Canadian Forest Service Publications
FORCYTE-11 and intensive management of Douglas-fir: Examination of some of the model's short- and long-term predictions of biomass production. 1991. Trofymow, J.A.; Sachs, D. Pages 38-57 in H. Grewal, Compiler. Forestry Canada modeling working group: Proceedings of the fifth annual workshop, December 13-14, 1990. Forestry Canada, Northern Forestry Centre, Edmonton, Alberta.
Issued by: Pacific Forestry Centre
Catalog ID: 3066
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Concern over the long-term productivity of forests with intensive biomass harvest has led to the development of FORCYTE-11, an ecosystem-based model which can be used to examine the impacts of different management schemes. Although calibrated and used to examine management impacts for several of forest types, the model has not been tested against an independent data set. FORCYTE-11 predictions were compared to 15 years of data from a thinning and fertilization experiment in a low site quality, 40-year-old stand of Pseudotsuga menziesii at Shawnigan Lake, B.C. (east coast of Vancouver Island). Data for 23 variables were compared but only data on stand biomass and density are reported in this paper. Initial comparisons with the uncalibrated model showed that model simulations were reasonable, with growth in treated plots tending to be more accurately predicted than in control plots. This was probably due to the model's weakness in its simulation of decomposition and soil organic matter. After calibration with control plot data and inclusion of an understory species, Gaultheria shallon, model fit improved, but its accuracy showed strong biases which varied with the thinning and fertilization treatments. The model was able to correctly predict the rankings of all 15 treatments. Using the control plot dataset for Shawnigan Lake, FORCYTE-11 was then used to examine the effects of intensive forest management on long-term productivity. The model predicted that yield would decline the most over time with short-rotation, whole-tree harvest. Effects of initial site conditions caused high biomass yields in either the first or second rotation, depending upon rotation length. Iterative simulations with the model suggested that to keep yield constant with successive rotations, large fertilizer additions were needed, especially with short-rotations. The model proved quite sensitive to variation in N inputs through precipitation, cumulative 360-year yields declined by 18% when N inputs were reduced from 2.0 to 0.5 kg N (ha yr)-1.