Plot was set in a single forest gap with irregular shape and about 250 m² area in Pinus koraiensis-dominated broadleaved mixed forests in Xiao Xing'an Mountains, locations of measurement were established by the method of regular grids at the space of 4m. Soil water content (SWC) in three different depths in this gap was periodically measured during the growing season in 2008. Its spatiotemporal distribution patterns were systematically analyzed and temporal and small-scale spatial variations were further compared by traditional statistics and geostatistical methods. The aim of the study was to provide data and theoretical reference for gap regeneration, biodiversity preservation, deeper understanding of the role of a canopy opening on the physical environment in this type of natural forest and nature-based sustainable management of Pinus koraiensis-dominated broadleaved mixed forest in this area. The results showed that: for SWC, its spatial heterogeneity was obvious in this single gap and its intensity, scale and spatial structure proportion ranged from 0.005 to 0.073, 3.4 to 6.6 m and 0.625 to 0.935, respectively, these indicators which described SWC spatial heterogeneity were different between different months. The heterogeneity in shallow layer was greater than that in deep layer, the mean monthly SWC for 0-7.6 cm, 0-12 cm and 0-20 cm depth in the gap was highest in September, then decreased with the sequence of July, August and June, and the mean monthly SWC in the gap, understory and bare ground was highest in 0-7.6 cm, then decreased with the sequence of 0-12 cm and 0-20 cm. The largest variation in SWC among different locations occurred in June, monthly change in SWC fell into middle variability; the sill and range of monthly SWC was highest in 0-7.6 cm, and then decreased with the sequence of 0-12 cm and 0-20 cm. The connectivity of patches of mean monthly SWC was high and the complex degree of patch shapes was also different between different months, mean monthly maximum SWC were all located in the central part of the gap, mean monthly minimum SWC was not fixed at the same locations. Mean monthly SWC and its variation degree were highest in the bare ground, medium in forest gap and lowest in understory during growing season in 2008.
In general, the effect of this single, small irregular forest gap in Pinus koraiensis-dominated broadleaved mixed forests in Xiao Xing'an Mountains on SWC was influenced by many factors, such as within-gap position, seasonal change, soil depth, precipitation and evaporation, vegetation cover and litter thickness of the forest floor. All these factors should be discussed in future further researches.