•Consider species-richness by aggregation into plant functional types.•Model the impact of disturbances on forest dynamics.•Upscale carbon dynamics from the leaf to the global carbon budget ...level.•Process-based and individual-based philosophy is important for application.•FORMIND is generic and flexible to be applied to forest sites worldwide.
Forests worldwide are threatened by various environmental and anthropogenic hazards, especially tropical forests. Knowledge on the impacts of these hazards on forest structure and dynamics has been compiled in empirical studies. However, the results of these studies are often not sufficient for long-term projections and extrapolations to large spatial scales especially for unprecedented environmental conditions, which require both the identification and understanding of key underlying processes. Forest models bridge this gap by incorporating multiple ecological processes in a dynamic framework (i.e. including a realistic model structure) and addressing the complexity of forest ecosystems. Here, we describe the evolution of the individual-based and process-based forest gap model FORMIND and its application to tropical forests. At its core, the model includes physiological processes on tree level (photosynthesis, respiration, tree growth, mortality, regeneration, competition). During the past two decades, FORMIND has been used to address various scientific questions arising from different forest types by continuously extending the model structure. The model applications thus provided understanding in three main aspects: (1) the grouping of single tree species into plant functional types is a successful approach to reduce complexity in vegetation models, (2) structural realism was necessary to analyze impacts of natural and anthropogenic disturbances such as logging, fragmentation, or drought, and (3) complex ecological processes such as carbon fluxes in tropical forests – starting from the individual tree level up to the entire forest ecosystem – can be explored as a function of forest structure, species composition and disturbance regime. Overall, this review shows how the evolution of long-term modelling projects not only provides scientific understanding of forest ecosystems, but also provides benefits for ecological theory and empirical study design.
Water availability has a decisive impact on plant growth, survival and distribution. Climate change is expected to alter both the amount and variability of precipitation. To predict and understand ...plant responses to water stress, efficient and robust mechanisms for describing their functional responses to water availability are needed. However, most ecohydrological processes and models which take into account these responses are inherently complex, difficult to understand and require large amounts of data. We develop a novel straightforward approach and hypothesize that: (1) Plants exhibit two archetypical response patterns under water stress, one typical to slow-growing plants and one typical to fast-growing ones, with most plants being situated between these two. (2) Differences within and between these functional types can be adequately described by a single parameter - the threshold of relative soil water content - at which plants reduce their transpiration in response to water stress. This indicator is straightforward and relies on data which is relatively easy to measure. Its effect has been previously described and it is already used in several models to simulate the effect of water stress on plants. In our approach, we combine this indicator with a description of reactions patterns. This combination provides a general and efficient way of classifying plant responses and allows the assessment of the impact of water stress on a wide variety of plants. Due to its simplicity, our approach offers the opportunity to include water relations of plants in a larger set of models and descriptions than it is possible with more complex ecohydrological descriptions. It also can be used to explain biodiversity in fluctuating environments.
Understanding the structure and dynamics of highly diverse tropical forests is challenging. Here we investigate the factors that drive the spatio-temporal variation of local tree numbers and species ...richness in a tropical forest (including 1250 plots of 20 × 20 m2). To this end, we use a series of dynamic models that are built around the local spatial variation of mortality and recruitment rates, and ask which combination of processes can explain the observed spatial and temporal variation in tree and species numbers. We find that processes not included in classical neutral theory are needed to explain these fundamental patterns of the observed local forest dynamics. We identified a large spatio-temporal variability in the local number of recruits as the main missing mechanism, whereas variability of mortality rates contributed to a lesser extent. We also found that local tree numbers stabilize at typical values which can be explained by a simple analytical model. Our study emphasized the importance of spatio-temporal variability in recruitment beyond demographic stochasticity for explaining the local heterogeneity of tropical forests.
