Disturbance Ecology, Geomorphology, and Plant Dynamics in Grass Invaded Sites, Hawai‘i Completed
The Keamuku Maneuver Area (KMA) is a 9,227 ha. unit of Army Pohakuloa Training Area (PTA) on Hawai‘i Island. The Army’s mission at KMA is threatened by erosional processes that could make parts of the training area too hazardous or too degraded for sustained use. These processes depend on vegetation dynamics and the nature of the soils underlying KMA. Knowledge of the training area was insufficient to give Army the guidance it needs to manage the unit, so we provided information on vegetative community types and extents across KMA as well as how the commonly found plant species respond to disturbance.
Overview:
The Keamuku Maneuver Area (KMA) is a 9,227 ha. unit of Army Pohakuloa Training Area (PTA) on Hawai‘i Island. The Army’s mission at KMA is threatened by erosional processes that could make parts of the training area too hazardous or too degraded for sustained use. These processes depend on vegetation dynamics and the nature of the soils underlying KMA. Our current knowledge of the training area is insufficient to give Army the guidance it needs to manage the unit. The following narratives describe the environmental science needed to support sustained use of the Keamuku Maneuver Area at Army Pohakuloa Training Area, Hawai‘i Island.
KMA landcover consists primarily of dry shrublands and grasslands of native and introduced plant species. Rainfall at KMA is infrequent, and the threat of wildfire is so high that live fire has been prohibited. The largest rainfalls occur at decadal frequencies, causing flash flooding and other rapid runoff events. In addition to native and introduced bird species, KMA is inhabited by large numbers of introduced ungulates (feral goats, feral sheep, mouflon, donkey), foraging by which causes chronic damage to vegetation, increasing susceptibility to erosion by wind and water. There are four ESA-listed plant species, with all known populations managed on hills (Pu‘u Papapa and Pu‘u Nohonaohae) that are protected from ungulate damage by fencing.
Usage of the KMA is ramping up and the tempo is expected to increase in coming years. The environment at KMA is vulnerable to wildfire and erosion. These processes lead to dust and deep gullies, both of which adversely impact sustained use of the training facility. Where gullies erode deeply into silt, vehicle maneuvers may become hazardous. Because of the fragile nature of vegetation cover, this kind of erosion can be accelerated by training.
This project was developed at the request of the Army, and is funded primarily by the Army. Because populations of ESA-listed plants are present, this project will also benefit US Fish and Wildlife Service. Research will be led by a team of three scientists: botanist Linda Pratt (Pacific Island Ecosystems Research Station, U.S. Geological Survey), geologist Jonathan Stock (Menlo Park Science Center, U.S. Geological Survey), and dryland forest and wildfire expert Susan Cordell (Institute of Pacific Island Forestry, U.S. Forest Service).
Highlights and Key Findings:
In the vegetation survey we found that six species (four exotic grasses, 1 native grass, and 1 native shrub) tend to make up a large percentage of the percent cover across the landscape, although these tend not to coexist with each other. We tried to reduce the dimensions of the vegetation cover data using principal components analysis, de-centered correspondence analysis, and principal coordinates analysis (a.k.a. multidimensional scaling) using a composition distance metric.
No method demonstrated clear clusters of species associations, but rather indicated that communities were driven by grass type, or grass type plus Dodonea viscosa shrub cover. That is to say, six species tended to dominate the vegetation signal, and as one lost dominance, another came into dominance. We also found that we could account for 96% of the percent cover with only 10 species.
Results from our disturbance experiment show that these six main vegetation types respond differently to disturbance, and that “habitat suitability” (which is driven by microtopography, mainly slope and aspect) alters this dynamic. One exotic grass, Cenchrus clandestinus (kikuyu grass), which is a rhizomatous C4 species, quickly gained vegetative cover in disturbed plots. In medium suitability plots, which have a slope of zero (i.e., they are flat), tended to collect more soil moisture and organic matter, and showed the greatest percent cover and regrowth after disturbance for this species. In one of five replicates, there was 100% cover of C. clandestinus less than 2 months post disturbance. High and Low suitability plots did not show this great of a response. For other species, however, high suitability plots seem to have the highest rates of regrowth.
