Chapter

The Annual Cycle of Development of Trees and Process-Based Modelling of Growth to Scale Up From the Tree To the Stand

Authors:
  • Land Life Company
  • Zhejiang Agriculture & Forestry University
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Abstract

Climate change affects both the annual cycle of tree development and the processes related to tree growth. The annual cycle of development manifests as observable phenological events such as leaf unfolding, flowering and leaf fall, but also includes less apparent traits, such as changes in frost hardiness and photosynthetic capacity. Seasonality in these traits can be due either to a fixed sequence of events that take place even in a constant environment, or to fluctuations in environmental factors. Thus, in a constant environment, the latter mode of development displays no seasonality. In addition, and depending on the trait considered, the internal state of development affects the tree’s capacity to respond to environmental factors. Given that the effects of climate change on the seasonality of a particular phenological trait may depend on interactions between fixed and fluctuating development traits, in order to explore these effects the entire annual cycle of development must be modelled. The processes related to tree growth include photosynthesis, respiration and allocation at the level of the individual tree; at stand level they include resource availability and biotic interactions. In this chapter we present the general theory of the annual cycle of development of trees, with examples of climate change effects on phenological traits with different mode of development for tree species in the boreal, temperate and Mediterranean zone of Europe. A process-based model on tree growth is outlined, with focus on scaling up from the tree to the stand level in time and space. Examples of climate change are presented, based on a model that couples the annual cycle of development and the growth of trees. Phenological events are characterized by responses to temperature that are under strong selective pressure. Future lines of development in this field of research include an assessment of the adaptive potential of phenological events to climate change. An example of this genetic approach is also presented.

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... As it is increasingly clear that phenology has a strong impact on ecosystem functioning (Kramer et al., 2000;Leinonen and Kramer, 2002;Noormets, 2009;Schwartz, 2013) and that climate change has a strong impact on phenology (Menzel, 2000;Menzel and Fabian, 1999;Schwartz, 1994), models have been developed that describe such phenological responses and applied to assess climate change impacts on the distribution of trees and functioning of forest ecosystems (Chuine et al., 1999;Chuine, 2000;Hänninen, 1990;Kramer, 1994;Murray et al., 1994). See Hänninen and Kramer (2007); Kramer and Hänninen (2009) and Chuine et al. (2013) for reviews on plant development models and their application in climate change studies. ...
... See Hänninnen and Kramer (2007), Kramer and Hänninen (2009) and Chuine et al. (2013) for reviews on these approaches to model plant development, and Kramer (1994) for considerations how to include photoperiod in phenological models. ...
Article
The timing of foliar budburst is an important component of the fitness of trees. Adaptation of budburst to local temperatures and phenotypic plasticity in the date of budburst to changes in temperature can therefore be expected. In this study, we analysed provenance trials of European beech (Fagus sylvatica L.) established over a wide geographic and climatic range in Europe. The analysis was based on a phenological model that represents the key processes at budburst phenology of temperate- and boreal zone deciduous trees. We conclude that adaptive differences exist between provenances in the critical chilling- and forcing requirements triggering budburst. Moreover, it is likely that these provenances show a plastic response to local environmental conditions for these two factors. Chilling- and forcing temperature requirements are key traits determining a tree’s response of the date of foliar budburst to temperature. We infer from our results that trees would be able to adjust this response when climatic conditions change. Implications for climate change assessment studies and suggestions to incorporate this second order phenotypic plasticity in phenological models are discussed.
... With an increasing interest in how climate impacts forest ecosystems, studies of plant phenology have become more common, spanning from single site field studies (Badeck et al., 2004) to continental remote sensing assessments (White, Thornton, & Running, 1997). In the northeastern United States and northern latitudes these studies indicate that warming trends have extended the growing season, with both an earlier spring and later autumn (Badeck et al., 2004;McNeil, Denny, & Richardson, 2008;Menzel, 2002;Tucker et al., 2001;White, Running, & Thornton, 1999;Zhang, Friedl, Schaaf, & Strahler, 2004), with implications for productivity (Badeck et al., 2004;White et al., 1999), carbon cycling (Cleland, Chuine, Menzel, Mooney, & Schwartz, 2007), nutrient and water cycling (McNeil et al., 2008), species interactions (Badeck et al., 2004), and disturbance regimes (Dukes et al., 2009;Kramer & Hänninen, 2009). ...
... While these studies offer a regional perspective, there are several scale-based limitations. Because of the large degree of heterogeneity in species composition, soil type, forest fragmentation, land use (mixed pixels) and elevation found in northeastern forests, the use of such coarse resolution assessments limits the evaluation of spatial variability in phenology (Fisher et al., 2006;Ibanez et al., 2010;Kramer & Hänninen, 2009). The success and interpretation of such efforts are also limited by the difficulty in linking plot level field measurements to satellite derived pixel values; as well as uncertainty in which phenological field metrics match sensor reflectance metrics (Fisher et al., 2006). ...
Article
Full-text available
Current remote sensing studies of phenology have been limited to coarse spatial or temporal resolution and often lack a direct link to field measurements. To address this gap, we compared remote sensing methodologies using Landsat Thematic Mapper (TM) imagery to extensive field measurements in a mixed northern hardwood forest. Five vegetation indices, five mathematical fits to model a continuous temporal response, and a suite of threshold estimates for “start of spring/season” (SOS) assessments were compared to field measurements of bud burst stage and hemispherical photo derived canopy structural metrics (transparency, leaf area index, greenness). Results indicated that a four-parameter logistic model based on at least five spring coverages of the Enhanced Vegetation Index (EVI) and a SOS threshold of 0.3 was most closely related to field metrics and most accurate in predicting the date of full leaf out. Plot level SOS was predicted with a mean absolute error of 11 days for all species and elevation combinations, but improved to 9 days for hardwood dominated plots and 7 days for sugar maple dominated plots. Mean absolute error was improved to 8 days when forest type (mixed, conifer hardwood) was used to refine predictions. The consistency of prediction errors across forest types indicates that while overall accuracy across pixels may be low, inter-annual comparisons of changes in phenology on a pixel basis may provide accurate assessments of changes in phenology over time. This was confirmed by application to seven years of independent phenology data predicted with 12 days of mean absolute error. However, image availability will be a limiting factor in areas of frequent cloud cover.
... To provide insight into the climate change impacts on the terrestrial carbon balance in the long term, both shortand long-term vegetation responses to a constantly changing environment should be better understood and represented. This implies better model representations of indirect shortterm processes such as the mechanisms governing vegetation phenology (Cleland et al., 2007; Kramer and Hänninen, 2009; Wolkovich et al., 2012), dynamic carbon and nutrient allocation (Litton et al., 2007; Epron et al., 2012; Franklin et al., 2012 ), photosynthetic temperature acclimation (Gea-Izquierdo et al., 2010 ), as well as better representations of indirect long-term processes such as soil, nutrient and carbon dynamics. Before addressing these complex process representations within models, however, it can be useful to test whether IAV cw can be explained by rather simple relationships with direct environmental drivers, such as drought, temperature, and radiation, which can affect, e.g. ...
... How long it takes for the photosynthetic capacity to diminish during extended cold periods – and possibly recover when temperatures rise again (e.g. see Suni et al., 2003a, b; Kramer et al., 2008; Kramer and Hänninen, 2009) – is not known for this site and will be investigated in a winter measurement campaign of leaf photosynthesis over the next few years. ...
Conference Paper
Full-text available
Long-term measurements of terrestrial fluxes through the FLUXNET Eddy Covariance network have revealed that carbon and water fluxes can be highly variable from year-to-year. This so-called interannual variability (IAV) of ecosystems is not fully understood because a direct relation with environmental drivers cannot always be found. Many dynamic vegetation models allocate NPP to leaves, stems, and root compartments on an annual ba- sis, and thus do not account for seasonal changes in productivity in response to changes in environmental stressors. We introduce this vegetation seasonality into dynamic vegetation model LPJ-GUESS by implementing a new carbon allocation scheme on a daily basis. We focus in particular on modelling the observed flux seasonality of the Amazon basin, and validate our new model against fluxdata and MODIS GPP products. We expect that introducing seasonal variability into the model improves estimates of annual productivity and IAV, and therefore the model’s representation of ecosystem carbon budgets as a whole.
... To provide insight into the climate change impacts on the terrestrial carbon balance in the long term, both shortand long-term vegetation responses to a constantly changing environment should be better understood and represented. This implies better model representations of indirect shortterm processes such as the mechanisms governing vegetation phenology (Cleland et al., 2007;Kramer and Hänninen, 2009;Wolkovich et al., 2012), dynamic carbon and nutrient allocation (Litton et al., 2007;Epron et al., 2012;Franklin et al., 2012), photosynthetic temperature acclimation (Gea-Izquierdo et al., 2010), as well as better representations of indirect long-term processes such as soil, nutrient and carbon dynamics. Before addressing these complex process representations within models, however, it can be useful to test whether IAV cw can be explained by rather simple relationships with direct environmental drivers, such as drought, temperature, and radiation, which can affect, e.g. ...
... How long it takes for the photosynthetic capacity to diminish during extended cold periods -and possibly recover when temperatures rise again (e.g. see Suni et al., 2003a, b;Kramer et al., 2008;Kramer and Hänninen, 2009) -is not known for this site and will be investigated in a winter measurement campaign of leaf photosynthesis over the next few years. ...
