PARENT SESSION
Organized Oral Session 40: Understory and epiphytic vegetation as indicators of the ecological integrity of managed forests
Organizer(s): S Haeussler, S Gachet, Y Bergeron, and E MacDonald
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 510a, Level 5, Palais des congrès de Montréal

Understory plant composition and diversity as indicators of ecological condition in partially-harvested boreal forests.

Macdonald, Ellen^*,1, ¹ University of Alberta, Edmonton, Alberta, Canada

ABSTRACT- Partial–harvesting has become popular as an approach to maintaining biodiversity and ecological integrity in managed forest. This is true even in the boreal forest which, as a fire–dominated landscape, was traditionally managed by clearcut systems. Partial harvesting has many possible ecological objectives: 1) preserve species associated with mature forest (life–boat effect); 2) move mature forest towards the structure and biotic composition of old forest; 3) achieve a certain desired structural and compositional state supportive of particular biotic elements; 4) leave a biological legacy in support of faster recovery of biodiversity post-harvesting. I will present a synthesis from studies examining variable retention and understory protection harvesting in mixedwood forest (various mixtures of aspen-white spruce) and thinning in conifer (lodgepole pine – black spruce) forest in Alberta. The analysis was aimed at uncovering approaches to the use of understory vascular plants to assess success with respect to different objectives for partial harvesting. Effects of the harvesting treatments were superimposed on patterns of association between the understory community and the associated canopy and soil nutrients. Thus, to some extent, utilization of understory plants as indicators needs to be ecosystem-specific as well as specific to a particular objective. In general, impacts of partial harvesting were more dramatic in forests with a conifer component. Indicator species associated with mature or old, closed-canopy forest, and which were susceptible to declines in abundance following opening of the canopy, could be useful for assessing success with respect to objectives 1) and 2). For objectives 3) and 4) an effective approach might be to examine the occurrence of characteristic groups of species (indicator communities), which are indicative of forest structure, canopy composition, and successional stage. At a larger scale, beta diversity can reveal much about changes in within– and between– stand heterogeneity, and associated impacts on biodiversity and composition at the landscape scale. It is at this scale that we see some of the most obvious broad–scale effects of partial harvesting: increased heterogeneity within and among conifer stands but homogenization in aspen-dominated forest.

Key words: partial harvest, boreal forest, understory plants, community composition