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We investigated the genetic makeup of Lutz spruce, a natural hybrid between white and Sitka spruce on the Kenai Peninsula, Alaska. Microsatellites indicate 72% of individuals sampled had predominantly white spruce ancestry, whereas 14% had predominantly Sitka spruce ancestry; some individuals classified as white spruce had Sitka spruce plastid genotypes. As Picea mitochondria are maternally inherited and plastids are paternally inherited, it appears that white spruce was the ancestral seed parent of nearly all spruce on the western peninsula, whereas Sitka spruce alleles originated from pollen. Pollen records show that white spruce colonized the western peninsula ~8500 YBP from glacial refugium, whereas Sitka spruce arrived on the eastern peninsula ~4000 YBP after migrating up the Pacific coast. Our data suggest that Sitka spruce colonization west of the Kenai Mountains may have occurred not via seed dispersal but by long distance transport of wind-borne pollen and subsequent hybridization with established white spruce populations. Hybridization was an important mechanism that allowed Sitka spruce to expand the leading edge of its range in response to historical climate change. As the climate continues to warm, climate envelope modeling suggests Lutz spruce may ultimately displace white spruce on the western peninsula even as Sitka spruce is constrained to the eastern peninsula where it will continue to hybridize. Key words: Alaska, climate change, DNA analysis, hybridization, Lutz spruce, Picea x lutzii, Introduction In response to a rapidly changing climate, Aitken et al. (2008) suggested that tree populations have three fates: adaptation, migration, or extirpation. Interspecific hybridization facilitates adaptation and may indeed [...]

In Yukon, Canada, average air temperature has increased by 2 [degrees]C over the past 50 years and, by the end of the century up to 6.9 [degrees]C of further warming is predicted, along with increased climate variability. As a result of these and other changes, vegetation communities are predicted to shift in space and composition. Changes to the vegetation assemblages across multiple ecological units or bioclimate zones will impact carbon and nutrient cycling, animal habitat, biodiversity levels, and other ecosystem processes. Yukon has a wide variety of vegetation communities, and paleoecological evidence indicates that significant vegetation changes have occurred throughout the territory in the past. No documented synthesis of changes to vegetation assemblages exists, restricting predictions of their future likelihood, abundance, and influence. Here, we review the literature of documented examples of vegetation change throughout Yukon that have occurred (i) in different vegetation communities due to the persistent press of climate change and (ii) after natural disturbances. Future research into all vegetation responses under ongoing climate change is warranted. We identify critical research gaps for each vegetation community and disturbance type that should be addressed to produce a more encompassing understanding of the response of Yukon bioclimate zones and vegetation communities to future warming and disturbances. Key words: subarctic, climate change, vegetation change, range shift, disturbance, bioclimate zones Au Yukon, au Canada, la température moyenne de l'air a augmenté de 2 [degrees]C au cours des 50 dernières années et, d'ici la fin du siècle, on prévoit un réchauffement supplémentaire de 6,9 [degrees]C, ainsi qu'une variabilité climatique accrue. En raison de ces changements et d'autres, les communautés végétales devraient se déplacer dans l'espace et changer en matière de composition. Les changements apportés aux assemblages végétaux àtravers plusieurs unités écologiques ou zones bioclimatiques auront une incidence sur le cycle du carbone et des nutriments, l'habitat animal, les niveaux de biodiversité et d'autres processus écosystémiques. Le Yukon possède une grande variété de communautés végétales, et les preuves paléoécologiques indiquent que des changements importants de la végétation se sont produits sur tout le territoire par le passé. Il n'existe aucune synthèse documentée des changements survenus dans les assemblages végétaux, ce qui limite les prédictions sur leur probabilité, leur abondance et leur influence futures. Les auteurs passent ici en revue la littérature qui comporte des exemples documentés de changements de la végétation àtravers le Yukon qui se sont produits (i) dans différentes communautés végétales en raison de la pression persistante des changements climatiques et (ii) après des perturbations naturelles. Des recherches futures sur toutes les réponses de la végétation dans le cadre des changements climatiques en cours sont justifiées. Les auteurs identifient les lacunes critiques en matière de recherche pour chaque communauté végétale et chaque type de perturbation qui devraient être comblées afin de conduire àune compréhension plus globale de la réponse des zones bioclimatiques et des communautés végétales du Yukon au réchauffement et aux perturbations àvenir. Mots-clés : subarctique, changements climatiques, changement de végétation, déplacement de l'aire de répartition, perturbation, zones bioclimatiques, 1. Background Arctic and boreal regions are being significantly impacted by climate change. Between 1971 and 2017, pan-Arctic average annual air temperatures rose by 2.7 [degrees]C, a change 2.4-times greater [...]

