The area in the park near the picnic shelter where there is is higher elevation near the picnic shelter which is closer to the road and elevation gradually slopes downwards towards the creek I noticed as the elevation slopes downwards the amount of trees decreases and by the time you read the creek (lowest elevation) there are no trees but other species like cattail and blackberry bushes were present. Also, the soil near the creek was higher in moisture (it was more wet). I also noticed a rabbit in the blackberry bushes next to the creek in addition to ducks that were present in the Creek. The reason for the rabbit being present here could be that there is vegetation for it to consume and hide in. Near the picnic area there were mainly just western red cedar and Douglas fir and dawn redwood. As you go further into the park there are still red cedars and Douglas fir present but their population decreases and there are a lot of more different plant and shrub species which are not present in the picnic area. I believe that this could be due to disturbance caused by humans to build the picnic shelter and continuous disturbance caused by trampling and visiting this area often as Douglas fir and red cedar tend to grow in disturbed areas also there is lot’s of sunlight available in this area which favors the growth of these species, and higher elevation.
The Three Location’s
- Location 1 (Near the picnic shelter): Highest elevation, mainly Western red cedar and Douglas fir with some dawn redwood. Lots of sunlight, closer to the road, no animal or even bird species present.
- Location 2 (Midway between picnic shelter and creek): Elevation gradually sloping downwards, decreasing abundance of cedar and fir, with more shrub species.
- Location 3 (Near the creek): Lowest elevation, no trees, higher soil moisture, presence of mainly blackberry shrubs,cattails and some more plants that I wasn’t able to recognize, rabbit and ducks were also present.
Hypothesis:
The distribution of tree species is influenced by disturbance and elevation, with higher elevations favoring Western red cedar and Douglas fir,dawn redwood while lower elevations exhibit a decrease in tree abundance due to higher soil moisture and increased competition from other plant species. The prediction is as elevation decreases, the abundance of tree species will decrease, while the diversity of plant and shrub species will increase. The potential response variable is Species diversity (categorical) and explanatory variable is Elevation (continuous).
You have 3 variables changing – elevation, moisture and disturbance and so it is hard to say which one is causing the changes that you see. The first two, elevation and moisture, are related in this case as the slope is going down towards the creek so those you can’t untangle and are interrelated anyway so you don’t need to.
However, I am unclear on the human disturbance factor and how it changes along your gradient. You note the picnic shelter is disturbed but still has trees. How big of an area is cleared and how big of an area around the creek is your proposed study area? These types of details will be important for you to consider when planning your sampling strategy. I also find it strange that you note the trees like cedar and Douglas fir are associated with disturbance as I am not sure that is true. I think it is more likely related to moisture, the lowest areas of the floodplain around streams are often shrubby as those species can tolerate submergence better.
I would suggest that you either:
a) find an area around the creek that has no or minimal human disturbance and study vegetation changes with distance from the creek (studying moisture / elevation as distance from the creek). This is a fairly common study that students choose as it is an easy gradient to find and study. You could also consider measuring soil moisture which I’ve had a lot of students do.
OR
b) Find an area that is disturbed and undisturbed that are similar in terms of moisture and elevation and the only difference is human disturbance and compare species diversity between the two areas.
Note, either of these options (a or b) would work with vegetation diversity / tree diversity specifically / bird diversity or another species abundance / diversity.
In both cases, you need a large enough area for replicates. If measuring vegetation, for trees, usually a 10 m circular plot is used, shrubs are usually 5 m circular plots and ground species 1 m quadrats. You want to aim for 15 or so replicates total across your gradient.