Developing Planting Designs for Forest Restoration
We are testing different planting mixtures and densities to refine restoration efforts in the Hakalau Forest National Wildlife Refuge.
Overview:
The Hakalau Forest National Wildlife Refuge - Hakalau - on the Big Island of Hawaiʻi provides habitat for rare and endangered native forest birds and plants. Established in 1985 by the U.S. Fish and Wildlife Service - USFWS, Hakalau originally had 2000 hectares of degraded non-native pasture caused by tree clearing and grazing.
The USFWS Comprehensive Conservation Plan aims to restore and maintain native koa - Acacia koa - and ‘ōhi‘a - Metrosideros polymorpha - forests. Koa and ‘ōhi‘a forest refers to the two dominant forest canopy trees as well as native woody underbrush. Over 390,000 koa trees planted stretch in corridors from the intact forest at lower elevations, upwards into the former pasture areas. The hope is to create suitable, avian malaria-free habitat for forest birds, since disease spreading mosquitos do not tend to inhabit higher elevations due to cooler temps.
The problem is the native underbrush, which includes shrubs and fruiting trees, is not naturally renewing in the koa corridors. This leads to low diversity forests with limited food resources for birds. Since koa trees let in more light through the canopy than others, and increase soil nutrients by adding nitrogen, more pasture grass grows, stalling renewal of native underbrush.
To increase diversity, the USFWS transplants native underbrush species from nurseries into the koa forests. Some of the underbrush plants are old enough to reproduce abundant seed, but there continues to be a lack of natural renewal partly due to the dominant thick mats of exotic kikuyu pasture grass.
Work from our previous studies shows that an increase in seed rain via bird droppings combined with less grass increases the natural spread of native seedlings. Additionally, native woody plant species such as pilo - Coprosma rhyncocarpa - decrease grass growth underneath them by 30 percent within three years. Therefore, it is possible that planting underbrush species in higher densities may lead to lowered grass and higher seed renewal over time.
Objectives:
-
Test how planting density and diversity effects the following: resource levels -light, water-, invasive species abundance -exotic grass and blackberry vine-, and native plant growth and survival. We hypothesize that plots with higher diversity and/or density will have lower levels of available resources for invasive species, leading to an increase in native plants over time.
-
Test effects of pre-treatment soil turnover on invasive grass and blackberry abundance and native plant growth and survival. Soil turnover involves breaking up grass mats to temporarily reduce competition for native species. We predict that after two years there will be similar levels of invasive species in turnover plots, but that native plant survival will be greater.
-
Calculate the cost of different planting strategies and compare success in relation to monetary cost. We predict that soil turnover will lower costs due to less person time needed to plant an area.
We are testing different planting mixtures and densities to refine restoration efforts in the Hakalau Forest National Wildlife Refuge.
Overview:
The Hakalau Forest National Wildlife Refuge - Hakalau - on the Big Island of Hawaiʻi provides habitat for rare and endangered native forest birds and plants. Established in 1985 by the U.S. Fish and Wildlife Service - USFWS, Hakalau originally had 2000 hectares of degraded non-native pasture caused by tree clearing and grazing.
The USFWS Comprehensive Conservation Plan aims to restore and maintain native koa - Acacia koa - and ‘ōhi‘a - Metrosideros polymorpha - forests. Koa and ‘ōhi‘a forest refers to the two dominant forest canopy trees as well as native woody underbrush. Over 390,000 koa trees planted stretch in corridors from the intact forest at lower elevations, upwards into the former pasture areas. The hope is to create suitable, avian malaria-free habitat for forest birds, since disease spreading mosquitos do not tend to inhabit higher elevations due to cooler temps.
The problem is the native underbrush, which includes shrubs and fruiting trees, is not naturally renewing in the koa corridors. This leads to low diversity forests with limited food resources for birds. Since koa trees let in more light through the canopy than others, and increase soil nutrients by adding nitrogen, more pasture grass grows, stalling renewal of native underbrush.
To increase diversity, the USFWS transplants native underbrush species from nurseries into the koa forests. Some of the underbrush plants are old enough to reproduce abundant seed, but there continues to be a lack of natural renewal partly due to the dominant thick mats of exotic kikuyu pasture grass.
Work from our previous studies shows that an increase in seed rain via bird droppings combined with less grass increases the natural spread of native seedlings. Additionally, native woody plant species such as pilo - Coprosma rhyncocarpa - decrease grass growth underneath them by 30 percent within three years. Therefore, it is possible that planting underbrush species in higher densities may lead to lowered grass and higher seed renewal over time.
Objectives:
-
Test how planting density and diversity effects the following: resource levels -light, water-, invasive species abundance -exotic grass and blackberry vine-, and native plant growth and survival. We hypothesize that plots with higher diversity and/or density will have lower levels of available resources for invasive species, leading to an increase in native plants over time.
-
Test effects of pre-treatment soil turnover on invasive grass and blackberry abundance and native plant growth and survival. Soil turnover involves breaking up grass mats to temporarily reduce competition for native species. We predict that after two years there will be similar levels of invasive species in turnover plots, but that native plant survival will be greater.
-
Calculate the cost of different planting strategies and compare success in relation to monetary cost. We predict that soil turnover will lower costs due to less person time needed to plant an area.