Evergreen Broadleaf Forest Research Articles

Ecosystem-Dependent Responses of Vegetation Coverage on the Tibetan Plateau to Climate Factors and Their Lag Periods

The spatiotemporal variation characteristics of the Normalized Difference Vegetation Index (NDVI) and its climate response patterns are of significance in deepening our understanding of regional vegetation and climate change. The response of vegetation to climate factors varies spatially and may have lag periods. In this paper, we studied the spatiotemporal responses of vegetation to climatic factors on an ecosystem-dependent scale using GIMMS NDVI3g data and climatic parameters. Pure pixels with a single vegetation type were firstly extracted to reduce the influence of mixed vegetation types. Then, a lag correlation analysis was used to explore the lag effects of climatic parameters affecting NDVI. Finally, the stepwise regression method was adopted to calculate the regression equation for NDVI and meteorological data with the consideration of effect lag times. The results show that precipitation has significant lag effects on vegetation. Temperature is the main climatic factor that affects most vegetation types at the start of growing season. At the end of growing season, the temperate desert, temperate steppe, and temperate desert steppe are greatly affected by precipitation. Moreover, the alpine steppe, alpine desert, alpine meadow, and alpine sparse vegetation are greatly affected by temperature. The needleleaf forest, subalpine scrub, and broadleaf evergreen forest are sensitive to sunshine percentage during almost the whole growing season. These findings could contribute to a better understanding of the drivers and mechanisms of vegetation degradation on the Tibetan Plateau.

Improving modeling of ecosystem gross primary productivity through re-optimizing temperature restrictions on photosynthesis

The terrestrial ecosystem gross primary productivity (GPP) plays an important role in the global carbon cycle and ecosystem functions. However, the estimates of GPP still have large uncertainties due to insufficient understanding of the photosynthesis-temperature relationship and maximum light use efficiency (LUEmax). We used satellite-derived proxies of GPP to derive optimum, minimum, and maximum temperature for photosynthesis at the ecosystem scale, which was then used to construct a new temperature stress expression. This study improves the MODIS-based light use efficiency model through coupling the optimized LUEmax with the new proposed temperature stress expression. The new model (R2 = 0.81, RMSE = 17.8 gC m−2 (16 d)−1) performed better than the MODIS GPP products (R2 = 0.67, RMSE = 30.4 gC m−2 (16 d)−1), especially for evergreen broadleaf forests and croplands. The mean annual GPP over China is 5.7 ± 0.27 PgC, and the GPP significantly increased by 0.046 ± 0.006 PgC year−1 during 2001–2018. This study provides a potential method for future projections of terrestrial ecosystem functioning.

Detection of signals linked to climate change, land-cover change and climate oscillators in Tropical Montane Cloud Forests

Tropical Montane Cloud Forests (TMCFs) form biodiverse communities that are characterized by frequent occurrence of low-level clouds from which they capture a substantial proportion of their precipitation — here referred to as occult precipitation. TMCFs provide important ecosystem services, in particular the supply of water to their wider surroundings. Throughout the tropics (here 23.5∘ S to 23.5∘ N), they are under pressure from deforestation and poor land management which leads to loss of both forest area and species diversity, and reduces their capture of occult precipitation. Climate change may also reduce occult precipitation in TMCFs since the cloud base may lift in response to higher temperatures — the ‘lifting cloud-base hypothesis’. These threats to TMCFs are well understood, but their quantitative assessment is hampered by 1) uncertainty in the location and spatial extent of TMCFs and 2) limited availability of representative meteorological data. We use a Random Forest Classifier — informed by topographic data, MODIS vegetation data, TRMM precipitation data and ERA5-Land and MERRA-2 reanalysis products — to estimate the spatial distribution and extent of TMCFs (2.1 × 106 km2 ± 0.5 × 106 km2). We analyze temporal changes in climate, tree-cover and greenness of TMCFs over the past two to four decades to detect 1) multi-decadal trends, and 2) associations with the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Evidence for the ‘lifting cloud-base hypothesis’ in reanalysis products was inconsistent across the tropics; a lifting of the cloud base during the past four decades occurred for about 20% of TMCFs, predominantly in the Americas and a few locations in Africa, while in Asia a downward movement of the cloud base was found. However, these results in part depend on the bias correction applied to the reanalyses. Changes in TMCF tree cover and greenness varied by continent; in Africa in 50% of TMCFs tree cover declined, whereas TMCFs in the Americas and in Asia exhibited a net increase in tree cover, despite a reduction in tree cover in ~20% of these TMCFs. An important limitation of the tree-cover data is that they do not distinguish between natural tree cover and agro-forestry. ENSO signals were more strongly present in precipitation in American and Asian TMCFs, whereas IOD signals were stronger in TMCF temperature and dewpoint temperature across the tropics. ENSO and IOD signals were approximately equally important for precipitation in African TMCFs and in cloud-base height across the tropics. An arbitrary warming of 1 ∘C and a 100 m lifting of the cloud base, in accordance with the ‘lifting cloud hypothesis’, imposed on the Random Forest classifier showed a decline in the extent of TMCFs in the Americas and Africa, but an increase in Asia — mostly at the expense of evergreen broadleaf forests. The greater vulnerability of TMCFs in Africa may be linked to their more isolated and scattered distribution across the continent and drier conditions compared to a more continuous distribution and wetter conditions in the Americas and Asia.

