Dynamics of old-growth forests of Minnesota.

Abstract

Disturbances are an essential part of almost every ecosystem. I studied disturbances in three different old growth forests in Minnesota. These old-growth remnants include the white and red pine forest of the Lost 40 in northern Minnesota, the balsam fir and white spruce forest at Itasca State Park in northern Minnesota, and the hardwood forest of the Big Woods in south-central Minnesota. In the Lost 40, white and red pine are not regenerating and shade-tolerant trees are abundant in the understory and canopy. This lack of regeneration is probably due to the lack of a disturbance like fire. If a management plan were to be implemented, the advancement of the shade-tolerant species into the canopy and the shifting climate space of white and red pine need to be taken into consideration. The white and red pines in Itasca State Park are actively managed, but not the fir-spruce forest. Now, mature fir-spruce forest is dying because of a recent spruce budworm outbreak. Spruce budworm, a defoliating insect that prefers balsam fir and spruce, has been in the park before the most recent outbreak. Before the two outbreaks that were reconstructed, the climate was wet, whereas other studies found dry conditions before an outbreak of the spruce budworm. In reconstructing canopy disturbances of eight remnants, I tested several methods for evaluating canopy disturbance in closed canopy forests. The sequential t-test (regime shift) method had best results when reconstructing canopy disturbances of these forests. I then used the sequential t-test method to reconstruct the canopy-disturbance history. Although a drought-disturbance relationship was detected by other authors, I did not find a consistent relationship in my data. I studied three different old-growth forests in Minnesota. In these stands, disturbances are an integral part. Methods of disturbance-history reconstructions were tested and one (sequential t-test) subsequently used. I made contributions to reconstructing canopy disturbances using release and suppression periods in tree rings of forest types that previously had not been studied this way. The information that I gathered could now be used to inform a management plan, to apply a possibly more precise method to reconstruct a canopy-disturbance history, and to inform the public.