Tree of Life ( Guariacum sanctum)

Study at Palo Verde National Park, Costa Rica 2000

Guariacum sanctum is endangered species because of its value and use for specialized construction. The study was conducted on a five plot area on a straight-lined slope in the park behind the OTS headquarters. Each plot measured 20 meters x 20 meters and contained previously tagged study trees of varying sizes. The purpose of the study was to identify abiotic factors that may or may not be responsible for differences between the number and size of trees lower on the slope versus the number and size of trees higher on the slope. Factors considered were soil chemistry, light and canopy cover, and relative humidity. These findings were then compare to the biotic factors of tree height and diameter at breast height (dbh).

Soil Samples

The intent of the soil tests were to determine abiotic characteristics of the soil in the sample plot sites. The lower three plots out of a total of five plots were tested. The soil samples were analyzed for pH, phosphorus, nitrogen, and potassium using a LaMotte soil test kit. Because there appeared to be no significant difference between the soil chemistry for the three sites sampled, the results for all plots are as follows:

PH = 7.5

Phosphorus – levels were low

Nitrogen – trace levels

Potassium – very low levels

Although no difference was found between the three plots, an interesting situation exists. The remaining two plots that were untested contained the highest number of trees. Therefore, no conclusion could be made linking soil chemistry to tree abundance.

Light and Canopy Cover Samples

Digital pictures were processed using the Adobe PhotoDeluxe program to measure percent canopy opening. A 8 x 10 grid (80 squares) was used to fit over the digital picture. The boxes that showed the sky (or light) were counted. If 50% or more of each box showed the sky (white or blue shade) it was counted as open. To enhance the contrast between open sky and dark canopy cover, the pictures were processed using the “patchwork” function of the program.

The average canopy opening showed that quadrants one through four had a relatively low percentage of opening (<15%). However, quadrant five had an average of 25.2% opening. This correlates directly with the light intensity measurements.

The average light intensity for each quadrant showed that there was no significant difference in quadrants one through four. However, a significant increase was noted in the fifth (highest elevation) quadrant.

Relative Humidity Samples

Relative Humidity was measured using a sling psychrometer. Samples were taken at 10 meter intervals from the bottom plot (Plot 1) to the top plot (Plot 5). The relative humidity ranged from 75% to 85%.

Plots 2 and 3 recorded the highest readings while plots 1, 4 and 5 had lower average readings. Relative humidity is apparently not a factor for tree growth and dispersal in the study area.

Tree Survey Samples

The five plots were surveyed to determine the tag number of previously measured trees, height of trees, and number of trees with measurable dbh. The survey was conducted by walking up the slope through the plots in a line in two meter intervals. The results were as follows:

Plot Number of Trees Average Height (cm) Number of Trees with Measurable dbh

1 50 63 0

2 27 120 4

3 36 36 9

4 115 81 21

5 141 62 7

There were fewer number of trees on plots 2 and 3. Trees on plot 1 tended to be smaller in general than those found in plots 4 and 5.

Conclusion

There were more Guariacum sanctum in the upslope plots 4 and 5. Over 50% of the large trees were found in plot 5. There appeared to be no correlation between soil chemistry, relative humidity and the number and size of Guariacum sanctum in the study plots. There appeared to be no correlation between light and the number and size of the trees in plots 1 through 4, although plot 5 appeared to have more available sunlight than the other plots and more trees.

Future studies may want to consider the role of a source tree in the seed dispersal and reproductive patterns suggested in the plot survey. In addition, dbh growth may increase at a greater rate in plot 5 if more sunlight remains available.

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