Abundance and species composition of amphibians, small mammals, and songbirds in riparian forest buffer strips of varying widths in the boreal mixedwood of Alberta

Abstract

Forested buffer strips are left along water bodies after forest harvesting to protect water quality and fish stocks, but little is known about their utility as reserves for forest species in managed landscapes. We report on changes in terrestrial vertebrate communities from pre-to post-harvest in experimentally created buffer strips (20, 100, 200, and 800 m wide) in a boreal mixedwood forest in Alberta, Canada. We trapped anuran amphibians and small mammals and spot-mapped bird territories around 12 lakes (4 treatment levels, 3 replicates) before and after harvesting. Changes in small mammal or amphibian abundance were not detected for any treatment relative to controls; however, these species are habitat generalists that used and even bred in clearcuts. Total bird abundance did not change after harvesting, with the exception of crowding in 20-m buffers 1 year post-harvest. Species composition did not change for amphibians and small mammals after harvest, but forest-dependent bird species declined as buffer width narrowed from 200 to 100 m and narrower. We concluded that 20-100 m buffers would not serve as reserves for forest songbirds in managed landscapes, but that 200 m wide strips conserved the pre-harvest passerine bird community, at least up to 3 years post-harvest.Résumé : Lors de coupes forestières, des lisières boisées sont laissées le long des plans d'eau pour protéger la qualité de l'eau et les stocks de poissons. On sait peu de choses de leur utilité comme réserves pour les espèces forestières dans les paysages aménagés. Nous avons documenté les changements dans les communautés de vertébrés terrestres avant et après coupe, dans des lisières boisées expérimentales (20, 100, 200 et 800 m de largeur), dans une forêt boréale mixte de l'Alberta, au Canada. Nous avons piégé les anoures (amphibiens) et les petits mammifères et inventorié les oiseaux par cartographie des territoires autour de 12 lacs (4 niveaux de traitements, 3 répétitions), avant et après coupe. Aucun changement d'abondance des petits mammifères et des amphibiens n'a été détecté dans les traitements par rapport aux témoins, mais ces espèces sont des généralistes qui utilisent et même nichent dans les coupes à blanc. L'abondance totale d'oiseaux n'a pas changé après coupe, à l'exception d'une concentration dans les lisières de 20 m l'année après coupe. La composition spécifique en amphibiens et petits mammifères n'a pas changé après coupe, mais les espèces d'oiseaux dépendants de la forêt ont décliné en relation avec le rétrécissement des lisières de 200 à 100 m et moins. Nous concluons que les lisières de 20-100 m ne servent pas de réserves pour les oiseaux forestiers dans les paysages aménagés tandis que les lisières de 200 m de largeur conservent les communautés d'oiseaux d'avant coupe au moins durant les 3 années suivant la coupe. [Traduit par la Rédaction]Hannon et al. 1800

Riparian Partial Harvesting and Upland Clear Cutting Alter Bird Communities in a Boreal Mixedwood Forest

“…This is contrary to the results of many other studies in which total avian abundance in buffer strips actually increased post-harvest [10,15,17,[45][46][47]. Post-harvest increases in abundance in buffer strips have been attributed to "crowding in" of individuals of mature forest species displaced from nearby clear cuts [10,17,45]. We did not see a crowding effect in our study, possibly because (1) partial harvesting rendered our buffer strips less suitable for forest interior species; or (2) the area surrounding our cut blocks was not as extensively harvested as elsewhere and displaced birds were able to find suitable habitat elsewhere [16].…”

“…It has been suggested that riparian buffer strips are generally too narrow to provide adequate breeding habitat for forest dependent and interior bird species [10,11], although they may contribute to habitat connectivity [19,22]. Since riparian buffers were originally designed to protect aquatic resources, for which the benefits are clear, and only incidentally upland species and habitats [11], current riparian management objectives might be more appropriately focused on water body protection, the conservation of specific riparian habitat features and species, and the creation of movement corridors for aquatic and terrestrial wildlife [25].…”

“…Forested buffer strips are typically prescribed around water bodies during forest harvesting operations to minimize effects on aquatic communities, processes and functions, and to maintain fish and wildlife habitat [2,5,[10][11][12][13]. These remnant forest strips provide several potential benefits to forest bird communities.…”

“…These include maintaining breeding habitat for forest interior and riparian species [13][14][15][16] and providing additional habitat for ubiquitous, generalist and edge-associated species [2,13,15,17,18]. Riparian buffer strips may also function as dispersal and movement corridors [19,20], facilitating landscape connectivity [10], but see [21], and thereby reducing songbird turnover in connected forest patches [22].…”

LiDAR derived ecological integrity indicators for riparian zones: Application to the Houille river in Southern Belgium/Northern France

“…Riparian zones monitoring is based on measurable attributes describing the riparian zone conditions and their ability to carry out their functions. As example, the longitudinal continuity is important for plant dispersal (Johansson et al, 1996;Hughes, 2003), production of stream insects (Hannon et al, 2002;Whitaker et al, 2000) or migration of birds (Decamps et al, 1987;Tewksbury et al, 2002) and mammals (Darveau et al, 2001;Cockle and Richardson, 2003). Monitoring often combines observable physical, chemical and biological attributes, which can vary in response to human alteration.…”