[Variation of stem radius of Larix principis-rupprechtii and its influencing factors in the semi-humid Liupan Mountains, China].

We measured stem radius of Larix principis-rupprechtii at the semi-humid Liupan Mountains using the automatic band dendrometer over the growing season in 2016. We examined the diurnal and seasonal variations of stem radius, determined the main stem growth period, and analyzed the response of stem radius to environmental factors during the main stem growth period. The aim was to accurately understand the effects of short-term environmental variation on tree growth. The results showed that stem radius had a clear diurnal variation, with the phases of daytime shrin-kage, nighttime recovery, and increment. The seasonal variation of stem radius could be divided into three distinct stages, including stem relatively stable, stem continuous increasing, and stem swell-shrinking fluctuation. Under the meteorological, soil moisture and topographic conditions of 2016, main stem growth period of L. principis-rupprechtii started from 14th May and ended on the 31th July, with the maximum radius growth rate occurred on 8th June. The environmental factors influencing the daily radius shrinkage at different phases (shrinkage phase, daily, cycle) were gene-rally the same, including temperature (including the air and soil temperature), solar radiation intensity, saturation vapor pressure deficit and soil water content. Temperature had the highest contribution (50.3%-71.0%). However, the influencing factors of daily radius increment varied at different phases. Precipitation (with a contribution of 86.9%) and maximum air temperature (13.1%) were the influencing factors at the radius increment phase. Precipitation (50.3%), saturation vapor pressure deficit (29.9%), relative humidity (12.7%) and solar radiation intensity (7.1%) were the factors at stem cycle. Precipitation and solar radiation intensity were the factors at diurnal scale. Radius increment was more sensitive to environmental variation at the time of stem cycle than that at diurnal scale.