Facilitation among Woody Plants Establishing in an Old Field

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Trees and shrubs establishing in grasslands frequently occur in clumps associated with increased soil moisture and N availability. We tested whether the presence of conspecifics or enhanced soil resources increased the growth and survivorship of a shrub (Symphoricarpos occidentalis) and a tree (Picea glauca) in the presence of the perennial grass (Bromus inermis). Rhizomes of Symphoricarpos and seedlings of Picea were transplanted into plots either singly or with four nonspecific neighbors, and with grass neighbors present or removed. Half the plots received additional water, N, and shade to simulate a forest environment. Roots and shoots of transplants were harvested after two growing seasons. Soil moisture and available N were lowest at high transplant density, and highest in the simulated-forest environment and in treatments where grass was removed. Transplant survivorship was generally enhanced in plots where grasses were removed and in the simulated-forest environment. Picea survivorship was reduced by grasses in plots without resource manipulations but was unaffected by grasses in the simulated-forest environment, suggesting that the simulated-forest environment enhanced the ability of Picea to compete with grasses. Picea growth, however, was reduced by nonspecific neighbors in all cases. For Symphoricarpos, nonspecific neighbors significantly decreased growth rates with grasses absent but significantly increased growth rates with grasses present. Thus the direct effect of high density in monoculture was to reduce Symphoricarpos growth, but the indirect effect of high density in the presence of grass was to facilitate Symphoricarpos growth. In summary, nonspecific neighbors increased the growth rate of Symphoricarpos in competition with grass, and a simulated-forest environment enhanced the ability of Picea to survive in the presence of grasses. The results support the idea that contagious distributions of woody species invading grasslands enhance woody plant establishment. Ecology, Vol. 79, No. 8 the possibility that invasions will be irreversible while feedbacks continue. ACKNOWLEDGMENTS We thank R. Callaway, M. Huston, M. Kdchy, R. Mitchell, D. Peltzer, and an anonymous reviewer for improving earlier drafts of this paper, L. Ambrose for technical help, R. Douslin of Saskatchewan Environment and Resource Management for allowing Symphoricarpos collection, J. Thompson of the same organization for supplying Picea, the University of Regina for support, and NSERC for a postdoctoral fellowship to X. Li and a research grant to S. Wilson.

Growth of White Spruce, <em>Picea glauca</em>, Seedlings in Relation to Microenvironmental Conditions in a Forest-Prairie Ecotone of Southwestern Manitoba

“…Better moisture retention due to increased shading may explain significantly higher surface and profile soil moisture in aspen groves when compared to SI-S. Due to different degrees of shading, both soil surface and profile moisture were also slightly higher on the northern versus southern aspect of spruce islands. These results support the hypothesis of soil moisture retention which asserts that soil moisture is expected to be greater in areas of increased shading (Wilson and Kleb 1996;Li and Wilson 1998;Wilson 1998). The significantly higher soil surface moisture found in OP-G, and the lack of significant difference between open prairies and spruce islands or aspen groves in soil profile moisture are, however, difficult to explain.…”

“…In many prairie environments, shrubs are known to facilitate tree seedling establishment (Callaway 1995;Chambers 2001) by suppressing grass competition (Bird 1961;Werner and Harbeck 1982) and by providing protective conditions from abiotic forces such as fire (Coupland 1950;Bird 1961). The presence of previously established trees in open prairie not only reduces evaporative water loss from plants (Kellman and Kading 1992) but also increases soil moisture and nutrients (Wilson and Kleb 1996;Li and Wilson 1998;Wilson 1998). Furthermore, woody canopies modify the understory microclimate, including shading, interception of precipitation, litter fall (Vetaas 1992), reduced wind speed (Archibold et al 1996), lower soil temperature, and higher humidity (Carlson and Groot 1997).…”

Competitive effects of herbaceous vegetation on tree seedling emergence, growth and survival: Does gap size matter?

“…We suggest that the small gaps, which had a smaller soil volume and a large evaporative surface due to a poor connection with surrounding soil (a result of soil shrinkage under the unusual weather conditions), dried out more rapidly than the larger gaps, causing reduced seedling biomass. Intraspecific competition may also have reduced seedling growth more in the small and middle gaps than in the large gaps, as has been found for Picea (Li & Wilson 1998).…”

Secondary succession of mixed plantations established to rehabilitate abandoned pasture in the Peruvian Amazon

“…Therefore, both environment conditions and competition between plants must be considered in relation to secondary succession. The reproductive effort of a species significantly affected the areas it occupied and its mean diversity, and this correlated with either a facilitation or competition process (Tilman et al, 1996;Callaway and Walker, 1997;Holmgren et al, 1997;Tilman, 1997;Li and Wilson, 1998). I. brasiliensis has a tillering structure associated with its predominantly vegetative reproduction method, with sexual reproduction occurring only after exposure to fire (FAO-RAP, 2003).…”

“…To answer these questions, we surveyed initial vegetation recovery and classified undergrowth vegetation types to predict changes in several types of abandoned pasture and secondary forest. We investigated the influences and roles of vegetation types on secondary succession affected by anthropogenic activities, i.e., facilitation or competition processes relating to environmental changes (Holmgren et al, 1997;Li and Wilson, 1998), their interactions (Callaway and Walker, 1997), the allocation pattern of photosynthesis products of each indicated species (Kawano 1974), and biodiversity of each forest (Kobayashi 1984a). The aims of this study were to: (1) investigate dynamic processes of vegetation recovery in the context of soils found in abandoned agricultural and pasture lands, (2) determine changes in biomass composition and species diversity, and (3) define vegetation types in terms of facilitators or competitors in processes of secondary secession.…”