Article

Simulating the effects of thinning and species mixing on stands of oak (Quercus petraea (Matt.) Liebl./Quercus robur L.) and pine (Pinus sylvestris L.) across Europe

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Abstract

Tree species mixing of oak (Quercus petraea (Matt.) Liebl./Quercus robur L.) and pine (Pinus sylvestris L.) has been shown to have positive effects on ecosystem service provision. From a management perspective, however, it is still uncertain which thinning regime provides the highest possible productivity of mixed oak–pine forests in the long term. Because of a lack of empirical studies dealing with thinning and species mixing effects on oak–pine forests, we simulated forest growth in order to test which thinning type and intensity may provide the highest productivity in the long-term. To achieve this, we simulated the growth of pure and mixed stands of oak and pine for 100 years in 23 triplets located on an ecological gradient across Europe. For this purpose, we applied four different growth simulators and compared their results: the distance-independent single-tree simulator PROGNAUS, the distance-dependent single-tree simulator SILVA, the gap model ForCEEPS, and the process-based simulator 3D-CMCC-FEM. We investigated the effects of species mixing and thinning from the upper (thinning from above) and lower tail (thinning from below) of the diameter distribution by reducing the stand basal area to 50 and 80% of the maximum basal area. We compared simulated results of the relative volume productivity of mixed versus pure stands and of thinned versus unthinned stands to empirical results previously obtained on the same set of triplets. Simulated relative volume productivity ranged between 61 and 156%, although extremes of 10% and of 300% could be observed. We found the relative volume productivity to be influenced by stand age, but not by stand density, except for PROGNAUS. Relative volume productivity did not increase with the site water supply of the triplet location. Highest long-term productivity for oak, pine and oak–pine stands can be expected in consequence of thinning from above, but the effect of thinning intensity differed between simulators. Thinning effects were positively affected by stand density, but not by stand age, except for thinning from above predicted by PROGNAUS. Predicted thinning effects showed good approximation of results from thinning experiments for oak, but not for pine stands. We hypothesize the results might be caused by the insufficient simulator representation of climate and its interaction with other site variables and stand structure. Further work is needed to reduce the revealed limitations of the existing growth models, as we currently see no alternative to such kind of studies and simulators.

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... Kelty et al., 1992). Positive effects prevail, so that on average in mixtures, there are beneficial effects (Pretzsch and Schütze, 2009;Pretzsch et al., 2020), but results for individual plots can largely deviate from this mean (Huber et al., 2014;Pretzsch et al., 2020). The main reasons for positive mixture effects are tree specific differences in crown and root morphology (Canham et al., 1994;Kelty et al., 1992), water and nutrient use strategy (Pretzsch and Schütze, 2009), and different leaf and litter composition (Thelina et al., 2002;Aubert et al., 2006). ...
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... Mixture gains for Quercus spp. and Pinus sylvestris are minor with 7% and 9%, respectively, because these two species have similar ecological traits (Pretzsch et al., 2020). Negative mixture effects are observed, if one tree species outcompetes the other species. ...
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Quercus robur L., (pedunculate oak) and Quercus petraea (Matt.) Liebl., (sessile oak) are common broadleaved tree species in Europe, found from Scandinavia to the Iberian Peninsula. The two species are quite similar in appearance and have a broadly overlapping range. Oak trees have cultural significance for people throughout Europe and the trees or leaves are frequently used in national or regional symbols. Oak trees can live for more than 1 000 years and grow to be 30 to 40 m in height. The wood from oaks is hard and durable and has been valued for centuries. It is favoured for construction and for wine and spirit barrels; historically it was a major source of ship timbers. Recently, concerns have arisen about the fate of oaks in the face of Acute Oak Decline, a little understood syndrome.
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Mixing of complementary tree species may increase stand productivity, mitigate the effects of drought and other risks, and pave the way to forest production systems which may be more resource-use efficient and stable in the face of climate change. However, systematic empirical studies on mixing effects are still missing for many commercially important and widespread species combinations. Here we studied the growth of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) in mixed versus pure stands on 32 triplets located along a productivity gradient through Europe, reaching from Sweden to Bulgaria and from Spain to the Ukraine. Stand inventory and taking increment cores on the mainly 60–80 year-old trees and 0.02–1.55 ha sized, fully stocked plots provided insight how species mixing modifies the structure, dynamics and productivity compared with neighbouring pure stands. In mixture standing volume (+12 %), stand density (+20 %), basal area growth (+12 %), and stand volume growth (+8 %) were higher than the weighted mean of the neighbouring pure stands. Scots pine and European beech contributed rather equally to the overyielding and overdensity. In mixed stands mean diameter (+20 %) and height (+6 %) of Scots pine was ahead, while both diameter and height growth of European beech were behind (-8 %). The overyielding and overdensity were independent of the site index, the stand growth and yield, and climatic variables despite the wide variation in precipitation (520–1175 mm year-1), mean annual temperature (6–10.5 0C), and the drought index by de Martonne (28–61 mm 0C-1) on the sites. Therefore, this species combination is potentially useful for increasing productivity across a wide range of site and climatic conditions. Given the significant overyielding of stand basal area growth but the absence of any relationship with site index and climatic variables, we hypothesize that the overyielding and overdensity results from several different types of interactions (light-, water-, and nutrient-related) that are all important in different circumstances. We discuss the relevance of the results for ecological theory and for the ongoing silvicultural transition from pure to mixed stands and their adaptation to climate change.
