The relationship between climate and forest is critical to understanding the influence of future climate change on terrestrial ecosystems. Research on trees at high elevations has uncovered the relationship in the Hengduan Mountains region, a critical biodiversity hotspot area in southwestern China. The relationship for the area at low elevations below 2800 m a.s.l. in the region remains unclear. In this study, we developed tree ring width chronologies of Pinus yunnanensis Franch. at five sites with elevations of 1170–1725 m in this area. Monthly precipitation, relative humidity, maximum/mean/minimum air temperature and the standardized precipitation evapotranspiration index (SPEI), a drought indicator with a multi-timescale, were used to investigate the radial growth-climate relationship. Results show that the growth of P. yunnanensis at different sites has a similar response pattern to climate variation. Relative humidity, precipitation, and air temperature in the dry season, especially in its last month (May), are critical to the radial growth of trees. Supplemental precipitation amounts and reduced mean or maximum air temperature can promote tree growth. The high correlations between chronologies and SPEI indicate that the radial growth of trees at the low elevations of the region is significantly limited by the moisture availability. Precipitation in the last month of the previous wet season determines the drought regime in the following dry seasons. In spite of some differences in the magnitudes of correlations in the low-elevation area of the Hengduan Mountains region, chronologies generally matched well with each other at different elevations, and the differences are not evident with the change in elevation.

Glacial extent and mass balance are sensitive climate proxies providing solid information on past climatic conditions. However, series of annual mass-balance measurements of more than 60 years are scarce. To our knowledge, this is the first time the latewood density data (MXD) of the Swiss stone pine (Pinus cembra L.) have been used to reconstruct the summer mass balance (B s) of an Alpine glacier. The MXD-based B s well correlates with a B s reconstruction based on the May to September temperature. Winter precipitation has been used as an independent proxy to infer the winter mass balance and to obtain an annual mass-balance (B n) estimate dating back to the glaciological year 1811/12. The reconstructed MXD/precipitation-based B n well correlates with the data both of the Careser and of other Alpine glaciers measured by the glaciological method. A number of critical issues should be considered in both proxies, including non-linear response of glacial mass balance to temperature, bedrock topography, ice thinning and fragmentation, MXD acquisition and standardization methods, and finally the ‘divergence problem’ responsible for the recently reduced sensitivity of the dendrochronological data. Nevertheless, our results highlight the possibility of performing MXD-based dendroglaciological reconstructions using this stable and reliable proxy.

For ancient types of barley at sites in the Scottish Isles, Faroes, and Iceland, we calculated minimum temperature requirements for grain production (grain production threshold, GPT) as accumulated degree days over the cropping season. Site suitability for barley from AD 1200 to 2000 was investigated by comparing these thresholds with reconstructions of annual cropping season degree days (CSDD) using temperature and tree-ring data. In Iceland, between AD 1200 and 1500, reconstructed CSDD were more favorable in the southwest (Reykjavik), with fewer years below the GPT, than in the North, East and West, but there were two periods (1340–1389 and 1426–1475) with low average CSDD and several years below the GPT which possibly influenced the abandonment of barley cultivation around this time. Reconstructed CSDD for the Faroes (Tórshavn) had only one year below the GPT, but 15 periods of four or more consecutive years with low CSDD which would have challenged barley cultivation, especially in the thirteenth century. Reconstructed CSDD were highest for the Scottish Isles, allowing a more prominent role of barley in the farming system and economy. Nevertheless, years with poor harvests or famines were common and about half were associated with low CSDD, resulting in a significant temperature link but also demonstrating the important contribution of other factors. Despite frequent unfavorable years in both the Faroes and Scottish Isles, resilient production systems, well-adapted barley strains and socio-economic factors allowed barley cultivation to continue, and some ancient types to survive to the present day.