Initial Trends of Bird Assemblages Before and After River Diversion in an Endemic-rich African Forest

The Lower Kihansi Hydropower Project in southern Tanzania caused the diversion of the Kihansi River from the Kihansi Gorge in the year 2000. By sampling the understorey avifauna prior to diversion, we examined (i) whether the adjacent Udagaje Gorge was an adequate control for observations in the Kihansi Gorge; (ii) which species of conservation interest occurred; and, (iii) which season best suited annual monitoring. Species composition and capture rates at three and two elevational transects in the Kihansi Gorge and Udagaje Gorge, respectively, confirmed that Udagaje had a comparable avifaunal assemblage to Kihansi. The cold season was most appropriate for population monitoring because >2 times more individuals were captured in the cold than hot season at both gorges, and at least four altitudinal migrants were present in the cold but not hot season. Post-diversion sampling revealed that only the Upper Kihansi transect suffered a significant decrease in number of individuals, a result that was driven largely by a decline in the Little Greenbul, Andropadus virens. This transect is closest to the Kihansi waterfall and associated spray zone which were lost after river diversion. Lack of differences in bird communities at other transects after diversion illustrates that early post-diversion effects on birds are probably concentrated near the base of the main falls. Together with studies of other biota in Kihansi, we propose that long-term monitoring is necessary to understand the factors that regulate changes in species composition of this threatened forest site.     

Elevational gradients during the Late-Glacial/Holocene vegetational transition in southern Bulgaria

The Late Glacial and early-Holocene vegetational history of a newly dated pollen and macrofossil diagram from Besbog, a cirque lake at 2250 m just above the forest limit in the Pirin Mountains of southwestern Bulgaria, is compared with a newly dated pollen diagram for the mire Shiroka Polyana at 1400 m in the conifer forest of the nearby Rhodope Mountains in order to investigate the chronology of major changes in the vegetation at different elevations. In the Lake Besbog record the non-arboreal pollen assemblage of the Late Glacial changed abruptly to that of Betula, Quercus and other deciduous types. The date for this change is about 11.6 ka cal b.p. The Quercus assemblage may be composed of pollen blown from intermediate elevations, to which deciduous forest had expanded because of higher summer temperatures related to high summer insolation. At Shiroka Polyana (1400 m) in the modern conifer belt, a similar change did not occur until about 8.8 ka cal b.p. The persistence of the dry steppe or steppe forest in the early Holocene at this lower site can also be attributed to high summer insolation. Thus as atmospheric temperature increased at the end of the Late Glacial, deciduous forests expanded first at intermediate elevations in the Pirin Mountains and only later in the Rhodope Mountains at lower elevations as summer insolation decreased.     

Tree recruitment at the treeline across the Continental Divide in the Northern Rocky Mountains,USA: the role of spring snow and autumn climate

ABSTRACT

Background: Topoclimate can influence tree establishment within treeline ecotones. Yet much less is known about how regional topography, such as the Continental Divide, Rocky Mountains, mediates the role of climate in governing treeline dynamics.

Aims: To utilise the Continental Divide to test whether contrasts in growing-season moisture regimes to the west (summer-dry) and east (summer-wet) impact the spatio-temporal patterns of tree establishment and rates of treeline advance in the Northern Rocky Mountains.

Methods: We sampled trees at sites on north- and south-facing slopes, west and east of the Continental Divide. We used dendroecological techniques to reconstruct patterns of tree establishment. Age-structure data were quantitatively compared with climate to evaluate possible mechanistic linkages.

Results: Across all sites, 96% of trees established after 1950. There was a treeline advance (range = 39–140 m) accompanied by increases in tree density. Significantly more trees established during wet springs on both sides of the Divide.

Conclusions: Overall, snow duration in spring and autumn temperatures appear to influence patterns of tree recruitment at the treeline. Continued warming will likely amplify the role of autumn climate in regulating tree establishment throughout treeline ecotones in the Northern Rocky Mountains, particularly west of the Divide where summer-dry conditions persist.     