Effects of various driving factors on potential evapotranspiration trends over the main grain-production area of China while accounting for vegetation dynamics

Potential evapotranspiration (PET) is an important consideration in the study of agricultural water management and climate change. Although a number of studies have already explored the effects of climate factors on changes in PET, the quantitative effects of various driving factors needs to be further studied, as most studies have not accounted for vegetation dynamics by characterizing changes in leaf area and stomatal resistance. Here, we used the Shuttleworth–Wallace (S-W) model based on climate, vegetation, and energy factors to quantitatively analyze the effects of various driving factors at multiple spatial scales over the main grain-producing area of China (MGPAC) from 1982 to 2016. The S-W model had a satisfactory performance because S-W based Standardized Precipitation Evapotranspiration Index (SPEI) had a higher determination coefficient (0.33 VS. 0.26) than Penman-Monteith based SPEI for soil moisture standardized anomaly over MGPAC. MGPAC had a mean annual PET of 926.20 mm and showed a marked increase of 3.844 mm yr−1 during the study period. Evergreen broadleaf forest and grassland had the highest and lowest annual average PET values (1535.65 mm and 633.67 mm), respectively. Although climate factors could directly explain 79.42% of the PET increase over the MGPAC, vegetation dynamics were also identified to be a non-negligible factor explaining the increase in PET (directly explaining 18.91% of the PET trend). Specifically, vegetation dynamics contributed to explaining 67.30% and 48.91% of the PET trend in the Huang-Huai-Hai and Loess Plateau regions. These findings are closely related to changes in the temperature and leaf area index (LAI), which notably increased by 0.04 °C yr−1 (P < 0.01) and 0.0038 m2 m−2 yr−1 (P < 0.01), respectively. Regarding single drivers, variation in temperature and LAI significantly increased the PET by 3.582 mm yr−1 (P < 0.01) and 1.127 mm yr−1 (P < 0.01) across the MGPAC, respectively. This study can provide a new insight to improve agricultural production and management in China.

Forest Land Quality Evaluation and the Protection Zoning of Subtropical Humid Evergreen Broadleaf Forest Region Based on the PSO-TOPSIS Model and the Local Indicator of Spatial Association: A Case Study of Hefeng County, Hubei Province, China

Forest land is the carrier for growing forests. It is of great significance to evaluate the forest land quality scientifically and delineate forestland protection zones reasonably for realizing better forest land management, promoting ecological civilization construction, and coping with global climate change. In this study, taking Hefeng County, Hubei Province, a subtropical humid evergreen broad-leaved forest region in China, as the study area, 14 indicators were selected from four dimensions—climatic conditions, terrain, soil conditions, and socioeconomics—to construct a forest land quality evaluation index system. Based on the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) model, we introduced the Particle Swarm Optimization (PSO) algorithm to design the evaluation model to evaluate the forest land quality and analyze the distribution of forest land quality in Hefeng. Further, we used the Local Indicator of Spatial Association (LISA) to explore the spatial distribution of forest land quality and delineate the forest land protection zones. The results showed the following: (1) the overall quality of forest land was high, with some variability between regions. The range of Forest Land Quality Index (FLQI) in Hefeng was 0.4091–0.8601, with a mean value of 0.6337. The forest land quality grades were mainly first and second grade, with the higher-grade forest land mainly distributed in the central and southeastern low mountain regions of Zouma, Wuli, and Yanzi. The lower-grade forest land was mainly distributed in the northwestern middle and high mountain regions of Zhongying, Taiping, and Rongmei. (2) The global spatial autocorrelation index of forest land quality in Hefeng County was 0.7562, indicating that the forest land quality in the county had a strong spatial similarity. The spatial distribution of similarity types high-high (HH) and low-low (LL) was more clustered, while the spatial distribution of dissimilarity types high-low (HL) and low-high (LH) was generally dispersed. (3) Based on the LISA of forest land quality, forest land protection zones were divided into three types: key protection zones (KPZs), active protection zones (APZs), and general protection zones (GPZs). The forest land protection zoning basically coincided with the forest land quality. Combining the characteristics of self-correlated types in different forestland protection zones, corresponding management and protection measures were proposed. This showed that the PSO-TOPSIS model can be effectively used for forest land quality evaluation. At the same time, the spatial attributes of forest land were incorporated into the development of forest land protection zoning scheme, which expands the method of forest land protection zoning, and can provide a scientific basis and methodological reference for the reasonable formulation of forest land use planning in Hefeng County, while also serving as a reference for similar regions and countries.

