End Of Growing Season Research Articles

Vegetation phenology and its variations in the Tibetan Plateau, China

ABSTRACTUnderstanding the vegetation phenology and its variations in the Tibetan Plateau is critical to the study of ecological responses to global climate change. In this study, several pre-processed methods or techniques were applied to filter the Global Inventory Modelling and Mapping Study’s Normalized Difference Vegetation Index (GIMMS NDVI) data from 1982 to 2006, and construct the daily NDVI series. Firstly, vegetation and non-vegetation were determined by NDVI quantity contour, and cloud-covered pixels were also eliminated by NDVI change characteristics in a year. Then, the NDVI series were filtered by three-standard deviation and Savitzky-Golay method. Finally, the Savitzky–Golay method was employed to fit and construct the daily NDVI series. These methods guarantee a more reliable subsequent calculation of subsequent vegetation phenology. The vegetation phenology parameters including the start of growth season (SOG), the end of growth season (EOG), the lengths of growth season (LOG) and the absolute increase in vegetation (AIV), defined as the difference between the maximum NDVI and the NDVI for SOG in a year, were derived from the daily NDVI series based on the maximum ratio threshold method and their variations were analysed. The results showed that the SOGs were gradually delayed from the southeast to the northwest of the Tibetan Plateau, but the distribution pattern of the EOGs was opposite to that of the SOGs. From 1982 to 2006, SOGs were advanced approximately 3–18 days and EOGs delayed around 0–24 days in the southeast, whereas AIVs decreased around 0–0.3. In the northwest, these phenology parameters followed inverse trends compared with those of the southeast. Over the 25-year period, LOG changes had no constructive or active effects on the vegetation absolute increase. These complex phenological shifts were mainly due to the spatial differences in the environmental changes. However, in some extent, they might be related to the vegetation itself, such as its fractional cover. These findings may help to understand the alpine vegetation responds to climate change in the Tibetan Plateau.

Evaluating changes in treeline position and land surface phenology in Sikkim Himalaya

Mountain ecosystems of the Himalaya have warmed more rapidly in recent decades than other areas of the globe. Landscape-level delineation of treeline position and its dynamics can give insight regarding climatic variability. Landsat-2 Multispectral Scanner (MSS), Resourcesat-2 Linear Imaging Self Scanning Sensor (LISS-III) and National Oceanic and Atmospheric Administration- Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived normalized difference vegetation index (NDVI) was used to study the long-term treeline dynamics. The treeline has shifted vertically 301 ± 66 m upward in 37 years at a rate of c. 81 m decade−1. The minimum air temperature has increased at a rate of 0.3 °C decade−1 (p < 0.001) depicting the favourable scenario for treeline growth in this temperature limited ecosystem. The annual cumulative precipitation has decreased at a rate of 206.5 mm decade−1. The length of growing season (LOS) has increased and the start (SOS) and end of growing season (EOS) has got earlier in the 1977 treeline. The elevation shifts and phenological changes of the treeline were observed in the warming scenario.

English

Reliable information on the starting and ending of growing season as well as its length will greatly assist in appropriate planning for rainfed agriculture farming practices. The objective of this study is to determine the start, end and length of growing season, based on dependable rainfall during wet (20%), normal (50%) and dry (80%) years, which were retrieved from historical rainfall records analysis of seven stations in Gedarif state for the period 1985 to 2014. The seven studied stations were categorized into two groups according to the total seasonal rainfall. During wet years, Group I had about 900 mm/year and Group II about 700-790 mm/year. In normal years, Group I had about 660-700 mm/year and Group II had 515-570 mm/year. During dry years, Group I had 490-550 mm/year and Group II had 350-425 mm/year. The results showed consistent trend of starting dates of the growing seasons; regardless of the high seasonal variability and variation in amount and distribution of rainfall among the stations and seasons. Similar results were obtained using the MODIS Enhanced Vegetation Index (EVI) for three different years representing different probability levels (2013, dry; 2000, Normal; 2007, wet). Groups I and II in normal and wet years had 70 to 90% of the total annual rainfall during the growing season. In dry years, Group I had 70 to 80% of the total rainfall during the growing season, while Group II had only 50 to 65%. The two groups have indicated different seasonal characteristics (start of growth season, end of growth season and length of growth season) in the dry, normal and wet years. Length of the growth season increases with early start of the season and in wetter years. Key words: Season start, season end, sowing date, dry season, normal season, wet season. &nbsp

