Student Spotlight - Maskit Ronen
Stand Age, Regeneration, the Understory
by Maskit Ronen
Spring 2006
Human activities have been the main cause of disturbance in northeastern forests since European settlement. In Black Rock Forest, the most common land use was clearcutting for timber production.
With clearcutting, all the trees in a site are cleared, and a new, even-aged stand is allowed to grow. When all trees are cut regardless of their commercial value, species that are ecologically important for conserving nutrients, minimizing erosion, and serving as a source of food for wildlife are removed as well. This limits regeneration since there are no mature trees to produce seeds after the seeds initially on the ground are exhausted, and it may significantly change the understory layer of the forest as different types of plants colonize the area. The goal of my study was to examine how this so-called forest succession affects understory vegetation by looking at the relationship between forest age (years since clearcut) and the understory layer.
In July 2005, I surveyed five stands in the Forest that were clear-cut in various years. The canopy trees in each stand are all approximately the same age, with averages of 36, 71, 92, 92 and 131 years in 2005. I collected data on the species and diameter of canopy trees, the number and species of tree seedlings, and the percentage of ground covered by each understory plant group or species.
I found that the understory species composition was most similar in the two 92-year-old stands, and generally differed the most between the oldest and youngest stands.
Although forest succession models predict increasing ground cover with increasing stand age, I found no significant relationship. This may be partly due to the limited number of samples collected from each stand and/or the lack of replication sites.
An interesting finding was the nonlinear relationship between tree regeneration and stand age. When the number of seedlings in a stand was plotted as a function of stand age, the total number of seedlings, especially of red oak and red maple, first increased and then decreased. Conversely, the numbers of shade-intolerant black birch seedlings first decreased and then increased. This may be due to factors that change as trees mature: varying light conditions, increasing competition for nutrients and moisture, and changing amounts of seeds available. Additionally, the stands were thinned after the initial clearcut, changing the natural growth of the trees and influencing the understory community.
Further study of the understory community is required, since my study was limited to one stand of each forest age, the number of samples was limited by the size of the stands, and it would be preferable to add very young and very old forests.
Maskit Ronen worked on this study for her undergraduate thesis at Columbia University . She plans to go to veterinary school.