Abstract: Predicting the distribution of alien species in areas not yet reached or where the species are still found in low abundance is crucial for implementing timely management strategies. Miconia [...]

Identification of factors explaining diversity in plant responses to industrial pollution is crucial for predicting fates of polluted ecosystems. Meta-analysis based on 203 publications demonstrated that plants growing near point polluters showed similar decreases in characters reflecting growth (-13.1%) and reproduction processes (-8.5%). In herbaceous plants, root growth was reduced, while aboveground biomass did not change, because the decrease in leaf size was compensated by an increase in leaf number. In contrast, woody plants demonstrated no changes in allometry and their growth was reduced to a greater extent than growth of herbaceous plants. Raunkiaer's classification of life forms appeared the best predictor of species' responses to pollution. Within woody plants, trees and shrubs, but not dwarf shrubs, showed strong decreases in growth and reproduction. Within herbaceous plants, significant growth reduction was observed only in annuals. Longevity of foliage or plant phylogeny did not explain variation in species' responses. Adverse effects of pollution were stronger in regions with higher temperature and precipitation, hinting that existing pollution loads may become more harmful for plants as climate changes. Relatively minor explanatory value of the characteristics of individual polluters removes one of the principal obstacles to accounting for the effects of pollution in vegetation models and allows extrapolation of the effects observed near point polluters to both regional and global scales. We conclude that losses in productivity of plant communities due to aerial pollution can be approximately estimated on the basis of the life form spectra and climate. Key words: biomass, climate, life forms, point polluters, plant species, resource allocation, temperature. L'identification des facteurs expliquant la diversite des reactions des plantes envers la pollution industrielle represente un enjeu critique pour predire le devenir des eecosystemes polluees. Une meta-analyse portant sur 203 publications demontre que les plantes poussant pres de pollutions ponctuelles montrent des diminutions similaires pour des domrees refletant la croissance (-13.1 %) et les processus de reproduction (-8.5 %). Chez les plantes herbaceees, on observe une diminution de la croissance racinaire, alors que la biomasse eepigeee ne change pas, parce que l'augmentation du nombre de feuilles compense la dimension de leur surface. Au contraire, les plantes ligneuses ne demontrent aucun changement dans l'alleilomeetrie et leur croissance montre une plus forte diminution que les plantes herbaceees. La classification des formes de vie des plantes semble constituer le meilleur moyen pour predire les reactions des plantes a la pollution. Chez les plantes ligneuses, seuls les arbres et les arbustes, mais pas les arbustes nains, montrent de fortes diminutions de croissance et de reproduction. Chez les plantes herbaceees, l'on observe de fortes diminutions de croissance seulement chez les plantes annuelles. La longevite du feuillage et la phylogeenie veegetale n'expliquent pas la variation dans les reactions des especes. Les effets de la pollution s'aggravent dans les regions chaudes a fortes precipitations, ce qui suggere que les charges polluantes en place pourraient devenir plus nuisibles pour les plantes avec les changements climatiques. La valeur explicative relativement faible des caracteristiques des polluants individuels elimine un des principaux obstacles pour rendre compte des effets de la pollution dans les modeles de vegetation, permettant d'extrapoler les effets observes pres des pollutions ponctuelles, aux echelles regionales et globales. Les auteurs concluent que l'on peut estimer approximativement les pertes de productivite des communautesveegetales dues a la pollution aerienne sur la base des spectres des formes de vie et du climat. Mots-cles: biomasse, climat, formes de vie, polluants ponctuels, especes vegetales, allocation des ressources, temperature. [Traduit par la Redaction], Introduction Vegetation shapes terrestrial ecosystems and serves several crucial functions in the biosphere. Due to both the economic and psychological importance of vegetation for mankind, deterioration of plant communities caused [...]

