ORCID Profile
0000-0001-9867-7893
Current Organisation
University of Helsinki
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Publisher: Wiley
Date: 10-2013
DOI: 10.1890/13-0379.1
Abstract: Tree cover varies enormously across tropical ecosystems-from arid savannas to closed rain forests-and yet a general predictive theory of tropical tree cover remains elusive. Here we use the maximum-entropy method to predict the most likely s le frequency distribution of ecosystems with different tree and grass fractional cover if balance between water supply and demand were the dominant constraint on community assembly. Assuming a hierarchy of in idual plant water demand in which trees require more water than grasses, we reproduce observed trends in the means and the upper and lower limits of tropical tree and grass cover across the entire spectrum of tropical ecosystem water supply. Finer details not captured by our predictions indicate the influence of additional factors, such as disturbance. Our results challenge the view that tropical tree-grass coexistence is largely sustained by disturbances in moist environments ("unstable" coexistence) with water supply playing a dominant role only in arid conditions ("stable" coexistence). More generally, they suggest that macroecological patterns can be understood and predicted as the most likely outcome of a large number of stochastic processes being played out within a relatively small number of ecological constraints.
Publisher: Canadian Science Publishing
Date: 06-2000
DOI: 10.1139/X00-026
Abstract: Predicting the responses of forest growth to elevated temperature (T) and atmospheric CO 2 concentration ([CO 2 ]) on decadal time scales presents a formidable challenge because of the many interacting processes involved. A key uncertainty concerns the relative importance of plant and soil processes to the overall long-term response. In this study, the plant-soil model G'DAY was used to simulate forest growth responses to T and [CO 2 ] on different time scales for forests in cool and warm climates. An equilibrium-based graphical analysis was used to distinguish the roles played by plant and soil processes in determining the response. Doubled [CO 2 ] caused a large initial increase (~20%) in net primary productivity (NPP), but this did not persist in the long term. By contrast, a 2°C increase in T caused a persistent long-term increase in NPP of approximately 10-15%. These responses were similar at cool and warm sites. The equilibrium analysis indicated that soil processes dominated the long-term responses predicted by the model. In particular, the predicted long-term increase in NPP under elevated T reflected an increase in predicted N mineralization and plant N uptake, assuming that a constant fraction of mineralized N is taken up by plants. The analysis highlights key uncertainties for future research.
Publisher: Oxford University Press (OUP)
Date: 07-1992
Abstract: A carbon-flow model for managed forest plantations was used to estimate carbon storage in UK plantations differing in Yield Class (growth rate), thinning regime and species characteristics. Time-averaged, total carbon storage (at equilibrium) was generally in the range 40-80 Mg C ha(-1) in trees, 15-25 Mg C ha(-1) in above- and belowground litter, 70-90 Mg C ha(-1) in soil organic matter and 20-40 Mg C ha(-1) in wood products (assuming product lifetime equalled rotation length). The rate of carbon storage during the first rotation in most plantations was in the range 2-5 Mg C ha(-1) year(-1).A sensitivity analysis revealed the following processes to be both uncertain and critical: the fraction of total woody biomass in branches and roots litter and soil organic matter decomposition rates and rates of fine root turnover. Other variables, including the time to canopy closure and the possibility of accelerated decomposition after harvest, were less critical. The lifetime of wood products was not critical to total carbon storage because wood products formed only a modest fraction of the total.The average increase in total carbon storage in the tree-soil-product system per unit increase in Yield Class (m(3) ha(-1) year(-1)) for unthinned Picea sitchensis (Bong.) Carr. plantations was 5.6 Mg C ha(-1). Increasing the Yield Class from 6 to 24 m(3) ha(-1) year(-1) increased the rate of carbon storage in the first rotation from 2.5 to 5.6 Mg C ha(-1) year(-1) in unthinned plantations. Thinning reduced total carbon storage in P. sitchensis plantations by about 15%, and is likely to reduce carbon storage in all plantation types.If the objective is to store carbon rapidly in the short term and achieve high carbon storage in the long term, Populus plantations growing on fertile land (2.7 m spacing, 26-year rotations, Yield Class 12) were the best option examined. If the objective is to achieve high carbon storage in the medium term (50 years) without regard to the initial rate of storage, then plantations of conifers of any species with above-average Yield Classes would suffice. In the long term (100 years), broadleaved plantations of oak and beech store as much carbon as conifer plantations. Mini-rotations (10 years) do not achieve a high carbon storage.
