Case study 1: The effects of climate on the growth of lodgepole pine

1. BACKGROUND To compete successfully in the world economy, the commercial forestry industry requires an understanding of how changes in climate influence the growth of trees. The goal of this case study was to examine how well-known climate variables, combined with estimated crown biomass, can predict wood accumulation in lodgepole pine. In order to model the growth and yield of trees over time, we need to determine how much wood a tree accumulates each year. Each year, a tree lays down an annual ring of wood in a layer under the bark. Pressler’s hypothesis states that area of wood laid down annually, measured by the cross-sectional area increment, increases linearly from the top of the tree to the base of the crown (the location of the lowest live branches) and is based on the assumption that area increment in the crown increases with the amount of foliage above the point of interest. Below the crown, the area increment in any given year remains constant down the bole until the region of butt swell at the base of most trees. The growth of a tree in any given year is strongly influenced by growth in the previous years. One reason for this is that buds are formed the year before they start to grow and carbohydrates from good years can be stored to fuel growth in subsequent years. The effects of previous growing conditions can last from 1 to 3 years, depending on tree species and location. Climate affects growth and influences both the size of the annual ring of wood and the proportions of early and late wood. Low density early wood is laid down during the spring when water is plentiful. Late wood, which is laid down from mid-summer until growth ceases in the fall, has a high density. Cessation of wood formation is sensitive to weather conditions such as temperature and drought. Lodgepole pine (Pinus contorta Doug. ex Loud.) stands dominate much of western Canada and the United States, covering over 26 million hectares of forest land. It is an important commercial species in British Columbia; stands consisting of more than 50% lodgepole pine occupy 58% of the forests in the interior of the province. Lodgepole pine is primarily used for lumber, poles, railroad ties, posts, furniture, cabinetry, and construction timbers. It is commercially important to be able to predict how lodgepole pine will grow and accumulate wood over time. Using high resolution satellite images of lodgepole pine stands to predict wood attributes is under consideration, but first the relationship of crown properties such as the amount of foliage must be linked to wood properties and growth.