Évolution des forêts québécoises au regard des habitats fauniques : analyse des grandes tendances sur trois décennies | Evaluation of Quebec forests with regard to faunal habitats: analysis of large trends over three decades

As forest management intensified between the 1970s and the 1990s, we tested the prediction that three forest attributes, likely essential for some wildlife species, became rarer during this time interval: old (> 100 years) stands, dead wood and woody species diversity.We used a network of about 7000 permanent plots, surveyed at least three times, for determining trends followed by these variables during the last three decades of the 20th century.We stratified our analysis according to the six vegetation domains of the southern half of Québec where forest management occurs, i.e., from the sugar maple-bitternut to the spruce-moss domain. The proportion of old stands clearly diminished only in the western part of the sugar maple- and balsam fir-yellow birch domains.However, stands composed of old trees were already very scarce during the 1970s everywhere except in the spruce-moss domain where they could have increased in importance during the study period. Snags tended to become rarer only in the western part of sugar maple- and balsam fir-yellow birch domains whereas their abundance increased elsewhere, sometimes substantially, because of the spruce budworm epidemic that affected Québec between 1975 and 1990. Results suggest that tree diversity was impoverished in the two southernmost forest domains; the same tendency existed also for saplings, particularly because of intense browsing by white-tailed deer. In the boreal forest, the spruce budworm epidemic favoured sapling diversity during the 1980s and 1990s. Our analysis indicates that we must: 1) quickly exclude some typical old stands from forest management in all vegetation domains; 2) determine if some woody species became rarer in forest stands of southern Québec; 3) identify which elements of the forest fauna depend on old stands, rare tree species and senescent trees, and 4) continue to monitor the trend of dead wood present in Québec forests.