Differences and variations in the elevation-dependent climatic growing season of the northern and southern slopes of the Qinling Mountains of China from 1985 to 2015

Based on daily mean temperature data from 32 meteorological stations in the study area, this paper discusses the relationship between the changes in the climatic growing season and altitude and the differences in the northern (NSQM) and southern (SSQM) slopes of the Qinling Mountains (QMs) from 1985 to 2015. Our analyses generated three primary results. First, the spatial distribution patterns of the growing season start (GSS), growing season end (GSE), and growing season length (GSL) exhibited an altitudinal gradient and differences between the NSQM and SSQM. The occurrence time of the GSS, GSE, and the GSL of the NSQM was approximately 15 days later, 10 days earlier, and 25 days shorter respectively than that of the SSQM. Second, the three factors exhibited regular changes with an increasing elevation gradient: the GSS, GSE, and GSL were gradually delayed, advanced, and shortened, respectively. In the area below 1800 m above sea level, the GSS, GSE, and GSL of the NSQM was later, earlier, and shorter, respectively, than that of the SSQM; while the changing trends in the three were opposite in the areas above 2700 m; and the three in the areas between 1800 and 2700 m varied little in the NSQM and SSQM. The sensitivities of the GSS, GSE, and GSL of the NSQM and SSQM to elevation also reflected in the trends of inter-annual variability. Third, among the different altitudinal vegetation belts from low-altitude to high-altitude areas, the occurrence time of the GSS and GSE and the duration of the GSL in the alpine meadow areas were all exchanged in the NSQM and SSQM. The GSS, GSE, and GSL of the NSQM were earlier, later, and longer respectively than that of the SSQM.

Study on the growth of (Achillea millefolium L.) medicinal plant by soil inoculation of mountainous area with selected mycorrhizal fungi

In recent years, the use of soil microbial potential including arbuscular mycorrhizal fungi is widely considered to enhance the better growth and nutrition of plants. This research was conducted in order to study the impact of mycorrhizal fungi on the increase of yarrow production and the plant establishment affected by the symbiotic relationships between fungi and yarrow plant, based on factorial experiment as a randomized complete block (RCB) design with 4 treatments. Inoculated treatments included non-inoculated condition as control mode, inoculated with G. fasciculatum, G. mosseae and G. intraradice fungi. At the end of growth season, some growth parameters such as colonization, plant establishment, essential oil percentage and also morphological properties including fresh and dry weight of shoot and root and the root volume were measured. Results showed that the inoculation of Achillea millefolium L. with arbuscular mycorrhizal fungi have a significant effect on the measured parameters. This means that the inoculation with mycorrhizal fungi leads to increasing the plant establishment and essential oil percentage, fresh and dry weight of shoots and roots, and also the root volume compared to the control mode. It is noteworthy that among the three treatments done with fungi, the treatment of G. fasciculatum showed the most increase in the above parameters.

Soil Moisture Availability at Early Growth Stages Strongly Affected Root Growth of Bothriochloa ischaemum When Mixed With Lespedeza davurica.

Rainfall is the main resource of soil moisture in the semiarid areas, and the altered rainfall pattern would greatly affect plant growth and development. Root morphological traits are critical for plant adaptation to changeable soil moisture. This study aimed to clarify how root morphological traits of Bothriochloa ischaemum (a C4 herbaceous species) and Lespedeza davurica (a C3 leguminous species) in response to variable soil moisture in their mixtures. The two species were co-cultivated in pots at seven mixture ratios under three soil water regimes [80% (HW), 60% (MW), and 40% (LW) of soil moisture field capacity (FC)]. At the jointing, flowering, and filling stages of B. ischaemum, the LW and MW treatments were rewatered to MW or HW, respectively. At the end of growth season, root morphological traits of two species were evaluated. Results showed that the root morphological response of B. ischaemum was more sensitive than that of L. davurica under rewatering. The total root length (TRL) and root surface area (RSA) of both species increased as their mixture ratio decreased, which suggested that mixed plantation of the two species would be beneficial for their own root growth. Among all treatments, the increase of root biomass (RB), TRL, and RSA reached the highest levels when soil water content increased from 40 to 80% FC at the jointing stage. Our results implied that species-specific response in root morphological traits to alternated rainfall pattern would greatly affect community structure, and large rainfall occurring at early growth stages would greatly increase their root growth in the semiarid environments.

