UNDERSTANDING AND MITIGATING THE EFFECTS OF A DOMINANT INVASIVE GRASS ON NATIVE HAWAIIAN DRY FOREST ECOSYSTEMS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: NRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 0192584
• Grant No.: 2002-35320-12220
• Proposal No.: 2002-00631
• Project Start Date: Sep 15, 2002
• Project End Date: Sep 14, 2006
• Grant Year: 2002
• Program Code: [51.9]- (N/A)

Recipient Organization
RESEARCH FOUNDATION OF SUNY
(N/A)
ALBANY,NY 12201

Performing Department
(N/A)

Non Technical Summary
Invasion by an exotic African bunchgrass (fountain grass Pennisetum setaceum) on the island of Hawaii has completely transformed a formerly extensive and diverse native dry forest ecosystem into a series of small, highly fragmented and degraded native forest remnants. Although the devastating effects wrought by fountain grass in the system are obvious, the fundamental underlying causal mechanisms and consequences of this invasion remain unclear. This research will investigate these underlying casual mechanisms through a series of complementary experiments and descriptive investigations. We will examine how fountain grass affects water movement within this ecosystem by exploiting distinct isotopic signatures from different storm systems to trace water acquisition and utilization patterns for fountain grass and native dry forest species. Because tropical dry forests in general and in Hawaii in particular are also among the most endangered and exploited ecosystems in the world, we will also investigate the mechanism(s) by which fountain grass limits native plant establishment and growth by manipulating fountain grass, available water, and available light separately and in concert. This research is designed to explicitly guide and facilitate management efforts that are urgently needed to control fountain grass and preserve and restore what remains of Hawaii's native dry forests before species are lost to extinction. This project examines how alien invasive fountain grass affects water movement within native Hawaiian dry forest ecosystems.

Animal Health Component

50%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	2300	1020	50%
213	2300	1070	50%

Knowledge Area
213 - Weeds Affecting Plants;

Subject Of Investigation
2300 - Weeds;

Field Of Science
1070 - Ecology; 1020 - Physiology;

Keywords

invasive species

exotic species

pennisetum ruppellii

tropical forests

hawaii

endangered species

water use

preservation

restoration

stable isotopes

forest ecosystems

forest ecology

weeds

weed control

plant physiology

water movement

plant growth

plant establishment

native plants

communities (ecology)

plant ecology

field studies

cooperative research

Goals / Objectives
Examine how alien invasive fountain grass affects water movement within native Hawaiian dry forest ecosystems. Investigate the mechanisms by which fountain grass limits native plant establishment and growth. Guide and facilitate management efforts to control fountain grass and preserve and restore Hawaii's native dry forest communities.

Project Methods
Distinct stable isotopic signatures from different storm systems will be exploited to trace water acquisition patterns for fountain grass and nine native dry forest species. Field experiments manipulating fountain grass, available water, and available light separately and in concert will be used to investigate the mechanisms by which fountain grass limits native plant establishment and growth. To guide and facilitate management and conservation efforts, this project will be conducted in close collaboration with the North Kona Dry Forest Working Group. This Working Group represents a consortium of government and non-government organizations, scientists, landowners, local citizens, and native Hawaiians dedicated to preserving and restoring Hawaii's native dry forest communities.

Progress 09/15/02 to 09/14/06

Outputs
Invasions by alien species may cause substantial ecological and economic damage as well as significantly change community composition and biodiversity and alter whole ecosystem processes. Our research investigated the underlying ecological and physiological causal mechanisms and consequences of whole-scale ecosystem invasion by a noxious, invasive alien grass (Pennisetum setaceum or fountain grass) into endangered native Hawaiian dry forests. We investigated two major questions: 1) Does fountain grass utilize different water resources than native dry forest species? And 2) What is the mechanism(s) by which fountain grass limits native plant establishment and growth, and how can this be mitigated or reversed? To address the first question, we collected soil samples and woody stem sections from a native canopy tree within control (unaltered, fountain grass present) and removal (fountain grass removed) plots and performed isotope analyses on the extracted the water within these samples. We also collected and compared photosynthetic gas exchange and water potential data between trees growing within these control and removal plots. To address the second question, we examined the effects of manipulating fountain grass and available water and light separately and in concert. The results of our experiments for the first question indicate that removal of fountain grass significantly increased the water status of native trees, and that they utilized 10 to 30% more surface water when fountain grass was removed relative to when it was present. The results of our experiments for the second question showed that both above and below-ground biomass and reproductive output decreased in native plants grown in the presence of fountain grass at low light levels relative to native plants grown in areas where fountain grass was removed. We conclude that successful native dry forest restoration in fountain grass invaded sites will in general require grass removal, shading, and introduction of targeted native species. Because native plant responses to restoration treatments are often highly species specific, the most effective treatment combinations for a given individual species will most likely depend on its specific morpho-physio-phenological characteristics.

Impacts
Impact The results of this research program have been extensively disseminated through numerous technical and lay-audience presentations and outreach programs. We have also played key leadership roles in facilitating and guiding the North Kona Dryland Forest Working Group's resource management, education, and outreach programs. To date this Working Group has outplanted over 10,000 plants from federally listed endangered species to common dry forest trees. In addition, while conducting this research program, we have trained one postdoctoral fellow and several interns and research technicians.

Publications

• Cabin, R. J. 2007. Science and restoration under a big, demon haunted tent: reply to Giardina et al. (2007). Restoration Ecology 15: 377-381.
• Cabin, R. J. 2007. Science-driven restoration: A square grid on a round earth? Restoration Ecology: 15:1-7.
• Sandquist, D. R. and S. Cordell. 2007. Functional diversity of carbon-gain, water-use, and leaf allocation traits in trees of a threatened lowland forest in Hawaii. American Journal of Botany 94:1459-1469
• Litton, C. M., D. R. Sandquist, and S. Cordell. 2006. Effects of non-native grass invasion on aboveground carbon pools and tree population structure in a tropical dry forest of Hawaii. Forest Ecology and Management 231:105-113.