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Shallow landslides are an important type of natural ecosystem disturbance in tropical montane forests. Due to landslides, vegetation and often also the upper soil layer are removed, and space for primary succession under altered environmental conditions is created. Little is known about how these altered conditions affect important aspects of forest recovery such as the establishment of new tree biomass and species composition. To address these questions we utilize a process-based forest simulation model and develop potential forest regrowth scenarios. We investigate how changes in different trees species characteristics influence forest recovery on landslide sites. The applied regrowth scenarios are: undisturbed regrowth (all tree species characteristics remain like in the undisturbed forest), reduced tree growth (induced by nutrient limitation), reduced tree establishment (due to thicket-forming vegetation and dispersal limitation) and increased tree mortality (due to post-landslide erosion and increased susceptibility). We then apply these scenarios to an evergreen tropical montane forest in southern Ecuador where landslides constitute a major source of natural disturbance. Our most important findings are

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This paper presents a daily water balance model where the main aim is to quantify drought intensity and duration in forest stands. This model requires daily potential evapotranspiration and rainfall as input climatic data. Required site and stand parameters are only maximum extractable soil water and leaf area index, the latter controlling (i) stand transpiration; (ii) forest floor evapotranspiration; and (iii) rainfall interception. Other informations, like root distribution and soil porosity, can be used if available, improving the simulation of short term soil water recharge. Water stress is assumed to occur when relative extractable soil water (REW) drops below a threshold of 0.4 under which transpiration is gradually reduced due to stomatal closure. The model was calibrated using sap flow measurements of stand transpiration in oak and spruce stands during several successive dehydration–rehydration cycles. Validation of the model was performed by comparing predicted soil water content to weekly neutron probe measurements in various forest stands and climatic conditions. The model simulated accurately the dynamics of soil water depletion and recharge, and predicted the main components of forest water balance. Day-to-day estimates of soil water content during the growing season allows to quantify duration and intensity of drought events, and to compute stress indexes. A dendroecological application is presented: a retrospective analysis of the effects of drought on radial tree growth, based on long term climatic time series, is shown. Some limitations and potential applications of the model are discussed.

Simulations representing tree locations on a rectangular grid (cellular automaton) imply that spatial

patterns associated with f'we, seed dispersal, and the distributions
of plants and resources affect forest

dynamics profoundly. Simulated fires ignited at random locations in
a uniform environment create

non-uniform habitats and lead to patches dominated by different vegetation
types. Short-range seed

dispersal promotes vegetation clumping; fires cause these clumps to
coalesce into vegetation zones

separated by sharp borders, especially across an environmental gradient.
In simulation of competition

within vegetation mosaics, tree populations with a competitive advantage
still require the intervention of

fire to eliminate rivals. Also, the availability of local seed sources
enables established tree populations

to exclude invaders, but fires can trigger sudden changes in the composition
of such systems. In models

of simple succession systems, 'climax' vegetation tends to displace
'pioneer' vegetation, even under harsh

fire regimes.</div>

Understanding forest succession is required when designing management strategies, analyzing forest functioning, and forecasting the effects of changes in disturbance regime of forests. However, assigning a certain successional stage to forests in nature is challenging, especially when long-lived tree species dominate succession. Temperate rainforests commonly harbor emergent pioneer trees with long lifespans (>500 years) and may persist even when forest have reached stability in tree species composition (compositional equilibrium) and stability in structure (e.g. biomass). Thus, it is difficult to locate stands along a successional trajectory. Here, we propose a method for identifying the successional stages of forests using a dynamic forest model that estimate the time taken for a forest to reach the late successional stage, i.e. when forests have reached stability. Using this method, we examined the successional stages of 13 old, unmanaged stands of temperate rainforests located on Chiloé Island (Chile, 42S). We parameterized the model for 17 tree species using field data and a comprehensive literature search. The model predicted varied successional pathways for reproducing the observed structural variability of studied forests stands. Model results suggest that forests in this region can take 490–850 years to reach the late successional stage. We found 6 out of the 13 studied forests represent a transient successional stage. Forest stands in the late successional stage commonly contained pioneer species with basal area <20 m2/ha. According to our simulations, pioneers can persist until the late successional stage because of their long lifespans and the occurrence of small canopy openings (<1.6 ha) produced by windstorms. Above-ground biomass in the studied forests (estimated at 539 t/ha, average among stands) tended to decrease as forests approach the late successional stage because large pioneers are replaced by smaller late-successional trees. These results can assist in the classification of natural forest according to their successional stages as well as in developing management and conservation strategies of primary forests in this region.

1. Net primary production (NPP) by terrestrial ecosystems appears to be proportional to absorbed photosynthetically active radiation (APAR) on a seasonal and annual basis. This observation has been used in 'diagnostic' models that estimate NPP from remotely sensed vegetation indices. In 'prognostic' process-based models carbon fluxes are more commonly integrated with respect to leaf area index assuming invari- ant leaf photosynthetic parameters. This approach does not lead to a proportional relationship between NPP and APAR. However, leaf nitrogen content and Rubisco activity are known to vary seasonally and with canopy position, and there is evidence that this variation takes place in such a way as to nearly optimize total canopy net photosynthesis. 2. Using standard formulations for the instantaneous response of leaf net photosynthe- sis to APAR, we show that the optimized canopy net photosynthesis is proportional to APAR. This theory leads to reasonable values for the maximum (unstressed) light-use efficiency of gross and net primary production of C3 plants at current ambient C02, comparable with empirical estimates for agricultural crops and forest plantations. 3. By relating the standard formulations to the Collatz-Farquhar model of photosyn- thesis, we show that a range of observed physiological responses to temperature and CO2 can be understood as consequences of the optimization. These responses include the CO2 fertilization response and stomatal closure in C3 plants, the increase of leaf N concentration with decreasing growing season temperature, and the downward accli- mation of leaf respiration and N content with increasing ambient CO2. The theory pro- vides a way to integrate diverse experimental observations into a general framework for modelling terrestrial primary production.

