Picea mongolica is an endemic but endangered species in China. The spruce forest is only found in sandy forest-steppe ecotones. In this study, we examined the initial response of the quantity and refilling process of fine roots in an artificial canopy gap with a diameter of 36 m in a P. mongolica forest. Under the canopy, the fine root length densities of trees, shrubs and herbs were 2,622, 864 and 3,086 m·m–2, respectively. The fine root biomass of trees, shrubs and herbs were 148, 62 and 65 g·m–2, respectively. In the gap, the fine root length density of trees was 151 m·m–2. The mean fine root densities of shrubs and herbs in the gap were 756 and 2,568 m·m–2. The fine root biomass of trees, shrubs and herbs were 9, 52 and 47 g·m–2, respectively. Two growing seasons after the gap creation, hardly any fine tree roots were found in the middle of the gap. The living tree roots in the gap edge zone were mainly located within a 4.5 m distance from the standing trees. Indices developed to show the influence of trees on fine root length density clearly revealed the effect of the vicinity of living trees on fine root length density. The root densities of shrubs and herbs did not show a clear response to gap creation despite the increase of their foliage. Our results suggest that in P. mongolica forests a gap disturbance creates a distinct tree root gap and that the gap edge trees do not extend their root systems rapidly into the formed root gap.
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