Alien grass invasion and fire in the seasonal submontane zone of Hawaii

Author:

Hughes, Flint, Vitousek, Peter M., Tunison, Timothy.

Title:

Alien grass invasion and fire in the seasonal submontane zone of Hawaii

Periodical:

Ecology

Year:

1991

Volume:

72

Pages:

743-747

Subject:

Alien plants Alien plants ecology Fire ecology

Summary:

This document discusses how island ecosystems are susceptible to biological invasions of alien grasses and how 86 species of alien plants have colonized the Hawaiian islands that pose a serious threat to the Hawaiian communities and ecosystems. Tropical and subtropical grasses that now dominate extensive areas of dry and seasonally dry habitats in Hawaii, compete with native species. These grasses may also alter hydrological properties in the areas that they invade and may introduce or promote fire into areas where it was previously absent or rare. This alters the structure and functioning of the previously native-dominated ecosystems. This is because some of the alien species such as the Melinis minutiflora, Andropogon, and Schizachyrium, are capable of supplying a continuous bed of fine fuels needed to carry fire. In addition, while all three of these species are capable of recovering quickly and with increased vigor following a fire, the Andropogon and Schizachyrium are able to resprout and grow within 96 hours following a fire. Since most native species in Hawaii have little background with fire, they have few or no such mechanisms which, in turn, favor alien grasses over native species. While land clearing by humans initiates colonization by alien grasses in some areas around the world, grass invasion in Hawaii occurs without any direct human intervention. As a result, there is evidence that grass invasion already has altered fire frequency and extent within Hawaii Volcanoes National Park (HVNP), particularly in seasonal submontane climatic zone. Prior to the widespread of grass invasion, the area was an open woodland with an understory of shrubs and it is believed that native grasses were infrequent or non-existent. As a result, only nine fires were recorded in the seasonal submontane zone that burned less than 2.3 ha from 1920 - 1968. However, between 1969 and 1988, 32 fires burned over 7800 ha of the seasonal submontane zone. While these increases in fire were accompanied by an increase in volcanic and human activity, it is believed that the increase and extent of fires could not have occurred without the continuous cover of the invaded grass species. It is believed that not only do these grasses provide the fuel for the fires but it also burns at very high relative humidities (85-90%) throughout most of the year, and will also burn at high fuel moistures (20-25%). As a result, the effects of grass-fueled fires on species composition and structure in the seasonal submontane ecosystem with an emphasis on relative differences in postfire response of the vegetation as a means of evaluating the impact of the grass/fire cycle on a previously intact native ecosystem were examined by this author. In addition, short and longer term responses were measured to determine how long the successional patterns seen immediately after fire can persist and to document the immediate impacts of fire.

Label:

Botany

URL:

http://cletus.uhh.hawaii.edu:2074/10.2307/2937215

Date:

1991

Collection:

Periodicals