Local and regional-scale processes interact to govern the assembly, diversity and functioning of ecological communities. Evaluating the interplay of these differently-scaled processes in the regulation of ecological systems is a challenging problem, but is crucial towards understanding and predicting the potential effects of accelerated human activity on biological diversity and ecosystem sustainability. Since 2000, two long-term field experiments have been underway in grasslands of eastern Kansas to investigate the interplay of soil resource availability, species interactions and regional processes governing plant secondary succession, community assembly, biodiversity, and ecosystem functioning.
Both experiments involve manipulations of soil nutrients in permanent grassland study plots and employ multi-species seed addition treatments to evaluate the contribution of dispersal limitation and regional constraints on local species pools to the regulation of plant community dynamics.
Our long-term field studies are conducted at the Nelson Environmental Studies Area (NESA) in eastern Kansas in the prairie-forest ecotone region of the central USA. NESA is part of the University of Kansas (KU) Field Station and Ecological Reserves (KSR) and is located just north of Lawrence, Kansas. Historically, the area was dominated by tall-grass prairie and savanna vegetation prior to settlement. Experiments 1 and 2 were established in a 20 hectare former cool-season hay field that had been maintained as grassland by periodic mowing since abandonment from hay production in the early 1980ís. At the start of our studies in 2000, the field was dominated by introduced C3 hay-grasses, Bromus inermis and Lolium arundenaceum.
Experiment 1 (Old-field succession experiment), previously funded by the National Science Foundation, was initiated in 2001 in a section of the abandoned hay field that was sprayed with herbicide, plowed and disked prior to the start of the study to investigate plant community dynamics in the context of old-field succession initiated on bare soil. The experimental design involves factorial experimental gradients of nitrogen (N) supply (four levels of N fertilization), phosphorus (P) supply (two levels of P fertilization) and plant propagule input achieved by adding seeds of 50 native and naturalized species to half of the study plots. With annual sampling this experiment allows us to examine old-field succession and community assembly unfolding along gradients of N and P fertilization and under conditions of ambient and experimentally-enriched species pools.
Experiment 2 (Hay meadow restoration experiment), previously funded by USDA, was established in 2000 in a section of the field that was left unplowed at the start of the experiment. Thus Experiment 2 was initiated in the context of secondary succession on recently abandoned cool-season hayfield where hay grass species were dominant at the start of the study. In this experiment we have been monitoring plant community change annually since 2001 in response to two aspects of hay management important in our area: annual fertilization and annual haying. The experimental design involves factorial manipulations of nutrient supply (two levels of NPK fertilization), annual haying (two levels: hayed; not hayed) and propagule input achieved by adding seeds of 41 native prairie species to half of the plots. Experiment 2 parallels Experiment 1 with manipulations of soil resources and species pools, but does so in the contexts of hay management and native prairie hay meadow restoration.
These core experiments, and a number of associated auxiliary studies conducted at the same site by graduate students, postdocs and other collaborators, have allowed us to address a wide array of questions in community ecology that can be organized conceptually into five interrelated research themes: 1) species coexistence and biodiversity; 2) patterns and mechanisms of succession; 3) communty assembly and meta-community dynamics; 4) linkages between community structure and ecosystem function; 5) grassland restoration and management.
Research Themes, Project Hypotheses and Selected Results