Calibration and assessment of seasonal changes in leaf area index of a tropical dry forest in different stages of succession

A simple measure of the amount of foliage present in a forest is leaf area index (LAI; the amount of foliage per unit ground surface area), which can be determined by optical estimation (gap fraction method) with an instrument such as the Li-Cor LAI-2000 Plant Canopy Analyzer. However, optical instruments such as the LAI-2000 cannot directly differentiate between foliage and woody components of the canopy. Studies investigating LAI and its calibration (extracting foliar LAI from optical estimates) in tropical forests are rare. We calibrated optical estimates of LAI from the LAI-2000 with leaf litter data for a tropical dry forest. We also developed a robust method for determining LAI from leaf litter data in a tropical dry forest environment. We found that, depending on the successional stage of the canopy and the season, the LAI-2000 may underestimate LAI by 17% to over 40%. In the dry season, the instrument overestimated LAI by the contribution of the woody area index. Examination of the seasonal variation in LAI for three successional stages in a tropical dry forest indicated differences in timing of leaf fall according to successional stage and functional group (i.e., lianas and trees). We conclude that when calculating LAI from optical estimates, it is necessary to account for the differences between values obtained from optical and semi-direct techniques. In addition, to calculate LAI from litter collected in traps, specific leaf area must be calculated for each species rather than from a mean value for multiple species.     

A comparison of decomposition dynamics among green tree leaves,partially decomposed tree leaf litter and their mixture in a warm temperate forest ecosystem

Decomposition dynamics were compared among green tree leaves, partially decomposed tree leaf litter (i.e., decayed tree leaf litter on forest floor) and a mixture of the two in a warm temperate forest ecosystem in central China to test the influence of litter chemical quality on the degree of decomposition. The study was conducted in situ at two contrasting forest sites, an oak forest dominated by Quercus aliena var. acuteserrata Maxim., and a mixed pine and oak forest dominated by Pinus armandii Franch. and Q. aliena var. acuteserrata. We found marked differences in the rate of decomposition among litter types at both forest sites; the litter decomposition constant, k, was about 39 % greater at the oak forest site and more than 70 % greater at the pine-oak forest site, for green leaves than for partially decomposed leaf litter. The decomposition dynamics and temporal changes in litter chemistry of the three litter types also greatly differed between the two forest sites. At both forest sites, the higher rate of decomposition for the green leaves was associated with a higher nitrogen (N) content and lower carbon to N ratio (C/N) and acid-unhydrolyzable residue to N ratio (AUR/N). We did not find any non-additive effects when mixing green leaves and partially decomposed leaf litter. Our findings support the contention that litter chemical quality is one of the most important determinants of litter decomposition in forest ecosystems at the local or regional scale, but the effect of litter chemical quality on decomposition differs between the contrasting forest types and may vary with the stage of decomposition.     

Comparison and Dynamic Calibration between LAI Values of Larix principis-rupprechtii Plantation Determined by Canopy Scanner and Litter-fall Collection

In order to test the accuracy of the usually-used fixed calibration factor of the canopy scanner of LAI-2000 for measuring the leaf area index(LAI),a Larix principis-rupprechtii plantation was chosen in the small watershed of Xiangshuihe located at the Liupan Mountains of Ningxia Hui Autonomous Region of NW China,the LAI was measured in October 2010,a period from full canopy to the total fall of needles,by using both the LAI- 2000 and litterfall collection method.Then,a comparison was made between the LAI values determined by the litter-fall collection and that calculated based on the figures read from LAI-2000 and the fixed calibration factor(1.49).It showed that the average of LAI measurements of the 2 methods was very close,with a difference of only 5%.However,the calculated LAI from LAI-2000 was obviously higher than the true values determined by litter-fall collection when the canopy was full of needles;and obviously lower than the true value when the canopy was sparse after needle falling.The reason may be that LAI-2000 takes the projection of twigs as needles.So,a dynamic calibration factor is needed,especially in the seasons when the needle amount and the percentage of twigs projection in crown projection change quickly.Therefore,a statistic relation in a quadratic polynomial form between the 2 series of LAI data was well fitted. This relation can be used for a more accurate estimation of LAI based on the data read from the easilyused canopy scanners like LAI-2000.     

