Subtropical Forests In China Research Articles

Soil heterotrophic respiration and active carbon pools under subtropical forests in China

Soil heterotrophic respiration and active carbon pools under subtropical forests in China

Phytophthora pseudopolonica sp. nov., a new species recovered from stream water in subtropical forests of China.

A new species of the genus Phytophthora was isolated from stream water in the subtropical forests of China during a survey of forest Phytophthora from 2011 to 2013. This new species is formally described here and named Phytophthora pseudopolonica sp. nov. This new homothallic species is distinct from other known Phytophthora species in morphology and produces nonpapillate and noncaducous sporangia with internal proliferation. Spherical hyphal swellings and thin-walled chlamydospores are abundant when the species is kept in sterile water. The P. pseudopolonica sp. nov. forms smooth oogonia with paragynous and sometimes amphigynous antheridia. The optimum growth temperature of the species is 30 °C in V8-juice agar with β-sitosterol, yet it barely grows at 5 °C and 35 °C. Based on sequences of the internal transcribed spacer and the combined β-tubulin and elongation factor 1α gene sequence data, isolates of the new species cluster together into a single branch and are close to Phytophthora polonicabelonging to clade 9.

Effect of climate and competition on radial growth of Pinus massoniana and Schima superba in China’s subtropical monsoon mixed forest

Tree growth is affected by many exogenous and endogenous factors, especially climate and competition. To address the issue of how these factors influence tree growth under global warming, dendroclimatology combined with competition analysis was used to examine the radial growth response of two major species – Pinus massoniana and Schima superba in subtropical monsoon mixed forests in southern China. For growth-climate relationship analysis, residual and ARSTAN chronologies of these two species were compared for the response function analysis over the past several decades. In terms of competition analysis, annual basal area increment (BAI) over several time intervals was calculated and linear mixed model techniques were employed. Several distance-independent competition indices were measured, including density (N), basal area (BA), and sum of diameter at breast height (SDBH). For competition trees with greater diameter (GR) than the subject tree, NGR, BAGR, SDBHGR were also calculated. Growth-climate relationship analysis suggested that tree growth varied in response to climate and was mostly correlated with minimum, mean and maximum air temperature as indicated by the adjusted R2 value. Summer and winter temperatures had a negative effect on tree growth, while early spring temperature showed positive effects. Competition analysis suggested that subtropical trees had been affected by competition in varying degrees. Trees in the oldest forest had the most competition stress, while trees in younger forests were less affected by competition according to the adjusted R2 value. Given that subtropical forests in China have been found to have more smaller trees with recent warming, it is expected that these forests will experience a decreasing effect of competition in near future. This can have profound effects on forest productivity and carbon sequestration potentials in Chinese subtropical forests.

Response of soil respiration to nitrogen addition in two subtropical forest types

Anthropogenic activities have increased nitrogen (N) deposition in terrestrial ecosystems, which directly and indirectly affects soil biogeochemical processes, including soil respiration. However, the effects of the increases in N availability on soil respiration are not fully understood. In this study, soil respiration was measured using an infrared gas analyzer system with soil chambers under four N treatments (0, 5, 15, and 30 g N m–2 year–1 as control, low N (LN), moderate N (MN), and high N (HN), respectively) in camphor tree and slash pine forests in subtropical China. Results showed that soil respiration rates decreased by 37% in the camphor tree forest and 27% in the slash pine forest on average on an annual base, respectively, in the N-fertilized treatments when compared with the control. No significant differences were found in the soil respiration rate among the LN, MN, and HN treatments in both forest types as these fertilized plots reached an adequate N content zone. In addition, soil microbial biomass carbon (C) content and fine root biomass declined in N-treated plots compared to the control. Our results indicated that elevated N deposition might alter the tree growth pattern, C partitioning, and microbial activity, which further affect soil C sequestration by reducing soil respiration in subtropical forests of China.

