Forest Investment Account (FIA) - Forest Science Program
FIA Project Y073286

    Montane Alternative Silvicultural Systems (MASS): growth limitations on regeneration
Project lead: Mitchell, Alan
Contributing Authors: Mitchell, Alan K.; Maynard, Douglas G.; Titus, Brian D.; Macey, Donna E.; Koppenaal, Ross S.; Benton, Ross A.; Bown, Tom; Hogg, Karen; Goodmanson, Graeme; Prescott, Cindy E.; Bradley, Robert L.; Feller, Michael C.; Beese, W.J. (Bill); Seely, Brad A.; Senyk, John P.; Hawkins, Barbara J.
Imprint: Victoria, B.C. : Canadian Forest Service, 2007
Subject: Forest Investment Account (FIA), Forest Management, British Columbia, Forest Reproduction, Variable retention harvesting
Series: Forest Investment Account (FIA) - Forest Science Program
FSP Strategic Theme best fit topic: Timber Growth and Value Topic 2.1 Design and analysis of silvicultural systems. Development and monitoring of silvicultural systems for complex stands Relationship between residual stand structure and understory recruitment and development In coastal British Columbia, montane sites (over 700 m) comprise 30% of the land base for timber supply for forest companies and as a result it has become crucial that the effects of various silvicultural options are understood (Arnott and Beese 1997. Forestry Chronicle 73:670-678). This has led to concerns that regeneration of natural and planted trees may not be meeting expectations as a result of irregular stocking, unfavourable environmental conditions, poor nutrition, or limitations on other ecosystem processes (Koppenaal and Mitchell 1992. FRDA Report 192).The overall objective is to assess the influence of aggregate and dispersed retention systems on growth limitations to conifer regeneration. This project will build on previous work in 2004-2005 supported by FIA characterizing ten year survival and growth of regenerating conifers at the Montane Alternative Silviculture Systems (MASS) field site and advance our knowledge by investigating the ecological sources of limitations to growth arising from overstory retention. Results to date have shown that that there are growth limitations associated with overstorey retention stemming from above- and below-ground competition for light and nutrients that may require the calculation of adjustment factors for predicting seedling growth and yield under retention harvesting systems. Part 1: Growth Modeling Implementation of retention harvesting systems is being undertaken by forest managers on many coastal sites. However clearcut-based estimates of regeneration growth and yield may not accurately depict the trajectories of seedling growth when overstory trees are retained. This is particularly important for estimating impacts of dispersed and aggregated retention retention systems on stand establishment and potential delays in reaching free to grow criteria. In addition, growth stagnation, which can occur approximately ten years after clearcut harvesting on montane sites, may seriously compromise future growth and yield estimates. It has been suggested that retention systems may mitigate the problem through their moderating effects on climate and inputs to nutrient cycling processes. Results to date have shown that growth rates of regenerating conifers have changed in each successive year after planting. It is now ten years after harvesting at MASS and an ideal time to assess the impacts of retention systems on growth stagnation. The objective is to determine adjustment factors for seedling productivity under retention harvesting systems at MASS. Using seedling growth data from previous studies, equations will be developed to describe growth and yield trajectories that will allow comparisons between clearcut and alternative silviculture (retention) systems (Patch Cut, Shelterwood, Green Tree Retention) with respect to early stand establishment through the free to grow stage. These equations will also be used to characterize possible impacts of growth stagnation on future seedling growth and yield. Part 2: Nutrient Cycling MASS offers a unique opportunity to examine long-term (10-year) changes in nutrient process rates after clearcutting, and the extent to which these changes are mitigated through variable retention harvesting in montane forests of coastal BC. Research during the first 5 years after harvesting at MASS revealed that changes in several processes associated with the cycling of N after clearcutting were mitigated to varying degrees by alternative silvicultural systems. Although this information is important for estimating site nutrient losses, it is arguably more important to determine the long-term differences among treatments and establish if retention of live trees alters the recovery trajectories of nutrient cycling processes after different harvesting methods. The potential impacts of harvesting on nutrient cycling include: (i) loss of soil nutrients (ii) changes in nutrient availability to seedlings and leave-trees, (iii) changes in nutrient turnover and nutrient supply rates (iv) reduced seedling nutrient contents and growth, and (v) reduced long-term stand growth. Guided by growth data from studies in Year 1, the underlying causes of growth limitations on regeneration will be investigated by measuring variations in nutrient supply, turnover and availability that supported seedling growth. The objective is to determine the duration, magnitude and trajectories of soil nutrient cycling processes under clearcut and alternative (retention) silvicultural systems (Patch Cut, Shelterwood and Green Tree Retention) treatments. To do this we will establish studies to tie together measures of: (1) seedling nutrient uptake estimated from current–year foliage nutrients (N, P, K, Ca, Mg), (2) soil chemical composition (N, P, K, Ca, Mg), (3) supply of ammonium and nitrate measured using PRS? ion exchange probes, (4) incubations of soils for estimates of nutrient turnover rates, (5) estimates of decomposition rates using buried wood and (6) pilot studies to characterize microbial communities active in nutrient cycling. These measures will be conducted in all the silvicultural systems treatments and replicates.
Related projects:  FSP_Y051286FSP_Y062286


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Updated August 16, 2010 

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