The impact of the Olympic marmot on subalpine vegetation structure [Impact de la marmotte olympique sur la structure de la végétation subalpine].

Résumé

Examen par des techniques descriptives des conséquences de la présence d'une population de marmottes sur les sols (nature, états) et sur la végétation (composistion, diversité). Dans les champs secs, les marmottes affouragent sur de grandes distances et leur impact est moins concentré autour des tertres. Dans les prairies humides, l'impact est intense autour des monticules. Quand l'impact des marmottes augmente les graminés déclinent quelque peu, les espèces palatables déclinent fortement et les espèces non palatables augmentent fortement. Une activité modérée des marmottes réduit la dominance des espèces commune et augmente la diversité. Ces observations mettent l'accent sur le fait que les paysages naturels, qui semblent en harmonieux équilibre avec l'environnement physique, sont fortement modelés par les activités des animaux. The impact of Olympic marmots on subalpine meadow vegetation was examined by descriptive methods. Differential grazing and various earth moving activities of marmots produce marked vegetational contrasts between mound vegetation and the surrounding meadows, between heavily impacted and lightly impacted vegetation immediately surrounding mounds, and between vegetation in the central portion of a colony and that on its periphery. The patterns differed in degree between a dry meadow, with lower production and a wet meadow with higher production. In dry meadows, marmots forage over greater distances and their impacts are less concentrated near mounds. ln wet meadows, impacts are intense near mounds. Differences were documented in structural features such as species richness, equitability, and percent vegetation cover and in shifts of species composition. As marmot impact increased graminoid species declined somewhat, palatable species declined markedly, and both ruderal and unpalatable species increased greatly. Moderate marmot activity reduced the dominance of common species and thereby enhanced community diversity. These observations emphasize that much of the natural landscape, seemingly in harmonious equilibrium with its physical environment, is strongly molded by the activities of native animals.