Relationships between lake macrophyte cover and lake and landscape features

We examined the ability of lake and landscape features to predict a variety of macrophyte cover metrics using 54 north temperate lakes. We quantified submersed cover, emergent cover, floating leaf cover, Eurasian watermilfoil cover and total macrophyte cover. Measured lake features included lake physio-chemical and morphometric variables and landscape features included hydrologic, catchment and land use/cover variables. Univariate regression analyses demonstrated that these macrophyte cover metrics are predicted by a wide range of predictor variables, most commonly by: Secchi disk depth, maximum or mean depth, catchment morphometry, road density and the proportion of urban or agricultural land use/cover in the riparian zone or catchment (r² = 0.06–0.46). Using a combination of lake and landscape features in multiple regressions, we were able to explain 29–55% of the variation in macrophyte cover metrics. Total macrophyte cover and submersed cover were related to Secchi disk depth and mean depth, whereas the remaining metrics were best predicted by including at least one land use/cover variable (road density, proportion local catchment agriculture land use/cover, proportion cumulative catchment urban land use/cover, or proportion riparian agriculture land use/cover). The two main conclusions from our research are: (1) that different macrophyte growth forms and species are predicted by a different suite of variables and thus should be examined separately, and (2) that anthropogenic landscape features may override patterns in natural landscape or local features and are important in predicting present-day macrophytes in lakes.     

Factors influencing the spatial distribution of forest plant species in hedgerows of North-western Germany

In North-western Germany woodland fragmentation has caused a decline in many forest plant species. Hedgerows partly offer a similar environment as forests and have been identified as potential habitats for forest plants in various studies from North America and Western Europe. The objective of this study was to examine whether this applies also to Central Europe and which variables affect the spatial distribution and abundance of forest plant species in hedgerows on a local scale. Three hedgerow networks north of the city of Bremen, Germany, were selected as study areas and divided into totally 515 hedgerow segments. In each segment we recorded all vascular plants and a large number of explanatory variables relating to structure, spatial configuration, environment and management. Averaged across species there was a predominant effect of environmental factors on the occurrence of forest species in the hedgerows, followed by spatial configuration and management. Hedgerow structure was found to be less important. In general, forest species were favored by low nutrient and light availability as well as high connectivity with other hedgerows or forest; they avoided hedgerows with a west-easterly orientation and an adjacent land use in the form of fields or grasslands. Forest species found and not found in hedgerows did not differ in their environmental preferences or life history traits. The number of threatened forest species in the hedgerows, however, was lower than expected with respect to their overall proportion to the total number of forest species in the region.     

西双版纳农田弃耕后橡胶园的建立对碳的固存作用

 由于温室气体的大量排放引起的全球气候变暖等环境问题日益严重,近年来人们开始考虑通过植被和土壤的碳固存,以缓解大气中CO2浓度的升高速度,减缓温室效应的影响。有研究表明,热带原始森林的保护和人工林的建立能有效地固存大气中的碳。但是,在建立热带种植园和人工林以固存大气CO2的可行性及其碳的固存潜力大小等方面还存在较大争议。云南省西双版纳自治州是我国重要的热带地区之一,目前橡胶(Hevea brasiliensis)园的面积为1.3×105 hm2,约占该地区林地面积的14%。在本研究中,选择11块在弃耕后的农田上建立的橡胶园（定植年限为3至38年）,初步探讨了橡胶园建立后植被和土壤中碳的固存规律。两个生物量模型（唐建维等的模型和Brown模型）的模拟结果显示,橡胶园建立后植被中生物量的平均增长速率分别为10.2×103和9.4×103 kg·hm-2·a-1,40和100 cm表层土壤碳的平均固存速率分别为0.61×103和0.72×103 kg C·hm-2·a-1,植被和100 cm表层土壤中碳的平均固存速率为5.82×103和5.42×103 kg C·hm-2·a-1,而定植40年后植被和100 cm表层土壤碳的固存潜力为232.8×103和216.8×103 kg C·hm-2。对两个模型的比较结果显示,唐建维等的模型生物量计算结果明显高于Brown模型,尤其是在对中幼龄橡胶园生物量估算时更是如此。     

Spatial Controls of Pre–Euro-American Wind and Fire Disturbance in Northern Wisconsin (USA) Forest Landscapes

We elucidate spatial controls of wind and fire disturbance across northern Wisconsin (USA), where climatic and topographic gradients are not strong, using data from the original US Public Land Survey (PLS) notes. These records contain information on the location and extent of heavy windthrows and stand-replacing fires prior to Euro-American settlement. The spatial patterns of windthrow and fire were spatially clustered at all scales in this historical environment, with stronger associations at local than regional scales. Logistic regression shows environmental variables to have a strong influence on this pattern. In the case of heavy windthrow, environmental drivers of disturbance pattern are fairly consistent across the region. The effects of climate and vegetation are predominant at all scales, but effects are often indirect, with strong interactions between them. Interactions between these two drivers and soil characteristics are also sometimes present. In contrast, models of stand-replacing fire show simple and direct control within and across fire-prone landscapes of historical northern Wisconsin, with climate and physiography as the main factors explaining the distribution of fire disturbance. This simple and direct control is lost at the regional scale, where climate, physiographic, soil, and vegetation variables, along with interactions between them, are significant factors. Contrary to other regions, the topographic effects are generally not important in predicting either wind or fire disturbance. Our work suggests that, in landscapes that lack strong environmental patterning, climate maintains its role as a primary driver of these natural disturbances, but topography is replaced by interactions and feedbacks with other forms of environmental heterogeneity.     

