Multidecadal shifts in forest plant diversity and community composition across glacial landforms in northern lower Michigan, USA

Understanding how plant community assemblage is affected by spatial and temporal patterns is crucial to understanding forest ecosystem responses to disturbance, including future climate change. In this article, we tracked how diversity and composition are distributed through space and time in a midsuccessional mixed hardwood forest in northern lower Michigan, United States. This region's geographically and abiotically distinct glacial landforms influence both the spatial and temporal dynamics of its forest communities. Vegetation sampling plots (n = 87) were established at the University of Michigan Biological Station in 1990 and resampled in 2015. Vegetation in the overstory, sapling, and groundcover layers was censused. Abiotic variables, including elevation, pH, and soil nutrients, were measured in a subset of plots (n = 40). There were strong differences in diversity and community composition among glacial landforms, with the moraine having a 31% greater species richness in the groundcover layer compared with those of the other glacial landforms. Surprisingly, plant communities across all three vegetation layers showed little change over the 25-year period, and we found no evidence of differences in successional rates among glacial landforms. Our findings indicate that glacial landforms have a large influence on the production and maintenance of local plant diversity and community composition in this area and suggest that successional dynamics may manifest themselves over much longer time periods in these northern biomes. Key words: diversity, composition, landform, forest, community. Il est crucial de decouvrir de quelle facon l'assemblage des communautes vegetales est influence par des configurations spatiales et temporelles pour comprendre les reactions des ecosystemes terrestres aux perturbations, incluant le changement climatique a venir. Dans cet article, nous avons suivi de quelle facon la diversite et la composition sont reparties dans le temps et l'espace dans une foret feuillue mixte en milieu de succession dans le nord du Michigan inferieur, aux Etats-Unis. Les formations glaciaires distinctes du point de vue geographique et abiotique de cette region influencent la dynamique spatiale et temporelle de ses communautes forestieres. Des placettes (n = 87) servant a echantillonner la vegetation ont ete etablies a la station biologique de l'Universite du Michigan en 1990 et reechantillonnees en 2015. La vegetation presente dans la strate dominante, celle des gaules et celle du couvert vegetal au sol a ete recensee. Les variables abiotiques, incluant l'altitude, le pH et les elements nutritifs du sol, ont ete mesurees dans un sous-ensemble (n = 40) de placettes. Il y avait d'importantes differences dans la diversite et la composition des communautes selon la formation glaciaire : la richesse en especes du couvert vegetal au sol etait 31 % plus elevee sur la moraine que sur les autres formations glaciaires. Etonnamment, les communautes vegetales dans les trois strates de vegetation ont tres peu change durant la periode de 25 ans et nous n'avons trouve aucun indice indiquant que le taux de succession differe selon le type de formation glaciaire. Nos resultats montrent que les formations glaciaires ont exerce une grande influence sur la production et le maintien de la diversite locale de la vegetation ainsi que sur la composition des communautes dans cette region et indiquent aussi que la dynamique successionnelle peut se manifester sur des periodes de temps beaucoup plus longues dans ces biomes nordiques. [Traduit par la Redaction] Mots-cles : diversite, composition, relief, foret, communaute.
Introduction The forces shaping plant diversity and community composition in the forests of the Upper Great Lakes of North America are important to understand, as it is predicted that this [...]