Browsing by Author "Jacobi, James"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    A landscape-based assessment of climate change vulnerability for all native plants.
    (2016-01-25) Fortini, Lucas; Price, Jonathan; Jacobi, James; Vorsino, Adam; Burgett, Jeff; Brinck, Kevin; Amidon, Fred; Miller, Steve; Gon III, Sam; Koob, Gregory; Paxton, Eben
    In Hawaiʽi and elsewhere, research efforts have focused on two main approaches to determine the potential impacts of climate change on individual species: estimating species vulnerabilities and projecting responses of species to expected changes. We integrated these approaches by defining vulnerability as the inability of species to exhibit any of the responses necessary for persistence under climate change (i.e., tolerate projected changes, endure in microrefugia, or migrate to new climate-compatible areas, but excluding evolutionary adaptation). To operationalize this response-based definition of species vulnerability within a landscape-based analysis, we used current and future climate envelopes for each species to define zones across the landscape: the toleration zone; the microrefugia zone; and the migration zone. Using these response zones we calculated a diverse set of factors related to habitat area, quality, and distribution for each species, including the amount of habitat protection and fragmentation and areas projected to be lost to sea-level rise. We then calculated the probabilities of each species exhibiting these responses using a Bayesian network model and determined the overall climate change vulnerability of each species by using a vulnerability index. As a first iteration of a response-based species vulnerability assessment (VA), our landscape-based analysis effectively integrates species-distribution models into a Bayesian network-based VA that can be updated with improved models and data for more refined analyses in the future. Our results show that the species most vulnerable to climate change also tend to be species of conservation concern due to non-climatic threats (e.g., competition and predation from invasive species, land-use change). Also, many of Hawaiʽi’s taxa that are most vulnerable to climate change share characteristics with species that in the past were found to be at risk of extinction due to non-climatic threats (e.g., archipelago endemism, single-island endemism). Of particular concern are the numerous species that have no compatible-climate areas remaining by the year 2100. Species primarily associated with dry forests have higher vulnerability scores than species from any other habitat type. When examined at taxonomic levels above species, low vulnerabilities are concentrated in families and genera of generalists (e.g., ferns or sedges) and typically associated with mid-elevation wet habitats. Our results replicate findings from other regions that link higher species vulnerability with decreasing range size. This species VA is possibly the largest in scope ever conducted in the United States with over 1000 species considered, 319 of which are listed as endangered or threatened under the U.S. Endangered Species Act, filling a critical knowledge gap for resource managers in the region. The information in this assessment can help prioritize species for special conservation actions, guide the management of conservation areas, inform the selection of research and monitoring priorities, and support adaptive management planning and implementation.
  • Thumbnail Image
    Item
    Local to landscape-level controls of water fluxes through Hawaiian forests: Effects of invasive animals and plants on soil infiltration capacity across substrate and moisture gradients
    (2020-05-19) Fortini, Lucas Berio; Leopold, Christina; Perkins, Kim; Chadwick, Oliver; Yelenik, Stephanie; Jacobi, James; Bishaw, Kai‘ena II; Gregg, Makani; Rosa, Sarah
    Given the potential effect of invasive plants and animals to water fluxes through forests, the invasive-driven degradation of native ecosystems is a topic of great concern for many downstream land and water managers. The infiltration rate determines the partitioning between runoff and infiltration into soil in Hawaiian forests and beyond. Thus, to explore the ecohydrological effects of plant and animal invasion in mesic and wet forests in Hawaii, we measured soil infiltration capacity in multiple fenced (i.e., ungulate-free)/unfenced and native/invaded forest sites along moisture and substrate age gradients across the islands of Hawai‘i and Kaua‘i. We also characterized forest composition and structure and soil characteristics at these sites to assess the direct and vegetation-mediated impacts of invasive species on infiltration capacity. Infiltration capacity is highly variable across forested sites and the wider landscape. Much of this variability is determined by a complex set of soil, vegetation, and disturbance factors that affect infiltration capacity at the immediate surrounding of measurement plots. Consequently, the effect of any given factor can be masked by