Changes of soil bacterial community structure at the secondary successional stages in the Pinus yunnanensis forest.

Soil bacterial diversity is a key factor for the maintanence of forest ecosystem function. Soil bacterial community would change along forest succession. We analyzed the variations of soil bacterial diversity and community composition at different successional stages in the Pinus yunnanensis forest, which would help understand the mechanism underlying forest restoration. We investigated soil bacterial diversity, community composition, and effect factors at different successional stages (including coniferous forest, mixed coniferous and broadleaf forest, and evergreen broadleaf forest) using Illumina Hiseq platform. The results showed that OTUs, Chao1 index, Ace index, and Shannon index of soil bacterial community decreased with the process of secondary succession. The highest soil bacterial total OTUs, richness, and complexity appeared at early successional stage. Soil bacterial community composition varied across different stages, with the mixed coniferous and broadleaf forest showing largest variation. Proteobacteria and Acidobacteria were common dominant phyla at secondary successional stages. Actinobacteria, Chloroflexi, and Patescibacteria were dominant phyla at the early successional stage, the abundance of which decreased with successional process in the P. yunnanensis forest. Proteobacteria and WPS-2 increased with the succession. Soil pH and tree species richness were key factors in driving soil bacterial community structure. The soil bacterial diversity decreased with forest succession, while the variations of soil bacterial community composition became larger.

Simplified Priestley–Taylor Model to Estimate Land-Surface Latent Heat of Evapotranspiration from Incident Shortwave Radiation, Satellite Vegetation Index, and Air Relative Humidity

An operational and accurate model for estimating global or regional terrestrial latent heat of evapotranspiration (ET) across different land-cover types from satellite data is crucial. Here, a simplified Priestley–Taylor (SPT) model was developed without surface net radiation (Rn) by combining incident shortwave radiation (Rs), satellite vegetation index, and air relative humidity (RH). Ground-measured ET for 2000–2009 collected by 100 global FLUXNET eddy covariance (EC) sites was used to calibrate and evaluate the SPT model. A series of cross-validations demonstrated the reasonable performance of the SPT model to estimate seasonal and spatial ET variability. The coefficients of determination (R2) of the estimated versus observed daily (monthly) ET ranged from 0.42 (0.58) (p &lt; 0.01) at shrubland (SHR) flux sites to 0.81 (0.86) (p &lt; 0.01) at evergreen broadleaf forest (EBF) flux sites. The SPT model was applied to estimate agricultural ET at high spatial resolution (16 m) from Chinese Gaofen (GF)-1 data and monitor long-term (1982–2018) ET variations in the Three-River Headwaters Region (TRHR) of mainland China using the Global LAnd-Surface Satellite (GLASS) normalized difference vegetation index (NDVI) product. The proposed SPT model without Rn provides an alternative model for estimating regional terrestrial ET across different land-cover types.

