contribute to modulate species response to future climate scenarios. We analysed the functional relationships between growth, climate and competition for Pinus sylvestris, Quercus pyrenaica and Quercus faginea to investigate how stand competition modifies forest sensitivity to climate and simulated how annual growth rates of these species with different drought tolerance would change throughout the 21st century. Dendroecological data from stands subjected to thinning were modelled using a novel multiplicative nonlinear approach to overcome biases related to the general assumption of a linear relationship between covariates and to better mimic the biological relationships involved. Growth always decreased exponentially with increasing competition, which explained more growth variability than climate in Q. faginea and P. sylvestris. The effect of precipitation was asymptotic in all cases, while the relationship between growth and temperature reached an optimum after which growth declined with warmer temperatures. Our growth projections indicate that the less drought-tolerant P. sylvestris would be more negatively affected by climate change than the studied sub-Medi-terranean oaks. Q. faginea and P. sylvestris mean growth would decrease under all the climate change scenarios assessed. However, P. sylvestris growth would decline regardless of the competition level, whereas this decrease would be offset by reduced competition in Q. faginea. Conversely, Q. pyrenaica growth would remain similar to current rates, except for the warmest scenario. Our models shed light on the nature of the species-specific interaction between climate and competition and yield important implications for management. Assuming that individual growth is directly related to tree performance, trees under low competition would better withstand the warmer conditions predicted under climate change scenarios but in a variable manner depending on the species. Thinning following an exponential rule may be desirable to ensure long-term conservation of high-density Mediter-ranean woodlands, particularly in drought-limited sites.
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A drier climate together with intense management can be detrimental for species when they are found at their xeric limit. We analyzed the dynamics of Pinus syl-vestris in Central Spain in relation to colonization by more drought-tolerant Quercus pyrenaica. The studied forest presents high biodiversity and is one of the last stands relict from a widespread pine-dominated forest in West-Central Iberian Mountains demised by human deforestation. The observed age patterns could suggest a natural regeneration origin of the current stand for both species. However, while oaks regenerated continuously since the 1950s, there was almost no pine regeneration after the 1870s. Therefore, the lack of pine regeneration was previous to recent climatic changes. Pine stands with ongoing oak colonization were likely thinned in the 1920s in opposition to pure pine stands. Mixed and pure stands expressed certain differences in their response to climate. Pines suffered more from high temperatures from spring to fall, which would reflect their lower tolerance to drought than oaks. Cross-wavelet analysis showed that pine exhibited an increase in their sensitivity to drought intensity in the last years. However, the dominant pine canopy established in the nineteenth century does not show symptoms of growth decline in response to climate change. The factors determining the disruption of pine regeneration need to be determined. Management could have played a dominant role constraining stand dynamics, threatening pine sustainability through modifications of the understory vegetation and soil properties. Keywords Mediterranean Á Forest management Á Land-use changes Á Quercus pyrenaica Á Pinus sylvestris Á Pine–oak
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Large trees (>76 cm breast-height diameter) are vital components of Sierra Nevada/Cascades mixed-conifer ecosystems because of their fire resistance, ability to sequester large amounts of carbon, and role as preferred habitat for sensitive species such as the California spotted owl. To investigate the likely performance of large trees in a rapidly changing climate, we analyzed growth rings of five conifer species against 20th century climate trends from local weather stations. Over the local station period of record, there were no temporal trends in precipitation, but maximum temperatures increased by 0.10 to 0.13 °C/decade (summer and autumn), and minimum temperatures increased by 0.11 to 0.19 °C/decade in all seasons. All species responded positively to precipitation, but more variation was explained by a significant positive response to minimum winter temperatures. High maximum summer temperature adversely affected growth of two species, and maximum spring temperatures in the year prior to ring formation were negatively associated with growth of one species. The strong coherent response to increasing minimum temperatures bodes well for growth of large trees in Sierra/Cascades region mixed conifer forest under continued climatic warming, but these trees will still be under threat by the increased fire intensity that is a indirect effect of warming.