Article
Vegetation – atmosphere carbon and water exchange at one particular site can strongly vary from year to year, and understanding this interannual variability in carbon and water exchange (IAVcw) is a critical factor in projecting future ecosystem changes. However, the mechanisms driving this IAVcw are not well understood. We used data on carbon and water fluxes from a multi-year Eddy Covariance study (1997–2009) in a Dutch Scots pine forest and forced a process-based ecosystem model (LPJ-GUESS) with local data to, firstly, test whether the model can explain IAVcw and seasonal carbon and water exchange from direct environmental factors only. Initial model runs showed low correlations with estimated annual gross primary productivity (GPP) and annual actual evapotranspiration (AET), while monthly and daily fluxes showed high correlations. The model underestimated GPP and AET during winter and drought events. Secondly, we adapted the temperature inhibition function of photosynthesis to account for the observation that at this particular site, trees continue to assimilate at very low atmospheric temperatures (up to daily averages of −10 °C), resulting in a net carbon sink in winter. While we were able to improve daily and monthly simulations during winter by lowering the modelled minimum temperature threshold for photosynthesis, this did not increase explained IAVcw at the site. Thirdly, we implemented three alternative hypotheses concerning water uptake by plants in order to test which one best corresponds with the data. In particular, we analyse the effects during the 2003 heatwave. These simulations revealed a strong sensitivity of the modelled fluxes during dry and warm conditions, but no single formulation was consistently superior in reproducing the data for all time scales and the overall model-data match for IAVcw could not be improved. Most probably access to deep soil water leads to higher AET and GPP simulated during the heat wave of 2003. We conclude that photosynthesis at lower temperatures than assumed in most models can be important for winter carbon and water fluxes in pine forests. Furthermore, details of the model representations of water uptake, which are often overlooked, need further attention, and deep water access should be treated explicitly.
... To provide insight into the climate change impacts on the terrestrial carbon balance in the long term, both shortand long-term vegetation responses to a constantly changing environment should be better understood and represented. This implies better model representations of indirect shortterm processes such as the mechanisms governing vegetation phenology (Cleland et al., 2007;Kramer and Hänninen, 2009;Wolkovich et al., 2012), dynamic carbon and nutrient allocation (Litton et al., 2007;Epron et al., 2012;Franklin et al., 2012), photosynthetic temperature acclimation (Gea-Izquierdo et al., 2010), as well as better representations of indirect long-term processes such as soil, nutrient and carbon dynamics. Before addressing these complex process representations within models, however, it can be useful to test whether IAV cw can be explained by rather simple relationships with direct environmental drivers, such as drought, temperature, and radiation, which can affect, e.g. ...
... How long it takes for the photosynthetic capacity to diminish during extended cold periods -and possibly recover when temperatures rise again (e.g. see Suni et al., 2003a, b;Kramer et al., 2008;Kramer and Hänninen, 2009) -is not known for this site and will be investigated in a winter measurement campaign of leaf photosynthesis over the next few years. ...
Article
Full-text available
The vegetation–atmosphere carbon and water exchange at one particular site can strongly vary from year to year, and understanding this interannual variability in carbon and water exchange (IAVcw) is a critical factor in projecting future ecosystem changes. However, the mechanisms driving this IAVcw are not well understood. We used data on carbon and water fluxes from a multi-year eddy covariance study (1997–2009) in a Dutch Scots pine forest and forced a process-based ecosystem model (Lund–Potsdam–Jena General Ecosystem Simulator; LPJ-GUESS) with local data to, firstly, test whether the model can explain IAVcw and seasonal carbon and water exchange from direct environmental factors only. Initial model runs showed low correlations with estimated annual gross primary productivity (GPP) and annual actual evapotranspiration (AET), while monthly and daily fluxes showed high correlations. The model underestimated GPP and AET during winter and drought events. Secondly, we adapted the temperature inhibition function of photosynthesis to account for the observation that at this particular site, trees continue to assimilate at very low atmospheric temperatures (up to daily averages of −10 °C), resulting in a net carbon sink in winter. While we were able to improve daily and monthly simulations during winter by lowering the modelled minimum temperature threshold for photosynthesis, this did not increase explained IAVcw at the site. Thirdly, we implemented three alternative hypotheses concerning water uptake by plants in order to test which one best corresponds with the data. In particular, we analyse the effects during the 2003 heatwave. These simulations revealed a strong sensitivity of the modelled fluxes during dry and warm conditions, but no single formulation was consistently superior in reproducing the data for all timescales and the overall model–data match for IAVcw could not be improved. Most probably access to deep soil water leads to higher AET and GPP simulated during the heatwave of 2003. We conclude that photosynthesis at lower temperatures than assumed in most models can be important for winter carbon and water fluxes in pine forests. Furthermore, details of the model representations of water uptake, which are often overlooked, need further attention, and deep water access should be treated explicitly.
... However, as ForGEM has a modular structure, it facilitates the introduction of novel sub-models for different genetic and ecophysiological processes. Thus, Kramer and Hänninen (2009) introduced an ecophysiological sub-model to simulate the onset of growth in ForGEM. By means of scenario simulations with the ForGEM thus refined, they then examined the evolutionary change caused by climatic warming in the ecophysiological phenomena related to growth onset. ...
... Though limited in scope, Kramer and Hänninen's (2009) preliminary modelling exercise shows how the models of the annual cycle discussed in various chapters of the present volume can also be applied to studies addressing the evolutionary changes likely to be caused by the projected climate change. By allowing populations in different parts of the geographic area to adapt to the local conditions, i.e., to attain local parameter values for the models of the annual cycle, this approach opens new possibilities for modelling the impacts of climate change. ...
Chapter
The hypothetico-deductive modelling framework introduced in Chap. 2 is applied to examining the evolutionary aspects of the annual cycle in boreal and temperate trees. For use of growth resources and competition (capacity adaptation), early onset and late cessation of growth are selected for. However, due to the risk of spring and autumn frost damage (survival adaptation), they are simultaneously selected against. This trade-off is examined by means of computer simulations with models representing various regulation principles of the annual cycle. Considerable differences among the principles are reported. When the principles are equally constrained for avoidance of frost damage, some of them allow the trees to use the growing season more comprehensively than others. Next, differences among the provenances of the tree species are examined within the framework of the modelling approach. The annual cycle of each provenance is adapted to its native climate, and this adaptation is manifested in several traits associated with the environmental regulation of the annual cycle. In the models of the annual cycle, this genetic differentiation is readily addressed via the values of the model parameters, such as critical night length of growth cessation or the chilling requirement of rest break. The possibilities of addressing the effects of the maternal environment on the annual cycle traits of the offspring are also discussed, and so is the emerging approach of combining genetic and ecophysiological modelling of the annual cycle.
... As a rule, warming has accelerated the spring phenology over the last decades (Menzel et al., 2006;Piao et al., 2019), but more recently a levelling off of the acceleration has also been found (Fu et al., 2015). Changes in the spring phenology affect essential ecosystem processes, such as the cycling of water, carbon and nutrients (Kramer and Hänninen, 2009;Richardson et al., 2009), ecosystem productivity (Keenan et al., 2014), plant-animal relationships (Senior et al., 2020), population dynamics and competition of plant and animal species (Delpierre et al., 2017;Zettlemoyer et al., 2019), and ultimately, shifts in the geographical ranges of species (Chuine and Beaubien, 2001;Chuine, 2010). ...
Article
Full-text available
Process-based phenological models are currently used for assessing the effects of climatic warming on the timing of spring phenological events, such as leafout and flowering, in trees. However, the biological realism of the models may be undermined by the practices of often formulating the models solely on the basis of observational records of the phenological event rather than addressing the physiological processes actually modelled. Here we introduce a framework for developing process-based phenological models on the basis of experiments explicitly designed for this purpose and apply the framework to developing process-based models for leafout in four subtropical tree species. Our method is based on a hypothetico-deductive approach, where the air temperature responses of the simulated processes are inferred from their implications for the occurrence and timing of leafout in the experimental conditions. That approach has only rarely been taken with boreal or temperate trees, and to the best of our knowledge, never before with subtropical trees. Big differences were found between the four species in the air temperature responses modelled, and these differences implied major differences in the dormancy dynamics predicted for the four species. Together with the results of a recent modelling study based on observational data, our results highlight the importance of experimental studies for the development of biologically realistic process-based models of spring phenology in trees. The framework developed in the present study can be applied to developing such models for all tree species that show the phenomena of rest (endo-dormancy) and chilling requirement, no matter whether the trees are boreal, temperate, or subtropical.
... In this study, a calendar year is used as the basic unit in temporal synchronisation. This is a meaningful unit because it corresponds to the standard development cycle of plants and animal (Zhang et al., 2003;Peñuelas et al., 2009;Kramer and Hanninen, 2009). It also facilitates the study of patterns of inter-annual dynamics of plants and animals in a further study. ...
Article
Full-text available
Analysing spatio-temporal weather patterns is fundamental to better understand the system Earth. Such patterns depend on the spatial and temporal resolution of the available data. Here, we study a particular spatio-temporal pattern, namely, synchronisation, and how this is affected by different temporal resolutions and temporal heterogeneity. Twenty years of daily temperature data collected in 28 Dutch meteorological stations are used as case study. Given the complexity of the analysis, we propose a geovisual analytic approach based on self-organizing maps (SOMs). This approach allows exploring the data from two perspectives: (1) station-based, in which spatially synchronous weather stations are grouped into clusters; and (2) year-based, in which temporal synchronisation is analysed using a calendar year as basic unit and similar years are clustered. Clusters are identified using the SOM U-matrices and maps. Next, the spatial distribution of synchronous stations is displayed in the geographic space. Trend plots are used to illustrate trends in every cluster and the temperatures of stations and years are compared with the corresponding cluster representative values to identify anomalies in the temperature records. The analysis is repeated at daily, weekly and monthly resolutions to study the effects of different temporal resolutions on synchronisation. Also daily spatial synchronisation results for all years with those for groups of daily synchronous years are analysed to study the effects of temporal heterogeneity. Results show that synchronisation results are different at different temporal resolutions. Monthly results are the most stable ones both in station-based and year-based. It is also observed that spatial synchronisation results are simplified when considering temporal heterogeneity.
