Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates

Areas of 2,800–3,000 m a.s.l. represent the alpine-nival ecotone in the Alps. This transition zone connecting the closed swards of the alpine belt and the scattered vegetation of the nival belt may show particularly strong climate warming driven fluctuations in plant species richness compared to the nival belt. To test this hypothesis, 12 summits within this range were investigated in the canton of Grisons, Switzerland in 2004. Complete lists of vascular plant species consisting of 5–70 species were collected on each summit and the elevation of the uppermost occurrence of each species was recorded. These data were compared to historical records over 120 years in age. Within this time, vascular plant species richness increased by 11% per decade on summits in the alpine-nival ecotone. Despite this considerable change, a comparison with nival summits did not support the hypothesis that species richness increase at the alpine-nival ecotone is higher than in the nival belt. A general trend of upward migration in the range of several metres per decade could be observed. Anemochorous species were more often found to be migrating than zoochorous or autochorous species and migration was higher on calcareous than on siliceous bedrock. A comparison between the summits with the adjacent slopes in our study revealed that changes in species number could be used as an indicator for climate-induced changes—if at all—only for the narrow summit areas.     

黑龙江西部生态脆弱带景观格局研究

运用景观生态学格局的分析方法,对黑龙江西部生态脆弱带典型的土地景观进行了分析,并对各种分析方法进行了对比,探讨了各种景观类型的关系,并对人类活动的影响与景观之间的关系进行了分析。     

Substrate Availability May Be More Important than Aquatic Insect Abundance in the Distribution of Riparian Orb-web Spiders in the Tropics

Spiders that are abundant along streams may depend on energy subsidies across land–water ecotones, but the effects of season and habitat structure on this trophic linkage remain poorly understood in the tropics. We carried out surveys and a manipulative experiment to investigate the effects of season and substrate availability on the distribution of riparian orb-web spiders in Hong Kong, southern China. In the surveys, spider abundance, prey, substrate use, and web orientation were recorded. The experiment involved installation of in-stream artificial substrates (ropes and bamboo poles) to increase substrate availability for web attachment. We found no seasonal difference in web abundance, but seasonal differences were observed for the prey on webs: aquatic insects (mostly Ephemeroptera and chironomid midges) contributed 69 percent of total prey collected during the wet season, but only 38 percent during the dry season. Most webs (50–80%) were < 0.5 m above the water and 45–51 percent of them tended to be orientated horizontally to the water surface and supported by overhanging vegetation and boulders. The addition of artificial substrates resulted in a 23–34 percent increase in the number of webs at the four treatment sites compared to controls, indicating that availability of web-building substrates is a critical determinant of the spider distribution. Our results suggest that riparian zones are potential 'hotspots' of food availability for spiders, and that the aquatic insect subsidy allows this habitat to support increased densities of spiders when the constraint of substrate availability is relaxed.     

Effects of grassland conversion to cropland and forest on soil organic carbon and dissolved organic carbon in the farming-pastoral ecotone of Inner Mongolia

Effects of grassland conversion to cropland and forest on soil organic carbon (SOC), dissolved organic carbon (DOC) in the farming-pastoral ecotone of Inner Mongolia were investigated by direct field sampling. SOC content and DOC content in soil decreased after grassland were shifted to forest or cropland, in the sequence of grassland soil > forest soil > cropland soil. SOC stock declined by 18% after grassland shifted from to forest. Reclamation of cropland for 10 years, 15 years and 20 years lost SOC in 0–30 cm soil layer, by 34%, 14% and 18%, respectively, compared with that of grassland. DOC in 3 soil layers was within 21.1–26.5 mg/L in grassland, 12.1–14.6 mg/L in forest soil, and 8.0–14.0 mg/L in cropland soil. Correlation analysis indicated that SOC content and DOC content were positively dependent on total nitrogen content (p < 0.05), but negatively on bulk density or land use type (p < 0.05). DOC was positively correlated SOC (p < 0.01). Moreover, SOC content could be quantitatively described by a linear combination of land use types (p = 0.000, r² = 0.712), and DOC content by a linear combination of two soil-related variables, land use types and SOC (p = 0.000, r² = 0.861).     

Which Extent is Plasticity to Light Involved in the Ecotypic Differentiation of a Tree Species from Savanna and Forest?