•The number of functional groups is an important parameter in forest models.•This number has far reaching consequences for the simulation results.•Modeling of dynamic changes requires a higher number ...of groups.•We compare a neutral vs. non-neutral versions of a physiological forest model.
Tropical forests are vital ecosystems which provide numerous ecological functions and forest models can be used to simulate their dynamics. However, due to the high species diversity of tropical forests and the common lack of detailed knowledge about these species, simulating the behavior of each species separately is not feasible. Therefore, species with common characteristics are usually aggregated into species groups.
Although the number of species groups is likely to be an important characteristic of forest models, little research has been done on its effect on the results of the model. In this article, we compare the effect of the number of species groups using a physiological forest gap model and review our results using 28 years of field data from a 50ha forest plot in Panama as well as a chronosequence over four centuries from the same area. The number of simulated groups ranged from 1 to 4, 9 and 16. The parameterization with a single species group is a “neutral” parameterization with all simulated trees being ecophysiologically identical.
The number of groups turned out to be an important characteristic of the model which influences its results on a fundamental level. Steady-states characteristics of forests like stem-numbers and stem-size distributions can be successfully simulated with even a single species group while modeling the long-term dynamics requires a higher number of groups. On the downside, a higher number of groups makes parameterization and fitting of the model more difficult. We conclude that the number of species groups is a vital characteristic of a forest model which has far-reaching consequences for its results and needs to be chosen with care.
Density‐dependent mortality (DDM) is major driver of species coexistence in tropical forests. We assessed the occurrence and strength of this mechanism among saplings (i.e. trees with a diameter of ...1–4 cm) in the moist tropical forest of Barro Colorado Island (BCI), Panama, over six inter‐census periods (26 years), by using spatial point pattern analysis. We considered conspecific density‐dependent mortality, but also total DDM (i.e. the effects of conspecific and heterospecific neighbours all together) upon saplings of all species (i.e. at the community level), and on saplings of light‐demanding and shade‐tolerant ones, separately (i.e. at the light‐guild level). We also analysed the effects of conspecific DDM at the community and light‐guild levels. Conspecific density‐dependent mortality affected a lower proportion of species than was to be expected. Its strength was not significantly related with species abundance, and it had relatively weak effects at the community and light guild levels. Conversely, we detected a significant spatial signature of total DDM among all saplings, and among saplings of the light‐demanding and shade‐tolerant species, but its strength showed pronounced temporal variation. Total DDM among light‐demanding saplings was stronger than among shade‐tolerant ones and its effects were particularly marked 10–15 years after the occurrence of unusually severe droughts associated with El Niño events. Our study indicates that conspecific DDM is relatively unimportant among saplings in comparison with total DDM at community and light‐guild levels. This finding contrasts strongly with the results for seedlings, where conspecific DDM was constituted the dominant process. The pronounced temporal variations observed in the occurrence and strength of total DDM among saplings indicate that time‐varying events associated with climatic disturbances such as canopy openings or episodes of high recruit emergence might be important drivers of this process. They also emphasize the importance of considering time frames longer than one decade to study density‐dependent effects among saplings in tropical forests.
Understanding the structure and dynamics of highly diverse tropical forests is challenging. Here we investigate the factors that drive the spatio-temporal variation of local tree numbers and species ...richness in a tropical forest (including 1250 plots of 20 × 20 m²). To this end, we use a series of dynamic models that are built around the local spatial variation of mortality and recruitment rates, and ask which combination of processes can explain the observed spatial and temporal variation in tree and species numbers. We find that processes not included in classical neutral theory are needed to explain these fundamental patterns of the observed local forest dynamics. We identified a large spatio-temporal variability in the local number of recruits as the main missing mechanism, whereas variability of mortality rates contributed to a lesser extent. We also found that local tree numbers stabilize at typical values which can be explained by a simple analytical model. Our study emphasized the importance of spatio-temporal variability in recruitment beyond demographic stochasticity for explaining the local heterogeneity of tropical forests.