... This phenomenon, more recently called "false spring" (Marino et al., 2011;Chamberlain et al., 2019), may cause considerable damage even under the present climate (Gu et al., 2008;Kaur et al., 2020). However, if the advancement of spring phenology is not accompanied by the increased incidence of cold damage, then climatic warming may increase the productivity of trees and forests by prolonging the growing season (Kramer and Hänninen, 2009). In all, trustworthy projection of the effects of warming on the spring phenology of trees calls for biologically realistic process-based models. ...
Article
Full-text available
Pecan ( Carya illinoinensis ) is an important nut tree species in its native areas in temperate and subtropical North America, and as an introduced crop in subtropical southeastern China as well. We used process-based modeling to assess the effects of climatic warming in southeastern China on the leaf-out phenology of pecan seedlings and the subsequent risk of “false springs,” i.e., damage caused by low temperatures occurring as a result of prematurely leafing out. In order to maximize the biological realism of the model used in scenario simulations, we developed the model on the basis of experiments explicitly designed for determining the responses modeled. The model showed reasonable internal accuracy when calibrated against leaf-out observations in a whole-tree chamber (WTC) experiment with nine different natural-like fluctuating temperature treatments. The model was used to project the timing of leaf-out in the period 2022–2099 under the warming scenarios RCP4.5 and RCP8.5 in southeastern China. Two locations in the main pecan cultivation area in the northern subtropical zone and one location south of the main cultivation area were addressed. Generally, an advancing trend of leaf-out was projected for all the three locations under both warming scenarios, but in the southern location, a delay was projected under RCP8.5 in many years during the first decades of the 21st century. In the two northern locations, cold damage caused by false springs was projected to occur once in 15–26 years at most, suggesting that pecan cultivation can be continued relatively safely in these two locations. Paradoxically, more frequent cold damage was projected for the southern location than for the two northern locations. The results for the southern location also differed from those for the northern locations in that more frequent cold damage was projected under the RCP4.5 warming scenario (once in 6 years) than under the RCP8.5 scenario (once in 11 years) in the southern location. Due to the uncertainties of the model applied, our conclusions need to be re-examined in an additional experimental study and further model development based on it; but on the basis of our present results, we do not recommend starting large-scale pecan cultivation in locations south of the present main pecan cultivation area in southeastern subtropical China.
... 16,No. 8 of the annual cycle [29,30] provide a useful tool for generating quantitative projections for the trees [14,[31][32][33] and for scaling up these projections to higher organisational levels, ranging from stands and ecosystems to entire biogeographical areas [75][76][77][78]. For reliable projections of phenological changes, however, further species-, ecotype-and even cultivar-specific experimental data are needed in order to develop these models further and to better understand the underlying ecophysiology summarised in Figure 1. ...
Article
Climate warming has increased researchers' interest in plant phenology and its modelling. Although the main focus is on projections of accelerated springtime phenological events, also a further extension of the growing season by delayed growth cessation is often projected. However, ecophysiological studies indicate that, for boreal and temperate trees, such generalisations are precluded owing to differential climatic conditions and inter- and intraspecific genetic differences. The annual cycle of these trees is an integrated system, where one phase affects subsequent phases, resulting in delayed impacts, which are only partially addressed in current ecophysiological models. Here, we outline an updated integrated conceptual model of the annual cycle by identifying ecophysiological phenomena that are particularly significant under climate warming.
... 16,No. 8 of the annual cycle [29,30] provide a useful tool for generating quantitative projections for the trees [14,[31][32][33] and for scaling up these projections to higher organisational levels, ranging from stands and ecosystems to entire biogeographical areas [75][76][77][78]. For reliable projections of phenological changes, however, further species-, ecotype-and even cultivar-specific experimental data are needed in order to develop these models further and to better understand the underlying ecophysiology summarised in Figure 1. ...
Book
This book provides an overview of how boreal and temperate tree species have adapted their annual development cycle to the seasonally varying climatic conditions. Therefore, the frost hardy dormant phase, and the susceptible growth phase, are synchronized with the seasonality of the climate. The volume discusses the annual cycle, including various attributes such as timing of bud burst and other phenological events, seasonality of photosynthetic capacity or the frost hardiness of the trees. During the last few decades dynamic ecophysiological models have been used increasingly in studies of the annual cycle, particularly when projecting the ecological effects of climate change. The main emphasis of this volume is on combining modelling with experimental studies, and on the importance of the biological realism of the models.
... A trade-off in the timing occurs because a premature bud burst early in the spring increases the risk of damage by late frosts, while a delayed bud burst late in the spring causes a partial loss of the growing season [1,2]. Changes in spring tree phenology (see Glossary) have major implications for crucial ecological phenomena, ranging from carbon sequestration of the forest ecosystem [3][4][5] to the synchronisation of the phenological timing of the trees with that of animals [6,7]. The ecological implications often have further economic implications because many of the boreal and temperate tree species are important in practical forestry or horticulture [8]. ...
Article
In boreal and temperate trees, air temperature is a major environmental factor regulating the timing of spring phenological events, such as vegetative bud burst, through underlying physiological processes. This has been established by experimental research, and mathematical process-based tree phenology models have been developed based on the results. The models have often been applied when assessing the effects of climate change. Currently, there is an increasing trend to develop process-based tree phenology models using only observational phenological records from natural conditions. We point out that this method runs a high risk of producing models that do not simulate the real physiological processes in the trees and discuss experimental designs facilitating the development of biologically realistic process-based models for tree spring phenology.
... The conceptual growth curves shown in Figure 2 aim to demonstrate a general growth process in NEC, but the asymmetric indices can quantitatively describe the vegetation development process from three dimensions. Additionally, there are a number of shape parameters that can depict time series curves [9,59,60]. Therefore, one asymmetric index may not necessarily correspond uniquely to a single specific seasonal growth curve. The combination of several key phenological events may be conducive to identifying a specific plant growth type. ...
Article
Full-text available
Land surface phenology is a response of vegetation to local climate and to climate change, leading to crucial impacts on plant growth rhythm and productivity. Differences in vegetation growth activities in earlier and latter parts of the growing season are tightly correlated to phenological changes and the temporal distribution of plant productivity. However, its spatiotemporal pattern and climatic constraints are poorly understood. For Northeast China (NEC), long-term remotely-sensed vegetation greenness records (NDVI) were employed to quantify seasonally asymmetrical characteristics of vegetation growth in detail, which consists of asymmetry in growing rate (AsyR), mean vegetation greenness (AsyV), and growing period length (AsyL) during vegetation green up and senescence stages (simply termed as spring and autumn). Furthermore, the impact of temperature and precipitation on these indices were examined using relative importance analysis. The results indicate these asymmetric metrics present a pronounced interannual variability profile with a potential cycle of ten years (significant in AsyV and AsyR) for the entire NEC. AsyV is changing synchronously with AsyL but asynchronously with AsyR. The geographical distribution of asymmetric indices shows a similar pattern to identified vegetation cover types, especially in distinguishing crops from natural vegetation. Spatial-averaged asymmetric indices indicate spring production is greater than autumn production (reflected by negative AsyV) across most vegetation types in NEC, yet autumn is longer than spring in all vegetation types, which is identified by positive AsyL. Negative AsyR is mainly found in forests implying there is rapid green up and slow senescence in trees. From a temporal perspective, AsyV decreases with time in forested regions but increases in cropland and grassland, which is similar to the pattern for AsyL. AsyR primarily exhibits a positive trend in forest and a negative trend in cropland and grassland. A relative importance analysis indicates that asymmetries of temperature (AsyTemp) and precipitation (AsyPrcp) play an equal role in significantly affecting vegetation asymmetries in greenness and growth rate but are insignificant to growing season length. AsyTemp mainly presents an obvious contribution to changes in AsyR and AsyV over cropland and grassland. AsyPrcp shows a more widespread controlling effect on AsyR and AsyV over the NEC, except in eastern broad-leaved forest. For the entire NEC, asymmetries of temperature and precipitation are negatively correlated with AsyR but are positively correlated with AsyV and AsyL. This finding may imply that a warmer (positive AsyTemp) autumn tends to improve the length and intensity of vegetation activity. Thus, the long-term change in vegetation growth asymmetries may provide insights for the altering functions of ecosystems and provide information to more accurately build plant growth models in the context of global climate change. Additionally, when combined with other information, asymmetric indices can serve as a supporting tool in classification of vegetation types.
... Phenology of temperate deciduous trees is characterized by distinct seasonality and periodicity, which is mainly controlled by weather and climate, especially photoperiod and temperature changes (Leinonen and Hänninen 2002;Hänninen and Kramer 2007;Kramer and Hänninen 2009;Korner and Basler 2010;Chen 2017;Chen et al. 2017;Fu et al. 2019;Lang et al. 2019). Each year, temperate deciduous trees spread leaves as temperatures increase in early spring and begin vigorous photosynthesis in summer to provide energy for reproduction and growth. ...
