by Marie-Claude Boileau | 30 January 2019
Published in Canadian Journal of Forest Research 39: 1928-1938
Modelling volumes by log grades in standing hardwood trees is often hindered by the nature of the response variable. In this paper, we used a two-part conditional model to account for the excess of zero responses for some log grades. Moreover, this approach was used as a framework to compare three different tree classifications in their ability to predict volumes by log grades in standing yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh.) trees. A tree grade classification was compared with two preharvest tree classifications based on mortality risk assessment. A cross-validation was also carried out to evaluate the two parts of the model. The results showed that the two-part conditional approach was efficient in this case study. Compared with a general model, the three classifications improved the maximum likelihood. According to the Akaike and Bayesian information criteria, the tree grade classification was the ‘‘best’’ one. All three classifications proved to be better able to distinguish log grade occurrence than log grade volume. Although it implies additional cost, the implementation of the tree grade classification into the preharvest inventories would improve the prediction of volumes by log grades for yellow birch and sugar maple trees.
by Claire Morin | 30 January 2019
Published in Ecoscience 6(2): 264-271
To better understand the causes of sugar maple (Acer saccharum Marsh.) replacement by beech (Fagus grandifolia Ehrh.) in the Boisé-des-Muir old-growth forest (Québec), we studied, i) the effect of beech litter on soil properties, ii) the effect of low light availability on maple survival, and iii) beech regeneration via root sprouts. Soil properties, understory light, seedling emergence and survival, height growth, and density distribution of maple and beech were compared between the old-growth stand and an adjacent managed stand where the abundance of maple regeneration was high. We did not observe any detrimental effect of beech litter on soil properties and maple early establishment. Overall light availability and maple stocking were lower, and maple density declined more markedly with increasing size in the old-growth stand than in the managed stand. The deficient maple regeneration in the old-growth stand might be related to a lack of microsites where light availability is high enough for maple survival, and not to a lack of initial recruitment in this species. In the old-growth stand, beech was located in more shaded microsites than maple but had a higher growth. Size class distributions of maple and beech suggest that beech had a higher survival rate than maple and that beech sprouts had a higher survival rate than beech seedlings. Beech seems to be better adapted than maple to survive in the deep shade of the old-growth stand. However, we expect that maple will regain its dominance in the understory of the Boisé-des-Muir with increasing stand breakup that is likely to occur in the future.
by Audrey Verreault | 30 January 2019
Published in Ecology 89(10): 2879-2888
Understanding coexistence of highly shade-tolerant tree species is a long-standing challenge for forest ecologists. A conceptual model for the coexistence of sugar maple (Acer saccharum) and American beech (Fagus grandifolia) has been proposed, based on a low-light survival/high-light growth trade-off, which interacts with soil fertility and small-scale spatiotemporal variation in the environment. In this study, we first tested whether the spatial distribution of seedlings and saplings can be predicted by the spatiotemporal variability of light availability and soil fertility, and second, the manner in which the process of environmental filtering changes with regeneration size. We evaluate the support for this hypothesis relative to the one for a neutral model, i.e., for seed rain density predicted from the distribution of adult trees. To do so, we performed intensive sampling over 86 quadrats (5 x 5 m) in a 0.24-ha plot in a mature maple–beech community in Quebec, Canada. Maple and beech abundance, soil characteristics, light availability, and growth history (used as a proxy for spatiotemporal variation in light availability) were finely measured to model variation in sapling composition across different size classes. Results indicate that the variables selected to model species distribution do effectively change with size, but not as predicted by the conceptual model. Our results show that variability in the environment is not sufficient to differentiate these species’ distributions in space. Although species differ in their spatial distribution in the small size classes, they tend to correlate at the larger size class in which recruitment occurs. Overall, the results are not supportive of a model of coexistence based on small-scale variations in the environment. We propose that, at the scale of a local stand, the lack of fit of the model could result from the high similarity of species in the range of environmental conditions encountered, and we suggest that coexistence would be stable only at larger spatial scales at which variability in the environment is greater.
by Audrey Verreault | 30 January 2019
Published in Tree Seed Working Group – News Bulletin. Canadian forest genetics association. 50(December): 27-31
The theme of this News Bulletin is “Seed Testing” and I’d like to provide a brief overview of seed
testing history and some additional links for those interested in more information. I generally think of
seed testing in reference to two primary associations – Association of Official Seed Analysts (AOSA) and International Seed Testing Association (ISTA) that provide standardized rules, guidance, and a forum for the exchange of information.
by Audrey Verreault | 30 January 2019
Published in Silvæ Genetica 58(4): 152-161
We determined the degree to which families differ in seed and germination characteristics and examined the extent to which these characteristics influence the early growth of 75 open-pollinated white spruce families. Seed characteristics (1000-seed weight, length, width, area, volume) were measured for 400 seeds per family. Germination variables (germination capacity, peak value, germination value) were determined for each of the 75 families under controlled conditions and germination patterns were modeled using the Weibull function. Seedling characteristics (height, diameter, shoot and root dry weights) were measured at the end of the first and second growing seasons under standard nursery cultural practices. Statistically significant family variation (p < 0.0001) was found for all seed characteristics and germination variables measured. The between-family variance explained 23% to 98% of the total variance of morphological and physiological seed characteristics. Family differences at the seed stage explained up to 33% (root dry weight) and 12% (shoot dry weight) of the family differences observed at the one-year and two-year seedling stages, respectively. Since, in this study based on a comparison of family means, a maximum of only 12% of the family differences observed at the two-year seedling stage were explained by the effect of seed size, a selection for families with better juvenile characteristics could be envisaged without considering the maternal effect of seed size.
