Landscape-level determinants of the spread and impact of invasive grasses in protected areas

Ecosystem variables importance in the presence and abundance of a globally invasive fish

Changes in physical habitat that are associated with anthropogenic disturbances facilitate the establishment and expansion of non-native species in receiving environments. Here, we evaluated the relative importance of ecosystem variables for the presence and abundance of the invasive fish Poecilia reticulata in Brazil. We collected fish species and assessed environmental variables through an established physical habitat protocol in 220 stream sites located in southeastern and midwestern Brazil. A total of 14,816 P. reticulata individuals were collected in 43 stream sites, and 258 variables that describe the physical characteristics of streams were assessed, including measures of channel morphology, substrate size and type, habitat complexity and cover, riparian vegetation cover and structure, and human influence. Dimensionality reduction methods were employed to limit redundancy, resulting in a smaller set of the most relevant environmental variables. Subsequently, we used random forest models to assess the relative importance of these variables in determining the presence and abundance of P. reticulata. The presence of this invasive fish was primarily explained by human disturbance variables related to urbanization (total impact, pavement, artificial structure areal cover, riparian canopy cover, electrical conductivity, mean thalweg depth, and sand), whereas channel morphology (mean bank full height) and fish cover variables (natural fish cover, and aquatic macrophyte areal cover) were important predictors of its abundance. Identifying which ecosystem variables are favorable to the establishment of non-native species is an important step in preventing future biological invasions, as well as managing those that already occur.

Effects of surrounding landscape on the performance of Solidago canadensis L. and plant functional diversity on heavily invaded post-agricultural wastelands

High invasiveness and well-documented negative impact on biodiversity and ecosystem functioning make Solidago canadensis L. a species of global concern. Despite a good understanding of the driving factors of its invasions, it remains unclear how the surrounding landscape may shape invasion success of this species in human-transformed ecosystems. In our study, we investigated the impacts of different landscape features in the proximity of early successional wastelands on S. canadensis biomass allocation patterns. Further, we examined the relationships between the surrounding landscape, S. canadensis cover, and plant functional diversity, used as a supportive approach for the explanation of mechanisms underlying successful S. canadensis invasion. We found that increasing river net length had positive impacts on S. canadensis rhizome, stem, and total above ground biomass, but negative effects on leaf biomass, indicating that vegetative spread may perform the dominant role in shaping the competitiveness of this invader in riverine landscapes. A higher proportion of arable lands positively influenced S. canadensis above ground and flower biomass; thus promoting S. canadensis invasion in agricultural landscapes with the prominent role of habitat filtering in shaping vegetation structure. Concerning an increasing proportion of settlements, flower biomass was higher and leaf biomass was lower, thereby influencing S. canadensis reproductive potential, maximizing the odds for survival, and indicating high adaptability to exist in an urban landscape. We demonstrated high context-dependency of relationships between functional diversity components and surrounding landscape, strongly influenced by S. canadensis cover, while the effects of surrounding landscape composition per se were of lower importance. Investigating the relationships between the surrounding landscape, invasive species performance, and plant functional diversity, may constitute a powerful tool for the monitoring, controlling, and predicting of invasion progress, as well as the assessment of ecosystem invasibility.

Response of Five Miscanthus sinensis Cultivars to Grasshopper Herbivory: Implications for Monitoring of Invasive Grasses in Protected Areas

Introduced grasses can aggressively expand their range and invade native habitats, including protected areas. Miscanthus sinensis is an introduced ornamental grass with 100+ cultivars of various invasive potential. Previous studies have demonstrated that the invasive potential of M. sinensis cultivars may be linked to seed viability, and some of the physiological traits, such as growth rate. Little is known, however, about whether these traits are associated with response of M. sinensis to insect herbivory, and whether plant tolerance and resistance to herbivory vary among its cultivars; which, in turn, can contribute to the invasive potential of some of M. sinensis cultivars. To address this issue, in our study we explored the response of five cultivars of M. sinensis to herbivory by Melanoplus grasshoppers. We demonstrated that plant responses varied among the cultivars during a season; all the cultivars, but “Zebrinus”, demonstrated a significant increase in plant tolerance by the end of the growing season regardless of the amount of sustained leaf damage. Different patterns in plant responses from “solid green” and “striped/spotted” varieties were recorded, with the lowest plant resistance detected for “Autumn Anthem” in the cage experiment. Our results have important applications for monitoring low-risk invaders in protected areas, as well as for biotic resistance of native communities to invasive grasses.

Forest Area Change in the Shifting Landscape Mosaic of the Continental United States from 2001 to 2016

The landscape context (i.e., anthropogenic setting) of forest change partly determines the social-ecological outcomes of the change. Furthermore, forest change occurs within, is constrained by, and contributes to a dynamic landscape context. We illustrate how information about local landscape context can be incorporated into regional assessments of forest area change. We examined the status and change of forest area in the continental United States from 2001 to 2016, quantifying landscape context by using a landscape mosaic classification that describes the dominance and interface (i.e., juxtaposition) of developed and agriculture land in relation to forest and other land. The mosaic class changed for five percent of total land area and three percent of total forest area. The least stable classes were those comprising the developed interface. Forest loss rates were highest in developed-dominated landscapes, but the forest area in those landscapes increased by 18 percent as the expansion of developed landscapes assimilated more forest area than was lost from earlier developed landscapes. Conversely, forest loss rates were lowest in agriculture-dominated landscapes where there was a net loss of five percent of forest area, even as the area of those landscapes also increased. Exposure of all land to nearby forest removal, fire, and stress was highest in natural-dominated landscapes, while exposure to nearby increases in developed and agriculture land was highest in developed- and agriculture-dominated landscapes. We discuss applications of our approach for mapping, monitoring, and modeling landscape and land use change.