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Extending and safeguarding tropical forest ecosystems is critical for combating climate change and biodiversity loss. One of its constituents, lianas, is spreading and increasing in abundance on a global scale. This is particularly concerning as lianas negatively impact forests’ carbon fluxes, dynamics, and overall resilience, potentially exacerbating both crises. While possibly linked to climate-change-induced atmospheric CO₂elevation and drought intensification, the reasons behind their increasing abundance remain elusive. Prior research shows distinct physiological differences between lianas and trees, but it is unclear whether these differences confer a demographic advantage to lianas with climate change. Guided by extensive datasets collected in Panamanian tropical forests, we developed a tractable model integrating physiology, demography, and epidemiology. Our findings suggest that CO₂fertilization, a climate change factor promoting forest productivity, gives lianas a demographic advantage. Conversely, factors such as extreme drought generally cause a decrease in liana prevalence. Such a decline in liana prevalence is expected from a physiological point of view because lianas have drought-sensitive traits. However, our analysis underscores the importance of not exclusively relying on physiological processes, as interactions with demographic mechanisms (i.e., the forest structure) can contrast these expectations, causing an increase in lianas with drought. Similarly, our results emphasize that identical physiological responses between lianas and trees still lead to liana increase. Even if lianas exhibit collinear but weaker responses in their performance compared to trees, a temporary liana prevalence increase might manifest driven by the faster response time of lianas imposed by their distinct life-history strategies than trees. 

Abstract Ecological communities frequently exhibit remarkable taxonomic and trait diversity, and this diversity is consistently shown to regulate ecosystem function and resilience. However, ecologists lack a synthetic theory for how this diversity is maintained when species compete for limited resources, hampering our ability to project the future of biodiversity under climate change. Water‐limited plant communities are an ideal system in which to study these questions given (1) the diversity of hydraulic traits they exhibit, (2) the importance of this diversity for ecosystem productivity and drought resilience, and (3) forecast changes to precipitation and evapotranspiration under climate change. We developed an analytically tractable model of water and light competition in age‐structured perennial plant communities and demonstrated that high diversity is maintained through phenological division of the time between storms. We modeled a system where water arrives in the form of intermittent storms, between which plants consume the limited pool of soil water until it becomes dry enough that they must physiologically shut down to avoid embolism. Competition occurs because individuals, by consuming the shared water pool, cause their competitors to shut down earlier, harming their long‐term growth and reproduction. When total precipitation is low, plants in the model compete only for water. However, increases in precipitation can cause the canopy to close and individuals to begin competing for light. Variation among species in the minimum soil water content at which they can sustain growth without embolizing leads to emergent phenological variation, as species will shut down at varying points between storm events. When this variation is paired with a trade‐off such that species that shut down early are compensated by faster biomass accumulation, higher fecundity, or lower mortality, there is no limit to the number that can coexist. These results are robust to variation in both total precipitation and the time between storms. The model therefore offers a plausible explanation for how hydraulic trait diversity is maintained in a wide array of natural systems. More broadly, this work illustrates how the phenological division of an apparently singular resource can emerge because of common trade‐offs and ultimately foster high taxonomic and trait diversity. 

Abstract Lianas, woody vines acting as structural parasites of trees, have profound effects on the composition and structure of tropical forests, impacting tree growth, mortality, and forest succession. Remote sensing could offer a powerful tool for quantifying the scale of liana infestation, provided the availability of robust detection methods. We analyze the consistency and global geographic specificity of spectral signals—reflectance across wavelengths—from liana‐infested tree crowns and forest stands, examining the underlying mechanisms of these signals. We compiled a uniquely comprehensive database, including leaf reflectance spectra from 5424 leaves, fine‐scale airborne reflectance data from 999 liana‐infested canopies, and coarse‐scale satellite reflectance data covering 775 ha of liana‐infested forest stands. To unravel the mechanisms of the liana spectral signal, we applied mechanistic radiative transfer models across scales, establishing a synthesis of the relative importance of different mechanisms, which we corroborate with field data on liana leaf chemistry and canopy structure. We find a consistent liana spectral signal at canopy and stand scales across globally distributed sites. This signature mainly arises at the canopy level due to direct effects of more horizontal leaf angles, resulting in a larger projected leaf area, and indirect effects from increased light scattering in the near and short‐wave infrared regions, linked to lianas' less costly leaf construction compared with trees on average. The existence of a consistent global spectral signal for lianas suggests that large‐scale quantification of liana infestation is feasible. However, because the traits responsible for the liana canopy‐reflectance signal are not exclusive to lianas, accurate large‐scale detection requires rigorously validated remote sensing methods. Our models highlight challenges in automated detection, such as potential misidentification due to leaf phenology, tree life history, topography, and climate, especially where the scale of liana infestation is less than a single remote sensing pixel. The observed cross‐site patterns also prompt ecological questions about lianas' adaptive similarities in optical traits across environments, indicating possible convergent evolution due to shared constraints on leaf biochemical and structural traits. 