Temporal changes in litterfall, litter decomposition and their chemical composition in Sasa dwarf bamboo in a natural forest ecosystem of northern Japan

We investigated the dynamics of litterfall and litter decomposition of Sasa dwarf bamboo (Sasa senanensis) and trees to clarify the characteristics of organic matter and nitrogen cycling between plant and soil in a natural cool-temperate mixed forest ecosystem dominated by an understory vegetation of Sasa. Mean annual Sasa litterfall over the 3-year study period was 164 g m^?2 year^?1, which accounted for approximately 29% of total litterfall. Litter decomposition of Sasa leaf and Sasa culm was significantly slower than that of tree leaf during first and second years. The slow decomposition rates of both Sasa litter types were caused by a significantly higher silicate than in tree leaf. Nitrogen concentration in litter increased as decomposition progressed, especially in Sasa leaf and tree leaf. As a result of the slow decomposition of both Sasa litter types, 111 and 73% of nitrogen to the initial amounts were retained in Sasa leaf and Sasa culm after 3 years, respectively. The amounts of retained nitrogen in Sasa leaf, Sasa culm, and tree leaf after 3 years were 1.29, 0.47, and 3.92 g N m^?2, respectively, indicating that the differences of litter decomposition rates among the litter types influence on the nitrogen cycling in forest ecosystem through the differences of the nitrogen release from litter.     

Remote estimation of canopy leaf area index and chlorophyll content in Moso bamboo (<Emphasis Type="Italic">Phyllostachys edulis</Emphasis> (Carrière) J. Houz.) forest using MODIS reflectance data

Key message

We estimated the leaf area index (LAI) and canopy chlorophyll content (CC) of Moso bamboo forest by using statistical models based on MODIS data and field measurements. Results showed that the statistical model driven by MODIS data has the potential to accurately estimate LAI and CC, while the structure of the calibration models varied between on- and off-years because of the different leaf change and bamboo shoot production characteristics between these types of years.

Context

LAI and CC (gram per square meter of ground area) are important parameters for determining carbon exchange between Moso bamboo forest (Phyllostachys edulis (Carrière) J. Houz.) and the atmosphere.

Aims

This study evaluated the ability of a statistical model driven by MODIS data to accurately estimate the LAI and CC in Moso bamboo forest, and differences in the LAI and CC between on-years (years with great shoot production) and off-years (years with less shoot production) were analyzed.

Methods

The LAI and CC measurements were collected in Anji County, Zhejiang Province, China. Indicators of LAI and CC were calculated from MODIS data. Then, a regression analysis was used to build relationships between the LAI and CC and various indicators on the basis of leaf change and bamboo shoot production characteristics of Moso bamboo forest.

Results

LAI and CC were accurately estimated by using the regression analysis driven by MODIS-derived indicators with a relative root mean squared error (RMSEr) of 9.04 and 13.1%, respectively. The structure of the calibration models varied between on- and off-years. Long-term time series analysis from 2000 to 2015 showed that LAI and CC differed largely between on- and off-years.

Conclusion

This study demonstrates that LAI and CC of Moso bamboo forest can be estimated accurately by using a statistical model driven by MODIS-derived indicators, but attention should be paid to differences in the calibration models between on- and off-years.

     

华北落叶松人工林叶面积指数实测值与冠层分析仪读数值的比较和动态校正

叶面积指数(LAI)是森林生态系统的重要结构参数,用来反映植物叶量和群体生长特征[1-4],对生态系统水分和养分循环、地表和大气之间的相互作用等诸多过程都有重要影响[5-6],广泛应用于植物生态、植物生理、生态水文以及一些交叉学科的研究中,也可作为科学培育森林、评价林分质量的定量指     

Allometric models for leaf area and leaf mass predictions across different growing seasons of elm tree (<Emphasis Type="Italic">Ulmus japonica</Emphasis>)