Effects of nitrogen deposition on soil microbial communities in temperate and subtropical forests in China

Increasing nitrogen (N) deposition has aroused large concerns because of its potential negative effects on forest ecosystems. Although microorganisms play a vital role in ecosystem carbon (C) and nutrient cycling, the effect of N deposition on soil microbiota still remains unclear. In this study, we investigated the responses of microbial biomass C (MBC) and N (MBN) and microbial community composition to 4–5years of experimentally simulated N deposition in temperate needle-leaf forests and subtropical evergreen broadleaf forests in eastern China, using chloroform fumigation extraction and phospholipid fatty acid (PLFA) methods. We found idiosyncratic effects of N addition on microbial biomass in these two types of forest ecosystems. In the subtropical forests, N addition showed a significant negative effect on microbial biomass and community composition, while the effect of N addition was not significant in the temperate forests. The N addition decreased MBC, MBN, arbuscular mycorrhizal fungi, and the F/B ratio (ratio of fungi to bacteria biomass) in the subtropical forests, likely due to a decreased soil pH and changes in the plant community composition. These results showed that microbial biomass and community composition in subtropical forests, compared with the temperate forests, were sensitive to N deposition. Our findings suggest that N deposition may have negative influence on soil microorganisms and potentially alter carbon and nutrient cycling in subtropical forests, rather than in temperate forests.

Growth responses of trees and understory plants to nitrogen fertilization in a subtropical forest in China

Abstract. Reactive nitrogen (N) increase in the biosphere has been a noteworthy aspect of global change, producing considerable ecological effects on the functioning and dynamics of the terrestrial ecosystems. A number of observational studies have explored responses of plants to experimentally simulated N enrichment in boreal and temperate forests. Here we investigate how the dominant trees and different understory plants respond to experimental N enrichment in a subtropical forest in China. We conducted a 3.4-year N fertilization experiment in an old-aged subtropical evergreen broad-leaved forest in eastern China with three treatment levels applied to nine 20 m × 20 m plots and replicated in three blocks. We divided the plants into trees, saplings, shrubs (including tree seedlings), and ground-cover plants (ferns) according to the growth forms, and then measured the absolute and relative basal area increments of trees and saplings and the aboveground biomass of understory shrubs and ferns. We further grouped individuals of the dominant tree species, Castanopsis eyrei, into three size classes to investigate their respective growth responses to the N fertilization. Our results showed that the plot-averaged absolute and relative growth rates of basal area and aboveground biomass of trees were not affected by N fertilization. Across the individuals of C. eyrei, the small trees with a DBH (diameter at breast height) of 5–10 cm declined by 66.4 and 59.5 %, respectively, in N50 (50 kg N ha−1 yr−1) and N100 fertilized plots (100 kg N ha−1 yr−1), while the growth of median and large trees with a DBH of > 10 cm did not significantly change with the N fertilization. The growth rate of small trees, saplings, and the aboveground biomass of understory shrubs and ground-cover ferns decreased significantly in the N-fertilized plots. Our findings suggested that N might not be a limiting nutrient in this mature subtropical forest, and that the limitation of other nutrients in the forest ecosystem might be aggravated by the enhanced N availability, potentially resulting in an adverse effect on the development of natural subtropical forest.

Low net primary productivity of dominant tree species in a karst forest, southwestern China: first evidences from tree ring width and girth increment

Aboveground net primary productivity (ANPP) of two dominant species, one deciduous tree (Platycarya strobilacea) and one evergreen tree (Machilus cavaleriei), was estimated based on the tree-ring width and the girth increment as well as allometric functions in a karst evergreen and deciduous broadleaved mixed forest in central Guizhou Province, southwestern China. Results showed that the ANPP increased from 1961 to 2015, especially during the last 20–30 years, but with strong variations. The deciduous tree had higher ANPP than the evergreen tree according to two kinds of estimates by the tree ring and girth increment. The averaged ANPP for these two mature trees was 2.27 kg/individual/year, ca. 8 t/ha/year considering the normal stand density. Such karst forest productivity was lower than the natural subtropical forests in China and in the world.

