Site fertility drives temporal turnover of vegetation at high latitudes

Experimental evidence shows that site fertility is a key modulator underlying plant community changes under climate change. Communities on fertile sites, with species having fast dynamics, have been found to react more strongly to climate change than communities on infertile sites with slow dynamics. However, it is still unclear whether this generally applies to high-latitude plant communities in natural environments at broad spatial scales. We tested a hypothesis that vegetation of fertile sites experiences greater changes over several decades and thus would be more responsive under contemporary climate change compared to infertile sites that are expected to show more resistance. We resurveyed understorey communities (vascular plants, bryophytes, and lichens) of four infertile and four fertile forest sites along a latitudinal bioclimatic gradient. Sites had remained outside direct human disturbance. We analyzed the magnitude of temporal community turnover, changes in the abundances of plant morphological groups and strategy classes, and changes in species diversity. In agreement with our hypothesis, temporal turnover of communities was consistently greater on fertile sites compared to infertile sites. However, our results suggest that the larger turnover of fertile communities is not primarily related to the direct effects of climatic warming. Furthermore, community changes in both fertile and infertile sites showed remarkable variation in terms of shares of plant functional groups and strategy classes and measures of species diversity. This further emphasizes the essential role of baseline environmental conditions and nonclimatic drivers underlying vegetation changes. Our results show that site fertility is a key determinant of the overall rate of high-latitude vegetation changes but the composition of plant communities in different ecological contexts is variously impacted by nonclimatic drivers over time.Peer reviewe

Anthropogenic disturbance modifies long-term changes of boreal mountain vegetation under contemporary climate warming

Abstract Aims: Accelerating high-latitude climate warming drives shrub expansion in open landscapes and alters species distributions and compositions of plant communities. Simultaneously, various land use practices cause disturbance to the vegetation. However, not much documentation exists on how long-term intensive land use disturbance modifies high-latitude vegetation under climate warming. Here, we study how the composition of boreal mountain plant communities has changed during three decades in response to heavy land use disturbance, related to ski resort construction and management, and how these changes compare to those observed in adjacent less disturbed communities. Location: Iso-Syöte, Finland. Methods: We resurveyed vegetation along four elevational gradients (240–426 m a.s.l.) on a boreal mountain in 2013–14. After the original study in 1980, half of the gradients were subjected to continuous heavy land use disturbance, while the other half remained only slightly disturbed. All the gradients experienced a similar amount of macroclimatic warming over time. We analysed temporal changes in plant group covers, species richness and species’ elevational range means in relation to disturbance levels and elevation. Results: Under slight disturbance, the cover of shrubs increased on the originally open upper slopes and elevational range means of several species shifted upward. In contrast, heavy disturbance resulted in a uniform, yet modest, shrub cover increase along the whole elevational gradient and promoted both up- and downward shifts of species. Bryophyte cover decreased considerably over time, regardless of the disturbance level. Species richness increased throughout, yet more under heavy disturbance. Conclusions: Long-term changes in boreal mountain vegetation are substantially influenced by heavy land use disturbance compared to less disturbed sites where the vegetation changes are more comparable to those expected under a warmer climate. Therefore, along with the climatic effects, land use effects on vegetation are important to consider in management actions and in projections of future vegetation