by Marie-Claude Boileau | 30 January 2019
Published in Trees 28: 1723–1735. https://doi.org/10.1007/s00468-014-1080-4
Partial cutting is frequently applied to increase the volume growth of residual stems. However, the opening of the forest increases the wind speed within the site, and consequently, the risk of windthrow. In the case of black spruce, uprooted trees are normally characterized by a lifting of the root plate. This research was conducted to compare the root systems of standing and uprooted black spruces, after commercial thinning, by looking at root architecture, volume and radial growth. For this purpose, data from a pool of 18 standing and 18 uprooted trees from three study areas were analyzed. The distribution of roots around the stump was compared between both types of trees, standing and uprooted. The radial growth was measured at 30 cm in the stem, 10 cm and 60 cm in the roots. The shape (I and T-beam) and volume were recorded for each root system. The structure of the roots was also mapped to obtain a spatial overview of the angle between roots. The root shape (at 10 and 60 cm) and the angle between roots combined with the diameter of the stem at stump height seem to determine the vulnerability of black spruce to windthrow. Uprooted trees developed fewer roots, with a large sector around the stump without lateral roots which suggests its major implication in the resistance to windthrow.
by Marie-Claude Boileau | 30 January 2019
Published in American Journal of Plant Sciences 4: 1278-1284
Plants acclimate to nitrogen (N) or moisture stress by respectively increasing photosynthetic N use efficiency (PNUE) or water use efficiency (WUE), in order to maximize their relative growth rate (RGR). These two phenotypic adaptations have opposite effects on specific leaf area (SLA). Thus, intraspecific variations in the SLA-RGR relationship should reflect the relative importance of N vs. moisture stress in plants. In this study, we measured needle gas exchanges and N concentrations in order to derive PNUE and WUE, as well as SLA and RGR of black spruce (Picea mariana) seedlings growing on a rapidly drained site in the presence or absence of Kalmia angustifolia. The eradication of Kalmia had resulted in a ~140% increase in seedling growth over a 6 year period. We found a negative SLA-RGR relationship where Kalmia had been eradicated, and a positive one where Kalmia had been maintained. Kalmia eradication resulted in higher WUE when measurements were made directly on the seedlings, and in lower PNUE when twigs were rehydrated prior to gas exchange measurements. Our data suggest that the bigger seedlings on Kalmia-eradicated plots increase RGR by decreasing SLA, as a means of coping with moisture stress. By contrast, increasing SLA on non-eradicated plots may be a means of coping with nutrient stress exerted by Kalmia. The SLA-RGR relationship could potentially be used to identify the limiting resource for black spruce seedlings in different environments.
by Claire Morin | 30 January 2019
Published in Scandinavian Journal of Forest Research 31(1): 8-18. https://doi.org/10.1080/02827581.2015.1068369
The foliage biomass–sapwood relationship (the pipe model) is critical for tree growth and is used in tree growth models for understanding the implications of this structural relationship on the allocation of resources. In this research, we compared this relationship for two commercially important and sympatric species, black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss). At locations in eastern Canada, 57 black and 50 white spruce trees were destructively sampled to obtain foliage biomass, crown structure, and tree stem measures. Using a model-based approach, we compared foliage biomass–branch basal area and foliage biomass–sapwood relationships at the tree and disk (i.e. along the tree stem) levels (i.e. pipe-model ratios) between these two species. We found that (i) branch foliage biomass–branch basal area was greater for black spruce than white spruce and (ii) pipe-model ratios along the tree stem given tree size were greater for black spruce than for white spruce. We attributed these differences to: (i) greater shade tolerance and leaf longevity of black spruce; (ii) slower growth rates of black spruce; and (iii) differing hydraulic strategies and mechanical requirements.
by Marie-Claude Boileau | 30 January 2019
Published in Ecology 95(5): 1127-1133
It is recognized that the coexistence of herbaceous species in N-depleted habitats can be facilitated by N partitioning; however, the existence of such a phenomenon for trees has not yet been demonstrated. Here, we show from both foliage and soil 15N natural abundance values and from a 12-year in situ 15N addition experiment, that black spruce (Picea mariana) and jack pine (Pinus banksiana), two widespread species of the Canadian boreal forest, take up N at different depths. While black spruce takes up N from the organic soil, jack pine acquires it deeper within the highly N-depleted mineral soil. Systematic difference in foliar 15N natural abundance between the two species across seven sites distributed throughout the eastern Canadian boreal forest shows that N spatial partitioning is a widespread phenomenon. Distinct relationships between d15N and N concentration in leaves of both species further emphasize their difference in N acquisition strategies. This result suggests that such complementary mechanisms of N acquisition could facilitate tree species coexistence in such N-depleted habitats and could contribute to the positive biodiversity–productivity relationship recently revealed for the eastern Canadian boreal forest, where jack pine is present. It also has implications for forest management and provides new insights to interpret boreal forest regeneration following natural or anthropogenic perturbations.
by Svetlana Savin | 30 January 2019
Published in Forest Ecology and Management 323: 138-147. http://dx.doi.org/10.1016/j.foreco.2014.03.014
With increased rates of climate change, it is imperative for forest managers to have access to models that can take into account the expected effects of climate change on tree growth. To this end, growth function are sometimes used that include climatic variables such as mean annual temperature or precipitation averaged over decades. Such growth models are usually relatively easy to develop but they do not take into account the fact that tree diameter growth on a given year is determined not by climatic conditions that prevailed up to 30 years before but mainly by climatic conditions that prevailed during the current and previous year. Our objective is determine if including climatic variables obtained from dendroclimatic response function will lead to growth models having a better fit to data than versions with 30-year average climatic conditions, or no climate at all. Growth models were developed for Betula alleghaniensis, Acer saccharum, Acer rubrum and Fagus grandifolia using data from south-eastern Quebec. Three types of growth function were compared. A first set of growth function was developed in which the potential growth of a tree was modeled as a function of tree size and site characteristics (vegetation type and drainage) to be further modified as a non-linear function of plot basal area. The effect of climate was not explicitly accounted for in this fort set of growth function, therefore they will be refered to as Climateimplicit models. A second set of growth function was developed in which we explicitly accounted for the effect of climate by incorporating 30-year mean annual temperature and precipitation in the growth function. In a third type of growth function, also climate-explicit, we incorporated the most significant recent climatic variables identified using climatic response function developed for each species based on dendrochronological and climatic data. The three types of models were compared based on the Akaike information criterion (AIC). Our results showed that Climate-explicit growth models with climatic variables obtained from response function analysis outperformed other growth models for three out of four species (B. alleghaniensis, A. saccharum and F. grandifolia). Incorporating climate in the form of 30-year average climatic conditions brought some improvement over a non-climatic function for A. rubrum, but this was not the case for other species. Accounting for growth dependency on climate by including recent monthly climatic variables provided by response function could be a potentially useful approach for the development of a new lineage of tree growth models dealing with climate change.
