‘Ōhi‘a lehua (Metrosideros polymorpha) overstory of the native (no pigs) forest plot.
Photo Credit: Jeannine Rossa
We collected plant growth form and species data at each foot along two to four 100-foot transects at four sites: fenced `ōhi`a, unfenced `ōhi`a, E. robusta, and C. macrocarpa. We also collected soil samples and recorded bird calls in each plot.
The native plots had much greater plant species richness than both non-native plots, and a higher Simpson's Diversity Index (SDI) than C. macrocarpa. We also found that native ʻolapa seedlings (Cheirodendron trigynum) were common in the understory of the C. macrocarpa plot. Nitrogen, pH, Phosphorus, and potash (Potassium) all differed between the plots. We couldnʻt tell the difference between the number or type of bird calls between plots.
Based on our results, it appears that non-native forests on Moloka`i provide less habitat for native plants and animals than native forests. Differences between native and non-native forest could also be affecting water storage. Our results also show hope for passive restoration of native forest.
Native forest plots had an obvious greater number of understory species (ferns and small shrubs), while non-native forest plots were dominated by large tree.
The native plots had a wide variety of plant growth forms and species richness in each plant growth form category, compared to non-native forests which were dominated by a tall overstory (large and medium trees), and a short understory (mostly ferns and scattered patches of small shrubs).
Relative Percentage of Native and Non-native Species in Each Forest Type
Fig 4.
There appeared to be an obvious difference in plant species diversity between the native (SDI: 0.76 with pigs, and 0.86 without pigs) and cypress forests (SDI: 0.63). Surprisingly, the Eucalyptus forest had almost identical species diversity to the native forest with pigs. This result was unexpected since there were so few species in the non-native plots: nine in each, compared to 22 and 18 in the native plots. However, SDI includes abundance, not just presence. In the Eucalyptus plot, there were 3 trees common in the understory, and that may have increased the SDI.
Eucalyptus overstory with sword fern Feral pig (Sus scrofa) in native forest
(Nephrolepis cordifolia) understory Photo Credit: (Center for Tropical
Photo Credit: Jeannine Rossa Agriculture UH)
Maps Created by M.Powell with assistance from P. Hosten
1. Study Sites: We selected four study sites: one near the Wailoku overlook in a stand of eucalyptus (E. robusta), one at the same elevation but with a Monterey cypress overstory, one near the Hanalilolilo Trail with a `ōhi`a lehua overstory outside the Kamakou fence, and one with a `ōhi`a lehua overstory within the fenced area of the Kamakou Preserve.
2. Transects: At each site, we selected non-biased starting points for four, 100-ft. (30.5 m) transects, eliminating cliff slopes or other terrain safety issues, stream channels, and road edges. Each transect ran North to South or East to West.
3. Plant Data: At every foot (0.3 m) of all transects, we measured litter depth and/or moss depth (inches) with a ruler, recorded plant growth forms present below and above each point, and identified plant species below and above each point. Plant growth forms were as follows: nonvascular (e.g. moss, liverworts, mushrooms), grass, small herbs growing near or on moss, ferns, including tree ferns, small shrub (<3 feet), medium shrub (3-5 feet tall), large shrub (6+ feet tall), small tree (seedlings to 6 feet tall), medium tree (6 feet to 20 feet), large tree (greater than 20 feet tall). We then calculated Simpsonʻs Diversity Index (SDI) for plant species at each location.
4. Soil Data: Collected approximately one cup of mineral soil from each transect. Soil was collected approximately 4 inches below the top of the mineral soil layer, using a small trowel, which was cleaned in between samples. Soil was analyzed using a “Rapitest” soil test kit; we tested each soil sample for pH, Nitrogen, Phosphorus and Potash (Potassium) levels, following directions provided by the kit.
5. Bird Data: Recorded bird calls in all plots on the same day, using an iPhone 5c.
a. Count number of distinct bird calls within a two minute time period.
b. Discuss findings among team members
c. Repeat step 6a and 6b
Collecting a cup of mineral soil from Eucalyptus Transect 4 inches below top mineral soil layer
Photo Credit: Jeannine Rossa
Measuring litter depth (inches) in Eucalyptus overstory
Photo Credit: Jeannine Rossa
Native undergrowth in native (no pigs) transect
Photo Credit: Jeannine Rossa
Based on the data collected, our hypothesis is supported. The native (ʻōhia overstory) and non-native forest (eucalyptus and cypress overstories) are not equal; there are differences in plant growth form, plant species diversity and soil characteristics.
Recording plant growth form and species Measuring litter depth in native
(with pigs) forest type in native (with pigs) forest
Photo Credit: Jeannine Rossa
Soil Characteristics
Native (with pigs) overstory
Photo Credit: Marion Powell
Through discovering the difference diversities between Native and Non-native plots, we hope that we can help make the community of Moloka’i aware of this issue, and become active in the process of saving our native forests.
Decreasing the area of non-native forests on Moloka’i (can also be applied to the other islands) will have significant beneficial impacts through the “Mountain to Ocean” (Mauka to Makai) thinking. There are multiple ways that we can combat the threat that non-native forests present. We can plant native trees where the non-native species were previously (active restoration), allow the native species to spread naturally (passive restoration) such as they have already begun to do in the Cypress and Eucalyptus plots, or we can combine both restoration processes (active and passive) as with TNC’s management in their fenced section of the preserve where our native forest without pigs plot is located.
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Acknowledgements:
Mentor: Jeannine Rossa, MS (Ecology), UH Maui-Moloka‘i.
Kōkua: Stephanie Dunbar-Co, PhD (Botany), The Nature Conservancy; Paul Hosten, PhD (Plant Ecology), U.S. National Park Service, Kalaupapa National Park; Eric Brown, PhD (Marine Science), U.S. National Park Service, Kalaupapa National Park; Joseph Latsha, BS (Botany); Arleone Dibben-Young.