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We examined the relationship between thinning intensity and volume increment predicted by four commonly used individual-tree growth models in Central Europe (i.e., BWIN, Moses, Prognaus, and Silva). We replicated conditions of older growth and yield experiments by selecting 34 young, dense plots of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and European beech (Fagus sylvatica L.). At these plots, we simulated growth, with mortality only, to obtain the maximum basal area. Maximum basal area was then decreased by 5% or 10% steps using thinning from below. Maximum density varied considerably between simulators; it was mostly in a reasonable range but partly exceeded the maximum basal area observed by the Austrian National Forest Inventory or the self-thinning line. In almost all cases, simulated volume increment was highest at maximum basal area and then decreased with decreasing basal area. Critical basal area, at which 95% of maximum volume increment can be achieved, ranged from 0.46 to 0.96. For all simulators, critical basal area was lower for the more shade-tolerant species. It increased with age, except for Norway spruce, when simulated with the BWIN model. Age, where mean annual increment culminated, compared well with yield tables. © 2015, National Research Council of Canada. All rights Reserved.
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Key message Competition-density relationships and self-thinning are major principles in forest growth. They are combined, describing self-thinning as a marginal case of the competition-density relationship. Robust estimation techniques allow parameterizing of both from national forest inventory data even for minor species. ContextThe competition-density principle, which can mathematically be described by the competition-density rule, is an important principle in plant ecology. The border line relationship is the self-thinning rule. Despite the importance of both rules for forest management, they have been fit for few species. AimsThe aim of this study is to compare competition-density rule and self-thinning rule in particular with respect to potential density for 15 species from the Austrian National Forest Inventory (ANFI). Methods The self-thinning line was estimated using quantile regression. The competition-density rule was fit as four- and as three-parameter model, where the fourth parameter was substituted (a) with a specific slope from the self-thinning line estimated from the ANFI and (b) Reineke’s slope (−1.605). ResultsPotential density was highest for Austrian pine and Norway spruce, followed by silver fir and Scots pine; it was considerably lower for European larch, stone pine and broadleaf species. Species-specific slopes of the self-thinning line ranged between −1.5 and −2.0 and were significantly different from Reineke’s slope for Norway spruce, European larch and European beech. Conclusions Using robust estimation techniques, both competition-density rule and self-thinning line can also be fit for minor species, providing an important guide for practical forest management.
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Graphical abstract Left: In canopies of un-thinned or just moderately thinned mixed species stands (95% and 75% line, respectively) the sum of the crown cross section area mostly exceeds pure stands (100% reference line) due to multiple crown overlaps. Right: Mixing species with varying morphological traits can cause a selection effect (a–c) but beyond this may trigger a morphological plasticity which can lead to denser canopy space filling, completer light capture, and productivity gains of mixed versus pure stands (d–f).Figure optionsDownload full-size imageDownload as PowerPoint slide
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Species mixing is widely held to stabilize productivity, increase resilience and contribute to risk minimization in forest stands in need of special as a result of longevity. However, research on the effects of mixing on productivity and resource consumption so far yielded fairly incoherent results rather than general findings. We focused on the effects of the spatial mixing pattern and the annual climate conditions on the mixing effect, which to date have seldom been considered as modifiers of mixing effects. Nine years of intensive survey of four pure stands of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) and two mixed plots with different mixing pattern showed: (1) mixing hardly changed annual net primary productivity at stand level when Norway spruce and European beech are cultivated group-wise but increased by 37 % on account of a higher efficiency of water and light use in individual tree-wise mixture. (2) Favourable climatic conditions increased the superiority of mixed versus pure stands productivity, while, in particular, water stress cancelled the benefit of mixing considerably. (3) An interaction between the spatial pattern and variable climatic conditions was revealed. Both improved light and water use were found in favourable years in close inter-specific intermingling. However, in unfavourable years the spatial pattern played a less pronounced role in terms of productivity.
