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Natural regeneration in a cutover (clearcut) and the adjacent old-growth stand on the outer central coast of British Columbia McClarnon, Christine Fietkau

Abstract

Given increased interest in harvesting lowland cedar-hemlock rainforests in the Very Wet Hypermaritime Coastal Western Hemlock subzone of British Columbia, this observational study was initiated to seek better understanding of how these forests regenerate naturally, both in the absence of, and following, harvesting. Plots were established in a clearcut and an immediately adjacent old-growth stand, within which small trees (less than 1.3 m) were examined. Small tree presence, height, and age distributions were constructed according to stand type, species, reproductive origin, stand edge distance (in the clearcut), microtopography, substrate, soil moisture and nutrient regime, and non-crop vegetation. Potential future crop trees per hectare were also estimated. Based on this study: 1) Ingress could not be relied upon to regenerate the clearcut within 5-years, whereas advanced regeneration, some of which lacked apical dominance of shoot terminal leaders, appeared to be important. 2) Proportionally more veglings than seedlings reached 5-years of age and 30 cm in height. In the clearcut, proportionally more Tsuga heterophylla than Thuja plicata reached 30 cm in height, and advanced regeneration consisted of proportionally more Tsuga heterophylla than Thuja plicata. 3) Proportionally more small trees occurred on Lignomor, mineral, and moss substrates than on other substrates in both stand types. 4) Microtopographic influence was related to substrate and soil moisture and nutrient regime, and differed between stand types. In the clearcut, increased soil nutrient regime on inclines/mounds positively influenced small tree presence and height growth beyond 30 cm, while increased soil moisture regime on inclines/mounds negatively influenced height growth beyond 30 cm. In the old-growth, proportionally fewer small trees reached 30 cm in height on inclines/mounds, and proportionally fewer reached 5-years of age on wet organic or moss substrates on inclines/mounds. 5) In the old-growth, increased soil nutrient regime negatively influenced small tree presence, and increased soil moisture regime positively influenced survival beyond 5 years. In the clearcut, increased soil nutrient regime negatively influenced small tree height growth beyond 30 cm, yet positively influenced height growth beyond 30 cm on Lignomors; increased soil moisture regime negatively influenced survival beyond 5-years; and increased soil nutrient regime negatively influenced Tsuga heterophylla survival beyond 5-years. 6) Blechnum spicant and Calamagrostis nootkatensis were more extensive in the clearcut, and Blechnum spicant negatively influenced small tree presence. Grass/sedge presence may also limit regeneration.

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