Changes in ecosystem carbon stocks following grassland afforestation of semiarid sandy soil in the southeastern Keerqin Sandy Lands, China

The ecological consequences of grassland afforestation in arid/semiarid sandy regions are not well known with respect to tree species and stand age. The present study quantifies the changes in above- and belowground carbon (C) stocks following afforestation in the southeastern Keerqin Sandy Lands with species of Mongolian pine and poplar. We studied 15-, 24-, and 30-year-old Mongolian pine plantations, 7-, 11-, and 15-year-old poplar plantations, and adjacent grasslands. The results show that total ecosystem C stocks increased following grassland afforestation. Aboveground C stocks increased at a rate of 2.75 Mg C ha⁻¹ yr⁻¹ in the poplar plantations, and 1.06 Mg C ha⁻¹ yr⁻¹ in the Mongolian pine plantations. Mineral soil C stocks decreased during the early stage of forest establishment, but recovered with increasing stand age. Root C stock increased significantly in the Mongolian pine plantations, but the poplar plantations showed no such increase relative to the grassland. Our results indicate that afforestation of the grassland in the southeastern Keerqin Sandy Lands would sequester more C than would continuous grassland. Tree species selection and stand developmental age should be considered in planning future afforestation projects.     

Response to climate change of different tree species and NDVI variation since 1923 in the middle arid region of Ningxia, China

The normalized difference vegetation index (NDVI) is used extensively to describe vegetation cover and ecological environment change. The purpose of this study was to contrast the response of different tree species growing in the same habitat to climate change and retrieve past NDVI using tree-ring width data from tree cores collected from the transitional zone of Pinus tabulaeformis and Picea crassifolia in the Luoshan Mountains in the middle arid region of Ningxia. Correlation analysis indicated that radial growth of P. tabulaeformis is more sensitive to precipitation and temperature change than that of P. crassifolia. Natural factors such as water availability and heat at this elevation are more suited to the growth of P. crassifolia, and are more advantageous to its renewal and succession. P. crassifolia is probably the better of the two species for protecting the forest ecosystem and conserving water in the Luoshan desertification area. Ring width of P. crassifolia correlates significantly with average NDVI for April–May (r =0.641, p <0.01), and both of them are influenced positively by precipitation in April–May. The reconstructed NDVI for 1923–2007 shows the relatively low vegetation cover occurred in the 1920s–1930s, the 1960s–1970s, and the early 21st century. The reconstructed NDVI better reflected the drought climate in the study area.     

沙地彰武松在不同基质上扦插生根性状研究

彰武松在3种基质中插穗生根性状存在显著差异。综合分析生根率、生根性状和根系效果指数等三个因素,发现蛭石基质最好,草炭基质次之,细沙基质较差。草炭基质虽生根率较高,但根系效果指数却没有蛭石好。生根能力较差的细沙基质,生根性状离散度最大。彰武松插穗生根性状的相关分析表明,侧根数、不定根（插穗底部切面不同位置上长出的主根）数、最长不定根长分别与根总长度存在极显著正相关,侧根数、不定根数及最长不定根长相互存在极显著正相关,最长不定根长与最长不定根粗有显著负相关关系。     

林分密度对华北土石山区油松人工林土壤有机碳及养分特征的影响

 以木兰围场国有林场管理局实施间伐后6种保留密度下（540、650、1 084、1 104、1 408和1 860 株 / hm2）油松人工林为研究对象,研究各土层的土壤有机碳和N、P、K等养分元素含量及其相关关系。研究结果显示：(1) 土壤有机碳含量和碳密度垂直递减特征明显,均随土壤深度的增加而显著减小,当林分密度由540 株 / hm2增加到1 860 株 / hm2时,土壤有机碳含量及碳密度变化规律不尽一致,其分布区间分别为10.56~21.21 g / kg,与5.48~11.70 kg / m2;(2) 林分密度对土壤有机碳及碳密度有显著的影响,1 408 株 / hm2油松林下土壤有机碳含量及碳密度分别与650 株 / hm2和1 860 株 / hm2油松林下土壤有机碳含量及碳密度呈显著性差异,而其它林分密度间无显著差异。当林分密度为1 104 株 / hm2时,各土层土壤全N和P、K的有效量及全量均保持在一个相对较高的水平,在0~60 cm深度土壤全N、全P、全K、有效P和速效K含量均值均达到最高,分别为1.38 g/kg、0.34 g/kg、32.75 g/kg、33.10 mg/kg和118.85 mg/kg;(3) 不同林分密度、不同土层土壤有机碳含量、碳密度与土壤全N及P、K的全量和有效量的相关显著性有差异,对整个土壤剖面而言,土壤有机碳含量及碳密度与土壤全N、全P、速效K均呈显著或极显著正相关;(4) 在本研究林分密度范围内,从林地土壤固碳的角度,建议将油松人工林的林分密度控制在1 104 株 / hm2。     

Tree-ring-based reconstruction of the April to September mean temperature since 1826 AD for north-central Shaanxi Province, China

Long-time series of high-resolution temperature record from Chinese Loess Plateau is rare. An April-September mean temperature reconstruction (1826-2004) has been developed for the north-central Shaanxi Province, China, based on tree-ring width analysis. The reconstruction captures 39.3% (p<0.001) of the variance in the instrumental data over the calibration period from 1951 to 2002. The reconstruction shows a high temperature period of 1928-1933, which coincides with the timing of the extreme drought event in 1920s in the entire northern China. The two low temperature periods in reconstruction are 1883-1888 and 1938-1942. With the global warming, the April-September mean temperature in study area has also increased since the 1970s, but has not exceeded the temperature in 1928-1933. Besides the statistical analysis, the reconstruction is also verified by the local dryness/wetness index and other dendroclimatological results.     

