Comparing the Difference in Plant Diversity and Soil Characteristics Between Native and Non-native Forests (Kamakou Preserve, Moloka‘i)
Authors: Marion Rose Powell and Cameryn Rae Kahalewai, Moloka‘i High School.
‘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.
ABSTRACT
‘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
- Species richness was much higher in the native forest plots than the non-native plots: 22 for native with pigs, 18 for the native no pigs, and 10 for cypress and 9 for eucalyptus.
- There was also a striking difference in the ratio of native to non-native species in the different plots. The fenced native without pigs (which is fenced) was 100% native species in comparison to the unfenced native forest with pigs which had 3 widespread, invasive understory species mixed with invasive natives species such as uluhe, the false staghorn fern (Dicronopteris linearis). This is not surprising since pigs are known to spread weeds (TNC 2011).
- The non-native forests were dominated by non-natives; however, native ferns and moss were common on downed logs and small areas without deep litter. Average litter depth in the eucalyptus plot was 3.4 inches (8.6 cm), compared to 1.3 inches (3.3 cm) in the cypress plot, and only 0.5 inches (1.3 cm) in both native plots.
- An exciting find was the widespread presence of ʻolapa (Cheirodendron trigynum) in the understory of the cypress plot, including seedings. ʻOlapa was also present in the Eucalyptus plot, but much less abundant. ʻOlapa make berries, so they may be spread by birds eating them in the nearby unfenced native forest areas and then perching in the overstory. These results differ from Mascaro et al. (2008) on the Big Island, who found almost no native plant regeneration under a wide variety of non-native overstories.
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.
RESULTS: PLANTS
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
- Species richness was much higher in the native forest plots than the non-native plots: 22 for native with pigs, 18 for the native no pigs, and 10 for cypress and 9 for eucalyptus.
- There was also a striking difference in the ratio of native to non-native species in the different plots. The fenced native without pigs (which is fenced) was 100% native species in comparison to the unfenced native forest with pigs which had 3 widespread, invasive understory species mixed with invasive natives species such as uluhe, the false staghorn fern (Dicronopteris linearis). This is not surprising since pigs are known to spread weeds (TNC 2011).
- The non-native forests were dominated by non-natives; however, native ferns and moss were common on downed logs and small areas without deep litter. Average litter depth in the eucalyptus plot was 3.4 inches (8.6 cm), compared to 1.3 inches (3.3 cm) in the cypress plot, and only 0.5 inches (1.3 cm) in both native plots.
- An exciting find was the widespread presence of ʻolapa (Cheirodendron trigynum) in the understory of the cypress plot, including seedings. ʻOlapa was also present in the Eucalyptus plot, but much less abundant. ʻOlapa make berries, so they may be spread by birds eating them in the nearby unfenced native forest areas and then perching in the overstory. These results differ from Mascaro et al. (2008) on the Big Island, who found almost no native plant regeneration under a wide variety of non-native overstories.
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)
- Currently, only 15% of native forests remain on the island of Molokai (Sarhangi 2017); and about 25% of the state of Hawaii’s native flora, 90% of which is endemic, is listed as threatened or endangered (Harrington 1997)
- Kamakou Preserve, where this this study is located, is the primary groundwater recharge and surface water source area feeding the Moloka‘i agricultural irrigation system, as well as the main source of freshwater for the island of Moloka‘i (TNC 2011). The annual rainfall in this area averages 2607.2 mm (Giambelluca et al. 2013).
- The 'ōhi‘a tree is the primary overstory in the preserve. Studies on the Island of Hawai‘i reported that the 'ōhi‘a had lower evapotranspiration rates than strawberry guava (Psidium cattleianum) (Giambelluca et al., 2008); lower sap flux density (sap movement affected by the amount of water going into the tree from the ground) than Eucalyptus saligna and ash (Fraxinus uhdei) (Kagawa et al., 2009); and greater canopy water storage capacity and more annual cloud water interception than strawberry guava (Takahashi et al. 2001).
- The Kamakou Preserve is also home to 44 rare plant taxa, 23 of which are listed as endangered, and a portion of the preserve is Critical Habitat for the endangered Blackburn’s sphinx moth (Manduca blackburni) (TNC 2011).