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Forest gap models, initially conceived in 1969 as a special case of individual-tree based models, have become widely popular among forest ecologists for addressing a large number of applied research questions, including the impacts of global change on long-term dynamics of forest structure, biomass, and composition. However, they have been strongly criticized for a number of weaknesses inherent in the original model structure. In this paper, I review the fundamental assumptions underlying forest gap models, the structure of the parent model JABOWA, and examine these criticisms in the context of the many alternative formulations that have been developed over the past 30 years.Four assumptions originally underlie gap models: (1) The forest is abstracted as a composite of many small patches of land, where each can have a different age and successional stage; (2) patches are horizontally homogeneous, i.e., tree position within a patch is not considered; (3) the leaves of each tree are located in an indefinitely thin layer (disk) at the top of the stem; and (4) successional processes are described on each patch separately, i.e., there are no interactions between patches. These simplifications made it possible to consider mixed-species, mixed-age forests, which had been difficult previously mainly because of computing limitations.The structure of JABOWA is analysed in terms of the functional relationships used for formulating the processes of tree establishment, growth, and mortality. It is concluded that JABOWA contains a number of unrealistic assumptions that have not been questioned strongly to date. At the same time, some aspects of JABOWA that were criticized strongly in the past years are internally consistent given the objectives of this specific model.A wide variety of formulations for growth processes, establishment, and mortality factors have been developed in gap models over the past 30 years, and modern gap models include more robust parameterizations of environmental influences on tree growth and population dynamics as compared to JABOWA. Approaches taken in more recent models that led to the relaxation of one or several of the four basic assumptions are discussed. It is found that the original assumptions often have been replaced by alternatives; however, no systematic analysis of the behavioral effects of these conceptual changes has been attempted to date.The feasibility of including more physiological detail (instead of using relatively simple parameterizations) in forest gap models is discussed, and it is concluded that we often lack the data base to implement such approaches for more than a few commercially important tree species. Hence, it is important to find a compromise between using simplistic parameterizations and expanding gap models with physiology-based functions and parameters that are difficult to estimate. While the modeling of tree growth has received a lot of attention over the past years, much less effort has been spent on improving the formulations of tree establishment and mortality, although these processes are likely to be just as sensitive to global change as tree growth itself. Finally, model validation issues are discussed, and it is found that there is no single data source that can reliably be used for evaluating the behavior of forest gap models; instead, I propose a combination of sensitivity analyses, qualitative examinations of process formulations, and quantitative tests of gap models or selected submodels against various kinds of empirical data to evaluate the usefulness of these models for assessing their utility for predicting the impacts of global change on long-term forest dynamics.
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Successful implementation of ecosystem management requires strategic forest management planning, including the ability to forecast future forest composition. With advances in ecological modeling, many forms of succession models are available. In this review, we provide a broad synthesis of the methods used to model forest succession and discuss their suitability for strategic forest management planning. Qualitative models underpin theoretical understanding of forest succession but require expression in more formal quantitative forms to be applicable to strategic planning. Quantitative modeling methods can be differentiated as empirical or mechanistic. Empirical models rely on observational data of successional change. Mechanistic models rely on knowledge of underlying ecological processes to simulate succession. Hybrid mechanistic models represent a compromise in ecological modeling between empirical robustness and theoretical understanding. With their increased flexibility for scenario planning and enhanced representation of ecosystem processes, hybrid models are well suited to addressing the multiple environmental and social factors increasingly being considered under ecosystem management. However, empirical models still remain a suitable and practical alternative because hybrid models require increased resources to initialize, operate, and interpret; emphasize understanding rather than prediction; and assume that the modeled processes they represent are adequately understood.
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Tree species mixing has become a crucial tool in European forest management as positive interactions between species have been found to promote the provision of multiple ecosystem services, while at the same time reducing the risks associated with climate change. However, mixing effects have proven to be strongly context-dependant and some species combinations have still not been studied in detail. Here we focus on mixed forests of Scots pine and oak, which are likely to become increasingly popular for balancing wood production and other ecosystem services under climate change. Using 20-year growth data from newly established triplets in Germany and Denmark, this study investigates how mean tree and stand characteristics as well as productivity in mixed Scots pine-oak stands compare with adjacent monocultures and how stable the observed productivity relation is, considering inter-annual variations in local climate. Species mixing on average resulted in 15% higher standing volume and 14% higher volume productivity compared with the weighted mean of the adjacent monocultures. Oak profited most in mixture, showing overyielding of 19%. Overyielding on the stand and species level increased in years with higher water supply. In mixture, standing volume of Scots pine was 25% higher than in monocultures. Both species were found to modify their morphology in mixture. Oak in mixture showed a significantly higher inequality in stem volume compared with monocultures. We hypothesise that the observed overyielding of Scots pine-oak mixtures mainly results from complementary light use, where differences in shade tolerance, crown architecture and leaf phenology may be contributing factors.