There is a lack in representation of biosphere-atmosphere interactions in current climate models. To fill this gap, one may introduce vegetation dynamics in surface transfer schemes or couple global climate models (GCMs) with vegetation dynamics models. As these vegetation dynamics models were not designed to be included in GCMs, how are the latest generation dynamic global vegetation models (DGVMs) suitable for use in global climate studies? This paper reviews the latest developments in DGVM modelling as well as the development of DGVM-GCM coupling in the framework of global climate studies. Limitations of DGVM and coupling are shown and the challenges of these methods are highlighted. During the last decade, DGVMs underwent major changes in the representation of physical and biogeochemical mechanisms such as photosynthesis and respiration processes as well as in the representation of regional properties of vegetation. However, several limitations such as carbon and nitrogen cycles, competition, land-use and land-use changes, and disturbances have been identified. In addition, recent advances in model coupling techniques allow the simulation of the vegetation--atmosphere interactions in GCMs with the help of DGVMs. Though DGVMs represent a good alternative to investigate vegetation--atmosphere interactions at a large scale, some weaknesses in evaluation methodology and model design need to be further investigated to improve the results. Key words: dynamic global vegetation model (DGVM), vegetation modelling, climate change, coupling, global climate model (GCM), land surface scheme (LSS). Dans les modeles climatiques actuels, il y a un manque de representation des interactions biosphere- atmosphere. Pour palier a ce manque, il est possible d'introduire la dynamique de la vegetation dans les schemas de transfert de surface ou encore coupler les modeles de climat global (<< GCMs >>) avec les modeles dynamiques de vegetation. Puisque ces modeles dynamiques de la vegetation n'ont pas ete concus pour inclure les GCMs, jusqu'a quel point les modeles de globaux dynamiques vegetation (<< DGVMs >>) peuvent ils etre utilises dans les etudes climatiques globales? Les auteurs passent1 en revue les derniers deeveloppements dans la modelisation DGVM ainsi que le developpement de couplage des DGVMGCM dans le cadre d'etudes sur le climat global. On souligne les limites du DGVM et du couplage et on met en lumiere les defis poses par de ces methodes. Au cours de la derniere eennie, les DGVMs ont subi des modifications majeures dans la representation des meecanismes biogeochimiques tels que les processus de photosynthese et de respiration ainsi que la representation des proprietesregionales de la vegetation. Cependant, on a identified plusieurs limitate comme les cycles du carbone et de l'azote, la competition, l'utilisation des terres et les modifications de ces utilisations, ainsi que les perturbations. D'autre part, de recentes avanceees dans les techniques de couplage permettent de simuler les interactions vegetation--atmosphere dans les GCMs a l'aide des DGVMs. Bien que les DGVMs representent une bonne alternative pour etudier les interactions vegetation--atmosphere a grande echelle, il faudra examiner de plus pres certaines faiblesses dans les methodologies devaluation et la conception des modeles afin d'ameeliorer les resultats. Mots-cles: modeles de globaux dynamiques vegetation (<< DGVM >>), modelisation de la vegetation, changement climatique, couplage, modele global de climat (<< GCM >>), schema de surface continentale (<< LSS >>) . [Traduit par la Redaction], 1. Introduction Vegetation interacts with the atmosphere in many ways including photosynthesis, productivity, competition, disturbances, etc. (Deman et al. 2007). Biophysical, ecological, and physiological processes of vegetation and soils have [...]

The SHRUB BATTLE board game gives awareness to the students about the landscape and agricultural practices.

Spatial structure in plant communities occurs in the forms of (1) single-species aggregation and dispersion patterns, (2) distance-dependent interactions between species, and (3) the response to the spatial structure of environmental conditions. Different methods deal with these components of spatial variation: geostatistical analysis reveals autocorrelation in a spatial sample; the variance of species richness has been used as an indicator for interspecific interactions due to niche limitation; and ordination techniques describe multispecies responses to environmental factors. Based on the mathematical properties of presence-absence data, it is shown how variogram modeling, the testing of interspecific associations, and multiscale ordination can be integrated using the same set of distance-dependent variance-covariance matrices (variogram matrix). The variogram matrix partitions the variance of community data into spatial components at the levels of the individual species, species composition, and species richness. It can be used to factor out the effects of single-species aggregation patterns, interspecific interactions, or environmental heterogeneity. The mathematical integration of traditionally unrelated methods increases the interpretability of variograms of plant communities, provides a spatial extension and an empirical null model for the variance test of species richness, and extends multiscale ordination to nonsystematic spatial samples. Beyond the individual applications, the variogram matrix provides a framework for a mathematical unification of geostatistics, multivariate data analysis, and the analysis of variance that may enable ecologists from a broad range of fields to incorporate spatial effects into their research and to integrate analyses across different levels of biological organization. Key words: interspecific associations; multiscale ordination; multivariate geostatistics; nonstationarity; spatial variance; species richness; variance test; variogram matrix.

In this letter, a method called visual computing was used to solve angular four-components' proportions and directional vegetation cover fraction for discrete canopies and continuous row-planted plants. It proved effective to predict the angular characteristics on pixel scale. The method could be an alternative way to classical solution of geometrical optical models. Visual computing method would be effective especially when the canopies' spatial distribution and shapes were irregular and could not be described statistically. Index Terms--Four components, geometrical optical (GO) model, quantitative remote sensing, visual computing.

