Changes in Soil Functions Following Invasions of Exotic Understory Plants in Deciduous Forests

Abstract

Eastern deciduous forests have been invaded by two exotic species that often dominate the understory vegetation. Berberis thunbergii, a woody shrub, forms dense thickets, while Microstegium vimineum, a C 4 grass, forms continuous lawns; the two species often co-occur. We hypothesized that a variety of characteristics of the exotic species may cause soil-based ecosystem processes to change following invasion, and that such changes could establish positive feedback processes that enhance the spread of the exotic. We examined changes in soil pH, nitrogen cycling, and litter dynamics in stands infested with both species in three locations in northern New Jersey (USA). Soils directly beneath each of the two exotics had higher pH values and higher nitrification rates and often had higher net N mineralization rates than did soils beneath adjacent patches of the most common native understory shrub, Vaccinium pallidum. These differences could be replicated in the greenhouse by growing the exotics in previously uninvaded soils. Berberis litter was much higher in N concentration than was litter of the native species; it decomposed more rapidly than litter of native dominant tree species, with little or no immobilization of N. In contrast, Microstegium litter decomposed more slowly than the native species' litters, and it immobilized N. We suggest that the same change in soil-increased pH and nitrificationresult from different combinations of mechanisms in the two exotic species. Both species evidently favor uptake of nitrate, which may elevate pH. However, Berberis combines large biomasses of N-rich roots with N-rich leaf litter, while Microstegium populations combines small biomasses of N-rich roots with small biomasses of N-poor litter that leave much of the surface soil with few roots. The ability to change soil functions may be an important and previously unrecognized characteristic that renders species capable of invading intact communities, while the likelihood that changes in soil functions can alter the growth of the exotics may be an important component of invasibility.

Exotic Guavas are Foci of Forest Regeneration in Kenyan Farmland

“…GUAVA TREES AND MANAGEMENT.-Our results showed that exotic fruiting guava trees could be important tools for forest restoration, by attracting frugivorous birds and enhancing local seed rain and seedling establishment. Before recommending guava trees to managers, further investigations on the more subtle impacts of this exotic species on local ecological communities are required concerning, for example, interactions with pathogens and herbivores and its impact on soil water relations and nutrient cycling (Callaway & Aschehoug 2000, Ehrenfeld et al 2001, Meiners et al 2001, Weber 2003). Long-term interactions with indigenous plant species are of particular interest.…”

“…They might be competitively superior to indigenous species due to release from natural enemies (Keane & Crawley 2002). Furthermore, they have been shown to alter soil conditions, nutrient cycles, light conditions, or allocation of resources (Callaway & Aschehoug 2000, D'Antonio & Mahall 1991, Ehrenfeld et al 2001, Reinhart et al 2006. Nevertheless, exotic trees could positively affect regeneration processes in degraded sites.…”

Litter drives ecosystem and plant community changes in cattail invasion

“…A feedback is positive if a plant modifies the environment in a way that benefits itself, by increasing its population or individual growth (Ehrenfeld et al 2005). Positive feedbacks may be a very effective mechanism of invasion (Ehrenfeld 2003, Levine et al 2006, and positive feedbacks through nutrient dynamics have been hypothesized as a mechanism of invasion for Berberis thunbergii and Microstegium vimineum in deciduous forests (Ehrenfeld et al 2001), Bromus tectorum invasion in arid grasslands (Sperry et al 2006), as well as a number of invaders in Hawaii (Allison and Vitousek 2004).…”

Invasion of Euryops floribundus in degraded South African communal grassland: Unpacking the invasion relationship with elevation, soil properties, the quality and quantity of the herbaceous layer

“…With regard to the invasion intensity gradient, effects on soils are possibly feedback to above-ground plant communities (Kuebbing, Classen, & Simberloff, 2014) (Liao et al, 2008;Wei et al, 2017); and (b) changes in microclimates (e.g., low soil temperature and evaporation) or water retention accompanying the changes in the shrub density and vegetation growth (Ehrenfeld, Kourtev, & Huang, 2001), and the subsequent low rate of organic matter decomposition.…”