Publisher: AIP Publishing LLC
Date: 2014
DOI: 10.1063/1.4903723
Publisher: Wiley
Date: 08-2009
DOI: 10.1111/J.1365-3040.2009.01989.X
Abstract: The carbon and oxygen stable isotope composition of wood cellulose (delta(13)C(cellulose) and delta(18)O(cellulose), respectively) reveal well-defined seasonal variations that contain valuable records of past climate, leaf gas exchange and carbon allocation dynamics within the trees. Here, we present a single-substrate model for wood growth to interpret seasonal isotopic signals collected in an even-aged maritime pine plantation growing in South-west France, where climate, soil and flux variables were also monitored. Observed seasonal patterns in delta(13)C(cellulose) and delta(18)O(cellulose) were different between years and in iduals, and mostly captured by the model, suggesting that the single-substrate hypothesis is a good approximation for tree ring studies on Pinus pinaster, at least for the environmental conditions covered by this study. A sensitivity analysis revealed that the model was mostly affected by five isotopic discrimination factors and two leaf gas-exchange parameters. Modelled early wood signals were also very sensitive to the date when cell wall thickening begins (t(wt)). Our model could therefore be used to reconstruct t(wt) time series and improve our understanding of how climate influences this key parameter of xylogenesis.
Publisher: Oxford University Press (OUP)
Date: 10-1992
Publisher: Elsevier BV
Date: 04-1992
Publisher: Wiley
Date: 06-1999
Publisher: Springer Science and Business Media LLC
Date: 04-1992
DOI: 10.1007/BF00317163
Publisher: Wiley
Date: 09-2004
Publisher: Stockholm University Press
Date: 2009
Publisher: Springer Berlin Heidelberg
Date: 2014
Publisher: IOP Publishing
Date: 10-05-2005
Publisher: Springer Berlin Heidelberg
Date: 03-12-2013
Publisher: Wiley
Date: 05-2020
DOI: 10.1111/NPH.16436
Abstract: Photosynthetic rate is concurrently limited by stomatal limitations and nonstomatal limitations (NSLs). However, the controls on NSLs to photosynthesis and their coordination with stomatal control on different timescales remain poorly understood. According to a recent optimization hypothesis, NSLs depend on leaf osmotic or water status and are coordinated with stomatal control so as to maximize leaf photosynthesis. Drought and notching experiments were conducted on Pinus sylvestris, Picea abies, Betula Pendula and Populus tremula seedlings in glasshouse conditions to study the dependence of NSLs on leaf osmotic and water status, and their coordination with stomatal control, on timescales of minutes and weeks, to test the assumptions and predictions of the optimization hypothesis. Both NSLs and stomatal conductance followed power-law functions of leaf osmotic concentration and leaf water potential. Moreover, stomatal conductance was proportional to the square root of soil-to-leaf hydraulic conductance, as predicted by the optimization hypothesis. Though the detailed mechanisms underlying the dependence of NSLs on leaf osmotic or water status lie outside the scope of this study, our results support the hypothesis that NSLs and stomatal control are coordinated to maximize leaf photosynthesis and allow the effect of NSLs to be included in models of tree gas-exchange.
Publisher: Springer Berlin Heidelberg
Date: 03-12-2013
Publisher: Springer Science and Business Media LLC
Date: 2000
Publisher: Oxford University Press (OUP)
Date: 02-2009
Publisher: Wiley
Date: 21-05-2012
DOI: 10.1002/ECE3.266
Publisher: Elsevier
Date: 1986
Publisher: Wiley
Date: 04-1995
Publisher: Springer Science and Business Media LLC
Date: 11-05-2020
Publisher: IOP Publishing
Date: 11-03-1987
Publisher: Wiley
Date: 09-1997
Publisher: Stockholm University Press
Date: 04-2009
Publisher: Oxford University Press (OUP)
Date: 1995
Publisher: Informa UK Limited
Date: 2000
Publisher: Elsevier BV
Date: 09-2019
Publisher: Oxford University Press (OUP)
Date: 02-1999
Publisher: Wiley
Date: 08-07-2011
Publisher: Oxford University Press (OUP)
Date: 1996
DOI: 10.1093/TREEPHYS/16.1-2.173
Abstract: We used an existing analytical model of stemwood growth in relation to nitrogen supply, which we describe in an accompanying paper, to examine the long-term effects of harvesting and fire on tree growth. Our analysis takes into account the balance between nitrogen additions from deposition, fixation, and fertilizer applications, and nitrogen losses from stemwood harvesting, regeneration burning, leaching and gaseous emissions. Using a plausible set of parameter values for Eucalyptus, we conclude that nitrogen loss through fire is the main factor limiting sustainable yield, defined as the maximum mean annual stemwood volume increment obtained in the steady state, if management practices are continued indefinitely. The sustainable yield is 30 m(3) ha(-1) year(-1) with harvesting only, 15 m(3) ha(-1) year(-1) with harvesting and regeneration burning, and 13 m(3) ha(-1) year(-1) with harvesting, fire, leaching and gaseous emissions combined. Our approach uses a simple graphical analysis that provides a useful framework for examining the factors affecting sustainable yield. The graphical analysis is also useful for extending the application of the present model to the effects of climate change on sustainable yield, or for interpreting the behavior of other models of sustainable forest growth.