Article
Full-text available
Examining whether a phenophase occurrence date in the current year affects the same phenophase occurrence date in the following year is crucial for developing cross-year phenological prediction models. Here, we carried out correlation analyses between leaf unfolding start (LUS)/leaf fall end (LFE) dates in the current and following years for four dominant tree species in temperate northern China from 1981 to 2012. Then, we calculated the recurrence intervals of LUS and LFE between two adjacent years for each species. Moreover, we investigated temperature effects on LUS/LFE dates, growing season and non-growing season lengths. Results show that correlation coefficients between LUS/LFE dates in the current and following years are nonsignificant at most stations. The recurrence interval of a phenophase has slight interannual variation and correlates significantly (and negatively) with the phenophase occurrence date of the current year. Further analyses indicate that LUS dates correlate significantly (and negatively) with spring mean temperatures, while LFE dates correlate significantly (and positively) with autumn mean temperatures, but negatively with growing season mean temperatures. In addition, spring mean temperatures can influence growing season length by controlling LUS date but cannot influence the following non-growing season length. Similarly, autumn mean temperatures and growing season mean temperatures can influence the subsequent non-growing season length but cannot influence the growing season length of the following year. Our study highlights that recurrence interval and time restrictions in the effects of seasonal temperatures on phenophase dates are the main environmental causes of nonsignificant correlations between phenophase occurrence dates in the current and following years.
... Plant phenology is primarily modulated by the seasonal variation in climate, which involves a stage of dormancy when the climate is adverse and a period of growth when conditions are favorable for vegetation activity. Temperature, water availability, and day length have been proposed as the main environmental drivers that constrain vegetation activity and regulate plant phenology, acting eventually as confounded restraints for vegetation growth (Chuine and Régnière, 2017;Jolly et al., 2005;Kramer and Hänninen, 2009). Temperature is the main climatic factor regulating plant phenology for the onset of vegetation in the northern high latitudes (Schwartz, 2003). ...
Article
Soil temperature remains isothermal at 0 °C and water shifts to a liquid phase during soil thawing. Vegetation may receive this process as a signal and a key to restore physiological activity. We aimed to show the relationship between the timing of soil thawing and the spring growth onset. We estimated the delay between the soil thawing and the spring growth onset in 78 sites of the FLUXNET network. We built a soil thawing map derived from modeling for the northern hemisphere and related it to the greenness onset estimated with satellite imagery. Spring onset estimated with GPP time series occurred shortly after soil surface thawing in tundra (1.1 ± 3.5 days) and alpine grasslands (16.6 ± 5.8 days). The association was weaker for deciduous forests (40.3 ± 4.2 days), especially where soils freeze infrequently. Needleleaved forests tended to start the growing season before the end of thawing (−17.4 ± 3.6 days), although observations from remote sensing (MODIS Land Cover Dynamics) indicated that the onset of greenness started after the thawing period (26.8 ± 3.2 days). This study highlights the role of soil temperature at the spring growth onset at high latitudes. Soil thawing becomes less relevant in temperate forests, where soil is occasionally frozen and other climate factors become more important.
... Predictions from plant phenological models could be validated and refined with the aid of UAV fine-scale observations. This would benefit a wide range of disciplines due to the multiple applications of such models in (Chuine et al., 2013): forecasting the effects of climate change on plant phenology (Hanninen and Tanino, 2011;Mulder et al., 2017); improvement of tree growth/forest productivity models (Kramer and Hänninen, 2009;Lempereur et al., 2017); predicting the timing of pollen production, particularly of allergenic pollens (Garcia-Mozo et al., 2009;Khwarahm et al., 2017); predictions of tree species distribution changes (Morin et al., 2008;Case and Lawler, 2017), macro-scale phenological analysis (macroecology) (Phillimore et al., 2013). ...
Thesis
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Vegetation phenology is the study of plant natural life cycle stages. Plant phenological events are related to carbon, energy and water cycles within terrestrial ecosystems, operating from local to global scales. As plant phenology events are highly sensitive to climate fluctuations, the timing of these events has been used as an independent indicator of climate change. The monitoring of forest phenology in a cost-effective manner, at a fine spatial scale and over relatively large areas remains a significant challenge. To address this issue, unmanned aerial vehicles (UAVs) appear to be a potential new platform for forest phenology monitoring. The aim of this research is to assess the potential of UAV data to track the temporal dynamics of spring phenology, from the individual tree to woodland scale, and to cross-compare UAV results against ground and satellite observations, in order to better understand characteristics of UAV data and assess potential for use in validation of satellite-derived phenology. A time series of UAV data were acquired in tandem with an intensive ground campaign during the spring season of 2015, over Hanging Leaves Wood, Northumberland, UK. The radiometric quality of the UAV imagery acquired by two consumer-grade cameras was assessed, in terms of the ability to retrieve reflectance and Normalised Difference Vegetation Index (NDVI), and successfully validated against ground (0.84≤R2≥0.96) and Landsat (0.73≤R2≥0.89) measurements, but only NDVI resulted in stable time series. The start (SOS), middle (MOS) and end (EOS) of spring season dates were estimated at an individual tree-level using UAV time series of NDVI and Green Chromatic Coordinate (GCC), with GCC resulting in a clearer and stronger seasonal signal at a tree crown scale. UAV-derived SOS could be predicted more accurately than MOS and EOS, with an accuracy of less than 1 week for deciduous woodland and within 2 weeks for evergreen. The UAV data were used to map phenological events for individual trees across the whole woodland, demonstrating that contrasting canopy phenological events can occur within the extent of a single Landsat pixel. This accounted for the poor relationships found between UAV- and Landsat-derived phenometrics (R2<0.45) in this study. An opportunity is now available to track very fine scale land surface changes over contiguous vegetation communities, information which could improve characterization of vegetation phenology at multiple scales. (Permalink to thesis@ http://hdl.handle.net/10443/4131)
... Process-based tree phenology models are currently used for assessing the effects of climatic change on boreal and temperate trees (Hänninen and Kramer, 2007;Kramer and Hänninen, 2009;Chuine et al., 2013;Hänninen, 2016;Chuine and Régnière, 2017;Hänninen et al., 2019). Our experimental results suggest that when the scope of process-based tree phenology modelling is broadened to cover subtropical trees (Chen et al., 2017), the concept of chilling has to be broadened to include higher temperatures than those usually assumed for boreal and temperate trees (Table 1). ...
Article
A R T I C L E I N F O Keywords: Bud burst chilling requirement climatic variation endodormancy flowering leafout subtropical trees tree phenology A B S T R A C T Spring phenology is a key phenomenon mediating the effects of climate change on terrestrial plants and ecosystems , but in regard to subtropical trees, the dormancy mechanisms that regulate spring phenology are still poorly understood. It has been suggested recently that similarly to temperate and boreal trees, subtropical tree species also show endodormancy and a chilling requirement of endodormancy release. However, there are no previous experimental results on the chilling temperature range that is effective for endodormancy release in subtropical trees. We studied endodormancy and the chilling requirement in four subtropical tree species experimentally. In addition to chilling in natural conditions, we applied controlled chilling at several constant temperatures ranging from-2 to +15 • C. Our results show endodormancy and a chilling requirement in the tree species studied and reveal several differences among the four species in the manifestation and depth of endo-dormancy. Most importantly, our findings indicate that contrary to the prevailing mainline conception that chilling temperatures are generally restricted to those below +10 • C, higher temperatures of up to +15 • C are also effective for endodormancy release in the subtropical tree species examined. An exact upper threshold of +10.4 • C has been experimentally established for boreal Betula pubescens. We hypothesized that this difference would be explained by differences in the occurrence of low autumn temperatures between the two respective climates. We developed a method for testing the hypothesis by analysing long-term climatic records in relation to the experimental findings. Tentative results supported our hypothesis. On the basis of this novel result, we put forward the testable generalized hypothesis that in any climatic conditions where trees show endodormancy, the range of temperatures physiologically effective in endodormancy release represents the range of typical autumn air temperatures occurring in those particular climatic conditions.
Chapter
Boreal and temperate trees grow under climatic conditions in which the ambient air temperature displays pronounced seasonal variation. Unlike herbs and grasses, trees overwinter without a sheltering snow cover, so that they are exposed to all the harsh climatic conditions. That is why their climatic adaptation is based on their annual cycle of development, whereby the frost-hardy dormant phase and the susceptible growth phase are synchronised with the seasonality of the climate. The main aspects of this adaptive strategy of trees are briefly discussed, emphasising both the geographical and the year-to-year variation of the seasonal air temperature conditions. Many boreal and temperate tree species have large ranges of geographical distribution, so that their different provenances have adapted to the particular local climate prevailing at their native growing site. The extent of the geographical variation in air temperature crucial for this adaptation is highlighted by examining the climatic records of four locations within the European distribution range of Pinus sylvestris. The extent of the year-to-year variation is similarly highlighted by examining a 92-year climatic record from Jyväskylä, central Finland. In the coolest summer, the temperature sum in Jyväskylä was similar to the average temperature sum 600 km north of Jyväskylä; and in the warmest summer it was similar to the average temperature sum 600 km south of Jyväskylä. This limited analysis suffices to reveal the extent of the climatic year-to-year variation that trees need to acclimate to at their native growing site.
Chapter
The hypothetico-deductive modelling framework introduced in Chap. 2 is applied to examining the effects of climatic change on the annual cycle of boreal and temperate trees. Most emphasis is devoted to the paradoxical hypothesis that climatic warming will increase the incidence of frost damage in these trees. According to early computer simulations, trees in boreal conditions in particular would deharden and even start to grow during such mild spells in winter as are commonly projected to prevail in the future climate, so that serious damage would result during subsequent periods of frost. Empirical tests of the frost damage hypothesis suggest that the catastrophic frost damage projected in the early computer simulations will not be realised. Even so, the frost damage hypothesis cannot be ruled out. Available experimental evidence remains limited, and theoretical work with computer simulations has shown that relatively small changes in the ecophysiological traits of trees may cause premature dehardening and growth onset during mild spells in the scenario climate. There have also been several reports of considerable frost damage to boreal and temperate trees and other plants in natural conditions after unseasonally warm spells in winter even in the present climate. For these reasons, nothing conclusive can be said about the frost damage hypothesis. However, the research discussed in this and other chapters of the present volume has pointed out not only the ecophysiological traits of the trees that are critical for the frost damage hypothesis but also the experimental designs that facilitate the determining of those traits in any tree population. Overall, the importance of ecophysiological realism and continuous critical testing of the models are emphasised. Finally, the implications of the effects of climatic change on tree seasonality to the stand and ecosystem level are briefly discussed.
