| Citation |
Maloney, D., S. Bennett, A. de Groot, and A. Banner (2002) Canopy Interception in a Hypermaritime Forest on the North Coast of British Columbia, Forest Sciences, Prince Rupert Forest Region, BC Forest Service. Extension Note #49, November, 2002. |
| Abstract/Description or Keywords |
Canopy interception plays an important role in determining the amount of rainfall reaching the forest floor. During a rainfall event, water either penetrates the canopy falling directly to the understory of the forest floor, or is intercepted by the canopy. From there it can drip to the ground surface, flow down tree stems, or be held and evaporated. The portion that falls directly to the ground or drips from the canopy is termed throughfall. Rainfall that is intercepted and flows down the tree trunk is known as stemflow, and the remainder is called interception. The amount of rainfall intercepted by a forest canopy depends on storm size, intensity, duration, rainfall frequency, forest structure, tree species and architecture, tree age, tree density, and epiphytic growth such as moss and lichens (Crockford and Richardson 1990; Calder 1998; Spittlehouse 1998). Depending on these conditions, canopy interception can account for 15 to 35% of annual rainfall. The removal of the forest canopy in a wet environment will introduce more water to already saturated soils. Before any harvesting occurs it is important to know the role of the forest canopy in the water cycle and to determine the effects of this extra input of water. Potential effects of increased water include: larger peak water flows, decreased slope stability, road and streambank erosion, and damage to fish habitat (Spittlehouse 1998). The ecology of the site could also be affected; this includes a higher water table leading to regeneration problems, lower tree productivity, and paludification (peatland formation). This research is part of the HyP3 Project (Pattern, Process and Productivity in Hypermaritime Forests) initiated in the North Coast Forest District in 1997 to develop ecologically based guidelines for the management of lower productivity cedar-dominated forests on north coastal B.C. (see Extension Note 38, Banner and Shaw 1999 for project details). These forests are currently outside the operable land base. At present there is considerable uncertainty regarding the feasibility and sustainability of harvesting these wet, slow growing forests. One of the goals of the research project is to document the ecology and hydrology of the blanket bog – upland forest complex of the CWHvh2. This extension note documents: • interception, throughfall and stemflow as a percentage of total rainfall. • interception, throughfall and stemflow in relation to weather conditions, storm size and storm intensity. • the potential effects of changes in the interception rate due to harvesting. Two locations were used as study areas, one in Diana Lake provincial Park, 15 km southeast of Prince Rupert, and the second on Smith Island, 20 km south of Prince Rupert (Figure 1). The areas were selected as being representative of the forest type being studied. Both watersheds are located in the Coastal Western Hemlock biogeoclimatic zone, Very Wet Hypermaritime subzone – Central variant (CWHvh2); (Banner et al. 1993). Forests in the watersheds are comprised primarily of western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata), yellow cedar (Chamaecyparis nootkatensis) and amabilis fir (Abies amabilis); shore pine (Pinus contorta var. contorta), mountain hemlock (Tsuga mertensiana) and Sitka spruce (Picea sitchensis) also occur. Instrumentation was located at 72 m elevation on a southeast facing slope at Diana Lake, and at 52 m on a northeast facing slope at Smith Island. Both canopy interception sites were representative of the 01 Western redcedar-Western hemlock-Salal site series (Banner et al. 1993). |