Publisher: Oxford University Press (OUP)
Date: 02-1993
Publisher: Oxford University Press (OUP)
Date: 25-01-2012
Abstract: We review approaches to predicting carbon and nitrogen allocation in forest models in terms of their underlying assumptions and their resulting strengths and limitations. Empirical and allometric methods are easily developed and computationally efficient, but lack the power of evolution-based approaches to explain and predict multifaceted effects of environmental variability and climate change. In evolution-based methods, allocation is usually determined by maximization of a fitness proxy, either in a fixed environment, which we call optimal response (OR) models, or including the feedback of an in idual's strategy on its environment (game-theoretical optimization, GTO). Optimal response models can predict allocation in single trees and stands when there is significant competition only for one resource. Game-theoretical optimization can be used to account for additional dimensions of competition, e.g., when strong root competition boosts root allocation at the expense of wood production. However, we demonstrate that an OR model predicts similar allocation to a GTO model under the root-competitive conditions reported in free-air carbon dioxide enrichment (FACE) experiments. The most evolutionarily realistic approach is adaptive dynamics (AD) where the allocation strategy arises from eco-evolutionary dynamics of populations instead of a fitness proxy. We also discuss emerging entropy-based approaches that offer an alternative thermodynamic perspective on allocation, in which fitness proxies are replaced by entropy or entropy production. To help develop allocation models further, the value of wide-ranging datasets, such as FLUXNET, could be greatly enhanced by ancillary measurements of driving variables, such as water and soil nitrogen availability.
Publisher: Wiley
Date: 25-01-2020
DOI: 10.1111/PCE.13709
Abstract: Understanding stomatal regulation is fundamental to predicting the impact of changing environmental conditions on vegetation. However, the influence of soil temperature (ST) and soil water content (SWC) on canopy conductance (g
Publisher: Wiley
Date: 06-1998
Publisher: Wiley
Date: 10-01-2020
DOI: 10.1111/PCE.13706
Abstract: To further our understanding of how sustained changes in temperature affect the carbon economy of rice (Oryza sativa), hydroponically grown plants of the IR64 cultivar were developed at 30°C/25°C (day/night) before being shifted to 25/20°C or 40/35°C. Leaf messenger RNA and protein abundance, sugar and starch concentrations, and gas-exchange and elongation rates were measured on preexisting leaves (PE) already developed at 30/25°C or leaves newly developed (ND) subsequent to temperature transfer. Following a shift in growth temperature, there was a transient adjustment in metabolic gene transcript abundance of PE leaves before homoeostasis was reached within 24 hr, aligning with R
Publisher: Oxford University Press (OUP)
Date: 12-1990
Abstract: This paper discusses the general formulation of a model that describes carbon storage in a forest and its timber products as a function of the forest growth curve, the rotation period and the carbon retention curves for the timber products. After a number of rotations, the rotation-averaged quantity of stored carbon approaches an asymptotic value. It is shown that, when forests are managed for maximum sustained yield of biomass, the contribution to asymptotic carbon storage from timber products is about 2.5D/T* times the contribution from living trees, where D is the characteristic decay time for reconversion of timber products to carbon dioxide, and T* is the normal rotation period for maximum sustained yield. For a given value of D/T*, carbon storage can be optimized if the policy of maximizing sustained yield is relaxed. For D/T* 1, there is a finite, optimal rotation period, T(o), greater than T*, for which asymptotic carbon storage is greater than g(f). As D/T* tends to large values, however, T(o) tends to T*, so that, in this limit, management for maximum sustained yield also ensures maximum carbon storage. From initial planting, the time taken to reach asymptotic carbon storage decreases as the normal rotation period, T*, decreases, but increases almost linearly with increasing decay time of timber products, D. This result qualifies the short-term value of any particular planting strategy.
