PARENT SESSION
Oral Session # 52: Fire Ecology III: Grasslands; Scrub.
Presiding: J Grace
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 102.

Increasing grassland heterogeneity with fire and grazing: Implications for grassland birds.

Harrell, Wade^*,1, Fuhlendorf, Samuel¹, Engle, David¹, Hamilton, Robert², ¹ Oklahoma State University, Stillwater, OK² The Nature Conservancy, Pawhuska, OK

ABSTRACT- Disturbance-driven heterogeneity has been suggested as a critical process in the maintenance of species in many ecosystems. For example, in grasslands, fire and grazing interact to generate variably scaled disturbance patches across the landscape, contributing to a shifting mosaic that presumably enhances biodiversity. Grassland birds, a declining group within grasslands, have species-level affinities for certain structural characteristics of vegetation, thus changes in spatial heterogeneity may alter bird community dynamics. Our objective was to investigate grassland bird community dynamics in relation to changes in spatial heterogeneity. Our study site was located on the Tallgrass Prairie Preserve in Northeast Oklahoma, USA. We varied the spatial and temporal extent of fire and introduced livestock within management units in an attempt to increase spatial heterogeneity (patch burn treatment, n=2) and contrasted this disturbance regime with a relatively uniform application of fire and grazing (control, n=2). We monitored bird abundance during the spring of 2001-2003 (May-June) using point counts to determine the influence of our patch burn treatment on the bird community. Our patch burn treatment resulted in more spatially heterogeneous management units than our controls. Increased heterogeneity in the patch burn treatment led to greater coexistence of grassland bird species with one species, Henslow′s sparrow, only occurring within the unburned portion of the patch burn treatment. Species-level abundance varied among the patch types that occurred within the patch burn treatment, with some species exhibiting greater abundance in unburned patches and other species occurring in the greatest abundance in the most recently burned and grazed areas. The more uniform application of disturbance in our controls resulted in less spatial heterogeneity and a subsequent reduction in the abundance of some bird species. Our study demonstrates that increased spatial heterogeneity can alter grassland bird community dynamics, and may assist in the conservation of declining species within grassland ecosystems.

Key words: grasslands, grazing, heterogeneity, fire