COMPARATIVE ECOLOGY OF THE INVASIVE RUBUS PHOENICOLASIUS AND THE NATIVE RUBUS ARGUTUS

Abstract

Invasive species are one of the most significant factors in human influenced global change. Management actions that prevent the spread and impacts of invasive species require knowledge of their ecological characteristics. The characteristics of the invasive wine raspberry (Rubus phoenicolasius Maxim.) and the native sawtooth blackberry (Rubus argutus Link) were examined in two forest habitats on the Maryland Coastal Plain. The invasive had greater negative effects on a common herbaceous plant (Duchesnea indica Andr. Focke) than the native. The invasive, R. phoenicolasius had higher leaf nitrogen concentrations (Nleaf), greater specific leaf areas (SLA) and higher maximal rates of photosynthesis (Amax) for a given dark respiration rate (Rd) than R. argutus. R. phoenicolasius depended less upon pollinators for fruit development and had higher fruiting rates with more seeds per fruit than the native species. In addition, seeds of R. phoenicolasius had higher germination rates. Survival of invasive seedlings was negatively affected by leaf litter additions, but seedling growth was not negatively influenced by shading. R. phoenicolasius seedlings grown in a greenhouse and inoculated with arbuscular mycorrhizal fungi produced less biomass than seedlings that were not inoculated. The distribution of R. phoenicolasius may be affected by leaf litter, but presence of AMF is probably not necessary for seedling success. A three year demographic study showed that both species were negatively impacted by drought, but the invasive recovered faster than the native species in the higher light forest.

Overall, results of these studies indicate that the invasive R. phoenicolasius was more likely to competitively exclude understory herbs which can coexist with the native R. argutus. The ability of R. phoenicolasius to adapt physiologically to different light levels helps explain its ability to form dense populations under varying environmental conditions. The combination of high fruit production, plasticity and lower mortality in high light habitats is in agreement with previous studies on invasive species. The combined characteristics demonstrated by R. phoenicolasius allow this invader to spread, expand and persist in mid-successional forests in the Coastal Plain of Maryland.