Comparative effects of sulfuric and nitric acid rain on litter decomposition and soil microbial community in subtropical plantation of Yangtze River Delta region

Acid rain is mainly caused by dissolution of sulfur dioxide and nitrogen oxides in the atmosphere, and has a significant negative effect on ecosystems. The relative composition of acid rain is changing gradually from sulfuric acid rain (SAR) to nitric acid rain (NAR) with the rapidly growing amount of nitrogen deposition. In this study, we investigated the impact of simulated SAR and NAR on litter decomposition and the soil microbial community over four seasons since March 2015. Results first showed that the effects of acid rain on litter decomposition and soil microbial were positive in the early period of the experiment, except for SAR on soil microbes. Second, soil pH with NAR decreased more rapidly with the amount of acid rain increased in summer than with SAR treatments. Only strongly acid rain (both SAR and NAR) was capable of depressing litter decomposition and its inhibitory effect was stronger on leaf than on fine root litter. Meanwhile, NAR had a higher inhibitory effect on litter decomposition than SAR. Third, in summer, autumn and winter, PLFAs were negatively impacted by the increased acidity level resulting from both SAR and NAR. However, higher acidity level of NAR (pH=2.5) had the strongest inhibitory impact on soil microbial activity, especially in summer. In addition, Gram-negative bacteria (cy19:0) and fungi (18:1ω9) were more sensitive to both SAR and NAR, and actinomycetes was more sensitive to SAR intensity. Finally, soil total carbon, total nitrogen and pH were the most important soil property factors affecting soil microbial activity, and high microbial indices (fungi/bacteria) with high soil pH. Our results suggest that the ratio of SO42− to NO3− in acid rain is an important factor which could affect litter decomposition and soil microbial in subtropical forest of China.

Dominant Trees in a Subtropical Forest Respond to Drought Mainly via Adjusting Tissue Soluble Sugar and Proline Content.

It is well-known that drought has considerable effects on plant traits from leaf to ecosystem scales; however, little is known about the relative contributions of various traits within or between tree species in determining the plant’s sensitivity or the tolerance to drought under field conditions. We conducted a field throughfall exclusion experiment to simulate short-term drought (∼67% throughfall exclusion during the dry season from October to March) and prolonged drought (∼67% throughfall exclusion prolonging the dry season from October to May) and to understand the effects of drought on two dominant tree species (Michelia macclurei and Schima superba) in subtropical forests of southern China. The morphological, physiological, and nutritional responses of the two species to the two types of drought were determined. There were significantly different morphological (leaf max length, max width, leaf mass per area), physiological (leaf proline) and nutritional (P, S, N, K, Ca, Mg) responses by M. macclurei and S. superba to prolonged drought. Comparison between the drought treatments for each species indicated that the trees responded species–specifically to the short-term and prolonged drought, with S. superba exhibiting larger plasticity and higher adaption than M. macclurei. M. macclurei responded more sensitively to prolonged drought in terms of morphology, proline content, and nutritional traits and to short-term drought with regard to soluble sugars content. The differential species-specific responses to drought will allow us to estimate the changes in dominant trees in subtropical forests of China that have experienced a decade’s worth of annual seasonal drought.

The effects of different human disturbance regimes on root fungal diversity ofRhododendron ovatumin subtropical forests of China

Ericoid mycorrhizal associations are a symbiotic relationship between soil fungi and ericaceous plants. Diversity of fungi associated with hair roots of ericaceous plants may vary as a result of frequent disturbances by human activities. The fungal diversity and communities associated with hair roots of Rhododendron ovatum were investigated along a human disturbance gradient in subtropical forests of China. Nine hundred fungal operational taxonomic units were determined by high-throughput sequencing, including different phyla such as Ascomycota, Basidiomycota, Zygomycota, Chytridiomycota, and Glomeromycota. The dominant phylum in Cunninghamia lanceolata plantations and old-growth forest was Ascomycota, while Basidiomycota was the dominant phylum in secondary forests. The indicator species analyses showed that more pathogenic indicator fungi appeared in the disturbed forests, whereas more putative ericoid mycorrhizal fungi existed in the old-growth forests. Principal component analysis also showed that the fungal communities in the hair roots of R. ovatum were distinct between natural forests and plantations, suggesting that the fungal communities associated with hair roots of R. ovatum after logging were resilient and could recover to predisturbance status. The results of envfit analysis showed that performance of host plants rather than accompanying plant community and soil parameters of plots was the key determinant of the root-associated fungal community of R. ovatum.

