Ecology Lab 5: The Effects of Density and Sunlight Exposure to a Maple Trees Growth

Hypothesis: Testing the effects of density and sunlight availability on a trees growth or its diameter at breast height (DBH). Methods: Observations and data were collected at the York University Keele campus in the woodlot. A target species was selected to be Maple trees. The target tree to be observed was selected randomly by walking 10 steps north and 5 steps east. A 10 meter radius was laid around the target tree, the number of plants within the radius were counted and recorded in order to determine the density. This includes adult trees and saplings, which were defined to be any tree at least 3 meters in height. The diameter at breast height was measured and recorded as well as the percentage of sunlight coverage. This was done by standing directly against the tree facing towards the direction of sunlight, using a 4′ by 6″ quadrant to estimate the amount of sunlight the tree is exposed to. A new tree was selected at least 5 meters away from the outside of previous radius to avoid recounting. A random maple tree was selected once again by walking 10 steps north and 5 steps east and selecting the closest maple tree outside the previous radius. The process was repeated for a total sample size of 35 maple trees. Predictions: Assuming that the density and sunlight availability are independent of each other the following predictions can be made. - High density creates competition amongst species for resources (water, space, nutrients), negatively effecting the tree growth (small dbh) - High density can mean there is an abundance of resources available in that location which positively effects the trees growth (large dbh) - Large canopy coverage means there is competition for sunlight, negatively effects growth (small dbh) - Small canopy coverage, low competition, high exposure to sunlight which positively effects growth (large dbh)

研究假设：探究林分密度与光照可获得性对树木生长及胸径（Diameter at Breast Height, DBH）的影响。
研究方法：数据采集于约克大学基尔校区的小片林地。本研究选取槭树（Maple trees）作为目标树种。目标观测树的选取方式为：向北步行10步、向东步行5步后随机确定点位，以该点位为中心设置10米半径的样圆，统计该样圆内所有植株（包括成年树及高度≥3米的幼树）的数量以计算林分密度。同时测量并记录目标树的胸径，以及其接收的光照百分比：测量时站在树干正对光照方向，采用4英尺×6英寸的样方（quadrant）估算树木的光照暴露程度。选取新样树时，需使其与前一样圆的外缘至少相距5米以避免重复计数，同样通过向北10步、向东5步后选取该范围内最近的槭树作为新样本。本研究共采集35株槭树作为有效样本。
研究预测：假设林分密度与光照可获得性相互独立，可提出如下预测：
- 高林分密度会引发物种间对水分、空间、养分等资源的竞争，对树木生长产生负面影响（胸径偏小）；
- 高林分密度也可能意味着该区域资源充足，对树木生长产生正面影响（胸径偏大）；
- 冠层覆盖度较高时，树木间会产生光照竞争，抑制生长（胸径偏小）；
- 冠层覆盖度较低时，光照竞争少且树木光照暴露度高，可促进生长（胸径偏大）。