Shifts in Growing Season of Tropical Deciduous Forests as Driven by El Niño and La Niña during 2001–2016

This study investigated the spatiotemporal dynamics of tropical deciduous forest including dry dipterocarp forest (DDF) and mixed deciduous forest (MDF) and its phenological changes in responses to El Niño and La Niña during 2001–2016. Based on time series of Normalized Difference Vegetation Index (NDVI) extracted from Moderate Resolution Imaging Spectroradiometer (MODIS), the start of growing season (SOS), the end of growing season (EOS), and length of growing season (LOS) were derived. In absence of climatic fluctuation, the SOS of DDF commonly started on 106 ± 7 DOY, delayed to 132 DOY in El Niño year (2010) and advanced to 87 DOY in La Niña year (2011). Thus, there was a delay of about 19 to 33 days in El Niño and an earlier onset of about 13 to 27 days in La Niña year. The SOS of MDF started almost same time as of DDF on the 107 ± 7 DOY during the neutral years and delayed to 127 DOY during El Niño, advanced to 92 DOY in La Niña year. The SOS of MDF was delayed by about 12 to 28 days in El Niño and was earlier about 8 to 22 days in La Niña. Corresponding to these shifts in SOS and LOS of both DDF and MDF were also induced by the El Niño–Southern Oscillation (ENSO).

The Response of Vegetation Phenology and Productivity to Drought in Semi-Arid Regions of Northern China

A major disturbance in nature, drought, has a significant impact on the vulnerability and resilience of semi-arid ecosystems by shifting phenology and productivity. However, due to the various disturbance mechanisms, phenology and primary productivity have remained largely ambiguous until now. This paper evaluated the spatio-temporal changes of phenology and productivity based on GIMMS NDVI3g time series data, and demonstrated the responses of vegetation phenology and productivity to drought disturbances with the standardized precipitation evapotranspiration index (SPEI) in semi-arid ecosystems of northern China. The results showed that (1): vegetation phenology exhibited dramatic spatial heterogeneity with different rates, mostly presented in the regions with high chances of land cover type variation. The delayed onset of growing season (SOS) and advanced end of growing season (EOS) occurred in Horqin Sandy Land and the eastern Ordos Plateau with a one to three days/decade (p &lt; 0.05) rate and in the middle and east of Inner Mongolia with a two days/decade rate, respectively. Vegetation productivity presented a clear pattern: south increased and north decreased. (2) Spring drought delayed SOS in grassland, barren/sparsely vegetated land, and cropland, while autumn drought significantly advanced EOS in grassland and barren/sparsely vegetated lands. Annual drought reduced vegetation productivity and the sensitivity of productivity regarding drought disturbance was higher than that of phenology.

Antagonistic effects of growing season and autumn temperatures on the timing of leaf coloration in winter deciduous trees.

Autumn phenology remains a relatively neglected aspect in climate change research, which hinders an accurate assessment of the global carbon cycle and its sensitivity to climate change. Leaf coloration, a key indicator of the growing season end, is thought to be triggered mainly by high or low temperature and drought. However, how the control of leaf coloration is split between temperature and drought is not known for many species. Moreover, whether growing season and autumn temperatures interact in influencing the timing of leaf coloration is not clear. Here, we revealed major climate drivers of leaf coloration dates and their interactions using 154 phenological datasets for four winter deciduous tree species at 89 stations, and the corresponding daily mean/minimum air temperature and precipitation data across China's temperate zone from 1981 to 2012. Results show that temperature is more decisive than drought in causing leaf coloration, and the growing season mean temperature plays a more important role than the autumn mean minimum temperature. Higher growing season temperature and lower autumn minimum temperature would induce earlier leaf coloration date. Moreover, the mean temperature over the growing season correlates positively with the autumn minimum temperature. This implies that growing season mean temperature may offset the requirement of autumn minimum temperature in triggering leaf coloration. Our findings deepen the understanding of leaf coloration mechanisms in winter deciduous trees and suggest that leaf life-span control depended on growing season mean temperature and autumn low temperature control and their interaction are major environmental cues. In the context of climate change, whether leaf coloration date advances or is delayed may depend on intensity of the offset effect of growing season temperature on autumn low temperature.

