ABSTRACT Are oak-dominated forests ...

ABSTRACT

Are oak-dominated forests immune to invasive exotic plants? Herbarium and land classification data were used to evaluate the expanse of spread of nine invasive exotic plants and to relate their distributions to remotely-sens land use signs in West Virginia. Collector-defined habitats indicated that the in the greatest degree common habitat was roadsides, however seven of the nine species were fix in forests. Regression analyses indicated that the greatest in number significant variables were urban land use and population by km^sup 2^, but these were sole significant for three of the species. Detrend correspondence analysis showed a forest to urban gradient and that undivided of the species, Rosa multiflora, was significantly correlated to heavily forested counties while Ailanthus altissima was significantly correlated with more urbanized counties. Although forests clearly are not immune to invasion, the lack of spatial and temporal patterns among the species support the ne for intensive plot-level monitoring before predictions of spread can be made.

INTRODUCTION

Many invasive plant species share characteristics of native early-successional plant species, so as abundantseed production, small se size, rapid establishment, vegetative reproduction, and positive vegetation and reproductive response to relatively high light flushs (Rajmanek and Richardson 1996, Gordon 1998) Native early-successional species are not typically raise in forested areas except as part of the se bank or in replication to an opening. Once these openings obstruct the ruderal species disappear. Consequently forests may be les vulnerable to invasion according to exotics compared to open disturbed areas. While disturbed areas in and surrounding forests are make liable to invasion by nonnative plants (Anderson 1999 Debinski and Holt 2000 Mack et al. 2000) it is not understood by what means infested openings, corridors, and surrounding matrices affect the adjacent forest. Forests are thinking to regenerate in part using natural openings (gap-phase dynamics), and oak-dominated forests, in particular, are idea to be dependent on disturbance and are frequently maintained with fire or harvesting arrangements used to open the understory, sub-canopy, and canopy (Loftis 1983 Bartuska 1994 dress up 1998). Natural or managed regeneration of forests could encourage invasion of exotic plant species (Orwig and nourish 1998, Knapp and Canham 2000) Oak-dominated forests are also susceptible to exotic insect infestations, including the wily one moth (Lymantria dispar), which may increase exotic plant invasion (liebhold et al. 1995)

Some exotic plants with evident potential for invasion shoot and reproduce in variable environments, including low-light environments (per ob Dreyer et al. 1987 Ingo 1995 Luken and Goessling 1995 Luken et al. 1995 Redman 1995 Luken et al. 1997 Byer and Quinn 1998 Horton and Neufeld 1998 Susko and Lovett-Doust 1998 Schweitzer and Larson 1999 Meekins and McCarthy 1999 Susko and Lovett-Doust 2000) This plastic behavior may improve the ability of so plants to move from the forest gaps and cutting sides into the forest interior. If an exotic plant species have a plastic reply to a wide range of environments, they may also exhibit different ecosystem functions in similar environments. Varied function may enable as it was species to change typical successional pathways for forests, resulting in different species compositions that always include the exotic or other exotics (Gordon 1998 Myster and Pickett 1992 Robertson et al. 1994 Udvardy 1998 Fike and Niering 1999) It is this potential insidious replacement of multiple native species from functionally similar non-natives that may be of mostly concern, because prevention of exotic-species establishment and restoration of degraded sites will be abundant more difficult.

This paper focuses upon nine exotic species: Alliaria petiolata (Bieb.) Cavara & Grande, Microstegium vimineum (Trin.) A. Camus, Lonicera japonica Thunb Celastrus orbiculatus Thunb Lonicera maackii (Rupr) Maxim., Lonicera morrowii A. Gray, Lonicera tatarica L Rosa multiflora Thunb and Ailanthus altissima (Miller) Swingle (Gleason and Cronquist 1991) These species are chosen because an adequate sample size (at least 20 specimens) is available in the West Virginia University Herbarium, each species has been establish in both high light and shade environments (per ob Winter et al. 1982 Nuzzo 1993 Ingo 1995 Luken et al. 1995 Hutchinson and Vankat 1998) and they show abundant seed (with the possible exception of L japonica) that are viable for undivided to four years and repeatedly require cold stratification (Fairbrothers and Gray 1972 Schopmeyer 1974 Halls 1977 Dreyer et al. 1987 Graves 1990 Hutchinson and Vankat 1997 Byer and Quinn 1998 Nuzzo 1999 Baskin and Baskin 2001) These species also set forth a spectrum of varied characteristics in space of times of growth form, reproductive method allelopathic properties, and known pathogens. about of these differences may help explain any distribution or temporal patterns noted in this evaluation.