The shortgrass steppe (SGS) LTER has been in operation since 1982. Three questions guide its work: (1) What factors regulate ecological structure and function over space and time? (2) How do factors that regulate structure and function and coupling of biotic and abiotic components vary spatially and temporally? (3) What are the thresholds that determine the vulnerability to changes in the factors influencing structure and function?
The conceptual framework asserts that ecological structure and function are governed by climate, natural disturbance, physiography, human use, and biotic interactions. SGS work is divided into three topic areas, population dynamics (plants and heterotrophs), biogeochemistry, and land-atmosphere interactions. Disturbances are of such importance that they are embedded in each topic area. In addition to continuing long-term experiments, SGS will initiate new studies that primarily focus on Question 3.
In the area of population dynamics, one grass species, Bouteloua gracilis, contributes most to biomass and net primary production (NPP) and has been the focus of most past work. New long-term studies of Opuntia polyacantha (prickly-pear cactus), a species that makes up a small proportion of NPP, will be initiated; its spiny growth form affords protection to other species and therefore may have a large effect under cattle grazing. Even though the SGS has proven quite resistant to invasive plants, the introduction of species that can successfully invade the SGS is inevitable. So the potential for invasion by plants with different life history attributes will be studied and surveys conducted to detect new invasions.
In the area of faunal dynamics, small mammals simultaneously reflect and affect both the structure and function of the SGS ecosystem. Long-term studies will be continued that track small mammal populations, their resources and predators. New research will emphasize the dynamics of the black-tailed prairie dog (Cynomys ludovicianus) and its effects on biological diversity and ecosystem function. The once abundant prairie dog is now a candidate for listing under the Endangered Species Act.
Under biogeochemistry, SGS conceives of biogeochemical processes as an integrated function of biotic components and those processes responsible for carbon and nutrient fluxes: primary production, decomposition, weathering, mineralization, and trace gas flux. Variations in biogeochemistry will continue to be studied as a function of climatic controls, and new studies that evaluate geologic (textural) and topographic controls, and the N budget will be initiated.
Regarding land-atmosphere interactions, the processes of primary concern are water, energy, and gaseous fluxes. One of the most important alterations that has occurred and continues to occur on the SGS LTER is land-use change, which will be evaluated in terms of the interactions among human land use, biotic responses, and atmospheric processes at local to regional scales.
The SGS has a major investment in simulation analysis, and each of topic areas has a simulation component. Models will continue to be used for synthesizing long-term data both within and across research areas. A new synthesis volume will be published during the next funding cycle.
Finally, data management supports SGS research and contributes to ecoinformatics. The building of new interactions with federal land management agencies, NGO's, and the interested public will be continued. Through the use of supplemental funding, SGS will focus its sLTER on K-12 and community outreach through student mentoring, curriculum development, teacher professional development, community partnerships, and education research.