Spatial analysis of carbon storage density of mid-subtropical forests using geostatistics: a case study in Jiangle County, southeast China

The mid-subtropical forest is one of the biggest sections of subtropical forest in China and plays a vital role in mitigating climate change by sequestering carbon. Studies have examined carbon storage density (CSD) distribution in temperate forests. However, our knowledge of CSD in subtropical forests is limited. In this study, Jiangle County was selected as a study case to explore geographic variation in CSD. A spatial heterogeneity analysis by semi-variogram revealed that CSD varied at less than the mesoscale (approximately 2000–3000 m). CSD distribution mapped using Kriging regression revealed an increasing trend in CSD from west to east of the study area. Global spatial autocorrelation analysis indicated that CSD was clustered at the village level (at 5% significance). Some areas with local spatial autocorrelation were detected by Anselin Local Moran’s I and Getis-Ord G*. A geographically weighted regression model showed different impacts on the different areas for each determinant. Generally, diameter at breast height, tree height, and stand density had positive correlation with CSD in Jiangle County, but varied substantially in magnitude by location. In contrast, coefficients of elevation and slope ranged from negative to positive. Based on these results, we propose certain measures to increase forest carbon storage, including increasing forested area, improving the quality of the current forests, and promoting reasonable forest management decisions and harvesting strategies. The established CSD model emphasizes the important role of mid-subtropical forest in carbon sequestration and provides useful information for quantifying mid-subtropical forest carbon storage.

The role of transcriptomes linked with responses to light environment on seedling mortality in a subtropical forest, China

Summary Differences in seedling survival in trees have a lasting imprint on seedling, juvenile and adult community structure. Identifying the drivers of these differences, therefore, is a critical research objective that ultimately requires knowledge regarding how organismal function interacts with the local environment to influence survival rates. In tree communities, differences in light use strategies are frequently invoked to explain differences in seedling demographic performance through growth and survival trade‐offs. For example, shade‐tolerant species grow slowly and have higher survival rates, whereas shade‐intolerant species grow quickly but have lower survival rates. Thus, functional traits related to photosynthesis should be strong predictors of demographic rates, but results in the literature are mixed indicating that additional or alternative information regarding organismal function should be considered. Here, we provide a community‐wide inventory of transcriptomes in a subtropical tree community. This information is utilized to determine the degree to which species share homologous genes related to gene ontologies for light use and harvesting. These species similarities are used in neighbourhood generalized linear mixed‐effects models of seedling survival that evaluated seedling survival as a function of the transcriptomic, functional trait and phylogenetic composition of the local neighbourhood. The results show neighbourhood similarity in three of the 15 gene ontologies evaluated are significantly related to survival rates based on neighbourhood composition. For two of these ontologies, survival rates increase when neighbours are similar in their gene tree composition indicating the importance of abiotic filtering and performance hierarchies. Synthesis. The present work takes a novel approach by sequencing the transcriptomes of naturally co‐occurring tree species in a subtropical forest in China. The results show that the transcriptomic similarity of species is a significant predictor of differential survival. The study demonstrates that exploring the functional genomic similarity of non‐model species in nature has the potential to increase the breadth and depth of our understanding of how gene function influences species co‐occurrence and population dynamics in communities.

Geographical and climatic gradients of evergreen versus deciduous broad-leaved tree species in subtropical China: Implications for the definition of the mixed forest.

