A concern over high elevation regeneration performance in large clearcuts was the primary reason for establishing the Montane Alternative Silvicultural Systems (MASS) study (Arnott and Beese 1997). This project examines the biological suitability, feasibility and long-term site productivity of alternatives to clearcutting. Inconsistent stocking and growth slow-down or check occurs in many montane (700-1100m) clearcuts. These growth problems are hypothesized to be caused by unfavorable microclimate, vegetation competition, nutrient availability or alterations to ecosystem processes affecting forest regeneration. Silvicultural systems that provide canopy protection to reduce microclimatic extremes and to provide continued litter-fall may help regenerate the shade tolerant amabilis fir and western hemlock that dominate these forests. Clearcutting, green tree retention, shelterwood and patch cutting create different forest structure and microclimate conditions that may affect natural and planted regeneration, nutrition and vegetation competition. Forest managers need to know these impacts in order to prepare appropriate silvicultural prescriptions to meet various management objectives.
Conifer growth check, a problem often encountered on coastal montane clearcuts of lower nutritional status, is characterized by variable or reduced height increment and chlorotic foliage and does not appear to affect regeneration until approximately seven to ten years following harvesting (Husted 1982, Koppenaal and Mitchell 1992). Potential consequences include plantation or natural regeneration failure, delay in free-to-grow status and significantly longer rotations. Growth check is often associated with nutrient-poor sites with vigorous ericaceous shrub competition in low elevation coastal cedar-hemlock-salal forests (i.e. SCHIRP, Prescott 1996) in B.C. and black spruce-Kalmia forests in eastern Canada (Mallik 2003) where the problem has received considerable study. The impact of ericaceous shrubs on conifer regeneration in these forest types can severely reduce growth through direct and indirect competition for nutrients, including allelopathic effects resulting in recalcitrant organic soils that degrade site quality (de Montigny and Weetman 1990, Mallik 2003). However, in higher elevation HwBaCw forests where regeneration is constrained by cold soils and a shorter growing season, little is known about the underlying causes of growth check and the potential for silvicultural mitigation using alternative silvicultural systems. On many of these montane sites Vaccinium species and fireweed are the dominant competitors following harvesting (Titus et al 2007) and are major sinks for N (Mitchell et al 2007, Kimmins et al 2002), considered the most growth limiting nutrient in coastal B.C. forests. Vaccinium species, ericaceous shrubs, have been implicated in conifer growth check in eastern Canada (Thiffault et al 2005) and parts of Europe, but very little is known about their competitive and allelopathic effects on conifer regeneration on coastal montane and high elevation sites in B.C.
At MASS, almost 15 years after inception, there are strong indications that conifer regeneration has gone into check providing a unique opportunity to evaluate the growth response of planted and natural regeneration during this critical period by comparing performance in alternative systems. Vegetation control and fertilizer (at time of planting) treatments were included as split plots in all silvicultural systems at MASS and will be evaluated for their effectiveness in forestalling the onset and development of growth check. In addition to a 15-year assessment of planted and natural conifer growth we will undertake an intensive sampling of a subset of the planted amabilis fir to quantify growth check by determining height increments over the past 8 years. The growth check assessment will also determine the cover and proximity of ericaceous shrubs, conifer stem
Beese, W.J. (Bill), Mitchell, Alan K.; Koppenaal, Ross S.; Bown, Tom. 2009. Growth of montane conifers 15 years after clearcutting and alternative systems at MASS. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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