1. Effects of spatial configuration of habitat patches on the abundance of woodpeckers in the boreal forest of north-western Quebec
Caroline Gagné* 1,2, Pierre Drapeau1,2 and Louis Imbeau1,2
1. Groupe de Recherche en Écologie Forestière interuniversitaire, Département des sciences biologiques, Université du Québec à Montréal, Montréal, QC, Canada;
Chaire industrielle CRSNG UQAT-UQAM en Aménagement Forestier Durable, Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, QC, Canada. *
Results
To evaluate whether the spatial configuration of clear-cuts influenced the probability of occurrence of each sampled species, we realized the Fisher’s Exact Test and the significant differences are shown in Figure 3.
Figure 3. Probability of occurrence of eight cavity excavators
We then performed hierarchical logistic regressions to evaluate the real influence of the landscape variables on the probability of occurrence of these species. We used the Akaike information criterion (AIC) to select the “best” model. Because no single “best” model were ever existing, we used the model averaging method to determine the most important variables from the entire set of models. These results are shown below in Table 1.
Table 1. Scale of influence of habitat variables on cavity excavators
Introduction
Aggregated and dispersed clear-cuts are two management strategies that are currently used by several forest legislations in Canada. These management strategies generate an artificially fragmented landscape and a temporary loss of habitat for late successional species. Those who are dependant on dead wood for nesting and foraging, such as cavity excavator birds, are particularly vulnerable.
Our objectives were to 1) determine whether structural attributes differ between the two habitat types, 2) determine whether cavity excavators are influenced by spatial configuration of clear-cuts and 3) determine at what scales (local vs landscape) do habitat variables influence the occurrence of these species.
Method
The study area was located in the bioclimatic zone
of black spruce and feather moss, in the north-
western Quebec.
We sampled eight cavity excavator bird species
with playback and point count methods. Eighty
sites were located in residual blocks of dispersed
clear-cuts and 80 in leave strips of aggregated
clear-cuts, the sites being distant of at least 500 m
from each other.
Living trees, snags and woody debris were sampled according to their diameter at breast height (dbh), their deterioration state and tree species composition (Figure 1).
Figure 1. Schema of the sampling design used in both residual habitats
% occurrence
Aggregated clear-cuts
Dispersed
clear-cuts
Species
Habitat variables
Scale
Yellow-bellied Sapsucker
American Three-toed Woodpecker
Red-breasted Nuthatch
Black-backed Woodpecker
Boreal Chickadee
Northern Flicker
Large living trees (+)
Woody debris (+)
Mature forest area (+)
Forest cuts (-)
Forest cuts (+)
Distance to uncut forests (-)
Local
Landscape (composition)
Landscape (composition
& configuration)
Results
The basal area of snags and woody debris is significantly higher in leave strips of aggregated clear-cuts than in residual blocks of dispersed clear-cuts. On the other hand, residual blocks contain a higher basal area of living trees compared with leave strips (Figure 2).
Figure 2. Mean basal area with 95% confidence interval of snags and woody debris (Comp. 1) against living trees (Comp. 2)
Discussion
Snags are important structural attributes for closed canopy species such as many cavity excavators. Despite the fact that there are more snags in leave strips of aggregated clear-cuts, several species are more abundant in the residual blocks of dispersed clear-cuts. There may then exist another, more important, factor that leads the habitat selection by individuals. In this way, our results show that the area of mature forests seems to be an important variable influencing the probability of occurrence of these bird species. While managing at a landscape scale, large tracks of uncut mature forests should be left on the land base, interspersed in cut areas, to meet the needs of these species and many others.
Comp. 2
Comp. 1 -2 -1 1 2
Residual blocks
Riparian buffers
Clear-cut separators
Acknowledgements
Field work assistants: Marie-Claude Fontaine, Marie-Joëlle Touma, Jean-Rémi Julien, Yan Cossette and Marianne Cheveau
Financial support: FQRNT- Fond Forestier, SFMN, Chaire industrielle CRSNG UQAT-UQAM en Aménagement Forestier Durable, P. Drapeau NSERC Discovery grant, and L. Imbeau NSERC Discovery grant.