Avian Assemblages Differ between Old-Growth and Mature White Pine Forests of Ontario, Canada: A Role for Supercanopy Trees?

• Main Authors: David Anthony. Kirk, Daniel A. Welsh, James A. Baker, Ian D. Thompson, Myriam Csizy
• Format: Article
• Language: English
• Published: Resilience Alliance 2012-06-01
• Series: Avian Conservation and Ecology
• Subjects: avian abundance; avian assemblage; avian diversity; forest management; old-growth pine stands; Ontario; Canada; supercanopy pine; white pine
• Online Access: http://www.ace-eco.org/vol7/iss1/art4/

We predicted that bird diversity and abundance of some bird species would be higher in old-growth stands than in mature pine stands because of the greater structural diversity in old growth. We also predicted that patch size of stands should be influential. To test these predictions, we modeled counts of 79 bird species from 52 stands in 5 regions in the province of Ontario, Canada in relation to habitat at the local and landscape extents. Neither total species richness nor abundance differed between stand types. No significant difference was found in bird assemblages between stand types using ordination analysis. However, more Neotropical migrants were found in old-growth stands than in mature stands, while the reverse was true for short-distance migrants. Twenty-five species had higher counts in old-growth stands - three significantly so: Brown Creeper Certhia americana, Northern Parula Setophaga americana, and Scarlet Tanager Piranga olivacea. Supercanopy pine (> 60 cm dbh) was a significant (P < 0.05) positive predictor for Black-throated Green Warbler Setophaga virens, Northern Parula, and total species richness, while medium/large pine (> 40 cm/dbh) was a significant positive predictor for Brown Creeper, Pine Warbler Setophaga pinus, and total species richness. The density of supercanopy and medium/large pine explained a small but significant amount of variation in bird assemblages (1%), after considering age, other tree variables (9%), and landscape metrics. Patch size was significant for Evening Grosbeak Coccothraustes vespertinus and total abundance. According to receiver operating characteristic (ROC) thresholds, Brown Creeper required a minimum of 62 stems/ha of medium/large pine. Pileated Woodpecker Dryocopus pileatus and Black-throated Green Warbler required a minimum of 14 and 23 stems/ha of supercanopy pine, respectively. Blackburnian Warbler Setophaga fusca required a minimum stand age of 66 years. Current targets in shelterwood seed cuts for pine appear to be just within range for Brown Creeper - at least for the first cut, but not for subsequent cuts. We recommend that forest management seek to emulate increased old-growth characteristics in a proportion of managed stands that fall within the range of variation expected under natural variation.