1 As peatlands form they create a temporal archive of community development, allowing the reconstruction of vegetation dynamics through the analysis of sediments and the development of detailed chronologies of successional change. Peatland formation occurs through two mechanisms: (i) terrestrialization, when a water body fills with sediments and peat; and (ii) paludification, the conversion of dry land to peatland. In temperate regions, where high summer temperatures may limit peat accumulation, general models of peatland development suggest that allogenic factors such as climate change control peatland development and that terrestrialization is the primary mechanism of formation. 2 This study evaluates this widely accepted model by comparing the developmental histories of three peatlands within the same climate region in New England in order to: (i) describe the development and timing of successional events among peatlands; (ii) document the roles of paludification and terrestrialization as developmental mechanisms; and (iii) evaluate the importance of climate change vs. autogenic factors in peatland development in this temperate region. 3 Basin morphometry, sediment stratigraphies, and chronologies of community change determined through radiocarbon dating indicate that peatland development at each site involved terrestrialization followed by paludification, with no apparent influence of broad-scale climate change on the timing of these processes. Paludification was consistently initiated coincident with the consolidation of a shrub mat across each lake-basin, and was controlled in extent and rate by the topography of the adjoining uplands. The timing of stratigraphic changes varied among sites, suggesting that autogenic factors associated with the accumulation of peat rather than regional climate change controlled development. These results provide the foundation for a model of temperate peatland development driven by autogenic factors and caution against the use of temperate peatland development as a proxy for climatic reconstruction. Key-words: allogenic control, autogenic control, climate, paludification, terrestrialization, peatland, stratigraphy, New England

In the boreal biome, fire is the major disturbance agent affecting ecosystem change, and fire dynamics will likely change in response to climatic warming. We modified a spatially explicit model of Alaskan subarctic treeline dynamics (ALFRESCO) to simulate boreal vegetation dynamics in interior Alaska. The model is used to investigate the role of black spruce ecosystems in the fire regime of interior Alaska boreal forest. Model simulations revealed that vegetation shifts caused substantial changes to the fire regime. The number of fires and the total area burned increased as black spruce forest became an increasingly dominant component of the landscape. The most significant impact of adding black spruce to the model was an increase in the frequency and magnitude of large-scale burning events (i.e., time steps in which total area burned far exceeded the normal distribution of area burned). Early successional deciduous forest vegetation burned more frequently when black spruce was added to the model, considerably decreasing the fire return interval of deciduous vegetation. Ecosystem flammability accounted for the majority of the differences in the distribution of the average area burned. These simulated vegetation effects and fire regime dynamics have important implications for global models of vegetation dynamics and potential biotic feedbacks to regional climate.

Models of semiarid vegetation dynamics incorporating concepts of equilibrium and stability have been largely replaced by nonequilibrium models in recent years. However, neither equilibrium nor disequilibrium and neither stability nor instability have been formally demonstrated. Most records of semiarid vegetation are inadequate for conclusive tests. We tested for equilibrium at seven study sites in six locations and vegetation types, in grazed semiarid grassland in central Otago, New Zealand, using data collected twice annually over 5-13 yr. Some sites showed overall directional change in composition over time, but others appeared to fluctuate about an average equilibrium state. At one site, an instantaneous perturbation experiment was used to test formally for stability, and to seek evidence for intrinsic stabilizing processes. In this experiment, three herbicide treatments removed or decreased different components of the community, and recovery and convergence with the untreated control was monitored over time. Although all exotic species increased or rapidly re-invaded the treated plots, many native species failed to re-invade, and treatments had not recovered by 194 wk after perturbation. We conclude that the vegetation is not stable, but that some stabilizing processes are evident. Contrary to some nonequilibrium theory, we observed strong competitive interactions between species. We suggest that New Zealand semiarid vegetation exists on a continuum between equilibrium and nonequilibrium dynamics. Key words: competitive interactions; equilibrium; fluctuation; nonequilibrium; recovery from perturbation; selective species removal; semiarid grassland, New Zealand; stability; theoretical model.

A deterministic linear optimization module was used to develop a forage allocation model for ungulates inhabiting North Dakota's Theodore Roosevelt National Park. The model's deficiencies in reflecting plant productivity changes due to factors such as fires and invasive species may have led to overprotection of unthreatened plant communities and in turn underestimation of supportable ungulate population figures.

A model is presented to describe the self-thinning rule as applied to vegetation dynamics, which incorporates maximum plant mass diversity. The model is based on given stochastic variables and probability densities.

Research indicates that saturation does not necessarily produce species richness, and is not likely to be an accurate predictor of a plant population's invasion resistance. Correlations between invasion resistance and species richness is dependent on the cause of the richness gradient and the specific model considered.