Diversification in a biodiversity hot spot: landscape correlates of phylogeographic patterns in the African spotted reed frog

The Eastern Afromontane Biodiversity Hotspot is known for microendemism and exceptional population genetic structure. The region's landscape heterogeneity is thought to limit gene flow between fragmented populations and create opportunities for regional adaptation, but the processes involved are poorly understood. Using a combination of phylogeographic analyses and circuit theory, I investigate how characteristics of landscape heterogeneity including regional distributions of slope, rivers and streams, habitat and hydrological basins (drainages) impact genetic distance among populations of the endemic spotted reed frog (Hyperolius substriatus), identifying corridors of connectivity as well as barriers to dispersal. Results show that genetic distance among populations is most strongly correlated to regional and local hydrologic structure and the distribution of suitable habitat corridors, not isolation by distance. Contrary to expectations, phylogeographic structure is not coincident with the two montane systems, but instead corresponds to the split between the region's two major hydrological basins (Zambezi and East Central Coastal). This results in a paraphyletic relationship for the Malawian Highlands populations with respect to the Eastern Arc Mountains and implies that the northern Malawian Highlands are the diversity centre for H. substriatus. Although the Malawian Highlands collectively hold the greatest genetic diversity, individual populations have lower diversity than their Eastern Arc counterparts, with an overall pattern of decreasing population diversity from north to south. Through the study of intraspecific differentiation across a mosaic of ecosystem and geographic heterogeneity, we gain insight into the processes of diversification and a broader understanding of the role of landscape in evolution.     

Introgressive hybridization of Senecio hercynicus and S. ovatus (Compositae,Senecioneae) along an altitudinal gradient in Harz National Park (Germany)

Introgressive hybridization of Senecio hercynicus and S. ovatus (Compositae, Senecioneae) was studied in a hybrid zone on the southern slopes of Mt Brocken (Harz Mountains, Germany). A total of 415 plants representing 10 stands along an altitudinal gradient were investigated using multivariate statistical analyses of morphological characters and molecular markers (random amplified polymorphic DNA[RAPD]). Both types of traits detected pure S. hercynicus stands on the summit plateau, pure S. ovatus stands at the lowest elevations, and hybrid swarms at intermediate elevations. While morphological and molecular patterns coincided, some individuals in hybrid stands combined morphological patterns typical of S. ovatus with RAPD patterns typical of S. hercynicus, and vice versa. In general, introgression was symmetrical within stands, though one stand combined S. ovatus characters with the glandular hair typical for S. hercynicus, and two stands combined a S. hercynicus typical RAPD genotype with morphological characters shifted towards S. ovatus. Because pure stands of S. hercynicus occurred only on the summit plateau of Mt Brocken, and markers typical for S. ovatus were detectable in stands up to 1040 m a.s.l., future fusion or assimilation of the rare form, S. hercynicus, by the more widespread S. ovatus appears possible at Mt Brocken.     

Riparian roots through time, space and disturbance

Riparian zones are landscape features adjacent to streams and are widely recognized as important in reducing erosion and filtering groundwater. Few studies directly investigate rooting dynamics of riparian areas, and little information exists concerning riparian root densities, biomass, depth profiles, changes through time, or vulnerability to disturbance. This study examined spatial and temporal patterns in root systems in streamsides influenced by season, hydrologic regime, vegetative composition, and ice storm disturbance in the eastern Adirondacks, New York. Sequential root cores and in-growth cores were collected from June 2000 through August 2001 in a riparian area with minimal ice storm damage adjacent to a third-order stream. Data were used to assess seasonal trends in root biomass and to provide a reference for spatial comparisons. The biomass and surface area of roots collected in the reference site cores were compared with cores collected at nine additional riparian sites differing in degree of canopy damage from the January 1998 ice storm. Average root biomass at the reference site was 1330 g/m², comparable to or greater than values reported for terrestrial and other riparian systems. Root biomass varied seasonally with a maximum root biomass in August, 2000; this result was not repeated the following year after the water table inundated much of the rooting zone in mid-June. Root biomass was spatially variable on a range of scales. Although the maximum root surface area occurred in the upper 10 cm, root biomass peaked at 20–30 cm belowground, unlike observations from most other root studies where the maximum root biomass has been found in the top 10 cm. Areas severely damaged by the ice storm had significantly less root biomass and surface area than areas with low damage. This study demonstrates that root biomass in riparian areas is highly dynamic over time, space, and across disturbance sites. Our findings suggest that the spatial variability in root densities has direct implications for riparian vulnerability to erosion.     