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Distance-dependent individual-tree models have commonly been found to add little predictive power to that of distance-independent ones. One possible reason is plasticity, the ability of trees to lean and to alter crown and root development to better occupy available growing space. Being able to redeploy foliage (and roots) into canopy gaps and less contested areas can diminish the importance of stem ground locations. Plasticity was simulated for 3 intensively measured forest stands, to see to what extent and under what conditions the allocation of resources (e.g., light) to the individual trees depended on their ground coordinates. The data came from 50 × 60 m stem-mapped plots in natural monospecific stands of jack pine, trembling aspen and black spruce from central Canada. Explicit perfect-plasticity equations were derived for tessellation-type models. Qualitatively similar simulation results were obtained under a variety of modelling assumptions. The effects of plasticity varied somewhat with stand uniformity and with assumed plasticity limits and other factors. Stand-level implications for canopy depth, distribution modelling and total productivity were examined. Generally, under what seem like conservative maximum plasticity constraints, spatial structure accounted for less than 10% of the variance in resource allocation. The perfect-plasticity equations approximated well the simulation results from tessellation models, but not those from models with less extreme competition asymmetry. Whole-stand perfect plasticity approximations seem an attractive alternative to individual-tree models.
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European forests have a prominent role in theglobal carbon cycle and an increase in carbon storage has been consistently reported during the twentieth century. Any further increase in forest carbon storage, however, could be hampered by increases in aridity and extreme climatic events. Here, we use forest inventory data to identify the relative importance of stand structure (stand basal area and mean d.b.h.), mean climate (water availability), and recent climate change (temperature and precipitation anomalies) on forest basal area change during the late twentieth century in three major European biomes. Using linear mixedeffects models we observed that stand structure, mean climate, and recent climatic change strongly interact to modulate basal area change. Although we observed a net increment in stand basal area during the late twentieth century, we found the highest basal area increments in forests with medium stand basal areas and small to mediumsized trees. Stand basal area increases correlated positively with water availability and were enhanced in warmer areas. Recent climatic warming caused an increase in stand basal area, but this increase was offset by water availability. Based on recent trends in basal area change, we conclude that the potential rate of aboveground carbon accumulation in European forests strongly depends on both stand structure and concomitant climate warming, adding weight to suggestions that European carbon stocks may saturate in the near future.
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Individual trees, not forests, respond to climate. Such an individual-scale approach has seldom been used to retrospectively track the radial growth responses of trees to climate in dendrochronology. The aim of this study is to adopt this individual view to retrospectively assess tree sensitivity to climate warming, and to evaluate and compare the potential drivers of tree growth responses to climate acting at species, site and individual scales.Following a dendroecological framework, we sampled a network of 29 Pinus uncinata forests in NE Spain and obtained tree-ring widths series from 642 trees. Individual features as northness, elevation, slope, basal area, sapwood area, tree height and tree age were used to evaluate the potential drivers of tree growth responses to climate. The analyzed dataset includes diverse ecological and biogeographical conditions. The tree growth responses to climate were assessed by relating growth indices to climatic variables using linear-mixed effects models.Maximum November temperatures during the year prior to tree-ring formation enhanced P. uncinata growth mainly in mid-elevation sites, whereas at higher elevations growth was more dependent on the positive effect of warmer minimum May temperatures during the year of tree-ring formation. Current June precipitation was the positive main climatic driver of growth in sites prone to water deficit such as the southernmost limit of the species distribution area or very steep sites. Elevation was the main factor controlling how much growth variability is explained by climate at the site and tree scales. Climate warming was more intense during the early 20th century, when the importance of elevation as an indirect modulator of growth declined as compared with the late 20th century.Synthesis. The individual-scale approach taken in this study allowed detecting that trees growing at southern and low-elevation sites were the most negatively affected by warm and dry summer conditions. Our results emphasize that both (i) an individual-scale approach to quantify tree growth responses to climate and (ii) a detailed evaluation of the potential biotic and abiotic drivers of those individual responses are necessary to understand climate sensitivity of trees.This article is protected by copyright. All rights reserved.