Chapter
Upscaling of the models of the annual cycle of boreal and temperate trees to higher levels of organisation is briefly discussed. The models of the annual phenological cycle (Chap. 3), the annual cycle of photosynthesis in evergreen conifers (Chap. 4), and the annual cycle of frost hardiness (Chap. 5) address the modelled phenomena at the level of individual trees. Over the last decades, these models have been increasingly introduced as sub-models into large-scale process-based ecosystem models. In particular, models for the annual cycle of photosynthesis have often been used as sub-models. A simulation study reviewed here shows that unless the boreal restrictions described by the annual cycle model are taken into consideration, a drastic overestimate of the Gross Primary Production of the tree stand is obtained in simulations. About 15 years ago the models of the annual cycle were upscaled to the continental level in modelling the geographical ranges of tree species. The large-scale models thus refined predicted the geographical ranges of tree species accurately, suggesting that the seasonal phenomena of trees are major determinants of the geographical ranges of the tree species. While this approach opens an entirely new promising avenue for research, the annual cycle models applied in these studies still require further development for better realism. These models have also been addressed to a limited extent in the Dynamic Global Vegetation Models, but in this case, too, the annual cycle models applied evidently require further development.
Chapter
Laburnum anagyroides, a small tree or shrub from the Fabaceae family, is a promising object for its use in decorative landscaping and as a source of pharmaceuticals. The conventional propagation methods are not always successful for L. anagyroides. Herein, we describe an approach involving the application of tissue culture techniques for its micropropagation. This approach is based on activation of the pre-existing meristems from the axillary buds taken from a mature tree or seedling explants and includes the following phases: (1) preparation of primary explants and their cultivation on the Murashige and Skoog (MS) medium supplemented with 2.22 μM 6-benzylaminopurine (BAP), hot water pretreatment with subsequent cultivation of the seeds on a MS medium used to overcome the physical dormancy of seeds, (2) proliferation of the initiated explants on the full-strength (for seedling explants) or ½ MS medium (for axillary buds) with 2.22 μM BAP, (3) rooting of individual shoots on the ¼ MS medium supplemented with 2.68 μM α-naphthaleneacetic acid, and (4) acclimatization of the plants by spraying with the Emistim® elicitor. It was found that the explanting season also affected the initiation frequency from axillary buds but did not influence the culture initiation from seedling explants. In the tissue culture of both buds and seedlings, BAP not only stimulated higher number of shoots but also ensured the development of normal shoots compared with the thidiazuron-containing medium. The results of our study can be used for the mass propagation of L. anagyroides and for obtaining good-quality seedlings suitable for gardening and for pharmaceutical industry.
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A carbon-balance model of the growth of an even-aged, self-thinning, mono-specific stand of trees is derived using a structural framework based on pipe-model theory. Within the pipe-model framework, dry matter arising from extension of roots and shoots is separable from that arising from the cross-sectional expansion of stems. This permits the derivation of models describing the growth of average stem length, total basal area, and total volume of the stand. Variations of these models are described for two situations: (1) where the annual rates of substrate production and feeder-root turnover can be assumed constant over time; and (2) where these rates are expected to change over time, such as in polluted environments. The model describing the growth of stand volume for the first situation fits published yield tables. Growth-rate models applicable to individual trees are also described.
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The frost hardiness of 15- to 25-year-old Scots pine (Pinussylvestris L.) and Norway spruce (Piceaabies (L.) Karst.) growing under central Finnish conditions was followed during 1985–1987. Shoots were subjected to artificial frost in the laboratory. Frost hardiness was assessed by the impedance method and by visual scoring. Frost hardiness varied during the years from −3.5 °C to lower than −40 °C. The rate of dehardening increased after about mid-April in both tree species when the daily mean temperature increased by several degrees above 0 °C. The maximum rate of dehardening varied slightly from year to year. In both species the frost hardiness of the previous year's shoot decreased during shoot elongation. This phenomenon was more prominent in pine than in spruce. Shoots were most susceptible to frost damage at the time when shoot elongation was ceasing. The onset and development of hardiness in autumn varied from year to year, especially in spruce. Some difference in hardening was found between the current and the previous year's shoots. The rate of hardening increased typically around mid-September in both species, when the mean daily temperatures decreased to within the range of 5–10 °C.
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A framework is presented for modelling bud burst phenology of trees from the cool and temperate regions. Three ecophysiological aspects affecting the timing of bud burst are considered: (i) effects of environmental factors on the rest status of the bud, (ii) effect of rest status on the ability for bud burst, and (iii) direct effect of air temperature on the rate of development towards bud burst. Any model for bud burst phenology can be presented within the framework with three submodels, each of them addressing one of the corresponding three ecophysiological aspects. A total of 96 hypothetical models were synthesized by combining submodels presented in the literature. The models were tested in two experiments with saplings of Pinus sylvestris L. growing in experimental chambers at their natural site in eastern Finland. In the first experiment, air temperature and (or) concentration of atmospheric CO2 was elevated. Elevation of the air temperature hastened bud burst, whereas elevation of the concentration of CO2 did not affect it. Several models accurately predicted the timing of bud burst for natural conditions but too early for bud burst at the elevated temperatures. This finding suggests that (i) the risk of a premature bud burst with subsequent frost damage, as a result of climatic warming, was overestimated in a recent simulation study, and (ii) bud burst observations in natural conditions alone are not sufficient for the testing of these mechanistic models. Several models did predict the timing of bud burst accurately for all treatments, but none of them obtained sufficiently strong support from the findings to stand out as superior or uniquely correct. In the second experiment a photoperiod submodel for rest break was tested by exposing the saplings to short-day conditions. The short-day treatment had only a minor effect on the timing of bud burst. These results demonstrated the importance of the concept of model realism: the accuracy of a model can be lost in new conditions (e.g., global warming), unless the model correctly addresses the essential ecophysiological aspects of the regulation of timing of bud burst. Key words: annual cycle of development, chilling, dormancy, field test, photoperiod, rest break.
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The magnitude of measurement errors of the specific impedance difference was estimated and a formula to approximate the variance of the estimated frost resistance was derived. The measurements of specific impedance difference include the measurement errors of impedance before and after frost treatment and cross-sectional area. These errors in connection with the population variation cause variation in the estimated frost resistance. The frost resistance is estimated by first expressing the specific impedance difference values as a logistic sigmoid function of the treatment temperature, and then evaluating the inverse function at a given value of the specific impedance difference. The error variance between the estimated and the measured frost resistance was calculated using the estimated parameters, their standard deviations and correlations. In an example the impedance estimated frost resistance (LT.i0Qm) was - 10.9°C and its standard deviation 0.8°C.
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Genetic variability of 21 Italian populations of beech (Fagus sylvatica L.) was studied using starch gel electrophoresis and nine polymorphic enzyme gene loci. Expected mean heterozygosity varied from 13.6 per cent to 20.3 per cent. Observed heterozygosity was less than expected in all but two populations. No association between allele frequencies and soil type or altitude was found. As in other forest tree species, the among-populations component of variability was low (average FST = 0.046). Despite low genetic differentiation, principal components analysis of allelic frequencies revealed a geographical pattern. The first principal component, significantly correlated with latitude and longitude, snowed a clear separation of southern and northern populations. The statistical significance of the geographical pattern was tested by a resampling technique (bootstrap). The origin of Italian beech populations from eastern and southern refugia during the last glaciation is discussed. First principal component values and the higher allele variability found in southern populations seem to concord with the palynological evidence for a southern origin of beech in the peninsular part of Italy.Keywords: Fagus sylvatica, genetic variability, geographical variation, postglacial colonization
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The aim of the present study was to test the four commonly used models to predict the dates of flowering of temperate-zone trees, the spring warming, sequential, parallel and alternating models. Previous studies concerning the performance of these models have shown that they were unable to make accurate predictions based on external data. One of the reasons for such inaccuracy may be wrong estimations of the parameters of each model due to the non-convergence of the optimization algorithm towards their maximum likelihood. We proposed to fit these four models using a simulated annealing method which is known to avoid local extrema of any kind of function, and thus is particularly well adapted to fit budburst models, as their likelihood function presents many local maxima. We tested this method using a phenological dataset deduced from aeropalynological data. Annual pollen spectra were used to estimate the dates of flowering of the populations around the sampling station. The results show that simulated annealing provides a better fit than traditional methods. Despite this improvement, classical models still failed to predict external data. We expect the simulated annealing method to allow reliable comparisons among models, leading to a selection of biologically relevant ones.
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The transpiration, sap flow, stomatal conductance and water relations ofPinus pinaster were determined during spring and summer in a 64-year-old stand in Ribatejo (Portugal). The transpiration of the pine canopy was determined from sap flow or eddy covariance techniques. Canopy conductance values (g c) were estimated from inversion methods using eddy covariance or sap flow data, respectively, and from scaling-up methods using stomatal conductance values measured in the field and leaf area index (LAI) values. The transpiration was closely controlled by the stomatal conductance of pines ( was 0.05–0.15). For wet soil conditions, the various estimates ofg c showed reasonable agreement.g c peaked in the morning at 0.01 ms-1, exhibited a midday depression and showed a secondary peak in late afternoon. This behaviour could be predicted simply on the basis of the stomatal sensitivity to air vapour pressure deficit. On a seasonal basis, monthly average values ofg c decreased from 410-3 ms-1 in spring to 1.710-3 ms-1 in late summer. Accordingly, the transpiration peaked at 3 mmd-1 on wet soil in May. It decreased progressively during the summer drought to 0.8 mmd-1 at the end of August. The minimal value of needle water potential was maintained at -1.9 MPa but predawn values decreased from -0.6 MPa in May to -0.9 MPa in July. It may have reached lower values in August. The amount of water stored in the trunk accounted for a 12% (10 kgtree-1day-1) of the daily transpiration in spring. The storage capacity of the canopy was within the same order of magnitude. The trunk storage increased to 25% (13 kgtree-1day-1) of the daily transpiration at the end of summer under drought conditions. The sap flow beneath the crown lagged accordingly behind transpiration with a time constant estimated between 26 min in spring and 40 min at the end of summer.