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A classification of spatial simulation models of fire and vegetation dynamics (landscape fire succession models or LFSMs) is presented. The classification was developed to provide a foundation for comparing models and to help identify the appropriate fire and vegetation processes and their simulation to include in coarse scale dynamic global vegetation models. Other uses include a decision tool for research and management applications and a vehicle to interpret differences between LFSMs. The classification is based on the four primary processes that influence fire and vegetation dynamics: fire ignition, fire spread, fire effects, and vegetation succession. Forty-four LFSMs that explicitly simulated the four processes were rated by the authors and the modelers on a scale from 0 to 10 for their inherent degree of stochasticity, complexity, and mechanism for each of the four processes. These ratings were then used to group LFSMs into similar classes using common ordination and clustering techniques. Another database was created to describe each LFSM using selected keywords for over 20 explanatory categories. This database and the ordination and clustering results were then used to create the final LFSM classification that contains 12 classes and a corresponding key. The database and analysis results were used to construct a second classification key so managers can pick the most appropriate model for their application based on computer resources, available modeling expertise, and management objective. Published by Elsevier B.V.

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Southeastern Asian tropical rain forests are among the most important biomes in terms of annual productivity and water cycling. How their hydrologic budgets are altered by projected shifts in precipitation is examined using a combination of field measurements, global climate model (GCM) simulation output, and a simplified hydrologic model. The simplified hydrologic model is developed with its primary forcing term being rainfall statistics. A main novelty in this analysis is that the effects of increased (or decreased) precipitation on increased (or decreased) cloud cover and hence evapotranspiration is explicitly considered. The model is validated against field measurements conducted in a tropical rain forest in Sarawak, Malaysia. It is demonstrated that the model reproduces the probability density function of soil moisture content (s), transpiration (T

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Forests are likely to show complex transient responses to rapid changes in climate. The model described here simulates the dynamics of forest landscapes in a changing environment with simple phenomenological equations for tree growth processes and local environmental feedbacks. Tree establishment and growth rates are modified by species-specific functions describing the effects of winter and summer temperature limitations, accumulated annual foliage net assimilation and sapwood respiration as functions of temperature, CO2 fertilization, and growing-season drought. These functions provide external conditions for the simulation of patch-scale forest dynamics by a forest succession model, FORSKA, in which all of the trees on each 0.1 ha patch interact by competition for light and nutrients. The landscape is simulated as an array of such patches. The probability of disturbance on a patch is a power function of time since disturbance. Forest structure, composition and biomass simulated for the landscape average in boreal and temperate deciduous forests approach reasonable equilibrium values in 200-400 years. A climatic warning scenario is applied to central Sweden, where temperature and precipitation increases are shown to interact with each other and with soil water capacity in determining the transient and equilibrium responses of the forest landscape to climate change.

We report the development of a new spatially explicit individual-based Dynamic Global Vegetation Model (SEIB–DGVM), the first DGVM that can simulate the local interactions among individual trees within a spatially explicit virtual forest. In the model, a sample plot is placed at each grid box, and then the growth, competition, and decay of each individual tree within each plot is calculated by considering the environmental conditions for that tree as it relates to the trees that surround it. Based on these parameters only, the model simulated time lags between climate change and vegetation change. This time lags elongated when original biome was forest, because existing trees prevent newly establish trees from receiving enough sunlight and space to quickly replace the original vegetation. This time lags also elongated when horizontal heterogeneity of sunlight distribution was ignored, indicating the potential importance of horizontal heterogeneity for predicting transitional behavior of vegetation under changing climate. On a local scale, the model reproduced climate zone-specific patterns of succession, carbon dynamics, and water flux, although on a global scale, simulations were not always in agreement with observations. Because the SEIB–DGVM was formulated to the scale at which field biologists work, the measurements of relevant parameters and data comparisons are relatively straightforward, and the model should enable more robust modeling of terrestrial ecosystems.

* 1Disturbances from fire, wind-throw, insects and other herbivores are, besides climate, CO2, and soils, critical factors for composition, structure and dynamics of most vegetation. To simulate the influence of fire on the dynamic equilibrium, as well as on potential change, of vegetation at the global scale, we have developed a fire model, running inside the modular framework of the Lund–Potsdam–Jena Dynamic Global Vegetation Model (LPJ-DGVM). * 2Estimated litter moisture is the main driver of day-to-day fire probability. The length of the fire season is used to estimate the fractional area of a grid cell which is burnt in a given year. This affected area is converted into an average fire return interval which can be compared to observations. * 3When driven by observed climate for the 20th century (at a 0.5 longitude/latitude resolution), the model yielded fire return intervals in good agreement with observations for many regions (except parts of semiarid Africa and boreal Siberia). We suggest that further improvement for these regions must involve additional process descriptions such as permafrost and fuel/fire dynamics.

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