Convenient and effective methods to determine seasonal changes in individual leaf area (LA) and leaf mass (LM) of plants are useful in research on plant physiology and forest ecology. However, practical methods for estimating LA and LM of elm (Ulmus japonica) leaves in different periods have rarely been reported. We collected sample elm leaves in June, July and September. Then, we developed allometric models relating LA, LM and leaf parameters, such as leaf length (L) and width (W) or the product of L and W (LW). Our objective was to find optimal allometric models for conveniently and effectively estimating LA and LM of elm leaves in different periods. LA and LM were significantly correlated with leaf parameters (P < 0.05), and allometric models with LW as an independent variable were best for estimating LA and LM in each period. A linear model was separately developed to predict LA of elm leaves in June, July and September, and it yielded high accuracies of 93, 96 and 96%, respectively. Similarly, a specific allometric model for predicting LM was developed separately in three periods, and the optimal model form in both June and July was a power model, but the linear model was optimal for September. The accuracies of the allometric models in predicting LM were 88, 83 and 84% for June, July and September, respectively. The error caused by ignoring seasonal variation of allometric models in predicting LA and LM in the three periods were 1–4 and 16–59%, respectively.     

Leaf litter and its nutrient contribution in the cacao agroforestry system

Cacao agroforestry systems (cacao-AFS) produce abundant litter. After decomposing, litter releases nutrients into the soil. The aim of this research was to estimate litter production and its nutrient content in 35- and 55-year-old cacao-AFS. The research was conducted in three cacao-AFS of each age, in Cardenas, Tabasco, México. Four traps per cacao-AFS were used to collect litter. Litter was collected every 15 days for one year. It was then fractioned into cacao leaves, shade tree leaves, petioles, branches and stems, and cacao flowers and fruits. To determine nutrient content of litter, samples were composited by age of cacao-AFS and by season of the year. Then chemical analysis was done in triplicate. Data were subjected to analysis of variance, orthogonal contrasts, and Student t and Duncan tests. Cacao-AFS produce litter all year. Thirty-five-year-old cacao-AFS produced more litter than 55-year-old cacao-AFS (2042 vs 1570 kg DM ha^?1 year^?1). Except for the shade tree leaf fraction (559.5 vs 642 kg DM ha^?1), 35-year-old cacao-AFS were superior to 55-year-old cacao-AFS in all the other litter fractions. Cacao leaf fraction was the main source of litter in cacao-AFS of both ages. Neither age of cacao-AFS nor the season of the year affected N, K, Zn or S content in litter. Orthogonal contrasts indicated statistical differences between ages of cacao-AFS for P, Ca, and Fe content in litter. Both N–P–K–Ca–Mg contents in litter of 35-year-old cacao-AFS (1.2–0.4–1.2–1.7–0.4%) and in litter of 55-year-old cacao-AFS (1.1–0.6–1.2–1.4–0.4%) are enough to recover the nutrients extracted by the cacao crop.     

Deposition of litter and nutrients in leaves and twigs in different plant communities of northeastern Mexico

Studies on litterfall and decomposition provide estimations of decomposition rates of different ecosystems.This is key information to understanding ecosystem dynamics and changes in a scenario of global warming.The objective of this research was to assess litterfall production,the potential deposition of macro and micronutrients through leaf and twig fall as well as macronutrient—use efficiency in three forest ecosystems at different altitudes: a pine forest mixed with deciduous species(S1); a Quercus spp.forest(S2); and,a Tamaulipan thornscrub forest(S3).Total annual litterfall deposition was 594,742 and 533 g m~(-2) for S1,S2 and S3.Leaf litter was higher (68%) than twigs(18%),reproductive structures(8%) or miscellaneous material(6%).Micronutrient leaf deposition was higher for Fe followed by Mn,Zn and Cu.Macronutrient leaf deposition was higher for Ca followed by K,Mg and P.Even though P deposition in leaves and twigs was lower than other macronutrients,its nutrient use efficiency was higher than Ca,Mg or K.Altitude and species composition determine litter and nutrient deposition,with higher values at mid-altitudes(550 m).Altitude is an important factor to consider when analyzing litter production as well as nutrient deposition as shown in this study.Litter production and nutrient deposition are expected to change in a scenario of global warming.     

