| White birch (Betula papyrifera Marsh.) is one of the most widely distributed species in Canada, found in all forested regions and north to the tree line. It can be found in different soil, topographic and moisture regions. The genetic diversity of white birch has allowed it to adapt to several different environments, leading to the question of what hydraulic or water transportation characteristics allowed the species to evolve in this manner?;In total thirty sites were sampled across Canada ranging from Ontario to B.C. Three trees from each site were selected for sampling and from each tree three branches were sampled at the base of the live crown. Each branch was sampled at the 1cm diameter mark and transported to the lab in coolers. Leaves were removed with the petiole and analyzed for total leaf area. Microscopic images were created from the branch samples and analyzed for total vessel area, average vessel area, vessel diameter and number of vessels. Climactic variables were measured including average annual rainfall and the sites were divided into three moisture regimes: xeric (dry), Mesic (moderate) and hydric (wet).;Vessel diameter and leaf area were both positively correlated with rainfall and total vessel area was also positively correlated with total leaf area in the mesic and xeric site, therefore we fail to reject the null hypothesis for xeric and mesic sites. Hydric sites had contradicting results, with smaller leaf areas and several negative relationships. It was assumed that yearly average rainfall would account for all rainfall in the growing season, as the rest of the sites experience precipitation mostly in the form of snow during the winter. The hydric sites receive rainfall all year round, with the majority falling in the winter months. This means that the trees in this site experience a more xeric environment during summer and are susceptible to water stress.;I recommend further sampling of white birch from areas of the natural distribution that were not sampled (i.e. Costal B.C., Alaska, east coast, Quebec) to further explore the hydraulic architecture. Also I recommend common garden tests and DNA testing to deduce whether the difference across moisture regimes is an ecotypic response to physical environments or a phenotypic response.;One of the key hypotheses of this research is that white birch that has evolved in wet areas will have larger vessels than those trees that evolved in dry areas. Since the wet areas are less likely to experience drought they can therefore produce larger vessels while dry areas produce smaller vessels to ward off any embolism that may occur during a drought. The second hypothesis is that birch trees in dry areas will produce lower sapwood to leaf area ratios then those in wetter environments. Trees in the wet areas can support higher leaf area per unit of sapwood area while trees in dry areas have made structural modifications to leaf area as a result of water stress.;Key Words: white birch, vessel diameter, vessel area, total leaf area, moisture gradient, average annual rainfall, xeric regime, mesic regime, hydric regime... |
