PARENT SESSION
Contributed Oral Session 4: Forest Management
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal
Explaining three decades of change in a bark lichen community: pollution vs. land management.
Will-Wolf, Susan *,1, Nelsen, Matthew1, Makholm, Martha2, Roth, John2, 1 University of Wisconsin-Madison, Madison, Wisconsin2 Wisconsin Department of Natural Resources, Madison, Wisconsin
ABSTRACT- A long-term study of bark lichen communities originally designed to monitor response to a local air pollution source in southern Wisconsin has found that changes in woodlands linked to land management are as important as patterns of air pollution to explain changes in community composition. Short-term (1974 -78) changes in lichen communities (29 sites, 10 Quercus subgen Erythrobalanus/site) were small (avg 1974-78 Sorenson similarity, plots between years = 0.70), and included subtle though significant shifts in composition related to the local pollution source (1975 startup). In a 2003 resurvey of 25 of the sites, we found that communities had changed much more (avg 1974-2003 Sorenson similarity= 0.54). There are still subtle species patterns related to the local pollution source; there are also now community patterns related to regional pollution higher at sites in the ESE part of the study area, closer to Milwaukee WI and Chicago, IL. However, the strongest 1974-2003 shifts are area-wide and unrelated to pollution: significant reduction in large foliose lichens and increases in small foliose lichens, reduction in fertile Lecanora (crustose) lichens and increases in non-fertile crustose lichens. Lichen communities of the 25 resurveyed sites are on average 17% more similar to each other (p<0.004, 2 tests, Sorenson similarities between plots in year) in 2003 than they were in 1974. This homogenization reflects declines in frequency of less common and sun-loving species, and expansion of more common and shade-loving species, without strong changes in regional species pool. These patterns are related to shadier conditions for trunks linked to shifts in tree species composition (increases in Acer species and Prunus serotina and decreases in all Quercus species) and invasion of exotic shrubs. 1974-2003 changes in both woody species and lichen species are least at the driest sites.
Key words: lichen, resurvey, forest, homogenization