Demographic trade-offs predict tropical forest dynamics

Rüger, Nadja; Condit, Richard; Dent, Daisy H.; DeWalt, Saara J.; Hubbell, Stephen P.; Lichstein, Jeremy W.; López, Omar R.; Wirth, Christian; Farrior, Caroline E.

doi:10.1126/science.aaz4797

Cited by 133 publications

(179 citation statements)

References 39 publications

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“…The importance of big trees, (typically defined as cm diameter-at-breast height, DBH), is widely-recognised in terms of carbon storage, demographics and impact on their surrounding ecosystems 11 – 14 . Unfortunately the importance of big trees is in direct proportion to the difficulty of measuring them, particularly for AGB.…”

Section: Introductionmentioning

confidence: 99%

New 3D measurements of large redwood trees for biomass and structure

Disney

Burt²,

Wilkes³

et al. 2020

Sci Rep

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Large trees are disproportionately important in terms of their above ground biomass (AGB) and carbon storage, as well as their wider impact on ecosystem structure. They are also very hard to measure and so tend to be underrepresented in measurements and models of AGB. We show the first detailed 3D terrestrial laser scanning (TLS) estimates of the volume and AGB of large coastal redwood Sequoia sempervirens trees from three sites in Northern California, representing some of the highest biomass ecosystems on Earth. Our TLS estimates agree to within 2% AGB with a species-specific model based on detailed manual crown mapping of 3D tree structure. However TLS-derived AGB was more than 30% higher compared to widely-used general (non species-specific) allometries. We derive an allometry from TLS that spans a much greater range of tree size than previous models and so is potentially better-suited for use with new Earth Observation data for these exceptionally high biomass areas. We suggest that where possible, TLS and crown mapping should be used to provide complementary, independent 3D structure measurements of these very large trees.

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Section: Introductionmentioning

confidence: 99%

New 3D measurements of large redwood trees for biomass and structure

Disney

Burt²,

Wilkes³

et al. 2020

Sci Rep

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“…The combination of these four drivers can represent the growth–survival trade‐off (e.g., the ratio of mortality over radial growth

μ G

appearing in Equation 12) and the stature–recruitment trade‐off (which distinguishes long‐lived pioneers from short‐lived breeders). These two trade‐offs are important for understanding forest dynamics (Rüger et al., 2020, for tropical forest).…”

Section: Discussionmentioning

confidence: 99%

Climate‐induced variation in the demography of 14 tree species is not sufficient to explain their distribution in eastern North America

Squin

Boulangeat²,

Gravel

2020

Global Ecol. Biogeogr.

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Aim Dynamic range models are proposed to investigate species distributions and to project range shifts under climate change. They are based upon the Hutchinsonian niche theory, specifying that the occurrence of a species in an environmental space should be limited to positions where the intrinsic growth rate is positive. Evaluating population growth rate is, however, difficult for physiologically structured populations, such as forest stands, owing to size‐induced individual variation in performance. Therefore, we still have a limited understanding of which aspect of tree demography contributes the most to their geographical range limit. We develop an index of demographic performance for size‐structured populations and study its variation across a climatic gradient. We then investigate the relationship between the demographic performance index and species distribution. Location North America (57–124° W, 26–52° N). Time period 1963–2010. Major taxa studied Fourteen tree species. Methods We represent forest dynamics with a size‐structured population model and neighbourhood competition with the perfect plasticity approximation. We then derive the lifetime reproduction per individual, R0, in the absence of density dependence. Using forest inventory data, we assess how tree demography for each species varies with climate. We test the model by comparing R0 and the probability of occurrence within species ranges. Results We find that both growth and mortality rates vary across species distributions, but climate explains little of the observed variation. Individual size and neighbourhood competition are the primary explanatory variables of tree demography. Finally, we find that R0 relates weakly to the probability of occurrence, with no systematic decline in population growth rates towards the range limits. Main conclusions Spatial and size‐induced variation in tree growth and mortality do not explain range limits and are insufficient to enable an understanding of tree dynamics. We propose that phenomena perceived mostly at the metapopulation scale should also be considered.

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“…1A). Recent work has suggested that tree functional composition change over succession, in terms of differentiation on growth–survival and stature–recruitment tradeoffs, can explain forest structural change, highlighting the likely importance of community and demographic dynamics in forest transitions (Rüger et al 2020). Furthermore, understanding the specific long‐term impacts of forest disturbances on demographic components, recruitment, growth, and mortality is increasingly recognized as central to predicting climate forcing (McDowell et al 2020).…”

Section: Section 1: Reframing Tropical Forest Savannization As Transimentioning

confidence: 99%

“…In this case, the feedback results from regional alterations of temperature and precipitation, which impacts the forest via its sensitivity to variations in these factors. Other factors influencing forest sensitivity and resilience to disturbance such as forest functional composition (Brum et al 2019, Rüger et al 2020) would also play a critical role.…”

Section: Section 3: Reframing Tropical Forest Savannization Challengmentioning

confidence: 99%

Reframing tropical savannization: linking changes in canopy structure to energy balance alterations that impact climate

et al. 2020

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Tropical ecosystems are undergoing unprecedented rates of degradation from deforestation, fire, and drought disturbances. The collective effects of these disturbances threaten to shift large portions of tropical ecosystems such as Amazon forests into savanna‐like structure via tree loss, functional changes, and the emergence of fire (savannization). Changes from forest states to a more open savanna‐like structure can affect local microclimates, surface energy fluxes, and biosphere–atmosphere interactions. A predominant type of ecosystem state change is the loss of tree cover and structural complexity in disturbed forest. Although important advances have been made contrasting energy fluxes between historically distinct old‐growth forest and savanna systems, the emergence of secondary forests and savanna‐like ecosystems necessitates a reframing to consider gradients of tree structure that span forest to savanna‐like states at multiple scales. In this Innovative Viewpoint, we draw from the literature on forest–grassland continua to develop a framework to assess the consequences of tropical forest degradation on surface energy fluxes and canopy structure. We illustrate this framework for forest sites with contrasting canopy structure that ranges from simple, open, and savanna‐like to complex and closed, representative of tropical wet forest, within two climatically distinct regions in the Amazon. Using a recently developed rapid field assessment approach, we quantify differences in cover, leaf area vertical profiles, surface roughness, albedo, and energy balance partitioning between adjacent sites and compare canopy structure with adjacent old‐growth forest; more structurally simple forests displayed lower net radiation. To address forest–atmosphere feedback, we also consider the effects of canopy structure change on susceptibility to additional future disturbance. We illustrate a converse transition—recovery in structure following disturbance—measuring forest canopy structure 10 yr after the imposition of a 5‐yr drought in the ground‐breaking Seca Floresta experiment. Our approach strategically enables rapid characterization of surface properties relevant to vegetation models following degradation, and advances links between surface properties and canopy structure variables, increasingly available from remote sensing. Concluding, we hypothesize that understanding surface energy balance and microclimate change across degraded tropical forest states not only reveals critical atmospheric forcing, but also critical local‐scale feedbacks from forest sensitivity to additional climate‐linked disturbance.

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Demographic trade-offs predict tropical forest dynamics

Cited by 133 publications

References 39 publications

New 3D measurements of large redwood trees for biomass and structure

New 3D measurements of large redwood trees for biomass and structure

Climate‐induced variation in the demography of 14 tree species is not sufficient to explain their distribution in eastern North America

Reframing tropical savannization: linking changes in canopy structure to energy balance alterations that impact climate

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