科尔沁沙地植被恢复演替进程中群落土壤种子库研究

研究了科尔沁沙地植被恢复演替进程中各群落土壤种子库种类组成、密度以及物种多样性等特征。主要结论是:①科尔沁沙地植被退化后的恢复演替是一种次生的中途恢复演替。演替各阶段土壤种子库密度为流动沙丘<半流动沙丘<固定沙丘,从流动到半流动沙丘阶段,土壤种子库密度平均增加了709%;从半流动到固定沙丘阶段,土壤种子库密度平均增加了393%。从流动到半流动沙丘阶段是土壤种子库密度的快速增长期。②植被恢复演替过程中,土壤种子库组成均以1年生草本植物为主(优势度为60.40%~91.83%),到演替中后期阶段,多年生草本植物的种类有所增加,但其所占比例仍很小。③演替各阶段群落种子库物种多样性指数分别为0.6616、0.7736、0.7281、1.0939、1.0648和0.9682,可见种子库物种多样性最高的群落并非是演替历史最大的群落。④恢复演替系列各阶段土壤种子库间的相似性系数都较大,在0.368~1.000范围之内,任一群落总是与其下一阶段最邻近的群落具有最高的相似性系数。     

The cause of mollusk decline on the Ogasawara Islands

Decline of land snails on the Ogasawara Islands was studied. In Hahajima, major alien predators such as Euglandina rosea and Platydemus manokwari are not present, but some small endemic snails, for example, Hirasea spp. and Ogasawarana spp., are already rare and more common endemic snails, for example, Mandarina spp., are also declining in the northern mountains. The decline cannot be directly explained by forest deforestation and by its subsequent regeneration. Three species of flatworms were found to eat small snails under captive conditions. The distribution of these flatworms is restricted to the northern mountains of Hahajima where Mandarina is declining and its survival is low. These predators are plausible candidates as a cause of the decline of the endemic snails.     

遥感探测土地植被覆盖指数的准确度评估

GIS数据的准确度一直是GIS应用的考虑事项。用虚例和实例揭示了土地植被覆盖指数的准确度与图像分类的准确度之间的复杂关系,并进一步用数学方式进行了解释。土地植被覆盖指数的准确度取决于图像分类准确度,但与分类总准确度没有直接关系。用户和产家准确度比总准确度对土地植被覆盖指数的准确度具有更直接的控制,所以在图像分类报告中不应被忽略为了保证土地植被覆盖指数的准确度,某土地类型的用户和产家准确度应该尽可能一致,同时要使得这两个准确度数值越高越好。     

六盘山林区几种土地利用方式下土壤活性有机碳的比较

 应用KMnO4氧化法测定分析了六盘山林区天然次生林（杂灌林、山杨（Populus davidanda）和辽东栎（Querces liaotungensis）林）、农田、草地和人工林（13、18和25年华北落叶松（Larix principis-rupprechtii））土壤活性有机碳含量及分配比例的差异。结果表明：农田和草地土壤活性有机碳含量比天然次生林分别低60%和36%,差异主要在0～70 cm土层;人工林比农田和草地分别高129%和29%,差异主要在0～50 cm土层。农田和草地土壤活性有机碳分配比例比天然次生林分别低11%和4%以上, 差异主要在0～20 cm与70～110 cm土层;人工林比农田和草地分别高13.3%和5.3%,差异主要在0～110 cm土层。土壤活性有机碳含量和分配比例随土层加深而递减,其中天然次生林和人工林土壤活性有机碳含量随土层加深而递减的幅度比农田和草地中大,农田土壤活性有机碳分配比例随土层加深而递减幅度较大。不同土地利用方式间土壤活性有机碳含量的差异比活性有机碳分配比例的差异大,土壤活性有机碳含量随土层加深而递减的幅度比分配比例随土层加深而递减的幅度大。这可能由土壤有机碳的输入、稳定性、质量和根系分布等差异所致。结果说明土壤活性有机碳含量和分配比例随天然次生林变成农田或草地而降低,随农田或草地中造林而增加,且土壤活性有机碳含量的变化幅度比分配比例大。另外,土壤活性有机碳含量和分配比例在土壤剖面的分布也随土地利用变化而改变,其中活性有机碳含量的变化幅度比分配比例大。     

中国第四纪冰期与陆生脊椎动物残留分布

在第四纪冰期中 ,中国东部地区是否发生过冰川 ,长期存在争议。中国东部地区冰川说的创始人李四光教授在提出该学说时 ,从古生物方面未得到冰期生物群的证据。现存生物种的地理残留现象可反映地质历史时期的气候变化。本文作者依据中国陆生脊椎动物的北方残留、热带 -亚热带残留、温带湿润带残留等现象 ,推断 :(1)在冰期的冷期中喜暖动物南迁时 ,中国东部地区是一避难地 ;(2 )在中国东部地区未见有典型冰川残留种的存在 ;(3)一些湿润种的间断残留分布与中国北方黄土及干旱气候的发展有密切的关系。此结论似不支持中国东部冰川说     

贵州省安顺市土地资源信息空间数据库的建立与应用

1　引　　言要制订不会危及环境的土地资源开发和保护计划 ,必须首先掌握可靠的、较新的有关土地资源的时空信息[3 ] .近年来 ,以ＧＩＳ和遥感技术为主的现代信息科学技术在土地覆盖/利用调查与填图[2 ,6] 、土地资源动态变化监测[13 ] 、土地质量退化与土壤侵蚀监测[5,8] 、土地资源评价[12 ] 与管理[10 ] 中得到了广泛应用 .这些技术可以较好地解决以往传统方法在获取、分析和处理大量、复杂土地信息中的众多限制 ,使我们得以动态地、综合地分析土地资源环境信息[4,7] .贵州省安顺市地处我国西南岩溶山区 ,生态环境脆弱 ,土地资源相对不足…