Land-use legacies in Wisconsin: Regional vegetation change and carbon dynamics (mid-1800s to 1930s to present)

Historical land use can influence forest composition, structure, and function for centuries after direct use has ceased. In Wisconsin, Euro-American settlement was accompanied by logging, clearing, and fire suppression. I examined the influence of historical land use on the magnitude, rate, and trajectories of change in regional land cover, forest composition and structure, and above-ground live forest biomass (AGB) across Wisconsin from the mid-1800s to the present. Data sources included: U.S. Public Land Survey records (mid-1800s), collected at the onset of settlement; Wisconsin Land Economic Inventory (1930s), conducted at the height of agricultural clearing; and several contemporary sources. I assessed changes in land cover and forest composition and structure using spatial error models, multinomial logistic regression, and ordination methods. I used Monte Carlo simulation to estimate fine-resolution changes in AGB including the magnitude of uncertainty due to the historical records and error in the allometric equations.; The greatest changes occurred between the mid-1800s and 1930s, with less change thereafter. Southern oak savannas and prairies were greatly reduced, mostly converted to cropland. Most northern forests were logged, but there was less agricultural clearing and subsequent abandonment than expected. Within forest ecosystems, dominance of coniferous species and percent of large diameter trees declined. Since the 1930s, a decrease in early successional species and increase in tree diameter has led to some recovery in northern forests, while an increase in late successional hardwoods has led to novel trajectories of change in former oak savannas in the South. There is evidence of regional homogenization in land cover, but the broad north-south environmental gradient still constrains overall species composition. AGB declined 3.5-fold from the mid-1800s to the 1930s, and, despite forest regrowth, is still only 60% of its former level. Spatial variability in AGB declined due to deforestation in the north and forest ingrowth in the south. Monte Carlo simulation was a useful method for estimating AGB from historical survey records, and suggested that the greatest source of uncertainty stems from uncertainties in tree diameter distributions. The legacies of historical land use are extensive in Wisconsin and likely to persist in the foreseeable future.