Although cambial reactivation is considered to be strongly dependent on temperature, the importance of water availability at the onset of xylogenesis in semi-arid regions still lacks sufficient evidences. In order to explore how environmental factors influence the initiation of cambial activity and wood formation, we monitored weekly cambial phenology in Qilian juniper (Juniperus przewalskii) from a semi-arid high-elevation region of northwestern China. We collected microcores from 12 trees at two elevations during the growing seasons in 2013 and 2014, testing the hypothesis that rainfall limits cambial reactivation in spring. Cambium was reactivated from late April to mid-May, and completed cell division from late July to early August, lasting 70–100 days. Both sites suffered from severe drought from January to April 2013, receiving < 1 mm of rain in April. In contrast, rainfall from January to April 2014 was 5–6 times higher than that in 2013. However, cambial reactivation in 2014 was delayed by 10 days. In spring, soil moisture gradually increased with warming temperatures, reaching 0.15 m³/m³ before the onset of xylogenesis, which may have ensured water availability for tree growth during the rainless period. We were unable to confirm the hypothesis that rainfall is a limiting factor of cambial reactivation. Our results highlight the importance of soil moisture in semi-arid regions, which better describe the environmental conditions that are favorable for cambial reactivation in water-limited ecosystems.

Carbon and oxygen isotope ratios (δ¹³C and δ¹⁸O) were measured in annual tree-ring cellulose samples dated from 1756 to 2015 CE. These samples were extracted from Chinese pine (Pinus tabulaeformis Carr.) trees located in a semi-arid region of north-central China. We found that tree-ring δ¹³C and δ¹⁸O values both recorded similar climatic signals (e.g., temperature and moisture changes), but found that tree-ring δ¹³C exhibited a stronger relationship with mean temperature, precipitation, average relative humidity, self-calibrating Palmer drought severity index (scPDSI), and standard precipitation evaporation index (SPEI) than δ¹⁸O during the period 1951–2015 CE. The strongest correlation observed was between tree-ring δ¹³C and scPDSI (previous June to current May), which explains ~43% of the variance. The resulting 130-year reconstruction reveals severe drought events in the 1920s and a sustained drying trend since the 1980s. This hydroclimate record based on tree-ring δ¹³C data also reveals similar dry and wet events to other proxy data (i.e., tree-ring width and historical documentation) that have allowed reconstructions to be made across the northern fringe of the Asian summer monsoon region. Our results suggest that both large-scale modes of climate variability (e.g., El Niño-Southern Oscillation, Pacific Decadal Oscillation, and North Atlantic Oscillation) and external forcing (e.g., solar variability) may have modulated moisture variability in this region. Our results imply that the relationship between tree-ring δ¹⁸O and local climate is less well-characterized when compared to δ¹³C and may be affected more strongly by the influences of these different atmospheric circulation patterns. In this semi-arid region, tree-ring δ¹³C appears to represent a better tool with which to investigate historical moisture changes (scPDSI).

The Greater Ordos Region (GOR), located at the interface between the East Asian Summer Monsoon and mid-latitude westerly circulation systems, is highly sensitive to both oceanic forcing and regional land–atmosphere interactions. This study synthesises annually resolved tree-ring and documentary records with lower-resolution evidence from lake sediments, aeolian archives, and pollen data to reconstruct hydroclimatic and temperature variability over the past ~3500 years. The multi-proxy evidence reveals pronounced alternations between wetter and drier conditions across successive dynastic periods. High-resolution records resolve the timing, duration, and severity of extreme events, including multi-decadal droughts during the late Han and Tang periods and a widespread megadrought in the early seventeenth century CE associated with crop failures and societal stress. Lower-resolution archives provide longer-term context, documenting progressive shifts towards increased aridity, steppe expansion, and desertification, particularly following major drought episodes. The combined proxy approach demonstrates how recurrent hydroclimatic extremes, interspersed with phases of recovery, have exerted a persistent influence on agricultural systems, land-use dynamics, and societal stability. Integrating high- and low-resolution climate records allows assessment of both abrupt climate shocks and longer-term environmental trends that have shaped regional vulnerability through time.