Phenology of Woody Species in Yuanjiang Dry-Hot Valley in Yunnan Province

Shoot elongation,leaf dynamics,flowering and fruiting events,as well as fruit types of 32 woody species were investigated over three successive years in a valley of Yuanjiang,which is one of the typical dry-hot valleys in southwestern China.Shoot elongation of the species studied can be classified into four types:the succeeding type,the flush type,the intermediate type,and the shoot-dieback types.Succeeding type(including thirteen species) was dominant,successively extending their shoots in the rainy season.The shoot elongation in nine species was similar to that of succeeding type in the rainy season,but with upper shoot dieback in the late dry season.Six species belonged to flush type which elongates their shoots once a year with shoots reaching the maximum length within two weeks.Other four species belonged to intermediate type,which extends their shoots after budbreak,stops growing for some time,and then elongates their shoots again.According to the leaf phenology,deciduous species dominated the Yuanjiang valley.The majority of the deciduous species were winter-deciduous(19 species),with leaf falling during the cool dry season(November to February),while the other four species were drought-deciduous,with leaf dropping during the hot dry season(March to April).Except for Indigofera pulchella and Trema angustifolia that started to fall leaves in the middle of the rainy season,other 30 species started to drop their leaves from the late rainy season,and leaf dropping lasted for at least three months.The evergreen species fell 1/3 to 1/2 of their current-year leaves.Among the species studied,six species showed leaf flush in the late dry season.Evergreen species had smaller leaf area and total leaf area per shoot,lower ratio of total leaf area to shoot length(an index of shoot support) than deciduous species.Although flowering and fruiting events occurred throughout the year,the flowering of the most plants(29 species, 91% of the total species investigated) was in the dry season and early rainy season.Fruit(seed) ripening of these plants lasted from the late rainy season to the end of the dry season or the start of the next rainy season.Most fruits were drupe-type.