User: | Open Learning Faculty Member:
I plan to study lichen growth on tree bark in Stanley Park. In the field, I chose to observe a line of 10 trees (approx. 75 m in length, North to South) in an immature stand (30 – 99 years) that ran from north to south. The environmental gradient spanned multiple locations that varied by canopy coverage and sunlight penetration. I recorded observations for each tree, which included my best in-field description of the tree genus (spruce, fir, cedar, beech). What was classified as spruce in the field, was determined to be hemlock. I recorded the approximate percent coverage of lichen, from eye-level to the base of the tree trunk. I recorded the side of the tree (ie. north, south, east, or west) with the predominant lichen coverage. I scored each tree trunk for light penetration based on canopy coverage and forest density, which I estimated in the field. The following described how each tree was scored for approximate sunlight penetration in the forested area:
0 – Full canopy coverage, dense forest; no light penetration to tree base/trunk
1 – Some openings in canopy, dense forest; minimal light penetration to tree base/trunk
2 – Medium openings in canopy coverage; forested area; visible light penetration to tree base/trunk
3 – No canopy coverage, wide open area; full visible light penetration to tree base/trunk for most of the day
Moss and or lichen coverage was visually estimated from eye level to the base of the tree. Moss/lichen percent (%) coverage was approximated using the following score system:
0 – Little to no visible lichen coverage (i.e. 0 – 10% coverage from eye level to base of tree)
1 – Minimal, patchy lichen coverage (i.e. 10 – 30% coverage from eye level to base of tree)
2 – Medium lichen coverage (i.e. 30 – 70% coverage from eye level to base of tree)
3 – High lichen coverage (i.e. 70 – 100%).
Summary of Observations:
Estimating sunlight penetration based on canopy coverage was difficult to quantify, and would present a challenge to accurately measure in the field without proper instrumentation. Overall, 6 of 6 fir/hemlock trees had some degree of lichen coverage. When compared to beech, only 1 of 3 had observable lichen growth. No lichen growth was observed on the 1 cedar observed. One notable difference between these three tree types is the visible rugosity, texture, and thickness of their bark. The fir and hemlock trees had thick, textured bark. In contrast, the beech and cedar bark was noticeably more sooth, with less cracks and crevasses. In summary, I have chosen a hypothesis that applies to one point on the gradient, specifically an area of trees that experience the same exposure to sunlight.
Hypothesis:
Fir and hemlock tree bark provides more suitable growth substrate for lichen in Stanley park.
Prediction:
Lichen growth is more common on bark of fir and hemlock trees, compared to beech and cedar bark in Stanley Park.
The presence or absence of lichen is a response variable, that could be treated as a categorical variable (i.e. yes or no) or a continuous variable (i.e. if yes = 1, and no = 0). A predictor variable could be the tree genus (categorical).