Chapter
Silvicultural approaches for mixed-species stands typically aim at creating and maintaining stand compositional and structural diversity to provide the desired ecosystem function. An important aim of regeneration and tending is to develop stable mixtures that facilitate the anticipated interactions among the participating tree species and at the same time require little silvicultural input to maintain the composition of compatible tree species. To ensure survival and vigorous growth of trees in mixture in the long term, it is often necessary to separate species in space and time during the regeneration phase. Weaker competitors can be given a head start through advance regeneration or may be regenerated in patches that protect the majority of individuals from interspecific competition. In managed forests, tree species in mixture may also have a service function. For example, nurse crops may be used to facilitate establishment of sensitive tree species and to accelerate ecosystem recovery following disturbances. Trainer species are typically used to improve the quality development of stems of economically important species. Whereas the regeneration of mixtures has received considerable attention in research, there is little specific information regarding the thinning of mixed-species stands, which are often treated like an agglomerate of monospecific stands of the companion species. In the absence of quantitative information on optimal tree spacing, stand density, or the growth response to thinning in mixtures, crop tree thinning approaches are recommended. These facilitate the maintenance of desired species proportions as well as stand stability and development of quality attributes in crop trees through simple indicators. Although it is often assumed that the development of stem quality in mixtures is inferior to that in monospecific stands, there is so far little solid evidence to support this assumption. Rather, it appears that stem quality depends on specific interactions between species and the structural heterogeneity of stands.
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The maximum size-density relationship (MSDR) reflects the boundary site occupancy and the self-thinning line for a given species, being a useful tool in forestry. Studies focusing on the MSDR often do not cover the whole distribution of the studied species, which results in different boundaries for a given species in different regions. A common MSDR is lacking for the increasingly demanded large-scale studies. However, this information is important where silvicultural responses must be prioritized among monospecific stands or where comparisons among maximum and relative stand densities between and within species are required.
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Key messageThe mixture of Douglas-fir and European beech produced more biomass compared to what would have been expected from a weighted average of pure stands. Overyielding of the mixed stands improved with increasing stand age and under better site conditions. ContextThe mixture of Douglas-fir and European beech has the intrinsic potential to be one of the most productive forest types in Central Europe. AimsThe study investigated how the structure and productivity of mixed stands changed in comparison to pure ones. It analyzed whether there is overyielding in mixed stands and if it was modified due to stand development or along an ecological gradient. Methods Throughout Germany, 18 research plot triplets with 1987 trees were established in seven different ecological regions from dry to moist site conditions at ages 30 to 120 years. To investigate the growth of the stands, tree cores were collected from 1293 stems. ResultsThe study revealed significant overyielding of biomass in mixed stands of 6 % or 0.81 Mg ha−1 year−1. It was found that: (i) Overyielding in mixed stands was driven by an increase in Douglas-fir growth. (ii) Both species modified their morphology in mixture. Compared to the species in pure stands, Douglas-fir diameters in mixed stands were significantly larger, whereas European beech had a smaller diameter at breast height in the mixture. The effect increased with the age. (iii) The analyses revealed more pronounced overyielding in older stands and on better sites. Conclusion The findings show that overyielding of Douglas-fir and European beech in mixed stands results from a higher light interception by complementary space occupation.Graphical abstractᅟ
Article
Recent studies show that mixed species forests sometimes have higher stand productivity than monospecific forests, which we refer to as overyielding. Yet, results for temperate forests are ambiguous, possibly because forests differ in local site conditions, thinning history and forest age. In line with the niche complementarity hypothesis, we expect stronger overyielding for forests with species differing in both leaf phenology (evergreen or deciduous) and shade tolerance. We also hypothesize that overyielding will decrease with stand development because of decreasing resource availability. We compared 4 two-species mixtures with their corresponding monospecific stands from long-term field measurements in the Netherlands. The mixtures were Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)–common beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.)–common oak (Quercus robur L.), common oak–common beech, and common oak–silver birch (Betula pendula Roth). Overyielding was observed in 2 of the 4 mixtures: Douglas-fir–common beech mixtures had 35.9% and 36.7% higher volume growth relative to Douglas-fir and common beech monocultures, respectively; Scots pine–common oak mixtures had 20.3% and 31.2% higher volume growth relative to Scots pine and common oak monocultures, respectively, on average over time. Furthermore, overyielding was relatively constant for the two mixtures through stand development. This result was robust after accounting for possible effects of site quality and thinning history, where site quality contributed independently to stand productivity and thinning history had no effect. No significant overyielding effects were observed for the two deciduous mixed stands, i.e. common oak–common beech and common oak–silver birch. Mixing tree species in temperate forests resulted in overyielding for evergreen–deciduous species mixtures, but not for deciduous–deciduous species mixtures. This indicates that leaf phenology contributes to overyielding effects. Overyielding was higher in the Douglas-fir–common beech mixtures than the Scots pine–common oak mixtures, which coincides with a stronger contrast in shade tolerance between Douglas-fir and common beech and thus stronger complementarity. Our results support the complementarity hypothesis and imply that such mechanisms are maintained with stand development. It therefore appears that mixing evergreen with deciduous species with contrasting shade tolerance is a valid management strategy for increasing diversity and productivity of temperate forests in the Netherlands.
