Postfire seedling recruitment at the southern limit of lichen woodland

Although fire is the primary mechanism driving regeneration in open black spruce (Picea mariana (Mill.) BSP) lichen woodland, there are limited data concerning the sources of seedling mortality across the range of burn severity. We monitored planted seedlings in areas of high and low burn severity in Terra Nova National Park (Newfoundland, Canada) to determine sources and patterns of mortality of black spruce seedlings among burn treatments following a recent burn (2002). The importance of herbivory by small mammals as a source of seedling mortality was evaluated using small cages that excluded voles and non-native snowshoe hare. Overall seedling mortality was high (79%) in all areas; mortality was similar in areas of low (73%) and high (76%) burn severity, and highest in edge areas adjacent to closed-canopy forest (90%). Drought, rather than herbivory, was the most common cause of mortality during the first two seasons following germination. Seedling mortality at the southern edge of the lichen woodland was comparable to that found in other studies, but sources differed, emphasizing the spatially variable nature of mortality. Based on the level of seedling recruitment, our results suggest lichen woodland will return at this site. Resume: Bien que le feu soit le principal mecanisme de regeneration des pessieres ouvertes a epinette noire (Picea mariana (Mill.) BSP) et a lichens, il y a peu d'informations concernant les sources de mortalite des semis en fonction du gradient d'intensite du feu. Nous avons suivi des semis plantes sur des stations brulees ou l'intensite du feu avait ete soit forte, soit faible, dans le Parc national Terra Nova (Terre-Neuve, Canada) pour determiner les sources et les patrons de mortalite des semis d'epinette noire selon l'intensite du feu a la suite d'un feu recent (2002). L'importance de l'herbivorisme par les petits mammiferes pour expliquer la mortalite des semis a ete evaluee en utilisant de petites cages qui excluaient les campagnols et les lievres non indigenes. La mortalite totale des semis etait elevee (79 %) dans toutes les stations. La mortalite etait semblable que l'intensite du feu ait ete faible (73 %) ou forte (76 %), mais elle etait plus elevee en bordure d'une foret fermee (90 %). La secheresse, plutot que l'herbivorisme, constituait la cause de mortalite la plus commune au cours des deux premieres saisons de croissance qui ont suivi la germination. La mortalite des semis a la limite sud de la pessiere a lichens etait semblable a celle qui a ete observee dans d'autres etudes, mais les causes de mortalite etaient differentes, ce qui met en evidence la variabilite spatiale de la mortalite. Sur la base du niveau de recrutement de semis, nos resultats indiquent que la pessiere a lichens reviendra a son etat initial a cet endroit. [Traduit par la Redaction]
Introduction Although fire is the primary mechanism driving regeneration in open black spruce (Picea mariana (Mill.) BSP) lichen woodland (Chen and Popadiouk 2002), there are limited data concerning the sources [...]