Importance of woody materials for seasonal variation in leaf area index from optical methods in a deciduous needleleaf forest

Woody materials (woody area index, WAI) is a key error source in estimating leaf area index (LAI) by optical methods, but how to correct the error caused by WAI during different seasons has not reached consensus. In this study, effective plant area index (PAI_e) was first estimated using two indirect optical methods (digital hemispherical photography, DHP, and LAI-2000) in a deciduous needleleaf forest, and then four different schemes for correcting the contribution of WAI to PAI_e were tested here. We also directly estimated the seasonality of LAI by a litter collection method and an allometric method. Directly subtracting WAI from PAI resulted in a greater degree of uncertainty in correcting seasonal changes of PAI_e from both DHP and LAI-2000. Therefore, we introduced a new correction factor, the stem-to-total area ratio, which was reasonable and useful for quantifying seasonal changes in the contribution of WAI to PAI_e. We finally recommend a practical scheme for correcting PAI_e from both DHP and LAI-2000, with accuracies as high as 88% and 87% during most growing seasons, respectively. Additionally, LAI values estimated from allometry were concordant with those estimated from litter collection, indicating that the allometry method is useful for tracking seasonal changes in LAI.     

Temporal variation and efficiency of leaf area index in young mountain Norway spruce stand

Temporal variation of leaf area index (LAI) in two young Norway spruce stands with different densities was monitored during eight consecutive growing seasons (1998–2005). We focused on: (1) LAI dynamics and above-ground mass production of both spruce stands and their comparison, (2) leaf area duration (LADU), crop production index (CPI) and leaf area efficiency (LAE) evaluation, and (3) thinning impact on the above-mentioned parameters. Also, we tried to deduce the most effective LAI value for the Norway spruce forest investigated. The LAI values of both spruce stands showed a typical seasonal course. To describe the LAI dynamics of the stand, we recommend taking LAI measurements within short time intervals at the time of budding and needle expansion growth (i.e., in early spring) and close to the LAI peak, when the twig growth has been completed. The reason was that after reaching the seasonal maximum, no significant differences between subsequently obtained values were found in the following 2 months. Therefore, we recommend this period for the estimation of seasonally representative LAI values, enabling the comparison of various spruce stands. The maximum hemi-surface LAI value reached 12.4. Based on our results, the most effective LAI values for maximum above-ground biomass production were within the range of 10–11. We found an LAI over these values to be less effective for additional production of above-ground biomass. In forest practice, thinning intensity is mostly described by percentage of stocking reduction. We want to show that not only thinning intensity, but also the type of thinning is important information. The type of thinning significantly affected the stand above-ground biomass increment, canopy openness, stand LAI and LAI efficiency. The stimulating effect of high-type thinning was observed; the LAE as well as the CPI increased. Low-type thinning had no such effects on LAE increments compared to the high-type thinning with similar intensity.

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Individual leaf area estimations of a dioecious tropical tree species <Emphasis Type="Italic">Carpotroche brasiliensis</Emphasis> (Raddi) A. Gray,Achariaceae

Carpotroche brasiliensis is a dioecious tree species native of the Brazilian Atlantic rainforest. Due to medical and industrial use of the oil extracted from its seeds, C. brasiliensis has a great potential for cultivation as non-timber forest product in agroforestry systems. This study was conducted with the objective to analyze the leaf dimensions of male and female adult trees and seedlings of C. brasiliensis. Two hypotheses were tested: (a) leaf dimensions do not differ between male and female adult genotypes; and (b) it is possible to develop single regression models for predicting leaf area (LA) from dimensional variables encompassing male and female adult genotypes and seedlings. LA, leaf length (L) and maximum leaf width (W) were measured in leaves collected from seven male and seven female adult genotypes and three seedling lots. The feasibility of using a single model for leaves of males and females, and seedlings and adults, was tested by analysis of covariance (ANCOVA). The prediction errors (PE) for each of the regression models were calculated from the cross-validation method. The average values of L, W and LA were, respectively, 136, 142 and 457 % higher in adults than in seedlings, and the average values of leaf shapes (L:W) of seedlings were intermediate between the average values of L:W of adult males and females. The average values of L did not differ between adult males and females, but significant differences were observed between males and females for W, LA and L:W (both p < 0.01, nested ANOVA). The mean L:W values of adult males and females, and seedlings, indicate that leaf shape should be used as a criterion for sex differentiation in this species. It was not possible to develop single models encompassing adult males and females, and seedlings; but high accurate predictive models of LA from L × W measurements were developed for adult males (R² = 0.98, PE = 0.69, n = 350), adult females (R² = 0.98, PE = 0.01, n = 350), and seedlings (R² = 0.99, PE = 6.80, n = 150).     