- Significant impacts to our native vegetation have been the introduction of invasive animals, ranching, and alien plant introductions (DOFAW 2009).
- Eucalyptus spp. are the primary overstory tree in non-native plots of Molokai’s Kamakou Forest; these non-native (and sometimes invasive) tree plantings began in 1901, organized by George Munro, the land manager of Moloka‘i Ranch, to hasten watershed protection.
- Passive and Active Restoration are key restorational processes. The Nature Conservancy is doing what it can to prevent the advancement of weeds and hooved animals with fencing, monitoring systems, community outreach, fundraising, and involvement with island-wide fire and invasive species efforts (TNC 2011).
BACKGROUND
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)
- Currently, only 15% of native forests remain on the island of Molokai (Sarhangi 2017); and about 25% of the state of Hawaii’s native flora, 90% of which is endemic, is listed as threatened or endangered (Harrington 1997)
- Kamakou Preserve, where this this study is located, is the primary groundwater recharge and surface water source area feeding the Moloka‘i agricultural irrigation system, as well as the main source of freshwater for the island of Moloka‘i (TNC 2011). The annual rainfall in this area averages 2607.2 mm (Giambelluca et al. 2013).
- The 'ōhi‘a tree is the primary overstory in the preserve. Studies on the Island of Hawai‘i reported that the 'ōhi‘a had lower evapotranspiration rates than strawberry guava (Psidium cattleianum) (Giambelluca et al., 2008); lower sap flux density (sap movement affected by the amount of water going into the tree from the ground) than Eucalyptus saligna and ash (Fraxinus uhdei) (Kagawa et al., 2009); and greater canopy water storage capacity and more annual cloud water interception than strawberry guava (Takahashi et al. 2001).
- The Kamakou Preserve is also home to 44 rare plant taxa, 23 of which are listed as endangered, and a portion of the preserve is Critical Habitat for the endangered Blackburn’s sphinx moth (Manduca blackburni) (TNC 2011).
- Significant impacts to our native vegetation have been the introduction of invasive animals, ranching, and alien plant introductions (DOFAW 2009).
- Eucalyptus spp. are the primary overstory tree in non-native plots of Molokai’s Kamakou Forest; these non-native (and sometimes invasive) tree plantings began in 1901, organized by George Munro, the land manager of Moloka‘i Ranch, to hasten watershed protection.
- Passive and Active Restoration are key restorational processes. The Nature Conservancy is doing what it can to prevent the advancement of weeds and hooved animals with fencing, monitoring systems, community outreach, fundraising, and involvement with island-wide fire and invasive species efforts (TNC 2011).
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
METHODS
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.
CONCLUSION
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
RESULTS: SOIL
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.
REFERENCES
Anonymous, 1956. Report by the Hawaii Dept. of Agriculture to the Hawaii Board of Commissioners of Agriculture and Forestry, and Hawaii. Dept. of Agriculture and Conservation. N.p.: Pennsylvania State U, 1956. Print.
Giambelluca, T.W., Q. Chen, A.G. Frazier, J.P. Price, Y.-L. Chen, P.-S. Chu, J.K. Eischeid, and D.M. Delparte, 2013: Online Rainfall Atlas of Hawai‘i. Bull. Amer. Meteor. Soc. 94, 313-316, doi: 10.1175/BAMS-D-11-00228.1.
Harrington, Robin A., and John J. Ewel. 1997. Invasibility of tree plantations by native and non-indigenous plant species in Hawaii. Forest Ecology and Management, 99:153-162.
Giambelluca, T.W, Delay, J.K., Asner, G.P.,Martin, R.E., Nullet, M.A., Huang, M.,Mudd, R.G., and Takahashi, M., 2008. Stand structural control on evapotranspiration in native and invaded tropical Montane cloud forest in Hawai’i. American Geophysical Union, Fall Meeting 2008.
Hawai‘i Department of Land and Natural Resources Division of Forestry and Wildlife, Forest Management Section (DOFAW) 2009. Moloka‘i Forest Reserve Management Plan. DOFAW, Honolulu, HI. 47 pp.
