[Response of tree seedlings to altitudinal gradient and its seasonal variation in Ailao Mountain and Yulong Mountain, Yunnan Province, China.]

Tree seedlings under forests serve as an important part of forest ecosystem and play a role in the natural regeneration of forests. To understand the altitudinal distribution patterns of tree seedlings and the response to seasonal variation, we investigated the species composition and individual numbers of tree seedlings, and their seasonal dynamics in Ailao Mountain (subtropical region) and Yulong Mountain (subalpine region) in Yunnan Province. The results showed that the species richness of tree seedlings increased with altitude, peaked in the middle of the mountains, and followed a decline at higher altitudes, and the dominant species also changed significantly. Species richness of tree seedlings was significantly higher at the end of rainy season than that at the end of dry season, and the dominant species had obvious seasonal difference.