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Trees do not form a natural group but share attributes such as great size, longevity, and high reproductive output that affect their mode and tempo of evolution. In particular, trees are unique in that they maintain high levels of diversity while accumulating new mutations only slowly. They are also capable of rapid local adaptation and can evolve quickly from nontree ancestors, but most existing tree lineages typically experience low speciation and extinction rates. We discuss why the tree growth habit should lead to these seemingly paradoxical features.
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Modern climate change is producing poleward range shifts of numerous taxa, communities and ecosystems worldwide. The response of species to changing environments is likely to be determined largely by population responses at range margins. In contrast to the expanding edge, the low-latitude limit (rear edge) of species ranges remains understudied, and the critical importance of rear edge populations as long-term stores of species' genetic diversity and foci of speciation has been little acknowledged. We review recent findings from the fossil record, phylogeography and ecology to illustrate that rear edge populations are often disproportionately important for the survival and evolution of biota. Their ecological features, dynamics and conservation requirements differ from those of populations in other parts of the range, and some commonly recommended conservation practices might therefore be of little use or even counterproductive for rear edge populations.
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A model for the succession of the forest ecosystem is described. The growth and development of trees and ground cover are controlled by temperature and light conditions and the availability of nitrogen and water. In addition, the effects of the annual cycle of trees including the risk of frost damage, wild fire, and wind damages are contained in the model as factors which control the survival and productivity of trees. The model also makes it possible to evaluated the risk of insect attack assuming that this risk is inversely related to the growth efficiency of trees. The PDF includes an abstract in Finnish.
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The net photosynthetic rate in Scots pine was recorded during three springs in field experiments. Mathematical models were developed from the data to quantify the changes in CO2 uptake. Models which included only temperature and light as independent variables gave a poorer approximation of the CO2 uptake at the beginning of the measuring period than one which included mathematically determined additional parameters. Two different features of the internal control of CO2 uptake the gross level effect and the sensitivity to high temperatures, were found as a result of this analysis. The modelling approach used in this study was similar to the one used earlier to quantify the effect of water stress on photosynthesis.
Article
The field data for photosynthetic CO2 uptake was analyzed and a simulation model for the recovery of CO2 uptake then developed that expressed the stage of development of the trees in spring. Four different hypotheses were tested concerning the relationship between the rate of maturation and temperature. A certain double sigmoid-curve was found to be best in prediction. Warm periods increased and cool ones decreased the rate of maturation. According to the results this relationship between the rate of maturation and temperature was not the same throughout the whole springtime period, but instead appeared to depend apart from on temperature, on the stage of development. The presented approach allowed the approximation of photosynthetic rate and its control during the whole spring using pure environmental data.
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To investigate the risk of frost damage to Scots pine (Pinus sylvestris L.) in northern regions under climatic warming, a submodel for such damage to trees was included in a forest ecosystem model of the gap type. An annual growth multiplier describing the effects of frost was calculated with the help of simulated daily frost hardiness and daily minimum temperature. The annual growth multiplier was used in the main ecosystem model when simulating the development of a tree stand using a time step of one year. Simulations of the growth and development of Scots pine stands in southern Finland (60@?N) under an elevating temperature indicated that climatic warming could increase the risk of frost damage due to premature onset of growth during warm spells in the late winter and early spring. Risk of frost damage implies uncertainty in yield expectations from boreal forest ecosystems in the event of climatic warming.
Article
1. To evaluate the impacts of climate change on the primary production of temperate deciduous tree species, the onset and cessation of the growth must be accurately described. The aim of this study is to find a model which predicts the onset of growth of Fagus sylvatica (European beech) accurately. 2. Several models have been proposed for the prediction of the timing of budburst of woody plants. Most of these models have been evaluated for species other than Fagus sylvatica, and in some cases for flower buds. Six models were fitted to data on leaf unfolding of Fagus sylvatica, collected in the Netherlands over 57 years (1901-68). 3. All models require only temperature as input. For Fagus sylvatica, however, photoperiod may influence the timing of the onset of growth. Therefore, photosensitivity was incorporated in these models. This reduced the predictive power compared to models that do not incorporate photosensitivity. 4. The model proposed by Sarvas (1974), in which the development of rest and quiescence is strictly separated in time, resulted in the best predictions of the average date of leaf unfolding in Fagus sylvatica.
Article
(1) The dates of budhurst of lateral shoots on 2- to 10-year old trees of Picea sitchensis were recorded on fourteen occasions at sites near meteorological stations in lowland and upland Britain between 1960 and 1980. (2) The following relationship accounted for 92% of the variation in thermal time from 1 February to the date of budburst among the fourteen observations: thermal time = 67.4 + 4401.8 exp (-0.042 x chill days) where thermal time was day degrees >5 ⚬C accumulated from 1 February, and chill days were the number of days ⩽5 ⚬C counted from 1 November, both based on mean daily air temperature ((max. + min.)/2). This model may be used to estimate the date of budburst on young P. sitchensis of most provenances growing in upland Britain. (3) The following features or assumptions of the model were examined with reference to the literature and/or by experimentation: the small effect of provenance; linearity in the relationship between bud growth rate and temperature; the large effect of chilling on thermal time to budhurst; the omission of daylength and soil temperature as variables; the choice of starting dates for effective chilling and thermal time; and the use of simple fixed base temperatures. (4) The model was applied to mean daily temperatures at Eskdalemuir for the period 1912-82. The predicted dates of budburst ranged from 23 April in 1961 to 30 May in 1923, with a mean date of 12 May.
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Abstract Five population-specific response functions were developed from quadratic models for 110 populations of Pinus sylvestris growing at 47 planting sites in Eurasia and North America. The functions predict 13 year height from climate: degree-days > 5 °C; mean annual temperature; degree-days 5 °C to mean annual precipitation. Validation of the response functions with two sets of independent data produced for all functions statistically significant simple correlations with coefficients as high as 0.81 between actual and predicted heights. The response functions described the widely different growth potentials typical of natural populations and demonstrated that these growth potentials have different climatic optima. Populations nonetheless tend to inhabit climates colder than their optima, with the disparity between the optimal and inhabited climates becoming greater as the climate becomes more severe. When driven by a global warming scenario of the Hadley Center, the functions described short-term physiologic and long-term evolutionary effects that were geographically complex. The short-term effects should be negative in the warmest climates but strongly positive in the coldest. Long-term effects eventually should ameliorate the negative short-term impacts, enhance the positive, and in time, substantially increase productivity throughout most of the contemporary pine forests of Eurasia. Realizing the long-term gains will require redistribution of genotypes across the landscape, a process that should take up to 13 generations and therefore many years.
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Respiration is poorly represented in whole plant or ecosystem models relative to photosynthesis. This paper reviews the principles underlying the development of a more mechanistic approach to modelling plant respiration and the criteria by which model behaviour might be judged. The main conclusions are as follows: (1) Models should separate C substrate from structure so that direct or indirect C substrate dependence of the components of respiration can be represented. (2) Account should be taken of the fact that some of the energy for leaf respiration is drawn from the light reactions of photosynthesis. (3) It is possible to estimate respiration associated with growth, nitrate reduction, symbiotic N2fixation, N-uptake, other ion uptake and phloem loading, because reasonable estimates are available of average specific unit respiratory costs and the rates of these processes can be quantified. (4) At present, it is less easy to estimate respiration associated with protein turnover, maintenance of cell ion concentrations and gradients and all forms of respiration involving the alternative pathway and futile cycles. (5) The growth-maintenance paradigm is valuable but ‘maintenance ' is an approximate concept and there is no rigorous division between growth and maintenance energy-requiring processes. (6) An alternative ‘process-residual’ approach would be to estimate explicitly respiratory fluxes associated with the six processes listed in (3) above and treat the remainder as a residual with a phenomenological ‘ residual maintenance’ coefficient. (7) Maintenance or ‘residual maintenance’ respiration rates are often more closely related to tissue N content than biomass, volume or surface area. (8) Respiratory fluxes associated with different processes vary independently, seasonally and during plant development, and so should be represented separately if possible. (9) An unforced outcome of mechanistic models should be a constrained, but non-constant, ratio between whole plant gross photosynthesis and respiration.
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To investigate the risk of frost damage to Scots pine (Pinus sylvestris L.) in northern regions under climatic warming, a submodel for such damage to trees was included in a forest ecosystem model of the gap type. An annual growth multiplier describing the effects of frost was calculated with the help of simulated daily frost hardiness and daily minimum temperature. The annual growth multiplier was used in the main ecosystem model when simulating the development of a tree stand using a time step of one year. Simulations of the growth and development of Scots pine stands in southern Finland (61° N) under an elevating temperature indicated that climatic warming could increase the risk of frost damage due to premature onset of growth during warm spells in the late winter and early spring. Risk of frost damage implies uncertainty in yield expectations from boreal forest ecosystems in the event of climatic warming. 38 refs., 9 figs., 4 tabs.
