by Marie-Claude Boileau | 30 January 2019
Published in Canadian Journal of Forest Research 40: 1930-1939
In most large-scale inventories, volume models rely on predicted heights instead of measured heights. The effect of height predictions over volume estimate uncertainty is therefore a crucial issue. In this study, we designed a statistical estimator that enables the propagation of tree height prediction errors into a general volume model. The proposed estimator relies on the assumption that both the volume model and the height-diameter model that provides the height predictions do not exibit any lack of fit. This estimator was tested against a Monte Carlo simulation for 90 plots from three typical forest types in Québec, Canada (hardwood, mixedwood, and softwood). The results show that the estimator provides plot volume predictions with error variances that fit those estimated using the Monte Carlo simulation. The estimator developed in this study may be useful to quickly provide the uncertainty associated with plot volume predictions in large-scale inventories.
by Audrey Verreault | 30 January 2019
Published in Forest Ecology and Management 257: 1839-1846
The role of lianas (woody vines) in the development and diversity of both tropical and temperate forests under differing management scenarios has not been thoroughly explored. We examined changes in grapevine (Vitis spp.) densities over time in clearcut stands as influenced by manual tending, physiography, and host tree associations. We used data from long-term studies on 66 clearcut stands dominated by temperate deciduous forest tree species on the Hoosier National Forest in south-central Indiana, USA. Fourteen of the stands had grapevines removed manually, approximately during the stem exclusion stage of development. Grapevine densities steadily increased from age 5 until age 15, which coincides with the period of stem exclusion of these stands. Subsequent grapevine mortality may have been related to light competition. Manually treated stands had similar grapevine densities as untreated stands after 20 years across sites, and it appeared that only on the most xeric area was the grapevine treatment effective in reducing grapevine densities. During early stand development, ranging from ages 5 to 17, grapevine density was strongly related to slope position, but as stands developed through the stem exclusion stage, aspect emerged as a stronger factor influencing grapevine density. Black cherry (Prunus serotina Ehrh.), walnut (Juglans spp.), and elm (Ulmus spp.) were the most common grapevine host trees under both treated and untreated scenarios, which may be associated with the crown architecture of these species. Results suggest lianas play a critical role in the early development of disturbed forest sites in temperate deciduous forests. With concerns that lianas are increasing in abundance and distribution in these forest types, understanding their role in forest dynamics, such as host tree associations at different stages of development, competition dynamics on different sites and corresponding influences on tree growth, species composition, and diversity, will be critical to decision-making processes in achieving desired management goals in the future.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 165: 235-248
We parameterized the light model of SORTIE for northern hardwoods in eastern Canada, and performed a sensitivity analysis and validation tests of the model before using it to predict the effect of various types of partial cutting on understorey light conditions. The parameterization was done by characterizing the crown geometry and openness of sugar maple (Acer saccharum Marsh.), yellow birch (Betula alleghaniensis Britt.), and beech (Fagus grandifolia Ehrh.). Those results indicated that beech casts a deeper shade than sugar maple and yellow birch. The sensitivity analysis showed that the model predictions were more sensitive to variations in the crown geometry parameters, especially the crown radius parameter, than to variations in crown openness. Validation tests of the model were performed in both mapped and unmapped plots by comparing light predicted by SORTIE to light measured in the field using hemispherical photographs and sensor-based measurements. In mapped stands, the model provided reasonably accurate predictions of the overall variation in understorey light levels between 2 and 30% full sunlight, but the predictions tended to lack spatial precision. In unmapped stands, SORTIE accurately predicted stand-level mean light availability at 5 m aboveground for stands ranging in basal area from 19 to 27 m2/ha. At heights lower than 5 m, SORTIE accurately predicted the light availability in a recent selection cut with a low density of understorey vegetation, but tended to overestimate light availability in stands with relatively dense undergrowth. Finally, a demonstration of the possible usefulness of the SORTIE light model is presented by using the model to compare the proportion of various light microsites created by a variety of selection cutting systems in use in eastern Canada (selection cutting with different harvesting intensities, group selection, and patch selection).
by Audrey Verreault | 30 January 2019
Note de recherche forestière hors série. Published for the XIIe Congrès forestier mondial. 21 au 28 septembre 2003, Québec QC.
The hardwood forest zone in Québec covers 110,000 km2 in the extreme south of the province, or 15% of the forested area. Sugar maple stands are the most widespread types of stands in the hardwood zone. Softwood stands, such as hemlock, white pine and red pine, typical in this zone, are found in smaller numbers.
The hardwood forest covers the most populated portion of Québec and contains great natural wealth, which bestows it with inestimable value. This hardwood zone plays an important economic role by supplying high-quality timber and producing maple syrup. This vast zone nevertheless underwent the effect of colonization, and cutting practices that were poorly adapted to the natural stand dynamics greatly reduced their timber production potential.
The Direction de la recherche forestière (Forest Research Branch) of the ministère des Ressources naturelles, de la Faune et des Parcs du Québec (MRNFP) started by undertaking research to work out hardwood forest dynamics. It then conducted studies on partial cuts adapted to the hardwood forest, such as selection cutting. Currently, a range of harvest modalities is being studied to determine the behaviour of treated stands. An experimental network also covers southern Québec. Results of this research will help to orient the types of silvicultural interventions to practise related to characteristics of the forest, and will contribute to ensuring its sustainability for the benefit of all Québecers.
by Audrey Verreault | 30 January 2019
Published in American Journal of Botany 97(10): 1688-1697
Premise of the study: Poplars and their hybrids are seen as important candidates for bioenergy initiatives. However, many concerns have been raised about large-scale plantations of new poplar cultivars. The deployment of such plants with novel traits brings the risk of potential spread of novel genome regions (including exotic genes, transgenes, or other heritable modifications) into natural populations of related species. The possibility of introgression is especially high in poplars because reproductive barriers between species are weak. Knowledge of the frequency of hybridization between cultivated trees and natural populations is one important step in the risk-assessment process.
Methods: We studied the rate of spontaneous hybridization from two sexually mature poplar plantations into adjacent natural populations of Populus deltoides and P. balsamifera. The two plantations, both in eastern Canada, contain many different complex hybrid clones with components from exotic species, mostly P. nigra, P. trichocarpa, and P. maximowiczii. We analyzed 12 species-specific single nucleotide polymorphisms from six different genes in 5373 offspring sampled from the natural populations.
Results: Contributions from all three exotics were found in the offspring, confirming low reproductive barriers among poplar species in these sections. The frequency of hybrid offspring varied among pollen donors, recipient populations, and years.
Conclusions: The remarkably high rate of hybridization that was found in the smallest natural population sampled suggests that small peripheral populations carry a higher risk of introgression. These results could be used as a starting point for developing regulatory guidelines for the introduction of plants with novel traits.