Publisher: Oxford University Press (OUP)
Date: 04-1997
DOI: 10.1093/TREEPHYS/17.4.259
Abstract: An existing model of light and water use by crops (RESCAP) was adapted and evaluated for trees. In the model, growth on any given day is determined either by the amount of intercepted radiation (by means of the light utilization coefficient, epsilon) or by the maximum rate of water extraction by roots (a function of root biomass and soil water content). In either case, transpiration and growth are related by the water-use efficiency (q), which is inversely proportional to the daily mean saturation vapor pressure deficit (D). The model was applied to two Pinus radiata (D. Don) stands (control (C) and fertilized (F)) growing near Canberra, Australia, using data collected during the Biology of Forest Growth experiment (1983-1988). For both stands, predicted and measured soil water contents were in close agreement (r(2) > 0.9) over a 4-year period involving several wet-dry cycles. The parameter combination epsilon/qD was estimated to be 0.28 and 0.26 kg H(2)O (MJ total)(-1) kPa(-1) for the C and F stands, respectively. Because of the close physiological link between water use and CO(2) uptake, the results suggest that tree growth may be realistically simulated by simple models based on conservative values for epsilon and qD.
Publisher: IOP Publishing
Date: 21-01-1988
Publisher: Oxford University Press (OUP)
Date: 08-2000
Publisher: Elsevier
Date: 1999
Publisher: IOP Publishing
Date: 08-01-2003
Publisher: Oxford University Press (OUP)
Date: 08-2001
DOI: 10.1093/TREEPHYS/21.12-13.831
Abstract: The terrestrial biosphere is currently thought to be a significant sink for atmospheric carbon (C). However, the future course of this sink under rising [CO2] and temperature is uncertain. Some contrasting possibilities that have been suggested are: that the sink is currently increasing through CO2 fertilization of plant growth but will decline over the next few decades because of CO2 saturation and soil nutrient constraints that the sink will continue to increase over the next century because rising temperature will stimulate the release of plant-available soil nitrogen (N) through increased soil decomposition that, alternatively, the sink will not be sustained because the additional soil N released will be immobilized in the soil rather than taken up by plants or that the sink will soon become negative because loss of soil C through temperature stimulation of soil respiration will override any CO2 or temperature stimulation of plant growth. Soil N immobilization is thus a key process however, it remains poorly understood. In this paper we use a forest ecosystem model of plant-soil C and N dynamics to gauge the importance of this uncertainty for predictions of the future C sink of forests under rising [CO2] and temperature. We characterize soil N immobilization by the degree of variability of soil N:C ratios assumed in the model. We show that the modeled C sink of a stand of Norway spruce (Picea abies (L.) Karst.) in northern Sweden is highly sensitive to this assumption. Under increasing temperature, the model predicts a strong C sink when soil N:C is inflexible, but a greatly reduced C sink when soil N:C is allowed to vary. In complete contrast, increasing atmospheric [CO2] leads to a much stronger C sink when soil N:C is variable. When both temperature and [CO2] increase, the C sink strength is relatively insensitive to variability in soil N:C significantly, however, with inflexible soil N:C the C sink is primarily a temperature response whereas with variable soil N:C, it is a combined temperature-CO2 response. Simulations with gradual increases of temperature and [CO2] indicate a sustained C sink over the next 100 years, in contrast to recent claims that the C sink will decline over the next few decades. Nevertheless, in using a relatively simple model, our primary aim is not to make precise predictions of the C sink over the next 100 years, but rather to highlight key areas of model uncertainty requiring further experimental clarification. Here we show that improved understanding of the processes underlying soil N immobilization is essential if we are to predict the future course of the forest carbon sink.
Publisher: Springer Science and Business Media LLC
Date: 04-1999
DOI: 10.1038/19215
Publisher: Springer Netherlands
Date: 1992
Publisher: JSTOR
Date: 06-1993
DOI: 10.2307/2390216
Publisher: CSIRO Publishing
Date: 2008
DOI: 10.1071/FP08128
Abstract: Experimental evidence indicates that the stomatal conductance and nitrogen concentration ([N]) of foliage decline under CO2 enrichment, and that the percentage growth response to elevated CO2 is lified under water limitation, but reduced under nitrogen limitation. We advance simple explanations for these responses based on an optimisation hypothesis applied to a simple model of the annual carbon–nitrogen–water economy of trees growing at a CO2-enrichment experiment at Oak Ridge, Tennessee, USA. The model is shown to have an optimum for leaf [N], stomatal conductance and leaf area index (LAI), where annual plant productivity is maximised. The optimisation is represented in terms of a trade-off between LAI and stomatal conductance, constrained by water supply, and between LAI and leaf [N], constrained by N supply. At elevated CO2 the optimum shifts to reduced stomatal conductance and leaf [N] and enhanced LAI. The model is applied to years with contrasting rainfall and N uptake. The predicted growth response to elevated CO2 is greatest in a dry, high-N year and is reduced in a wet, low-N year. The underlying physiological explanation for this contrast in the effects of water versus nitrogen limitation is that leaf photosynthesis is more sensitive to CO2 concentration ([CO2]) at lower stomatal conductance and is less sensitive to [CO2] at lower leaf [N].
