Partial cutting is extensively used for harvesting dry belt forests in the southern BC interior. However, the lack of a high-quality, long-term database is an impediment to improving both uneven-aged stand management prescriptions and yield estimation for these stand types. Furthermore, little reliable information is available on the amounts of natural ingress and rates of sapling recruitment following partial cutting. Improved partial cutting practices and further refinements and improvements to growth models for these complex stands will greatly depend on the availability of local, high quality, long-term data.
With funding from the Forest Resource Development Agreement (FRDA II), the MoFR Research Branch established a partial cutting experiment (EP987.04) in an uneven-aged Douglas-fir stand north of Westwold (IDFdk2) in 1993 (Johnstone 2000). Replicated, factorial combinations of 3 levels of residual basal area and 2 levels of stand structure are being tested, along with an untreated control, for a total of 21, 0.25-ha permanent growth and yield plots. The single-tree harvest treatments removed between 33% and 60% of the initial basal area from the treatment plots. The two stand structures were achieved by setting the ?q-value? (negative exponential constant between 5-cm dbh classes) for a given residual basal area to values of approximately 1.3 and 1.5. (The smaller the value of q, the larger the proportion of growing stock contained in larger trees.) The growth of the residual stand was reassessed in 1998 (5-year) and 2003 (10-year) with funding from Forest Renewal BC (FRBC) and Forestry Innovation Investment (FII), respectively. In conjunction with the 2003 assessment, 84 permanent understory regeneration subplots were installed to measure ingress and follow the development of small trees below the tagging limit of the main treatment plots (FII Project R04-038). Recruits were tagged and assessed by species, quality, age and size and compared among the partial cut treatments (Bealle Statland and Johnstone 2004). Since 2005, these subplots have been assessed annually for mortality and vigour of the tagged seedlings (FIA-FSP Project L088030).
We propose to remeasure the entire installation and report the effects of different levels of residual growing stock and structure on overstory tree growth, stand development, recruitment and natural ingress fifteen years after the single-tree selection harvesting treatments. Since canopy development has a strong influence on understory conditions, measuring both overstory and understory at the same time will ensure that correlations between the two are properly observed. Tagged overstory trees, saplings and seedlings in all treatment plots will be measured for height, crown length, diameter at breast height (if taller than 1.3 m), vigour and survival.
It is anticipated that the results will be applied in the design of partial cut silviculture prescriptions in dry Douglas-fir forests, and in the ongoing development of stocking standards for partial cut treatments. The data will also be an important addition to our database of growth and yield information from multi-cohort stands, to be used in improving existing growth and yield simulation models such as TASS and PrognosisBC.
This project is one of only a few rigorously designed partially cutting experiments in southern BC, and will compliment the more observational studies of uneven-aged Dry Douglas-fir stand development, growth and yield, and regeneration that are ongoing at the Pothole Creek Study Area (FIA-FSP Projects Y082285 and L088029) and the Opax Mountain Silviculture Systems Trial (Y081280 and L88033). The work also compliments the Isobel dry Douglas-fir Management Project (L88032) which is testing a less regulated approach to partial cut design based on group retention.
Bealle Statland, Catherine A., Johnstone, Wayne D.. 2009. Growth and development of overstory and regeneration following partial cutting of dry-belt Douglas-fir. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2009MR019
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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