Maturation of forested island vegetation in Lake Winnipesaukee, NH

Background/Question/Methods

Studies of changes in plant species composition have been underway since 1978 after a land use plan was implemented on three islands in Lake Winnipesaukee, New Hampshire.  Data were summarized from the understory herbaceous and woody vascular plant species, along with woody overstory species, found in 25 long-term monitoring plots on the islands owned and/or managed by the Appalachian Mountain Club in Lake Winnipesaukee.  Floristic surveys had begun on these islands in 1901, and provided valuable information about earlier vascular plant composition.  Three Mile Island, Hawk's Nest Island, and Blueberry Island were first sampled quantitatively in 1978, again in 1991 and 2001, and most recently in 2011.

Results/Conclusions

Distributions of overstory and understory species were modeled by bootstrapping data (sampling with replacement) for each sampling period.  An increase in total overstory species in the protective and compromise zones between 1978 and 1991 was significant and could be the result of the institution of the land use plan, along with a major storm in the early 1980s.  Total overstory species in any of the other land-use zones over the periods 1978-1991, 1991-2001, or 2001-2011 were not significantly different.  The number of understory species increased significantly in every zone between 1978 and 1991.  No difference in species richness was captured by the data from 1991 to 2001 or from 2001 to 2011.