Publisher: MDPI AG
Date: 27-11-2009
DOI: 10.3390/E11040931
Publisher: Oxford University Press (OUP)
Date: 1996
DOI: 10.1093/TREEPHYS/16.1-2.161
Abstract: We derived a simplified version of a previously published process-based model of forest productivity and used it to gain information about the dependence of stemwood growth on nitrogen supply. The simplifications we made led to the following general expression for stemwood carbon (c(w)) as a function of stand age (t), which shows explicitly the main factors involved: c(w)(t) = eta(w)G*/ micro (w)(1 - lambdae(- micro (w)t) - micro (w)e(-lambdat)/lambda - micro (w)), where eta(w) is the fraction of total carbon production (G) allocated to stemwood, G* is the equilibrium value of G at canopy closure, lambda describes the rate at which G approaches G*, and micro (w) is the combined specific rate of stemwood maintenance respiration and senescence. According to this equation, which describes a sigmoidal growth curve, c(w) is zero initially and asymptotically approaches eta(w)G*/ micro (w) with the rate of approach dependent on lambda and micro (w). We used this result to derive corresponding expressions for the maximum mean annual stem-wood volume increment (Y) and optimal rotation length (T). By calculating the quantities G* and lambda (which characterize the variation of carbon production with stand age) as functions of the supply rate of plant-available nitrogen (U(o)), we estimated the responses of Y and T to changes in U(o). For a plausible set of parameter values, as U(o) increased from 50 to 150 kg N ha(-1) year(-1), Y increased approximately linearly from 8 to 25 m(3) ha(-1) year(-1) (mainly as a result of increasing G*), whereas T decreased from 21 to 18 years (due to increasing lambda). The sensitivity of Y and T to other model parameters was also investigated. The analytical model provides a useful basis for examining the effects of changes in climate and nutrient supply on sustainable forest productivity, and may also help in interpreting the behavior of more complex process-based models of forest growth.
Publisher: Wiley
Date: 27-03-2015
DOI: 10.1111/NPH.13382
Abstract: Increased tree mortality during and after drought has become a research focus in recent years. This focus has been driven by: the realisation that drought-related tree mortality is more widespread than previously thought the predicted increase in the frequency of climate extremes this century and the recognition that current vegetation models do not predict drought-related tree mortality and forest dieback well despite the large potential effects of these processes on species composition and biogeochemical cycling. To date, the emphasis has been on understanding the causal mechanisms of drought-related tree mortality, and on mechanistic models of plant function and vegetation dynamics, but a consensus on those mechanisms has yet to emerge. In order to generate new hypotheses and to help advance the modelling of vegetation dynamics in the face of incomplete mechanistic understanding, we suggest that general patterns should be distilled from the erse and as-yet inconclusive results of existing studies, and more use should be made of optimisation and probabilistic modelling approaches that have been successfully applied elsewhere in plant ecology. The outcome should inform new empirical studies of tree mortality, help improve its prediction and reduce model complexity.
Publisher: Oxford University Press (OUP)
Date: 12-2001
DOI: 10.1093/JEXBOT/52.365.2313
Abstract: An experimental and modelling study of source-sink interactions in Vitis vinifera L., cv. Cabernet Sauvignon, rooted cuttings under non-limiting environmental conditions with a 12 h photoperiod is presented here. After 4 h, measured photosynthesis, stomatal conductance and leaf carbohydrate content reached maximum values. Over the remainder of the photoperiod, photosynthesis and stomatal conductance decreased continuously, whereas leaf carbohydrate content remained relatively constant. Because the experiment took place in a non-limiting environment, the results suggest that stomatal regulation of photosynthesis was mediated by an internal factor, possibly related to sink activity. A simple 1-source, 2-sink model was developed to examine the extent to which the data could be explained by a hypothetical sink-to-source feedback mechanism mediated by carbohydrate levels in either the mesophyll, the source phloem or the phloem of one of the two sinks. Model simulations reproduced the data well under the hypothesis of a phloem-based feedback signal, although the data were insufficient to elucidate the detailed nature of such a signal. In a sensitivity analysis, the steady-state response of photosynthesis to sink activity was explored and predictions made for the partitioning of photosynthate between the two sinks. The analysis highlights the effectiveness of a phloem-based feedback signal in regulating the balance between source and sink activities. However, other mechanisms for the observed decline in photosynthesis, such as photoinhibition, endogenous circadian rhythms or hydraulic signals in the leaf cannot be excluded. Nevertheless, it is concluded that the phloem-based feedback model developed here may provide a useful working hypothesis for incorporation into plant growth models and for further development and testing.
