Abstract:

In this paper,the disturbance regimes and the characteristics of the gaps from the Karst forest in Maolan National Nature Reserve of Guizhou Province were studied. Three sampling plots with the size of 5 000 m², representing three types of forest community in various ecological environment, were established. The gap size, disturbance frequency, forming pattern of gaps, the number and species composition of gap makers (GM) were recorded in the field. The results indicated that: 1) The size of most canopy and expanded gaps was small. The total area of the big gaps was much larger than that of small gaps, however. 2) Most of the gaps were formed 20 years ago. The rate was about 0.55 gap·hm^-2a^-1, with a return interval of 270 years. 3) Gap density was about 20 per hectare. The mean size of canopy gap was (69.7±45.71) m², and the mean size of expanded gap was (152.7±79.43) m². The canopy gaps and expanded gaps covered 13.9% and 30.6% of the forest area respectively. 4) Trunk snapping or breakage was the main pattern of gap forming but it varied with the topography. In the valley, hillside and funnel, the main pattern of gap forming was breakage on trunk, uprooted blown down and breakage at trunk base respectively. 5) Most of gaps in the forest were formed with 1 to 4 fallen trees. The average number of GM was 2.5 per gap. Most of the GM was the dominant species in the forest. The proportion of evergreen tree and deciduous tree was about 61.5% and 38.5% respectively. The distribution of GM size indicated that the gap disturbance was very frequent in the Karst forest.

Key words: gaps, disturbance regimes, Maolan, Karst forest