Spatial and temporal variation of vegetation phenology and its response to climate changes in Qaidam Basin from 2000 to 2015

Based on TIMESAT 3.2 platform, MODIS NDVI data (2000–2015) of Qaidam Basin are fitted, and three main phenological parameters are extracted with the method of dynamic threshold, including the start of growth season (SGS), the end of growth season (EGS) and the length of growth season (LGS). The spatial and temporal variation of vegetation phenology and its response to climate changes are analyzed respectively. The conclusions are as follows: (1) SGS is mainly delayed as a whole. Areas delayed are more than the advanced in EGS, and EGS is a little delayed as a whole. LGS is generally shortened. (2) With the altitude rising, SGS is delayed, EGS is advanced, and LGS is shortened and phenophase appears a big variation below 3000 m and above 5000 m. (3) From 2000 to 2015, the temperature appears a slight increase along with a big fluctuation, and the precipitation increases evidently. (4) Response of phenophase to precipitation is not obvious in the low elevation humid regions, where SGS arrives early and EGS delays; while, in the upper part of the mountain regions, SGS delays and EGS advances with temperature rising, SGS arrives early and EGS delays with precipitation increasing.

Analysis of changes in thermal growing season indices (tGSI) and their relations with some selected atmospheric teleconnection patterns (ATPs) over the northwest of Iran.

The daily minimum air temperature data from 18 stations located in the northwest of Iran during the period 1986-2015 was used to analyse the inter-annual variations and trends of thermal growing season indices (tGSI) and their relations with different atmospheric teleconnection patterns (ATPs). To analyze the changes in tGSI, tGSS (thermal growing season start), tGSE (thermal growing season end), and tGSL, the time period between tGSS and tGSE were considered. Using non-parametric Mann-Kendall and Spearman tests, the existence of a significant trend for time series of the tGSI and the correlation between ATPs and tGSI was evaluated. For eliminating the effect of serial correlation on test results, the trend-free pre-whitening approach was applied. Furthermore, residual bootstrap method was used to estimate the standard deviation of the Spearman correlation coefficient between tGSI and ATPs. The climate-based results showed the maximum tGSL increase (13.3daysperdecade) for SA-C-M climate. For SH-K-W climate, the maximum significant trends for tGSS and tGSE were 9.6 (earlier start) and 10.8 (delay) days per decade, respectively. In general, in all statistically significant cases, the main cause of the extended tGSL was both earlier tGSS and delayed tGSE. In regional scale, it was found that the most effective teleconnection pattern on tGSS and tGSE are MEI (positive correlation), occurring during late winter and spring, and PDO index (negative correlation) in the summer, respectively. Moreover, the tGSL demonstrated the highest correlation (negative) with PDO with 1-month delay. The findings highlight that the inter-annual variations of tGSI in northwest of Iran can be attributed to the influence of certain atmospheric teleconnection patterns such as MEI, PDO, NAO, AO, EA, and AMO.

Spatiotemporal variations of forest phenology in the Qinling Mountains and its response to a critical temperature of 10°C

Based on the fifth version MOD09A1 product of NASA LP DAAC (Land Processes Distributed Active Center) from 2001 to 2016, an enhanced vegetation index (EVI) time series dataset in the Qinling Mountains was reconstructed; it was used to extract the plant phenological parameters of the region by employing the maximal slopes of the alteration method and threshold method. The results show that the Whittaker filter method was better than other methods for the reconstruction of shrubland, farmland, and forest in the Qinling Mountains. Based on the reconstructed EVI, the characteristics of vegetation coverage, the start of growth season (SOG), the end of growth season (EOG), and the length of growth season (LOG) in the Qinling Mountains were all analyzed. There was an increasing trend of vegetation coverage in most regions (about 89.93% of the monitored areas) over the Qinling Mountains in the past decades, and the average phenological distribution pattern in the Qinling Mountains was closely related to the local hydrothermal conditions. From the high altitude mountainous areas to the farming areas, the SOG was gradually postponed, the EOG was gradually earlier, and the LOG gradually shortened. Furthermore, the time series variation of SOG, EOG, and LOG from 2001 to 2016 in the Qinling Mountains was also studied. The variation showed that the SOG shifted earlier, which was more prominent in high-altitude areas, while, for some southern and northern foothills altitude below 500 m and a few areas of the eastern Funiu Mountains, the SOG was delayed. The EOG shifted later, which was more apparent in the northern Qinling foothills and mid- to low-altitude areas of the eastern ranges, and the LOG was extended. Finally, the studies of correlation analysis between the plant phenology and a temperature threshold of 10°C showed that global warming was the major factor affecting the phytophenology of the Qinling Mountains, and the effects were concentrated mainly in the 1000- to 2000-m zones of the southern and northern Qinling Mountains. Moreover, the northern Qinling foothills showed a greater response to accumulated temperature than the southern foothills, and the low-altitude area of the eastern Funiu Mountains exhibited the lowest correlation with the accumulated temperature.

