Background Fire is an important disturbance of forest ecosystems and has important impacts on the subsequent succession of vegetation. To reveal the characteristics of natural understory revegetation and its response to environmental factors in burned areas, we studied a mountainous region with a subtropical climate (located in Xide County, China). Results Based on quadrat surveys and correlation analysis. the main results of this study were as follows. (1 ) Within four months after a fire, a

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... tal of 71 species, 52 genera, and 20 families of vegetation were found, representing significant increases from the first to second sampling periods. (2 ) The Shannon-Wiener, Simpson, and Margalef indexes increased between sampling periods, whereas the Pielou index decreased. The Margalef index had the most obvious change, increasing by 5.44 and 5.16 in lightly and severely burned areas, respectively. (3 ) The vegetation community stability in burned areas was low at the initial stage of revegetation. It tended to increase with the intensity of the fire that had affected a given sampling area. (4 ) Elevation and slope were the main physical factors affecting the vegetation biodiversity indexes and distribution. (5 ) The regrowth of understory vegetation was optimal in the gentle, shady slopes at low elevations. Conclusions This study elucidates the relationship between revegetation and topographic factors in burned areas and provides a scientific basis for guiding future ecological restoration.