Influence of season and frequency of fire on Bachman's and Henslow's sparrows in longleaf pine forests of the Gulf Coastal Plain.

摘要

Over 95% of longleaf pine (Pinus palustris) forests have been destroyed. Longleaf pine forests contain the most species rich plant communities in North America and most of the diversity is found within the herbaceous ground cover. Frequent fires are required to maintain natural diversity of these forests, but empirical evidence of the influence of season and frequency of fire on most species is lacking. Bachman's (Aimophila aestivalis ) and Henslow's Sparrows (Ammodramus henslowii) are associated with longleaf pine communities and are of extremely high management concern. Like most species associated with longleaf pine forests, both sparrows are dependent on condition of herbaceous ground cover. Bachman's Sparrows both breed and winter in longleaf pine forests, whereas Henslow's Sparrows only winter there, primarily in pitcher plant bogs. We examined the influence of season and frequency of fire on these two sparrows between 1999 and 2001 in longleaf pine forests in south Alabama and northwest Florida. During breeding seasons of 1999 and 2000, Bachman's Sparrows were most abundant in stands burned ≤3 years previously, but abundance did not differ between seasons of last burning. Percent coverage of grass affected abundance of Bachman's Sparrows more strongly than season or frequency of burning. Percent canopy cover had a strong negative effect on coverage by grass but had a weaker effect when stands had been burned during the growing season. During 2001, breeding productivity of Bachman's Sparrows mirrored abundance during 1999 and 2000 suggesting abundance is probably an accurate indicator of habitat quality for Bachman's Sparrows. Densities of Henslow's Sparrows on pitcher plant bogs during winters of 1999–2000 and 2000–2001 were greater the first winter after burning than two or more years after burning. Henslow's Sparrows were rarely found on bogs burned during the dormant season >1 year earlier, but they occurred on bogs burned during the growing season for 3 or more winters after burning. Seedstalks of grasses and density of forbs were the most important vegetation variables affecting Henslow's Sparrows. Results suggested that the best fire regime to accommodate conservation of both Bachman's and Henslow's Sparrows is probably biennial growing season fire.