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The relationships between the radial growth of Scots pine (Pinus sylvestris L.) and both temperature and precipitation were studied at 17 sites in the North-Eastern German lowlands. Furthermore, we investigated the influence of soil water availability on growth response to detect whether this integrative parameter better explains radial growth than climatic variables alone. Dendrochronological methods were applied to build tree-ring chronologies and calculate chronology statistics. Correlation coefficients, bootstrapped response functions, and pointer year analysis were used to analyse climate-growth relationships. Principal component analysis (PCA) was performed to explore differences in the strength of the climate signal. Chronology statistics showed similar radial growth patterns for the selected stands. Comparably low values for the expressed population signal (EPS) indicated a moderate common climate signal. The analyses revealed that radial growth is promoted primarily by a wet/warm February and secondarily by a wet/cool June. Although soil moisture availability in summer was not identified as the determining factor for radial growth, severe soil water stress can lead to substantial growth depression. Mean sensitivity and PCA suggest that climate sensitivity tends to slightly increase with increasing tree age. We conclude that the pine forests in North-Eastern Germany are far from being seriously threatened by inter-annual climatic variations in the near future.
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This research was carried out in two sample plots located in silver fir plantations mixed with beech (Fagus sylvatica) and spruce (Picea abies) in the Beskid Żywiecki Mountains (Węgierska Górka Forest District, Żabnica Forest sub-district). The aim of the study was to determine the influence of neighbouring trees (namely, fir, beech, spruce) on the basal area increment of the selected fir trees depending on the size (radius) of competition zones. During the study two static competition indices (Hegyi and Ch) and a retrospective dynamic competition index (Ci) were used. Based on the cumulative value of the latest competition index, all firs were clustered into groups of constant competition dynamics over time using Euclidean distance. The analysis indicated that the grouped firs were significantly different in terms of the basal area increment over the last 10 years, in terms of crown width, coefficient of slenderness and live crown ratio. These values decreased (apart from the coefficient of slenderness) with an increase in the cumulative retrospective dynamic competition index. In both stands, an increase in the total basal area of neighbouring trees, successively growing at a distance of 2, 3, 4 and 5 metres, had a negative influence on the basal area of the selected firs. In the Żabnica II sample, there were some differences in the competition interactions between the firs and the two other species. Because of the relationships between the cumulative retrospective dynamic competition index and many features of the subject trees and the neighbouring stand, and considering the time factor, we advise that this competition index is applied in studies of inter-specific and intra-specific tree competition.
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1. Competition for resources has long been considered a prevalent force in structuring plant communities and natural selection, yet our understanding of the mechanisms that underlie resource competition is still developing. 2. The complexity of resource competition is derived not only from the variability of resource limitation in space and time and among species, but also from the complexity of the resources themselves. Nutrients, water and light each differ in their properties, which generates unique ways that plants compete for these resources. 3. Here, we discuss the roles of supply pre-emption and availability reduction in competition for the three resources when supplied evenly in space and time. Plants compete for nutrients by pre-empting nutrient supplies from coming into contact with neighbours, which requires maximizing root length. Although water is also a soil resource, competition for water is generally considered to occur by availability reduction, favouring plants that can withstand the lowest water potential. Because light is supplied from above plants, individuals that situate their leaves above those of neighbours benefit directly from increased photosynthetic rates and indirectly by reducing the growth of those neighbours via shade. In communities where juveniles recruit in the shade of adults, traits of the most competitive species are biased towards those that confer greater survivorship and growth at the juvenile stage, even if those traits come at the expense of adult performance. 4. Understanding the mechanisms of competition also reveals how competition has influenced the evolution of plant species. For example, nutrient competition has selected for plants to maintain higher root length and light competition plants that are taller, with deeper, flatter canopies than would be optimal in the absence of competition. 5. In all, while more research is needed on competition for heterogeneous resource supplies as well as for water, understanding the mechanisms of competition increases the predictability of interspecific interactions and reveals how competition has altered the evolution of plants.
