Forest Community Dynamics Research Articles

Tree population and community dynamics in a Brazilian tropical semideciduous forest

Tree population and community dynamics in a Brazilian tropical semideciduous forest). The dynamics of the tree community and 30 tree populations were examined in an area of tropical semideciduous forest located on the margin of the Rio Grande, SE Brazil, based on surveys done in 1990 and 1997 in three 0.18 ha plots. The main purpose was to assess whether variations in dynamics were related to topography and the effects of a catastrophic flood in 1992. Rates of mortality and recruitment of trees and gain and loss of basal area in two topographic sites, lower (flooded) and upper (non-flooded), were obtained. Projected trajectories of mean and accelerated growth in diameter were obtained for each species. In both topographic sites, mortality rates surpassed recruitment rates, gain rates of basal area surpassed loss rates, and size distributions changed, with declining proportions of smaller trees. These overall changes were possibly related to increased underground water supply after the 1992 flood as well as to a c. 250-year-old process of primary succession on abandoned gold mines. Possible effects of the 1992 flood showed up in the higher proportions of dead trees in the flooded sites and faster growth rates in the flood-free sites. Species of different regeneration guilds showed particular trends with respect to their demographic changes and diameter growth patterns. Nevertheless, patterns of population dynamics differed between topographic sites for only two species.

EARLY PERFORMANCE PREDICTS CANOPY ATTAINMENT ACROSS LIFE HISTORIES IN SUBALPINE FOREST TREES

Few individuals in canopy tree species attain the canopy and reproduce. Understanding why these select few succeed is fundamental to tree population ecology and forest community dynamics. Yet our understanding remains poor, because the time required to reach the canopy is long relative to experimental and demographic studies. We used a simple, yet powerful, approach to examine the long-term process of canopy recruitment. We compared early growth in proven winners (extant canopy trees) with that of con- tenders (extant saplings 75 cm tall to 5 cm dbh). The resulting analyses relate early radial growth (after reaching 50 cm height) to survival, implicit in the long-term persistence of winners. We focused on the three major tree species of subalpine forests in the northeastern United States: shade-intolerant mountain birch (Betula cordifolia), shade-tolerant balsam fir (Abies balsamea), and highly shade-tolerant red spruce (Picea rubens). For all species, extant canopy trees grew faster than extant saplings at equivalent ages and sizes. For shade-intolerant B. cordifolia, no surviving canopy trees, or even saplings, had slow early growth. Even in shade-tolerant A. balsamea and P. rubens, surprisingly few individuals with slow early growth were represented in the canopy, even though both saplings and canopy trees survived slow growth for up to 50 years later in life. Thus, long- term success in reaching the canopy was strongly determined by fast early growth rates, across all species and life histories. We discuss implications for understanding the physi- ology of shade tolerance and for modeling forest dynamics. Most current models of forest tree population and community dynamics ignore individual growth history, but our results suggest that failure to account for growth history may overestimate long-term survival of shade-tolerant species.

Gypsy moth feeding in the canopy of a CO2‐enriched mature forest

AbstractRising atmospheric carbon dioxide (CO2) concentration is expected to change plant tissue quality with important implications for plant–insect interactions. Taking advantage of canopy access by a crane and long‐term CO2 enrichment (530 μ mol mol−1) of a natural old‐growth forest (web‐free air carbon dioxide enrichment), we studied the responses of a generalist insect herbivore feeding in the canopy of tall trees. We found that relative growth rates (RGR) of gypsy moth (Lymantria dispar) were reduced by 30% in larvae fed on high CO2‐exposed Quercus petraea, but increased by 29% when fed on high CO2‐grown Carpinus betulus compared with control trees at ambient CO2 (370 μ mol mol−1). In Fagus sylvatica, there was a nonsignificant trend for reduced RGR under elevated CO2. Tree species‐specific changes in starch to nitrogen ratio, water, and the concentrations of proteins, condensed and hydrolyzable tannins in response to elevated CO2 were identified to correlate with altered RGR of gypsy moth larvae. Our data suggest that rising atmospheric CO2 will have strong species‐specific effects on leaf chemical composition of canopy trees in natural forests leading to contrasting responses of herbivores such as those reported here. A future change in host tree preference seems likely with far‐ranging consequences for forest community dynamics.