2001-2014年博斯腾湖流域植被物候时空变化及其驱动因子

PDF HTML阅读 XML下载 导出引用 引用提醒 2001-2014年博斯腾湖流域植被物候时空变化及其驱动因子 DOI: 10.5846/stxb201708071416 作者: 作者单位: 1 新疆师范大学 地理科学与旅游学院,1 新疆师范大学 地理科学与旅游学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41461006，47164003）；变化环境下干旱区湖泊流域-生态-经济复合系统的协同进化与发展，模式研究（U1703341） Temporal and spatial variation of vegetation phenology and its driving factor analysis in the Bosten Lake Drainage Basin from 2001 to 2014 Author: Affiliation: Xinjinag Normal University,Xinjinag Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以博斯腾湖流域为研究对象，利用MODIS的MCD12Q2和LST产品、GHCN_CAMS气温观测/再分析资料与气象数据，采取趋势分析与相关性分析法探求了博斯腾湖流域2001-2014年植被物候的时空变化及其影响因素的相对作用，对博斯腾湖流域植被物候分区不同的驱动区域。结果表明：①在研究期内，整个研究区植被物候始期在第76-168天，末期在第172-295天；物候始期自南向北逐渐推迟、而末期逐渐提前，物候的空间分布特征与该区海拔高度的分布保持了较好的一致性；②2001-2014年植被始期和末期有明显提前趋势（提前3-6d），主要分布在流域的盆地和平原绿洲区，表示研究区植被物候受到人类活动的影响。③植被物候始期与末期变化受气候因子驱动影响的区域占比分别为57.10%和51.30%，主要分布在黄水沟流域，清水河流域，孔雀河流域，大尤路都斯盆地和小尤路都斯盆地周围地区；而非气候因子占42.90%和48.70%，主要位于博斯腾湖周围绿洲和库尔勒绿洲等地势较低的区域。④由植被生长季物候与降水、气温的偏相关性关系和复相关性关系可以得出，多年物候始期和末期与气温有关；而且随海拔升高，气温的敏感幅度越高。博斯腾湖流域植被物候的时空变化不仅是受气候变化的影响，还主要受人类活动和海拔高度差异等影响因素的共同作用。 Abstract:Vegetation phenology is widely used as an independent measure and powerful indicator of primary net productivity, crop yields, insect emergence, bird migration, climate change, carbon balance and cycle, and fundamental ecosystem function and is influenced at the local and global scales by climatic factors (including precipitation, temperature) and human activities. Studies of vegetation phenology are important, as solutions are needed to overcome issues such as environmental change, sustainable management, and biodiversity conservation. Hence, an in-depth understanding of the spatio-temporal variations and driving factors of vegetation phenology are important in the currently changing environment. The Bosten Lake Drainage Basin is located in northwest China and covers a vast area with a complicated terrain, including most of the middle Tianshan Mountains in the northwest, whole Yanqi basin, and northeast part of the Tarim basin in the south, which are characterized by distinctive distribution patterns of temperature, precipitation, and human activities. Here, based on the MCD12Q2, GHCN_CAMS air temperature, Digital Elevation Model(DEM), and metrological observed data, we established monthly geographical weighted regression (GWR) models and measured the near surface air temperature. Next, spatio-temporal evolution characteristics and driving factors of vegetation phenology in the Bosten Lake Drainage Basin were studied by determining slope, partial correlation, and multiple correlations. The results demonstrated that:(1) the start of growth season (SOG) was concentrated in 76-168 Julian days, whereas the end of growth season (EOS) was in 172-295 Julian days; the SOG was delayed and EOS was gradually advanced from north to south. Elevation played an important role in the regional differentiation of vegetation phenology; with increasing altitude, SOG was significantly delayed, EOG was advanced, and the length of the growth season (LOG) was significantly shortened. (2) SOG and EOG advanced synchronously in the plane oasis area during 2001 and 2014 because of the influence of human activities. (3) Climatic factors affected the area of SOG and BOG accounted for 57.10% and 51.30%, respectively, and was mainly located in the Huangshuigou river watershed, Qingshui river watershed, Konqi river watershed, Qongyultuz basin, and around the Kiqikyultuz basin. Non-climatic factors affected the area of SOG and BOG, accounting for 42.90% and 48.70%, and were located in low-altitude regions including the oasis around Bosten lake and the Korla oasis. (4) The correlation between vegetation phenology and climatic factors by partial correlation and multiple correlations demonstrated that variations in inter-annual SOG and BOG were mostly affected by air temperature. As altitude increased, vegetation showed obvious sensitivity of phenology to temperature. In summary, spatio-temporal variations in vegetation phenology in the Bosten Lake Drainage Basin are not only influenced by climate change, but are also influenced by the combined effects of human activities and altitude. 参考文献 相似文献 引证文献

