The final report states that for the more than 100,000 plant species worldwide thought to be at risk of extinction, a lack of suitable habitat is the major barrier to their recovery. The two primary conservation actions for threatened, endangered, and at-risk plant species (TER-S) are to restore suitable habitat areas so that extant populations can expand and to reintroduce individuals to restored or protected areas.
Reintroduction is an expensive and slow effort, but, is often essential when population sizes are very low or there are other barriers to dispersal among suitable habitats. The success rates of reintroduction projects are variable, and low success is often due to a lack of suitable habitat, the very cause of decline. This demonstration addresses a major challenge to reintroduction success -- finding suitable habitats in fragmented and degraded landscapes.
The researchers for this project used three tasks to demonstrate how their Habitat Suitability Model (HSM) technology can inform Threatened, Endangered, and At-Risk Plant Species (TER-S) reintroduction programs to increase plant performance and survival across US Department of Defense (DoD) installations:
Overcoming barriers to plant establishment in dryland environments is especially critical for TER-S management on DoD installations. The DoD spends over $10 million annually on environmental programs in Hawaii to protect TER-S and associated critical habitat; therefore, technology to increase the success of TER-S planting programs in dryland ecosystems in general, and Hawaiian dryland ecosystems in particular, can positively affect the outcome of TER-S management for the DoD. This technology also can enhance the DoD’s training capability by improving the quality of protected areas and planning training activities in lower quality habitat.
The HSM technology identifies habitat suitability based on topography using digital elevation models (DEM) made from high resolution airborne LiDAR data. The DEM is used to define areas of suitable topography for plant reintroduction by developing two criteria based on the landscape’s capacity to reduce water stress. The criteria are that an area is protected from the prevailing wind by a topographic feature (leeward protection); and is in a topographic depression (descending topography). These areas are shown to be less stressful to plants and to have higher resource availability. The criteria are combined to develop a mapped HSM for outplanting with three suitability classes: no criteria met (Low Suitability – LS); one criterion met (Moderate Suitability); and two criteria met (High Suitability – HS).
Overall, the researchers produced a method for others to implement HSMs into landscape planning for TER-S conservation. Based on their findings in this demonstration, this method is likely to have the greatest impact in regions with fairly low annual precipitation around 300-600 mm, similar to PTA, Vandenberg Airforce Base (VBG), and the Santa Monica Mountains National Recreation Area (SMMNRA) (but not PWW) and in areas with high wind speeds, similar to PTA and VBG.
The researchers developed topographic models of habitat suitability for plant restoration on the Island of Hawaii in a 49,000 ha military training area (PTA) and a state forest reserve (PWW), and in Southern California at VBG and SMMNRA. They used LiDAR data from The Carnegie Airborne Observatory to produce a DEM for PTA, then used the DEM to define areas of suitable topography for plant reintroduction by developing two criteria based on the landscape’s capacity to reduce water stress. The criteria were combined to develop a mapped HSM for outplanting with three suitability classes: no criteria met (LS); one criterion met (Moderate Suitability); and two criteria met (HS). Their demonstration validated the utility of the HSM to guide reintroduction efforts at PTA and demonstrated the use of this technology for TER-S restoration planning at other DoD installations.
Implementation of the HSM is straightforward and simple. During this demonstration, the researchers developed a user-friendly Geographic Information System (GIS) Toolbox that is available for others to use. They developed guides to assist users with creating the HSM for a site of interest. Implementation will be based on whether a DEM is available for the site or is cost-effective to acquire. Typical LiDAR datasets that map elevation with pixel sizes of five m or less are sufficient for mapping most topographic features. However, if very small features are of interest, then higher resolution data would be needed. Users in their workshop indicated a high level of interest in incorporating the HSM into future management plans, especially as LiDAR elevation data are becoming freely available for many regions. Their collaborators at PTA and PWW have already incorporated the HSM into their conservation plans for TER-S. The HSM is also easily combined with other data layers (roads, aspect, etc.) to facilitate selection of conservation areas.
Their demonstration results highlighted that the HSM was somewhat useful in designating high quality habitat at all sites, but it had the greatest impact in differentiating high quality and low quality sites in areas that were dry and windy, especially PTA and VBG. The HSM approach should be more effective in dry, windy sites than in wetter, less windy conditions. In addition, users should consider whether there may be species-specific responses to habitat suitability. The researchers found that numerous measures of growth and physiology were improved in HS habitats across all species. At PTA, there was a significant main effect of suitability across all species on four measures of leaf physiology; whereas only two species, Haplostachys haplostachya and Stenogyne angustifolia, showed increased growth and health in HS plots. At PWW, there was a significant main effect of Suitability across all species on six measures of leaf physiology; whereas three species, Haplostachys haplostachya, Colubrina oppositifolia, and Stenogyne angustifolia, showed lower water stress in HS plots and Euphorbia olowaluana had increased health ratings in HS plots. Thus, measures of physiology were improved in HS plots across all species, but certain species, especially H. haplostachya and S. angustifolia, showed more consistent positive responses to being planted in HS areas across both sites. Users should consider the potential responses of individual species when planning to incorporate habitat suitability into management and reintroduction plans.
To facilitate future outplanting projects for the native Hawaiian species that were studied, the researchers performed an extensive interview survey of regional managers and native plant growers to determine the best techniques for propagating each species (seed, cuttings, etc.). All propagation protocols were documented in their Hawaiian Native Plant Propagation Resource, available online. They also developed a standard method for evaluating plants for outplanting based on a health status rating of one to five as follows: (1) no foliage but living stem; (2) foliage less than 25% and damaged by pest or disease; (3) 25-60% foliage, foliage showing signs of stress; (4) 60-90% foliage and health, showing no sign of decline; and (5) greater than 90% foliage and extremely healthy with vigorous growth and no damage. Plants of health status class five were selected for outplanting, with a few plants of health status four included for species with fewer individuals.