Permanent Plots at Pisgah State Forest in Wincester NH since 1984

There are relatively few studies that have examined forest structure and
composition both before and after a catastrophic wind disturbance has altered the
forest. On a twenty acre parcel of old-growth forest located in the Pisgah State
Forest in southwest New Hampshire, the collection of a long term data set from
1907-1995 has made it possible to consider how the hurricane of 1938 altered forest
structure, species composition, and subsequent forest development in the stand.
Various types of information were gathered throughout the century that allowed the
quantification of forest structure and composition: species identification, diameter
measurements, tree status (living or dead), tree cores, and individual tree growth
and mortality have recently been tracked. The old-growth forest before 1938 was
dominated by a Pinus-Tsuga-Hardwood mix. The hurricane left the forest devastated and
incredibly altered. The total basal area of the forest was drastically reduced from
approximately 70m2/ha to about 5m2/ha after the disturbance. White pine was
effectively lost from the stand while many large Tsuga were also blown down. A large
increase in density was subsequently recorded as many post-disturbance species took
advantage of the resources that had been made available, especially light. Although
there was a high level of destruction, a good amount of Tsuga and Fagus that had
previously existed in the understory was released from suppression and grew to fill
in parts of the overstory. Both the forest structure and the species composition
changed from a relatively homogeneous state before the hurricane to an extremely
heterogeneous one after the hurricane. The overall development of the stand followed
the typical path of a recently disturbed area: after the initial increase in density
in the few years after the storm, basal area has been steadily increasing while
density has steadily decreased. It has also been possible to observe differences in
the ability of individual species to react to the hurricane. Tsuga and Fagus are
exhibiting a much-increased ability to remain in the stand while other
post-disturbance species such as Betula and Acer are suffering much higher mortality.
Although the forest already has very low tree species diversity, it will continue to
drop with time as more and more of the post-disturbance hardwoods are lost to
mortality.