FOREST INVESTMENT ACCOUNT FOREST SCIENCE PROGRAM Project Y051293 HYDROLOGIC DECISION MAKING TOOLS FOR SUSTAINABLE FOREST MANAGEMENT IN RAIN DOMINATED COASTAL BC WATERSHEDS Background Summary: Forest Recovery Parameters Contact: Younes Alila, Ph.D., P.Eng. Associate Professor Department of Forest Resources Management, University of British Columbia, #2030-2424 Main Mall Vancouver, BC, Canada V6T 1Z4 E-mail: alila@interchange.ubc.ca Website: faculty.forestry.ubc.ca/alila/main.html 1
Introduction Within the distributed hydrology soil vegetation model (DHSVM), over- and under-story canopy vegetation is characterized using parameters describing structural and biophysical properties. With respect to recovery, insufficient information exists with which to quantify temporal changes in biophysical properties. As such, vegetation recovery is parameterized solely by describing changes in vegetation structural properties through time, specifically dominant vegetation height, percent canopy cover, and leaf area index (LAI). The following summary briefly describes the methodology used to derive forest recovery parameters with stand age. Also included with this summary are the resulting recovery curves. Study Area Carnation Creek watershed is located on the west coast of Vancouver Island and drains into Barkley sound, near the town of Bamfield, British Columbia (see Inset, Figure 1). The basin area of 9.8 km 2 contains rugged topography with elevation ranging from sea level to 900 m and basin slopes as steep as 40 to over 80%; although the lower 3 km of Carnation Creek flows through a relatively wide (50 to 200 m) valley bottom (Figure 1). Slope soils, which are underlain by watertight bedrock of volcanic origin, are derived from colluvial materials and are of gravely sandy-loam and loamy-sand texture. Soils are generally shallow, with a mean depth of 0.75 m, and are highly permeable. Figure 1. Carnation Creek study area. 2
The watershed lies entirely within the Coastal Western Hemlock (CWH) biogeoclimatic zone and prior to management was covered by climax forest composed primarily of western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata), and amabilis fir (Abies amabilis), with some Douglas fir (Pseudotsuga menziesii) in drier sites, Sitka spruce (Picea sitchensis) in the valley bottom, and red alder (Alnus rubra) along the stream margins. About 50% of the basin was clearcut logged in various stages between 1971 and 1991; this included 34 km of main haul and cutblock access roads, creating a road density of 3.5 km/km 2. The original climax forest has dominant overstory tree heights ranging from 23 to 43 m, and canopy density that ranges from 50 to 75%. Method and Results Pre-management vegetation was assigned to four forest classes based on mapping by Oswald [1982]: class 1 - channel communities, class 2 - lower slopes forests, class 3 - middle slopes forest, and class 4 - upper slopes forest (Figure 2; Table 1). Forest cover maps for the region surrounding Carnation Creek [FC1 092C095 and 092C096] were used to derive relationships between canopy closure and stand height versus stand age, classified by site index. The site index is used to describe areas as having either good, medium, or poor forest recovery potential. The pre-management forest classes were assigned to a site recovery index based on soil development. From the mapping of Oswald [1982] it is suggested that pre-management forest classes 1 and 2 correspond to areas of moderately deep soils; these two classes are assigned a site index of good. Forest class 3 tends to occupy areas of shallow soil to moderately deep soils and has been assigned a recovery potential of Figure 2. Carnation Creek pre-management forest classes. 3
Table 1. Pre-management Structural Characteristics of DHSVM Forest Classes. Class Description Height a (m) Canopy Cover b LAI (m 2 /m 2 ) 1 Channel Communities (Western Hemlock/Cedar/Spruce) 43 0.75 6.4 2 Lower Slopes (primarily Western Hemlock) 43 0.75 6.4 3 Middle Slopes (Western Hemlock/Douglas Fir) 37 0.60 6.4 4 Upper Slopes (Western Hemlock/Douglas Fir) 25 0.50 6.4 a Height of dominant overstory trees b Proportion of land area covered by overstory (vertical projection) medium. Forest class 4 primarily occupies areas of shallow soil or exposed bedrock and has been assigned a recovery potential of poor. Overstory recovery of canopy closure and stand height are based on the Chapman-Richards equation [Richards, 1959]: Y ( bx ) ( e ) c = a 1 (1) where Y is either stand height (in m) or canopy closure (in percent), X is stand age (in years) and a, b, and c were coefficients fit by eye to the data. Fitted coefficients are summarized in Table 2 and recovery relationships are shown in Figure 3 and Figure 4 for canopy cover and stand height, respectively. Recovery of overstory leaf area index (LAI) was based on LAI-2000 measurements taken for chronosequences in the CWH very wet biogeoclimatic sub zone [Frazer et al., 2000]. Recovery was estimated by fitting a modified Chapman-Richards equation of the form: Y = a ( bx ) c ( 1 e ) 1 d( X 50) ( ) (2) where d is an additional coefficient (fit by eye) and the added term accounts for the smaller canopy density in old-growth stands as compared to young forest stands, where measurements suggest that LAI is at a maximum near a stand age of 50 years. Overstory LAI recovery is shown in Figure 5 and parameters are summarized in Table 2. Understory recovery of percent canopy cover was based on Y ( bx ) ( e ) c = 24 + a 1 (3) fit to at-site data, where canopy cover at year zero is maintained at 24%. Understory height is taken to be a constant 0.6 m (F igure 6). Understory LAI for use in the model was calculated based on time since logging by multiplying the percent canopy cover recovery curve (3) with a value of 3.0 m 2 /m 2 [Running et al., 1986]. Physical characteristics of pre-management old-growth vegetation (Table 1) were determined by using the above relationships and assuming a stand age of 200 years. 4
Table 2. Forest Recovery Parameters. Parameter Canopy Cover (%) Stand Height (m) LAI (m 2 /m 2 ) Canopy Cover (%) Coefficients Good Medium Poor a b c d a b c d a b c d Overstory 75 0.100 3 --- 60 0.100 3 --- 50 0.100 3 --- 43 0.039 2 --- 37 0.035 2 --- 25 0.035 2 --- 8.27 0.100 3 0.0015 8.27 0.100 3 0.0015 8.27 0.100 3 0.0015 Understory 40 0.300 3 --- 40 0.300 3 --- 40 0.300 3 --- Figure 3. Overstory percent canopy cover recovery by site index. 5
Figure 4. Overstory stand height recovery by site index. Figure 5. Overstory leaf area index recovery. 6
Figure 6. Understory percent canopy cover recovery. References Frazer, G.W., J.A. Trofymow and K.P. Lertzman (2000), Canopy openness and leaf area in chronosequences of coastal temperate rainforests, Canadian Journal of Forest Research, 30, 239-256. Oswald, E.T. (1982), Pre-harvest vegetation and soils of Carnation Creek watershed, In Proceedings of the Carnation Creek workshop: A ten-year review, Hartmann, G.F. (ed.), Canadian Forest Service, Pacific Biological Station, Nanaimo, BC. Richards, F.J. (1959), A flexible growth function for empirical use, Journal of Experimental Biology, 10, 290-300. Running, S.W., L.D. Petersen, M.A. Spanner and K.B. Teuber (1986), Remote sensing of coniferous forest leaf area, Ecology, 67, 273-276. 7