Anna Marburg

Advisor: Monica Turner

PhD 2006:  SPATIAL AND TEMPORAL PATTERNSOF RIPARIAN LAND COVER, FORESTS AND LITTORAL COARSE WOOD IN THE NORTHERN HIGHLANDS LAKE DISTRICT, WISCONSIN, USA

In this dissertation I explore the ramifications of the combined pattern of abiotic drivers and human development in northern Wisconsin, USA for three aspects of the landscape: riparian land cover change, riparian forest composition and structure, and littoral coarse wood. A study of land-cover change in 50 lakes from 1938 to 1996 revealed two common trajectories: (1) 16 recovering clearcuts (15% of the study lakes), and (2) a combination of forest succession and increasing residential development (32% of lakes). Initial development in 1939 and subsequent 18 increases in development were not related to initial lake attributes, nor was development associated with a change in water chemistry.  In a survey of 60 lakes stratified along a development gradient, I found little variation in riparian forest composition among nearby lakes or between lakeshores and adjacent uplands. In contrast, stand structure did vary with fine-scale changes in shoreline slope, soil texture and drainage. Stem size distributions suggest that many of the stands are on the cusp of transitioning from successional to mature forest. Neither overstory composition nor stem density was related to building density. However, the density of snags and downed wood declined with increased development. Finally, a re-census of littoral coarse wood in four lakes initially surveyed in 1996 found a net accumulation of wood ranging from -1.1 to 1.9 logs km-1 yr-1. The net gain of logs observed in three lakes may result from the surrounding forest’s transition from early successional to mature forest. After only one year of submersion, there were detectable differences in decay rate among species submerged in the littoral zone (F10, 67 = 16.44, p < 0.0001). L. laricina had the highest rate of decay (9% of initial mass), followed closely by A. saccharum and B papyrifera (both 4%). Taken together, these three chapters paint a portrait of the NHLD as a landscape shaped largely by abiotic forces, often acting at coarse scales, but with some processes under the control of fine-scale drivers – both physical and anthropogenic. These results underscore the importance of historical context when studying spatial patterns of human development and their 16 consequences for ecosystems.

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