Canopy tree development and undergrowth bamboo dynamics in old-growth Abies– Betula forests in southwestern China: a 12-year study

Interactions between forest canopy characteristics and plants in the forest understory are important determinants of forest community structure and dynamics. In the highlands of southwestern, China the dwarf bamboo Bashania fangiana Yi is an understory dominant beneath a mixed canopy of the evergreen Abies faxoniana (Rheder & Wilson) and the deciduous Betula utilis (D. Don). The goal of this study was to better understand the role of bamboo dominance, canopy characteristics, and periodic bamboo dieback on forest development. To achieve this goal, we measured tree seedling, tree saplings, and trees, forest canopy characteristics, and bamboo cover in permanent forest ( n = 4) and gap plots ( n = 31) in a mixed A. faxoniana and B. utilis forest in Sichuan, China. Dwarf bamboos died off in 1983 in the gap plots, and in three of the four forest plots. Forest development was assessed for the period 1984–1996. The seedling bank in forest and gap plots increased after bamboo die-off. A. faxoniana seedlings increased more than B. utilis in forest plots; the opposite pattern characterized gap plots. The proportion of seedlings on raised micro-sites on the forest floor also changed and new seedling were more abundant on the forest floor. By 1996, bamboo seedling cover and biomass had recovered to ca. 45% or their pre-flowering values. Rates of bamboo seedling recovery were faster beneath canopy gaps and deciduous trees than beneath forest or evergreen trees. Tree mortality exceeded recruitment in plots with dense bamboo; the opposite pattern was found in the plot with little bamboo. The mortality rate for B. utilis trees (2.4% year −1) was higher than that for A. faxoniana (0.8% year −1) and forests with dense bamboos became more open over the census period. Tree mortality was size-dependent and intermediate sized trees had the lowest rates of mortality. Stand basal area increased mainly due to greater basal area gain than loss for A. faxoniana. Interactions between tree species life history, canopy type, and bamboo life-cycles create heterogeneous conditions that influence tree and bamboo regeneration and contribute to the coexistence of A. faxoniana and B. utilis in old-growth forests in southwestern China.

The effect of man-caused disturbances on the development dynamics of forest communities on Abruka Island (West Estonia)

The effect of man-caused disturbances on the development dynamics of forest communities on Abruka Island (West Estonia)

Does elevated CO2 facilitate naturalization of the non‐indigenous Prunus laurocerasus in Swiss temperate forests?

Summary An increasing abundance of the non‐indigenous evergreen woody plant species Prunus laurocerasus has been observed in the understorey of Swiss temperate forests. We addressed the question whether rising atmospheric CO2 concentration contributes to the success of this species in a comparative test with four co‐occurring native species (Ilex aquifolium, Hedera helix, Fraxinus excelsior, Carpinus betulus). We grew plants from germination to the end of the third growing season in open‐top chambers exposed to either ambient or two elevated CO2 concentrations (500 and 660 µmol mol−1) in a deeply shaded forest understorey (1·2–3·2% of full sun). Species differed greatly in their response to CO2. Biomass growth in Prunus increased by an average of 56% at the two elevated CO2 concentrations compared to ambient CO2; there was no significant difference between 500 and 660 µmol mol−1. In contrast the native Ilex, with the same functional traits, a similar life history and occurring in the same habitat, showed no significant CO2 response. A particularly large and nearly linear CO2 effect on seedling growth was observed in the liana Hedera with 100% more biomass and 137% longer stems at 660 µmol CO2 mol−1 compared to ambient CO2. Seedlings of the deciduous tree species Fraxinus produced 43% more biomass at elevated CO2 (no significant difference between 500 and 660 µmol mol−1), but there was no significant CO2 effect on Carpinus seedlings. Our results indicate that elevated CO2 might contribute to the current spread of Prunus in natural forests. The strong CO2 response in Hedera suggests an increasing rate of tree colonization with rising CO2. Increasing dominance of non‐indigenous understorey species and accelerated liana colonization of canopy trees could both have far‐ranging consequences for forest community dynamics and composition.

