Responses of boreal epiphytic bryophytes to different leveis of partial canopy harvest

Epiphytic mosses and liverworts contribute substantially to the bryophyte diversity of circumpolar boreal forests but are susceptible lo altered growing conditions after forest harvesting. Management practices that retain some trees after harvest may enhance epiphyte survival; however, the effectiveness or this emerging method needs lo be assessed. We examined the survival, composition, and nearest neighbour relationships of epiphytic bryophytes on trembling aspen (Populus tremuloides Michx.) across a range (10%-100%) of dispersed green-tree retention 5 years after harvest in boreal mixed- wood forest. Growth of the forest floor moss Hylocomium splendens (Hedw.) Schimp. in B.S.G. was used as an indicator of changes in moisture availability for epiphytes following harvesting. Epiphyte richness and abundance increased with canopy retention and were positively correlated with local abundance of coniferous trees. Positive associations among neighbouring species in intact forest demonstrated that interspecies relationships form naturally. However, there was a shift in species composition after harvesting and fewer interspecific associations with declining retention. These trends were accompanied by reduced Hylocomium splendens growth, which implies that moisture may be an important driver of epiphyte response. Although different levels of canopy retention were similarly capable of maintaining some epiphytes, the loss of species associated with intact forest will require consideration of alternative management practices for their conservation. Key words: corticolous, Hylocomium splendens, liverwort, moss, poikilohydric. variable retention. Les mousses et les hepatiques epiphytes contribuent subsiantiellement a la diversite des bryophytes des forets boreales circumpolaires, mais sont sensibles aux modifications des conditions de croissance, suite aux operations forestieres. Les methodes d'amenagement qui conservent certains arbres apres la recolte peuvent ameliorer la survie des epiphytes; cependant, on doit evaluer l'efficacite de ces methodes en emergence. Les auteurs ont examine la survie, la composition et les relations avec les voisins les plus rapproches des bryophytes epiphytes sur le peuplier faux-tremble (Populas tremuloides Michx.) pour l'ensemble d'une aire (10% a 100%) comportant des arbres vivants conserves et disperses, 5 ans apres la recolte dans une foret boreale mixte. Ils ont utilise la croissance d'une mousse du parterre forestier, l'Hylocomium splendens (Hedw.) Schimp, in B.S.G., colome indicatrice des modifications de la disponibilite de l'humidite pour les epiphytes, suite a la recolte des arbres. La richesse et l'abondance des epiphytes augmentent avec la retention de la canopee et montrent des correlations positives avec l'abondance localisee de coniferes. Les associations positives avec les especes avoisinantes dans la foret intacie demontrent que des relations interspecifiques se forment nalurellement. Cependant, on observe un deplacement de la composition en especes apres la recolte et moins d'associations interspecifiques avec une diminution de la retention. Ces tendances s'accompagnent d'une reduction de la croissance de l'Hylocomium splendens, ce qui implique que l'humidite pourrait etre un agent causal important de la reaction des epiphytes. Bien que differents degres de conservation de la canopee peuvent etre egalement aptes a maintenir certaines epiphytes, la perte d'especes associees aux forets intactes necessitera la definition de methodes alternatives d'amenagement pour leur conservation. Mots-cles: corticole, Hylocomium splendens, hepatiques, mousse, poikilohydrique, retention variable. [Traduit par la Redaction]
Introduction Forest management practices that retain a greater volume of standing trees after harvest are gradually becoming more widely accepted in place of traditional clearcut methods in North American and [...]