The Rapid Ecological Assessment for Grassland-Prairie-Savanna is about to be sent out for peer review. The process of generating both the rapid assessment and the Grassland Habitat condition index map highlighted a number of important issues.
The Importance of a Regional Assessment
Destruction and fragmentation are primary threats to wildlife habitats, and perhaps no system has been destroyed or fragmented more than natural grasslands. About one percent of the original system exists, comprised of small and widely scattered fragments. Plant and animal species associated with grasslands, such as Bewwick's Wren, Bachman's Sparrow, Northern Bobwhite, and Prairie Warbler, are listed as Species of Greatest Conservation Need (SGCN), in the revised State Wildlife Action Plans of many states of the GCPO LCC.
Southeastern grasslands have only recently been acknowledged as an important component of our regional ecology. Until the second half of the twentieth century, most naturalists conceived of “natural” landscape conditions as those that would be likely to occur if humans were completely absent. Free-roaming fire was viewed as a human-generated disturbance. Given those paradigms, the disappearance of open grasslands from the Southern landscape was of little concern because they were not “natural” to begin with.
Reed Noss’ 2013 book Forgotten Grasslands of the South describes fire as a recurring ecological disturbance “as natural as substrate or climate.” Since the last glacial maximum, 12 -15 thousand years ago, indigenous people used fire to expand or enhance prairie openings caused naturally by interactions between droughty clay soils and lightning-set fires, resulting in an “archipelago” of open patches, many quite large, across the region. Many species of birds, mammals, invertebrates, plants and other organisms became adapted to these landscapes. During European settlement in the nineteenth century, these openings were usually the first to go under the plow.
Preliminary Results from the Grassland Ecological Assessment
We identified about 32 million acres of grassland within the Gulf Coastal Plain, Mississippi Alluvial Valley, and Ozark Highlands, about a million acres of which may be considered natural prairie. Grassland and prairie pixels are scattered widely through the East and West Gulf Coastal Plains. Desired site-level conditions were defined using recommended values for vegetation height, bare ground, tree density, and disturbance return interval. The presence of all four desired conditions was detected on only 3,388 acres of grassland pixels, mostly in Oklahoma and Missouri in the transition to the tallgrass prairie of the Central Plains, and some in the Black Belt of Mississippi and Alabama.
Challenges to a Regional Assessment
Assessments of forested and aquatic systems benefit from the fact that they are associated with natural resources widely acknowledged as valuable to society, and standardized metrics for assessing those resources, many of which apply also to wildlife habitat suitability, were established long ago. Grasslands, by contrast, have contributed to the national economy chiefly by being converted to cropland: large-scale monitoring of conditions suitable for wildlife using comprehensive, standardized metrics have not been developed.
There are many challenges to a regional assessment of natural grassland systems. The first issue involves identifying and describing various types of grasslands. Different terms have been used by different scientists working in different parts of the region at different times. Glades, outcrops, marshes, bogs, fens, woodlands, and pine savanna all have grass-dominated vegetative ground layers, but differ from calcareous or so-called “blackland” prairies in significant ways, and our assessment elects to address these separately from grassland/prairie/savanna.
The second issue is that grasslands are difficult to map rapidly at large scales. Algorithms for distinguishing warm season native grasses from cool season exotic grasses in aerial imagery do exist, but these tend to work only at local scales, and do not work at all when the two are intermingled with broadleaf herbaceous plants within pixels. Furthermore, the habitat conditions most important to the species of concern, such as amount of bare ground, vegetation height, and vegetation density, are traditionally measured at the scale of an individual research plot, and are difficult to assess over large areas.
The Landscape Conservation Cooperative Role in Grassland Conservation
The anticipated release of the grassland-prairie-savanna ecological assessment will be an important step in the process of understanding what little remains of this ecologically important system. A full determination of how much exists, where it is, and in what condition will require collaborative efforts across states, federal agencies, and non-governmental organizations. As a self-directed partnership of these very entities, the LCC network is highly suited for this task. We hope that the GCPO Grassland and Prairie Ecological Assessment provides a framework for regional conservation design of this critically imperiled habitat type.
Data: The draft Grassland Habitat System Condition Index is available for review on the GCPO LCC Conservation Planning Atlas.
Read the Grassland Assessment-in-Brief for a summary of Assessment results.
View the poster entitled A Condition Index for Grassland/Prairie/Savanna in the Gulf Coastal Plain, Mississippi Alluvial Valley, and Ozark Highlands, which summarizes the methodology and results.