Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.

Question What are the effects of rock climbing on diversity, abundance and composition on cliff‐face vegetation along environmental and use gradients typical of modern climbing? Location New River Gorge National River, WV, US. Methods We compared species richness, abundance and composition of vascular plants, bryophytes and lichens on 79 pre‐established rock climbs and 32 unclimbed ‘control’ sites across potential climb‐use intensity and cliff structure using linear models, residual analysis and NMDS ordination. Results Differences in species richness and abundance associated with potential climb‐use intensity and cliff structure were variable across taxonomic groups. Linear models indicated that cliff angle was the strongest explanatory variable of species richness and abundance for all three taxonomic groups. Once the effects of biophysical variables were modelled, analysis of the residuals indicated that potential climbing‐use intensity had a small but negative effect on species richness and abundance of vascular plants (range 3–6%), no effect on bryophytes (0%) and a substantial effect on lichens (range 10–12%). Similarly, NMDS ordination indicated that cliff angle, canopy height and aspect were the primary drivers of species composition. We observed no change in community composition due to climbing. Conclusions Other studies have observed significant impacts of climbing on vegetation at the base of cliffs. Here, we observe that potential climbing‐use intensity has some impact on species richness and abundance of vascular plants and more significant impacts on lichens, however cliff angle is a fundamental control on cliff vegetation. Because of the challenge in sampling steep and overhanging cliffs, we recommend that climbers be directly involved in the assessment, monitoring and management of cliff resources in order to ensure that the full range of biophysical conditions of cliff ecosystems are considered.

The original version of this Article contained an error in the Data Availability section, which incorrectly read 'All data will be freely available via https://www.ams.ethz.ch/research.html.' The correct version states 'http://www.ams.ethz.ch/research/published-data.html' in place of 'https://www.ams.ethz.ch/research.html'. This has been corrected in both the PDF and HTML versions of the Article.

The impact of settlement era fires on Appalachian forests was substantial, but whether these fires affected the extent of fire-adapted ridgetop plant communities is poorly understood. Here we present fire history and stand structure of an Appalachian ridgetop (Pike Knob, West Virginia) based on fire scars from three species (Pinus pungens Lamb., Pinus resinosa Soland., and Quercus rubra L.) and stand structure from two species (P. pungens and P. resinosa). Our research objectives are to determine (i) the degree to which the fire frequency on Pike Knob was affected by European American settlement (~1780–1900) and (ii) how the history of fire on Pike Knob shaped the current age structure of P. resinosa and P. pungens. All three species documented fire activity beginning in the mid- to late 1800s and continuing into the middle of the 20th century, when pasture lands were most active. The majority of P. pungens and P. resinosa established during or shortly after the ~85-year period of fires (1868–1953), suggesting a strong influence of past land use on current forest composition. Ridgetop pine communities have been resilient to both the absence of fire and frequent fire, indicating that pine communities will also be resilient to modern fire management, whether fire is excluded or re-introduced.

There is increasing momentum to implement conservation and management approaches that adapt forests to climate change so as to sustain ecosystem functions. These range from actions designed to increase the resistance of current composition and structure to negative impacts to those designed to transition forests to substantially different characteristics. A component of many adaptation approaches will likely include assisted migration of future climate-adapted tree species or genotypes. While forest-assisted migration (FAM) has been discussed conceptually and examined experimentally for almost a decade, operationalizing FAM (i.e., routine use in forest conservation and management projects) lags behind the acceptance of the need for climate adaptation. As the vulnerability of forest ecosystems in climate change increases, FAM may need to become an integral management tool to reduce long-term risks to ecosystem function, despite real and perceived barriers for its implementation. Here we discuss the concept of operational-scale FAM and why it remains a controversial, not yet widely adopted component of climate adaptation. We present three case studies of operational-scale FAM to illustrate how the practice can be approached pragmatically within an adaptation framework despite the barriers to acceptance. Finally, we discuss a path toward advancing the wide use of operational-scale FAM.