Article
Mixed stands of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) frequently over-yield, when compared to respective monospecific stands. Over-yielding is attributed to enhanced resource uptake efficiency through niche complementarity alleviating species competition, for example through enhanced root stratification in mixture. Under severe and frequent summer drought, however, water limitation may become crucial in modifying the prevailing competitive interaction in mixed beech-spruce forests. We hypothesize, therefore, that under drought (H I) inter-specific interaction with beech reduces water accessibility for spruce more than intra-specific conditions, thus (H II) exacerbating drought susceptibility of spruce in terms of reduced photosynthesis and stem growth. Reactions at the organ (leaf, fine root), tree and stand scale were analysed in a mature forest with beech-spruce group mixture. Under inter-specific conditions spruce’s fine-root production and depth of water uptake (assessed via δ18O of xylem water) shifted to shallow, drought-prone soil horizons, in agreement with H I. Overall, lowered fine root production and ramification along with a reduction in long-distance explorative ectomycorrhizal types resulted in decreased soil exploitation in spruce when growing together with beech. Spruce’s drought sensitivity was exemplified by a distinct decrease in stomatal conductance, net CO2 uptake rate and stem growth during periods of water limitation. Notwithstanding, species interaction effects were absent in leaf gas exchange and stem diameter growth, during a six-week summer drought period in 2013 as well as in the extremely dry year of 2003, hence rejecting H II. Based on results from soil moisture measurements and water uptake depth, we interpret the conflicting findings for H I and H II to result from: (i) seasonal shifts between positive (during spring drought) and negative (during summer drought) effects of beech neighbourhood on soil water availability for spruce, possibly overriding each other in their effect on annual stem diameter growth and (ii) the group-wise mixture pattern, where spruce is exposed to competition with beech only along group edges, i.e. laterally only, so that the putatively adverse beech effect on water accessibility stays limited. Our results suggest, compared to single tree mixture, group-wise mixture of beech and spruce to be a favourable silvicultural option in the face of climate change.
Article
Aim of the study: This paper presents the most appropriate ways to estimate the species proportions by area in mixed stands of Norway spruce (Picea abies L. Karst.) and European beech (Fagus sylvatica L.) by comparing stand level and individual tree level approaches. It also investigates whether different ways of describing species proportions by area can result in different judgments on the over- or under-yielding of species in mixtures. Area of the study: Three triplets of pure and mixed stands of Norway spruce and European beech in three locations in the northeast of Austria are investigated. The three locations differ considerably in slope, bedrock and soil type as well as in site index. Material and methods: In all 9 plots the coordinates of all trees, their dbh, height, height to the crown base and five year increment were measured. The potentially available areas of individual trees are calculated by Voronoi- diagrams and potential densities are estimated from the comparable pure stands, yield tables, and published equations for maximum basal area and Reineke’s maximum density line. Main results: The species proportions estimated by the individual tree approach with leaf area as growth characteristic gave the best fit with the stand approach with the most appropriate, regional maximum basal area equations. By using various definitions of species proportions, in the worst case the mixing effects on individual species can be seriously over- or underestimated while the mixing effects on the total increment is only negligibly affected. Research highlights: — Measures of species proportions by area are needed for comparing growth per hectare of a species in a mixed stand with that of the same species in a pure stand. — Species proportions at the stand level are based on estimates of the species’ potential densities, either in terms of maximum basal area or of maximum stand density index. — Species proportions at the tree level are derived from the area potentially available (APA) to the individual trees, based on the coordinates of trees in the stands, and on their growth characteristics, such as crown projection area or leaf area. — For the examples of Norway spruce - European beech stands, the species proportions derived according to the individual tree approach using leaf area as growth characteristics fits best with the stand approach using the most appropriate maximum basal area equations. © 2014 Ministerio de Agricultura Pesca y Alimentacion. All rights reserved.