The lottery model, the spatial competition model, the succession model and the seed size/number trade-off model are examined for accuracy in explaining emergent vegetation dynamics. Research revealed no correlation between seed size and abundance in either annual or perennial plant populations, suggesting that plant population dynamics are governed by complex relationships between plant attributes and environmental factors.

Logistic regression analysis is used to link field survey information to geographical and environmental predictors to create models for 153 plant and animal population dynamics in the northeast region of New South Wales, Australia. The model performed poorly when the specific habitats of species studied were not thoroughly sampled, or where the species were highly nomadic.

A computer simulation model of regional vegetation dynamics was applied to the terrestrial ecosystems of China to study the responses of vegetation to elevated CO(sub 2) and global climatic change. The primary production processes were coupled with vegetation structure in the model. The model was parameterized and partially validated in light of a large number of field observations made throughout China on primary productivity, 10 years of monthly meteorological data, 5 years of monthly normalized differential vegetation index observed by NOAA-11 satellite, and digital vegetation and terrain maps. Eight different climatic scenarios, set by perturbations from the present climate, 100% in atmospheric CO(sub 2) concentration, 2 degrees C in monthly mean temperature, and 20% in monthly precipitation, were applied to analyze the sensitivity of the Chinese terrestrial ecosystems to climatic change. Simulation results were obtained for each of the climatic scenarios with the model running toward equilibrium solutions at a time step of 1 month. Preliminary validation indicated that the model was capable of simulating the net primary productivity of most vegetation classes and the potential vegetation structure in China under present climatic conditions. The simulations for the altered climatic scenarios predicted that grasslands, shrubs, and conifer forests are more sensitive to environmental changes than evergreen broadleaf forests in warm, wet southeast China and desert vegetation in cold, arid northwest China. For less than 150% of changes in vegetation structure under altered climatic conditions, about three quarters of the changes in net primary productivity of individual vegetation classes were shown to be attributed to the changes in the corresponding distribution area.

An evaluation is presented on the concepts of tree material limitation and increased environmental hazard as tools to assess forest dynamics. It is posited that field manipulation of environmental conditions will be necessary to develop evaluation tools that are both predictive and explanatory, and that this manipulation will need to be applied to many tree species at and below the treeline in many geographic locations.

An assessment is presented on the top-down hypothesis as a model of terrestrial ecosystem trophic dynamics, in which plant biomass build-up is assumed to need top-down folivore control. While evidence exists to support the hypothesis, questions remaining include the role of folivorous insects, the impact of temperate and boreal browsers, and the sufficiency and relevance of energy constraints in trophic dynamic variances.

A model is presented for plant population dynamics of Cytisus scoparius, or broom, across prairie and urban fields at various stages of invasion. Results suggest that control of C. scoparius invasions requires the destruction of 70% of seeds in urban landscapes and more than 99.9% of sees in prairie landscapes.

A well-established and widely used correlative climate-vegetation model (Holdridge Life Zone model) was compared to three mechanistic simulation models (BIOME2, Dynamic Global Phytogeography Model (DOLY), and Mapped Atmosphere-Plant-Soil System (MAPSS)) for the conterminous United States under contemporary climate and a set of future climates prescribed by three Global Circulation Model experiments. Output from the mechanistic models were from the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) intercomparison. Holdridge modeling approaches, using a 'Simple' implementation (vegetation distribution based on biotemperature and precipitation alone) or a 'Full' implementation (vegetation distribution based on biotemperature, precipitation, altitudinal region, latitudinal belt, and transitional vegetation zones), represented current potential natural U.S. vegetation poor to fair, respectively. The more sophisticated mechanistic models were superior at reproducing potential vegetation under current climate compared to Holdridge, although there was significant variability among these models. The Holdridge implementations generally showed similar or greater climate sensitivity with respect to spatial redistribution of vegetation compared to the mechanistic models run both with and without doubled CO(sub 2) levels; however, the sensitivity of the Holdridge model depended on the implementation. Reduced sensitivity of the mechanistic models arises from direct (physiological) CO(sub 2) effects and other compensating feedbacks not captured by the Holdridge model. The greater degree of physical realism in the mechanistic models makes them the model class of choice for climate impact assessment. However, under circumstances of limited data availability, computation resources, and access to mechanistic models and model expertise, simple correlational models such as Holdridge may be the only method that can be applied. The paper makes some recommendations on the use of the Holdridge model for impact assessment if it is the only available model.

