Conceptual Framework
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The conceptual framework of SGS-LTER research depicting three key contemporary determinants (Climate; Physiography; Grazing, Fire and Land-Use) of SGS structure and function (center circle) and their interactions. The interplay of biotic, abiotic and anthropogenic factors ultimately determine the ecological trajectory at a given location, resulting in a range of possible ecosystem states or types (here, exurban development, cultivated row crops, native SGS, and seeded grasslands) that co-occur at landscape and regional scales. The spatial arrangement of these different ecosystem types can affect the states of adjacent types, or organisms that operate over large spatial scales. Hence, understanding the interaction depicted in the center circle at multiple points across the landscape and in response to changes in the three determinants is critical. As a social-ecological system, changes in land-use, policy and management decisions, or economic factors on the SGS can rapidly change the mosaic of ecosystem types over the landscape. SGS SGS-LTER researchers combine experimental and comparative approaches with long-term monitoring, cross-site studies and modeling to understand the interactions among these components and forecast responses of SGS structure and function to regional and global change. This work informs our cross site (SGS, BES, KBS, SBC, and LN) environmental literacy initiative as described in section 5 of our 2010 renewal proposal.
The following figures (a, b, c, and d) illustrate a historical view of the primary determinants of structure and function of the SGS ecosystem: Climate; Physiography; Grazing, Fire and Land-Use. These figures illustrate the social-ecological interactions that have transformed the SGS over the past 150 years have involved changes in grazing, fire and land-use. a) Before European settlement during the 1800s, grazing by herbivores (bison and prairie dogs) was the dominant determinant of the SGS ecosystem structure and function. The extent to which fire also influenced the effects of grazing and key species interactions is less well known. b) European settlers removed bison and replaced them with livestock, and began cultivation and tillage for agriculture. Recurring droughts, especially in the 1910s, 1930s, and 1950s led to development of irrigation systems and the unset of irrigated agriculture along the front range and riparian areas in conjunction with dryland framing. Fire is infrequent and largely suppressed. c) The current state(s) of the system, with return of tilled lands to grassland, with 10% of Weld County planted and managed under the Conservation Reserve Program (CRP) in part to conserve soil. Fire is used as a management tool. The ecosystem currently exists as a mosaic of land uses. d) With global change, temperatures have begun to rise, and changes in the timing and intensity of precipitation are expected. Interactions between CO2 concentrations, temperature, and precipitation may lead to several alternative states in the future. Forecasting these changes are an important focus of the current SGS-LTER program.
