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Stream surveys in the Laupahoehoe Wet Forest Unit

September, 2007

Boris Poff and Daniel Neary outside the Laupahoehoe Experimental Unit.
Boris Poff and Daniel Neary outside the Laupahoehoe Experimental Unit.
In 2007, the Institute for Pacific Islands Forestry (IPIF) asked the Rocky Mountain Research Station's Southwest Watershed Science Team to help establish baseline data for a long-term research on the newly established Hawai'ian Experimental Tropical Forest. The Institute for Pacific Islands Forestry is part of the U.S. Forest Service Pacific Southwestern Research Station, and its scientists do research in the State of Hawai'i, the Territory of Guam, the Territory of American Samoa, the Commonwealth of the Northern Mariana Islands, the Republic of the Marshall Islands, the Federated States of Micronesia, and the Republic of Palau.

The Southwest Watershed Science Team's knowledge of watershed-related research was invaluable to IPIF as they set up a stream gauging system on the Hawai'ian Experimental Tropical Forest. Even though the Team primarily conducts research in Arizona, they could easily transfer their research experience to Hawai'i because of ecological commonalities between these States. Both Arizona and Hawai'i have volcanically derived soils and stream washes with flashy precipitation events that drive stream flow.

Map of the Hawai'i Experimental Tropical Forest.
Map of the Hawai'i Experimental Tropical Forest.


The Hawai'ian Experimental Tropical Forest

Aerial photo of the Laupahoehoe Wet Forest Unit.
Aerial photo of the Laupahoehoe Wet Forest Unit.
The Hawaii Experimental Tropical Forest established in 2007 as a center for long-term research and the transfer of knowledge about management of tropical forests. The Hawai'ian Experimental Tropical Forest is managed cooperatively between the State of Hawai'i Department of Land and Natural Resources, IPIF, and the Pacific Southwest Research Station. Research in the Experimental Forest focuses on tropical forestry, hydrology, conservation biology, invasive species control, native forest restoration and ecology, and sustainable commercial timber practices, along with education, training, outreach and preservation of cultural values.

The Experimental Forest is divided into two units: the Laupahoehoe Wet Forest Unit and the Puu Waawaa Dry Forest Unit. The Southwest Watershed Science Team worked with IPIF on the Laupahoehoe Unit, which is located on the windward side of the island and on the slopes of the Mauna Kea volcano.

The 5,000 ha Laupahoehoe Unit is located upslope of former sugarcane lands, and it contains timber plantations, degraded pastures, primary wet rainforest, and numerous streams. The Laupahoehoe unit contains five streams, of which only two are perennial and contain aquatic organisms. Average annual rainfall in the lower part of the Laupahoehoe Unit is about 420 cm and approximately 160-260 cm at the upper part.

Stream Surveys

Boris Poff (left) and Daniel Neary (right) conducting research on the Hawai'i Experimental Tropical Forest.
Boris Poff (left) and Daniel Neary (right) conducting research on the Hawai'i Experimental Tropical Forest.
In September 2007, Daniel Neary and Boris Poff with the Southwest Watershed Science Team surveyed 900 m of the 2 km reach of the Kaawalii Stream in the Experimental Forest. This was the first channel survey of the Kaawalii Stream and provided necessary information for establishing stream gauging stations. The surveys also provided baseline data of channel conditions for future research and provided ground-truth observations for the LiDAR survey.

Cross-sections were installed at randomly-selected locations on successive 100 m stream segments. The cross-sections were permanently marked, photo-documented, located with GPS coordinates, channel-typed using the Rosgen method, and measured for substrate composition using the pebble-count method. Also in the summer of 2007, the Carnegie Airborne Observatory LiDAR was flown over the Hawai'i Experimental Tropical Forest to help analyze vegetation and geomorphic characteristics of the area.

Key Findings

A key question of the Southwest Watershed Science Team was whether LiDAR data could be used in establishing a stream gauging network and determining other channel characteristics. Their experience showed them that LiDAR output is helpful in planning field work, determining access points, channel paths, major channel alterations, etc., but it cannot serve as a replacement for actual field work. On-the-ground surveys are still necessary for identifying geomorphic features of interest when establishing a stream gauge network. These features include substrate type and size range, channel type, and the degree of stream entrenchment.




Go to the Southwest Watershed Science Team home page.

Project Contact: 

Principal Investigators:
Boris Porr - Rocky Mountain Research Station
Gregory P. Asner - Stanford University