The impact of indicator selection on assessment of global greening

ABSTRACT Greening represents a significant increase in vegetation activity. Accurate quantification of global greening in peak growth is vital for quantifying changes in terrestrial productivity. Normalized Difference Vegetation Index (NDVI) is the remote sensing indicator most commonly applied for this purpose. However, there is limited knowledge about how the applications of other improved or newly available products can impact global greening assessments. This study reports the first systematic investigation of the impact of vegetation indicator selection on global greening in peak growth. It examines the period from 2003 to 2017 using six indicators with a spatial resolution of 500 m: Near Infrared Reflectance of terrestrial vegetation (NIRv) and the coupled diagnostic biophysical modeled Gross Primary Production (PML-GPP), together with NDVI, Enhanced Vegetation Index with two bands (EVI2), Leaf Area Index (LAI) and Moderate Resolution Imaging Spectroradiometer (MODIS) GPP (MOD-GPP) calculated based on MODIS images. Vegetation trends were estimated using the Mann–Kendall test, the unanimous trends by six vegetation indicators were derived, and the concordance ratio in estimated trends by each pair of indicators was investigated among different biomes and their sensitivity to changes in climate were investigated. We found that the estimated greening and browning varied between 12–23% and 2–13% of the vegetated areas, respectively. There was more net greening estimated from NDVI and MOD-GPP (around 19%) compared to the other indicators (8–11%). The concordance ratio between EVI2 and NIRv was much higher (>94%) than other combinations (61–76%) at the global scale. The concordance ratio between one specific indicator and the other indicators gradually increased with its change magnitude. Unanimous results from these six indicators were exhibited in less than two-fifths (38.71%) of vegetated areas. Apart from the EVI2 and NIRv, the concordance ratio varied among different biomes: high in cropland (67–81%), but low in deciduous needle-leaf forest (51–62%) and very low in evergreen broadleaf forest between PML-GPP and others (37–49%). The diverse sensitivity to changes in climate contributed to the discrepancies: greening was more pronounced during warming conditions for the GPP products when compared with the greenness indices. At the global scale, the concordance ratio was higher during cooling conditions among all the indicators except between PML-GPP. Datasets supporing these findings are available online at https://github.com/FuzhouSIRC/Greening_6indicators.2

Linking enhanced soil nitrogen mineralization to increased fungal decomposition capacity with Moso bamboo invasion of broadleaf forests

Plant invasion can markedly alter soil fungal communities and nitrogen (N) availability; however, the linkage between the fungal decomposition capacity and N mineralization during plant invasion remains largely unknown. Here, we examined the relationship between net mineralization rates and relevant functional genes, as well as fungal species composition and function following Moso bamboo (Phyllostachys edulis) invasion of evergreen broadleaf forests, by studying broadleaf forests (non-invaded), mixed bamboo-broadleaf forests (moderately invaded) and bamboo forests (heavily invaded). Fungal species composition and functional genes involved in organic matter decomposition (laccase and cellobiohydrolase), N mineralization (alkaline peptidases) and nitrification (ammonia monooxygenase) were determined via high-throughput sequencing and real-time PCR. Both net ammonification and nitrification rates were generally increased with bamboo invasion into the broadleaf forest, where the net ammonification rate, on average, was 10.8 times higher than the nitrification rate across the three forest types. The fungal species composition and ecological guilds were altered with bamboo invasion, as demonstrated by the increased proportion of saprotrophs but decreased proportion of symbiotrophs in the bamboo forest. The increased net ammonification rate in bamboo forest was positively correlated with both fungal species composition and functional groups, and the fungal lcc gene (for lignin breakdown) abundance explained 67% of the variation of the net ammonification rate. In addition, the gene abundance of ammonia-oxidizing bacteria (AOB) explained 62% of the variation of net nitrification rate across the three forest types. The increased soil ammonification and nitrification rates following bamboo invasion of broadleaf forests suggest that the bamboo-invasion associated increase in soil N supply provided a positive feedback that facilitated bamboo invasion into broadleaf forests.

