More of our class explores Lighthouse Cave, San Salvador, Bahamas.
|
|
Abstract
Biodiversity is important to the proper functioning of an ecosystem. However,little has been done on the biodiversity of steep slopes (defined as >30 degrees). This study attempted to relate the total number of plant, lichen and fungi species on a slope in terms of slope angle. It was thought that biodiversity would increase to a maximum slope angle and then begin to decrease. Five slopes of varying angles were studied in the Monteverde and Corocvado regions of Costa Rica. It was found that the opposite effect seemed to hold true. Itermediate slopes seemed to have the least biodiversity with the extreme slopes in both directions were highest in biodiversity. Much more research needs to be done in this area and this paper offers a few areas to go from here.
Introduction
Biodiversity is crucial to the proper function of an ecosystem. Also known as species richness, biodiversity is the total number of different species found within a given ecosystem (Naeem et al. 2002). This concept has received a lot of attention lately as worldwide declines in biodiversity have been indicated in ecosystem distress. It has been implicated in the control of various ecosystem processes such as plant productivity, soil fertility, water quality, atmospheric chemistry, and food web structure (Naeem et al., 2002).
While there is much research that has been performed on many ecosystems in terms of biodiversity, one ecosystem type has been virtually ignored. This specialized ecosystem is the steep slope ecosystem. Steep slopes, defined for our purposes to be any slope greater than a 30¡ angle, are a difficult ecosystem for life to survive on (Lewis, 2002). Many identified factors such as slope angle, aspect, soil depth, soil composition, light intensity, and drainage patterns make it difficult for plants, fungi and lichens, the main colonizers of steep slopes, to live (Lewis, 2002).
It was due to the lack of information that this research project was launched in the summer of 2002 in the rainforests of Costa Rica. Our research group began this project in the hopes of determining which factors played the most crucial role in biodiversity of steep slopes. We decided to use the factors identified previously, those of slope angle, aspect, soil depth, soil composition, light intensity, anddrainage patterns, as the factors of inquiry. Of these, we felt that slope angle was the most critical aspect due to published reports (Lewis, 2002). Thus, we based our research around the following hypotheses:
1. Biodiversity of plants, fungi, and lichens on slopes will increase up to a maximum slope angle and then begin to decrease.
The reasoning was simply that there would be organisms that were good colonizers of gentle slopes and organisms that were good colonizers of steep slopes. These species would have some common angle that they both could colonize well, thus opening up a competition regime and increasing biodiversity to its maximum.
Materials and Methods
This study was conducted at five slope sites in Costa Rica: 1. A recent disturbance area on the El Camino Trail in the Monteverde Forest Preserve, 2. The Hurricane Mitch Devastation Area on the El Camino Trail, Monteverde Forest Preserve, 3. A recent landslide area on the El Camino Trail, Monte Verde Forest Preserve, 4. A slope on Sirena Path in Corcovado National Park, and 5. A cliff face on the San Padrillo Path in Corcovado National Park.
Aspect
In order to determine aspect, or the direction, in which a slope faced, two basic methods were employed. In the Monteverde region, direction was determined based on sun position and location on the map. In Corcovado, sun position was also used. However, the aid of a hand held GPS system was employed in lieu of a map.
Angle of Slope
The angle of the slope was determined through the use of a field protractor.
Mineral Soil Composition
Soil composition was determined using standard ribbon and molding tests. These tests could only give an approximation of the soil content to the point where it could be said that the soil was mostly clay, mostly organic, or mostly sand and rock. These were the categories used to describe the soil.
Drainage Pattern
The drainage pattern for the slope was estimated by taking into account the slope angle, soil composition, and vegetative cover. It was categorized as high, low, or moderate using this method.
Light Intensity
Light intensity was quantified visually as a percentage of the light that one would receive in an open field. This intensity was set at 100%. Visual inspection of the amount of light reaching the slope was used to quantify this variable.