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A model is presented which solves simultaneously for leaf-scale stomatal conductance, CO2 assimilation and the energy balance as a function of leaf position within canopies of well-watered vegetation. Fluxes and conductances were calculated separately for sunlit and shaded leaves. A linear dependence of photosynthetic capacity on leaf nitrogen content was assumed, while leaf nitrogen content and light intensity were assumed to decrease exponentially within canopies. Separate extinction coefficients were used for diffuse and direct beam radiation. An efficient Gaussian integration technique was used to compute fluxes and mean conductances for the canopy. The multilayer model synthesizes current knowledge of radiation penetration, leaf physiology and the physics of evaporation and provides insights into the response of whole canopies to multiple, interacting factors. The model was also used to explore sources of variation in the slopes of two simple parametric models (nitrogen- and light-use efficiency), and to set bounds on the magnitudes of the parameters.
Article
The changes in the frost hardiness of Scots pine were modelled by a dynamic model where the input variables were temperature and photoperiod and the phase of annual development. The damage caused by freezing was described by the sigmoidal relationship between the relative needle damage and freezing temperature. The model simulations were carried out using temperature data from two sites in central Finland—Suonenjoki and Tampere. The validity of the frost hardiness model was tested with measured frost hardiness data from Suonenjoki. The effects of climatic warming were also simulated by increasing temperature of the long-term climatic data. Genotypic differences in chilling requirement, which determines the timing of the reduction of hardening competence, were included in the simulations. The simulated needle damage increased as a result of climatic warming, and the differences in the chilling requirement had a stronger effect on the amount of damage in the warmed climate than in the present climate. A large variation between years was found in the level of damage.
Article
The development of frost hardiness in forest trees is described by a dynamic model in which the input variables are the prevailing environmental conditions and the developmental stage of trees. The assumption of the model is that for each temperature and photoperiod there is a discrete stationary level of frost hardiness, which is attained if these environmental factors remain constant. The dependence of the stationary level on temperature and photoperiod is assumed to be piece-wise linear and additive. The rate of acclimation, i.e. frost hardening or dehardening, is described as a second-order dynamic process with two time constants, the second of which changes depending on the stage of the annual development of the trees. The frost hardiness model was calibrated and tested using experimental data from Douglas fir [Pseudotsuga menziesii var. glauca (Beissn.) Franco] seedlings. The results suggest that the second-order model describes the changes in frost hardiness better than the first-order model with only one time constant.Copyright 1995, 1999 Academic Press
Article
The chilling requirement of rest completion and the high temperature requirement of growth initiation were determined in three origins of silver birch (Betula pendula Roth.) seedlings and five origins of Scots pine (Pinus sylvestris L.) seedlings. In both the pine and birch the chilling requirement was highest in maritime Scottish origins and lowest in the most continental Finnish and Russian origins. The requirement for southern mountainous Spanish and Bulgarian pine origins was in between. In terms of the high temperature requirement, there were no clear differences between origins. These results suggest that owing to their high chilling requirement, which prevents the beginning of growth and the loss of frost hardiness during the frost-exposed season, origins from a maritime climate could be the most tolerant under climatic warming.
Article
Gas-exchange measurements on Eucalyptus grandis leaves and data extracted from the literature were used to test a semi-empirical model of stomatal conductance for CO2 gSc=go+a1A/(cs-I) (1+Ds/Do)] where A is the assimilation rate; Ds and cs are the humidity deficit and the CO2 concentration at the leaf surface, respectively; g0 is the conductance as A → 0 when leaf irradiance → 0; and D0 and a1 are empirical coefficients. This model is a modified version of gsc=a1A hs/cs first proposed by Ball, Woodrow & Berry (1987, in Progress in Photosynthesis Research, Martinus Mijhoff, Publ., pp. 221–224), in which hs is relative humidity. Inclusion of the CO2 compensation point, τ, improved the behaviour of the model at low values of cs, while a hyperbolic function of Ds for humidity response correctly accounted for the observed hyperbolic and linear variation of gsc and ci/cs as a function of Ds, where Ci is the intercellular CO2 concentration. In contrast, use of relative humidity as the humidity variable led to predictions of a linear decrease in gsc and a hyperbolic variation in ci/cs as a function of Ds, contrary to data from E. grandis leaves. The revised model also successfully described the response of stomata to variations in A, Ds and cs for published responses of the leaves of several other species. Coupling of the revised stomatal model with a biochemical model for photosynthesis of C3 plants synthesizes many of the observed responses of leaves to light, humidity deficit, leaf temperature and CO2 concentration. Best results are obtained for well-watered plants.
Article
Seven two-trait combinations (e.g. breeding system and seed dispersal mechanism) of five life history characteristics were used to analyse interspecific variation in the level and distribution of allozyme genetic diversity in seed plants. Highly significant differences were seen among categories for all seven comparisons. Life form and breeding system had highly significant influences on genetic diversity and its distribution. Regardless of other traits, outcrossing species tended to be more genetically diverse and had less genetic differentiation among their populations. Similarly, woody plants have less among population differentiation and somewhat more genetic diversity than non-woody species with similar life history traits. An analysis of twelve plant families indicated that species within families with predominately outcrossing, woody species had more genetic diversity and less interpopulation differentiation than species within families with predominately herbaceous species.
Article
A nitrogen-based model of maintenance respiration (Rm) would link Rm with nitrogen-based photosynthesis models and enable simpler estimation of dark respiration flux from forest canopies. To test whether an N-based model of Rm would apply generally to foliage of boreal and subalpine woody plants, I measured Rm (CO2 efflux at night from fully expanded foliage) for foliage of seven species of trees and shrubs in the northern boreal forest (near Thompson, Manitoba, Canada) and seven species in the subalpine montane forest (near Fraser, Colorado, USA). At 10°C, average Rm for boreal foliage ranged from 0.94 to 6.8μmol kg−1 s−1 (0.18–0.58 μmol m−2 s−1) and for subalpine foliage it ranged from 0.99 to 7.6 μmol kg−1 s−1 (0.28–0.64μmol m−2 s−1). CO2 efflux at 10°C for the samples was only weakly correlated with sample weight (r = 0.11) and leaf area (r = 0.58). However, CO2 efflux per unit foliage weight was highly correlated with foliage N concentration [r = 0.83, CO2 flux at 10°C (mol kg−1 s−1) = 2.62 × foliage N (mol kg−1)J, and slopes were statistically similar for the boreal and subalpine sites (P=0.28). CO2 efflux per unit of foliar N was 1.8 times that reported for a variety of crop and wildland species growing in warmer climates.
Article
Although it is widely recognised that allocation patterns are sensitive to environmental conditions, only few models that are used for assessing forest growth under changing environmental conditions have implemented a mechanistic description of this process. In this paper, a new approach for modelling the daily allocation of carbon and nitrogen is presented. It is based on the sink strength of each plant compartment. A relative carbon demand is calculated for each tree compartment based on its relationship to foliage biomass. The demand is zero when the ratio between both meets an optimum value, which itself is not constant but shifts according to the relative supply of water and nitrogen (i.e., the fine root to foliage ratio), or to tree height and crown length (sapwood / foliage ratio). The ratios between the compartments become unbalanced when carbon is relocated from the reserve pool to foliage during shoot growth, and when the mortality rates of specific tissues change according to the actual environmental conditions. Considering these principles, a dynamic carbon allocation scheme was developed that realistically reflects the effects of climatic conditions as well as changing allocation patterns due to changing tree dimensions.Three Scots pine (
Article
To evaluate the potential responses of individual trees to climatic warming, phenological observations of clones of Larix decidua (Mill.), Betula pubescens (Ehrh.), Tilia cor-data (Mill.), Populus canescens (Ait.), Quercus robur (L.), Fagus sylvatica (L.) and Picea abies (L.) relocated over a large latitudinal range in Europe were analysed. The magnitude of the response of the clone was compared to that of genetically different trees of the same species in part of the latitudinal range, which were assumed to have adapted to their local climates. It was found that the responses of the date of leaf unfolding and the date of leaf fall in the clones to temperature were similar in magnitude to those in the genetically different trees. This demonstrates that trees possess considerable plasticity and are able to respond phenotypically to a major change in their local climate.
Article
Two studies presented in the literature (Murray, Canned & Smith 1989; Hanninen 1991) evaluate the effect of increasing winter temperature on the probability of spring frost damage to trees, but yield contradictory results. It is unclear whether the disparity can be ascribed to the fact that different models were used, or is the result of different climatic warming scenarios being used, or is because the tree species at the different locations do indeed respond differently to warmer winters. To evaluate the effects of climatic warming to tree species in The Netherlands and in Germany, both models were fitted to long series of observations on the date of leaf unfolding of eleven tree species. The impact of the two scenarios (uniformly and non-uniformly changing winter temperature) on the date of leaf unfolding and on the probability of freezing temperature around that date was evaluated. To test the importance of adaptation to local climate, hypothetical provenance transfers were analysed. It was concluded that, for tree species in The Netherlands and Germany, the probability of spring frost damage will decrease. The contradictory results found in the literature could be ascribed to differences between provenances adapted to their local climate, and is not because different models and different climatic warming scenarios were used in these studies.
Article
Climate is a potent selective force in natural populations, yet the importance of adaptation in the response of plant species to past climate change has been questioned. As many species are unlikely to migrate fast enough to track the rapidly changing climate of the future, adaptation must play an increasingly important role in their response. In this paper we review recent work that has documented climate-related genetic diversity within populations or on the microgeographical scale. We then describe studies that have looked at the potential evolutionary responses of plant populations to future climate change. We argue that in fragmented landscapes, rapid climate change has the potential to overwhelm the capacity for adaptation in many plant populations and dramatically alter their genetic composition. The consequences are likely to include unpredictable changes in the presence and abundance of species within communities and a reduction in their ability to resist and recover from further environmental perturbations, such as pest and disease outbreaks and extreme climatic events. Overall, a range-wide increase in extinction risk is likely to result. We call for further research into understanding the causes and consequences of the maintenance and loss of climate-related genetic diversity within populations.