Light intensity and heterogeneity are some of the main environmental factors that differ between forest and savanna habitats, and plant species from these habitats form distinct functional types. In this study, we tested the hypothesis that not only differences in morphological and physiological traits but also phenotypic plasticity in response to light are involved in adaptation to forest and savanna habitats by investigating ecotypic differentiation between populations of Plathymenia reticulata (Leguminosae: Mimosoideae), a tree from the Brazilian Atlantic Forest and the Brazilian Cerrado (savanna). Seeds from four natural populations (one from each biome core area and two from ecotonal regions) were grown in a common garden with four light treatments. Fifteen morphological and physiological characteristics were evaluated until individuals reached 6 mo old. Comparisons among populations showed differences for seven traits in at least one light treatment. These differences pointed to local adaptation to different biomes. Populations showed different levels of phenotypic plasticity in response to light in seven traits. Higher plasticity was found either in the forest core population or ecotonal populations; lower values were found in the cerrado core population. Lower plasticity in the cerrado population emphasizes the stress resistant syndrome, as lower plasticity is probably advantageous in a habitat where a conservative resource use is crucial. Higher plasticity in forest individuals suggests higher ability in exploiting the light heterogeneity in this habitat. Also, higher plasticity in ecotonal populations can be important to ensure the maintenance of P. reticulata in these temporally and spatially dynamic areas. Abstract in Portugese is available at http://www.blackwell‐synergy.com/loi/btp .     

Contrasting long‐term records of biomass burning in wet and dry savannas of equatorial East Africa

Rainfall controls fire in tropical savanna ecosystems through impacting both the amount and flammability of plant biomass, and consequently, predicted changes in tropical precipitation over the next century are likely to have contrasting effects on the fire regimes of wet and dry savannas. We reconstructed the long‐term dynamics of biomass burning in equatorial East Africa, using fossil charcoal particles from two well‐dated lake‐sediment records in western Uganda and central Kenya. We compared these high‐resolution (5 years/sample) time series of biomass burning, spanning the last 3800 and 1200 years, with independent data on past hydroclimatic variability and vegetation dynamics. In western Uganda, a rapid (<100 years) and permanent increase in burning occurred around 2170 years ago, when climatic drying replaced semideciduous forest by wooded grassland. At the century time scale, biomass burning was inversely related to moisture balance for much of the next two millennia until ca. 1750 ad , when burning increased strongly despite regional climate becoming wetter. A sustained decrease in burning since the mid20th century reflects the intensified modern‐day landscape conversion into cropland and plantations. In contrast, in semiarid central Kenya, biomass burning peaked at intermediate moisture‐balance levels, whereas it was lower both during the wettest and driest multidecadal periods of the last 1200 years. Here, burning steadily increased since the mid20th century, presumably due to more frequent deliberate ignitions for bush clearing and cattle ranching. Both the observed historical trends and regional contrasts in biomass burning are consistent with spatial variability in fire regimes across the African savanna biome today. They demonstrate the strong dependence of East African fire regimes on both climatic moisture balance and vegetation, and the extent to which this dependence is now being overridden by anthropogenic activity.     

Ecological Restoration and Sustainable Agricultural Paradigm of Mountain-Oasis-Ecotone-Desert System in the North of the Tianshan Mountains

The mountain-basin system(MBS) in the north of the Tianshan Mountains consists of mountain vegetation vertical belt system and concentric circular vegetation (geologic and geomorphic) system of desert basin. The MBS contains three “circles”: montane, piedmont fan and alluvial plain, including nine belts, viz. alpine belt, montane forest-grassland belt, low-mountain desert belt, gravel gobi desert belt, agricultural oasis, marginal belt of diluvial fan, alluvial desert plain, sandy desert belt, and lake. The above-mentioned zonation is the most essential existence and functional pattern of those precious natural resources. It is the representation of an irresistible rule of the nature and, also, the guidance system of ecological conservation and land use. Basing on this foundation, a “mountain-oasis-oasis/desert ecotone-desert eco-productive paradigm”is proposed. The MBS is its basic frame. Its driving forces are the biogeochemical cycles, biogeophysic process, and biogeosocial interaction, which run through the whole system. Thus, the establishment of a sustainable agricultural system and an optimized land use and land cover structure and pattern, which aimed at ecological conservation, may be possible.     

