Tree cover changes in māmane (Sophora chrysophylla) forests grazed by sheep and cattle.

Using aerial photographs taken in 1954, 1965, and 1975, percentage of tree cover was determined for three sections of the sheepand cattlegrazed mdmane (Sophora chrysophy lla) forest of Mauna Kea , Hawaii. In one section , the Ka'ohe Game Management Area, where grazing by sheep was judged light, tree cover increased slightly during the 21-yr period , and tree cover did not change significantly along an elevation gradient. This condition was probably the result of the predominance of naio (Myoporum sandwicense) trees, which are not as palatable as mdmane and, therefore, are less sensitive to browsing. In the Mauna Kea Forest Reserve, the most heavily sheep browsed of the three sections, a significant loss of tree cover was observed between 1965and 1975near tree line where feral sheep tended to concentrate their browsing. Of the three sections examined, Parker Ranch, which was grazed mainly by cattle, sustained the greatest loss of tree cover during the 21-yr period, reflecting the more destructive nature of cattle browsing as compared to sheep browsing. Increases of tree cover in areas relatively free of sheep within the Mauna Kea Forest Reserve indicated that habitat for the palila, an endangered bird that depends on the mdmane forest , will improve slowly after feral sheep are removed. AT MAUNA KEA ON THE ISLAND of Hawaii the mdmane (Sophora chrysophy lla) forest has been adversely affected by feral sheep (Ovis aries) and other herbivores for more than 150yr (Kramer 1971). Damage from sheep was so severe that an effort to eradicate them, begun in 1937 (Bryan 1937), was continued through 1949. As a result introduced and native herbaceous and woody vegetation became established and proliferated in many areas (Tomich 1969). At the same time, however, feral sheep became valued as a game species; consequently, the policy of eradication was replaced by sustained-yield game management in 1959 (Walker 1978). But in areas where the remaining sheep concentrated, especially near tree line, mdmane and other vegetation did not regenerate (Warner 1960), a condition prevalent even as recently 1 Manuscript accepted 30 December 1982. 2 Institu te of Pacific Islands Forestry, Pacific Southwest Forest and Range Experiment Station , Forest Service, U.S. Department of Agriculture , 1151 Punchbowl Street, Honolulu, Hawaii 96813. as 1980 (Scowcroft and Giffin, in press). Forest areas used by cattle (Bos taurus) for pasture also showed little evidence of successful mdmane regeneration. The continued decimation of the mdmane overstory-from the death of old trees and from the failure to regenerate-was a significant threat to the palila iPsittlrostra bailleui) , an endangered endemic Hawaiian bird restricted to the mdmane forest of Mauna Kea (Berger 1972). Palila depend on mdmane and, to a lesser extent, on naio trees (Myoporum sandwicense) for food and nest sites (van Riper 1980a). Their breeding season coincide s with the time of year when mdmane bear seed pods (van Riper 1980a). Palila were found most abundant and in highest densities near tree line (van Riper, Scott, and Woodside 1978). The birds probably were attracted to this area because it contained a high proportion of large mdmane trees capable of producing more food than smaller ones. If large trees are as necessary to the palila as these findings suggest, then death of such trees could further restrict the bird's acceptable habitat (van