关键词: 稳定同位素, 跳虫, 食物来源, 营养级

Abstract: Taking the secondary natural Pinus tabulaeformis forest in hilly loess region as research object, the shape, size structure, distribution, gap-maker features, and renewal dynamics of gaps were investigated. The results showed that the areas of canopy gap (CG) and extended gap (EG) appeared to have a skewed and small gap-dominated distribution. The CGs had an average area of 31.15 m², and those with an area of 20-40 m² made up the highest proportions in number and area, accounting for 38.24％ and 30.50％, respectively; while the EGs had an average area of 58.04 m², and those with an area of 30-60 m² made up the highest proportions in number and area, accounting for 36.77％ and 27.79％, respectively. The average CG area accounted for 53.67％of the average EG area. The gaps were mainly elliptical, and their ages were mainly within 10-20 years, which occupied 33.82％ of the total. The gaps were mainly with a height of 14-16 m, and those with a height of 18-22 m made up 36.8％ of the total. The gaps were mainly formed by the trees being broken at their bases and the standing dead trees, which made up 47.66％ and 23.44％ of all gap-makers, respectively, and thinning and unlawful felling were the major factors in gap formation. The tree deaths from lowered resistance due to tree- ageing, drought, and pest and diseases were one of the reasons for gap formation. The gap-makers per gap numbered 1.89 on average, and most of the gaps were formed by two gap-makers. The gap-makers were mainly Pinus tabulaeformis, followed by Populus davidiana, Betula platyphylla, and Quercus liaotungensis. The diameters of the gap-makers appeared to have a remarkably skewed normal distribution, and the diameters commonly ranged in 10-20 cm and 21-30 cm, taking up 25.0% and 45.31%, respectively. This skewed normal distribution agreed with the skewed area distribution of the gaps. In forest gap, trees had a better regeneration condition, and Chinese pine seedings had no age-discontinuity; while in the understory of Chinese pine, seedings had an obvious discontinuity in age-structure.

Key words: stable isotope, collembolan, food source, trophic level.