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Dr. David J. Mladenoff
Department of Forest Ecology and Management
University of Wisconsin-Madison

Home  >  Projects   >  Land-use legacies, vegetation change, and carbon dynamics

Effects of Historical Land Use on Regional Vegetation and Carbon Dynamics in Wisconsin, 1850-present

Contact  Jeanine Rhemtulla

Background:

Over the past 150 years, the landscapes of Wisconsin have been fundamentally transformed. Lumbermen logged the vast pine and hardwood-hemlock forests in the north; farmers ploughed the southern prairies and oak savannas and then trickled north in the wake of the loggers. Many of these northern farms were abandoned during the Depression, but although the land has slowly reverted to forest cover, these 'second forests' are different in composition and structure from those that preceded them.

Over 40% of the earth's surface has now been transformed by these kinds of land uses, with long-term consequences for biodiversity, biogeochemical cycling, and climate change. On a local scale, historical patterns of land-use can continue to influence species diversity for hundreds to thousands of years, even if the direct imprint of land use has long since faded from view (Dupouey et al. 2002). At a global scale, cumulative land use is also starting to have negative effects. For example, although we usually think of fossil fuel consumption as the main driver of climate change, over 35% of carbon dioxide emissions over the last 150 years have resulted from human alteration of ecosystems (Houghton 1999). Indeed, land use has been called the most important factor contributing to global environmental change (Foley et al. 2005).

Research question:

We are examining the effects of 150 years of land use on: (1) changes in forest species composition and structure, and (2) carbon storage, at the regional scale across Wisconsin.

Approach:

Using several remarkable historical sources, we are reconstructing land use/cover change for the whole state since 1850. The Public Land Survey, carried out in the mid-1800s to demarcate the land for settlement, documents millions of 'witness trees' (trees marked to show the corners of land parcels) that provide a record of what the region looked like prior to major land-use transformation. The Wisconsin Land Economic Inventory, a land survey carried out in the 1930s, provides a detailed view of land cover at the height of the agricultural period. We have digitized both of these surveys for the entire state, and combined them with annual lumber mill records (1870-1909), state agricultural census records (1870-1940), and Forest Inventory and Analysis data (1938-2002) to produce a detailed reconstruction of land use/cover trends since 1850.

Results to date:

Preliminary analysis of changes in forest ecosystems shows that there has been much less abandonment of agriculture than expected, especially in the north, and that there continues to be an imprint of land-use history on the contemporary species composition and structure of second-growth forests. Coniferous species are much less abundant, and there has been a regional homogenization of species composition from north to south. We are currently examining the influence of land-use history on successional trajectories within these forests.

To assess the effects of these changes on carbon storage, we are estimating the magnitude and variability in pre-settlement carbon stocks, as well as the total carbon flux (gain and loss) since that period due to logging, agriculture, and forest regrowth. Preliminary results suggest that total above-ground carbon stocks declined significantly to 1930 and then rose to 1996. Surprisingly, the total magnitude of carbon stocks in the state today is similar to that prior to Euro-American settlement, although the spatial distribution of these stocks across the state is quite different. We are currently undertaking a sensitivity analysis of these estimates.

References:

Dupouey et al.(2002) Ecology 83(11)2978-84.
Foley et al. (2005) Science 309:570-574.
Houghton (1999) Tellus 51B: 298-313.

Funding:

Wisconsin Department of Natural Resources
USDA Forest Service, North Central Research Station
Natural Sciences and Engineering Research Council Canada.