Niamh O’Hara
I.C.E. Intern (Fall 2003)

Internship in Conservation Biology with KRCP
(Testimonial)

Seldom have I found a place where I have felt so completely at home and fulfilled as I have in Koke’e. The work in conservation biology and the people here have helped me reaffirm my desire to be involved in environmental science. It has also helped me to understand where I want to go in my future endeavors. I have received complete support from the Katie, Ellen and David which they displayed by showing an intense desire to teach me about the forest ecosystem and guide me in any way possible.
When I arrived up on the mountain, I spent the first couple of weeks working out in the forest, just trying to identify the plants. This was no easy task considering that Hawaiian plant names are completely different than common names and usually consist of about one consonant and five vowels. I am still having trouble remembering the difference between A’ali’i, Ala’a , and Alahe’e. Despite the fact that my coworkers spoke about the overall ecosystem functioning, my energy was completely focused on the minute details of plant identification. I suppose now, looking back, that that was a good way to begin; it is important to build knowledge from the base up. I now have an understanding of the basic constituents of the mesic to wet forest here. However, it wasn’t until we took a four-day backpacking trip into Alakai swamp that the delicate balance between the plants and their environment really struck me.

Nine of us left for the swamp early on a Friday morning in order to hike into the Wainiha poli area. Until that time I had only seen patches of native forest and our constant battle against the weeds was feeling futile. The swamp on the other hand is almost entirely native; we only went there to eradicate small patches of incipient Kahili Ginger. The swamp’s forest was absolutely breathtaking. There were huge O’hia Lehua trees, that over the ages had formed complex structures as one tree has fallen and others had grown out of it. All the structures were covered in thick mats of hanging moss and there was an atmospheric lighting as the 10-foot tree ferns filtered the sunlight. On one tree alone there seemed to be thousands of functioning ecosystems, with millions of minute organisms living together in balance. It was quite a different spectacle than the areas in which we had worked, where strawberry guava was the only thing the eye could see. While in the swamp I also had the rare experience of seeing a Puaiohi. These dove- like birds are endangered with only 300 of their kind left. Unfortunately, I just wrote it off as being a dove, until later I heard there are no doves in the area.

The work we did in the swamp and in the rest of Koke’e was enhanced by my coworkers. I felt that they all wanted to share their understanding and intense love of the forest with me. Katie’s knowledge of plants is astounding. She knows the scientific, common, and Hawaiian name as well as each plant’s history and general information. Ellen was also especially helpful. She spent many hours discussing my independent research project with me. She gave me input and ideas and taught me about analyzing and graphing my results.

Overall my internship in Koke’e has been extremely rewarding and educational. However my experience here has shown me that I do not want to go into conservation biology; I don’t believe I have the tireless faith shown by the people here. Instead I hope to do research so I can feel that I am moving forward. However, the application of the work done here is so valuable that I have also realized I want to go into an applied science. So although I haven’t realized that my calling is to become a botanist, I have realized many things. The forest here is severely threatened and restoration projects are utterly under funded. There is a great need for researchers with funding to study the forest here so the conservation work isn’t done blindly. I would love to be one of those researchers. Ideally, just give me a few years and I’ll return to Kauai with my degree and funding to work on the problem.

RESARCH PAPER AND FINDINGS

(Not to be photocopied or quoted without
the written consent of the author)

The allelopathic effects of Psidium cattleianum
on some native Hawaiian plant species

Abstract

Hawaiian forests are extremely fragile and susceptible to invasion by non-native plants. Strawberry guava (Psidium cattleianum) is a problematic invasive tree that uses allelopathy to form monotypic stands. Its effects on plants native to the island of Kauai in the Hawaiian Island Chain have been little documented. In order to determine which native species is more resistant to P. cattleianum allelopathy, guava leaf litter was applied to seedlings of koa (Acacia koa), maile (Alyxia olivaeformis) and pilo (Coprosma spp). All three species health and growth rates were effected by P. cattleianum leaf litter application. Coprosma spp. seemed to be the most resistant with regards to health, while Alyxia olivaeformis seemed to be the most resistant with with regards to growth rate. The results were preliminary and more tests need to be done on a larger pool of seedlings for a longer period of time. In addition, other native plants need to be tested and the order of succession of such natives needs to be established.

