Abstract: An investigation on the size structure and spatial pattern of 26 major tree species with a diameter at breast height (DBH) ≥5 cm was made on a 1 hm² fixed plot in the mixed evergreen and deciduous broad-leaved forest in Houhe National Nature Reserve of Central China.The results showed that 7 populations of the 26 species,i.e.,Dipteronia sinensi,Aesculus wilsonii,Pterostyrax psilophyllus,Davidia involucrate,Euptelea pleiosperma,Tetracentron sinense and Cercidiphyllum japonicum,were rare endangered species,and two of the 7 populations,T.sinense and C.japonicum,were very limited in numbers.The population structure of P.psilophyllus was in declining,and that of the rest was in growing.The spatial distribution pattern of P.psilophyllus,/i>A.wilsonii and T.sinense was in random,and that of the others was clumped.Among the other 19 non-rare populations,the population structure of P.wilsonii was in declining,that of D.lotus,A.palmatum,A.wilsonii,A.franchetii,M.cuneifolia and H.dulcis was stable,and the rest was in growing.The spatial distribution pattern of D.lotus and H.dulcis was in random,and that of the others was clumped.On the whole,the growing populations were dominant,amounting to 61.54%,and the stable and declining populations accounted for 6.92% and 11.54%,respectively.The results of the two judging methods were consistent,showing that the distribution pattern of clumping (80.77%) was dominant,while the random and even distribution patterns were infrequent.

Key words: Houhe Nature Reserve, Rare plant community, Population structure, Distribution pattern