广西亚热带喀斯特岩溶石山区农业可持续发展道路探析——以平果县火龙果产业为例

针对广西亚热带喀斯特岩溶石山区的土壤、气候条件,对火龙果在喀斯特岩溶石山区发展条件进行适宜性分析,以广西平果县火龙果产业为例,对火龙果产业在平果的先天条件、发展规模、产值效益、市场前景以及火龙果对石漠化的治理作用等展开阐述,并根据调查中发现的火龙果产业发展遇到的石山地区土地流转难度大,栽培技术及苗木繁育基地未能满足发展需求、产业链短,产品附加值低等过程中一系列发展瓶颈,进行深入地分析探讨,有针对性地提出诸如实行区域布局、加快火龙果无病毒健康苗木基地的建立等对策建议。     

基于TM像元的湿地土地利用生态风险评价研究

为探讨人类活动对湿地土地利用生态风险的影响,以安徽省升金湖国家自然保护区为研究区,利用1986年、2002年、2011年TM遥感影像,将土地利用类型分为8类:建设用地、草地、耕地、林地、水域、未利用地、交通用地、园地,获取不同时期的土地利用变化信息,并结合社会经济等数据,以GIS为数据分析手段,通过多元线型回归及主成分分析,建立土地利用生态风险评价模型并将土地利用生态风险指数及社会经济因子予以像元化,分析升金湖湿地土地利用生态风险时空演变规律。结果表明:1986—2011年,升金湖地区耕地面积逐渐减少,建设用地和交通用地逐渐增加,受人类经济活动的影响,保护区土地利用生态风险不断上升,生态风险面积不断扩大,其中核心区和实验区变化剧烈,而缓冲区变化相对稳定。     

百山祖保护区低山常绿阔叶林的群落特征和α多样性

通过样地调查,对浙江百山祖自然保护区五岭坑低山常绿阔叶林群落的物种组成、群落结构、物种多样性进行研究。结果表明:1)群落内物种丰富,计33科58属124种,种类组成以冬青科、樟科、壳斗科、山茶科、蔷薇科、山矾科等为主,常绿阔叶树种104种3 040株,分别占种数和总株数的83.87%、98.51%,群落的树种组成反映了中亚热带常绿阔叶林植被的典型特征;2)群落幼树量大,自然更新良好。胸径与株数呈指数分布,立木径级分布连续,表明该群落处于成熟阶段。群落的平均胸径与密度之间存在负相关性;3)群落的Simpson指数、Gini均匀度指数、Pielou均匀度指数均较高,说明树种丰富,分布均匀,优势种不明显。     

Unreliable amphibian population metrics may obfuscate more than they reveal

Welsh et al. [Welsh, H.H., Jr. Pope, K.L., Wheeler, C.A., 2008. Using multiple metrics to assess the effects of forest succession on population status: a comparative study of two terrestrial salamanders in the US Pacific Northwest. Biological Conservation 141, pp. 1149–1160] argued for the use of four metrics to monitor population status of two terrestrial amphibians, the Siskiyou Mountains (Plethodon stormi) and Del Norte (Plethodon elongatus) salamanders. We show that inherent problems exist with Welsh et al.’s application of all four of these metrics, and that their inferences about population status are likely to be uncertain as a consequence and potentially misleading to managers. Welsh et al. (2008) used data from different populations and different years to estimate detection probabilities for both P. elongatus and P. stormi, a decision which assumes that detection probabilities do not differ across sites and populations are closed. In addition, Welsh et al. (2008) present count data for both salamanders, a metric that assumes capture probability does not vary by age, gender, size, other individual characteristics, and most importantly in their application, habitat characteristics. Welsh et al. (2008) estimated survival based upon age ratios. Age ratios are known to be biased when immigration and emigration are unequal Conn et al. [Conn, P.B., Doherty, P.F., Jr. Nichols, J.D., 2005. Comparative demography of New World populations of thrushes (Turdus spp.): comment. Ecology 86, pp. 2536–2541]. In source-sink systems, immigration and emigration are expected to be unequal. Thus, the use of this estimation technique to characterize survival in source-sink systems is invalid unless it can be shown that immigration and emigration are equal, a rare occurrence in source-sink systems. The final metric used by Welsh et al. (2008) was an index of body condition, i.e., the residuals of a least squares regression of mass on the length. Several recent articles have outlined a number of potential problems with the technique and a theoretically more robust and efficient alternative has been published. Unfortunately, Welsh et al. (2008) did not provide the details (model diagnostic statistics, tests of assumptions) needed to assess whether or not their analyses of body condition may be accurate. We think that evaluation of specific hypotheses, well-designed sampling programs, and methods such as mark–recapture and ratio sampling are more likely to provide reliable inference than re-analysis of old data sets that were collected for other purposes and obsolete methods (i.e., counting individuals on single occasions) that are known to be flawed. We agree that potential forest management impacts to sensitive taxa require evaluation and monitoring, and that changes in occupancy and abundance are useful metrics for this task (while recognizing that, when feasible to collect, information about reproductive success and survival is superior). However, reliable inference about potential impacts can only be made if reliable methods are employed and if critical assumptions receive empirical evaluation. We offer several suggestions to strengthen inference about management treatments.     