Kagawa, A., Sack, L., et al. “Hawaiian native forest conserves water relative to timber plantation: species and stand traits influence water use”, 2009
Mascaro, Joseph, Kristen K. Becklund, R. Flint Hughes, and Stefan A. Schnitzer. 2008. Limited native plant regeneration in novel, exotic-dominated forests on Hawai'i. Forest Ecology and Management, 256:593–606.
Sarhangi, Sheila. "On The Hunt." | On The Hunt. N.p., n.d. Web. 27 Feb. 2017. <http://www.honolulumagazine.com/core/pagetools.php?pageid=5618&url=%2FHonolulu-Magazine%2FMay-2008%2FOn-The-Hunt508%2F&mode=print>.
Takahashi, M., Giambelluca, T.W., Mudd, R.G., DeLay, J.K., Nullet, M.A., Asner, G.P., 2011. Rainfall partitioning and cloud water interception in native forest and invaded forest in Hawai'i Volcanoes National Park. Hydrol. Process. 25:448–464
The Nature Conservancy (TNC) 2011. Kamakou Preserve Draft Long-Range Management Plan, Fiscal Years 2013-2018; report submitted to the Hawaii Department of Land and Natural Resources Natural Area Partnership Program; The Nature Conservancy - Moloka‘i, Kaunakakai, HI. 54 pp.
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.
APPLICATION
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.
REFERENCES
Anonymous, 1956. Report by the Hawaii Dept. of Agriculture to the Hawaii Board of Commissioners of Agriculture and Forestry, and Hawaii. Dept. of Agriculture and Conservation. N.p.: Pennsylvania State U, 1956. Print.
Giambelluca, T.W., Q. Chen, A.G. Frazier, J.P. Price, Y.-L. Chen, P.-S. Chu, J.K. Eischeid, and D.M. Delparte, 2013: Online Rainfall Atlas of Hawai‘i. Bull. Amer. Meteor. Soc. 94, 313-316, doi: 10.1175/BAMS-D-11-00228.1.
Harrington, Robin A., and John J. Ewel. 1997. Invasibility of tree plantations by native and non-indigenous plant species in Hawaii. Forest Ecology and Management, 99:153-162.
Giambelluca, T.W, Delay, J.K., Asner, G.P.,Martin, R.E., Nullet, M.A., Huang, M.,Mudd, R.G., and Takahashi, M., 2008. Stand structural control on evapotranspiration in native and invaded tropical Montane cloud forest in Hawai’i. American Geophysical Union, Fall Meeting 2008.
Hawai‘i Department of Land and Natural Resources Division of Forestry and Wildlife, Forest Management Section (DOFAW) 2009. Moloka‘i Forest Reserve Management Plan. DOFAW, Honolulu, HI. 47 pp.
Kagawa, A., Sack, L., et al. “Hawaiian native forest conserves water relative to timber plantation: species and stand traits influence water use”, 2009
Mascaro, Joseph, Kristen K. Becklund, R. Flint Hughes, and Stefan A. Schnitzer. 2008. Limited native plant regeneration in novel, exotic-dominated forests on Hawai'i. Forest Ecology and Management, 256:593–606.
Sarhangi, Sheila. "On The Hunt." | On The Hunt. N.p., n.d. Web. 27 Feb. 2017. <http://www.honolulumagazine.com/core/pagetools.php?pageid=5618&url=%2FHonolulu-Magazine%2FMay-2008%2FOn-The-Hunt508%2F&mode=print>.
Takahashi, M., Giambelluca, T.W., Mudd, R.G., DeLay, J.K., Nullet, M.A., Asner, G.P., 2011. Rainfall partitioning and cloud water interception in native forest and invaded forest in Hawai'i Volcanoes National Park. Hydrol. Process. 25:448–464
The Nature Conservancy (TNC) 2011. Kamakou Preserve Draft Long-Range Management Plan, Fiscal Years 2013-2018; report submitted to the Hawaii Department of Land and Natural Resources Natural Area Partnership Program; The Nature Conservancy - Moloka‘i, Kaunakakai, HI. 54 pp.
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.
