406 Island Biogeography in Figure 2, in which the western Pacific atoll islands are aligned along mean annual rainfall gradients in both the northern and southern hemispheres Horizontal within Ecosystem Gradients In addition to the atoll islands there are several other Pacificwide biomes A particularly important one is the upland rain forest on the volcanic islands of the tropical Pacific This forest is important for two primary reasons: it is still extant on many volcanic high islands as indigenous forest harboring most of the endemic species, and it performs the function as watershed cover in the mountainous interiors of these islands The volcanic high islands typically are small, isolated land fragments that protrude as mountainous terrain above the vast Pacific ocean surface Their interior upland forests likewise are fragments that belong to the same larger ecosystem or biome However, from archipelago to archipelago, these biome fragments are occupied by different sets of species due to their past biogeographic isolation Connecting these biome fragments horizontally across the ocean by a system of transects provides for a within-biome research design Here, the broad habitat features are kept uniform, while the indigenous biodiversity sets change from island to island This truly is a research approach to biodiversity, which Pielou (1979) defined as ‘‘geoecology,’’ the study of recurrence of similar communities in similar habitats, which are occupied by different sets of species The term geoecology is an abbreviation of geographical ecology in the conceptual sense used by MacArthur (1972), who contributed substantially to the foundation of island biogeography Vertical Between Ecosystem Gradients A functioning watershed cover is an essential resource component in all Pacific high islands From here, the fresh water flow begins to be regulated and then influences almost all lower lying island ecosystems, the freshwater wetlands, mangroves, estuaries, fish ponds, fringing reefs, the entire coastal zone, and agriculturally used lowland areas The ecosystem services of the upland forest watersheds have not been studied in the Pacific islands, in spite of the fact that they have been part of the traditional land-use system in the Pacific high islands, in Hawaii known as the ahupua‘a system This vertically arranged land-use system was recognized in the Hawaiian Islands as comprising four integrated management zones, ‘‘wao la‘au,’’ upland forest or wilderness area, to be left alone, ‘‘kula,’’ the more open foot hill region, ‘‘wao kanaka,’’ the agricultural zone in the lowlands, and ‘‘kahakai,’’ the coastal zone This vertically arranged multiecosystem human support system proved to be an optimal land-management scheme for the indigenous islanders in the past Vertically arranged transect sites, using the fresh water flow and hydrology as unifying parameter, may also prove to be a good organizing principle for interdisciplinary research focused on the function of biodiversity at the landscape level The PABITRA Initiative The acronym PABITRA refers to the Pacific-Asia Biodiversity Transect outlined on Figure 10 The transect system connects the high island archipelagoes with indigenous tropical rain forests still extant in their interior uplands They range Figure 10 The PABITRA (Pacific-Asia Biodiversity Transect) network as currently being initiated For more information see text