科尔沁沙地人工林下结皮发育对表土特性影响的研究

通过野外取样和室内分析相结合,对科尔沁沙地不同生长年限人工林下土壤结皮的理化性质及结皮发育对表层土壤特性的影响进行了初步研究。结果表明,3 a、15 a生杨树林下分别发育了物理结皮、地衣结皮和苔藓结皮,15 a、25 a生樟子松林下均发育了苔藓结皮,结皮的厚度、紧实度、水分、粘粉粒含量及全效、速效养分等随物理结皮向苔藓结皮的发育依次增加。同时,结皮的存在增加了其下层土壤颗粒组成中的极细沙和粘粉粒含量,富集了结皮下土壤的有机质、全N、全P、速效N、速效P等养分,而且结皮对下层土壤的这些影响作用从物理结皮、地衣结皮到苔藓结皮呈逐渐增长的趋势。同一结皮下土壤粘粉粒含量、养分含量在0—5 cm范围内由表及里呈递减趋势,但均高于对照无结皮层相对应的值。25 a生樟子松林下发育的苔藓结皮及其下层土壤的理化状况明显优于其他人工林下结皮的情况。     

Using low-density discrete Airborne Laser Scanning data to assess the potential carbon dioxide emission in case of a fire event in a Mediterranean pine forest

The aim of study is to map the carbon dioxide (CO₂) emission of the aboveground tree biomass (AGB) in case of a fire event. The suitability of low point density, discrete, multiple-return, Airborne Laser Scanning (ALS) data and the influence of several characteristics of these data and the study area on the results obtained have been evaluated. A sample of 45 circular plots representative of Pinus halepensis Miller stands were used to fit and validate the model of AGB. The ALS point clouds were processed to obtain the independent variables and a multivariate linear regression analysis between field data and ALS-derived variables allowed estimation of AGB. Then, the influence of several characteristics on the residuals of the model was analyzed. Finally, conversion factors were applied to obtain the CO₂ values. The AGB model presented a R² value of 0.84 with a relative root-mean-square error of 27.35%. This model included ALS variables related to vegetation height variability and to canopy density. Terrain slope, aspect, canopy cover, scan angle and the number of laser returns did not influence AGB estimations at plot level.     

天柱山黄山松群落特征及其环境功能评价

应用样方法,通过野外实地调查、数理统计,分析了天柱山黄山松群落特征和物种多样性;采用因子分析法、专家评价法和模糊评价方法,评价了天柱山黄山松群落环境功能及价值。结果表明:天柱山黄山松群落物种组成较复杂,科属分散,共有52科105属,区系成分多样,覆盖了9个种子植物科的分布区类型,具有明显的从北亚热带常绿阔叶林向暖温带落叶阔叶林过渡的特点;物种多样,乔木层、灌木层、草本层的Shannon-Wiener指数分别为1.9814、2.3175、2.1077,但由于人类活动的影响,乔木层黄山松的相对密度和优势度较大,多样性指数相对较低;群落顺行演替,环境服务功能多样,保护价值较重要。     

腾格里沙漠南缘油松树轮宽度变化及其对气候因子的响应

树木年轮定年准确、连续性强、分辨率高,并且易于获取复本,已经成为过去气候变化研究的主要手段之一。在沙漠地区,受气候条件的限制,树轮研究工作开展的较少。通过分析腾格里沙漠南缘油松树木年轮宽度的变化及其对气候因子的响应,发现夏季（6~8月）温度以及年降水量是当地油松生长的重要限制因子。对树木年轮标准化年表的功率谱分析表明,树轮记录具有2.6 a,7.5 a,14 a以及16.5 a的显著周期,其中2.6a以及7.5a周期的树轮指数变化,可能与ENSO的周期有关。     

典型喀斯特地区马尾松纯林及马尾松-阔叶树混交林营养元素生物循环研究——以贵州龙里为例

以龙里典型喀斯特地区马尾松纯林及马尾松-阔叶树混交林为研究对象,研究了两个群落的生物量、营养元素贮量、分布及循环特征.结果表明:马尾松纯林、马尾松-阔叶树混交林的生物量分别为40.62t/hm2、48.32t/hm2,混交林的乔木层总生物量比马尾松纯林高18.97%,根系生物量较纯林高65.12%.混交林乔木层各器官营养元素的含量整体大于马尾松纯林,两群落乔木层N、P、K、S的含量表现出一致的趋势,叶>根>枝>干.混交林乔木层各元素的积累量分别比纯林高47.97%~197.67%,凋落物层各元素贮量比纯林高85.40%~318.301%.混交林的年归还量、年存留量和年吸收量均大于马尾松纯林,且各元素循环系数大于马尾松纯林.马尾松林与阔叶树混交可以有效地提高群落生物量和营养元素循环的能力.