Eight nonnative plants in western Oregon forests: Associations with environment and management

Abstract

Abstract. Nonnative plants have tremendous ecological and economic impacts on plant communities globally, but comprehensive data on the distribution and ecological relationships of individual species is often scarce or nonexistent. The objective of this study was to assess the influence of vegetation type, climate, topography, and management history on the distribution and abundance of eight selected nonnative plant taxa in forests in western Oregon. These eight taxa were selected as being reliably detected by a multi-resource inventory of 1127 systematically-placed plots on nonfederal forest lands from 1995 to 1997 by the USFS Forest Inventory and Analysis (FIA) program. One or more of the eight nonnative taxa studied were found on 20% of the sampled subplots in the study area, but relatively few stands were dominated by them. Overall abundance of nonnative taxa was likely much greater, because few composites and graminoids were identified to species in this general-purpose inventory. Distribution of most taxa was more closely associated with low density of overstory trees than with climate. Nonnative taxa were significantly more abundant in stands that had been recently clearcut or thinned than in stands that had not. Frequencies of several taxa decreased with elevation, which may reflect proximity to source populations and intensive land use rather than any climatic constraints. Although the greatest potential for displacement of native forest species appears to be in early-successional communities, the potential for spread of some shade-tolerant evergreen shrubs also seems high.

Canopy gaps facilitate establishment, growth, and reproduction of invasive Frangula alnus in a Tsuga canadensis dominated forest

“…Removal of canopy trees reduces competition and allows poorer competitors to successfully colonize and, for a time, avoid competitive exclusion (e.g., Forcier 1975;Henry and Swan 1974;Leak and Filip 1975;McClure and Lee 1993). Our results are also consistent with a growing literature inferring that timber harvest promotes invasion by non-native species that might otherwise be excluded by competition (Baret et al 2008;Belote et al 2008;Gray 2005;Rejmánek 1989;Totland et al 2005;West and Chilcote 1968). There are few studies of logging effects on invasive shrubs in the northeastern USA, and their results are not consistent.…”

“…Indeed, some studies have demonstrated increased abundance or species richness of exotic plants after logging (e.g., Gray 2005;Selmants and Knight 2003;West and Chilcote 1968) although others have reported no or minimal effects (Dodson et al 2008;Griffis et al 2001;Kern et al 2006;Roberts and Zhu 2002;Stapanian et al 1998). In some cases, logging facilitates invasion only when accompanied by scarification or burning (Dodson et al 2008;Griffis et al 2001;Haeussler et al 2002).…”

Meeting the challenge: invasive plants in Pacific Northwest ecosystems.

“…In contrast, Rubus discolor Weihe & Nees (Himalaya blackberry) was well-distributed in the western parts of the two states, but was primarily associated with low elevations. Although some of these relationships were similar to those found in a portion of western Oregon (Gray 2005), this analysis described a broader range of conditions, and climate tended to be more important.…”

Water relations advantages for invasive Rubus armeniacus over two native ruderal congeners

“…R. fruticosus unequivocally follows a high resource use strategy with respect to light throughout the growing season (Amor and Stevens 1976;McDowell 2002;Gray 2005;Caplan and Yeakley 2006). Rapid water-use would follow if transpiration and carbon uptake are tightly coupled under the wide range of water availability R. fruticosus experiences (Jones 1998).…”