Changes in cedar glades over five decades

Jason Mills recently published findings showing changes in plant community composition in cedar glades. In recent decades, this community has undergone changes largely driven by fire suppression efforts. Mills compared the current composition to that of 1952 (collected originally by Roger Bray and used in the publication of The Vegetation of Wisconsin) in 6 cedar glade communities. He found an 80% decline in graminoids, and increasees in both woody species and non-native plants. Red cedar remained the dominant tree on the site, accounting for 65% of the trees present in 1952 and 75% in 2004. Cedar density declined while basal area increased, creating shadier conditions that contributed to the decline of herbaceous plants. Woody species and vines, notably buckthorn and prickly ash, increased since 1952.

Changes in cedar glades reflect fire suppression and succession, and in many respects are following the same trends Dave Rogers found in southern Wisconsin forests. Details are in his PhD thesis, and a paper summarizing the findings are due out later this year in Ecology.

John Curtis (Roger Bray's advisor) predicted that with fire suppression, cedar glade communities would eventually undergo succession and become oak forest. This has not happened, and it seems more likely that cedar glades will become some sort of novel shrub community consisting of weedy and invasive shade-tolerant trees and shrubs. Time will tell.

The Mills study is significant because it provides a more complete picture of how the composition and stucture of plant communities are changing in the state. Prior to this study, we had a good picture of changes in the distribution of forests and forest tree communities since the presettlement era (1850-1870), thanks to the General Land Survey records. We only have a glimpse of changes in the entire vascular flora of northern forests and prairies, as the number of sites with such data is limited and basline surveys were not developed until the 1950s. As Dave Rogers' thesis data moves into the peer-reviewed literature, this picture of post-1950 changes in the vascular flora will become available for the southern forests.

MILLS J (2008) Fifty Years of Change in Wisconsin Cedar Glades. The American Midland Naturalist: Vol. 159, No. 1 pp. 214–224