Modeling potential global redistribution of terrestrial vegetation frequently is based on bioclimatic classifications which relate static regional vegetation zones (biomes) to a set of static climate parameters. The equilibrium character of the relationships limits our confidence in their application to scenarios of rapidly changing climate. Such assessments could be improved if vegetation migration and succession would be incorporated as response variables in model simulations. We developed the model MOVE (Migration Of VEgetation), to simulate the geographical implications of different rates of plant extirpation and in-migration. We used the model to study the potential impact on terrestrial carbon stocks of climate shifts hypothesized from a doubling of atmospheric greenhouse gas concentration. The model indicates that the terrestrial vegetation and soil could release carbon; the amount of this carbon pulse depends on the rate of migration relative to the rate of climate change. New temperate and boreal biomes, not found on the landscape today, increase rapidly in area during the first 100 years of simulated response to climate change. Their presence for several centuries and their gradual disappearance after the climate ceases to change adds uncertainty in calculating future terrestrial carbon fluxes.

Our objective was to evaluate the transient responses of grasslands in the central grassland region of North America to changes in climate. We used an individual plant-based gap dynamics simulation model (STEPPE-GP) linked with a soil water model (SOILWAT) to evaluate the effects of changes in climate on the composition and structure of grassland vegetation. Five functional types of plants were simulated based upon lifeform, physiology, and rooting distribution with depth. [C.sub.3] and [C.sub.4] perennial grasses with either a shallow or deep roofing distribution, and deeply rooted [C.sub.3] shrubs were simulated under current climatic conditions and under a GFDL climate change scenario for nine sites representative of the temperature and precipitation regimes in the grassland region. Although vegetation at the sites responded differently to climate change, shifts in functional types occurred within 40 years of the start of the climate change. [C.sub.4] grasses increased in dominance or importance at all sites with a change in climate, primarily as a result of increases in temperature in all months at all sites. The coolest sites that are currently dominated by [C.sub.3] grasses were predicted to shift to a dominance by [C.sub.4] grasses, whereas sites that are currently dominated by [C.sub.4] grasses had an increase in importance of this functional type with a change in climate. Current annual temperature was the best predictor of changes in [C.sub.3] biomass, and [C.sub.3] and [C.sub.4] biomass combined; current annual precipitation was the best predictor of changes in [C.sub.4] biomass. These predicted shifts in dominance and importance of [C.sub.3] versus [C.sub.4] grasses would have important implications for the management of natural grasslands as well as the cultivation of crops in the central grassland region.

Carbon storage and flow through forest ecosystems are major components of the global carbon cycle. The cycle of carbon is intimately coupled with the cycle of nitrogen and the flow of water through forests. The supply of water for tree growth is determined by climate and soil physical properties. The rate at which nitrogen mineralization occurs depends on climate and the type of carbon compounds with which the nitrogen is associated. Species composition, which is also affected by climate, can greatly influence the composition of carbon compounds and subsequently nitrogen availability. Climate change can therefore have a direct effect on forest ecosystem production and carbon storage through temperature and water limitations, and an indirect effect through the nitrogen cycle by affecting species composition. Model simulations of these interactions show that climate change initiates a complex set of direct and indirect responses that are sensitive to the exact nature of the project climate changes. We show results using four different climate-change projections for a location in northeastern Minnesota. Modeled forest responses to each of these climate projections is different indicating that uncertainties in the climate projections may be amplified further as a result of shifts in balance between positive and negative ecosystem feedbacks.

Forest gap models share a common structure for simulating tree population dynamics, and many models contain the same or quite similar ecological factors. However, a wide variety of formulations are being used to implement this general structure. The comparison of models incorporating different formulations is important for model validation, for assessing the reliability of model projections obtained under scenarios of climatic change, and for the development of models with a wide range of applicability. This paper reviews qualitative and quantitative comparisons of the structure and behaviour of forest gap models. As examples of qualitative model comparisons, the different formulations used for the height-diameter relationship, for the maximum growth equation, and for the effects of temperature and drought on tree growth are reviewed. The variety of formulations currently in use has the potential to influence simulation results considerably, but we conclude that little is known on the sensitivity of the models in this respect. The quantitative model comparisons performed so far allow us to draw the following conclusions: (1) Gap models are quite sensitive to the formulation of climate-dependent processes under current climate, and this sensitivity is even more pronounced under a changed climate. (2) Adaptations of forest gap models to specific regions have required detailed sub-models of species life history, thus complicating model comparison. (3) Some of the complex models developed for region-specific applications can be simplified without hampering the realism with which they simulate species composition. (4) Attempts to apply the models without modification beyond the area for which they were developed have produced controversial results. It is concluded that the sensitivity of forest gap models to the exact process formulations should be examined carefully, and that more systematic comparisons of model behaviour at a range of test sites would be desirable. Such studies could improve our understanding of forest dynamics considerably, and they would help to focus future research activities with gap models.