Article
Forest ecosystems are characterized by high spatial heterogeneity, often related to complex composition and vertical structure which is a challenge in many process-based models. The need to expand process-based models (PBMs) to take in account such structural complexity led to development and testing of a new approach into Forest Ecosystem Models (FEMs), named 3D-CMCC-FEM, able to investigate carbon and water fluxes, including biomass pools and their partitioning, for complex multi-layer forests. 3D-CMCC FEM integrates several characteristics of the functional–structural tree models and the robustness of the light use efficiency (LUE) approach to investigate forest growth patterns and yield processes. The modelling approach was tested by simulating the effects of competition for light and water, growth and yield of a two-layered deciduous forest dominated by Turkey Oak in central Italy for a period of eight years. The model outputs were validated against a series of independently measured data for the major biomass pools, the inter-annual stem increments and above-ground net primary productivity of the overstorey and understorey, respectively. The comparison of Leaf Area Index, Gross Primary Production, and evapotranspiration produced by the model against MODIS data showed agreement in results. In addition, the multi-layered model approach was evaluated against a series of simplified versions to determine whether the enhanced complexity of the model positively contributed to its predictive ability. The proposed model reduced the error in the estimates of forest productivity (e.g. NPP) and dynamics (e.g. growth, mortality) and indicates the importance of considering, as far as possible, the structural complexity in PBMs.
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Despite the increasing relevance of mixed stands due to their potential benefits; little information is available with regard to the effect of mixtures on yield in forest systems. Hence, it is necessary to study inter-specific relationships, and the resulting yield in mixed stands, which may vary with stand development, site or stand density, etc. In Spain, the province of Navarra is considered one of the biodiversity reservoirs; however, mixed forests occupy only a small area, probably as a consequence of management plans, in which there is an excessive focus on the productivity aspect, favoring the presence of pure stands of the most marketable species.
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Zusammenfassung Der Versuch Waldleiningen 88 wurde im Jahr 1934 bei einem Bestandesalter von 48 Jahren durch ProfessorFabricius angelegt. Die Versuchsfläche liegt in der Nähe von Kaiserslautern im Südlichen Pfälzer Wald. Der Standort ist durch ein günstiges Klima, eine mittlere Nährstoffversorgung und ausreichenden Niederschlag in der Vegetationszeit gekennzeichnet. Die ertragskundlichen Ergebnisse zeigen ein sehr hohes Leistungsvermögen der untersuchten Eichenbestände. Unbehandelte Bestände zeigen Maximalwerte der Bestandesdichte von 40 m2/ha für die Eiche. Das Zuwachsniveau liegt bei gleichbleibender bis steigender Tendenz deutlich über dem Niveau der Ertragstafel. Auffällig ist der kontinuierliche Anstieg der Jahrringbreite während der 65jährigen Beobachtungszeit. Ziel der Untersuchung ist die Quantifizierung der Dimensionsentwicklung von Krone und Stamm in Abhängigkeit von der Durchforstungsstärke. Vor allem die Eingriffe zu Versuchsbeginn kennzeichnen die Eingriffsstärke. Diese bedingen eine typische Vorratshaltung. Bei gleichem BHD werden auf den Parzellen mit starker Hochdurchforstung deutlich größere Kronen gebildet. Die vorherrschenden Bäume haben auf allen Parzellen trotz sehr unterschiedlicher Bestandesdichte relativ ähnliche Konkurrenzwerte, während sich für die mitherrschenden Bäume starke Unterschiede ergeben. Die Kronenentwicklung wird durch starke Eingriffe stärker gefördert als die Durchmesserentwicklung. Auch die schwach durchforsteten Bestände zeigen eine bemerkenswerte Durchmesserentwicklung. Die Jahrringbreiten liegen seit den 80er Jahren des letzten Jahrhunderts auch hier über 2 mm/Jahr. Im Vergleich dazu leisten die Bäume auf den stark durchforsteten Parzellen einen um 10 bis 20% höheren Durchmesserzuwachs. Die periodischen Schwankungen der Jahrringbreite sind auf den stark durchforsteten Parzellen stärker ausgeprägt. Besonders auffällig ist der Zuwachsanstieg auf allen Parzellen seit den 80er Jahren. Insgesamt kann ein allgemein steigender Zuwachs und eine darüber hinaus gehende Zuwachssteigerung am Einzelbaum durch die Durchforstung identifiziert und quantifiziert werden. Auf Basis der im Jahr 1999 erreichten Dimensionen wird die künftige Wertentwicklung der Bestände mit dem Wuchsmodell Silva 2.2 berechnet und eine Abschätzung der betriebswirtschaftlichen Auswirkungen unterschiedlicher Eingriffsstärken vorgenommen. Als Ergebnis zeigt sich, dass der Durchmesservorsprung von stark durchforsteten Beständen am Ende der Umtriebszeit 5 bis 10 cm beträgt. Die Umtriebszeit kann bei gleichem Zieldurchmesser auf Wertholzstandorten um 30 bis 50 Jahre verkürzt werden. Bei der Betrachtung der Wertleistung der Bestände wird deutlich, dass eine ausreichende Anzahl von Erntebäumen die Grundvoraussetzung für eine hohe Wertleistung sind.
