Studies on the Rapidly Eroding Reef

Science Center Objects

This study focuses on assessing changes in vegetation cover and composition inside and outside a fenced exclosure within the USGS Ridge-to-Reef study area on the island of Moloka‘i. This information will be delivered to federal, state, and private land managers who are trying to determine best management practices to reduce erosion and sediment runoff from this dry habitat which has been heavily browsed by feral goats.

Kawela ridge, Moloka'i, Hawaii

Kawela ridge looking towards the ocean on the island of Moloka'i, Hawai‘i. 

Overview:

Plant cover plays a very important role in regulating the amount of surface erosion and ground water recharge that occurs within a watershed. To better understand these processes within the Kawela watershed, located on the dry, leeward side of the island of Moloka‘i, we are conducting vegetation research on four components:

  1. mapping current plant communities on the Kawela watershed;
  2. assessing root distribution and abundance relative to the mapped plant communities;
  3. monitoring changes in plant community composition and distribution throughout the Kawela watershed; and
  4. developing a plant community restoration plan for this watershed based on plant species range modeling.

This research is aimed at providing sound, comprehensive science to resource managers to help them develop landscape management strategies for the areas they are responsible for in the Hawaiian Islands. The results will provide information on baselines, status, and trends of Hawaiian ecosystems relative to impacts from land use change, invasive species impacts, and conservation management actions on the island of Moloka‘i.  The information will be delivered to federal, state, and private land managers who are trying to determine best management practices to reduce erosion and sediment runoff from this dry habitat which has been heavily browsed by feral goats and invaded by non-native plants. Principal land owners and data users include the U.S. Fish and Wildlife Service, National Park Service, Natural Resources Conservation Service, Hawaii Department of Land and Natural Resources, The Nature Conservancy of Hawaii, The East Molokai Watershed Partnership, Kamehameha Schools, and Kawela Plantations Homeowners Association.

Before and after photo of effectiveness of fencing

Vegetation changes inside and outside an exclusion fence over a 5 year period in the Kawela study area.

This project focuses on assessing changes in vegetation cover and composition inside and outside a fenced exclosure within the USGS Ridge-to-Reef study area on the island of Molokai. This information will be delivered to federal, state, and private land managers who are trying to determine best management practices to reduce erosion and sediment runoff from this dry habitat which has been heavily browsed by feral goats. Principal land owners and data users include the U.S. Fish and Wildlife Service, National Park Service, Natural Resources Conservation Service, Hawaii Department of Land and Natural Resources, The Nature Conservancy of Hawai‘i, The East Moloka‘i Watershed Partnership, Kamehameha Schools, and Kawela Plantations Homeowners Association.

Project Objectives: 

We are sampling the vegetation to measure changes in plant species composition and and community structure within two watershed cells within the Kawela study area. One of these cells is fenced to exclude ungulates (primarily feral goats and Axis deer), while the other plot is outside the fence and subject to continued browsing and grazing by these animals. Both plots are instrumented to monitor rainfall, surface flow, and erosion. It will be important to follow the revegetation of the area within the fence as compared to outside the fence, particularly since both of these sites have a dense array of instruments to monitor erosion.

Highlights and Key Findings: 

Vegetation monitoring has been conducted in sampling areas inside and outside the fenced exclosure every April from 2009 through 2014, as well as in December 2008, 2009, and 2012, to track vegetation change during the wet season (April sample) as well as the dry (December). When the area was first sampled at the end of the dry season in December 2008, total plant cover was less than 1%, both inside and outside the fence. In April 2009 plant cover inside the fence had increased to 26.9% and to 22.9* outside. However, the amount of vegetation changed dramatically in April 2011 when the vegetation in both areas increased to approximately 50% cover, in this case with more vegetation outside the fence than inside the fence. The dramatic increase in vegetation in both areas appears to coincide closely with the intensive goat control effort that was initiated in June 2009 and has continued to the present. In effect, both of the areas (inside and outside the fence) have been released from goat browsing pressure and the plants that were previously suppressed are not able to grow more abundantly. There are still some differences inside (no goats) versus outside (reduced, but still a few goats) the fence – some plant species are more favored by goats and, although they are now found outside the fence, those plants often have signs of occasional browsing.