Species differences in timing of leaf fall and foliage chemistry modify nutrient resorption efficiency in deciduous temperate forest stands

Extensive variation in fractional resorption of mineral elements from plant leaves is still not fully understood. In multi-species forest stands, species leaf fall phenology and leaf constitution may significantly modify the timing of nutrient return to the soil and overall plant nutrient loss. We studied leaf fall and nutrient loss kinetics, and leaf composition in three natural, temperate, deciduous broadleaf forest stands to determine the role of timing of leaf abscission and nutrient immobilization in cell walls on nutrient resorption efficiency of senescing leaves. Nitrogen (N), phosphorus and potassium contents decreased continuously in attached leaves after peak physiological activity during mid-season. Changes in nutrient contents of attached leaves were paralleled by decreases in nutrient contents in freshly fallen leaf litter. In different species and for different nutrients, resorption of nutrients from senescing leaves proceeded with different kinetics. The maximum nutrient resorption efficiency (the fraction of specific nutrient resorbed from the leaves at the end of leaf fall) did not depend on the mid-seasonal nutrient concentration. Species with earlier leaf fall resorbed leaf nutrients at a faster rate, partly compensating for the earlier leaf fall. Nevertheless, the litter-mass weighted mean nutrient contents in leaf litter were still larger in species with earlier leaf fall, demonstrating an inherent trade-off between early leaf fall and efficient nutrient resorption. This trade-off was most important for N. Losses of the non-mobile nutrients calcium and magnesium were unaffected by the timing of leaf fall. There was large variation in the maximum N resorption efficiency among species. Correlations among leaf chemical variables suggested that the maximum N resorption efficiency decreased with the increasing fraction of cell walls in the leaves, possibly due to a greater fraction of N occluded in cell wall matrix. We conclude that species leaf fall phenology and leaf chemistry modify the timing and quantities of plant nutrient losses, and that more diverse forest stands supporting a spectrum of species with different phenologies and leaf types produce litter with more variable chemical characteristics than monotypic stands.     

Changes in above- and belowground biomass in early successional tropical secondary forests after shifting cultivation in Sarawak,Malaysia

Uncertainties in the rate of biomass variation with forest ageing in tropical secondary forests, particularly in belowground components, limit the accuracy of carbon pool estimates in tropical regions. We monitored changes in above- and belowground biomass, leaf area index (LAI), and biomass allocation to the leaf component to determine the variation in carbon accumulation rate with forest age after shifting cultivation in Sarawak, Malaysia. Nine plots in a 4-year-old forest and fourteen plots in a 10-year-old forest were monitored for 5 and 7 years, respectively. Forest and plant part biomass were calculated from an allometric equation obtained from the same forest stands. Both above- and belowground biomass increased rapidly during the initial decade after abandonment. In contrast, a much slower rate of biomass accumulation was observed after the initial decade. LAI also increased by approximately double from the 4-year-old to 10-year-old forest, and then gently increased to the 17-year-old forest. We also found that allocation variation in leaf biomass and nitrogen was closely related to the rate of biomass accumulation as a forest aged. During the first decade after abandonment, a high biomass and nitrogen allocation to the leaf component may have allowed for a high rate of biomass accumulation. However, reduction in those allocations to leaf component after the initial decade may have helped to suppress the biomass accumulation rate in older secondary forests. Roots accounted for 14.0–16.1% of total biomass in the 4–17-year-old abandoned secondary forests. We also verified the model predicted values for belowground biomass by Cairns et al. (1997) and Mokany et al. (2006), although both models overestimated the values throughout our data sets by 45–50% in the 10-year-old forest. The low root:shoot ratio in the secondary forests may have caused this overestimation. Therefore, our results suggest that we should modify the models to estimate belowground biomass considering the low root:shoot ratio in tropical secondary forests.     

