Mountain Ferns: What Determines Their Elevational Ranges and How Will They Respond to Climate Change?

Abstract

Mountains are the global centers of fern diversity and at the same time strongly affected by climate change, raising the question of how fern species and communities will respond to these changes. In the present review, which also includes our own unpublished data, we first outline the challenges of identifying distributional boundaries in ferns. We suggest that the elevational ranges of many fern species are determined by geographical constraints such as low mountain tops and sea level, as well as habitat availability rather than by climate. We then show that climate-range limits of ferns are driven by numerous physiological processes, not only involving the effects of cold and drought stress at high elevations, but also of drought stress coupled with high temperatures at low elevations, and possibly even of such poorly considered factors as low frost tolerance at low elevations in the absence of snow cover. Finally, there is also some evidence for biotic limitations, such as interspecific competition and the negative influence of leaf litter, especially in species-rich assemblages without extreme climatic factors. Overall, we find that elevational distributions of ferns are determined by a broad suite of factors, many of which do not involve physiological tolerance to climate or only indirectly so, and therefore that reactions of ferns to climate change will likely be species-and context-specific. We also emphasize the paucity of studies focusing both on the physiological limitations for fern growth and reproduction, and on biotic interactions affecting fern distributions. To overcome these knowledge gaps, we advocate a range of further studies, including resampling of old vegetation plots, lab experiments, and transplantation experiments, on both gametophytes and sporophytes.

Global patterns and climatic determinants of phylogenetic structure of regional fern floras

“…But the other continents also show distinct phylogenetic signatures whose specific history remains to be elucidated. We consider that besides macroecological studies such as this one, to fully understand the evolutionary history of ferns also requires detailed group‐specific analyses as well as ecophysiological studies that reveal the physiological basis of the climate–species distribution relationships in ferns (Kessler & Kluge, 2022).…”

Liverworts show a globally consistent mid‐elevation richness peak

“…This allows a direct comparison of mountain transects of different extensions and is somewhat independent of climate. We used it as an indicator of spatial processes, such as source‐sink effects (Kessler, Hofmann, et al, 2011 ), overlaps between lowland and highland floras (Grytnes, 2003a ), and island effects on small mountain ranges (Kessler & Kluge, 2022 ).…”

“…Elevation was included both as absolute elevation (absElev) and as relative elevation (relElev) in our analyses. absElev provides information on the environmental conditions that change in relation to elevation, whereas relElev places the liverworts richness in relation to the elevational extent of the transect, which can influence richness via source‐sink effects (Kessler, Hofmann, et al, 2011 ), overlaps between lowland and highland floras (Grytnes, 2003a ), and island effects on small mountain ranges (Kessler & Kluge, 2022 ). For this reason, relElev no longer reflects direct relationships with climate as does absElev but rather informs about independent biogeographical processes, which in contrast to climatic factors would also explain hump‐shaped elevational richness patterns in liverworts on mountains with short elevational extent.…”

“…Elevation was included both as absolute elevation (absElev) and as relative elevation (relElev) in our analyses. absElev provides information on the environmental conditions that change in relation to elevation, whereas relElev places the liverworts richness in relation to the elevational extent of the transect, which can influence richness via source-sink effects (Kessler, Hofmann, et al, 2011), overlaps between lowland and highland floras (Grytnes, 2003a), and island effects on small mountain ranges (Kessler & Kluge, 2022).…”

A comparative ecophysiological study of two forest understory ferns (Dryopteris marginalis and Polystichum acrostichoides) during summer drought and excessive heat

“…Under conditions of climate change and more variable patterns of precipitation, ferns in these locations are likely to incur stress due to insufficient moisture, a situation made more severe if temperatures are higher and evapotranspiration is elevated. Some of these aspects have been addressed more fully in publications that are particularly focused on changing climate and environmental stress (Proctor, 2009;Bystriakova et al, 2014;Rapp and Silman, 2014;Baer et al, 2016;Sharpe, 2019;Testo and Watkins, 2013;Alarcón and Cavieres, 2018;De Gasper et al, 2021;Anderson, 2022;Kessler and Kluge, 2022;Winkel and Wood, 2022). Pittermann et al (2013) published a review highlighting how functional morphology of the xylem combined with physiological analysis of water relations can account for the capacity of ferns to successfully endure drought-induced stress in the sporophyte stage as well as factors favoring survival of the gametophyte stage.…”