Estimation of Consumptive Water Use of Vicia faba Under Conditions of middle of Iraq – Kut city

Experiment field was conducted for irrigation scheduling depending on moisture depletion of available water for leguminosae in field of agriculture college-Wasit University at latitudes 32° 30′ 31.19″North and longitudes 45° 26′ 89″ East, Altitude 19 m through the autumn season 2016-2017 in loam soil. the aim of this study to determine the reference water consumptive ETo , actual consumptive use ETa , crop coefficient Kc of leguminosae and water use efficiency at irrigation scheduling on base of moisture depletion of available water at ratios 25, 50 and 75% and effect of climate factors on it. The experiment carried out using random complete block design (RCBD) with three replicates. The seeds of leguminosae planted at date 10/10/2016, the end of growth season at 15/4/2017. The quantities of added water used to calculate the actual consumptive use ETa by using water-balance equation, the gravimetric water content determined immediately after irrigation and before the following irrigation through the growth season to limit irrigation scheduling of studied treatments. The reference water consumptive ETo calculated by using three empirical equations (Blaney-criddle, Najib Kharrufa, Evaporation pan). The results showed that the Najib Kharrufa equation gave high value of ETo 675.49 mm comparatively with equations of evaporation Pan and Blaney–criddle that gave ETo values 591.92 and 544.77 mm alternately. The treatment of irrigation at depletion of 25% of available water gave high value of ETa 577.95 mm, comparatively with treatments depletion of 50 and 75% of available water that gave ETa values 531.5 and 472.1 mm, alternately. The results showed increasing of crop coefficient Kc, for all treatments, with progress of growth season and reached high value at flowering and spuds formation stage and reduced at maturation stage (end of growth season), the high value of Kc showed at irrigation treatment at depletion 25% of available water, its ranged between 0.62 to 1.44, but the low value of Kc showed at irrigation treatment at depletion 75% of available water, its ranged between 0.38 to 1.29. The irrigation treatments showed significant differences between studied characteristics crop , thus irrigation treatment at depletion 25% of available water increased significantly in comparison with irrigation treatment at depletion 75 % of available water in height plant and leaf area surface , but there are non-significant differences were noted in stem diameter , the irrigation treatment at depletion 25% of available water increased significantly in comparison with other treatments in total yield (spuds) . The irrigation treatment at depletion 50% of available water gave high water use efficiency (WUEf) that equal 1.43 kg m-3.

Effect of climate change on vegetation phenology of different land-cover types on the Tibetan Plateau

