Spatial and seasonal variations of leaf area index (LAI) in subtropical secondary forests related to floristic composition and stand characters

Abstract

<p><strong>Abstract.</strong> Leaf area index (LAI) is an important parameter related to carbon, water and energy exchange between canopy and atmosphere, and is widely applied in the process models to simulate production and hydrological cycle in forest ecosystems. However, fine-scale spatial heterogeneity of LAI and its controlling factors have not been fully understood in Chinese subtropical forests. We used hemispherical photography to measure LAI values in three subtropical forests (i.e. <i>Pinus massoniana – Lithocarpus glaber</i> coniferous and evergreen broadleaved mixed forests, <i>Choerospondias axillaris</i> deciduous broadleaved forests, and <i>L. glaber – Cyclobalanopsis glauca</i> evergreen broadleaved forests) during period from April, 2014 to January, 2015. Spatial heterogeneity of LAI and its controlling factors were analysed by using geostatistics method the generalised additive models (GAMs), respectively. Our results showed that LAI values differed greatly in the three forests and their seasonal variations were consistent with plant phenology. LAI values exhibited strong spatial autocorrelation for three forests measured in January and for the <i>L. glaber – C. glauca</i> forest in April, July and October. Obvious patch distribution pattern of LAI values occurred in three forests during the non-growing period and this pattern gradually dwindled in the growing season. Stand basal area, crown coverage, crown width, proportion of deciduous species on basal area basis and forest types affected the spatial variations in LAI values in January, while species richness, crown coverage, stem number and forest types affected the spatial variations in LAI values in July. Floristic composition, spatial heterogeneity and seasonal variations should be considered for sampling strategy in indirect LAI measurement and application of LAI to simulate functional processes in subtropical forests.</p>

Positive tree diversity effect on fine root biomass: via density dependence rather than spatial root partitioning

“…In 2013, we identified three 1‐ha forest sites corresponding to each forest type (PM, CA and CG). Each site was divided in 100 plots of 10 × 10 m. The stand characteristics of each plot have previously been reported (Liu et al 2014, Zhu et al 2016). A subset of 91 plots, representing a gradient in tree species richness, were chosen: 30 plots for PM (ranging from 2 to 9 tree species); 31 plots for CA (1–12 tree species); and 30 plots for CG (1–11 tree species; see overview in Supplementary material Appendix 1 Fig.…”

“…Adjacent to the location of each fine root sampling (within 30 cm distance) we collected an additional soil sample per plot (n = 91) for chemical analysis of nutrient concentrations using the same sampling method. In July 2014, the leaf area index (LAI) was estimated based on hemispherical photographs taken at the centre of each plot with a SY‐S01A device (Shiya Scientific and Technical Cooperation, Hebei, China), as previously described (Zhu et al 2016). We assumed that the LAI values sampled in July 2014 are representative of the actual values at the time of the fine root sampling in August 2016, since numerous studies show that the LAI in tropical forests varies only slightly between years (Le Dantec et al 2000, Barr et al 2004, Cristiano et al 2014).…”

Tree functional types simplify forest carbon stock estimates induced by carbon concentration variations among species in a subtropical area

“…Estimates of forest stand C stock. We used the measurements from four forests in Dashanchong Forest Park 50 (28°23′–28°24′N, 113°17′–13°19′E), Changsha County, Hunan Province, China, to quantify the error in stand C stock estimated using the generic C concentration constant (50.0%) and the C concentrations measured in this study. A 1-ha permanent plot was established for each forest and, within each, 20 m × 30 m subplots were established.…”

Atmospheric Wet Deposition of Organic Carbon and Dissolved Nitrogen in City, Countryside and Nature Reserve of Subtropical China

“…Evergreen broadleaved forest is the climax vegetation of the region. As a result of human disturbance until the late 1950s, and naturally restoration after that, the nature reserve possesses a range of secondary forests dominated by different tree species, including Pinus massoniana – Lithocarpus glaber coniferous and evergreen broadleaved mixed forests, Cyanotis axillaris deciduous broadleaved forests, and L. glaber – Casuarina glauca evergreen broadleaved forests (Zhu et al 2016).…”