PhD in functional ecology and biogeography
Effect of alder on the growth of black spruce and jack pine in plantations at the northern limit of commercial forests in Québec
Stands located at the northern limit of commercial forests become more and more open in Québec. Cold temperatures limiting growth as well as the failure of regeneration after natural perturbations as fires constrained these stands. Tree regeneration of subarctic boreal forests can be constrained by several factors: the absence of advanced regeneration, insufficient seed rain, the lack of suitable seedbeds, and the presence of ericaceous species. In this context, restauration planting can be used to avoid the loss of forest cover. Studies showed that scarification improved seedling establishment and growth by reducing competing vegetation cover, increasing soil temperature, mitigating air temperature extremes, and stimulating organic matter decomposition. Surrounding species, however, did not have always a negative effect on seedling growth. Indeed, the surrounding species could increase the soil water content, the nutrient availability, or regulate the planting species microclimate. Moreover, some species, such as the alder, can improve the growing substrate thanks to their ability to fix the atmospheric nitrogen. Then, they could have a facilitative effect on the planted species. The objectives of this study are (i) to test if the alder presence leads to a growth gain (facilitative effect) or a growth loss (competitive effect) for the black spruce and the jack pine, and (ii) to determine the mechanisms associated to this growth loss or gain. Data was surveyed within six year-old experimental plantations located at the northern limit of commercial forests. We studied the height, the diameter, the surrounding species and the 15N isotopic and chemical compositions of soil and needles from black spruce and jack pine for four different syviculture scenarios: (i) a direct plantation without mechanical preparation (scarification), (ii) a plantation preceded by a standard mechanical preparation (one passing of the disc trencher), (iii) a plantation preceded by a standard mechanical preparation and a plantation of alder, and (iv) a plantation preceded by an intensive mechanical preparation (two passings of the disc trencher). This data will allow to study the interaction between the alder and the planted species (black spruce or jack pine). Tests are carried out to determine the presence of hierarchical structures between the number of alder and the ericaceous vegetation cover around planted species, the competition with the alder for light, the soil and needle nitrogen composition, and the conifer growth thanks to structural equation modeling. Our results will contribute to predict the plantation growth in stands at the northern limit of commercial boreal forests and identify the best management practices.
Mont St Joseph in Parc national du Mont Mégantic (Québec)- Autumn 2014
Productivity, composition and structure of boreal stands along a gradient of silviculture intensity
Parc Jacques Cartier - Source :
Forest managers aim at reducing the ecological distance between natural and managed forests to reconcile ecological issues with production of socioeconomic services. Ecosystem-based management have thus been implemented in Québec to reduce the gap between variability of key attributes (e.g. composition, structure, deadwood, soil organic matter, regeneration processes) in managed and in natural forests while intensifying wood production. Hence, there is an apparent antagonism between maintaining key ecosystem attributes of natural forests and increasing management intensity to favour merchantable wood production of desired species.
To our knowledge, few studies have looked at the combined long-term effects of silviculture treatments on merchantable productivity and key ecosystem attributes of managed stands. That is why, we are studying the stand productivity as well as on stand composition, structure and snags, i.e. three key attributes of natural forests 20 years after the onset of siviculture scenarios of increasing intensity in balsam fir-white birch stands in Réserve Faunique des Laurentides, Québec.