Plant, Fungi and Lichen Biodiversity Assessment
In order to determine biodiversity, a five-foot long line was measured at the base of the steep slope. The number of visibly different species was counted, from the bottom to the top. Each species was assigned to one of the following categories:
1. Fern
2. Broadleaf
3. Vascular
4. Moss
5. Lichen
6. Fungi
Results
The gross results are presented in the following section for this study. With only five sites selected for measurement, it was not possible to do statistical analysis on these results. Thus, this study can only serve as a pilot study and provide some trends that may advance future research. The gross results are found in Table 1.
Table 1. Depiction of the physical data for the measured slopes. Note: 1=A recent disturbance area on the El Camino Trail in the Monteverde Forest Preserve, 2 =The Hurricane Mitch Devastation Area on the El Camino Trail, Monteverde Forest Preserve, 3=A recent landslide area on the El Camino Trail, Monte Verde Forest Preserve, 4=A slope on Sirena Path in Corcovado National Park, and 5=A cliff face on the San Padrillo Path in Corcovado National Park.
Site Aspect Slope Angle Soil Composition Drainage Pattern LightIntensity
1 S 45 Sandy High 85%
2 S 90 Clay Low 100%
3 NE 60 Clay High 40%
4 E 35 Humus Moderate 50%
5 W 85 Rock/Sand High 15%
The plant, fungi, and lichen data is located in Table 2.
Table 2. Depiction of the total number of plant species visually determined from each slope. See note from Table 1.
Site Fern Broadleaf Vascular Moss Lichen Fungi Total
1 1 2 0 6 0 1 10
2 3 5 2 1 0 0 11
3 0 1 0 2 0 1 4
4 2 5 2 2 3 2 16
5 1 0 0 2 0 0 3
This data was used to graph a relationship between slope angle and total biodiversity. This relationship is shown in Figure 1. This addresses the thrust of our hypothesis for this study. The data seems to fit a 2nd order polynomial function pretty well (R-square=. 85). It is the opposite of what was expected though, as biodiversity is high on the extreme slopes and lower towards the intermediate slopes.
However, after reviewing the data upon return to the United States, it occurred to this researcher that the data could be further treated in interesting ways. For example, it would be interesting to look at the other identified factors and see if there was any correlation between them and biodiversity. The first factor looked at in this revised data treatment was light intensity. As can be seen from Figure 2, light intensity seems to have a linear relationship with species diversity. The exception is the midpoint intensity measurement. It seems to be an outlier and when removed, the linear trendline that was fit to the curve (not shown) had an R-square of .97. The next data set that was reevaluated was the effect of aspect on biodiversity. As can be seen in Figure 3, the slopes that faced the east seemed to have the most biodiversity. Figure 4 shows that soil composed mostly of organic matter, or humus soil, seems to have the highest biodiversity. Finally, Figure 5 shows that a slope with a moderate drainage regime seems to have the highest biodiversity.
Discussion
Unfortunately, due to small sample size, the only thing that can truly be drawn from this study is possible trends that need to be further investigated. However, in terms of biodiversity, slope angle seems to play an odd role. The intermediate slopes (between 50 and 75 degrees) have the lowest biodiversity. This may make sense in that these may be the regions where the species that are good colonizers of steep slopes and those that are good colonizers of shallow slopes meet. A competition regime may be set up where one type of colonizer is superior to another and thus wins out, decreasing biodiversity. The other possibility is that the slope growing species are very specific to either shallow or steep slopes. Thus, there is no middle ground, as the shallow slope species and the steep slope species cannot grow in the intermediate slope zone.
Light intensity and its relation to biodiversity is a bit clouded. The line is fairly linear in Figure 2 if the one outlying point is excluded. If this were the case, it would seem to make sense that as light intensity increases, biodiversity would increase. Generally, it seems intuitive, there are more sun tolerant species of plants, lichens, and fungi than intolerant species. This is probably particularly true among plants and less true among fungi. It would be interesting to see how species type, in the categories that we defined, varies with light intensity. For example, are there more ferns and fungi in the shaded area and more vascular plants in the open area?