The forest model FORCLIM was used to evaluate the applicability of gap models in complex topography when the climatic input data is provided by a global database of 0.5 [degrees] resolution. The analysis was based on 12 grid cells along an altitudinal gradient in the European Alps. Forest dynamics were studied both under current climate as well as under four prescribed 2 x C[O.sub.2] scenarios of climatic change obtained from General Circulation Models, which allowed to assess the sensitivity of mountainous forests to climatic change. Under current climate, FORCLIM produces plausible patterns of species composition in space and time, although the results for single grid cells sometimes are not representative of reality due to the limited precision of the climatic input data. Under the scenarios of climatic change, three responses of the vegetation are observed, i.e., afforestation, gradual changes of the species composition, and dieback of today's forest. In some cases widely differing species compositions are obtained depending on the climate scenario used, suggesting that mountainous forests are quite sensitive to climatic change. Some of the new forests have analogs on the modern landscape, but in other cases non-analog communities are formed, pointing at the importance of the individualistic response of species to climate. The applicability of gap models on a regular grid in a complex topography is discussed. It is concluded that for their application on a continental scale, it would be desirable to replace the species in the models by plant functional types. It is suggested that simulation studies like the present one must not be interpreted as predictions of the future fate of forests, but as means to assess their sensitivity to climatic change.

A patch model was developed to characterize the effects of climate on succession of miombo dry forests of Zambezian Africa using Malawi as a case study. The model, called MIOMBO, is based on the FORSKA Version 1 gap model of forest succession by Prentice and Leemans (1990). The FORSKA model was modified to include the effects of moisture and fire; and how these affect processes of establishment, survival, growth and development. The impacts that four different GCM scenarios for a C[O.sub.2] doubling might have on dynamics of a number of miombo species were analyzed, Preliminary results show a gradual increase in the basal area of the more mesic species. This result is consistent with what might be expected with increased precipitation. Tree growth and development data with associated detailed climatic data are lacking and severely limit the ability to define quantitatively how species are influenced by given levels of environmental factors (such as climate and nutrient factors), and how they might respond to seasonal changes in climate variability.

A gap-typed forest dynamic model KOPIDE was used to assess the dynamic responses of a mixed broadleaved-Korean pine forest stand to climate change in northeastern China. The GFDL climate change scenario was applied to derive the changes in environmental variables, such as 10 [degrees] C based DEGD and PET/P, which were used to implement the model. The simulation result suggests that the climate change would cause important changes in stand structure. Korean pine, the dominant species in the area under current climate conditions, would disappear under the GFDL equilibrium scenario. Oak and elm would become the dominant species replacing Korean pine, ash and basswood. Such a potential change in forest structure would require different strategies for forest management in northeastern China.

We added certain aspects of species-specific phenology, and of local frost regimes to a standard invididual-based patch model of forest stand dynamics, which we used to explore the possible consequences of four climate-change scenarios in eight distinct forest regions in British Columbia, Canada. According to model projections, lowland temperate coastal forests will be severely stressed because forest tree species will no longer have their winter-chilling requirements met. High-elevation coastal forests may either remain stable or decrease in productivity, while interior subalpine forests may eventually resemble those now found in the coastal mountains. Southern interior forests are likely to persist relatively unchanged, while boreal and sub-boreal forests of the northern interior may become dominated by Douglas-fir and western larch, rather than by spruce and pine as at present. The rate of change in forest composition may be very high in some cases. Changes under the four climate-change scenarios generally vary in magnitude but not in direction. This exercise illustrates that different forest types might respond to a changing climate for different reasons, and at different rates.

Forest patch models are utilized to provide simulations for vegetation dynamics that deal with production forestry. The effects of environmental variables such as temperature, growth and mortality are included in gap patch models to enhance the accuracy of the simulations. Furthermore, patch models on forest ecosystems can be utilized to evaluate vegetation distribution and dynamics in response to global change.

