Abstract:

Self-thinning is a hot issue in ecological theoretical research, however, because of the long growth period and complex process in self-thing, relative research in woody plants’ self-thinning rule is very few and still no consensus has been reached up to the present. The research used natural phytocoenosium quadrat in different altitudes in Nanling nature protection area as the material to study the woody phytocoenosium’s self-thinning rule by means of spatial-temporal substitution and to analyze the relationship between space size and density, in addition, we discuss how their crown diameter and plant height response to the altitude change. The results showed that: 1) The self-thinning rule is also suitable to the natural woody phytocoenosium. The self-thinning exponent of arbor phytocoenosium is -1.305 6 and that of shrub phytocoenosium is -1.298 9, which are in accord with Enquist’s -4/3 self-thinning rule. The main reason may be that, Enquist put forward the -4/3 self-thinning rule at the point of the relationship between plants’ growth’s resource need and density. In this research we regard the plants’ living room as the biomass, which reflects how much resource that the plants gain. 2) Woody plants’ size and density have close correlation. When the density increases, both the average crown diameter and tree height reduce obviously in arbor quadrat, similarly, in Shrub quadrat the average crown diameter reduces, whereas, the plants’ height does not change obviously. In this research, it is shown that the crown diameter in the arbor phytocoenosium that live under altitude 900 m plays an important role in self-thinning process, in the phytocoenosium living between altitude 900 and 1 300 m, the plant height plays an important role in self-thinning process, and when the altitude is over 1 300 m, survival pressure plays a leading role in self-thinning process. Differently, in shrub communities, crown diameter plays a leading role in self-thinning process in different altitudes. 3) Arbor and shrub phytocoenosiums make a different response to habitat change caused by the change of altitude. In the equation of self-thinning, the coefficient k changes with the altitude. The higher the altitude is, the smaller the coefficient k will be. At the altitudes of ＜900 m, 900~1 300 m and 1 300~1 462 m, the arbor quadrats’ log k are 2.056 5, 1.372 6, 1.194 7, and the corresponding k values are 113.89, 23.58, 15.66 respectively, that means that the arbor’s largest living room reduces with the increase of altitude obviously. At the altitudes of ＜950 m and 950~1 800 m, the shrub quadrats’ log k are 0.050 3 and 0.016 8, and the corresponding k values are 1.12 and 1.04 respectively, meaning that the shrub ’s largest living room reduces with the increase of altitude, but it is not so obvious as that of arbor quadrats, showing that the altitude change has greater impact on arbor size.

Key words: arbor phytocoenosium, shrub phytocoenosium, self-thinning, altitude change, Nanling nature protection area