The Longevity of Tree Species Effects on Soil Fertility and

Sustainability of Second-Rotation Tropical Tree Plantations

This National Science Foundation funded project is a Research at an Undergradute Institution program centered at the University of Hawaii at Hilo in the College of Agriculture, Forestry and Natural Resource Management.

Collaborators include Colorado State University, The USDA Forest Service Pacific Southwest Research Station and The University of California at Davis.

Colorado State Principle Investigator: Dan Binkley

Forest Service Principal Investigators: Robert F. Powers and Matt Busse

University of California at Davis Principal Investigator: Thais Winsome

Map of Hawaii

A "Bird's Eye View" of the Research Site

In many tropical countries vast areas of land formerly used for cash crop agriculture are being planted with fast-growing tropical trees. A perfect example is Hawaii where former sugar-cane lands are now being planted with Eucalyptus species; over 20,000 acres since 1995.

The research site is a 500 ac 20-year old Eucalyptus plantation located approximately 15 miles north of Hilo on the east side of the Big Island of Hawaii. The primary study species within the site are E. saligna, and Falcateria molucana, (formerly known as Albizia falcataria) a nitrogen fixing tree. The plantation was established in the late 70's as a biofuels experiment funded by the US Department of Energy.

The elevation of the site is approx. 1200 ft  and the soil type is volcanic ash laid down over pahoehoe lava beds.

Before the harvest

At the time the plantation was established, forest scientists from the USDA Forest Service Pacific Southwest Research Station setup small scale experimental plots. Aboveground growth and production and soil nutirent levels were periodically monitored over the next two decades by the forest service and Colorado State. The plantation thus became a perfect future site to study the sustainability of mutliple rotations.

This is due to the soil under the NFT Falcateria now containing several-fold greater nitrogen (N) availability levels then soil under the Eucalyptus trees. In contrast there is now a 30 to 50% greater phosphorus (P) availability under Eucalyptus as compared to Falcateria.

The primary experimental design of the project is to harvest the first rotation trees and establish the second rotation by switching the overstory tree species, ie plant Eucalyptus where Falcateria was and Falcateria where Eucalyptus was. Growth and productivity will then be monitored in relation to the changing soil nutrients of N and P. 

Other project objectives include fractation of P nutrient pools, changes in understory plant species composition and rhizosphere fauna and microbial biodiversity.

Just after the harvest, before replant

Thais Winsome in a field lecture with the FOR 202 class from UH Hilo, Fall 1999

Thais and students discuss the important role earthworms play in organic matter breakdown and soil enrichment

In addition to the scientific and resource management value of the project, this program represented a unique opportunity to use state-of-the-art ecologcal sciences as the cornerstone for a new curriculum in tropical forestry.

UH Hilo is primarily an undergraduate teaching institution that qualifies under Title III as a minority institution owing ot the high enrollment of students with native Hawaiian ancestry.

UH Hilo recently implemented the nations first "Certificate in Tropical Forestry". This NSF project has significantly contributed to the infrastructure of tropical forest education and research at UH Hilo.

Currently all project collaborators combine their field  research with teaching opportunites for both University and local K-12 students. Future opportunities will involve the College of Forestry at Oregon State as collaborative arrangements allow for exchange of students and faculty.