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 examined plant species distributions and their relationships to landscape structure at varying spatial scales across a pine barrens landscape in northern Wisconsin, U.S.A. We recorded plant species cover in 1×1 m plots every 5 m along a 3575 m transect, along with variables describing macro- and micro-landscape structure. A total of 139 understory plant species were recorded. The distributions of many species appeared to be strongly associated with landscape structural features, such as distinct management patches and roads. TWINSPAN and detrended correspondence analysis (DCA) identified three groups of species that overlapped extensively in the ordination, possibly reflecting the relatively homogeneous nature of disturbance in the pine barrens landscape. Distribution of understory plants did not reflect all of the patch types we identified along the transect; plot ordination and classification resulted in three to five plot groups that differed in niche breadth. Wavelet transforms showed varying relationships between landscape features and plant diversity indices (Shannon–Weiner, Simpson's Dominance) at different resolutions. Wavelet variances indicated that patterns of Shannon diversity were dominated by coarse resolutions ranging from ∼900–1500 m, which may have been related to topography. Patterns of Simpson's Dominance were dominated by ∼700 m resolution, possibly associated with canopy cover. However, a strong correspondence between overstory patch type 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 apparent in the wavelet transforms at resolutions of about 5–1000 m, suggesting roads may have an important impact on plant diversity at landscape scales. At broad scales, landscape context appeared more important to diversity than individual patches, suggesting that changes in structure at fine resolutions could alter overall diversity characteristics of the landscape. Therefore, a hierarchical perspective is necessary to recognize potential large-scale change resulting from small-scale activities.