Tree canopy displacement and neighborhood interactions

Competitive interactions among plants are largely determined by spatial proximity. However, despite their sessile nature, plants have the ability to avoid neighbors by growing towards areas with high resource availability and reduced competition. Because of this flexibility, tree canopies are rarely centered directly above their stem bases and are often displaced. We sought to determine how a tree's competitive neighborhood influences its canopy position. In a 0.6-ha temperate forest plot, all trees greater than 10 cm DBH (n = 225) were measured for basal area, height, canopy depth, and trunk position. Canopy extent relative to trunk base was determined in eight subcardinal directions, and this information was used to reconstruct canopy size, shape, and position. We found that trees positioned their canopies away from large neighbors, close neighbors, and shade-tolerant neighbors. Neighbor size, expressed as basal area or canopy area, was the best indication of a neighbor's importance in determining target tree canopy position. As neighborhood asymmetry increased, the magnitude of canopy displacement increased, and the precision with which canopies avoided neighbors increased. Flexibility in canopy shape and position appears to reduce competition between neighbors, thereby influencing forest community dynamics.

NITROGEN-INDUCED CHANGES IN SEEDLING REGENERATION AND DYNAMICS OF MIXED CONIFER–BROAD-LEAVED FORESTS

Most research on forest dynamics has focused on species' light requirements as the major driver for successional change. However, soil resource availability may modify seedling responses to light and ultimately alter the course of succession. In the present study, we examined how seedlings in mixed conifer-broad-leaved forests in eastern North America differed in their growth and mortality responses to manipulated nitrogen avail- ability. We then incorporated these responses into an individual-based model of forest dynamics (SORTIE) to assess potential longer-term consequences of seedling responses to nitrogen for temperate forest community dynamics. We grew seedlings of six study species, both individually and in mixed-species competitive stands, in a common garden for two years. The earlier successional broad-leaved species (yellow birch and red maple) consis- tently showed the greatest increases in biomass in response to nitrogen addition, while the most late successional of the broad-leaved species (sugar maple) and all the coniferous species did not grow significantly larger with increased nitrogen. We found a significant correlation between species' early growth rate and nitrogen growth enhancement. For those species that underwent significant nitrogen-induced shifts in growth and/or mortality, we adjusted their parameters in the seedling/sapling growth and mortality submodels of SOR- TIE (covering up to 10 cm dbh). Simulations revealed that nitrogen effects on both seedling growth in high light and seedling mortality in low light (data from parallel experiment) changed overall forest structure and dynamics. Increased nitrogen led to: (1) further dom- inance of young forests by earlier successional species (yellow birch in particular), through its impacts on seedling high-light growth, and (2) even greater persistence of later suc- cessional species (predominantly hemlock) in older forests, through its impacts on seedling low-light mortality. These findings were robust to an uncertainty analysis that incorporated experimentally derived error into the seedling/sapling submodels. In contrast, the identity of the species replaced by yellow birch and hemlock was more sensitive to uncertainty in parameter values. We conclude that seedling physiological and demographic responses to increased nitrogen availability have the potential to scale up and influence successional dynamics in mixed temperate forests, provided these effects persist throughout seedling and sapling life stages.

FINE-SCALE PREDICTABILITY OF FOREST COMMUNITY DYNAMICS

We assayed the predictability of forest community dynamics by examining the internal structure of a 10-12-yr record of forest change for three sites in east Texas, USA. Within each site, the growth and fate of all adult tree stems within many small (0.04 ha) patches have been monitored. These data were reduced to community composition (basal area by species) for each of 28-30 spatially independent patches within each site. We measured predictability of compositional change by the rank correlation of (1) distances between vectors of initial composition vs. (2) distances between vectors of compositional change. Vectors of compositional change were predictable at two of the three sites; the third site was an old forest with somewhat high mortality of large adult stems. The data also allowed decomposition of the change vectors into components due to growth, mortality, and adult tree recruitment. Growth vectors were highly predictable from the initial com- position, but mortality and adult tree recruitment were not. The results support the idea that growth processes in forests are closely tied to interactions among adjacent trees, whereas recruitment and mortality have components that operate at different spatial or temporal scales and so are empirically decoupled from growth.

Tree species diversity in temperate and tropical forest gaps: The role of lottery recruitment

How canopy gaps promote tree species coexistence in temperate and tropical forests is reviewed. Given that evidence for traditional resource-based niche partitioning of canopy gaps is weak, lottery recruitment, whereby colonization of vacant living space is random with respect to species identity, may be key to maintaining diversity. Gap formation events are not highly predictable and species’ propagules tend to be patchily distributed. For these reasons the predictability of gap-phase recruitment is low and lottery principles apply. Recruitment limitation from discontinuities in species’ propagule supplies in space and time may permit lottery recruitment in temperate and tropical forests. However, the relative importance of recruitment limitation in species-rich versus species-poor communities is unclear. Although lottery models with purely random recruitment in vacant sites can be applied, relatively complex models appear to better capture the essential features of forest community dynamics. For example, models with recruitment probabilities weighted by species abundance can produce the non-random trajectories often observed in communities. Models with local competitive displacement by individuals of dominant species can also produce non-random trajectories. Models with spatial structure, localized competition, and dispersal limitations may provide further insight into the effects of biotic interactions and recruitment limitation on forest dynamics.

