Invasion of Fir Forest by Sugar Maple in Itasca Park, Minnesota

Abstract

Studies across an ecotone between deciduous and coniferous forest at Itasca State Park, Minnesota, in 1939-41 suggested that coniferous forest species were able to colonize openings in the adjacent deciduous forest and that coniferous vegetation might be the climatic climax vegetation in the study area. In 1959, published observations of the same study area suggested that the deciduous forest species were now colonizing the coniferous zone and that a change in climate to wetter conditions in the intervening period was responsible for the change in direction of advance of the ecotone boundary. In 1966 sugar maple (Acer saccharum) seedlings were abundant within the balsam fir (Abies balsamea) forest"in this study area, and extended 650 m into it from the maple forest border. The success of maple advance is correlated with the opening up of the fir forest canopy following blowdown of senescent fir trees. The occurrence of maple seedlings, contemporaneous with thickets of fir seedlings, within the fir forest suggested that "islands" of fir found within the maple forest in 1939 might have arisen from fir seedling thickets stranded during an earlier successional invasion of the fir forest by maple. The problem of attributing forest ecotone movements to climatic changes over short intervals of time is briefly discussed. Detailed quantitative description of the vegetation is needed to determine the extent to which the deciduous and coniferous vegetation types represent mutually exclusive plant communities in this region.