A prescribed fire at Gibbons Creek Barrens.
Restoration of vegetation typically attempts to redress ecological consequences of habitat loss and degradation and can occur at the species, community, landscape, or ecosystem scales. Restoration at the landscape or ecosystem levels can involve attempts at planting entire vegetation communities and can be defined more accurately as "reconstruction." Examples of species-level restoration include population enhancements, species (re)introductions, and control efforts targeting particular pest species such as a non-native, invasive species. Community-level efforts in the Midwest often involve the reintroduction of natural ecological processes such as a fire regime.
Studies of fire effects on vegetation are particularly informative to restoration ecologists because fire management increasingly is used to restore plant community types that appear to be dependent on periodic fire. Examining the effects of fire in terms of species-response types, survival mechanisms, physiognomic group response, and analysis of biodiversity trends leads to better understanding of how fire affects community structure and organization. These results, particularly from longer-term studies that exceed transient (short-term) responses, can lead to better predictions about the potential of restoration activities that rely on fire alone.
A prescribed fire at Gibbons Creek Barrens.
Results from a seven-year study of fire effects in a dry barrens remnant in southern Illinois (described briefly in the May/June issue) indicated that significantly more ground-cover species increased in frequency and percent cover in the fire-treatment vegetation than in the nearby fire-free control vegetation. Most of the increased occurrences among species appear to be from repositories in soil seed banks and all were native species appropriate for the habitat. The taxa that increased in frequency of occurrence and the numerous newly emerged species in the sample data following the fires indicate that the soil seed bank of barrens remnants can provide an important refugium for species to survive not only fire but changing ecological conditions. Such changes in ecological conditions are typically caused by increased shade from encroachment of woody overstory vegetation. While most species in the ground cover increased in occurrence frequency and many also increased in percent cover, only eight species declined in both cover and frequency and six of these were woody plants. Typical management goals of fire use in savannalike habitats include reducing the abundance of woody species because the shading effects on ground-cover species usually result in lowered percent cover and lower floristic diversity. Abundance of woody vines also declined with fire; however, most other physiognomic groups increased with fire including annuals, perennial forbs, grasses, and sedges. These changes were not always concurrent among these groups. Annual species increased dramatically following each fire, rapidly returning to near baseline levels in the second year, while perennial grasses initially declined in overall abundance and then increased greatly until the next fire. In contrast to the results from fire-treatment vegetation, about 58% of the species in unburned barrens vegetation decreased in frequency (32% of the ground-cover species decreased in both cover and frequency) including a much greater proportion of taxa that became extirpated from the sample area.
At each scale measured (0.25-m2, 0.05-ha, total site) there was an
increase in diversity at the treatment site and, perhaps equally as noteworthy,
a decline at the untreated (control) site. These results not only point to the
potential for recovering diversity with restoration activities, but also
indicate there can be a cost in the absence of restoration. In a highly
fragmented landscape such as in Illinois, where habitat remnants are isolated
from suitable sources of species enrichment, maintaining diversity among
individual sites is critical to the long-term potential for sustaining current
levels of biodiversity within the state. Presently, only a minority of sites
receive restoration efforts. If the trends detected in only a seven-year
period at the control barrens are occurring in other open woodland and savanna
habitats throughout Illinois, the erosion of floristic diversity may be
occurring at a pace that challenges even the most aggressive restoration
program and compounds our interest in the soil seed bank.
Plot at
Gibbons Creek
Barrens after recovery from
a prescribed burn.
John B. Taft, Center for Biodiversity
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