variability in other factors. However, by controlling for variability in soil and vegetation conditions at a local plot level, we found that the presence of invasive species in forests has complex and sometimes non-intuitive effects on infiltration. Our final models showed that invasive ungulates negatively affect soil infiltration capacity consistently across the wide moisture and substrate age gradients considered. Additionally, because several soil characteristics known to be affected by ungulates were associated with local infiltration rates (e.g., soil organic matter, bare soil cover, soil depth), the long-term secondary effects of high ungulate densities in Hawaiian forests may be higher than effects observed in this study. These results provide clear evidence for land managers that ungulate control efforts likely improve ecohydrologic function to mesic and wet forest systems critical to protecting downstream and nearshore resources and maintaining groundwater recharge. Compared to ungulate effects, the effect of invasive plants on water infiltration capacity in Hawaiian forests appeared much more complex. In general, elements of forest structure including increased canopy, understory and floor cover, greater presence of large roots, and lower grass and bare soil covers were positively associated with water infiltration. Whether native or not, a plant species’ potential to alter infiltration rates in Hawaiian forests was likely to depend on its physiognomy and how it affects forest community structure. For instance, while the cover of native dominant tree ‘ōhi‘a, Metrosideros polymorpha, was found to be positively associated with infiltration capacity (perhaps as an indicator of overall forest integrity), invasive Himalayan ginger, Hedychium gardnerianum, was also positively correlated with infiltration capacity, possibly due to preferential flow channels created by the presence of large root mats. Few studies have conducted comprehensive integrated ecological and hydrological sampling in forests of high conservation value. While we show there are large benefits to understanding how conservation efforts may help shape water fluxes, we also found that the commonly used study design for infiltration studies used here and elsewhere (i.e., adjacent paired sites) could be modified to provide more accurate effects of invasion in future studies for ecosystems in Hawaii and beyond.
  • Thumbnail Image
    Item
    Survey of roadside alien plants in Hawai`i Volcanoes National Park and adjacent residential areas 2001-2005.
    (2016-01-25) Pratt, Linda; Bio, Keali`i; Jacobi, James
    The sides of all paved roads of Hawai`i Volcanoes National Park (HAVO) were surveyed on foot in 2001 to 2005, and the roadside presence of 240 target invasive and potentially invasive alien plant species was recorded in mile-long increments. Buffer zones 5–10 miles (8–16 km) long along Highway 11 on either side of the Kīlauea and Kahuku Units of the park, as well as Wright Road that passed by the disjunct `Ōla`a Tract Unit, were included in the survey. Highway 11 is the primary road through the park and a major island thoroughfare. Three residential subdivisions adjacent to the park were similarly surveyed in 0.5–1 mile (0.8–1.6 km) intervals in 2003, and data were analyzed separately. Two roads to the east and northeast were also surveyed, but data from these disjunct areas were analyzed separately from park roads. In total, 174 of the target alien species were observed along HAVO roads and buffers, exclusive of residential areas, and the mean number of target aliens per mile surveyed was 20.6. Highway 11 and its buffer zones had the highest mean number of target alien plants per mile (26.7) of all park roads, and the Mauna Loa Strip Road had the lowest mean (11.7). Segments of Highway 11 adjacent to HAVO and Wright Road next to `Ōla`a Tract had mean numbers of target alien per mile (24–47) higher than those of any internal road. Alien plant frequencies were summarized for each road in HAVO. Fifteen new records of vascular plants for HAVO were observed and collected along park roads. An additional 28 alien plant species not known from HAVO were observed along the buffer segments of Highway 11 adjacent to the park. Within the adjacent residential subdivisions, 65 target alien plant species were sighted along roadsides. At least 15 potentially invasive species not currently found within HAVO were observed along residential roads, and several other species found there have been previously eliminated from the park or controlled to remnant populations. Data collected from this survey can be used by the park and other landowners to help detect and manage invasive plant species that threaten the natural resources of their lands, and survey findings will inform managers of threats from alien species established along corridors beyond park boundaries. Recommendations were made for refining the list of incipient invasive plant species to search for near the park and for the repetition of periodic roadside weed surveys in the park.