The impacts of the climate change predictions of four general circulation models (GFDL, GISS, OSU and UKMO) on net primary production (NPP) of Betula pubescens, Fagus sylvatica and Quercus robur in The Netherlands were analysed using the process-based model FORGRO. FORGRO is a model suitable to simulate growth of managed mono-species stands. For the GCMs mentioned, both transient and equilibrium 2 x C[O.sub.2] scenarios of temperature and precipitation change were evaluated and compared with responses under current climate. It was found that the NPP increases in the transient scenarios, but remains the same or declines in the 2 x C[O.sub.2] scenarios. This is because respiration increases more with rising temperature than photosynthesis. During the transient scenarios this effect gradually increases, while in the 2 x C[O.sub.2] scenario this effect is operating over the entire simulation period. If water limitation is taken into account, then the NPP of the reference scenario is reduced. In both the transient and 2 x C[O.sub.2] scenarios this water limitation is annulated, resulting in a stronger response of NPP compared to the situation without water limitation. This enhancement of the response is most pronounced in the transient scenario due to the gradual effect of temperature on respiration. Similar results were obtained with a version of FORGRO in which the photosynthesis module of HYBRID (PGEN) is incorporated, although the response in FORGRO-PGEN is usually higher than that of FORGRO. This is because the response of photosynthesis to C[O.sub.2] rises with increasing temperature as defined in the PGEN-model, but not according to FORGRO.

The forest succession model FORSKA was applied to a west-east transect across Central Europe using points from a global climate data set. Climate change experiments were undertaken for two general circulation model scenarios and two different site classes. The simulated climate changes lead to reduced forest productivity and a changed species composition on most sites. Under current climate, the broad scale pattern of the climatically driven distribution of forest communities is quite realistically reproduced. However, the resolution of climate data imposes limitations on the simulation of forest dynamics in subcontinental climate, because climate variability and extreme events are not well represented.

A generic one-compartment model to measure organic chemical uptake is developed using simplified multimedia factors. The model integrates translocation to shoots, gaseous deposition on leaves, volatilization from leaves and other processes. The technique generates a unique equation for uptake into aerial plant compartment and exhibits an adaptability that makes it better than regression analysis.

The British National Vegetation Classification (NVC) a is system used to determine habitats that are suitable to different plant species based on environment and management information. Comparisons of NVC-generated plant community predictions and actual observations were conducted to evaluate the system's accuracy. Results showed the NVC was more accurate in predicting plant species rather than plant communities.

A modified Budyko global vegetation model is used to predict changes in global vegetation patterns resulting from climate change (CO2 doubling). Vegetation patterns are predicted using a model based on a dryness index and potential evaporation determined by solving radiation balance equations. Climate change scenarios are derived from predictions from four General Circulation Models (GCM's) of the atmosphere (GFDL, GISS, OSU, and UKMO). Global vegetation maps after climate change are compared to the current climate vegetation map using the kappa statistic for judging agreement, as well as by calculating area statistics. All four GCM scenarios show similar trends in vegetation shifts and in areas that remain stable, although the UKMO scenario predicts greater warming than the others. Climate change maps produced by all four GCM scenarios show good agreement with the current climate vegetation map for the globe as a whole, although over half of the vegetation classes show only poor to fair agreement. The most6 stable areas are Desert and Ice/Polar Desert. Because most of the predicted warming is concentrated in the Boreal and Temperate zones, vegetation there is predicted to undergo the greatest change. Specifically, all Boreal vegetation classes are predicted to shrink. The interrelated classes of Tundra, Taiga, and Temperate Forest are predicted to replace much of their poleward (mostly northern) neighbors. Most vegetation classes in the Subtropics and Tropics are predicted to expand. Any shift in the Tropics favoring either Forest over Savanna, or vice versa, will be determined by the magnitude of the increased precipitation accompanying global warming. Although the model predicts equilibrium conditions to which many plant species cannot adjust (through migration or microevolution) in the 50-100 y needed for CO2 doubling, it is nevertheless not clear if projected global warming will result in drastic or benign vegetation change.

(1) The STORM simulation was developed to predict the response of regional stand age structure to a given disturbance regime. The outcome of STORM depends upon rotation periods of canopy disturbance, diameter growth rates of trees, and the relative susceptibility of pole, mature and large trees to windthrow. (2) The simulation was run using data on disturbance frequencies from remnants of primary forest in western Upper Michigan. Rotation periods ranged from 69 years for > 10% canopy removal to 3734 years for > 70% canopy removal. Stands were classified into eight structural types, ranging from even-aged sapling stands to steady-state stands, which reflect the state of recovery from recent disturbances. (3) The model suggests that most (87.4%) stands in the primeval hardwood forest were multi-aged, with several major and many minor age classes. Quasi-even-aged stands resulting from catastrophic disturbance occupied 9.2% of the landscape, and steady-state stands about 3.6%. The low frequency of steady-state stands on the landscape appears to be determined primarily by the high frequency of disturbances removing part of the canopy, rather than the interval between catastrophes. (4) Sensitivity analyses indicate that changes in disturbance rates result in disproportionately large changes in the proportion of even-aged stands on the landscape, while mean canopy residence time for trees shows a damped effect.