2001-2018年中国-老挝交通走廊核心区植被稳定性对极端干旱的响应

中国-老挝交通走廊核心区干旱事件的频繁发生威胁着该区域生态系统的稳定性。基于Palmer干旱指数（PDSI）和增强型植被指数（EVI）数据量化了中老交通走廊核心区不同植被类型的稳定性（年均EVI与其标准差之比）及其对干旱的抵抗力（干旱期间植被结构和功能保持其原始水平的能力）和恢复力（植被恢复到干旱前水平的速度）。结果表明：（1）2001-2018年间，中老交通走廊核心区共发生5次极端干旱事件，出现极端干旱的年份有2005年、2010年、2015年、2016年和2017年，以上年份极端干旱面积占总面积的比例分别为13.37%、47.46%、10.41%、12.00%和3.05%；（2）不同植被类型对极端干旱的响应不同，中老交通走廊核心区内常绿阔叶林的稳定性显著高于其他植被类型，和其他植被类型相比，常绿阔叶林虽然暴露在干旱环境中的时间更长，但其具有更高的稳定性，在维持中老交通走廊核心区的生态系统稳定性上发挥着重要作用；（3）常绿阔叶林和木本稀树草原对极端干旱的抵抗力和恢复力显著高于混交林、草地和农田，研究区内各植被类型对极端干旱的抵抗力与温度和降水呈显著正相关关系。;The core area of China-Laos transportation corridors have been frequently affected by drought events, which threatened the stability of terrestrial ecosystem functioning. Based on the Palmer Drought Severity Index (PDSI) data and enhanced vegetation index (EVI) products, we quantified the temporal stability (ratio of mean annual EVI to its SD), resistance (ability to maintain its original levels during droughts), and resilience (rate of EVI recovering to pre-drought levels) in the core area of China-Laos transportation corridors. The results showed that:(1) there were 5 extreme drought events in the core area of China-Laos transportation corridors from 2001 to 2018, appearing in 2005, 2010, 2015, 2016 and 2017. The area of extreme drought accounted for 13.37%, 47.46%, 10.41%, 12.00% and 3.05%, respectively. (2) Different vegetation types had different responses to droughts. The temporal stability of evergreen broadleaf forests was significantly higher than that of other vegetation types. Evergreen broadleaf forests had higher stability than other vegetation types despite the greater drought exposure, which played an important role in maintaining the ecosystem stability of the corridor core area. (3) The evergreen broadleaf forests and savannas illustrated significantly higher resistance and resilience of EVI than other vegetation types. The resistance of various vegetation types to extreme drought in the study area was positively associated with temperature and precipitation.

浙西南常绿阔叶林凋落物空间分布及其对土壤养分的影响

凋落物作为养分的有效载体对于森林养分循环具有重要作用。近年来学者们对凋落物开展了大量研究，但森林内部凋落物的空间分布及其对土壤养分空间异质性的作用一直没有得到充分重视。利用位于浙江西南部的百山祖亚热带中山常绿阔叶林5 hm²森林动态监测样地中50个凋落物收集器2009-2017年收集到的凋落物产量数据和相关的地形和土壤养分数据，运用同步自相关回归分析地形和群落结构因素对凋落物及其组分产量的影响，利用多元线性混合效应模型研究了地形和年均凋落物输入量与土壤养分含量的关系。结果表明（1）地形因子中仅凸度与总凋落物以及叶凋落物产量呈显著正相关；（2）邻域内的大树和中树（胸径≥ 5 cm）的平均胸径显著提高总凋落物、叶凋落物和小枝及树皮凋落物产量，而邻域物种数显著提高总凋落物、叶凋落物和繁殖器官凋落物产量；（3）地形凸度与表层（深0-10 cm）土壤有机质含量显著正相关，但与近表层（深10-20 cm）土壤总氮、有效磷和速效钾含量显著负相关；（4）凋落物输入量显著提高表层（深0-10 cm）土壤的碱解氮和有机质含量。总体来看，百山祖常绿阔叶林凋落物产量的空间变异受到地形和森林群落结构因素的制约，并影响林内土壤养分的空间异质性。;Litter, as an effective carrier of nutrients, plays an important role in forest nutrient cycles. In recent years, several studies have been carried out on litter; however, the spatial distribution of litter yield in a forest and its effects on the spatial heterogeneity of soil nutrients have not been thoroughly investigated. In August 2008, 50 litter traps with horizontal areas of 0.71 m×0.71 m along a path in the 5hm² forest dynamics plot in the Baishanzu midmountain subtropical evergreen broadleaf forest were set and all the litter falling into the traps was collected twice a month during a period from 2009 to 2017. The litter was dried in an oven at 80℃ at a constant weight and was weighed. In July 2014, soil samples were collected using an earth drill from three 1m×1m quadrats with an adjacent distance of 2 m for each of the 50 litter traps (50×3 samples). Each soil sample was divided into surface and near-surface layers (i.e., 0-10 cm and 10-20 cm, respectively). Total nitrogen, alkaline nitrogen, available phosphorus, available potassium, and organic matter contents of these soil samples were determined by common soil chemistry approaches. The elevation, convexity, and slope of each 10m×10m quadrat were assigned to the trap located in the quadrat. Simultaneous auto-regression was used to analyze effects of topography and community structure on the litter and its component yields. The community structure was described according to the total basal area, mean diameter at breast height (DBH), and species richness of trees with DBH ≥ 5 cm in the 5 or 10 m radius neighborhood of the traps. Further, the impact of the topography and annual litter input on the soil nutrient concentration was studied using a linear mixed effect model. The results showed that (1) only convexity was positively correlated with the total and leaf litter yields; (2) the mean DBH of the trees in the neighborhood significantly increased the total, leaf, twig and bark litter yields, while the number of species in the neighborhood significantly increased the total, leaf, and reproductive organ litter yields; (3) the terrain convexity significantly increased the soil organic matter content in the surface layer (0-10 cm deep) but significantly reduced the total nitrogen, available phosphorus, and available potassium contents in the near-surface layer (10-20 cm deep); and (4) the total litter input significantly increased the alkaline nitrogen and organic matter contents in the surface soil. Our results suggest that the spatial variation in the litter yield in the Baishanzu evergreen broadleaf forest is determined by the topography and forest structure and affects the spatial heterogeneity of soil nutrients in the forest.