Article
Because of the gradual shift from pure even-aged forest management in central Europe, existing yield tables are becoming increasingly unreliable for forest management decisions. Individual tree-based stand growth modeling can make accurate stand growth predictions for the full range of conditions between pure even-aged and mixed-species uneven-aged stands. The central model in such a simulator is basal area increment for individual trees. Spatial information is not needed, and age and site index are intentionally not used to gain generality for all possible stand conditions. A basal area increment model is developed for all the main forest species in Austria: spruce (Picea abies), fir (Abies alba), larch (Larix decidua), Scots pine (Pinus sylvestris), black pine (Pinus nigra), stone pine (Pinus cembra), beech (Fagus silvatica), oak (Quercus robur, Quercus petraea and Quercus cerris), and for all other broadleaf species combined. The Austrian National Forest Inventory provided 5-year basal area increment from 44 761 remeasured trees growing on 5416 forested plots in the 1980s. This large sample is representative of forest conditions and forest management practices throughout Austria and therefore provides an excellent data base for the development of an increment model. The resulting increment model explained from 20 to 63% of the variation for all nine species and from 33 to 63% of the variation if the minor species Pinus cembra is excluded. These results compared quite closely with those of Wykoff for mixed conifer stands in the Northern Rocky Mountains. In the Austrian model, size variables (breast height diameter and crown length) accounted for 14–47% of the variation in basal area increment, depending on tree species. The best competition measure was the basal area of larger trees, which provides a tree-specific measure of competition without requiring spatial information; crown competition factor provided only minor improvement. Competition variables accounted for 9% of the variation on average, and up to 15% for some species. Topographic factors (elevation, slope, aspect) explained up to 3% of the variation, as did soil factors. Remaining site factors; such as vegetation type and growth district accounted for a maximum of 3% of the variation in increment. In total, site factors explained from 2 to 6% of the variation. Even though site factors account for a small percentage of the variation, they are not only significant, but serve to localize a particular prediction. These species-specific interrelationships between basal area increment and the various size, competition, and site varibles correspond quite well with ecological expectations and silvicultural understanding of these species in Austria. Because the sample base is so strong, the resulting growth models can be recommended not only for all of Austria but for surrounding regions with similar growth conditions.
Article
Techniques for reducing edge bias are discussed and a new approach, termed the linear expansion method, is presented. This method is applicable to a wide variety of plot shapes and sizes and is unbiased under very general assumptions about the forest tree spatial pattern. The accuracy and efficiency of the linear expansion method were compared with (i) no edge bias correction and (ii) corrections by plot image translation techniques for several forest stands and spatial patterns. Results indicated translation and the linear expansion method behaved equally well on square plots 0.08 ha in size. As the plot size diminished or its shape deviated from square, the linear expansion method provided greater accuracy and lower bias than translation techniques. The linear expansion method also provided useful accuracy on circular plots where translation was not feasible.
Article
Self‐thinning models were developed to describe the relationship between the stem number and mean diameter of even‐aged and monospecific tree stands undergoing self‐thinning. The models were developed separately for Pinus sylvestris L., Picea abies (L.) Karst. and Betula pendula Roth. stands. Data from 41 unthinned permanent sample plots were used. According to Reineke's equation and the —3/2 power rule of self‐thinning, a log‐log plot of average tree size and stem density will give a straight, self‐thinning line of constant slope. According to this study, the slope of the line consistent with Reineke's equation varies for different tree species. Within tree species, the intercept of the self‐thinning line varies according to site index.
Article
While previous studies focused on tree growth in pure stands, we reveal that tree resistance and resilience to drought stress can be modified distinctly through species mixing. Our study is based on tree ring measurement on cores from increment boring of 559 trees of Norway spruce (Picea abies [L.] Karst.), European beech (Fagus sylvatica [L.]) and sessile oak (Quercus petraea (Matt.) Liebl.) in South Germany, with half sampled in pure, respectively, mixed stands. Indices for resistance, recovery and resilience were applied for quantifying the tree growth reaction on the episodic drought stress in 1976 and 2003. The following general reaction patterns were found. (i) In pure stands, spruce has the lowest resistance, but the quickest recovery; oak and beech were more resistant, but recover was much slower and they are less resilient. (ii) In mixture, spruce and oak perform as in pure stands, but beech was significantly more resistant and resilient than in monoculture. (iii) Especially when mixed with oak, beech is facilitated. We hypothesise that the revealed water stress release of beech emerges in mixture because of the asynchronous stress reaction pattern of beech and oak and a facilitation of beech by hydraulic lift of water by oak. This facilitation of beech in mixture with oak means a contribution to the frequently reported overyield of beech in mixed versus pure stands. We discuss the far-reaching implications that these differences in stress response under intra- and inter-specific environments have for forest ecosystem dynamics and management under climate change.