Publisher: Oxford University Press (OUP)
Date: 1989
Abstract: De novo mutation of the gene encoding chromodomain helicase DNA-binding protein 7 (CHD7) is the primary cause of CHARGE syndrome, a complex developmental disorder characterized by the co-occurrence of a specific set of birth defects. Recent studies indicate that CHD7 functions as a transcriptional regulator in the nucleoplasm. Here, we report based on immunofluorescence and western blotting of subcellular fractions that CHD7 is also constitutively localized to the nucleolus, the site of rRNA transcription. Standard chromatin immunoprecipitation (ChIP) assays indicate that CHD7 physically associates with rDNA, a result that is also observable upon alignment of whole-genome CHD7 ChIP coupled with massively parallel DNA sequencing data to the rDNA reference sequence. ChIP-chop analyses demonstrate that CHD7 specifically associates with hypomethylated, active rDNA, suggesting a role as a positive regulator of rRNA synthesis. Consistent with this hypothesis, siRNA-mediated depletion of CHD7 results in hypermethylation of the rDNA promoter and a concomitant reduction of 45S pre-rRNA levels. Accordingly, cells overexpressing CHD7 show increased levels of 45S pre-rRNA compared with control cells. Depletion of CHD7 also reduced cell proliferation and protein synthesis. Lastly, compared with wild-type ES cells, the levels of 45S pre-rRNA are reduced in both Chd7(+/-) and Chd7(-/-) mouse ES cells, as well as in Chd7(-/-) whole mouse embryos and multiple tissues dissected from Chd7(+/-) embryos. Together with previously published studies, these results indicate that CHD7 dually functions as a regulator of both nucleoplasmic and nucleolar genes and provide a novel avenue for investigation into the pathogenesis of CHARGE syndrome.
Publisher: IOP Publishing
Date: 07-12-1988
Publisher: Elsevier BV
Date: 10-2006
Publisher: Oxford University Press (OUP)
Date: 04-1991
Abstract: The carbon balance between managed forests and the atmosphere depends critically on the frequency and intensity of harvesting, and the lifetime of harvested products. To assess more quantitatively the nature of this dependence, a theoretical analysis, previously applied to carbon storage in trees and wood products only, is extended here to include the carbon in forest floor detritus and soil. A dimensionless combination of the parameters of the model, alpha, with critical value alpha(c), is identified such that for alpha alpha(c), long-term carbon storage is optimized by harvesting for maximum sustained yield.
Publisher: Canadian Science Publishing
Date: 2000
Publisher: Wiley
Date: 29-10-2002
Publisher: Wiley
Date: 31-10-2018
DOI: 10.1111/NPH.14848
Abstract: Optimization models of stomatal conductance (g
Publisher: Elsevier
Date: 1994
Publisher: Cogitatio
Date: 22-10-2021
Abstract: The literature on the security implications of climate change, and in particular on potential climate-conflict linkages, is burgeoning. Up until now, gender considerations have only played a marginal role in this research area. This is despite growing awareness of intersections between protecting women’s rights, building peace and security, and addressing environmental changes. This article advances the claim that adopting a gender perspective is integral for understanding the conflict implications of climate change. We substantiate this claim via three main points. First, gender is an essential, yet insufficiently considered intervening variable between climate change and conflict. Gender roles and identities as well as gendered power structures are important in facilitating or preventing climate-related conflicts. Second, climate change does affect armed conflicts and social unrest, but a gender perspective alters and expands the notion of what conflict can look like, and whose security is at stake. Such a perspective supports research inquiries that are grounded in everyday risks and that document alternative experiences of insecurity. Third, gender-differentiated vulnerabilities to both climate change and conflict stem from inequities within local power structures and socio-cultural norms and practices, including those related to social reproductive labor. Recognition of these power dynamics is key to understanding and promoting resilience to conflict and climate change. The overall lessons drawn for these three arguments is that gender concerns need to move center stage in future research and policy on climate change and conflicts.
