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Background and Aims The hart's tongue fern (HTF) complex is a monophyletic group composed of five geographically segregated members with divergent abundance patterns across its broad geographic range. We postulated hierarchical systems of environmental controls in which climatic and land-use change drive abundance patterns at the global scale, while various ecological conditions function as finer scale determinants that further increase geographic disparities at regional to local scales. Methods After quantifying the abundance patterns of the HTF complex, we estimated their correlations with global climate and land-use dynamics. Regional determinants were assessed using boosted regression tree models with 18 potential ecological variables. Moreover, we investigated long-term population trends in the USA to understand the interplay of climate change and anthropogenic activities on a temporal scale. Key Results Latitudinal climate shifts drove latitudinal abundance gradients, and regionally different levels of land-use change resulted in global geographic disparities in population abundance. At a regional scale, population isolation, which accounts for rescue effects, played an important role, particularly in Europe and East Asia where several hot spots occurred. Furthermore, the variables most strongly influencing abundance patterns greatly differed by region: precipitation seasonality in Europe; spatial heterogeneity of temperature and precipitation in East Asia; and magnitudes of past climate change, temperature seasonality and edaphic conditions in North America. In the USA, protected populations showed increasing trends compared with unprotected populations at the same latitude, highlighting the critical role of habitat protection in conservation measures. Conclusions Geographic disparities in the abundance patterns of the HTF complex were determined by hierarchical systems of environmental controls, wherein climatic and land-use dynamics act globally but are modulated by various regional and local determinants operating at increasingly finer scales. We highlighted that fern conservation must be tailored to particular geographic contexts and environmental conditions by incorporating a better understanding of the dynamics acting at different spatiotemporal scales. [ABSTRACT FROM AUTHOR]

Depletion of Ca from forest soils due to acidic deposition has had potentially pervasive effects on forest communities, but these impacts remain largely unknown. Because snails, salamanders, and plants play essential roles in the Ca cycle of northern hardwood forests, we hypothesized that their community diversity, abundance, and structure would vary with differences in biotic Ca availability. To test this hypothesis, we sampled 12 upland hardwood forests representing a soil Ca gradient in the Adirondack Mountains, New York (USA), where chronic deposition has resulted in acidified soils but where areas of well-buffered soils remain Ca rich due to parent materials. Along the gradient of increasing soil [[Ca.sup.2+]], we observed increasing trends in snail community richness and abundance, live biomass of redback salamanders (Plethodon cinereus (Green, 1818)), and canopy tree basal area. Salamander communities were dominated by mountain dusky salamanders (Desmognathus ochrophaeus Cope, 1859) at Ca-poor sites and changed continuously along the Ca gradient to become dominated by redback salamanders at the Ca-rich sites. Several known calciphilic species of snails and plants were found only at the highest-Ca sites. Our results indicated that Ca availability, which is shaped by geology and acidic deposition inputs, influences northern hardwood forest ecosystems at multiple trophic levels, although the underlying mechanisms require further study. Resume: L'epuisement du Ca dans les sols forestiers a cause des depots acides a eu des repercussions potentiellement generalisees sur les communautes forestieres mais ces impacts demeurent largement inconnus. Etant donne que les escargots, les salamandres et les plantes jouent un role essentiel dans le cycle du Ca des forets feuillues nordiques, nous avons emis l'hypothese que la diversite, l'abondance et la structure de leurs communautes varieraient en fonction de la disponibilite du Ca. Pour tester cette hypothese, nous avons echantillonne 12 forets feuillues en milieu sec dans les monts Adirondacks, dans l'Etat de New York aux Etats-Unis d'Amerique, ou des depots chroniques ont acidifie les sols mais ou il y a encore des en-droits ou les sols ont un pouvoir tampon eleve et demeurent riches en Ca a cause du materiau originel. A mesure que la concentration de [Ca.sup.2+] augmentait le long du gradient, nous avons observe des tendances a la hausse de l'abondance et de la richesse des communautes d'escargots, de la biomasse vivante de salamandres rayees (Plethodon cinereus (Green, 1818)) et de la surface terriere des arbres qui forment la canopee. Les communautes de salamandres etaient dominees par la salaman-dre sombre des montagnes (Desmognathus ochrophaeus Cope, 1859) dans les stations pauvres en Ca et changeaient progressivement le long du gradient de Ca pour devenir dominees par la salamandre rayee dans les stations riches en Ca. Plusieurs especes calcicoles connues d'escargots et de plantes ont ete observees seulement dans les stations les plus riches en Ca. Nos resultats indiquent que la disponibilite du Ca, qui est determinee par les conditions geologiques et les apports de depots acides, influence les ecosystemes de feuillus nordiques a de multiples niveaux trophiques bien que les mecanismes sous-jacents necessitent plus de recherche. [Traduit par la Redaction], Introduction Research on forest ecosystem processes has suggested that Ca availability plays a critical role in shaping ecosystem structure, function, and responses to change (McLaughlin and Wimmer 1999). In the [...]