The denied land rights of the indigenous peoples and their endangered livelihood and survival: the case of the Nuba of the Sudan

The current situation of indigenous peoples in the Sudan is the result of the independent state's adoption of land and other policies identical to those introduced by colonialists more than a century ago. The Sudanese state has not only unwittingly maintained some colonial coercive institutions and policies but it has introduced more aggressive ones and brutally deployed them against its indigenous peoples, particularly the Nuba. In the light of this, this paper attempts to demonstrate analytically how some historical and contemporary socio-political dynamics have continued systematically to deprive these indigenous Nuba peoples of their customary land, and to assess to what extent the recently concluded Comprehensive Peace Agreement (CPA) has been successful in addressing the land question as one of the root causes of the recurring civil wars in the Sudan in general and in the Nuba Mountains in particular.     

《山海经》三大神木的植物学考订

《山海经》中有太阳东出扶桑、日中建木、西归若木的传说,长期以来一直存疑,争论不休,直到四川广汉三星堆遗址出土了青铜神树,才证明了传说的真实性.我们结合《山海经》等相关典籍,从植物学角度对扶桑、建木、若木的原植物进行探讨,基于典籍描述、考古资料、植物形态特征、生态习性和地理分布等,初步考订扶桑的植物原型为桦木科白桦(Betula platyphylla),建木的植物原型为杉科杉木(Cunninghamia lanceolata),若木的植物原型为木棉科木棉(Bombax ceiba).     

贺兰山不同海拔典型植被带土壤微生物多样性

土壤微生物多样性在海拔梯度的分布格局研究近年来受到和植物动物一样的重视程度,但是干旱风沙区微生物多样性在海拔梯度上的多样性分布规律尚未揭示。本研究以处于干旱风沙区的贺兰山不同海拔的六个典型植被带（荒漠草原带、山地旱生灌丛带、温性针叶林带、针阔混交林带、寒温性针叶林带和亚高山草甸带）土壤为研究对象,利用Biolog微平板法和磷脂脂肪酸甲酯法(FAMEs)系统研究微生物多样性群落特征以及在不同植被带分布规律。结果表明：土壤微生物功能多样性随海拔增加发生变化,且微生物群落结构存在显著差异。Biolog分析显示土壤微生物群落代谢活性依次是：亚高山草甸>寒温性针叶林>针阔混交林>温性针叶林>山地旱生灌丛>荒漠草原,随海拔的升高土壤微生物群落物种丰富度指数（H）和均匀度指数（E）总体上均表现出增大的趋势,差异显著（P＜0.05）;FAMEs分析表明不同海拔的微生物区系发生了一定程度的变化,寒温性针叶林土壤微生物磷酸脂肪酸生物标记的数量和种类均最高,且细菌、真菌特征脂肪酸相对含量也最高;土壤微生物群落结构多样性次序是：寒温性针叶林带>针阔混交林带>温性针叶林带>亚高山草甸>山地旱生灌丛>荒漠草原。本研究结果表明贺兰山海拔梯度的微生物多样性分布规律不同于已有的植物多样性“中部膨胀”研究结果,这说明在高海拔地区有更多的适合该生境的微生物存在,这对维持干旱风沙区的生态系统功能稳定性具有重要意义。