ABSTRACTResearch in vegetation phenology change has been one heated topic of current ecological and climate change study. The Tibetan Plateau, as the highest plateau of the earth, is more vulnerable and sensitive to climate change than many other regions. In this region, shifts in vegetation phenology have been intensively studied during recent decades, primarily based on satellite-retrieved data. In this study, we explored the spatiotemporal changes of vegetation phenology for different land-cover types in the Tibetan Plateau and characterized their relationship with temperature and precipitation by using long-term time-series datasets of normalized difference vegetation index (NDVI) from 1982 to 2014. Diverse phenological changes were observed for different land-cover types, with an advancing start of growing season (SOS), delaying end of growing season (EOS) and increasing length of growing season (LOS) in the eastern Tibetan Plateau where meadow was the dominant vegetation type, but with the opposite changes in the steppe and sparse herbaceous or sparse shrub regions which are mostly located in the northwestern and western edges of the Tibetan Plateau. Correlation analysis indicated that sufficient preseason precipitation may delay the SOS of evergreen forests in the southeastern Plateau and advance the SOS of steppe and sparse herbaceous or sparse shrub in relatively arid areas, while the advance of SOS in meadow areas could be related to higher preseason temperature. For EOS, because it is less sensitive to climate change than SOS, the response of EOS for different land-cover types to precipitation and temperature were more complicated across the Tibetan Plateau.

Impacts of Urbanization on Vegetation Phenology over the Past Three Decades in Shanghai, China

Vegetation phenology manifests the rhythm of annual plant life activities. It has been extensively studied in natural ecosystems. However, major knowledge gaps still exist in understanding the impacts of urbanization on vegetation phenology. This study addresses two questions to fill the knowledge gaps: (1) How does vegetation phenology vary spatially and temporally along a rural-to-urban transect in Shanghai, China, over the past three decades? (2) How do landscape composition and configuration affect those variations of vegetation phenology? To answer these questions, 30 m × 30 m mean vegetation phenology metrics, including the start of growing season (SOS), end of growing season (EOS), and length of growing season (LOS), were derived for urban vegetation using dense stacks of enhanced vegetation index (EVI) time series from images collected by Landsat 5–8 satellites from 1984 to 2015. Landscape pattern metrics were calculated using high spatial resolution aerial photos. We then used Pearson correlation analysis to quantify the associations between phenology patterns and landscape metrics. We found that vegetation in urban centers experienced advances of SOS for 5–10 days and delays of EOS for 5–11 days compared with those located in the surrounding rural areas. Additionally, we observed strong positive correlations between landscape composition (percentage of landscape area) of developed land and LOS of urban vegetation. We also found that the landscape configuration of local land cover types, especially patch density and edge density, was significantly correlated with the spatial patterns of vegetation phenology. These results demonstrate that vegetation phenology in the urban area is significantly different from its rural surroundings. These findings have implications for urban environmental management, ranging from biodiversity protection to public health risk reduction.

Changes in resource allocation among vegetative organs during the clonal growth of Polygonatum humile (Liliaceae) grown in a temperate forest gap

BackgroundThe aim of this study was to examine the resource allocation among the organs and the leaf morphology of Polygonatum humile. The data were collected from June 2014 to May 2015 in a natural P. humile stand of a temperate forest gap.ResultsThe dry weight of new rhizome (R0) sharply decreased to the time of new shoot sprouting in next year and was constant for 2 ~ 3 years. However, dry weight of root on R0 increased to the end of growth season and, thereafter, decreased slowly along the time elapsed. The correlation coefficients between the rhizome and the leaf sizes were 0.5 for the last year’s rhizome (R1) and 0.6 for R0 and were significant at 0.1% level for R0. The increase of one leaf a plant led to increase of the total leaf area, total leaf weight, and stem length. Moreover, the organ sizes’ differences between two plants of the one leaf difference were almost significant at 1% level. In 11-leaf plant, the leaf length/width ratio and specific lea area increased to the second, relative leaf area to the fourth and relative leaf dry weight to the fifth, and thereafter, decreased to the last leaf. The differences in the values of these four parameters between two leaves on a stem were almost significant at 5% level.ConclusionP. humile examined showed the close relationships between the last year’s rhizome or this year’s one and the shoot system (leaf and stem) sizes. The leaf number a shoot greatly influenced specific leaf area. P. humile’s leaf might showed diverse morphology with leaf rank on a stem in a forest gap environment.