Publisher: Elsevier BV
Date: 04-2008
DOI: 10.1016/J.JTBI.2007.12.007
Abstract: Recently there has been growing interest in the use of maximum relative entropy (MaxREnt) as a tool for statistical inference in ecology. In contrast, here we propose MaxREnt as a tool for applying statistical mechanics to ecology. We use MaxREnt to explain and predict species abundance patterns in ecological communities in terms of the most probable behaviour under given environmental constraints, in the same way that statistical mechanics explains and predicts the behaviour of thermodynamic systems. We show that MaxREnt unifies a number of different ecological patterns: (i) at relatively local scales a unimodal bio ersity-productivity relationship is predicted in good agreement with published data on grassland communities, (ii) the predicted relative frequency of rare vs. abundant species is very similar to the empirical lognormal distribution, (iii) both neutral and non-neutral species abundance patterns are explained, (iv) on larger scales a monotonic bio ersity-productivity relationship is predicted in agreement with the species-energy law, (v) energetic equivalence and power law self-thinning behaviour are predicted in resource-rich communities. We identify mathematical similarities between these ecological patterns and the behaviour of thermodynamic systems, and conclude that the explanation of ecological patterns is not unique to ecology but rather reflects the generic statistical behaviour of complex systems with many degrees of freedom under very general types of environmental constraints.
Publisher: Springer-Verlag
DOI: 10.1007/11672906_4
Publisher: Oxford University Press (OUP)
Date: 1993
Publisher: Springer Science and Business Media LLC
Date: 06-03-2015
Publisher: Wiley
Date: 07-06-2020
DOI: 10.1111/NPH.16661
Publisher: Oxford University Press (OUP)
Date: 06-06-2011
Abstract: Measured values of four key leaf traits (leaf area per unit mass, nitrogen concentration, photosynthetic capacity, leaf lifespan) co-vary consistently within and among erse biomes, suggesting convergent evolution across species. The same leaf traits co-vary consistently with the environmental conditions (light intensity, carbon-dioxide concentration, nitrogen supply) prevailing during leaf development. No existing theory satisfactorily explains all of these trends. Here, using a simple model of the carbon-nitrogen economy of trees, we show that global leaf-trait relationships and leaf responses to environmental conditions can be explained by the optimization hypothesis (MAXX) that plants maximize the total amount of carbon exported from their canopies over the lifespan of leaves. Incorporating MAXX into larger-scale vegetation models may improve their consistency with global leaf-trait relationships, and enhance their ability to predict how global terrestrial productivity and carbon sequestration respond to environmental change.
Publisher: Oxford University Press (OUP)
Date: 05-2012
Abstract: A long-established theoretical result states that, for a given total canopy nitrogen (N) content, canopy photosynthesis is maximized when the within-canopy gradient in leaf N per unit area (N(a)) is equal to the light gradient. However, it is widely observed that N(a) declines less rapidly than light in real plant canopies. Here we show that this general observation can be explained by optimal leaf acclimation to light subject to a lower-bound constraint on the leaf mass per area (m(a)). Using a simple model of the carbon-nitrogen (C-N) balance of trees with a steady-state canopy, we implement this constraint within the framework of the MAXX optimization hypothesis that maximizes net canopy C export. Virtually all canopy traits predicted by MAXX (leaf N gradient, leaf N concentration, leaf photosynthetic capacity, canopy N content, leaf-area index) are in close agreement with the values observed in a mature stand of Norway spruce trees (Picea abies L. Karst.). An alternative upper-bound constraint on leaf photosynthetic capacity (A(sat)) does not reproduce the canopy traits of this stand. MAXX subject to a lower bound on m(a) is also qualitatively consistent with co-variations in leaf N gradient, m(a) and A(sat) observed across a range of temperate and tropical tree species. Our study highlights the key role of constraints in optimization models of plant function.
Publisher: The Royal Society
Date: 12-05-2010
Abstract: Plant ecologists have proposed a variety of optimization theories to explain the adaptive behaviour and evolution of plants from the perspective of natural selection (‘survival of the fittest’). Optimization theories identify some objective function—such as shoot or canopy photosynthesis, or growth rate—which is maximized with respect to one or more plant functional traits. However, the link between these objective functions and in idual plant fitness is seldom quantified and there remains some uncertainty about the most appropriate choice of objective function to use. Here, plants are viewed from an alternative thermodynamic perspective, as members of a wider class of non-equilibrium systems for which maximum entropy production (MEP) has been proposed as a common theoretical principle. I show how MEP unifies different plant optimization theories that have been proposed previously on the basis of ad hoc measures of in idual fitness—the different objective functions of these theories emerge as ex les of entropy production on different spatio-temporal scales. The proposed statistical explanation of MEP, that states of MEP are by far the most probable ones, suggests a new and extended paradigm for biological evolution—‘survival of the likeliest’—which applies from biomacromolecules to ecosystems, not just to in iduals.