Natural disturbance dynamics in the boreal forests of European Russia: a review

In the European part of the Russian boreal zone the dynamics of pristine forests (taiga) has been studied by several generations of researchers. Many studies have examined the patterns and role of fire, windthrow, insect outbreaks and other natural disturbances. An attempt is made to provide a brief review of these studies. The reviewed studies show that lightning strikes were the only natural source of fires in taiga. The frequency of fires varied in various types of pristine landscape from 1–2 per century to 1–2 per millennium. Fires maintained a dynamic equilibrium between compositionally different forest communities or their certain ratio and areal occurrence. Fires favored the regeneration and recovery of pine forests and prevented the replacement of shade-intolerant species (e.g. pine) by shade-tolerant ones (e.g. spruce). Taiga forests generally displayed a mosaic pattern that varied from pioneer plant communities, growing in open burns, to climax communities that were extremely seldom affected by fire. The reviewed studies suggest that fires were a powerful ecological factor in pristine taiga, being largely responsible for the structure and spontaneous dynamics of forest communities. Windfalls were also common in pristine taiga landscapes and they regulated spontaneous dynamics in a gap-mosaic regime, which is most characteristic of spruce forests.

Effects of Multiple Disturbances (Fire and Hurricane) on Epiphyte Community Dynamics in a Subtropical Forest, Florida, U.S.A.1

ABSTRACTWe addressed the interacting effects of a natural large–scale fire and a subsequent major hurricane on relative positions of epiphytes in a subtropical forest. In Everglades National Park, subtropical hammocks (hardwood tree “islands”; burned and unburned) during the Ingraham Fire (1989) were surveyed for trees and epiphytic bromeliads (Tillandsia spp.) one year before, as well as one and five years after, Hurricane Andrew (1992). We measured trees (species, diameter, and status [alive/dead]) and epiphytes (species, height, host tree characteristics, substrate life status, and density). The fire decreased the height of epiphytes during the hurricane because branches and bark of trees killed by the fire were unstable epiphyte substrates in the high winds. Proportions of epiphytes on Quercus virginiana were equally increased after the hurricane in both unburned and burned hammocks; the large size and bark characteristics resulted in greater proportional survival of epiphytes on this species. During the five years following the hurricane, changes in the distributions of epiphytes generally were toward pre–hurricane distributions, but recovery was faster in unburned than burned hammocks. We conclude that disturbances that kill trees are likely to amplify the vertical reduction of epiphytes during a subsequent hurricane and that effects of a single disturbance on plant populations can be influenced by the disturbance history of the system, including different types of disturbances.

Forest canopy and community dynamics in a temperate old‐growth evergreen broad‐leaved forest, south‐western Japan: a 7‐year study of a 4‐ha plot

Summary Forest canopy gap and community dynamics were studied in a 4‐ha permanent plot of an old‐growth evergreen broad‐leaved forest dominated by Castanopsis cuspidata var. sieboldii and Distylium racemosum in the Tatera Forest Reserve, Tsushima Islands, south‐western Japan. The forest was affected by a powerful typhoon in 1987 and was monitored from 1990 to 1997. In 1990, all woody stems ≥ 5 cm diameter at breast height (d.b.h.) in the plot were identified, mapped and marked, and the state of 1600 5 m × 5 m contiguous quadrats used to locate canopy gaps. Gaps occupied 17.1% of the plot, which contained 4494 tree and shrub stems (total basal area 63.48 m2 ha−1). Gaps were re‐censused in 1997 and both marked and newly recruited (≥ 5 cm d.b.h.) stems were recorded in 1992 and 1997. Over 7 years the rates of canopy gap formation and closure were 0.72% year−1 and 1.61% year−1, respectively, mortality and recruitment rates were 0.97% year−1 and 0.99% year−1, and the rates of loss and gain in basal area were 0.95% year−1 and 0.83% year−1. The mortality of stems was size‐dependent, with those in middle size classes having the lowest rates. Mortality of stems was lower in canopy and higher in the understorey, while the proportion of stems killed by disturbances increased with height. Stems that died during the 7 years were predominantly located in newly created gaps, whereas stems were recruited into both established and new gaps. Deciduous broad‐leaved species were largely restricted to gaps that remained open throughout the study. Both composition and structure of the forest changed in response to disturbance‐related effects on canopy dynamics.