Understanding climatic influences on the proportion of evergreen versus deciduous broad‐leaved tree species in forests is of crucial importance when predicting the impact of climate change on broad‐leaved forests. Here, we quantified the geographical distribution of evergreen versus deciduous broad‐leaved tree species in subtropical China. The Relative Importance Value index (RIV) was used to examine regional patterns in tree species dominance and was related to three key climatic variables: mean annual temperature (MAT), minimum temperature of the coldest month (MinT), and mean annual precipitation (MAP). We found the RIV of evergreen species to decrease with latitude at a lapse rate of 10% per degree between 23.5 and 25°N, 1% per degree at 25–29.1°N, and 15% per degree at 29.1–34°N. The RIV of evergreen species increased with: MinT at a lapse rate of 10% per °C between −4.5 and 2.5°C and 2% per °C at 2.5–10.5°C; MAP at a lapse rate of 10% per 100 mm between 900 and 1,600 mm and 4% per 100 mm between 1,600 and 2,250 mm. All selected climatic variables cumulatively explained 71% of the geographical variation in dominance of evergreen and deciduous broad‐leaved tree species and the climatic variables, ranked in order of decreasing effects were as follows: MinT > MAP > MAT. We further proposed that the latitudinal limit of evergreen and deciduous broad‐leaved mixed forests was 29.1–32°N, corresponding with MAT of 11–18.1°C, MinT of −2.5 to 2.51°C, and MAP of 1,000–1,630 mm. This study is the first quantitative assessment of climatic correlates with the evergreenness and deciduousness of broad‐leaved forests in subtropical China and underscores that extreme cold temperature is the most important climatic determinant of evergreen and deciduous broad‐leaved tree species’ distributions, a finding that confirms earlier qualitative studies. Our findings also offer new insight into the definition and distribution of the mixed forest and an accurate assessment of vulnerability of mixed forests to future climate change.

Seasonal dynamics of soil mineral nitrogen pools and nitrogen mineralization rate in different forests in subtropical China

We conducted an in situ incubation experiment to determine soil mineral N (NH4+-N and NO3--N) concentrations and soil net N mineralization rates (net ammonification rate and net nitrification rate) using close-top PVC tubes in three adjacent forests (natural forest, Castanopsis kawakamii and Cunninghamia lanceolata plantation) from September 2014 to August 2015 in subtropical China, investigating the effects of forest type and season on soil inorganic N concentrations and soil net N mineralization rates. Results showed that soil NO3--N was the dominant form in mi-neral N pool in all three forests, and the proportion of NO3--N to soil inorganic N content ranged from 55.1% to 87.5% and from 56.1% to 79.1% in natural forest and Cunninghamia lanceolata plantation, respectively. The effects of forest types on soil mineral N pool were only significant on soil NO3--N, and the concentration of NO3--N in Castanopsis kawakamii was significantly lower than in the other two forests. The NO3--N and mineral N pool varied seasonally in all forests, and were higher in dormant season (October to February) than in growing season (March to September). Soil nitrification rate was very low in the whole year in all three forests and soil net ammonification was the major process of soil net mineralization. Tree species significantly affected soil net ammonification rate, and the value under Chinese fir was significantly lower than the other two fore-sts. The seasonal patterns of the soil net ammonification rate were not similar in all the three forests, but with the lowest value occurring in November and February in the following year. Analysis using variance of repeated measures indicated that soil mineral N concentrations and soil N mineralization rates were significantly affected by forest type and season, and correlation analysis showed that soil mineral N and soil N mineralization rate were significantly affected by water moisture and temperature, and the effects of litter on soil N mineralization rate were mainly through quality control, ra-ther than the quantity control.

Responses of Soil CO2, CH4and N2O Fluxes to N, P, and Acid Additions in Mixed Forest in Subtropical China

Understanding how nitrogen (N) availability interacts with soil acidity and phosphorus (P) availability to affect soil-atmosphere exchanges in CO2, CH4 and N2O in forest ecosystems is important for understanding the mechanisms driving ecosystem responses to enhanced N deposition. Here, we conducted an experiment with N, P and acid (H) addition in a mixed forest in subtropical China to investigate how acid and P addition affects CO2, CH4 and N2O exchange under N addition. Our results showed that soil -N and -N increased after N addition, but CO2 emissions in N addition plots remained unaffected. CH4 uptake in N-, P-, NP-, NH- and NPH-addition plots were reduced by 21.1%, 15.7%, 39.1%, 26.6%, and 28.4%, respectively. CH4 uptake in NP-addition plots were lower compared to N-addition and P-addition plots, indicating that N and P addition had an additive effect on inhibiting CH4 uptake. N2O emission in N-, NP-, NH- and NPH-addition plots increased by 158.6%, 176.0%, 117.2%, and 91.8%, respectively. N2O emissions in NPH-addition plots were lower compared to NP-addition plots while showed no difference between N-addition and NH-addition plots. This suggests that only under P rich conditions, acid addition would greatly mitigate N2O emissions under N addition. Our results demonstrate that for N and P co-limited forest ecosystems with acidic soils, low P availability constrains the inhibition of soil CH4 uptake by N deposition. When P availability is low, a weak soil acidation induced by N deposition may have less influence on the stimulation of N2O emissions by N deposition.