Introduction

Due to the susceptibility of island forests to invasive species, Hawaii has had considerable problems with loss of biodiversity. Invasive plants are the main reason that 45% of endangered U.S. plants are Hawaiian plants (Lamoureux 1995). Non-native plants have had a massive impact on natives because non-natives are much more aggressive and can out-compete native plants.

Strawberry guava (P. cattleianum), introduced in 1825, is among the most aggressive of the invasive plant species on Kauai. It forms dense monotypic stands in which no seedlings other than its own can grow. Other seedlings won’t grow for an extended period of time under destroyed P. cattleianum forests. One reason that P. cattleianum is thought to be so aggressive is because its leaf litter is allelopathic. However, not much data has been collected on its allopathic qualities and its effects on different native species. It would be valuable to know which native plant species are the most resistant to its toxicity in order to out-plant those species into dead P. cattleianumm forests and begin succession back to native forest.

Usable nitrogen is one of the factors necessary for all plant life. There is evidence that shows that allelopathic plants send out monoterpenes that inhibit the nitrogen cycle (Adair 1998). Monoterpenes seem to interfere with the bacteria Nitrosomonas, which oxidize ammonium to nitrite, and Nitrobacter, which oxidizes nitrite to nitrate (Rice 1992). Since plants assimilate nitrogen as nitrate, as well as ammonium, lower levels of nitrate would not support plant life as well (Adair 1998). Allelopathic plants seem to send out monoterpenes which lower the amount of usable nitrogen in the soil and make the soil uninhabitable for most plants. P. cattleianum itself is extremely adaptable to different soil types, and can survive in highly acidic soils (Sem 1984). This would explain why it isn’t self-allelopathic.

In order to determine which native plants are the most resistant to the allelopathic qualities of P. cattleianum, three different plant species common to the montane mesic forests of Kauai, were chosen. Leguminous Acacia koa has been observed growing in P. cattleianum forests. It was thought to do well because it can fix its own nitrogen. Maile (Alyxia olivaeformis) has been found to be somewhat resistant to P. cattleianum (Smith). The third plant species chosen was pilo (Coprosma spp.) which was also observed growing near P. cattleianum. The plants were transplanted into pots. Native forest soil was used so to allow naturally occurring levels of nitrogen. Because of time constraints on the experiment, both fresh and decomposing P. cattleiaunum leaves were applied to separate plants. It was unclear how long it would take the allelopathic toxins to be released from the leaves. As such, fresh P. cattleianum leaves were collected and ground up in a blender in order to help speed the release process. When analyzing the data one inch was added as a correction factor to all final heights to correct for stress that resulted in the loss of leaves and apparent loss of height. This was only necessary because the experiment was conducted for such a short period of time, and a change in height wasn’t as pronounced.

Materials and Methods

1) Twenty-seven Acacia koa, twenty-seven Alyxia olivaeformis, and thirty-three Coprosma spp. seedlings were collected from firebreak areas. The seedlings were all transplanted into pots with topsoil collected from native forest. The topsoil was collected from nearby forest where all three native plants being tested were present in abundance, and there was no sign of invasive allelopathic plants.

2) Each plant species was divided into three groups. The first group for each plant species was the control where no P. cattleianum leaf litter was applied. The second group received application of fresh P. cattleianum leaf paste, and the third group received application of old P. cattleianum leaves. The P. cattleianum leaves were collected two days before each application from a dense 25-year old s. guava forest. The fresh leaves were stripped from the branches and blended along with water into a paste. The old P. cattleianum leaves were collected from the forest floor and applied with no treatment. Both fresh and old P. cattleianum leaves were reapplied to the native plants weekly to a 1-inch depth.

