Predicting and understanding forest dynamics using a simple tractable model

Abstract

The perfect-plasticity approximation (PPA) is an analytically tractable model of forest dynamics, defined in terms of parameters for individual trees, including allometry, growth, and mortality. We estimated these parameters for the eight most common species on each of four soil types in the US Lake states (Michigan, Wisconsin, and Minnesota) by using short-term (<15-year) inventory data from individual trees. We implemented 100-year PPA simulations given these parameters and compared these predictions to chronosequences of stand development. Predictions for the timing and magnitude of basal area dynamics and ecological succession on each soil were accurate, and predictions for the diameter distribution of 100-year-old stands were correct in form and slope. For a given species, the PPA provides analytical metrics for early-successional performance (H 20, height of a 20-year-old open-grown tree) and late-successional performance (Ẑ *, equilibrium canopy height in monoculture). These metrics predicted which species were early or late successional on each soil type. Decomposing Ẑ * showed that (i) succession is driven both by superior understory performance and superior canopy performance of late-successional species, and (ii) performance differences primarily reflect differences in mortality rather than growth. The predicted late-successional dominants matched chronosequences on xeromesic (Quercus rubra) and mesic (codominance by Acer rubrum and Acer saccharum) soil. On hydromesic and hydric soils, the literature reports that the current dominant species in old stands (Thuja occidentalis) is now failing to regenerate. Consistent with this, the PPA predicted that, on these soils, stands are now succeeding to dominance by other latesuccessional species (e.g., Fraxinus nigra, A. rubrum).climate change ͉ community ecology ͉ SORTIE ͉ TASS ͉ trade-offs

Individual-Based Allometric Equations Accurately Measure Carbon Storage and Sequestration in Shrublands

“…This is because it would permit application of individual-based forest dynamics models such as the perfect plasticity approximation (PPA) of Purves et al [10]. Our results show that an individual-based allometric approach gives a high degree of confidence in C storage estimates, so that we should be able to scale up individual-based growth models to predict stand-scale C storage.…”

“…Individual-level allometric approaches for shrublands are required for building mechanistic models of C sequestration (e.g., [10]) during succession from shrubland to forest, as these models require information on the establishment, growth, and mortality of individual plants. Use of an individual-level allometric approach in shrublands would allow these demographic processes to be documented from the very beginning of post-agricultural woody succession.…”

Decreased water limitation under elevated CO 2 amplifies potential for forest carbon sinks

“…To find the light level available to each individual, L i , we use the perfect plasticity approximation (PPA), an analytically tractable forest dynamics model that accurately approximates the dynamics of a fully spatial forest simulator (28,29). In its simplest form, the PPA is the approximation that there is a single size (i.e., diameter D*), above which tree crowns are in full sun (L 0 ) and below which trees are shaded by a single layer of canopy trees.…”

Predictive ecology: systems approaches

“…Further embedding evolution in ecological thinking would allow greater appreciation of the relationship between biological processes at the individual level and the population, community or ecosystem results of these processes. If novel environmental change imposes selection pressures that cause the components of an ecological system to evolve and if this evolutionary process affects the way that system functions, then evolution cannot be ignored.Despite the desirability of including evolution in ecological models, the most successful group of process-based models in ecology-the terrestrial biosphere models do not do so [27][28][29][30][31]. This may be due to the fact that their raison d'être is to predict changes in the forest community and so even though they have long simulated run times-typically 1000 years, the organisms within them also have long generation times.…”

“…The biosphere models are an example of a process-based approach applied to one trophic level of an ecosystem [27][28][29][30][31]35]. There have been moves in the direction of adding further trophic levels; for example, some similar models include bark beetle-induced mortality [49] and the effect of pine beetle outbreaks on productivity and carbon capture and storage [50].…”