Four Decades of Secondary Succession in Two Lowland Permanent Plots in Northern Lower Michigan

Abstract

Two 0. 1-acre lowland permanent plots in northern lower Michigan were compared for changes since 1938 in community structure and population dynamics. One was on wet sandy soil with Populus tremuloides dominant in 1938, and was severely affected by a storm in 1940. The other was on wet organic soil with Thuja occidentalis, Picea mariana and Abies balsamea present and was unaffected by the 1940 storm. In the conifer plot basal area continuously increased, whereas species richness and density peaked ca. 30 years after logging and burning and declined to a low in 1981. In general, survivorship was highest for trees already established in 1938, and numbers of recruits as well as their diameter growth and survivorship decreased as stand age increased. As a result, 85%o of the 1981 population of conifers was present in 1938. The present population of trees was most strongly influenced by conditions at the time of establishment at least 50 years ago, and events since then have been of minor importance. In contrast, a storm in 1940 destroyed the overstory aspen of Plot 6, causing an initial decrease in basal area, temporary increase in species richness, and shift in dominance from trees to shrubs. Eleven years later, the basal area had returned to prestorm levels, largely because of increases in Alnus rugosa. By 1981 Fraxinus nigra had increased in number; Acer rubrum, Populus tremuloides, Abies balsamea and Betula papyrifera had larger dbh but low density because of high mortality and low recruitment. In 1981, 41 years after the storm, the plot was still dominated by a dense shrub layer of Alnus rugosa and Ilex verticillata.