Sources of uncertainty in exploring rangeland phenology: A case study in an alpine meadow on the central Tibetan Plateau

Global climate change has been found to substantially influence the phenology of rangeland, especially on the Tibetan Plateau. However, there is considerable controversy about the trends and causes of rangeland phenology owing to different phenological exploration methods and lack of ground validation. Little is known about the uncertainty in the exploration accuracy of vegetation phenology. Therefore, in this study, we selected a typical alpine rangeland near Damxung national meteorological station as a case study on central Tibetan Plateau, and identified several important sources influencing phenology to better understand their effects on phenological exploration. We found man-made land use was not easily distinguished from natural rangelands, and therefore this may confound phenological response to climate change in the rangeland. Change trends of phenology explored by four methods were similar, but ratio threshold method (RTM) was more suitable for exploring vegetation phenology in terms of the beginning of growing season (BGS) and end of growing season (EGS). However, some adjustments are needed when RTM is used in extreme drought years. MODIS NDVI/EVI dataset was most suitable for exploring vegetation phenology of BGS and EGS. The discrimination capacities of vegetation phenology declined with decreasing resolution of remote sensing images from MODIS to GIMMS AVHRR datasets. Additionally, distinct trends of phenological change rates were indicated in different terrain conditions, with advance of growing season in high altitudes but delay of season in lower altitudes. Therefore, it was necessary to eliminate interference of complex terrain and man-made land use to ensure the representativeness of natural vegetation. Moreover, selecting the appropriate method to explore rangelands and fully considering the impact of topography are important to accurately analyze the effects of climate change on vegetation phenology.

Evaluation of seasonal variations of remotely sensed leaf area index over five evergreen coniferous forests

Seasonal variations of leaf area index (LAI) have crucial controls on the interactions between the land surface and the atmosphere. Over the past decades, a number of remote sensing (RS) LAI products have been developed at both global and regional scales for various applications. These products are so far only validated using ground LAI data acquired mostly in the middle of the growing season. The accuracy of the seasonal LAI variation in these products remains unknown and there are few ground data available for this purpose. We performed regular LAI measurements over a whole year at five coniferous sites using two methods: (1) an optical method with LAI-2000 and TRAC; (2) a direct method through needle elongation monitoring and litterfall collection. We compared seasonal trajectory of LAI from remote sensing (RS LAI) with that from a direct method (direct LAI). RS LAI agrees very well with direct LAI from the onset of needle growth to the seasonal peak (R2=0.94, RMSE=0.44), whereas RS LAI declines earlier and faster than direct LAI from the seasonal peak to the completion of needle fall. To investigate the possible reasons for the discrepancy, the MERIS Terrestrial Chlorophyll Index (MTCI) was compared with RS LAI. Meanwhile, phenological metrics, i.e. the start of growing season (SOS) and the end of growing season (EOS), were extracted from direct LAI, RS LAI and MTCI time series. SOS from RS LAI is later than that from direct LAI by 9.3±4.0days but earlier than that from MTCI by 2.6±1.9days. On the contrary, for EOS, RS LAI is later than MTCI by 3.3±8.4days and much earlier than direct LAI by 30.8±7.2days. Our results suggest that the seasonal trajectory of RS LAI well captures canopy structural information from the onset of needle growth to the seasonal peak, but is greatly influenced by the decrease in leaf chlorophyll content, as indicated by MTCI, from the seasonal peak to the completion of needle fall. These findings have significant implications for improving existing RS LAI products and terrestrial productivity modeling.

Asymmetric Diurnal and Monthly Responses of Ecosystem Carbon Fluxes to Experimental Warming

Quantifying the diurnal and monthly responses of ecosystem carbon (C) fluxes is critical to accurately understand the feedback between global climate change and ecosystem C dynamics. However, the diurnal and monthly responses of ecosystem C fluxes to climate warming remain unclear. In this study, a field simulated warming experiment was conducted by using open top chambers to explore the diurnal and monthly responses of ecosystem C fluxes during one growing season (GS) in a Tibetan Plateau grassland. The results showed that ecosystem C fluxes responded unevenly to the simulated warming during one GS. Warming significantly increased C uptake (gross primary production) and sequestration (net ecosystem exchange) during the start (May to June) and peak (July to August) of the GS, but promoted ecosystem respiration (ER) during the peak and end (September to October) of the GS. Warming also had more pronounced positive effects on ER during night than during day. In addition, although warming significantly decreased the temperature sensitivity (Q10) of ER over the whole GS, Q10 also responded positively to warming during the start and end of GS as well as during the night. These results highlight the hypothesis that asymmetrical responses of the diurnal and monthly variations of ecosystem C fluxes and Q10 should be taken into consideration to project the C‐climate feedback, especially under future non‐uniform warming scenarios.