Spatiotemporal Patterns and Mechanisms of Chinese Tallowtree (Triadica sebifera) Spread along Edge Habitat in a Coastal Landscape, Mississippi, USA

Abstract

Chinese tallowtree [Triadica sebifera (L.) Small] has reached unprecedented prevalence in coastal landscapes in the Gulf of Mexico, especially along edge habitat with low competition and abundant resource (e.g., light) availability. This study investigated the spatiotemporal patterns and mechanisms of T. sebifera spread along roadways and fire lines. Triadica sebifera individuals and landscape and community features were surveyed in equally spaced, spatially mapped plots. All T. sebifera individuals were felled to determine tree age and status (seed trees or non-seed bearing trees), and T. sebifera seed and seedling (≤2 yr old) densities and community and landscape features (over- and understory conditions, distance to seed trees) were measured. A zero-inflated negative binomial model was used to evaluate factors affecting T. sebifera seed dispersal and seedling recruitment contributing to the observed spatiotemporal patterns. Introduced into the Grand Bay National Wildlife Refuge around 30 yr ago, T. sebifera trees distribute in clustered patterns along roadways and fire lines and exhibit an exponential growth in density. High T. sebifera seed and seedling densities mainly occurred in sites that are ≤250 m from seed trees or have sparse overstory and high understory grass/herb coverage. With respect to the avian seed dispersal mechanism, the spatiotemporal patterns of T. sebifera spread along roadways and fire lines could be simply characterized by using landscape and community features that influence avian behaviors, including distance to seed trees, overstory tree density, and ground grass/herb coverage.

Effects of Prescribed Fire, Site Factors, and Seed Sources on the Spread of Invasive Triadica sebifera in a Fire-Managed Coastal Landscape in Southeastern Mississippi, USA

“…The strong clustered pattern of tallow spread along habitat edges suggests that tallow spread is mostly based on short-distance dispersal, for few or no tallow clusters were found along the roadways and fire breaks in the east and southeast parts and tallow colonization along habitat edges without seed trees is notably slow (Figure 3; Figure 4). Similar spatiotemporal spread patterns along habitat edges were observed in the Grand Bay National Wildlife Refuge, where prescribed fire was not used as an active management tool [36]. As for tallow spread along habitat edges, a conservative estimate for effective seed dispersal distance by birds might be approximately 250-300 m in the Gulf of Mexico coastal landscape, dominated by longleaf pine ecosystems and pine savannas ( Figure 3C) [7,51,53].…”

“…Of all factors contributing to tallow Using age data collected from rectangular plots (80 plots along the earlier invaded road and 64 plots along the recently invaded road), age distribution and cumulative density (number/ha) of tallow trees were plotted to visualize tallow colonization at microscales (plot) ( Figure 4). Taking the count number of tallow seedlings ≤2 years old in each plot as the response variable, and the measured overstory and understory condition, distance to the nearest seed trees, and time since last fire as the predictor variables, the mixture zero-inflated negative binominal models (ZINB) were used to evaluate potential factors contributing to tallow colonization [36]. The ZINB count and binary (logit) regression models aim to predict the mean number of tallow seedlings ≤2 years and the probability of having no tallow seedlings ≤2 years within a rectangular plot of 10 × 3 m 2 , respectively, with respect to a subset of selected predictor variables using the maximum likelihood method ( Table 1).…”

“…For many invasive species, especially tallow, current condition and dynamics are primarily the effect of a sequence of disturbance events varying by landscape/ecosystem. Landscape metrics and ecosystem features mostly serve as predisposing factors indirectly affecting seed dispersal by regulating avian-vegetation relationships [36]. To date, we have not noted landscape-level studies on tallow invasion history following long-term disturbances, especially on landscapes where prescribed fire has been applied to restore the declining pine savanna and coastal prairies and bogs.…”