Topographic distribution patterns of forest gap within an evergreen broad-leaved forest in Tiantong region of Zhejiang Province, Eastern China

To explore the effects of multi-dimensional topographic factors on forest gap distribution, the forest gaps in a 20 hm² dynamic monitoring plot of an evergreen broad-leaved forest in Tiantong region of Zhejiang were taken as the objects to study the distribution patterns of the gap fraction, gap density, and gap area under the effects of altitude, slope degree, slope shape, slope aspect, and slope position by using a geographic information system (GIS) software. In the plot, the gap fraction was 13.1%, gap density was 9.5 ind · hm^-2, and average gap area was 137.82 m². Because of the greater intensity of typhoon disturbance at high altitudes, the gap fraction and gap density at the high altitude (≥ 500 m) sections were significantly larger than those at the medium and low altitude (< 500 m) sections. The heavy precipitation produced by typhoon could easily cause small scale landslide, and thus, lead to the gap fraction and gap density being larger in valley area than in side-slope and ridge. It was suggested that typhoon and its produced heavy precipitation could be the main causes of the significant differences in the forest gaps along the gradients of altitude and slope position.