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The study of pointer years of numerous tree-ring chronologies of the central Iberian Peninsula (Sierra de Guadarrama) could provide complementary information about climate variability over the last 405 yr. In total, 64 pointer years have been identified: 30 negative (representing minimum growths) and 34 positive (representing maximum growths), the most significant of these being 1601, 1963 and 1996 for the negative ones, and 1734 and 1737 for the positive ones. Given that summer precipitation was found to be the most limiting factor for the growth of Pinus in the Sierra de Guadarrama in the second half of the 20th century, it is also an explanatory factor in almost 50% of the extreme growths. Furthermore, these pointer years and intervals are not evenly distributed throughout time. Both in the first half of the 17th and in the second half of 20th, they were more frequent and more extreme and these periods are the most notable for the frequency of negative pointer years in Central Spain. The interval 1600-1602 is of special significance, being one of the most unfavourable for tree growth in the centre of Spain, with 1601 representing the minimum index in the regional chronology. We infer that this special minimum annual increase was the effect of the eruption of Huaynaputina, which occurred in Peru at the beginning of 1600 AD. This is the first time that the effects of this eruption in the tree-ring records of Southern Europe have been demonstrated.
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Increased mortality of Scots pine (Pinus sylvestris L.) and spreading of deciduous trees are observed in the Swiss Rhone valley. Previous research identified climate change effects as main drivers of this trend. On the local scale, we hypothesize that legacies from past anthropogenic disturbances are superimposed on climate effects. • We reconstructed land-use history and quantified changes in tree species composition from 1930 to 1994 on 9468 ha of forested land. The aim was to analyze the contribution of anthropogenic disturbances to the observed changes and to disentangle human impact from climate change effects. • At altitudes below 1 200 m a.s.l. we found a shift from pine (–11.4%) to deciduous trees (+11%) with significantly lower increase of deciduous trees in stands formerly used for grazing and/or litter collecting. Conversely, pine decrease was not correlated with former anthropogenic disturbances. We interpret pine mortality as an effect of increased drought stress due to climate change while spread of deciduous trees is driven by land-use change. Grazing and litter collecting hindered deciduous tree regeneration and it was not until their abandonment a few decades ago that forest composition started to change. At higher elevations the shift from Norway spruce (Picea abies; –8.5%) to European larch (Larix decidua; +8.2%) corresponds to silvicultural management schemes, aimed at promoting larch recruitment. • Our study illustrates the importance of disentangling climate from land-use change effects for understanding shifts in forest composition. The findings are relevant for other regions in the European Alps where forests undergo comparable environmental changes.
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Mountain regions provide essential ecosystem goods and services (EGS) for both mountain dwellers and people living outside these areas. Global change endangers the capacity of mountain ecosystems to provide key services. The Mountland project focused on three case study regions in the Swiss Alps and aimed to propose land-use practices and alternative policy solutions to ensure the provision of key EGS under climate and land-use changes. We summarized and synthesized the results of the project and provide insights into the ecological, socioeconomic, and political processes relevant for analyzing global change impacts on a European mountain region. In Mountland, an integrative approach was applied, combining methods from economics and the political and natural sciences to analyze ecosystem functioning from a holistic human-environment system perspective. In general, surveys, experiments, and model results revealed that climate and socioeconomic changes are likely to increase the vulnerability of the EGS analyzed. We regard the following key characteristics of coupled human-environment systems as central to our case study areas in mountain regions: thresholds, heterogeneity, trade-offs, and feedback. Our results suggest that the institutional framework should be strengthened in a way that better addresses these characteristics, allowing for (1) more integrative approaches, (2) a more network-oriented management and steering of political processes that integrate local stakeholders, and (3) enhanced capacity building to decrease the identified vulnerability as central elements in the policy process. Further, to maintain and support the future provision of EGS in mountain regions, policy making should also focus on project-oriented, cross-sectoral policies and spatial planning as a coordination instrument for land use in general.