Publisher: Cold Spring Harbor Laboratory
Date: 22-01-2019
DOI: 10.1101/526764
Abstract: Aim: Maximum entropy (MaxEnt) models promise a novel approach for understanding community assembly and species abundance patterns. One of these models, the "Maximum Entropy Theory of Ecology" (METE) reproduces many observed species abundance patterns, but is based on an aggregated representation of community structure that does not resolve species identity or explicitly represent species-specific functional traits. In this paper, METE is compared to "Very Entropic Growth" (VEG), a MaxEnt model with a less aggregated representation of community structure that represents species (more correctly, functional types) in terms of their per capita metabolic rates. We examine the contribution of metabolic traits to the patterns of community assembly predicted by VEG and, through aggregation, compare the results with METE predictions in order to gain insight into the biological factors underlying observed patterns of community assembly. Innovation: We formally compare two MaxEnt-based community models, METE and VEG, that differ as to whether or not they represent species-specific functional traits. We empirically test and compare the metabolic predictions of both models, thereby elucidating the role of metabolic traits in patterns of community assembly. Main Conclusions: Our analysis reveals that a key determinant of community metabolic patterns is the "density of species" distribution, defined as the intrinsic number of species with metabolic rates in a given range that are available to a community prior to filtering by environmental constraints. Our analysis suggests that appropriate choice of of the density of species in VEG may lead to more realistic predictions than METE, for which this distribution is not defined, and thus opens up new ways to understanding the link between functional traits and patterns of community assembly.
Publisher: Wiley
Date: 08-1996
Publisher: Wiley
Date: 05-06-2013
DOI: 10.1111/NPH.12344
Abstract: Allocation of carbon ( C ) between tree components (leaves, fine roots and woody structures) is an important determinant of terrestrial C sequestration. Yet, because the mechanisms underlying C allocation are poorly understood, it is a weak link in current earth‐system models. We obtain new theoretical insights into C allocation from the hypothesis ( MaxW ) that annual wood production is maximized. MaxW is implemented using a model of tree C and nitrogen ( N ) balance with a vertically resolved canopy and root system for stands of Norway spruce ( Picea abies ). MaxW predicts optimal vertical profiles of leaf N and root biomass, optimal canopy leaf area index and rooting depth, and the associated optimal pattern of C allocation. Key insights include a predicted optimal C–N functional balance between leaves at the base of the canopy and the deepest roots, according to which the net C export from basal leaves is just sufficient to grow the basal roots required to meet their N requirement. MaxW links the traits of basal leaves and roots to whole‐tree C and N uptake, and unifies two previous optimization hypotheses (maximum gross primary production, maximum N uptake) that have been applied independently to canopies and root systems.
Publisher: Wiley
Date: 02-11-2021
DOI: 10.1111/NPH.17795
Abstract: Experimental evidence that nonstomatal limitations to photosynthesis (NSLs) correlate with leaf sugar and/or leaf water status suggests the possibility that stomata adjust to maximise photosynthesis through a trade‐off between leaf CO 2 supply and NSLs, potentially involving source–sink interactions. However, the mechanisms regulating NSLs and sink strength, as well as their implications for stomatal control, remain uncertain. We used an analytically solvable model to explore optimal stomatal control under alternative hypotheses for source and sink regulation. We assumed that either leaf sugar concentration or leaf water potential regulates NSLs, and that either phloem turgor pressure or phloem sugar concentration regulates sink phloem unloading. All hypotheses led to realistic stomatal responses to light, CO 2 and air humidity, including conservative behaviour for the intercellular‐to‐atmospheric CO 2 concentration ratio. Sugar‐regulated and water‐regulated NSLs are distinguished by the presence/absence of a stomatal closure response to changing sink strength. Turgor‐regulated and sugar‐regulated phloem unloading are distinguished by the presence/absence of stomatal closure under drought and avoidance/occurrence of negative phloem turgor. Results from girdling and drought experiments on Pinus sylvestris , Betula pendula , Populus tremula and Picea abies saplings are consistent with optimal stomatal control under sugar‐regulated NSLs and turgor‐regulated unloading. Our analytical results provide a simple representation of stomatal responses to above‐ground and below‐ground environmental factors and sink activity.
Publisher: Oxford University Press (OUP)
Date: 07-1996
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: No location found
No related grants have been discovered for Roderick Dewar.