不同经营模式对毛竹叶片特性和竹笋产量的影响

为了研究不同经营模式对毛竹Phyllostachys heterocycla ‘Pubescens’笋用林叶片特征以及竹笋产量的影响,以不同经营模式(带状、层状、加客土和常规经营)的毛竹笋用林为研究对象,对毛竹叶片SPAD值(soil and plant analyzer development value,SPAD value)和叶面积指数(Leaf Aea Index,LAI)进行监测,并于次年春统计春笋产量。结果表明:不同经营模式下的毛竹叶片SPAD值随时间呈现先升高后下降的变化趋势,而LAI变化不明显;机械化带状经营模式中处理D_3(条带宽度1 m,保留条带内立竹和适当竹鞭)的SPAD值及LAI均高于常规经营,且其LAI显著高于(P<0.05)层状和加客土经营中的各处理。层状经营模式中处理C_2(去除竹林地0～25 cm土层的竹鞭)的SPAD值和LAI均较低于同时期的其他处理;机械化经营模式中的处理D_3和处理T_6(加客土6 cm)的春笋产量最高;毛竹SPAD值、LAI及春笋产量三者均呈极显著正相关(P<0.01),其中SPAD值与春笋产量呈极显著正相关(P<0.01)。     

Influence of soil properties and burial depth on Persian oak (<Emphasis Type="Italic">Quercus brantii</Emphasis> Lindl.) establishment in different microhabitats resulting from traditional forest practices

In seasonally dry environments such as the Zagros woodlands (Iran), severe drought stress and lack of appropriate management practices can cause failure of oak afforestation or reforestation. We investigated the effect of soil properties and burial depth on Persian oak (Quercus brantii Lindl.) establishment in different microhabitats resulting from traditional forest practices. Four microhabitats that were based on forest structure were considered for oak acorn seeding: (1) inside old sprout clumps (ISPC); (2) under the canopy of tall trees (UCTT); (3) outside the canopy of tall trees and sprout clumps; and (4) near recent stumps or sprout clumps. Acorns were seeded at two depths (2 and 5 cm), and seedling survival and growth variables were recorded for 4 years, together with soil chemical and biological attributes. Stepwise discriminant analysis showed that a combination of total soil nitrogen, cation exchange capacity, available phosphorus and potassium, litter depth, microbial quotient, metabolic coefficient, substrate-induced respiration and earthworm abundance was the best variables to characterise the microhabitats. With the exception of pH, bulk density and soil texture, these variables were higher in UCTT and ISPC than in the other microhabitats. Seedling emergence and survival were greater at a seed depth of 5 cm than at 2 cm. Seedling height and shoot, root and leaf biomasses were higher in the UCTT microhabitat compared to the other microhabitats and correlated positively with soil nutrients contents and most of the soil biological variables but negatively with soil bulk density. This study emphasised the role of microhabitats in creating a “canopy effect” producing favourable physical, chemical and biological soil conditions. In particular, large oak trees form islands of fertility and therefore are of key importance for successful seedling establishment in forests subjected to intense human activities.     

Ozone fumigation of Quercus ilex L. slows down leaf litter decomposition with no detectable change in leaf composition

Context

The evaluation of changes in litter decomposition rate due to increasing trend in tropospheric ozone is an emerging field of investigation, providing relevant information on long-term forest ecosystem sustainability.

Aims

This research aims to clarify the effects of ozone exposure on Quercus ilex leaf chemical composition and decomposition slow down.

Methods

Young plants were fumigated in growth chambers at a cumulative dose of 17.15 ppm h. To assess the fumigation effectiveness, stomatal conductance and net photosynthesis were monitored. Leaves were analysed for C, N, S, Ca, Mg, K, Fe, Zn, Mn, total soluble sugars, starch, acid-detergent fibre (ADF), lignin and cellulose prior to the incubation in litter bags in mesocosms, and during decomposition along 395 days.

Results

Ozone-exposed leaves showed a significant reduction in net photosynthesis and stomatal conductance but did not differ from control leaves in all the chemical parameters analysed. Nevertheless, leaf decomposition rate was lower in treated leaves. The main differences between the models describing the mass loss in exposed and control leaves were played by ADF for exposed leaves and by lignin for control leaves, as well as by N, that showed a greater contribution in the model for the exposed leaves.

Conclusion

Ozone fumigation of Q. ilex results in leaf litter decomposition slowing down, mainly due to ADF joint dynamics with the other variables describing mass decay, even if no detectable changes in initial leaf composition occur.     

