We studied the three leaf traits leaf half-life (LHL), leaf mass per area (LMA) and nitrogen concentration in green leaves (Ngreen) and the wood trait wood density (WD) in 295 individuals belonging to 45 tree or shrub species in a Chinese subtropical forest from September 2006 to January 2009. Using multilevel ANOVA and decomposition of sums of products, we estimated the amount of trait variation and covariation among taxa, functional types (deciduous vs. evergreen), growth forms (trees vs. shrubs), individuals and seasons. We also examined phylogenetic signal and, using phylogenetically independent contrasts, the evolutionary coordination of these traits.

(1) We extracted one soil core (10 cm deep, 3 cm diameter) beneath 132 individual plants from 12 deciduous and 24 evergreen species in August 2009. Soil samples were oven-dried, ground and analyzed for total N concentration and organic matter concentration.(2) wood density were collected both in September 2006 and April 2007 to determine seasonal change in wood density (WD). We used an increment borer (diameter 5.15 mm, Haglöf, Sweden) to obtain a 5 cm long core (without bark) and measured the fresh volume with a water-displacement method immediately after sampling the core in order to maintain the samples at a constant humidity. The cores were then dried at 60 °C for 72 h and weighed. Wood density was calculated as wood dry mass divided by fresh volume.(3) In September 2006, we randomly selected 3–6 individuals from each species and marked them with aluminum tags. We collected 5–8 fully expanded leaves from the middle of the leaf crown of each individual. For tall trees in which the middle of the crown could not be reached, leaves were collected from the bottom of the crown. Only current-season, fully expanded leaves at the edge of the crown were included in each sample. We used a LI-3100C Area Meter (LI-COR company, Lincoln, NE, USA) to determine the cumulative area of each sample of green leaves excluding petioles. The samples were dried at 60 °C for 72 h and weighed. Leaf mass per area (LMA) was calculated as the ratio between leaf dry mass and leaf area. Total nitrogen content (% dry mass, Ngreen) of leaves was determined with a CHN analyzer (Leco CHNS–932, Leco instruments, St. Joseph, MI, USA).In order to determine seasonal changes in traits, we repeated the sampling and measurements in April 2007.(4) Leaf half-life (LHL) was determined demographically by following the fate of marked leaf cohorts. In April 2007, we selected one or two healthy sunlit branches per individual, marked a terminal section with 5−20 young leaves (occasionally more than 20 leaves for deciduous trees) with colored thread and counted the number of leaves between the marks. We sequentially revisited these branches in August 2007, March 2008, August 2008 and January 2009, added an additional mark at the tip of each branch and counted the living leaves in each of the marked cohorts. Side branches that started growing during the examination period were not taken into account.

The study was conducted in a secondary broad-leaved and coniferous mixed subtropical forest in Dujiangyan, Sichuan province, SW China. With the rising slopes of the Qinghai-Tibet plateau to the west and the fertile agricultural plains of the Sichuan basin to the east, the Dujiangyan area is one of eleven biodiversity hotspots in China (Chen, 2000). The climatic conditions are typically subtropical with a dry winter (November–April) and a warm and rainy summer (May–October). The annual average temperature is 15.2 °C and July average temperature is 25 °C. The mean annual precipitation is 1341 mm and the annual average relative humidity is above 80 % (Chen, 2000).The study site covers approximately 22 ha (31°03’43”–31°04’03” N, 103°42’55”–103°43’52” E), within an altitude range of 693–830 m. Previous vegetation survey shows there are 158 species of broad-leaved evergreen, deciduous and coniferous trees and shrubs coexist in the forest (Du, unpublished data). The canopy is dominated by Castanopsis fargesii, Betula luminifera, Quercus serrata and Quercus variabilis. Species nomenclature follows “Flora of China” (ECCAS, 1974-1999). Camellia oleifera and Eurya alata are the most abundant shrub species. The dominant soil types are Leptosols, Regosols and Cambisols from loess-like material, with an average nitrogen concentration of 0.29 % and organic matter concentration of 8.56 %.

September 2006 to January 2009.

We selected 295 individuals that belong to 45 woody angiosperm species representing 19 families, which were commonly found in the forest community. They were classified by functional type: deciduous (20 species) and evergreen (25 species) and by growth form: trees (34 species) and shrubs (11 species).