Assimilating leaf area index of three typical types of subtropical forest in China from MODIS time series data based on the integrated ensemble Kalman filter and PROSAIL model

Subtropical forest ecosystems play essential roles in the global carbon cycle and in carbon sequestration functions, which challenge the traditional understanding of the main functional areas of carbon sequestration in the temperate forests of Europe and America. The leaf area index (LAI) is an important biological parameter in the spatiotemporal simulation of the carbon cycle, and it has considerable significance in carbon cycle research. Dynamic retrieval based on remote sensing data is an important method with which to obtain large-scale high-accuracy assessments of LAI. This study developed an algorithm for assimilating LAI dynamics based on an integrated ensemble Kalman filter using MODIS LAI data, MODIS reflectance data, and canopy reflectance data modeled by PROSAIL, for three typical types of subtropical forest (Moso bamboo forest, Lei bamboo forest, and evergreen and deciduous broadleaf forest) in China during 2014–2015. There were some errors of assimilation in winter, because of the bad data quality of the MODIS product. Overall, the assimilated LAI well matched the observed LAI, with R2 of 0.82, 0.93, and 0.87, RMSE of 0.73, 0.49, and 0.42, and aBIAS of 0.50, 0.23, and 0.03 for Moso bamboo forest, Lei bamboo forest, and evergreen and deciduous broadleaf forest, respectively. The algorithm greatly decreased the uncertainty of the MODIS LAI in the growing season and it improved the accuracy of the MODIS LAI. The advantage of the algorithm is its use of biophysical parameters (e.g., measured LAI) in the LAI assimilation, which makes it possible to assimilate long-term MODIS LAI time series data, and to provide high-accuracy LAI data for the study of carbon cycle characteristics in subtropical forest ecosystems.

Spatial distribution of soil organic carbon stock in Moso bamboo forests in subtropical China

Moso bamboo (Phyllostachys heterocycla (Carr.) Mitford cv. Pubescens) is an important timber substitute in China. Site specific stand management requires an accurate estimate of soil organic carbon (SOC) stock for maintaining stand productivity and understanding global carbon cycling. This study compared ordinary kriging (OK) and inverse distance weighting (IDW) approaches to study the spatial distribution of SOC stock within 0–60 cm using 111 soil samples in Moso bamboo forests in subtropical China. Similar spatial patterns but different spatial distribution ranges of SOC stock from OK and IDW highlighted the necessity to apply different approaches to obtain accurate and consistent results of SOC stock distribution. Different spatial patterns of SOC stock suggested the use of different fertilization treatments in Moso bamboo forests across the study area. SOC pool within 0–60 cm was 6.46 and 6.22 Tg for OK and IDW; results which were lower than that of conventional approach (CA, 7.41 Tg). CA is not recommended unless coordinates of the sampling locations are missing and the spatial patterns of SOC stock are not required. OK is recommended for the uneven distribution of sampling locations. Our results can improve methodology selection for investigating spatial distribution of SOC stock in Moso bamboo forests.

Tree diversity increases levels of herbivore damage in a subtropical forest canopy: evidence for dietary mixing by arthropods?

Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities. So far, these links have mainly been studied in grasslands or in artificial tree plantations with low species richness. Furthermore, most studies provide results from newly established experimental plant communities where trophic links are not fully established or from stands of tree saplings that have not yet developed a canopy. Here, we test how tree diversity in a species-rich subtropical forest in China with fully developed tree canopy affects levels of herbivore damage caused by different arthropod feeding guilds. Methods We established 27 plots of 30×30 m area. The plots were selected randomly but with the constraint that they had to span a large range of tree diversity as required for comparative studies in contrast to sample surveys. We recorded herbivore damage caused by arthropod feeding guilds (leaf chewers, leaf skeletonizers and sap feeders) on canopy leaves of all major tree species. Important Findings Levels of herbivore damage increased with tree species richness and tree phylogenetic diversity. These effects were most pronounced for damage caused by leaf chewers. Although the two diversity measures were highly correlated, we additionally found a significant interaction between them, whereby species richness increased herbivory mostly at low levels of phylogenetic diversity. Tree species with the lowest proportion of canopy leaf biomass in a plot tended to suffer the highest levels of herbivore damage, which is in contrast to expectations based on the resource concentration hypothesis. Our results are in agreement with expectations of the dietary mixing hypothesis where generalist herbivores with a broad spectrum of food plants benefit from increased resource diversity in tree species-rich forest patches.

Seasonal characteristics and determinants of tree growth in a Chinese subtropical forest

Aims To quantify the seasonal differences in effects of leaf habit, species identity, initial diameter, neighborhood interaction and stand environment on tree absolute diameter growth rates in a subtropical forest in China. Methods We used man-made dendrometer bands to record radial increments of all trees with diameter at breast height (DBH) ≥5cm and height ≥3 m within 25 comparative study plots (30×30 m for each) of the ‘Biodiversity–Ecosystem Functioning Experiment China’ (BEF-China) in the Gutianshan National Nature Reserve, Zhejiang Province, China. We measured stem circumferences twice a year from 2011 to 2014 to calculate absolute diameter growth rate of a warm and wet season (WWS, April to September) and a dry and cold season (DCS, October to the next March) for each individual tree: annual growth (GRyear), growth during the WWS (GRWWS) and growth during the DCS (GRDCS). We firstly tested the differences in growth rates between different seasons using paired t-tests with Bonferroni correction. Then we applied linear mixed models to explore the effects of leaf habit, species identity, initial diameter, neighborhood interaction (indicated by richness, density and total basal area of all neighboring trees within a radius of 5 m around target trees), stand age and topography (elevation, slope and aspect) on tree growth rates of the two different seasons in three deciduous and 14 evergreen species. Important Findings GRyear, GRWWS and GRDCS varied between 0.04–0.50cm year−1 (mean = 0.21), 0.03–0.46cm season−1 (mean = 0.18) and 0.01–0.05cm season−1 (mean = 0.03) across the 17 species, respectively. GRWWS was significantly higher than GRDCS for all species. Growth rates of faster growing species tended to have larger absolute differences between the WWS and DCS. Tree growth rates of both seasons and of the year (GRyear, GRWWS and GRDCS) varied significantly among leaf habit and species, and increased allometrically with initial diameter, decreased with stand age, but were not significantly related to topography and neighborhood richness or density. GRWWS decreased with neighborhood total basal area, while GRDCS did not. In conclusion, species might the temporally complementary, contributing to plot growth at different times of the year.

Growth process and model simulation of three different classes of Schima superba in a natural subtropical forest in China

Schima superba is an important fire-resistant, high-quality timber species in southern China. Growth in height, diameter at breast height (DBH), and volume of the three different classes (overtopped, average and dominant) of S. superba were examined in a natural subtropical forest. Four growth models (Richards, edited Weibull, Logistic and Gompertz) were selected to fit the growth of the three different classes of trees. The results showed that there was a fluctuation phenomenon in height and DBH current annual growth process of all three classes. Multiple intersections were found between current annual increment (CAI) and mean annual increment (MAI) curves of both height and DBH, but there was no intersection between volume CAI and MAI curves. All selected models could be used to fit the growth of the three classes of S. superba, with determinant coefficients above 0.9637. However, the edited Weibull model performed best with the highest R2 and the lowest root of mean square error (RMSE). S. superba is a fast-growing tree with a higher growth rate during youth. The height and DBH CAIs of overtopped, average and dominant trees reached growth peaks at ages 5–10, 10–15 and 15–20 years, respectively. According to model simulation, the volume CAIs of overtopped, average and dominant trees reached growth peaks at ages 17, 55 and 76 years, respectively. The biological rotation ages of the overtopped, average and dominant trees of S. superba were 29, 85 and 128 years, respectively.