New Global MuSyQ GPP/NPP Remote Sensing Products From 1981 to 2018

Long time series of vegetation productivity products are significant for the research of global carbon cycle and climate change. In this article, the 0.05° global gross primary productivity (GPP) and net primary productivity (NPP) products from 1981 to 2018 were estimated by using the improved multisource data synergized quantitative (MuSyQ) NPP algorithm. The model was based on the fraction of absorbed photosynthetically active radiation (FPAR) and leaf area index (LAI) data from the global land surface satellite (GLASS) dataset, the light use efficiency (LUE) from the parameterization approach with the clearness index (CI), the ERA-Interim meteorological data, and other environmental factors. The results suggested that the accuracy of the MuSyQ GPP product was slightly higher than that of the MOD17 GPP product when compared with the FLUXNET GPP, especially for the evergreen broadleaf forest (EBF), deciduous broadleaf forest (DBF), wetland (WET), cropland (CRO), woody savanna (WSAV), and closed shrubland (CSH) land types. MuSyQ NPP product also has higher accuracy [ R 2 = 0.81, RMSE = 214.6 gC/(m2year)] than MOD17 NPP [ R 2 = 0.55, RMSE = 214.7 gC/(m2year)] when compared with the BigFoot NPP, which indicated the reliability of the improved MuSyQ-NPP algorithm in estimating global NPP. Our results showed a significant upward trend in global NPP, which was most affected by FPAR, followed by LUE, temperature, and PAR. The average NPP declined significantly in Asia and Amazon tropical rainforests and increased significantly in Africa tropical rainforest, which were affected by the local deforestation or the forest expansion, and also the climate factors.

Leaching of Dissolved Organic Carbon and Cations and the Buffering Capacity of Litters from Forest Stands in Southwestern China

Forest soil can buffer acidification and neutralize acidic airborne pollutants, but for acid rainwater, it makes contact with forest litter in the forest ecosystem first before reaching the soil. However, leachate chemistry of forest litter treated with different acid load rates is rarely studied. A leaching experiment was performed on forest litter from mixed conifer-broadleaf (MCB) and evergreen broadleaf (EB) forests in Jinyun Mountain, Three Gorges area, Southwestern China with simulated acid rain (SAR) of pH=2.7, 3.5 and 4.5. Dissolved organic carbon (DOC) and cations were exported from MCB and EB when treated with various acid load rates. The rainwater deacidification of forest litter was enhanced by considerable leachate concentrations of DOC, Ca2+and Mg2+. The acid buffering capacity of EB was stronger than MCB with different composition of forest litter. Leaching of cations increased with decreasing pH of SAR. Although more easily decomposed, EB released greater Al3+ than MCB, leachate Ca/Al ratios of EB did not reach the critical value of 1.0. Thus, in the study area, EB forest may be a better choice for afforestation and reforestation with better forest litter, showing good buffering capacity, keeping soil from acidification and being a greater nutrient pool for soil under it.

