Visiting Scholars to Present Seminars on Forest Dynamics and Carbon Cycling

On Tuesday, Augu. 19, from 1 to 3 p.m., the department will host two research seminars by visiting scientists from the Helmholtz Centre for Environmental Research in Germany. Thorsten Wiegand  (farthest right) and Andreas Huth  will present their work in River Road Room 325 as part of their two-day visit to UMD.

Wiegand will present a seminar titled “Spatial Aggregation, Animal Seed Dispersal and Forest Dynamics,” introducing new findings from the ERC SpatioCoexistence project. His seminar will explore how spatial patterns such as clustering and segregation among tree species relate to species coexistence and forest diversity.

Abstract: Ecologists have tried for long to explain coexistence of many competing species in communities such as tropical forests, but this key question of ecological theory remains largely unresolved. The overarching objective of our new ERC SpatioCoexistence project is to develop a spatially-explicit theory for understanding the dynamics and stability of plant communities of intermediate to high species. A key task of the project is to develop methods to transport critical information across scales. For example, spatial patterns such as intraspecific clustering and interspecific segregation, which emerge from neighborhood effects occurring at the “microscopic” scale of individual plants, may play an important role in diversity maintenance of plant communities at a “macroscopic” scale. We developed an upscaling approach where the macroscale interaction coefficients of traditional Lotka-Volterra multispecies models become function of microscale interaction coefficients and indices of the emerging spatial patterns. These “transfer functions” are derived from upscaling neighborhood crowding indices that describe neighborhood competition for individual trees.  Here we present a comprehensive analysis of the spatial patterns of 720 tree species in 21 large forest plots and its consequences for species coexistence. We find that species with low abundances tend to be more spatially aggregated than more abundant species, and a latitudinal gradient in the strength of this negative aggregation-abundance relationship that increases from tropical to temperate forests. We suggest, in line with recent work, that latitudinal gradients in animal seed dispersal11 and mycorrhizal associations may jointly generate this intriguing pattern. By integrating the observed spatial patterns into population models we derive the conditions under which species can invade from low abundances, in terms of spatial patterns, demography, niche overlap, and immigration. Evaluation of the spatial invasion condition for our 720 tree species suggests that temperate and tropical forests meet the invasion criterion to a similar extent, but through opposed strategies conditioned by their spatial patterns. Our approach opens up new avenues for integrating observed spatial patterns into ecological theory, and underscores the need to understand the interaction among spatial patterns at the neighborhood scale and multiple ecological processes in greater detail.

Huth will follow with “Tropical Forests and the Global Carbon Cycle – Linking Remote Sensing and Ecological Modelling." This presentation will highlight the role of tropical forests in the global carbon balance, with a focus on the Amazon.

Abstract: Forests play an important role in the global carbon cycle as they store large amounts of carbon. Understanding the dynamics of forests is an important issue for ecology and climate change research. In this presentation we will give an overview on the knowledge on global forests and their carbon balance. We will explain typical methods to model forests and their dynamics. Using an individual based forest model (FORMIND) we developed an approach to simulate dynamics of around 410 billion individual trees within 7.8 Mio km² of Amazon forests. We combined the simulations with remote sensing observations from Lidar in order to detect different forest states and structures caused by natural and anthropogenic disturbances. Under current conditions, we identified the Amazon rainforest as a carbon sink, gaining 0.56 Gt C per year. We found that successional states play an important role for the relations between productivity and biomass. Simulated values can be compared to observed local carbon fluxes.