Floristic Diversity and Vegetation Distribution in the Alaskan Boreal Forest

Abstract

Although modern forests have occupied interior Alaska for only 13,000 years, their floristic composition and patterns of distribution have remained relatively stable for the past 5,000 years (Chapter 5). Here, at the current northern limit of forests, severe environmental conditions have prevented migration of new species from the south. The Bering Sea has isolated Alaska from a taxonomically distinct flora in Eurasia. Mountains to the north (Brooks Range) and south (Alaska Range) of interior Alaska have restricted the potential for latitudinal shifts of species in response to millennial-scale variations in climate. The stability of the Alaskan vegetation mosaic for the past 5,000 years contrasts with the substantial vegetation movements that have occurred in the eastern Canadian boreal forest (Bergeron et al. 2004). Because of this long-term stability, the distribution of Alaska’s boreal vegetation reflects a clear imprint of current environmental patterns on the landscape. This strong link between current environment and vegetation facilitates the use of state factors (Chapter 1) as a framework for describing floristic patterns, although barriers to past migration could lead to rapid vegetation change, if new species were to arrive in Alaska. In this chapter we describe the major patterns of diversity and distribution in interior Alaska forests and discuss their potential future changes. The common and scientific names of species mentioned in this chapter are given in Table 6.1. The composition of the boreal forest varies greatly throughout its circumpolar range in response to differences in both current environment and geoclimatic history. The primary species, those that give the forest is distinctive appearance, include broadleafed deciduous trees, needle-leafed evergreens, and needle-leafed deciduous trees. In Alaska, the predominant conifers are white and black spruce (Picea glauca and P. mariana, respectively); larch (Larix laricina) tends to be local; and pine is absent in interior Alaska but a prominent component of the forests to the east in the Yukon and the Northwest Territory, Canada. Important deciduous trees are two poplars (aspen [Populus tremuloides] and balsam poplar [P. balsamifera]) and paper birch (Betula neoalaskana; previously treated as B. papyrifera).