Plotting of Vegetation

The purpose of this analysis is to describe the vegetation in the forest of the University of British Columbia, Okanagan Campus (UBCOC), which is located at the north end of the city of Kelowna, and to note the gradation of vegetation across the slope of the observed plot. Gradation is influenced by variables such as available light, rainfall and ambient moisture, the depth and quality of soil, and shocks to the environment such as soil runoff, pollution, or fire.

Observation was directed at a particular plot of the UBCOC forests area that measures 20 meters by 100 meters and consists of an east-facing slope in the northeast corner of the University of British Columbia campus in Okanagan, which was set aside for study in 2007. Conditions suitable for plant life exist across the plot of land, but not uniformly. For instance, give the slope of the observed plot, rainwater and snowmelt will soak into the soil and will also travel across the top surface of the soil, given sufficient saturation of the soil. This means that nutrients in the soil will be carried along with the moving water both across the surface and penetrating into soil layers. From this dynamic, it can be seen that nutrients will accumulate at the lower bounds of the slope, as will moisture on an intermittent basis. Given the overall arid conditions of the land in and around Kelowna, the presence or absence of moisture is a main variable in the growth and reproduction of vegetation on the observed plot of land.

Soil also accumulates at the bottom of slope, having been propelled by moving water, pulled by gravity, or disturbed and loosened by birds or animals. The eastern exposure of the slope permits more shade at the base during noontime and the afternoon hours. The exposure to sunlight is a factor in evaporation levels across the face of the slope, with higher levels of evaporation occurring at the upper reaches of the slope where sunlight is more direct and exposure occurs for a longer time than at the lower levels of the slope.

Research Questions

Given the descriptions of the environmental dynamics found on the observed plot, the following research questions are posed.

Does the environmental gradient of the plot slope control the growth of the vegetation?

Does the environmental gradient of the plot slope result in greater species variability in the basal area of the plot slope?

Research Hypotheses

The environmental dynamics on the slope suggest that more provident growing conditions are established along the base of the slope. Consideration of the key variables discussed in the paragraphs above, the following hypotheses appear relevant and reasonable:

Hypothesis #1 — The diversity of plant life will be greater at the base of the slope due to increased overall levels of moisture, nutrients, and soil depth.

Hypothesis #2 — The density of vegetation growth will be greater at the base of the slope due to increased overall levels of moisture, nutrients, and soil depth.

Hypothesis #3 — The basal area of the observed plot will show greater vegetation density and diversity than the upper portion of the plot due to increased overall levels of moisture, nutrients, and soil depth at the base.

Methods

Study Area

The geology of the Okanagan Valley is characterized by basaltic lava, carbonaceous sedimentary rock, foliated gneiss, and granitic rock (Meidinger & Pojar, 1991). Erosion in the area has been sufficiently substantial to result in the deposition of a valley floor that consists of a mixture of clay, gravel, sand, and silt ((Meidinger & Pojar, 1991). The soils in the area include brunisol and chenozem, with the area surrounding Kelowna predominately chernozem soil (Pidwirny, 2006). Geologists mark the formation of the Okanagan Valley to the Pleistocene Age, noting that it was a river valley that was further eroded by the Cordilleran glacier during the ice age (Pidwirny, 2006).

Vegetation Growth Analysis — UBCO Study Plot

Vegetation Growth Analysis — UBCO Study Plot

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Figure 1. Map of Kelowna (at red “A” pin) in Okanogan valley

Figure 2. Outline map of British Columbia showing the approximate location of Kelowna.

