An official website of the United States government
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 that differ in performance trade-offs between survival in shade and the ability to quickly grow in sunlight. 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 seedling 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 developmental 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. Our findings highlight the importance of cotyledon strategy in addition to seed mass as a key component of seed and seedling biology. These results also underscore the importance of matching the ontogenetic stage of the trait measurement to the stage of demographic dynamics. 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
Functional traits of young seedlings predict trade‐offs in seedling performance in three neotropical forests
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
- PAR ID:
- 10478175
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 111
- Issue:
- 12
- ISSN:
- 0022-0477
- Format(s):
- Medium: X Size: p. 2568-2582
- Size(s):
- p. 2568-2582
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The interspecific trade‐off between growth versus mortality rates of tree species is thought to be driven by functional biology and to contribute to species ecological niche differentiation. Yet, functional trait variation is often not strongly correlated with growth and mortality, and few studies have investigated the relationships of both traits and niches, specifically encompassing above and belowground resources, to the trade‐off itself. These relationships are particularly relevant for seedlings, which must often survive resource limitation to reach larger size classes.We investigated the functional basis of the interspecific growth–mortality trade‐off and its relationship with ecological niches for seedlings of 14 tree species in a tropical forest in southwest China.We found evidence for an interspecific growth–mortality trade‐off at the seedling stage using 15 functional traits and 15 ecological niche variables. None of the organ‐level traits correlated with growth, mortality, nor the trade‐off, whereas specific stem length (SSL), a biomass allocation trait, was the only trait to have a significant correlation (positive). Moreover, light‐defined niches were not correlated with growth, mortality or the trade‐off, but soil‐defined niches did. Species at the faster growth/higher mortality end of the trade‐off were associated with higher fertility defined by lower soil bulk density and slope, and higher soil organic matter concentration and soil total nitrogen.Our findings indicate the importance of stem elongation and soil fertility for growth, mortality and their trade‐off at the seedling stage in this Asian tropical forest. Our findings contrast with analogous studies in neotropical forests showing the importance of photosynthesis‐related leaf traits related to insolation. Therefore, the functional drivers of demographic rates and trade‐offs, as well as their consequences for ecological niches, can vary among forests, likely owing to differences in biogeography, canopy disturbance rates, topography and soil properties. Moreover, the effects of functional trait variation on demographic rates and trade‐offs may be better revealed when biomass allocation is accounted for in a whole‐plant context. Read the freePlain Language Summaryfor this article on the Journal blog.more » « less
-
Abstract Background and AimsUnderstanding 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. MethodsWe 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 ResultsThe 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. ConclusionsOur 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
-
Abstract All species must partition resources among the processes that underly growth, survival, and reproduction. The resulting demographic trade‐offs constrain the range of viable life‐history strategies and are hypothesized to promote local coexistence. Tropical forests pose ideal systems to study demographic trade‐offs as they have a high diversity of coexisting tree species whose life‐history strategies tend to align along two orthogonal axes of variation: a growth–survival trade‐off that separates species with fast growth from species with high survival and a stature–recruitment trade‐off that separates species that achieve large stature from species with high recruitment. As these trade‐offs have typically been explored for trees ≥1 cm dbh, it is unclear how species' growth and survival during earliest seedling stages are related to the trade‐offs for trees ≥1 cm dbh. Here, we used principal components and correlation analyses to (1) determine the main demographic trade‐offs among seed‐to‐seedling transition rates and growth and survival rates from the seedling to overstory size classes of 1188 tree species from large‐scale forest dynamics plots in Panama, Puerto Rico, Ecuador, Taiwan, and Malaysia and (2) quantify the predictive power of maximum dbh, wood density, seed mass, and specific leaf area for species' position along these demographic trade‐off gradients. In four out of five forests, the growth–survival trade‐off was the most important demographic trade‐off and encompassed growth and survival of both seedlings and trees ≥1 cm dbh. The second most important trade‐off separated species with relatively fast growth and high survival at the seedling stage from species with relatively fast growth and high survival ≥1 cm dbh. The relationship between seed‐to‐seedling transition rates and these two trade‐off aces differed between sites. All four traits were significant predictors for species' position along the two trade‐off gradients, albeit with varying importance. We concluded that, after accounting for the species' position along the growth–survival trade‐off, tree species tend to trade off growth and survival at the seedling with later life stages. This ontogenetic trade‐off offers a mechanistic explanation for the stature–recruitment trade‐off that constitutes an additional ontogenetic dimension of life‐history variation in species‐rich ecosystems.more » « less
-
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
