skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Friday, May 17 until 8:00 AM ET on Saturday, May 18 due to maintenance. We apologize for the inconvenience.

Title: Demographic trade-offs predict tropical forest dynamics
Understanding tropical forest dynamics and planning for their sustainable management require efficient, yet accurate, predictions of the joint dynamics of hundreds of tree species. With increasing information on tropical tree life histories, our predictive understanding is no longer limited by species data but by the ability of existing models to make use of it. Using a demographic forest model, we show that the basal area and compositional changes during forest succession in a neotropical forest can be accurately predicted by representing tropical tree diversity (hundreds of species) with only five functional groups spanning two essential trade-offs—the growth-survival and stature-recruitment trade-offs. This data-driven modeling framework substantially improves our ability to predict consequences of anthropogenic impacts on tropical forests.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Page Range / eLocation ID:
165 to 168
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Understanding the mechanisms that promote the coexistence of hundreds of species over small areas in tropical forest remains a challenge. Many tropical tree species are presumed to be functionally equivalent shade tolerant species but exist on a continuum of performance trade‐offs between survival in shade and the ability to quickly grow in sunlight. These trade‐offs can promote coexistence by reducing fitness differences.

    Variation in plant functional traits related to resource acquisition is thought to predict variation in performance among species, perhaps explaining community assembly across habitats with gradients in resource availability. Many studies have found low predictive power, however, when linking trait measurements to species demographic rates.

    Seedlings face different challenges recruiting on the forest floor and may exhibit different traits and/or performance trade‐offs than older individuals face in the eventual adult niche. Seed mass is the typical proxy for seedling success, but species also differ in cotyledon strategy (reserve vs. photosynthetic) or other leaf, stem and root traits. These can cause species with the same average seed mass to have divergent performance in the same habitat.

    We combined long‐term studies of seedling dynamics with functional trait data collected at a standard life‐history stage in three diverse neotropical forests to ask whether variation in coordinated suites of traits predicts variation among species in demographic performance.

    Across hundreds of species in Ecuador, Panama and Puerto Rico, we found seedlings displayed correlated suites of leaf, stem, and root traits, which strongly correlated with seed mass and cotyledon strategy. Variation among species in seedling functional traits, seed mass, and cotyledon strategy were strong predictors of trade‐offs in seedling growth and survival. These results underscore the importance of matching the ontogenetic stage of the trait measurement to the stage of demographic dynamics.

    Our findings highlight the importance of cotyledon strategy in addition to seed mass as a key component of seed and seedling biology in tropical forests because of the contribution of carbon reserves in storage cotyledons to reducing mortality rates and explaining the growth‐survival trade‐off among species.

    Synthesis: With strikingly consistent patterns across three tropical forests, we find strong evidence for the promise of functional traits to provide mechanistic links between seedling form and demographic performance.

    more » « less
  2. Abstract Background and Aims

    Understanding shifts in the demographic and functional composition of forests after major natural disturbances has become increasingly relevant given the accelerating rates of climate change and elevated frequency of natural disturbances. Although plant demographic strategies are often described across a slow–fast continuum, severe and frequent disturbance events influencing demographic processes may alter the demographic trade-offs and the functional composition of forests. We examined demographic trade-offs and the shifts in functional traits in a hurricane-disturbed forest using long-term data from the Luquillo Forest Dynamics Plot (LFPD) in Puerto Rico.


    We analysed information on growth, survival, seed rain and seedling recruitment for 30 woody species in the LFDP. In addition, we compiled data on leaf, seed and wood functional traits that capture the main ecological strategies for plants. We used this information to identify the main axes of demographic variation for this forest community and evaluate shifts in community-weighted means for traits from 2000 to 2016.

    Key Results

    The previously identified growth–survival trade-off was not observed. Instead, we identified a fecundity–growth trade-off and an axis representing seedling-to-adult survival. Both axes formed dimensions independent of resprouting ability. Also, changes in tree species composition during the post-hurricane period reflected a directional shift from seedling and tree communities dominated by acquisitive towards conservative leaf economics traits and large seed mass. Wood specific gravity, however, did not show significant directional changes over time.


    Our study demonstrates that tree demographic strategies coping with frequent storms and hurricane disturbances deviate from strategies typically observed in undisturbed forests, yet the shifts in functional composition still conform to the expected changes from acquisitive to conservative resource-uptake strategies expected over succession. In the face of increased rates of natural and anthropogenic disturbance in tropical regions, our results anticipate shifts in species demographic trade-offs and different functional dimensions.

    more » « less
  3. Abstract

    Organisms of all species must balance their allocation to growth, survival and recruitment. Among tree species, evolution has resulted in different life‐history strategies for partitioning resources to these key demographic processes. Life‐history strategies in tropical forests have often been shown to align along a trade‐off between fast growth and high survival, that is, the well‐known fast–slow continuum. In addition, an orthogonal trade‐off has been proposed between tall stature—resulting from fast growth and high survival—and recruitment success, that is, a stature−recruitment trade‐off. However, it is not clear whether these two independent dimensions of life‐history variation structure tropical forests worldwide.