Vegetation Expansion on the Tibetan Plateau and Its Relationship with Climate Change

The natural shift in land cover from non-vegetated to vegetated land is termed as vegetation expansion, which has substantial impacts on regional climate conditions and land surface energy balance. Barrens dominate the northwestern Tibetan Plateau, where vegetation is predicted to expand northwestward with the ongoing climate warming. However, rare studies have confirmed such a forecast with large-scale vegetation monitoring. In this study, we used a landcover dataset, classified according to the International Geosphere–Biosphere Program criteria, to examine previous model-based predictions and the role of climate on the expansion rate across the plateau. Our results showed that shrublands, open forests, grasslands, and water bodies expanded while evergreen and deciduous broadleaf forests, croplands and barrens shrank during the period 2001–2018. Vegetation expanded by 33,566 km2 accounting for about 1.3% of the total area of this plateau and the land cover shifting from barrens to grasslands was the primary way of vegetation expansion. Spatially, the vegetation expanded northwestward to lands with colder, drier, and more radiation in the climate. Increasing precipitation positively correlated with the vegetation expansion rate for the arid and semi-arid northwest Tibetan Plateau and warming contributed to the vegetation expanding in the semi-humid southeast Tibetan Plateau. Our results verified the predictions of models and highlighted the “greening” on barrens in recent years.

Latitudinal and altitudinal variations across temperate to subtropical forests from southern Kyushu to the northern Ryukyu Archipelago, Japan

ABSTRACT We studied the latitudinal and altitudinal variations in composition and species richness of trees in 24 plots across temperate to subtropical regions from southern Kyushu to the northern Ryukyu Archipelago, Japan. Cluster analysis based on presence/absence of species in 0.25-ha segments of the plots identified three forest zones reflecting climate and geohistory: cool-temperate mixed conifer-broadleaf forest (MF) north of the Tokara Gap (Kyushu and Yakushima), warm-temperate evergreen broadleaf forest (EBF) north of the Tokara Gap, and subtropical EBF south of the Tokara Gap (Amami-Oshima, Tokunoshima, and Okinawajima). The MF zone corresponded to Kira’s Warmth Index (WI) < 100°C. The two EBF zones overlapped in the range of WI, and thus their boundary was determined by geohistory rather than by climate. Plot-level species richness per 400 stems increased with increasing WI, with decreased values in Yakushima, suggesting that geohistory (isolations from Kyushu as well as by the Tokara Gap) depressed the species richness of Yakushima. Greater species richness in the subtropical EBF was explained by the presence of species whose distributions were restricted to the south of the Tokara Gap, indicating that the size of tree flora influences the plot-level species richness. By contrast, lower species richness of MF in Yakushima than in Kyushu was due to the absence of species whose distributions were restricted to Kyushu northward, indicating the impoverishment of the cool-temperate flora of Yakushima. In conclusion, climate and geohistory shape the tree-community composition and diversity of old-growth forests in this transitional zone from temperate to subtropical regions.

Acoustic characteristics of the island-endemic Parapelophryne scalpta (Anura: Bufonidae) from Hainan Island, China.

The Hainan Pygmy Toad Parapelophryne scalpta (Liu Hu) is the single species of the genus Parapelophryne Fei, Ye Jiang in the Family Bufonidae (Frost 2020) and is endemic to China's Hainan Island, which lies within the tropics at 18°09'-20°10'N, 108°37'-111°03'E, with a land area of ca. 33,900 km2. The taxonomy status of this species has obtained much debates since its discovery: it was originally described by Liu et al. (1973) as a member of the genus Nectophryne Buchholz Peters then allocated to Pelophryne Barbour by Ye Fei (1978). On the basis of its unique morphological characters, Fei et al. (2003) erected a new genus Parapelophryne to discriminate P. scalpta from other bufonids. Some researchers, however, still listed the species under the genus Pelophryne (Stuart et al. 2008; Shi et al. 2011). Recently, the validity of the genus Parapelophryne is further confirmed by Matsui et al. (2015) on the basis of molecular analyses. Interestingly enough, Matsui et al. (2015)'s result showed that this extremely small-sized toad is a sister taxon of the large-sized toads of the genus Bufo Garsault, which is mainly distributed in temperate and subtropical regions of Eurasia (Frost 2020). Parapelophryne scalpta is a forest-dependent species and only inhabits in well-preserved evergreen broadleaf forests (Fei Ye 2016). It is the smallest toad species in China with snout-vent length of 19-23 mm in adult males and 24-27 mm in females (Fei Ye 2016). Due to their small size and elusive habits, little is known about the natural history of P. scalpta and its acoustic characteristics are still undocumented (Fei Ye 2016). During a herpetological survey in Hainan in 2015, we luckily detected male calls of P. scalpta and obtained a short but clear record of the advertisement call of the species. Herein, we describe the acoustic characteristics and calling behavior of Parapelophryne scalpta.