The aspect results were different from what was intuitively thought. It was thought that the north and south facing slopes might be the most diverse because they would tend to get some degree of sunlight all day and would tend to be out of the direct path of the wind. The results indicate that east-facing slopes tend to be more diverse though. The reason for this is not readily apparent.
Soil and drainage pattern results in relation to biodiversity showed pretty much what would intuitively be expected. Soil rich in organic material and with a moderate drainage pattern seem to have the highest diversity. Organic soil provides a lot of nutrients to plants, lichens and fungi. It also provides decent water retention and stability. Clay soil is often hard and water tends to not penetrate it. Sandy soil is the opposite. Drainage pattern results showed that a moderate runoff rate was best for biodiversity. This makes sense, as too slow a runoff rate in an area of high rainfall would result in pooling and oversaturation. Too fast of a runoff rate would lead to erosion of soil and exposure of plant roots.
Future Direction
It is clear that there is a lot of work to be done here. This project merely scratched the surface of this issue and may provide many directions from whence to go from here. Clearly, more work needs to be done on slope angle and biodiversity. One way to go might be to classify species based on where they occur in slopes. For example, are lichens and mosses better colonizers at steep slopes? Are vascular plants better of on the shallower slopes? Another question that needs to be answered regards the species that do characterize the mid angle slope region. What are they? How are they able to gain this niche that seems prohibitive to species that inhabit the upper and lower extremes?
The light intensity question also needs to be pursued further. One area of inquiry might be to ask what type of species favor the lower light intensities. Is there a zonation along the light intensity gradient?
Aspect may have a big effect on biodiversity, as some researches have proposed. One avenue from this research might be looking at specific classes of species to see if they favor a certain facing of a slope. If so, is this tied in with light intensity?
Drainage pattern and soil type may well have interrelated effects on biodiversity of slopes. This is another avenue that could be pursued.
Finally, it would be very interesting if all these aspects could be compared in a linear regression type analysis to see if biodiversity could be predicted based on angle, light intensity, aspect, drainage, and soil composition. Is it possible to fit a model to all of these parameters? Are some of them redundant?
Conclusion
There is still a lot that is unknown about steep slopes and biodiversity. The factors that determine the amount of life on slopes are still being fleshed out. The steep slope is a very complex ecosystem with a lot of variables that make it difficult for a species to survive there. It will be very interesting to monitor future developments in this area.
Acknowledgements
The author would like to thank his research team, Paul Levy and Evelina Maciuleviciute. He would further like to thank Dr. R. Hays Cummins, Miami University, and the Costa Rican Government.
Works Cited
1. Lewis, Gary. Eagle Ridge: the Ecology of a Rare Urban Outcrop. Menziesia: Newsletter of the Native Plant Society of British Columbia. Accessed via the internet on 7/15/02. www.npsbc.org/Newsletter/newsletter.htm
2. Naeem, Shahid, F. S. Chapin III, Robert Costanza, Paul R. Ehrlich, Framk B. Golley, David U. Hooper, J.H. Lawton, Robert V. O'Neil, Harold A. Mooney. Osvaldo E. Sala, Amy J. Symstad, and David Tilman. Biodiversity and Ecosystem Functioning: Maintaining Natural Life Support Processes. Accessed via the internet on 7/15/02. www.esa.org/issues4.htm
We also have a GUIDE for depositing articles, images, data, etc in
your research folders. Article complete. Click HERE
to return to the Pre-Course Presentation Outline and Paper Posting Menu. Or, you can return to the course syllabus It is 6:51:39 AM on Monday, November 23, 2009. Last Update: Wednesday, December 10, 2008
Previous Article
Return to Topic Menu
Here is a list of responses that have been posted to your discussion topic...
Important: Press the Browser Reload button to view the latest contribution.
If you would like to post a response to this topic, fill out this form completely...
DOWNLOAD the Paper Posting HTML Formating HELP SHEET!
Listen to a "Voice Navigation" Intro!
(Quicktime or MP3)
WEATHER & EARTH SCIENCE RESOURCES
OTHER ACADEMIC COURSES, STUDENT RESEARCH, OTHER STUFF
TEACHING TOOLS & OTHER STUFF
