Research

Research Interests

I have a variety of research interests, most of which involve the ecology of forest and trees in human-modified landscapes. I am broadly interested in understanding how human land-use and ecological processes interact to shape plant community dynamics and affect the provision of ecosystem services in and across different landscapes. My work focusses on regrowing forests, which now encompass over 50% of the world’s tropical forests. My driving motivation is that a better understanding of the mechanisms and processes that determine the capacity of these new forests to recover from human-caused drivers of ecosystem change is essential the effective restoration, management and conservation of biodiversity and ecosystem services in transformed landscapes.

In our lab, we work on four closely related research themes: (1) Successional dynamics and pathways of secondary forests in human-modified landscapes, (2) Functional traits and ecological strategies, (3) Secondary forest succession as a way of restoring biodiversity and ecosystem services in human-modified landscapes, and (4) Selection of suitable tree species for reforestation. All four themes reoccur and are connected in our research projects. We use approaches from community and functional ecology and field studies that range from controlled experiments to long-term monitoring of natural succession. These studies offer alternative and complementary approaches to quantify and scale the influence of environmental conditions, functional composition, interactions and landscape-scale processes on biodiversity and ecosystem processes and services of ‘new forests’ in human-modified landscapes.

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Research Projects

Singapore

In Singapore, we investigate if plant-functional trait relationships fieldworkvary across co-occurring plant growth forms. To that end, we are collecting an extensive and detailed set of leaf traits for trees, forbs, lianas and other growth forms in forest fragments across Singapore and the Singapore Botanical Garden.

Together with Prof. Hugh Tan and his Botany Lab, we investigate how different-aged secondary forests communities re-assemble following re-occurring disturbances. We use a natural experiment offered by a windfall event in 2010 that affected a mosaic of young and old secondary forests in the Central Catchment area. For this study, we are collecting plant functional trait data for all tree species in plots that were laid out and monitored for five years by the Botany Lab. We will combine the trait and census data to assess what suite of traits are being selected for or against following disturbance, amidst coexisting species.


Secondary Forest Dynamics Study 

AS1

An important part of my research takes place in the framework of the Smithsonian Tropical research Institute’s Agua Salud Project that seeks to understand and quantify the ecosystem services provided by forests in the Panama Canal Watershed. I collaborate closely with Agua Salud’s PI Jeff Hall and with many others.  My strongest involvement is Agua Salud’s long-term secondary
forest dynamics (SFD) study, which I set up and of which I am currently co-PI. The main component of this study consists of pairs of permanent 0.1-ha plots in 54 secondary forest patches of different ages that represent a random and unbiased sample of the variation in forest structure and composition across the Agua Salud landscape. We established the plots in 2008-2009 and are monitoring tree growth, mortality and recruitment since. In 2009, we set up a similar study in a dry landscape in Panama, with 13 pairs of plots.

The set up of the SFD study allows us to study ecosystem functioning or community assembly processes during tropical secondary forest succession on both local and landscape level. With Jeff Hall, Dylan Craven (German Centre for Biodiversity Research) and others we investigate how differences in species diversity and functional composition affect successional pathways in community assembly and ecosystem processes and functions. From an applied perspective, we assess whether these new forests can significantly contribute to the conservation and provision of ecosystem services in human-dominated landscapes (e.g., water regulation (here and here), diversity and carbon).

The SFD study has generated – and continues to generate – a lot of data that can be used to address a broad range of questions related to secondary forest succession. You can find a list of some of the specific research questions we would like to ask here. If you are interested in working on any of these questions, or have other ideas, contact me.

Field experiments to disentangle the role of lianas and nitrogen fixing trees

LianaCuttingWithin the framework of our SFD study, we have set up two associated field experiments aimed at assessing the effects of specific functional plant groups on the dynamics and successional trajectories of secondary forests. In both experiments, I am collaborator. The first one is long-term liana removal experiment (with Stefan Schnitzer and Sergio Estrada, Marquette University, and Jefferson Hall). For this experiment, we have added a third plot to most of the existing pairs of SFD plots in which we eliminated all lianas. The second is a long-term nutrient addition experiment (+N, +P, +NP, control) that we are currently setting up (with Sarah Batterman and Lars Hedin, Princeton University, and Jefferson Hall and Ben Turner, STRI). Aim of this experiment is to address hypotheses on the role of N fixing species in secondary succession, some of which we postulated in an earlier Nature publication.

 

Reforestation Experiment with Mixed Native Species

P1070647Another long term study in the framework of STRI’s Agua Salud project is a 60 ha reforestation experiment. The experiment includes five timber species and five early successional species with contrasting resource acquisition and use strategies, planted in an explicit spatial design to isolate interactions between neighboring species and highly replicated to capture the main environmental variation across the landscape. I designed and help set up the experiment and my current role is that of collaborator. This experimental system is currently used by a large number of researchers and students from various institutions to study questions ranging from net primary productivity of monoculture versus mixed stands, intra versus interspecific competition, nutrient cycling, soil microbial communities. For example, Katherine Sinacore and Heidi Asbjornsen (University of New Hampshire) study how complementary and facilitative interactions may affect sap flow and water use in mixed versus single-species plots.


Native Species Selection Trials

species slection

The Native Species Reforestation Project (PRORENA) is a joined project of Yale School of Forestry and Environmental Studies and the Smithsonian Tropical Research Institute. The project has established species selection trials with >45 tree species in four sites across Panama that differ in rainfall and soil conditions, which were monitored annually for 5-7 years. I have used data from these trials to assess how contrasting edaphic conditions influences species survival and growth under varying amounts of rainfall and lengths of dry season and to discuss the importance of testing the performance of potential species under different site conditions to select suitable species and filter out unsuitable species based on explicit and quantitative criteria and data.

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