Research Themes

Overarching themes

Our research is focused on understanding the drivers of biogeochemical variation among terrestrial ecosystems, and mostly in the tropics.  Ecosystem ecologists and biogeochemists have long recognized that tropical systems function differently than their temperate counterparts, and exhibit remarkable biogeochemical heterogeneity. As the community has worked to develop a framework for explaining the causes of this variability, most investigators have taken one of two general approaches:  parsing out underlying drivers from observed spatial patterns across large regions, or isolating single drivers of ecosystem properties with less emphasis on scaling up to broader regions.   Our group seeks to do both simultaneously,  an approach we believe will help quantify and explain the biogeochemical diversity that typifies tropical ecosystems.  Part of the group works in unmanaged forests, and another on how tropical soils may mediate the consequences of rapidly-expanding industrial-scale agriculture. We iterate between field-based empirical work, modeling, and remote sensing, with our field work focused on sites that allow us to disentangle the relative importance of multiple drivers of ecosystem properties within the same experimental framework.

Landscape-scale biogeochemistry in intact tropical forests

Our approach has its foundation in the very simple conception that differences in state factors (climate, topography, organisms,  soil parent material and age) can explain the biogeochemical mosaic found across the terrestrial biosphere.  Decades of work to isolate the influence of these drivers (most notably soil age and climate) have fundamentally transformed our understanding of biogeochemistry, but left us short of explaining differences between systems across space or time. As an example, if two tropical forests vary by a factor of two in soil age, and a factor of two in rainfall, we can not use these data to predict whether nutrient limitation will differ, or how it will differ, between these two sites. until we can make such predictions among systems that vary in not two, but five or six independent driving variables, we are missing something fundamental about the way ecosystems work.  This, in turn, precludes us from providing data that might help elucidate the trajectory of terrestrial ecosystems as they respond to global changes. We are working in tropical forests across the globe to understand the relative importance of different state factors in structuring ecosystem properties, particularly those properties that may drive nutrient limitation and thus underpin a forests response to global change.

Biome restoration in Brazil’s Atlantic Forest

Brazil is known for the Amazon, a deforestation and biodiversity hotspot that has captured the world’s attention for decades as it has been progressively logged, cleared for cattle, and more recently for agriculture. But Brazil has another, equally diverse rainforest – the Mata Atlantica – which once stretched along Brazil’s entire Atlantic coast. Older and more diverse than the Amazon, the Mata Atlantica now exists only as remnants. 500 years of logging, farming, and intensive use in the region where 60% of Brazil’s people live has left little room for the once majestic forest, only 10% of which now remains. Our group is asking whether large-scale restoration is possible.

We know tropical forest can regrow if we set aside land and plant seedlings. But widespread restoration has to expand beyond parks and reserves, into landscapes where people live and work. In collaboration with Leah Van Wey, Dmitri Szerman, Daniel Piotto, Instituto Floresta Viva and many, many others, we are embarking on the largest payment for ecosystem services ever to ask whether it is possible to reforest for the benefit of people and ecosystems. Groups of farmers will be paid to participate in one of two restoration treatments (active planting vs passive regrowth), and payments will also vary among groups. We are asking what combination of payments and restoration treatment leads to the most forest regrowth AND improvement in the farmer’s socioeconomic wellbeing. With 3,000 farms arrayed across the state of Bahia, this project will be a major focus of the lab in the years to come.

Industrial-scale agriculture on tropical soils

In the past few years the group has become increasingly interested in a related set of questions pertaining to the biogeochemical implications of intensive agriculture in the tropics.  Shelby Riskin, the first graduate student in the lab, arrived interested in the fate and consequences of massive phosphorus fertilizer additions to the soy farms of Mato Grosso, Brazil.  Her work highlighted the importance of soil properties in mediating the environmental consequences of intensive agricultural management, particularly fertilizer additions. While it has been  known for millennia that soils matter for agriculture, we have most often thought of soil effects on crop yields, rather than on environmental consequences. Yet with massive inputs of lime and fertilizer, yields on the nutrient poor, acid soils of Mato Grosso can rival those of Iowa. Unlike in Iowa, however, this high fertilizer use has not led to any measurable change in stream water chemistry in Mato Grosso.  The deep soils readily retain both anions and cations, and thus act as a sponge for excess nutrients, while Iowa is plagued by runoff-driven eutrophication. Given the need to increase food production by 70% or more by 2050 in order to meet the demand of a more affluent and populous world, this is an exciting time to think about the interaction between intensive agriculture and the biogeochemical template upon which it occurs.