Fossil Evidence for a Diverse Biota from Kaua'i and Its Transformation since Human Arrival

Abstract

Abstract. Coring and excavations in a large sinkiiole and cave system formed in an eolianite deposit on tiie soutli coast of Kaua'i in tlie Hawaiian Islands reveal a fossil site with remarkable preservation and diversity of plant and animal remains. Radiocarbon dating and investigations of the sediments and their fossil contents, including diatoms, invertebrate shells, vertebrate bones, pollen, and plant macrofossils, provide a more complete picture of prehuman ecological conditions in the Hawaiian lowlands than has been previously available. The evidence confirms that a highly diverse prehuman landscape has been completely transformed, with the decline or extirpation of most native species and their replacement with introduced species.The stratigraphy documents many late Holocene extinctions, including previously undescribed species, and suggests that the pattern of extirpation for snails occurred in three temporal stages, corresponding to initial settlement, late prehistoric, and historic impacts. The site also records land-use changes of recent centuries, including evidence for deforestation, overgrazing, and soil erosion during the historic period, and biological invasion during both the Polynesian and historic periods. Human artifacts and midden materials demonstrate a high-density human presence near the site for the last four centuries. Earlier evidence for humans includes a bone of the prehistorically introduced Pacific rat (Rattus exulans) dating to 822 yr BP (calendar year [cal yr] AD 1039-1241).Vegetation at the site before human arrival consisted of a herbaceous component with strand plants and graminoids, and a woody component that included trees and shrubs now mostly restricted to a few higher, wetter, and less disturbed parts of the island. Efforts to restore lowland areas in the Hawaiian Islands must take into account the evidence from this study that the prehuman lowlands of dry leeward Kaua'i included plants and animals previously known only in wetter and cooler habitats. Many species may be restricted to high elevations today primarily because these remote locations have, by virtue of their difficult topography and climate, resisted most human-induced changes more effectively than the coastal lowlands.

Natural history, biogeography, and endangerment of Hawaiian dry forest trees

“…Paleo-ecological studies have long established that the most severe change since human arrival to the Hawaiian Islands occurred in the lowlands because these areas were favorable for human habitation and land-use such as agriculture (Kirch 1985;Athens and Ward 1993;Athens 1997;Burney and Burney 2003). One example is the near-complete destruction of Pritchardia palm forests that fossil pollen and seed evidence have shown were once widespread but is now extremely rare (Athens et al 1992(Athens et al , 2002(Athens et al , 1997Athens and Ward 1993;Hotchkiss and Juvik 1999;Burney et al 2001).…”

Detecting the initial impact of humans and introduced species on island environments in Remote Oceania using palaeoecology

“…The lag is difficult to reconcile with immediate human impacts that are usually detected following colonization on other Pacific islands, and where there is close agreement between archaeological and palaeoecological chronologies for initial colonization (e.g. Burney et al 2001;Fall 2005;Kennett et al 2006). It seems implausible that people could persist on the small island of Mangaia for 1,500 years and leave no archaeological evidence.…”

“…AD in Core C1T2, without the presence of multiple proxies for human presence including plant cultigen and weed pollen, could be interpreted as early Polynesian impact on the basis of a small spike in charcoal and disturbance fern taxa. Increasingly, in well-dated multi-proxy studies, initial signatures of human contact, agriculture, and exotic introductions are showing that the many facets of initial human impacts actually occur concurrently and immediately after arrival (Burney et al 2001;Hunt and Lipo 2006;Kennett et al 2006;Wilmshurst et al 2008). …”

“…Burney et al 2001;Athens et al 2002;Wilmshurst et al 2008). These studies have focussed on detecting initial human impacts from a variety of deposits that would have been considered unsuitable for palaeoecological studies in the past, for example small coastal swamps, many of which are now drained and pasture covered.…”

Rattus exulans and the catastrophic disappearance of Hawai’i’s native lowland forest

“…In considering the cause of forest loss, certainly some attention must be given to the possible role of the Polynesian-introduced Pacific rat, R. exulans. 3 It is known from paleontological studies that rats definitely were not in Hawai'i prior to the advent of humans (Athens et al 2002;Burney et al 2001;James et al 1987). It is also known from the dating of rat bones excavated in sinkholes on the 'Ewa Plain that rats were likely present there before humans began living on the 'Ewa Plain.…”