Visual observation of the forest in the location of the University of British Columbia campus in Okanagan and the observed plot suggests a preponderance of Ponderosa Pine (Pinus ponderosa), some lesser quantities of Douglas Fir (Pseudotsuga menziesii) and several varieties of shrubs. Moreover, the location of the plot on the campus has resulted in a human induced edge that runs along the Bunch Grass zone that occurs in the hottest and driest interior valleys, which transitions into stands of Ponderosa Pine. Indeed, the climate of the Okanagan valley is substantially impacted by its location proximal to the Pacific Ocean and the nearby Cascade and Coastal mountain ranges: as the wind moves inland from the sea, orographic uplift causes the wind to pull moisture along until it is primarily deposited on the windward side of the mountains, creating a moderate rain shadow and drier winds on the Okanagan valley side. The fact that dry winds prevail in the Okanagan valley in the summer months means that there is always the danger of forest fires and brush fires. Some biological plant adaptation can be seen in plants that have developed resistance to the forest fires. The diversity of vegetation in the Okanagan valley is fundamentally accounted for by these climate-controlling conditions, and a range of weather temperatures averaging from roughly 27° Centigrade in summer to 5° degrees Centigrade in winter.

Previous cycles of studies of the vegetation on the observed plot have identified and mapped the vegetation to within 0.1 meter. In addition, measures of the diameter at breast height (DBH) and overall height of the trees in the plot have been recorded. And all trees have been tagged, and cored for age at DBH, and a few trees were cored at the base to ascertain the true ages.

Field Data

To construct a slope profile of the study site, measurements of slope distance and slope angle were taken between points along the slope. These points were selected where there was a change in observed slope along the transect. The slope distance was estimated within each interval using existing survey pins placed 2 meters apart, and the slope angle was measured within each interval using a clinometer. Using the slope distance and slope angle, trigonometry was then used to calculate both the vertical and horizontal distance within each interval. A base datum and top datum elevation were used to ensure that all 11 transects would be measuring the same total distance. The elevation was calculated at each point of slope change along the slope transect by adding the vertical distance cumulatively from the base point. The change in elevation, or total vertical distance from the base datum to the top datum, was measured using an altimeter, and was compared to the value obtained by adding the vertical distances.

Analytical Data

Simpson’s Diversity Index formula (Magurran, 1988)

Results

Measurement of the slope was found to be relatively constant throughout the slope transect, with subtle changes at about 7 meters and 18 meters in elevation) (see Figure 3). A10° variation in slope angle was found throughout the slope transect, with measurements ranging from 9° to 19° and with the 9° measurement taken at the base of the slope. The calculated change in elevation from the base datum to the top datum was found to be 24.5 meters, whereas the change in elevation measured by the altimeter was found to be 25.9 meters.

Figure 3. Transect 8 — Slope profile from (16.0) at 0 horizontal distance to (16,100).

Figures and Tables

Data for Trees

Figure 4. # of stems (trees) (e.g. Abundance)

Figure 5. % of stems (trees) by species

Figure 6. Percentage of contribution by tree species to the total number of trees.

Figure 7. % of stems (trees) by species

Figure 8. Stem Density (trees) (per ha)

Figure 9. Stem Density (trees) (per ha)

Figure 10. Biomass (tree species)

Figure 11. Biomass (tree species)

Figure 4 represent the abundance of Ponderosa Pine (Pinus ponderosa) and Douglas Fir (Pseudotsuga menziesii) trees as measured in absolute numbers in the subsections of the plot as recorded in the field. The abundance trend for both species of trees was negative moving up the slope and positive moving down the slope. Figure 5 shows the percentage of tree species in each subsection. Figure 6 shows the percentage of contribution by tree species to the total number of trees in a subsection. The percentage contribution of Douglas Fir was higher at the basal end of the slope and less at the upper reach of the slope. The contribution of Ponderosa Pine to the tree species mixed reached 100% at the top of the slope. Figure7, Figure 8, and Figure 9 show the stem density of trees for each subsection. In order to accurately account for variation in each individual stem of the tree species, the overall biomass for each species was measured for each subsection. Overall biomass for tree species is shown in Figure 10 and Figure 11. Stem density showed the same overall trend as abundance with the highest density recorded at the basal end of the slope and the lowest density recorded at the upper reaches of the slope.

Data for Shrubs

Figure 12. # Stems (abundance) (shrubs)

The same overall measures were taken and recorded for shrubs growing in the subsections. The abundance of shrubs is shown in Figure 12, Figure 13, and Figure 14. The percent of contribution to the shrub density in the subsections is shown in Figure 15 and Figure 16.

