As part of the Montane Alternative Silviculture Systems (MASS) project, this study investigates limits on the growth of montane conifers resulting from varying overstory retention under conventional and alternative silvicultural systems. After harvesting treatments were complete in 1993, Abies amabilis (amabilis fir) and Tsuga heterophylla (western hemlock) seedlings were spring planted in replicated blocks of shelterwood (SW), patch cut (PC), green tree retention (GT) and clearcut (CC) systems. In addition, sub-plots were established within each silvicultural system in which fertilization (at planting) and vegetation control post-planting treatments were applied alone and in combination to test the extent to which growth limitations are related to nutrient availability and vegetative competition. The impact of overstory retention was most pronounced in the reduced light environment of the SW where height growth after seven years was 26-30% lower in both species compared to the untreated CC, GT and PC systems. Although the effect on growth of both species in the SW was mitigated somewhat by fertilization and vegetation control treatments, amabilis fir did not attain free-to-grow height (1.3 m) regardless of post-planting treatment. Time to free-to-grow height in the more open silvicultural systems was reduced in both fir and hemlock with fertilization and vegetation control alone and in combination, except in the CC where the initial growth response to fertilization alone was diminished by the end of the sevenyear study. In contrast to fertilization, the effects of vegetation control on height growth were not apparent until three to five years and seven years after planting in the CC and GT, PC, SW, respectively. Combining vegetation control and fertilization had an additive effect on growth in amabilis fir but not in western hemlock. The effect of silvicultural systems and post-planting treatments on the two species illustrate that both above-and below-ground resource availability (light and nutrients) availability was potentially limiting to growth, particularly in the shelterwood treatment.Key words: MASS, silviculture systems, regeneration, Tsuga heterophylla, Abies amabilis, shelterwood, patch cut, green tree retention, clearcut, fertilizer, vegetation control En tant qu'élément du projet sur les systèmes alternatifs de sylviculture dans la zone montagneuse, cette étude porte sur la réduction de la croissance des conifères alpins à la suite d'une rétention variable du couvert forestier selon des systèmes sylvicoles conventionnels et alternatifs. Suite aux travaux de récolte complétés en 1993, des semis d'Abies amabilis (sapin amabilis) et de Tsuga heterophylla (pruche de l'Ouest) ont été plantés au printemps dans des blocs d'une étude des régimes de jardinage, de coupe partielle, de coupe par troué, de coupe avec rétention d'arbres verts et de coupe à blanc. De plus, des sous-parcelles ont été établies dans chaque régime sylvicole pour lesquels des traitements de fertilisation (au moment de la plantation) e...
Conifer regeneration on clearcut montane sites is frequently affected by post-planting growth stagnation. The ability to predict such stagnation would be a valuable asset to forest managers. In this study, we tested the usefulness of above-ground biomass and photosynthetic efficiency (as estimated by foliar nitrogen concentration) in diagnosing growth limitations in western hemlock (Tsuga heterophylla) and amabilis fir (Abies amabilis). Seedlings were grown under different silvicultural systems (clearcut, patch cut, green tree retention and shelterwood) and post-planting treatments (fertilization, vegetation removal) at the Montane Alternative Silvicultural Systems (MASS) site on Vancouver Island, BC. Foliar nitrogen was found to be a poor predictor of height and stem volume growth. However, above-ground biomass predicted current height and stem volume (year 3 after planting), as well as future stem volume (year 7 after planting), in both species. Above-ground biomass therefore represents a useful measure of likely future growth performance, and may provide early warning of incipient growth stagnation in these species.Key words: amabilis fir, Abies amabilis, biomass, western hemlock, Tsuga heterophylla, growth limitation, photosynthetic capacity, biomass, seedling growth, regeneration La régénération résineuse sur les stations montagneuses coupées à blanc est fréquemment affectée de stagnation de la croissance post-plantation. La capacité de prédire une telle stagnation constituerait un actif important pour les aménagistes forestiers. Au cours de cette étude, nous avons testé l'utilité de la biomasse au-dessus du sol et l'efficience photosynthétique (estimé par la concentration foliaire en azote) pour établir un diagnostique d'entraves de la croissance pour la pruche de l'ouest (Tsuga heterophylla) et le sapin gracile (Abies amabilis). Les semis ont été plantés selon divers régimes sylvicoles (coupe à blanc, coupe par trouées, rétention d'arbres et coupe avec réserve de semenciers) et selon divers traitements post-plantation (fertilisation, coupe de la végétation) sur le site du Montane Alternative Silvicultural Systems (MASS) sur l'île de Vancouver en Colombie-Britannique. L'azote foliaire s'est révélé être un pauvre indicateur de la croissance en hauteur et en volume de la tige. Cependant, la biomasse au-dessus du sol a permis de prédire la hauteur actuelle et le volume de la tige (trois ans après la plantation), ainsi que le volume futur de la tige (7 ans après la plantation), pour les deux espèces. La biomasse au-dessus du sol représente donc une mesure utile de la performance probable de croissance future et pourrait constituer un signal précurseur du début de la stagnation en croissance de ces espèces.
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