- Overview
The Keamuku Maneuver Area (KMA) is a 9,227 ha. unit of Army Pohakuloa Training Area (PTA) on Hawai‘i Island. The Army’s mission at KMA is threatened by erosional processes that could make parts of the training area too hazardous or too degraded for sustained use. These processes depend on vegetation dynamics and the nature of the soils underlying KMA. Knowledge of the training area was insufficient to give Army the guidance it needs to manage the unit, so we provided information on vegetative community types and extents across KMA as well as how the commonly found plant species respond to disturbance.
Sources/Usage: Some content may have restrictions. View Media DetailsUSGS personnel collect data at a weather station at Keamuku Maneuver Area on Hawai‘i Island. Photo: J. Stock Overview:
The Keamuku Maneuver Area (KMA) is a 9,227 ha. unit of Army Pohakuloa Training Area (PTA) on Hawai‘i Island. The Army’s mission at KMA is threatened by erosional processes that could make parts of the training area too hazardous or too degraded for sustained use. These processes depend on vegetation dynamics and the nature of the soils underlying KMA. Our current knowledge of the training area is insufficient to give Army the guidance it needs to manage the unit. The following narratives describe the environmental science needed to support sustained use of the Keamuku Maneuver Area at Army Pohakuloa Training Area, Hawai‘i Island.
KMA landcover consists primarily of dry shrublands and grasslands of native and introduced plant species. Rainfall at KMA is infrequent, and the threat of wildfire is so high that live fire has been prohibited. The largest rainfalls occur at decadal frequencies, causing flash flooding and other rapid runoff events. In addition to native and introduced bird species, KMA is inhabited by large numbers of introduced ungulates (feral goats, feral sheep, mouflon, donkey), foraging by which causes chronic damage to vegetation, increasing susceptibility to erosion by wind and water. There are four ESA-listed plant species, with all known populations managed on hills (Pu‘u Papapa and Pu‘u Nohonaohae) that are protected from ungulate damage by fencing.
Usage of the KMA is ramping up and the tempo is expected to increase in coming years. The environment at KMA is vulnerable to wildfire and erosion. These processes lead to dust and deep gullies, both of which adversely impact sustained use of the training facility. Where gullies erode deeply into silt, vehicle maneuvers may become hazardous. Because of the fragile nature of vegetation cover, this kind of erosion can be accelerated by training.
This project was developed at the request of the Army, and is funded primarily by the Army. Because populations of ESA-listed plants are present, this project will also benefit US Fish and Wildlife Service. Research will be led by a team of three scientists: botanist Linda Pratt (Pacific Island Ecosystems Research Station, U.S. Geological Survey), geologist Jonathan Stock (Menlo Park Science Center, U.S. Geological Survey), and dryland forest and wildfire expert Susan Cordell (Institute of Pacific Island Forestry, U.S. Forest Service).
Sources/Usage: Some content may have restrictions. View Media DetailsMilitary missions underway at KMA. Photo: S. Yelenik. Highlights and Key Findings:
In the vegetation survey we found that six species (four exotic grasses, 1 native grass, and 1 native shrub) tend to make up a large percentage of the percent cover across the landscape, although these tend not to coexist with each other. We tried to reduce the dimensions of the vegetation cover data using principal components analysis, de-centered correspondence analysis, and principal coordinates analysis (a.k.a. multidimensional scaling) using a composition distance metric.
No method demonstrated clear clusters of species associations, but rather indicated that communities were driven by grass type, or grass type plus Dodonea viscosa shrub cover. That is to say, six species tended to dominate the vegetation signal, and as one lost dominance, another came into dominance. We also found that we could account for 96% of the percent cover with only 10 species.
Results from our disturbance experiment show that these six main vegetation types respond differently to disturbance, and that “habitat suitability” (which is driven by microtopography, mainly slope and aspect) alters this dynamic. One exotic grass, Cenchrus clandestinus (kikuyu grass), which is a rhizomatous C4 species, quickly gained vegetative cover in disturbed plots. In medium suitability plots, which have a slope of zero (i.e., they are flat), tended to collect more soil moisture and organic matter, and showed the greatest percent cover and regrowth after disturbance for this species. In one of five replicates, there was 100% cover of C. clandestinus less than 2 months post disturbance. High and Low suitability plots did not show this great of a response. For other species, however, high suitability plots seem to have the highest rates of regrowth.