You are here

Research projects in the Hobbie Lab

Cedar Creek LTER

Nitrogen Limitation of Decomposition

Decomposition (carried out primarily by soil bacteria and fungi) is a major bottleneck in the recycling of nutrients within ecosystems. It is also the main way that C fixed during photosynthesis is ultimately returned to the atmosphere. Thus, understanding the factors that control rates of decomposition is crucial to understanding the global C budget. Human activities such as fertilizer production, cultivation of legume crops, and fossil fuel combustion have doubled natural rates of N fixation. Nitrogen from agricultural or industrial areas can be transported downwind or downstream and be deposited on terrestrial ecosystems, where its effects on ecosystem C storage are unknown. I have been conducting long-term experiments to better understand the effects of elevated N inputs on decomposition. Most recently, we have begun examining N effects on decomposition in the Nutrient Network experiment and have expanded our focus from N effects on litter decomposition to N effects on soil organic matter decomposition.

Biodiversity, nitrogen enrichment, elevated CO2, water, and temperature effects on ecosystems

Human activities are causing widespread and diverse environmental changes on global scales. In an ongoing, long-term experiment at the CCNHA (the Biodiversity, CO2, and Nitrogen Experiment, BioCON), we are exploring the consequences of interactions among four such global changes: increased concentrations of atmospheric CO2, elevated inputs of N via deposition, alterations in both the composition and numbers of plant species in communities, warming, and changes in precipitation regimes.

This work is supported by DEB-0080302, DEB-0322057, and DEB-0347103 from the National Science Foundation. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Boreal Forest Warming at an Ecotone in Danger

We are studying the likely impact of climate warming on the ecotone between the southern boreal forest and the north temperate forest. In manipulations near Cloquet and Ely, Minnesota, we are examining the effects of experimental warming on recruitment of both boreal and temperate tree species.

This work is funded by the Department of Energy.

Connecting People, Land and Water in the Urban Environment

Urban vegetation confers numerous ecosystem services such as climate and air quality regulation, recreational opportunities, and psychological benefits. Yet the impacts of vegetation (trees, lawns, wetlands) versus impervious surface on hydrology and nutrient loading of urban streams and lakes is poorly known, despite implications for water quality. Nor is it well understood how sociopolitical factors influence decisions about urban vegetation on private and public lands within constraints imposed by multiple scales of governance. This project is aimed at better understanding the dynamic relationships between the social and natural landscapes in urban areas towards enhancing human well-being and environmental quality in urban ecosystems. Specifically, we aim to determine (1) what motivates actions related to management of urban vegetation on public and private lands, and how this influences social networking regarding urban vegetation and water quality, (2) how different cover types in urban landscapes in turn influence urban water quality, and (3) how current governance structures and institutions respond to perturbations in vegetation cover and water quality in urban systems in ways that either promote or hinder the development of human-environment feedbacks that improve human wellbeing. In this work, we are developing whole-watershed nutrient budgets and quantifying the contributions of tree litter to nutrient inputs to aquatic systems, towards improving urban water quality.

This work is funded by the Institute on the Environment.

Ecological Homogenization of Urban America

This project explores the hypothesis that across cities, similar values and preferences lead people to manage their residential landscapes such that yards across cities are more similar to one another in terms of ecological structure and function than they are to the natural and agricultural landscapes that they replace.

This research is funded by the National Science Foundation Macrosystems Biology program.