Vegetation responses to landscape structure at multiple scales across a Northern Wisconsin, USA, pine barrens landscape

Increasing awareness of the importance of scale and landscape structure to landscape processes and concern about loss of biodiversity has resulted in efforts to understand patterns of biodiversity across multiple scales. We e xamined plant species distributions and their relationships to landscape st ructure at varying spatial scales across a pine barrens landscape in northe rn Wisconsin, U.S.A. We recorded plant species cover in 1x1 m plots every 5 m along a 3575 m transect, along with variables describing macro- and micr o-landscape structure. A total of 139 understory plant species were recorde d. The distributions of many species appeared to be strongly associated wit h landscape structural features, such as distinct management patches and ro ads. TWINSPAN and detrended correspondence analysis (DCA) identified three groups of species that overlapped extensively in the ordination, possibly r eflecting the relatively homogeneous nature of disturbance in the pine barr ens landscape. Distribution of understory plants did not reflect all of the patch types we identified along the transect; plot ordination and classifi cation resulted in three to five plot groups that differed in niche breadth . Wavelet transforms showed varying relationships between landscape feature s and plant diversity indices (Shannon-Weiner, Simpson's Dominance) at diff erent resolutions. Wavelet variances indicated that patterns of Shannon div ersity were dominated by coarse resolutions ranging from similar to 900-150 0 m, which may have been related to topography. Patterns of Simpson's Domin ance were dominated by similar to 700 m resolution, possibly associated wit h canopy cover. However, a strong correspondence between overstory patch ty pe and diversity was found for several patch types at ranges of scales that varied by patch type. Effects of linear features such as roads were appare nt in the wavelet transforms at resolutions of about 5-1000 m, suggesting r oads may have an important impact on plant diversity at landscape scales. A t broad scales, landscape context appeared more important to diversity than individual patches, suggesting that changes in structure at fine resolutio ns could alter overall diversity characteristics of the landscape. Therefor e, a hierarchical perspective is necessary to recognize potential large-sca le change resulting from small-scale activities.