Human disturbances are changing forest ecosystems across the globe. These disturbance often have long long-lasting effects, and may be irreversible, when an ecosystem shifts into another state of equilibrium. Therefore, land use history is a key factor to understand present forest patterns, but detailed, long-term reconstructions of vegetation changes together with human disturbance history are rare. Our goal was to examine land use legacies in forests in and around Pictured Rocks National Lakeshore. Pictured Rocks is located in the north of Michigan’s Upper Penisula, contains 67 km of Lake Superior’s shoreline, and almost 300 km2 of typical post-glacial landscape types within the transistion zone between boreal and northern hardwood forests. We included a buffer zone around the park boundaries to compare patterns of change within the park area with those outside. We assessed land cover and vegetation changes over the past 170 years based on U.S. General Land Office Surveys (1840s), Michigan Land Economy Surveys (1928) and modern vegetation records. Records from the 1840s show conditions largely undisturbed by European settlers whereas the Land Economy Survey was conducted at the peak of forest clearing and agricultural expansion. Highly resolved data on logging history and agricultural land-uses provide key information on land use changes over the entire period.
Results/Conclusions
The area is extraordinary rich in human disturbance history. In the 19th and beginning of the 20th century white pine were logged in great quantities to provide lumber for fast growing Midwest towns. Hardwood was burned in local kilns to produce charcoal for iron production. Different cycles of forest clearing were followed by agriculture. The period since 1930 was dominated by farm abandonment and forest recovery. Our results show that total forest cover remained at about 80%. Northern hardwood forests was already the most dominant forest type on 60% of the study area in the 1840s but became even more dominant and covers now about 70 %. In contrast, pine forest communities decreased from 20% to less than 10 % most likely due to past logging activities. On finer scales we detected impact of past agricultural land uses on current tree species distribution. Our results underpin the importance of land-use history for the interpretation of past vegetation changes, the understanding of current patterns, and the projection of future changes.