Article
Characteristics of tree species may uniquely situate them to withstand environmental changes. Paleoecological evidence indicates that the geographic ranges of tree species have expanded and contracted several times since the last glacial epoch in response to directional environmental changes. For most tree species, these range fluctuations have been accomplished without any apparent loss of genetic diversity. A possible explanation that distinguishes most trees from many herbaceous plants is that much of the genetic variation within tree species is found within rather than among their populations. Thus, the extinction of a relatively large proportion of a tree species’ populations would result in relatively little overall loss of genetic diversity. Furthermore, phylogeographic studies indicate that for some tree species, habitat heterogeneity (elevation, slope aspect, moisture, etc.) in glacial refugia may have preserved adaptive genetic variation that, when recombined and exposed to selection in newly colonized habitats, gave rise to the local adaptation currently seen.The maintenance of genetic diversity in the face of extensive habitat fragmentation is also a concern. Many forest trees, however, may be buffered from the adverse effects of habitat fragmentation. First, the longevity of individual trees may retard population extinction and allow individuals and populations to survive until habitat recovery occurs. Second, considerable evidence is available that both animal and wind-pollinated tree species in fragments experience levels of pollen flow that are sufficient to counteract the effects of genetic drift. The combination of individual longevity, high intra-population genetic diversity and the potential for high rates of pollen flow should make tree species especially resistant to extinction and the loss of genetic diversity during changing environmental conditions.
Article
Interception, throughfall and stemflow were determined in an 18-year-old maritime pine stand for a period of 30 months. This involved 71 rainfall events, each corresponding either to a single storm or to several storms. Gash's analytical model of interception was used to estimate the sensitivity of interception to canopy structure and climatic parameters. The seasonal cumulative interception loss corresponded to 12.6–21.0% of the amount of rainfall, whereas throughfall and stemflow accounted for 77–83% and 1–6%, respectively. On a seasonal basis, simulated data fitted the measured data satisfactorily (r2 = 0.75). The rainfall partitioning between interception, throughfall and stemflow was shown to be sensitive to (1) the rainfall regime, i.e. the relative importance of light storms to total rainfall, (2) the climatic parameters, rainfall rate and average evaporation rate during storms, and (3) the canopy structure parameters of the model. The low interception rate of the canopy was attributed primarily to the low leaf area index of the stand.
Article
A stand growth model based on individual tree growth, with a time step of 1 year and a time span equivalent to the rotation period, is presented. The model applies to Scots pine (Pinus sylvestris) in the boreal zone. The individual tree model describes annual net photosynthetic production and its allocation to different growth compartments. The model differs from many related ones in that inter-tree competition is explicitly described through the physical environment. Instead of defining a competition index, the concept of photosynthetic light ratio is applied. This is the ratio between actual photosynthesis produced under shade from other trees and the potential, or unshaded photosynthesis. The model estimates mass flows of the system and describes the differentiation of individual trees during stand development. Canopy closure is defined as the attainment of maximum needle biomass, which is soon followed by a decline in the amount of needles. Stem volume growth declines in the later development of the stand. Biological assumptions underlying these phenomena are discussed. Behaviour of the model is demonstrated with the aid of simulations of a natural stand and a planted stand.
Article
The process-based growth model, BIOMASS, was modified to incorporate low-temperature effects on photosynthetic production in Norway spruce (Picea abies) stands growing in northern Sweden. The low-temperature features incorporated in BIOMASS made it possible to simulate and estimate the reduction in photosynthetic rates caused by boreal conditions. The following four simulation-scenarios were used: (i) `potential' photosynthesis without boreal restrictions; (ii) reduction caused by a frozen soil; (iii) reduction caused by incomplete recovery of photosynthetic capacity during spring as a result of damage caused by low winter temperatures; and (iv) reduction as an effect of frost-induced autumn decline. Annual photosynthetic production (or gross primary production (GPP)) was simulated for three calendar years, 1990–1992, for stands with low (control) and high (irrigated and fertilized) nutrient availability. The reduction of `potential' GPP, caused by the low-temperature effects, ranged from 35–44% for control (C) and from 34–42% for irrigated-fertilised (IL) stands, respectively. The most pronounced loss of `potential' GPP originated from reduced photosynthetic capacity, in spring and early summer, which led to losses of 21–28% for C and 19–26% for IL stands. The variation between years differed mainly as an effect of differences in spring temperatures, which resulted in different rates of recovery of photosynthetic capacity. Reductions caused by frozen soil and low photosynthetic capacity during winter were similar in C and IL stands (12–13%), as were the losses resulting from severe autumn frosts (3–4%). It is concluded that, unless the effects of frozen soils and reduced photosynthetic capacity during spring and early summer are considered, large errors (ca. 40%) will be introduced into estimates of the annual photosynthetic production of boreal conifer forests.
Article
The impact of forest management on genetic diversity and mating was examined in European beech (Fagus sylvatica L.). Ten beech stands located in Europe were studied in pair-wise plots, differing in management intensity. The stands were genotyped with four highly polymorphic microsatellite loci. Comparison for genetic diversity measures between the stands with limited management and the high management-intensity stands (mostly shelter wood system) revealed no significant differences for allelic richness (A), effective number of alleles (Ae), number of rare alleles (Arare), neither for observed (Ho) nor expected heterozygosity (He). In all stands a significant excess of homozygotes was found, which is in agreement with previous isozyme publications. However, the increase in the inbreeding coefficient (Fis) in the stands with limited management was significantly higher than in the highly managed stands. Expectedly a low, but significant, differentiation among all stands was found (Fst = 0.058) which still reveals a clear geographic structure.The results indicate that the shelter wood system has no or minimum impact on the genetic diversity in European beech.
Article
In modeling canopy photosynthesis, it is important to discriminate between the direct and diffuse components of incoming, global radiation. An equation is presented to estimate the share of both components from the measured daily global irradiance only. In this equation the share of the diffuse component is related to the ratio between global and extra-terrestrial radiation. This relation is based on a summary of literature data and of radiation measurements in The Netherlands. The diurnal trends of global, direct and diffuse radiation were derived from a sinusoid with a correction depending on solar angle. The random variation around this sine wave is characterized. For clear skies about 15% of the diffuse flux comes predominantly from directions near the sun and this circumsolar component has to be added to the direct flux. On the other hand, for clear skies the diffuse fraction in the photosynthetically active wave bands is about 40% larger than that for the total global radiation. In the past, the partitioning between direct and diffuse radiation was tackled by assuming that short periods of either fully clear or overcast conditions alternate within the day. That approach severely underestimated the share of the diffuse component in the total global radiation. The method presented in this paper is particularly useful for application in crop growth models.
Article
In this study we aimed to combine knowledge of the ecophysiology and genetics of European beech to assess the potential of this species to adapt to environmental change. Therefore, we performed field and experimental studies on the genetic and ecophysiological functioning of beech. This information was integrated through a coupled genetic–ecophysiological model for individual trees that was parameterized with information derived from our own studies or from the literature. Using the model, we evaluated the adaptive response of beech stands in two ways: firstly, through sensitivity analyses (of initial genetic diversity, pollen dispersal distance, heritability of selected phenotypic traits, and forest management, representing disturbances) and secondly, through the evaluation of the responses of phenotypic traits and their genetic diversity to four management regimes applied to 10 study plots distributed over Western Europe. The model results indicate that the interval between recruitment events strongly affects the rate of adaptive response, because selection is most severe during the early stages of forest development. Forest management regimes largely determine recruitment intervals and thereby the potential for adaptive responses. Forest management regimes also determine the number of mother trees that contribute to the next generation and thereby the genetic variation that is maintained. Consequently, undisturbed forests maintain the largest amount of genetic variation, as recruitment intervals approach the longevity of trees and many mother trees contribute to the next generation. However, undisturbed forests have the slowest adaptive response, for the same reasons.
Article
Given the rate of projected environmental change for the 21st century, urgent adaptation and mitigation measures are required to slow down the on-going erosion of biodiversity. Even though increasing evidence shows that recent human-induced environmental changes have already triggered species’ range shifts, changes in phenology and species’ extinctions, accurate projections of species’ responses to future environmental changes are more difficult to ascertain. This is problematic, since there is a growing awareness of the need to adopt proactive conservation planning measures using forecasts of species’ responses to future environmental changes.
Article
Ecological changes in the phenology and distribution of plants and animals are occurring in all well-studied marine, freshwater, and terrestrial groups. These observed changes are heavily biased in the directions predicted from global warming and have been linked to local or regional climate change through correlations between climate and biological variation, field and laboratory experiments, and physiological research. Range-restricted species, particularly polar and mountaintop species, show severe range contractions and have been the first groups in which entire species have gone extinct due to recent climate change. Tropical coral reefs and amphibians have been most negatively affected. Predator-prey and plant-insect interactions have been disrupted when interacting species have responded differently to warming. Evolutionary adaptations to warmer conditions have occurred in the interiors of species’ ranges, and resource use and dispersal have evolved rapidly at expanding range margins. Observed genetic shifts modulate local effects of climate change, but there is little evidence that they will mitigate negative effects at the species level.
Article
Recently there has been much interest in the hypothesis that competition between individual plants is asymmetric or onesided: larger individuals obtain a disproportionate share of the resources (for their relative size) and suppress the growth of smaller individuals. This has important implications for population structure, for the analysis of competition between plants at the individual, population and community levels, and for our understanding of competition as a selective force in the evolution of plant populations.