Landscape cover type and pattern dynamics in fragmented southern Great Plains grasslands,USA

We documented land cover and landscape pattern changes in an area of northwestern Oklahoma, USA using aerial photography from 1965, 1981, and 1995. This region of the southern Great Plains is fragmented by agricultural activity, and in recent years many remnant native grasslands have experienced extensive invasion by woody juniper (Juniperus virginiana L.). Concurrently, many cropland areas are being planted into perennial forage grasses and converted to intensively managed introduced grasslands as part of the U.S. Conservation Reserve Program (CRP). Our objectives were to document land cover and landscape pattern changes in the region relative to the expansion of juniper and CRP activity. We then examined how local landscape dominance by either anthropogenic or woody vegetation patches affected landscape pattern indices. Land cover changes from 1965 to 1995 included substantial increases in juniper woodlands and mixed woodlands that resulted from juniper encroachment into deciduous woodlands. Introduced grasslands also increased in many areas as a result of CRP implementation. Changes in landscape pattern generally reflected the influx of juniper into many areas. Landscapes dominated by woody vegetation had significantly more patches, smaller patches and patch core areas, more total edge, and higher patch diversity than landscapes dominated by anthropogenic cover types. Results indicate that expanding juniper is exacerbating the fragmentation process initiated by previous human activity, and represents a serious threat to the continued integrity and conservation of remaining southern Great Plains grasslands.This revised version was published online in May 2005 with corrections to the Cover Date.     

Markov models of land cover dynamics in a southern Great Plains grassland region

Grassland regions of the southern Great Plains are fragmented by agricultural activity and many habitat remnants have experienced encroachment by juniper (Juniperus virginiana L.). Recently, many cropland areas have been converted to monoculture grassland (pastures) and enrolled into the Conservation Reserve Program (CRP). Our objectives were to develop spatial and temporal Markov models to characterize land cover dynamics relative to juniper expansion and CRP using aerial photography from 1965, 1981, and 1995. We used landscapes surrounding three Breeding Bird Survey routes with varying levels of juniper encroachment in Oklahoma as study areas. As expected, land cover changes from 1965 to 1995 included increases in juniper woodland, mixed juniper-deciduous woodland, and pastures from CRP activity. Markov models revealed that juniper had a low likelihood of self-replacement in early stages of encroachment. In all areas, relatively little native grassland was lost to juniper encroachment, but other native habitat types such as deciduous woodland were heavily impacted. Transition probabilities for land cover dynamics varied significantly both spatially and temporally. Projections of these raw transition matrices produced widely varying models of future land cover conditions. By modifying the matrices to account for recent and potential socio-political and ecological changes occurring in this region, a number of more plausible land cover scenarios were produced than those resulting from simple projections of raw transition matrices.