Vorsino, A.E., Fortini, L.B., Amidon, F.A., et al. (2014). Modeling Hawaiian Ecosystem Degradation due to Invasive Plants under Current and Future Climates. PLOS One, 9(5), 1-18. https://doi.org/10.1371/journal.pone.0095427

Summary

Invasive plants that modify ecosystems can harm native biodiversity and degrade important ecosystem services. These species, which are a subset of non-native species, are also likely to be influenced by climate change which could exacerbate impacts. To assess the vulnerability of native ecosystems and federally designated critical habitat in Hawaiʻi to these harmful invaders, the authors used species distribution models to project the current (2013) and future (2100) distribution of 17 particularly detrimental invasive plants across the main Hawaiian Islands. The climate change scenario used in the analysis was the 2080-2100 SRES A1B, which projects a moderately warmer and wetter future. By combining models for multiple invasive species, they projected likely hotspots of non-native species richness and diversity. They used dynamically downscaled projections from the Hawaiian Regional Climate Model, and used three different methodologies (MAXENT, Random Forest, and Gradient Boosting Model), as well as seven bioclimatic and topographic variables, to model species distributions over geographic space. They found that most of the 17 species increased in area under climate change, with higher elevations facing greater invasion risk in 2100.

Results

The area available for occupation by the 17 selected invasive plant species increased by ~11% overall, and by ~12% in federally designated critical habitat in 2100. Invasibility, a metric that includes invasive species richness and diversity, is predicted to increase in Hawaiʻi’s upper elevation areas by 2100. While the majority of invasive species increased in area under climate change, a few species decreased in suitable area at lower elevations.

Management Considerations

• Of the ~8,000 to 10,000 plant species introduced to Hawaiʻi, only about 90 are considered extremely harmful due to their ability to degrade entire ecosystems1. If resources are limited, consider prioritizing the control and prevention of these particularly harmful invaders.
• The distribution of many of the most harmful plant invaders is expected to increase in both area and elevation with climate change. Consider revisiting management goals and objectives as conditions change.
• Consider increasing monitoring efforts in upper elevation native ecosystems for invasive plant species that may be shifting upslope as the climate warms, especially in areas with large concentrations of invasive plant species at lower elevations.
• The quality of current and future projections relies on location data, which is limited for many invasive species. Consider recording both presence and absence location information for invasive species and in areas of both high and low conservation value for use in future modeling efforts.

Take Home Points

• Under increasing temperatures, both native and invasive plant species in Hawaiʻi are expected to shift to upper elevations to find temperature equivalent zones.
• Control of invasive species within and at the boundaries of upper elevation ecosystems will be critical in the coming decades to maintain ecosystem health and integrity.
• Invasive plant species may lose suitable habitat at lower elevations with climate change, though many of these low elevation areas are of marginal value for conservation.
• Given that many critical habitat areas are in high-elevation ecosystems that are vulnerable to invasive species shifts due to climate change, new designations of critical habitat should consider potential climate change impacts.