Article
Processes governing tree interspecific interactions, such as facilitation and competition, may vary in strength over time. This study tried to unveil them by performing dendrometrical analyses on black spruce Picea mariana, trembling aspen Populus tremuloides and jack pine Pinus banksiana trees from pure and mixed mature boreal forest stands in the Clay Belt of northwestern Quebec and on the tills of northwestern Ontario. We cored 1430 trees and cut 120 for stem analysis across all stand composition types, tree species and study regions. Aspen annual growth rate was initially higher when mixed with conifers, but then progressively decreased over time compared to pure aspen stands, while jack pine growth rate did not differ with black spruce presence throughout all stages of stand development. When mixed with aspen, black spruce showed a contrary response to aspen, i.e. an initial loss in growth but a positive gain later. On the richer clay soil of the Quebec Clay Belt region, however, both aspen and spruce responses in mixed stands reversed between 37 and 54 years. Overall, our results demonstrate that interspecific interactions were present and tended to change with stand development and among species. Our results also suggest that the nature of interspecific interactions may differ with soil nutrient availability.
Article
The self-thinning rule established by Reineke in 1933, N ∝ d -1.605 (N, d = number of stems and quadratic mean diameter, respectively) assumes the same allometric relationship between size and density for a wide spectrum of species under self-thinning conditions. We re-evaluate this rule based on 28 fully stocked pure stands of common beech (Fagus sylvatica L.), Norway spruce (Picea abies [L.] Karst.), Scots pine (Pinus sylvestris L.), and common oak (Quercus petraea [Mattuschka] Liebl.) in Germany that date back to the year 1870. OLS regression of the model ln(N) = a + b·ln(d) results in b values of -1.789 for common beech, -1.664 for Norway spruce, -1.593 for Scots pine, and -1.424 for common oak. The allometric coefficient for common beech differs significantly from the other species. There is also a significant difference between the b values of Norway spruce and common oak. Except for Scots pine, the above allometric coefficients deviate significantly (common beech) and close-to-significantly (Norway spruce, common oak) from the coefficient -1.605 postulated by Reineke in 1933. To cover the species-specific oscillation of mortality rates, we additionally calculate the self-thinning coefficient for each survey period. Ecological implications of the species-specific scaling exponents are stressed and consequences regarding tools for regulating stand density are discussed.
Article
Aim Concern over the implications of climate change for biodiversity has led to the use of species–climate ‘envelope’ models to forecast risks of species extinctions under climate change scenarios. Recent studies have demonstrated significant variability in model projections and there remains a need to test the accuracy of models and to reduce uncertainties. Testing of models has been limited by a lack of data against which projections of future ranges can be tested. Here we provide a first test of the predictive accuracy of such models using observed species’ range shifts and climate change in two periods of the recent past. Location Britain. Methods Observed range shifts for 116 breeding bird species in Britain between 1967 and 1972 (t1) and 1987–91 (t2) are used. We project range shifts between t1 and t2 for each species based on observed climate using 16 alternative models (4 methods × 2 data parameterizations × 2 rules to transform probabilities of occurrence into presence and absence records). Results Modelling results were extremely variable, with projected range shifts varying both in magnitude and in direction from observed changes and from each other. However, using approaches that explore the central tendency (consensus) of model projections, we were able to improve agreement between projected and observed shifts significantly. Conclusions Our results provide the first empirical evidence of the value of species–climate ‘envelope’ models under climate change and demonstrate reduction in uncertainty and improvement in accuracy through selection of the most consensual projections.
Article
This paper summarises the results from 35years-observed thinning experiments on 256 permanent sample plots in 10–60year-old stands of ash, aspen, birch, oak, pine and spruce in Lithuania. Thinning enhanced crown projection area increment of residual trees. The largest effect was observed in stands of aspen and birch (growth increase by 200%), followed by ash and oak (over 100%), and spruce and pine (about 80%). Thinning also promoted dbh increment, especially in younger stands, and the increase of dbh increment was positively correlated with the thinning intensity. The strongest reaction was exhibited by oak and aspen, while ash, birch and conifers reacted to a lower extent. Low and moderate intensities of thinning stimulated volume production in younger stands while the opposite was observed in older stands with increasing removals. Spruce stands exhibited relatively strongest increase of volume increment and pine, –the weakest, while the effect on deciduous species was intermediate. The results demonstrate that significant increase in volume increment is achievable with thinning of only young forest stands, e.g. 10–20year-old pine, birch and ash, or 10–30year-old oak, aspen and spruce.