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  1. The influences of human and physical factors on species invasions have been extensively examined by ecologists across many regions. However, how habitat fragmentation per se may affect forest insect and disease invasion has not been well studied, especially the related patterns over regional or subcontinental scales. Here, using national survey data on forest pest richness and fragmentation data across United States forest ecosystems, we examine how forest fragmentation and edge types (neighboring land cover) may affect pest richness at the county level. Our results show that habitat fragmentation and edge types both affected pest richness. In general, specialist insects and pathogens were more sensitive to fragmentation and edge types than generalists, while pathogens were much less sensitive to fragmentation and edge types than insect pests. Most importantly, the developed land edge type contributed the most to the richness of nonnative insects and diseases, whether measured by the combination of all pest species or by separate guilds or species groups (i.e., generalists vs. specialists, insects vs. pathogens). This observation may largely reflect anthropogenic effects, including propagule pressure associated with human activities. These results shed new insights into the patterns of forest pest invasions, and it may have significant implications for forest restoration and management. 
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  2. Research Highlights: We demonstrate a macroscale framework combining an invasibility model with forest inventory data, and evaluate regional forest exposure to harmful invasive plants under different types of forest protection. Background and Objectives: Protected areas are a fundamental component of natural resource conservation. The exposure of protected forests to invasive plants can impede achievement of conservation goals, and the effectiveness of protection for limiting forest invasions is uncertain. We conducted a macroscale assessment of the exposure of protected and unprotected forests to harmful invasive plants in the eastern United States. Materials and Methods: Invasibility (the probability that a forest site has been invaded) was estimated for 82,506 inventory plots from site and landscape attributes. The invaded forest area was estimated by using the inventory sample design to scale up plot invasibility estimates to all forest area. We compared the invasibility and the invaded forest area of seven categories of protection with that of de facto protected (publicly owned) forest and unprotected forest in 13 ecological provinces. Results: We estimate approximately 51% of the total forest area has been exposed to harmful invasive plants, including 30% of the protected forest, 38% of the de facto protected forest, and 56% of the unprotected forest. Based on cumulative invasibility, the relative exposure of protection categories depended on the assumed invasibility threshold. Based on the invaded forest area, the five least-exposed protection categories were wilderness area (13% invaded), national park (18%), sustainable use (26%), nature reserve (31%), and de facto protected Federal land (36%). Of the total uninvaded forest area, only 15% was protected and 14% had de facto protection. Conclusions: Any protection is better than none, and public ownership alone is as effective as some types of formal protection. Since most of the remaining uninvaded forest area is unprotected, landscape-level management strategies will provide the most opportunities to conserve it. 
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