Abstract Understanding how diversity is maintained in plant communities requires that we first understand the mechanisms of competition for limiting resources. In ecology, there is an underappreciated but fundamental distinction between systems in which the depletion of limiting resources reduces the growth rates of competitors and systems in which resource depletion reduces the time available for competitors to grow, a mechanism we call ‘competition for time’. Importantly, modern community ecology and our framing of the coexistence problem are built on the implicit assumption that competition reduces the growth rate. However, recent theoretical work suggests competition for time may be the predominant competitive mechanism in a broad array of natural communities, a significant advance given that when species compete for time, diversity‐maintaining trade‐offs emerge organically. In this study, we first introduce competition for time conceptually using a simple model of interacting species. Then, we perform an experiment in a Mediterranean annual grassland to determine whether competition for time is an important competitive mechanism in a field system. Indeed, we find that species respond to increased competition through reductions in their lifespan rather than their rate of growth. In total, our study suggests competition for time may be overlooked as a mechanism of biodiversity maintenance. 

Many tropical regions are experiencing an intensification of drought, with increasing severity and frequency of the events. However, the forest ecosystem response to these changes is still highly uncertain. It has been hypothesized that on short time scales (from diurnal to seasonal), tropical forests respond to water stress by physiological controls, such as stomata regulation and phenological adjustment, to control increasing atmospheric water demand and cope with reduced water supply. However, the interactions among biological processes and co-varying environmental factors that determine the ecosystem-level fluxes are still unclear. Furthermore, climate variability at longer time scales, such as that generated by ENSO, produces less predictable effects, which might vary among forests and ecoregions within the tropics. This study will present some emerging patterns of response to water stress from five years of observations of water, carbon, and energy fluxes on the seasonal tropical forest in Barro Colorado Island (Panama), including an increase in productivity during the 2015 El Niño. We will show how these responses will depend critically on the combination of environmental factors experienced by the forest along the seasonal cycle. These results suggest a critical role of plant hydraulics in mediating the response to water stress on a broad range of temporal scales, including during the wet seasons when water availability is not a limiting factor. The study also found that the response to large-scale drought events is contingent and might produce a different outcome in different tropical forest areas. 

Although early theoretical work suggests that competition for light erodes successional diversity in forests, verbal models and recent numerical work with complex mechanistic forest simulators suggest that disturbance in such systems can maintain successional diversity. Nonetheless, if and how allocation tradeoffs between competitors interact with disturbance to maintain high diversity in successional systems remains poorly understood. Here, using mechanistic and analytically tractable models, we show that a theoretically unlimited number of coexisting species can be maintained by allocational tradeoffs such as investing in light-harvesting organs vs. height growth, investing in reproduction vs. growth or survival vs. growth. The models describe the successional dynamics of a forest composed of many patches subjected to random or periodic disturbance, and are consistent with physiologically mechanistic terrestrial ecosystem models, including the terrestrial components of recent Earth System Models. We show that coexistence arises in our models because species specialize in the successional time they best exploit the light environment and convert resources into seeds or contribute to advance regeneration. We also show that our results are relevant to non-forested ecosystems by demonstrating the emergence of similar dynamics in a mechanistic model of competition for light among annual plant species. Finally, we show that coexistence in our models is relatively robust to the introduction of intraspecific variability that weakens the competitive hierarchy caused by asymmetric competition for light. 

Abstract When species simultaneously compete with two or more species of competitor, higher‐order interactions (HOIs) can lead to emergent properties not present when species interact in isolated pairs. To extend ecological theory to multi‐competitor communities, ecologists must confront the challenges of measuring and interpreting HOIs in models of competition fit to data from nature. Such efforts are hindered by the fact that different studies use different definitions, and these definitions have unclear relationships to one another. Here, we propose a distinction between ‘soft’ HOIs, which identify possible interaction modification by competitors, and ‘hard’ HOIs, which identify interactions uniquely emerging in systems with three or more competitors. We show how these two classes of HOI differ in their motivation and interpretation, as well as the tests one uses to identify them in models fit to data. We then show how to operationalise this structure of definitions by analysing the results of a simulated competition experiment underlain by a consumer resource model. In the course of doing so, we clarify the challenges of interpreting HOIs in nature, and suggest a more precise framing of this research endeavour to catalyse further investigations.