Abstract
Three large-scale, experimental, dispersed residual tree sites established in coastal British Columbia, Canada were measured for planted Douglas-fir tree growth and survival five to six years after planting. The dispersed trees were predominantly large diameter (60 cm+) Douglas-fir left with a range of 0% to 30% of the original forest stand basal area (0 m2 ha−1 to 14 m2 ha−1). Two sites had 0%, 5% and 15% retention, while one site had 0%, 5%, 10% and 30% retention. The trees were measured in sector plots established to randomly sample the range of microsites in each treatment. There was no detectable difference between height and basal diameter growth or mortality rates between the retention treatments over the measurement period, except for a reduction of basal diameter growth at the 30% retention level (p < 0.05). Thus a statistically significant impact on growth was demonstrated for the 30% retention compared to the 0% retention level. We expected intermediate growth rates between the 0% and the other lower retention levels but were unable to demonstrate this due to the low statistical power of the test (10 observations) and high site variability for these very young trees.
Highlights
In order to meet a variety of societal and ecological needs more trees are being retained within harvested areas in some areas of the Pacific Northwest of North America and elsewhere using the Forests 2012, 3 variable retention approach [1]
The purpose of this paper is to examine the level of retention at which dispersed trees affect the growth of regenerating Douglas-fir (Pseudotsuga menziessi (Mirb.) Franco) in coastal British
This observation was supported by examining height-diameter rations (HDR) which ranged from 84 at 30% retention to 67 in the clearcut
Summary
In order to meet a variety of societal and ecological needs more trees are being retained within harvested areas in some areas of the Pacific Northwest of North America and elsewhere using the Forests 2012, 3 variable retention approach [1]. The variable retention (VR) system is a recent example of a silvicultural approach where trees are left either singly or in groups using dispersed or aggregated retention [2]. Variable retention is relatively new [3] so there has been little systematic data collected on the impacts of the increased tree and forest edge on the growth of the regenerating trees. Hypothesized that dispersed retention will reduce regeneration growth more than aggregated retention, because for a given level of retention dispersed retention leaves more forest edge than aggregated retention. The purpose of this paper is to examine the level of retention at which dispersed trees affect the growth of regenerating Douglas-fir (Pseudotsuga menziessi (Mirb.) Franco) in coastal British. The hypothesis tested is what is the level of dispersed retention that significantly impacts the growth and survival of young, planted Douglas-fir at an operational scale?
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