Litterfall,decomposition and nutrient release of <Emphasis Type="Italic">Shorea robusta</Emphasis> and <Emphasis Type="Italic">Tectona grandis</Emphasis> in a sub-tropical forest of West Bengal,Eastern India

We studied leaf litter fall, decomposition and nutrient release patterns of Shorea robusta and Tectona grandis by using a litter bag technique to better understand the release pattern of nutrients to soil from leaf litter. Annual litterfall varied from 13.40 ± 2.56 t ha^?1 a^?1 for S. robusta to 11.03 ± 3.72 t ha^?1 a^?1 for T. grandis and the decay constant (k) of decomposed leaf litter was distinctly higher for T. grandis (2.70 ± 0.50 a^?1) compared to S. robusta (2.41 ± 0.30 a^?1). Biomass loss was positively correlated with the initial litter C, WSC, C/N and ash content in S. robusta and N, P and K concentration for T. grandis. Biomass was negatively correlated with lignin and L/N ratio for S. robusta and L, WSC, L/N and C/N ratio for T. grandis (P < 0.01). Nutrient use efficiency (NUE) and nutrient accumulation index (NAI) of S. robusta was higher than for T. grandis. The retranslocation of bioelements from senescent leaves ranked as P > N > K. Annual N, P and K input to soil through litterfall differed significantly between the two species in the following order: N>K>P. S. robusta was superior in terms of K and P return and T. grandis was superior in terms of N return. The two tree species showed a similar patterns of nutrient release (K > P > N) during decomposition of their leaf litter. Nutrients of N, K and P were the primary limiting nutrients returned to soil through litterfall with important roles in soil fertility and forest productivity.     

Establishment success in a forest biodiversity and ecosystem functioning experiment in subtropical China (BEF-China)

Experimental forest plantations to study biodiversity–ecosystem functioning (BEF) relationships have recently been established in different regions of the world, but subtropical biomes have not been covered so far. Here, we report about the initial survivorship of 26 tree species in the first such experiment in subtropical China. In the context of the joint Sino–German–Swiss Research Unit “BEF-China,” 271 experimental forest plots were established using 24 naturally occurring tree species and two native commercial conifers. Based on the survival inventories carried out in November 2009 and June 2010, the overall survival rate was 87 % after the first 14 months. Generalized mixed-effects models showed that survival rates of seedlings were significantly affected by species richness, the species’ leaf habit (deciduous or evergreen), species identity, planting date, and altitude. In the first survey, seedling establishment success decreased with increasing richness levels, a tendency that disappeared in the second survey after replanting. Though evergreen species performed less well than deciduous species with establishment rates of 84 versus 93 % in the second survey, their planting success exceeded the general expectation for subtropical broad-leaved evergreen species. These results have important implications for establishing mixed-species plantations for diversity conservation and improvement of ecosystem functioning in the Chinese subtropics and elsewhere. Additional costs associated with mixed-species plantations as compared to conventional plantations also demonstrate the potential of upscaling BEF experiments to large-scale afforestation projects.     

Carbon dioxide sequestration capability of an unmanaged old-growth broadleaf deciduous forest in a Strict Nature Reserve

The seasonal trend of plant carbon dioxide (CO₂) sequestration is related to the photosynthetic activity, which in turn changes in response to environmental conditions. Great interest has turned to the CO₂ sequestration (CS) potential of temperate forests which play an important role in global carbon (C) cycle contributing to the lowering of atmospheric CO₂ concentration. In such context, the CS of an unmanaged old broad-leaf deciduous forest developing inside a Strict Nature Reserve, and its variations during the year were analyzed considering the monthly variations of leaf area index (LAI) and net photosynthetic rates (N_P). Overall, the total yearly CS of the forest was 141 Mg CO₂ ha^?1 year^?1 with the highest CS value monitored in June (405 Mg CO₂ month^?1) due to the highest LAI (5.0 ± 0.8 m² m^?2) and a high N_P in all the broadleaf species. The first CS decline was observed in August due to the more stressful climatic conditions that constrained N_P rates. Overall, the total CS of the forest reflects the good ecological health of the ecosystem due to its conservative management.