3) The plants were watered daily so soil was kept moist. There was no fertilizer used.

4) Once potted, the plants were allowed to sit for two days and then measurements of plant height and health were recorded. A system was developed to take quantitative measurements of the plant health:

1- Perfect health, new growth
2- Perfect health
3- Wilting
4- One or two discolored spots, wilting
5- A few discolored spots, wilting
6- Many discolored spots, wilting
7- Severely discolored, wilting
8- Severely browned and discolored wilting
9- Leaves falling off, severely browned and discolored, wilting
10- Dead

Height measurements were taken again at the end of the experiment, while health measurements were taken weekly
for the duration of the experiment.

5) Averages of change in health and height of each plant type were determined. Data was analyzed using statistical analysis in Microsoft Excel and results were graphed. Standard deviation was also determined.
Results

Conclusions/Discussion:

The preliminary results indicate that P. cattleianum’s leaf litter does effect Acacia koa, Alyxia olivaeformis, and Coprosma spp., both in health and growth rates. Seedlings with leaf litter applied degraded in health more than the control in all cases. Although Coprosma spp. degraded more than Alyxia olivaeformis overall, Coprosma spp. plants with applied guava leaves only degraded slightly more than the Coprosma spp. control did. This would indicate that Coprosma spp. showed the most resistance to P.cattleianum toxicity; Acacia koa was the next most resistant followed by Alyxia olivaeformis. The results were different than what was expected because it was thought that Acacia koa would be the hardiest due to its ability to fix nitrogen. However, it would make sense that Acacia koa is susceptible to P. cattleianum if the bacteria Acacia koa uses in nitrification is the same bacteria (Nitrosomonas and Nitrobacte) in the soil that aids in nitrification, and which is inhibited by monoterpenes.

Growth inhibition by fresh P. cattleianum leaves was the least for Alyxia olivaeformis, followed by Coprosma spp. and then Acacia koa. In all cases when fresh P. cattleianum leaf litter was applied there was either no growth, as in Alyxia olivaeformis’ case, or a loss of height due to loss of leaves. When old leaf litter was applied, growth inhibition was least for Acacia koa, followed by Alyxia olivaeformis and then Coprosma spp. When the effects of fresh guava leaves and old guava leaves on height is averaged together, Alyxia olivaeformis’ growth seems to be inhibited the least.
These results, however, are only preliminary as indicated by the high standard deviation. The results could be inaccurate because too few seedlings were used in the experiment. The experiment would need to be conducted again with more seedlings and over a longer period of time.

Although Coprosma spp.’s health seemed to be the most resistant to P. cattleianum’s allelopathy, it may not be the best species for out-planting. The Coprosma spp. control showed the most degradation and may indicate that Coprosma spp. transplants poorly. Its growth was also severely inhibited. Research needs to be conducted on other native plants, especially on native primary and secondary successors, so that native succession may be established. The ideal plant for out-planting would require less nitrogen to grow, but would put nitrogen back into the soil. It would also germinate quickly or transplant well, and create a suitable habitat for other natives to grow in. In the future, Osmanthus sandwicensi and Psychotria mariniana should also be tested because they have displayed resistance to P. cattleianum’s leaf litter (Sem 1984).

Sources Cited:

Lamoureux, C.H. 1995. Some data on endangered species.

Rice, E.L. 1984. Allelopathy. Academic Press Inc. The University of Oklahoma.

Sem, G.S. 1984. A population study and distribution of strawberry guava (Psidium cattelianum) in Hawaii Volcanoes National Park, Hawaii. Master’s Thesis. University of Hawaii, Honolulu. 84 pp.

Adair, Carol E. 1998. Allelopathic inhibition of the nitrogen cycle by monoterpenes. Colorado State University, Fort Collins, Colorado.

Smith, Clifford W. Impact of alien plants on Hawaii’s native biota. CPSU.