Fluxes, stocks and availability of nitrogen in evergreen broadleaf and fir forests: similarities and differences

In this study, nitrogen fluxes or flows in litterfall, nitrogen stocks and available nitrogen in soils of two plots representing evergreen broadleaf and Bulgarian fir forests were assessed. Both plots are in good quality sites and for this reason, the litterfall quantities and nitrogen fluxes were relatively high. The woody litterfall flux of nitrogen was significantly higher in the fir forest than in the evergreen broadleaf one. The total nitrogen stock was higher in the soil under the fir forest. However, the percentage of the available nitrogen (ammonium + nitrates) was significantly higher in the upper 20 cm soil layer of the evergreen broadleaf forest in spite of the higher average C/N ratios in the foliar litterfall of the broadleaf forest and insignificant difference of the C/N ratios in all soil layers of the two ecosystems. The microclimatic conditions (higher soil temperatures in the evergreen broadleaf forest) is probable possible cause for this difference. The available nitrogen in the soils and its retranslocation from senescing leaves cover the nitrogen requirements of trees. It is hypothesized that trees may also take up nitrogen from deeper soil layers.

Physiological and environmental control on ecosystem water use efficiency in response to drought across the northern hemisphere

Drought, a natural hydrometeorological phenomenon, has been more frequent and more widespread due to climate change. Water availability strongly regulates the coupling (or trade-off) between carbon uptake via photosynthesis and water loss through transpiration, known as water-use efficiency (WUE). Understanding the effects of drought on WUE across different vegetation types and along the wet to dry gradient is paramount to achieving better understanding of ecosystem functioning in response to climate change. We explored the physiological and environmental control on ecosystem WUE in response to drought using observations for 44 eddy covariance flux sites in the Northern Hemisphere. We quantified the response of WUE to drought and the relative contributions of gross primary production (GPP) and evapotranspiration (ET) to the variations of WUE. We also examined the control of physiological and environmental factors on monthly WUE under different moisture conditions. Cropland had a peak WUE value under moderate drought conditions, while grassland, deciduous broadleaf forest (DBF), evergreen broadleaf forest (EBF), and evergreen needleleaf forest (ENF) had peak WUE under slight drought conditions. WUE was mainly driven by GPP for cropland, grassland, DBF, and ENF but was mainly driven by ET for EBF. Vapor pressure deficit (VPD) and canopy conductance (Gc) were the most important factors regulating WUE. Moreover, WUE had negative responses to air temperature, precipitation, and VPD but had a positive response to Gc and ecosystem respiration. Our findings highlight the different effects of biotic and abiotic factors on WUE among different vegetation types and the important roles of VPD and Gc in controlling ecosystem WUE in response to drought.

Review of the genus Eurypteryx C. Felder R. Felder, 1874 from China, with a first description of the male E. dianae (Lepidoptera: Sphingidae).

The two species of the genus Eurypteryx C. Felder R. Felder, 1874 known from China, E. bhaga and E. dianae (Lepidoptera, Sphingidae, Macroglossinae, Macroglossini) were examined and compared with E. geoffreyi from Thailand. The male E. dianae is described for the first time based on a single specimen from an evergreen broad-leaf forest in Maolan Nature Reserve, Libo, Guizhou, China. The diagnostic features and a distribution map of the species of Eurypteryx in China are provided. A list of all Eurypteryx species presently known worldwide is also given.

Reduced Lignin Decomposition and Enhanced Soil Organic Carbon Stability by Acid Rain: Evidence from 13C Isotope and 13C NMR Analyses

Due to the emissions of air pollutants, acid rain in southern China poses a great threat to terrestrial ecosystems. However, its influences on ecological processes such as litter decomposition and soil organic carbon (SOC) accumulation are still not clear. The aim of this study was to understand the potential mechanisms of carbon sequestration change in response to long-term acid rain in a subtropical forest. A field experiment with simulated acid rain (SAR) treatment was conducted in a monsoon evergreen broadleaf forest in southern China. Four levels of SAR treatment were implemented by irrigating the plots with water of different pH values (4.5 as a control, 4.0, 3.5, and 3.0). The results showed that the concentration of SOC and recalcitrant index for the SAR pH = 3.0 treatment were significantly higher compared to the control. Lignin fractions in litter residue layers were significantly increased, while soil microbial biomass carbon and soil ligninolytic enzyme activities were reduced under the SAR treatment. The concentration of SOC and recalcitrant index had positive relationships with the litter residue lignin fraction, but negative relationships with soil ligninolytic enzyme activity. These findings indicate that soil carbon accumulation could be enhanced with more stable lignin input under prolonged acid rain in forest ecosystems in southern China.