祁连山中段林草交错带土壤水热特征及其对气象要素的响应

利用综合环境观测仪(ENVIS)的长期监测数据,分析了2002-06-01—2008-05-31期间祁连山阴坡林草交错带土壤水热特征及其与气象要素的统计关系,结果表明:1)土壤温度与空气温度年内变化格局相似,但存在滞后期,滞后时间随土壤深度增加而增加;土壤温度年际变化与气温一致,呈逐渐降低趋势。2)土壤水分表现为20—80 cm土壤水分易受外界降水过程影响,120 cm和160 cm深度土壤水分变化相对平缓;土壤水分季节性冻融过程中的主要控制因子为温度,但20—80 cm冻土的融化还受上层土壤水分融化和降雨下渗影响。3)月尺度上土壤水分和温度与气象要素的统计关系优于日尺度。利用气象要素在月尺度上建立的经验模型上对20—60 cm深度土壤温度的估算效果相对较好。     

荒漠绿洲过渡带柽柳灌丛沙堆特征及其空间异质性

以甘肃金塔县和内蒙古额济纳旗的荒漠绿洲过渡带为研究区,研究了戈壁和沙漠两种生境中柽柳灌丛沙堆的形态特征,定量分析了不同生境中柽柳灌丛沙堆形态参数间的关系、空间格局以及空间异质性.结果表明:(1)大部分沙堆为独立型,在沙漠生境通常沿风向形成沙堆链(额济纳NE 83°15',金塔NE 53°13').沙堆高度、体积和植被冠幅的均值在戈壁生境均小于沙漠生境,植被高度和盖度的均值在戈壁生境均大于沙漠生境.此外,沙堆高度、体积和植被冠幅、高度、盖度的最大均值都出现在额济纳,依次为4.47 m、1133.5 m3、534.5 m2、2.27 m和0.47.(2)沙堆长短轴间、体积和冠幅间均为线性关系;沙堆高度和面积间的回归曲线为抛物线;植被冠幅和高度的回归曲线在戈壁生境是抛物线,沙漠生境中却是线性关系.(3)戈壁生境中沙堆相互分隔呈斑块状格局,沙漠生境中呈沙丘链状分布.(4)空间异质性由非随机的结构原因形成的变异为主,在额济纳的空间异质性高于金塔.空间相关性在额济纳戈壁生境中较强,沙漠生境和金塔戈壁生境中属于中等程度;在金塔空间异质性存在由随机的原因形成变异为主的可能性,其环境因素对空间异质性产生大的影响.此外,结论表明高强度的风积产生较深的沙埋对柽柳灌丛生长的促进作用及灌丛与沙堆间的反馈效应是柽柳灌丛沙堆的适应性机理.     

鄂尔多斯高原生态过渡带气候特殊性和气候植物生长指数与畜牧业生产动态分析

鄂尔多斯高原位于我国典型的生态过渡带,气候变化明显,系统反应敏感,因此,现有的主要用于植被和气候空间分类的有关植物与气候关系的模型和指数,均不适合用于鄂尔多斯高原生态过渡带气候。植物动态分析。为此,本文利用位于鄂尔多斯高原中部的伊金霍洛旗３９ａ（１９５３－１９９１）气象资料,分析该地区的气候特点,构建一个可用于描述生态过渡带气候特征的气候植物生长指数,并用与植被动态密切相关的天然放牧条件下（１９５８－１９７９）,该旗牲畜的存栏数和出栏数的历史资料代替植被动态资料,进行鄂尔多斯气候植物生长指数与天然放牧条件下牲畜的存栏数和出栏数的动态分析,构建其ＡＲＭＡＸ模型。研究结果表明,鄂尔多斯高原气候敏感易变,降水年际变化大;高原光、温、水配合并不完全一致,光、温超前,降水滞后,天然植被生产力不高;气候植物生长指数与畜牧生产的动态分析结果表明,该地区在天然放牧情况下,主要依赖于牧场植被长势的畜牧生产与气候－植物生长指数密切相关,说明构建的气候植物生长指数确实在一定程度上反映了该地区的气候与植物生长的关系￣（６－８）。