The white pine (Pinus strobus) is a rapid-growing conifer used in reforestation, landscaping and christmas tree farming. Trees grow by annually multiplying basic units of branches - the maximum size is limited only by the ability of a tree to survive through time. Buds at the tips of branches break dormancy in the spring and grow outward, lengthening the branch. The central bud in the cluster extends the branch and the lateral buds form a new whorl of branches.
Trees increase height by the growth of a single main trunk or leader. The central bud of the leader tends to break dormancy before the lateral buds and becomes the dominant stem. The lateral buds form a whorl of branches around the leader. Generally, the distance between each whorl represents one year's growth.
Due to apical dominance, pines tend to grow in a conical shape with a single main trunk from which lateral branches arise. If a leader is damaged or lost, the tree may lose its conical growth form.
A careful examination of the trees should reveal that there was considerable variation in the rate at which individual trees grew since 1990. Your job is to consider biological and environmental factors that may explain this variation.