GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Effects of Forestry Practices on Species Composition and Taxonomic and Structural Diversity

Mark R. Roberts and Ian R. Methven
Faculty of Forestry and Environmental Management
University of New Brunswick
Fredericton, N.B. E3B 6C2

METHODS

A chronosequence of artificially regenerated clearcuts (plantations) and naturally regenerated clearcuts were compared to mature natural stands which have been affected by past Spruce Budworm outbreaks. Three plantations in each of three age classes (5-7, 10-12 and 14-16 years; 9 plantations total) and two naturally regenerated clearcuts (7 and 38 years) were selected in the Fundy Model Forest adjacent to Fundy National Park. Three natural stands with maximum tree ages of approximately 90 years were selected within the Park. All stands were dominated by Spruce and Fir on imperfectly to moderately-well drained sites with vegetation type (VT) 2, 3, 6, or 7 (Note: 2&3=low fertility sites, 6&7=moderate fertility sites). Species composition and diversity of all vascular plants and many common bryophytes in the herbaceous layer (<1 m tall) were assessed in all stands based on percent cover of each species.

RESULTS

Plant composition rather than diversity was affected most by disturbances. Fifty-five species occurred in the plantations that were not found in the mature natural stands; many of these were invader species which take advantage of disturbances (Table 1; Figure 1). Only six of the species found in mature natural stands were absent from the plantations, suggesting that species richness tends to increase in artificially regenerated stands compared to mature natural stands. However, species percent cover fluctuated widely between the natural stands and the plantations. A total of 20 species had lower abundance in the plantations (Figure 1). Along with the species that disappeared, these species should be the focus of biodiversity management efforts (Table 1).

Table 1. Species listed by type of response in plantations from local study

Table 1. (Continued)

Figure 1.

There were no significant differences among the three age classes of plantations nor between the old plantations (14-16 years) and the natural stands in any species diversity index, including species richness, Simpson's index, Shannon-Wiener index, Shannon evenness, and Margalef's index (Table 2).

Site conditions had a greater effect on species richness and diversity than stand management. Plantations on slightly richer sites (VT 6, 7) had significantly higher species richness, Shannon and Margalef diversity indices than stands on poorer sites (VT 2, 3; Table 2). Therefore, site conditions should be carefully assessed in any diversity study. Also, harvesting may have different effects on species diversity depending on site conditions.

IMPLICATIONS FOR MANAGEMENT

• Biodiversity management efforts should focus on species which have lower abundance in plantations as well as on species that have disappeared.
• Site conditions should be carefully assessed in any diversity study, since these have a greater effect on species richness and diversity than stand management
• Harvesting may have different effects on species diversity depending on site conditions.
• Criteria and indicators of sustainable forest management are being developed based on species changes.

Additional studies are currently under way to determine the life-history characteristics of species that control their response to harvesting disturbances. This information is needed to meet land management and conservation objectives that call for maintenance of species diversity.

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Information provided by:
Dr. Graham Forbes
Faculty of Forestry and Environmental Management at UNB
Last Update: May 7, 1998
This document: http://www.unb.ca/web/forestry/centers/cwru/soe/forpract.htm