Abstract: Standing dead trees are an important component of forest ecosystems, with a critical role in the stability and development of forest ecosystems. Based on survey data of a 1.08 hm² plot inPinus tabuliformis mixed forest in western Beijing, the spatial structure of standing dead trees was analyzed, including tree species composition, diameter structure, height structure, univariate and bivariate distribution of spatial structure parameters. There were 191 standing dead trees, with a density of about 177 stems·hm^-2. Pinaceae, which accounted for 64% of standing dead trees, was the dominant family. Larix principis rupprechtiiis the dominant species. The diameter distribution was an inverted “J” type, dominated by small trees with diameter less than 11 cm. The tree height distribution presented as unimodal with a narrow range. L. principisrupprechtii, Syringa pekinensis and P. tabuliformis distributed in most diameter and height classes. The standing dead trees were generally in a state of random distribution with significant size differentiation and low mingling, and they were mostly surrounded by living trees. The structural characteristics of L. principis rupprechtii, P. tabuliformis, S. pekinensis and Armeniaca sibiricawere roughly similar to the overall pattern. Most standing dead trees, which were surrounded by the same species or only one other species, were in a state of low mingling and disadvantage. About half of standing dead trees showed a random distribution, and most of them were at a disadvantage status and their surroundings were mostly living trees of the same species. There were different frequencies of standing dead trees with different dominance, but the number of non-dominant trees was higher than that of dominant trees. The spatial structure of standing dead trees in P. tabuliformis mixed forest reflected that intraspecific competition under density restriction was the main reason for the formation of standing dead trees. Our results would provide scientific basis for the protection and sustainable management of coniferous-broadleaved mixed forest.

Key words: barley, dry matter production, nitrogen accumulation, nitrogen utilization efficiency, grain yield.