TREE MORTALITY AND GROWTH IN 11 SYMPATRICMACARANGASPECIES IN BORNEO

Interspecific differences in tree performance due to variation in resource availability are expected to influence the structure and dynamics of tropical forest communities. Patterns of mortality and growth over 32 mo in 11 species of Macaranga were analyzed to investigate factors influencing tree spatial distributions and the dynamics of early successional communities. Tree performance was assessed in relation to variation in light levels, soil texture, and tree ontogeny. Rates of mortality and growth varied by over an order of magnitude among species. Species common in high-light microsites had higher mortality and growth rates. Higher low-light mortality for these species reflected lower shade tolerances, supporting the view that shade tolerance involves a trade-off between high-light growth and low-light mortality. Logistic and multiple regressions were used to test for independent effects of tree size and microenvironment on performance in the 11 species. Mortality and growth were significantly related to tree size in nine and eight species, respectively. Higher mortality and lower growth rates for juvenile trees were common. Despite positive correlations between light availability and tree size, mortality rates increased in three species, and growth rates decreased in four species at larger tree sizes. This pattern was particularly strong in smaller statured shade-intolerant species and may reflect changes in biomass allocation following reproductive onset. Declines in growth at larger tree sizes for only some species resulted in changes in species' performance rankings through succession. Low-light mortality rates were strongly correlated with species' distributions in the forest with respect to light levels, whereas biases in distributions with respect to soil texture were not supported by differential mortality. For all trees pooled and in several species, growth showed a threshold response to light levels, being light-limited in low light but not in high light. Across all light levels, soil texture significantly influenced growth in six species. Five species and all trees pooled had significantly lower growth on the more nutrient-poor and potentially drought-prone sandy soils. The dynamics of Macaranga-dominated early successional communities are strongly influenced by soil resource and light availability, coupled with species-specific ontogenetic trajectories of performance.

Spatial Patterns and Persistence of Woody Plant Species in Ecological Communities

The role of stochastic effects and seed dispersal limitations in maintaining the diversity of a tree community is investigated by means of a forest growth simulator called TROLL. This simulator makes it possible to investigate impacts on the spatial distribution and the extinction probability of plant species. I present the results of a two-species competition scenario. Coexistence is found to be possible for competitively dissimilar species, and the criterion for this coexistence is given analytically in the reaction-diffusion approximation. A higher frequency of tree falls implies a smaller extinction probability of least adapted species. The multispecies model is also investigated. A mathematical quantity-the persistence function-permits measurement of the ability of a species to out compete other species locally. This quantity is compared with the average time to extinction, and it is computed for the TROLL simulator. I interpret the shape of this function in light of available information on the persistence function in simple interacting particle systems. These results indicate an analogy between the dynamics of forest communities and a simple discrete and spatially explicit model, the voter model. The ecological implications of this analogy are discussed and are extended to species-rich communities.

Effects of Multiple Disturbances (Fire and Hurricane) on Epiphyte Community Dynamics in a Subtropical Forest, Florida, U.S.A.1

We addressed the interacting effects of a natural large-scale fire and a subsequent major hurricane on relative positions of epiphytes in a subtropical forest. In Everglades National Park, subtropical hammocks (hardwood tree “islands”; burned and unburned) during the Ingraham Fire (1989) were surveyed for trees and epiphytic bromeliads (Tillandsia spp.) one year before, as well as one and five years after, Hurricane Andrew (1992). We measured trees (species, diameter, and status [alive/dead]) and epiphytes (species, height, host tree characteristics, substrate life status, and density). The fire decreased the height of epiphytes during the hurricane because branches and bark of trees killed by the fire were unstable epiphyte substrates in the high winds. Proportions of epiphytes on Quercus virginiana were equally increased after the hurricane in both unburned and burned hammocks; the large size and bark characteristics resulted in greater proportional survival of epiphytes on this species. During the five years following the hurricane, changes in the distributions of epiphytes generally were toward pre-hurricane distributions, but recovery was faster in unburned than burned hammocks. We conclude that disturbances that kill trees are likely to amplify the vertical reduction of epiphytes during a subsequent hurricane and that effects of a single disturbance on plant populations can be influenced by the disturbance history of the system, including different types of disturbances.

