Shifting the Balance in a Lowland Mesic Forest: Maximizing the Native Acacia koa Seed Bank
Benjamin Duncan, Dr. Wendy Kuntz, Mike Ross, Jason Misaki, Kapi‘olani Community College, HI Division of Forestry and Wildlife
Working with the Hawai‘i Division of Forestry and Wildlife (DOFAW), we have built a partnership that allows Kapi‘olani Community College (KCC) students to work alongside community members restoring a two hectare exclosure in Wailupe Valley constructed by DOFAW in November 2013.
Our goals are to establish a transect grid, document current forest composition as a baseline for comparison prior to invasive species removal and establish removal comparison plots, to determine the most efficient restoration techniques that require minimal intervention. Removal of invasive species was initiated through the help of community partnerships. Creating opportunities for the community to volunteer is vital for the contingency of Wailupe and is becoming one of the projects’ focuses. These efforts are to restore native plant species and restore natural habitat for the endangered native bird, the ‘Elepaio (Chasiempis ibidis).
Recently, we’ve been using just hand-tools to remove invasive species in areas where there are potential native seed banks. We hypothesize that the removal of invasive species in plots adjacent to a large Acacia koa tree will reveal a fertile seed bank with potential for maximizing restoration of the natural habitat.
We targeted invasive species removal in a 10x10m plot adjacent to a large Acacia koa, suggesting a high potential of carrying a seed bank, and an adjoining plot with similar topography and species for comparison. We monitored and recorded everything within selected 10x10m plots (Figure 1). We monitored the plots by measuring the diameter at breast height (DBH) of everything above 1 meter and recorded the count of plants under 1 meter. We then calculated the basal area [BA=π(DBH/2)²] of the recorded flora and summed the total basal area for each species. Next, we removed invasive species that could be removed using hand-tools. Comparing the basal area of all species pre removal with post removal basal area helps us determine if hand pulling invasive species is an efficient reforestation technique for the exclosure.
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Methods
We targeted invasive species removal in a 10x10m plot adjacent to a large Acacia koa, suggesting a high potential of carrying a seed bank, and an adjoining plot with similar topography and species for comparison. We monitored and recorded everything within selected 10x10m plots (Figure 1). We monitored the plots by measuring the diameter at breast height (DBH) of everything above 1 meter and recorded the count of plants under 1 meter. We then calculated the basal area [BA=π(DBH/2)²] of the recorded flora and summed the total basal area for each species. Next, we removed invasive species that could be removed using hand-tools. Comparing the basal area of all species pre removal with post removal basal area helps us determine if hand pulling invasive species is an efficient reforestation technique for the exclosure.
In Figure 3, the pre monitor basal areas and the post monitor basal areas of all removal efforts are shown; which held very high efforts in native species removal. However, the return of native species was less than desirable. This is a strong contrasting data set compared to our new targeting method. In figure 4, there is a side by side comparison showing two 10x10m plots. The Control Plot was targeted for comparison due to its similar topography and ecology, and the Removal Plot, was targeted for having a potential seed bank. The figure shows the basal area documented plants within the plots prior to the removal effort. The section in braces of the Removal bar represents a large Araucaria columnaris, seen in Figure 2, that we are unable to remove with our current hand tool methods. This same data was collected after our removal of invasive species on November 17, 2018 in the Removal Plot and is represented in Figure 4. Figure 5 shows the reduced basal are of plot, excluding the A. columnaris, in contrast to our control. After allowing for new growth to develop, we did another post monitor of the Removal Plot, and discovered 622 sprouted A. koa seedlings at that time. This data is shown in contrast to our Control Plot, where no removal was conducted, and no new growth of A. koa seedlings were found.
In the Removal Plot, there is a large A. koa tree nearby and therefore a high probability of revealing a seed bank that was dormant. The invasive species in this plot were removed by hand, resulting in a large increase of A. koa seed growth. Removal of invasive species has relieved pressure on natives, allowing the native species to benefit from more available resources, such as sunlight. There is no A. koa seed growth in our control plot, suggesting that the modeled methods of removal allow for a potentially reproducible model for holistic native forest rehabilitation. In addition, looking back to previous data, this has been the most significant return of natives species throughout the project and from various methods. The data from this plot supports our hypothesis that removing invasive species near existing native trees maximizes restoration efforts. In future studies, we will continue to target potential seed banks and document the maintenance required to reach a point in which intervention is no longer required.
Discussion
In the Removal Plot, there is a large A. koa tree nearby and therefore a high probability of revealing a seed bank that was dormant. The invasive species in this plot were removed by hand, resulting in a large increase of A. koa seed growth. Removal of invasive species has relieved pressure on natives, allowing the native species to benefit from more available resources, such as sunlight. There is no A. koa seed growth in our control plot, suggesting that the modeled methods of removal allow for a potentially reproducible model for holistic native forest rehabilitation. In addition, looking back to previous data, this has been the most significant return of natives species throughout the project and from various methods. The data from this plot supports our hypothesis that removing invasive species near existing native trees maximizes restoration efforts. In future studies, we will continue to target potential seed banks and document the maintenance required to reach a point in which intervention is no longer required.