Density-dependent mortality (DDM) is major driver of species coexistence in tropical forests. We assessed the occurrence and strength of this mechanism among saplings (i.e. trees with a diameter of ...1–4 cm) in the moist tropical forest of Barro Colorado Island (BCI), Panama, over six inter-census periods (26 years), by using spatial point pattern analysis. We considered conspecific density-dependent mortality, but also total DDM (i.e. the effects of conspecific and heterospecific neighbours all together) upon saplings of all species (i.e. at the community level), and on saplings of light-demanding and shade-tolerant ones, separately (i.e. at the light-guild level). We also analysed the effects of conspecific DDM at the community and light-guild levels. Conspecific density-dependent mortality affected a lower proportion of species than was to be expected. Its strength was not significantly related with species abundance, and it had relatively weak effects at the community and light guild levels. Conversely, we detected a significant spatial signature of total DDM among all saplings, and among saplings of the light-demanding and shade-tolerant species, but its strength showed pronounced temporal variation. Total DDM among light-demanding saplings was stronger than among shade-tolerant ones and its effects were particularly marked 10–15 years after the occurrence of unusually severe droughts associated with El Niño events. Our study indicates that conspecific DDM is relatively unimportant among saplings in comparison with total DDM at community and light-guild levels. This finding contrasts strongly with the results for seedlings, where conspecific DDM was constituted the dominant process. The pronounced temporal variations observed in the occurrence and strength of total DDM among saplings indicate that time-varying events associated with climatic disturbances such as canopy openings or episodes of high recruit emergence might be important drivers of this process. They also emphasize the importance of considering time frames longer than one decade to study density-dependent effects among saplings in tropical forests.
Tropical forests are highly diverse ecosystems, but within such forests there can be large patches dominated by a single tree species. The myriad presumed mechanisms that lead to the emergence of ...such monodominant areas is currently the subject of intensive research. We used the most generic of these mechanisms, large seed mass and low dispersal ability of the monodominant species, in a spatially explicit model. The model represents seven identical species with long-distance dispersal of small seeds, competing with one potentially monodominant species with short-distance dispersal of large seeds. Monodominant patches emerged and persisted only for a narrow range of species traits; these results have the characteristic features of phase transitions. Additional mechanisms may explain monodominance in different ecological contexts, but our results suggest that percolation-like phenomena and phase transitions might be pervasive in this type of system.
In this trial in patients with relapsed CLL, progression-free survival at 2 years was 78% with zanubrutinib and 66% with ibrutinib. Infections were common with both; cardiac events were less frequent ...with zanubrutinib.
COVID-19 disease progression can be accompanied by a “cytokine storm” that leads to secondary sequelae such as acute respiratory distress syndrome. Several inflammatory cytokines have been associated ...with COVID-19 disease progression, but have high daily intra-individual variability. In contrast, we have shown that the inflammatory biomarker γ' fibrinogen (GPF) has a 6-fold lower coefficient of variability compared to other inflammatory markers such as hs-CRP. The aims of the study were to measure GPF in serial blood samples from COVID-19 patients at a tertiary care medical center in order to investigate its association with clinical measures of disease progression. COVID-19 patients were retrospectively enrolled between 3/16/2020 and 8/1/2020. GPF was measured using a commercial ELISA. We found that COVID-19 patients can develop extraordinarily high levels of GPF. Our results showed that ten out of the eighteen patients with COVID-19 had the highest levels of GPF ever recorded. The previous highest GPF level of 80.3 mg/dL was found in a study of 10,601 participants in the ARIC study. GPF levels were significantly associated with the need for ECMO and mortality. These findings have potential implications regarding prophylactic anticoagulation of COVID-19 patients.
•We found that COVID-19 patients can develop extraordinarily high levels of GPF.•We found the highest level of GPF ever measured, 260 mg/dL, in a COVID-19 patient.•These findings suggest that GPF could be used as an inflammatory biomarker.
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