The pattern of growth shown by the trees in the subsection is not mirrored in the shrubs, with the exception of Sheperdia canadensis.

Figure 13. # Stems (abundance) (shrubs)

Figure 14. # Stems (abundance) (shrubs)

Figure 15. Stem density (Shrubs)

Figure 16. Stem density (Shrubs)

Diversity Indices

The diversity indices illustrate the vegetation mix according to the number of stems within the subsection as a whole and also focusing on the basal section of the plot. In order to guage the diversity in the subplots, the field data was compared to Simpson’s Index and the Shannon-Wiener Index.

Figure 17. Comparison of Diversity Indices Using Number of Stems

Figure 18. Comparison of Diversity Indices Using Basal Area

Discussion

The study found that the diversity of plant life was greater at the base of the slope. The study also showed that vegetation density was greater at the base of the slope, and this pattern held true for all trees, but not for all shrubs. For vegetation growing in the basal area of the observed plot, there was greater vegetation density and diversity than was found on the upper portion of the plot. A notable exception to the growth patterns and trends was observed in Shepherdia canadensis, a plant that appeared to be more sensitive to altitude than variables related to moisture, sunlight, and soil nutrients.

The abundance and density growth patterns of the trees were most remarkable — which may be attributable to the fact that only two tree species were measured. The Ponderosa Pine grew all over the slope, and was most abundant at the lower levels of the slope. The Douglas Fir grew abundantly at the basal level of the slope but the density declined substantially further up the slope, with no trees of this species found growing at the very top of the slope. Thus, it can be said that the environmental gradient of the plot slope does control the growth of most species of vegetation, presumably due to increased overall levels of moisture, nutrients, and soil depth. Moreover the study confirmed that the environmental gradient of the plot slope contributed to greater species variability in the basal area of the plot slope.

An important variable that is not known with any precision is the habitual uptake of water required for the different shrubs growing in the plot. Overall the shrubs appear less sensitive to moisture content in the soil, which may be a related to the degree of shallowness exhibited by the root systems of shrubs compared to the large tree species also growing in the plot. Presumably, the shrubs and trees may not compete equally for moisture conducted to the soil surface given that the root systems of the trees tend to go much more deeply into the ground and more extensively across the underground area. And, too, given the preponderance of weight of the trees above ground, a strong root system is needed to keep the trees stable during wind and storms, and to withstand relatively weak patterns of erosion. The soil found closer to the midpoints on the slope and at the basal end of the slope is likely to be denser and better held in place by vegetation, thereby enabling the trees to gain a better hold than trees that are growing on the thinner or rockier soil at the upper reaches of the plot.

Conclusions

Clear relationships were observed with regard to location on the slope and the patterns of abundance, density, and diversity for large tree species growing in the subsection of the plot. The overall process of sampling a subplot to determine if a slope gradient is related to density and diversity of plant growth did show a relationship for most of the plants observed. Density was challenging to measure at the basal level of the slope since the relative size of the stems invariably impacts the number of stems that can grow in a particular area. This complication was reduces as measurement where taken higher up the slope where vegetation density was reduced and plant growth tended to be sparser. Shrubs did not evidence the same relationships to slope location and abundance, density, and diversity of growth.

References

Magurran, A.E. (1988). Ecological Diversity and its Measurement. Princeton, NJ: Princeton University Press.

Meidinger, D. & Pojar, J. (1991). Ecosystems of British Columbia. British Columbia Ministry of Forests. pp. 330. Retrieved from http://www.for.gov.bc.ca/hfd/pubs/Docs/Srs/SRseries.htm

____. (n.d.). Ministry of the Environment, Thompson Region Home. Retreived from http://www.env.gov.bc.ca/thompson/esd/hab/bunch_grass.html

Pidwirny, M. (2006). Soil classification. Fundamentals of Physical Geography, 2nd Edition. Retrieved from http://www.physicalgeography.net/fundamentals/10v.html