Landscape Ecosystems of the Mack Lake Burn, Northern Lower Michigan, and the Occurrence of the Kirtland's Warbler

Abstract

Abstract The Kirtland's warbler (Dendroica kirtlandii Baird) is a federally endangered songbird that nests only in ecosystems dominated by young jack pine (Pinus banksiana Lamb.) in northern Michigan. Although considerable research has focused on the bird, comparatively little information is available on the specific landscape ecosystems occupied by the warbler. The 9,700 ha Mack Lake burn provided an opportunity to track the pattern of Kirtland's warbler occurrence in relation to the ecosystems of a highly diverse and productive area of its breeding range. Using a multifactor landscape ecosystem approach, two high-elevation and four low-elevation landform-level ecosystems were identified, described, and mapped. The spatial pattern of warbler occurrence over time was strongly mediated by the physical and biotic components of the ecosystems. During the first 3 yr of warbler occupation (1986–1988), the high-elevation landforms, characterized by relatively warm temperatures, moister, more fertile soils, and faster growing jack pines, supported 62% of the population. Thereafter, a major shift occurred to the low-elevation landforms. During the last 3 yr of record (1995–1997), the low-elevation landforms, characterized by colder temperatures, drier, less fertile soils, and slow-growing jack pines, supported 86% of the population. The juxtaposition of high- and low-elevation landforms, and the fine-scale ecosystem diversity within them, prolonged the duration of warbler occupancy beyond what would be expected in less heterogeneous conditions. As demonstrated here, the landscape ecosystem approach provides a sound, ecological framework for understanding patterns of Kirtland's warbler occurrence and for assisting managers in identifying appropriate management areas for the continued recovery of the species. FOR. SCI. 49(1):119–139.