    We used data from 13 large‐scale and long‐term tropical forest monitoring plots in three continents to explore the principal trade‐offs in annual growth, survival and recruitment as well as tree stature. These forests included relatively undisturbed forests as well as typhoon‐disturbed forests. Life‐history variation in 12 forests was structured by two orthogonal trade‐offs, the growth−survival trade‐off and the stature−recruitment trade‐off. Pairwise Procrustes analysis revealed a high similarity of demographic relationships among forests. The small deviations were related to differences between African and Asian plots.

    Synthesis. The fast–slow continuum and tree stature are two independent dimensions structuring many, but not all tropical tree communities. Our discovery of the consistency of demographic trade‐offs and life‐history strategies across different forest types from three continents substantially improves our ability to predict tropical forest dynamics worldwide.

    more » « less
  4. Abstract

    Both tree size and life history variation drive forest structure and dynamics, but little is known about how life history frequency changes with size. We used a scaling framework to quantify ontogenetic size variation and assessed patterns of abundance, richness, productivity and light interception across life history strategies from >114,000 trees in a primary, neotropical forest. We classified trees along two life history axes: afast–slowaxis characterized by a growth–survival trade‐off, and astature–recruitmentaxis with tall,long‐lived pioneersat one end and short,short‐lived recruitersat the other.

    Relative abundance, richness, productivity and light interception follow an approximate power law, systematically shifting over an order of magnitude with tree size.Slowsaplings dominate the understorey, butslowtrees decline to parity with rapidly growingfastandlong‐lived pioneerspecies in the canopy.

    Like the community as a whole,slowspecies are the closest to obeying the energy equivalence rule (EER)—with equal productivity per size class—but other life histories strongly increase productivity with tree size. Productivity is fuelled by resources, and the scaling of light interception corresponds to the scaling of productivity across life history strategies, withslowandallspecies near solar energy equivalence. This points towards a resource‐use corollary to the EER: the resource equivalence rule.

    Fitness trade‐offs associated with tree size and life history may promote coexistence in tropical forests by limiting niche overlap and reducing fitness differences.

    Synthesis. Tree life history strategies describe the different ways trees grow, survive and recruit in the understorey. We show that the proportion of trees with a pioneer life history strategy increases steadily with tree size, as pioneers become relatively more abundant, productive, diverse and capture more resources towards the canopy. Fitness trade‐offs associated with size and life history strategy offer a mechanism for coexistence in tropical forests.

    more » « less
  5. Abstract

    Severe droughts have led to lower plant growth and high mortality in many ecosystems worldwide, including tropical forests. Drought vulnerability differs among species, but there is limited consensus on the nature and degree of this variation in tropical forest communities. Understanding species‐level vulnerability to drought requires examination of hydraulic traits since these reflect the different strategies species employ for surviving drought.

    Here, we examined hydraulic traits and growth reductions during a severe drought for 12 common woody species in a wet tropical forest community in Puerto Rico to ask: Q1. To what extent can hydraulic traits predict growth declines during drought? We expected that species with more hydraulically vulnerable xylem and narrower safety margins (SMP50) would grow less during drought. Q2. How does species successional association relate to the levels of vulnerability to drought and hydraulic strategies? We predicted that early‐ and mid‐successional species would exhibit more acquisitive strategies, making them more susceptible to drought than shade‐tolerant species. Q3. What are the different hydraulic strategies employed by species and are there trade‐offs between drought avoidance and drought tolerance? We anticipated that species with greater water storage capacity would have leaves that lose turgor at higher xylem water potential and be less resistant to embolism forming in their xylem (P50).

    We found a large range of variation in hydraulic traits across species; however, they did not closely capture the magnitude of growth declines during drought. Among larger trees (≥10 cm diameter at breast height—DBH), some tree species with high xylem embolism vulnerability (P50) and risk of hydraulic failure (SMP50) experienced substantial growth declines during drought, but this pattern was not consistent across species. We found a trade‐off among species between drought avoidance (capacitance) and drought tolerating (P50) in this tropical forest community. Hydraulic strategies did not align with successional associations. Instead, some of the more drought‐vulnerable species were shade‐tolerant dominants in the community, suggesting that a drying climate could lead to shifts in long‐term forest composition and function in Puerto Rico and the Caribbean.

    Read the freePlain Language Summaryfor this article on the Journal blog.

    more » « less