Eco-Economical Model of the Region Development Based on the Delphi Approach (at the Bieszczad Mountain Region, Poland)

A computer simulation has been developed for the dynamics of forest communities and abundance of wild animals in the Bieszczad mountain region (Carpathians, Southern Poland) at the background of changing water quality resulting from the development of tourism and agriculture. The simulation operates on scaled variables in the 0–1 range. The functional relationships in the simulation were determined by the Delphi evaluation. The simulation was used to consider scenarios of various environmental influences of the region—climatic factors (warming and changed rainfall) as well as anthropogenic disturbances (development of tourism, agriculture, and commercial hunting). The simulation can be adapted for other regions.

The Holocene forest history of the Montes Universales, Teruel, Spain

A radiocarbon-dated peat core from Ojos del Tremedal, Montes Universales, Spain, provides insights into the dynamics of high montane forest communities in Central Iberia from the Lateglacial to the late Holo cene. The Lateglacial landscape was characterized by grassland dominated by Gramineae, Cyperaceae and Artemisia, together with Juniperus, which was invaded from c. 9600 cal. BP by Betula and Pinus as climate conditions improved. Given the reduced role that Betula plays currently in the region, its presence throughout most of the Holocene suggests that the area experienced more mesic conditions until c. 2500 cal. BP. Distinct signs of human interference in the vegetation are apparent from c. 3500 cal. BP.

Primate Community Dynamics in Old Growth Forest over 23.5 Years at Ngogo, Kibale National Park, Uganda: Implications for Conservation and Census Methods

Few data exist regarding long-term changes in primate populations in old-growth, tropical forests. In the absence of this information, it is unclear how to assess population trends efficiently and economically. We addressed these problems by conducting line-transect censuses 23.5 years apart at the Ngogo study area in Kibale National Park, Uganda. We conducted additional censuses over short time intervals to determine the degree to which the temporal distribution of censuses affected estimates of primate numbers. Results indicate that two species, blue monkeys and red colobus, may have experienced significant reductions over the past 23.5 years at Ngogo. In contrast, five other species, baboons, black-and-white colobus, chimpanzees, mangabeys, and red-tailed guenons, have not changed in relative abundance. Additional findings indicate that different observers may vary significantly in their estimates of sighting distances of animals during censuses, thus rendering the use of measures of absolute densities problematic. Moreover, censuses conducted over short periods produce biased estimates of primate numbers. These results provide guidelines for the use of line-transect censuses and underscore the importance of protecting large blocks of forests for primate conservation.

Tropical forest diversity, environmental change and species augmentation: After the intermediate disturbance hypothesis

Abstract.It is not simple to predict how environmental changes may impact tropical forest species diversity. Published hypotheses are almost invariably too incomplete, too poorly specified and too dependent upon unrealistic assumptions to be useful. Ecologists have sought theoretical simplicity, and while this has provided many elegant abstract concepts, it has hindered the attainment of more practical goals. The problem is not how to judge the individual hypotheses and arguments, but rather how to build upon and combine the many hard‐won facts and principles into an integrated science.Controversy is inevitable when the assumptions, definitions and applications of a given hypothesis are unclear. Elegance, as an end in itself, has too often been used to justify abstract simplification and a lack of operational definition. Clarifying and combining hypotheses while avoiding assumptions provides a potentially more useful, if less elegant, standpoint. An appraisal of Connell's intermediate disturbance hypothesis, and its application to long‐term observations from a Ugandan forest illustrates these concerns.Current emphases encourage ecologists to exclude consideration of environmental instability and non‐pristine ecosystems. In reality, many environmental changes and ecological processes contribute to both the accumulation and erosion of diversity, at all spatial and temporal scales. Site histories, contexts, long‐term processes, species‐pool dynamics, and the role of people require greater emphasis. These considerations reveal that many environmental changes, even those associated with degradation, can lead to a transient rise in species densities. Drawing on related studies, such as forest yield prediction, suggests that the formulation and calibration of simulation models provides the most tractable means to address the complexity of real vegetation. Simulation‐based approaches will become increasingly useful both in unifying the study of vegetation dynamics and in providing improved predictive capacity. Quantification of the processes, scales and sensitivities of the dynamics of tropical forest communities remains a major challenge.