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After observing that certain lichens tend to prefer certain sides of trees, I plan to study whether it is a NSEW preference or simply a light availability preference. This is a snapshot, observational study. After the realization I had in Haida Gwaii regarding the difficulty of identifying lichens, even to the genus level, I have decided to stick to very general growth forms: crustose (dust), foliose (leaf), and fruticose (shrub).
Date: Feb 8, 2018, Time: 1130 hrs, Weather: sunny, partly cloudy, 11C
To collect my initial field data I used a stratified random sampling method. Mount Douglas is already divided into three areas including the lower forest, upper forest, and rocky outcrop, which I used as my strata. I used a distance based method to sample trees in each strata. To assure randomization I used a random number generator phone application where first I generated the amount of steps forward on the path I would take, then I randomly generated a second number that would tell me how many steps perpendicular to the path I would take, and a third number to tell me whether I would go right or left on the path.
For the initial observations I sampled 5 trees, or replicates, in each strata. In the lower and upper forest, most trees were coniferous except 1. Foliose lichens were not present in the lower and upper forests, except for the very last tree in the upper forest that I sampled that was quite close to where the rocky outcrop started. In the rocky outcrop, foliose lichens were present on all the trees, and all the trees were deciduous garry oaks (quercus garryana). The crustose lichens were present in all three strata and on all sides of each tree.
I estimated percent canopy cover to get an idea whether light availability has an effect on where the lichens grow. In the rocky outcrop garry oak ecosystem, the trees were all deciduous, much shorter, and there was much more opening in the canopy. Foliose lichens were present on all the trees, which could be a correlation.
My hypothesis will be (Ha, alternate hypothesis): There is a significant difference in percent cover of three lichen growth types depending on the aspect of the tree trunk.
Ho (null hypothesis): There is no significant difference in percent cover of lichens depending on aspect of tree trunk.
Response variable: Percent cover of lichen (continuous)
Predictor Variable(s): Aspect of tree (categorical)
I predict that I will accept the alternate hypothesis and reject the null hypothesis.
I could add more predictor variables, such as whether the tree is deciduous or coniferous, and the layer of the forest, but this might be too complicated and require too many replicates. I have to think about this one!
Hey fellow student here. Sounds like a fun and interesting experiment you have going. Just have a question about the predictor variable for when you say it is the aspects of the tree. Are you talking about the light exposer the tree has or are you also including the size and possibly the different types of trees you will be sampling. For me it might be easier to just have the predictor variable be the light exposer the different trees will have.
Hi there,
Thanks for your question. I chose to measure the coverage on each aspect of the tree to see if the distribution of lichens differed which may indicate that light exposure on certain aspects was more favourable. It would have been difficult to directly measure light exposure directly because I don’t have any fancy equipment like light meters and canopy openness meters! I have concluded that aspect isn’t so important, it is more about general light availability.