The effects of temporally variable dispersal and landscape structure on invasive species spread

Abstract

Abstract. Many invasive species are too widespread to realistically eradicate. For such species, a viable management strategy is to slow the rate of spread. However, to be effective, this will require detailed spread data and an understanding of the influence of environmental conditions and landscape structure on invasion rates. We used a time series of remotely sensed distribution maps and a spatial simulation model to study spread of the invasive Lepidium latifolium (perennial pepperweed) in California's Sacramento-San Joaquin River Delta. L. latifolium is a noxious weed and exhibited rapid, explosive spread. Annual infested area and empirical dispersal kernels were derived from the remotely sensed distributions in order to assess the influence of weather conditions on spread and to parameterize the simulation model. Spread rates and dispersal distances were highest for nascent infestations and in years with wet springs. Simulations revealed that spread rates were more strongly influenced by the length of long-distance dispersal than by temporal variation in its likelihood. It is thus important to capture long-distance dispersal and the conditions that facilitate spread when collecting data to parameterize spread models. Additionally, management actions performed in high-spread years, targeting long-distance recruits, can effectively contain infestations. Corridors were relatively unimportant to spread rates; their effectiveness at enhancing rate of spread was limited by the species' dispersal ability and the time needed to travel through the corridor. In contrast, habitat abundance and shape surrounding the introduction site strongly influenced invasion dynamics. Satellite patches invading large areas of invasible habitat present especially high risk.

Spread Dynamics of Perennial Pepperweed (Lepidium latifolium) in Two Seasonal Wetland Areas

“…Small patches expanded at a greater rate compared with larger initial patches. This observation is consistent with other research on spread of perennial pepperweed (Andrew and Ustin 2010). Consequently, high priority should be given to controlling new satellite infestations.…”

“…In general, as vegetative cover and soil moisture increased, the likelihood of perennial pepperweed density increased, whereas increased perennial dicot and bare-ground cover was associated with a reduced pepperweed density. The benefit of increased soil moisture on perennial pepperweed spread has also been shown by Andrew and Ustin (2010). They found that increased spring precipitation was correlated with enhanced spread.…”

“…Blank and Young (1997) found a similar spread distance of approximately 1 m yr 21 , with values never exceeding 3 m yr 21 . In another study, Andrew and Ustin (2010) found perennial pepperweed spread to average 3 to 6 m yr 21 but found some plants invaded locations . 100 m from known infestations.…”

Direct and Indirect Interactions between Landscape Structure and Invasive or Overabundant Species

“…Connectivity may also vary with landscape composition (e.g., habitat availability, specific land uses that are permeable to a given species) in addition to configuration, given that these two metrics often covary. Connectivity measured as habitat availability, independent of the existence of corridors, predicted spread in perennial pepperweed (Lepalium latifolium) in the San Joaquin River Delta [22], and, in simulation models, the potential spread of the exotic biofuel crop, Miscanthus x giganteus [23].…”

Invasive plants in conservation linkages: a conceptual model that addresses an underappreciated conservation issue

“…Th ere will be diff erences in research goals and applicability of the conceptual model for a nascent versus an established invader (Brady et al 2009, Andrew andUstin 2010). For example, an established, widespread invasion can obscure the infl uence of diff erent matrix types, especially if the landscape is highly fragmented (Brady et al 2009).…”