Ecosystem management and the niche gestalt of the Red-cockaded Woodpecker in longleaf pine forests

摘要

We use the term "optimal niche gestalt" to refer to the concept that there are structural features of the environment that allow a species to thrive over and above those that allow it to persist. Analyses of the covariation between demographic and habitat features can reveal a trajectory toward this optimal state. To help identify new criteria for foraging-habitat guidelines for the Red-cockaded Woodpecker (Picoides borealis) in the Apalachicola National Forest, we examine seven years of demographic data for the woodpecker population and habitat in core stands, the naturally regenerated prime habitat in the centers of their territories. For both districts of the forest, two compound habitat variables are highly related to the average number of adult birds per social group, the average number of young fledged per group, and the density of groups. These variables are, first, the difference between the density of trees > 35 cm dbh and that of trees 15-25 cm dbh and, second, the difference, in the ground cover, between the percentage of wiregrass and that of woody-plus-palmetto vegetation. Although the birds require a few old relict trees for their cavities, a regression analysis shows that including data for variation in the availability of relict trees in this forest does not improve the power of the above habitat variables to account for variation in the demography of the birds. Because covariation between demographic variables and the recommendations in the current federal guidelines for the management of foraging habitat of the Red-cockaded Woodpecker is low, we conclude that experimental tests of whether causal mechanisms underlie the much higher correlative relationships we have found are warranted. Such tests should use differing levels of prescribed fire, which has dramatic effects on the ground cover. Smaller size classes of trees in closed-canopy stands should be thinned, creating patchy openings in the forest that will promote natural pine regeneration. Traditional unevenaged silvicultural management could adopt a target tree distribution similar to that on the Apalachicola Ranger District, which supports a population of woodpeckers that is deemed to have recovered. We think that in addition to being beneficial for the birds the proposed program of habitat management is more likely to promote the long-term restoration of the longleaf pine/wiregrass ecosystem within Red-cockaded Woodpecker habitat than are alternative scenarios. [References: 86]