Importance of hedgerows as habitat corridors for forest plants in agricultural landscapes

Hedgerows have been proposed as habitat and conservation corridor for forest plant species, but their importance for the survival of these species is still not clear. The objective of our study was to examine the frequency of occurrence of forest species and total forest species richness in different parts of the hedgerows, and to relate these patterns of occurrence to the species’ habitat requirements and life history traits. We surveyed in total 130 forest-hedgerow transects in North-western Germany, including three age classes.About 77% of all forest plant species (including some endangered taxa) occurring in the neighbouring forests were also found in the adjacent hedgerows. In all age classes, there was a negative relationship between distance from the forest-hedgerow ecotone and the number of species. Ancient hedgerows were not significantly more species-rich than more recent ones. Within 100 m distance from the forest edge, forest species richness increased with an increasing number of species in the nearby forest and with an increasing cover of the tree canopy as well as a decreasing cover of the shrub layer. Species with high frequency had comparatively high Ellenberg indicator values for light, and were mostly associated with anemochorous and epizoochorous seed dispersal.The frequency of occurrence in hedgerows of species with common attributes was partly in agreement, partly in disagreement with the results obtained in previous studies. We conclude that patterns are difficult to generalize, probably due to a strong regional variation in the pool of forest species and in the specific environments of both forests and hedgerows.     

Conversion of a tropical forest into agroforest alters the fine root-related carbon flux to the soil

Large areas of remaining tropical forests are affected by anthropogenic disturbances of various intensities. These disturbances alter the structure of the forest ecosystem and consequently its carbon budget. We analysed the role of fine root dynamics in the soil carbon budget of tropical moist forests in South-east Asia along a gradient of increasing disturbance intensity. Fine root production, fine root turnover, and the associated carbon fluxes from the fine root system to the soil were estimated with three different approaches in five stands ranging from an old growth forest with negligible anthropogenic disturbance to a cacao agroforestry system with planted shade trees. Annual fine root production and mortality in three natural forest sites with increasing canopy openness decreased continuously with increasing forest disturbance, with a reduction of more than 45% between the undisturbed forest and the forest with large timber extraction. Cacao agroforestry stands had higher fine root production and mortality rates than forest with large timber extraction but less than undisturbed forest. The amount of carbon annually transferred to the soil carbon pool through fine root mortality was highest in the undisturbed forest and generally decreased with increasing forest use intensity. However, root-related C flux was also relatively high in the plantation with planted shading trees. In contrast, the relative importance of C transfer from root death in the total above- and below-ground C input to the soil increased with increasing forest use intensity and was even similar to the C input via leaf litter fall in the more intensively managed agroforest. We conclude that moderate to heavy disturbance in South-east Asian tropical moist forests has a profound impact on fine root turnover and the related carbon transfer to the soil.     

Proximity to a forest leads to higher honey yield: Another reason to conserve

Although tropical forest conservation is a top priority for human and environmental health, deforestation persists, mainly because of food and economic needs. No community will totally give up economic activities for the sake of ecological integrity, unless it is given alternative economic activities from which to draw its livelihood. Beekeeping in the forest buffer zone instead of traditional destructive honey-harvesting from forest trees is one such option at Arabuko Sokoke Forest (ASF) in Kenya. ASF is a dry coastal forest which is home to endangered and threatened fauna and is a hotspot considered a priority for conservation. In order to find out whether honey quantity and quality differed with distance from the forest, we studied honey yield per harvest (kg) and obtained samples from hives placed at varying distances from ASF in two successive years. Honey yield increased with proximity to the forest. Indeed the yield almost doubled in hives placed less than 1 km from the forest compared to those placed more than 3 km from the forest. All the honey samples met internationally required quality standards, although sugar levels were at the lower limit. This study demonstrates that the conservation of tropical forest ecosystems can have real local economic benefits. The documentation of the services provided by nearby natural areas should help make conservation of these areas a priority, even for the local communities.     

A variable edge effect on trees of Bwindi Impenetrable National Park, Uganda, and its bearing on measurement parameters

With tropical forests under increased pressure from fragmentation and nascent effects of climate change, it is imperative to reliably predict change for timely reduction of impacts. This depends on measuring the right variables and analyzing them in ways that best detect change. I compared the usefulness of density, species richness, species diversity, and size in detecting edge penetration; and other parameters in revealing edge effect on tree species in Bwindi Impenetrable National Park, Uganda. Trees were sampled in 104 1 km edge-interior transects set around the entire park. Density and species richness were better indicators of edge-width than girth size and diversity measurements, both showing edge penetration as most intense within 300 m, although effect was detectable up to 900-1000 m. This estimate compared closely with an earlier estimate of 300-350 m obtained using incidences of resource harvest. Among other measures, measures of tree species abundance and frequency showed significant response to the edge by both early succession and primary forest species; while analyses of density showed edge response primarily by forest interior species. Parameters of tree size and their derivatives showed edge response by the lowest number of species. These results suggest that to measure edge effects reliably, it is important to select the right parameters.     

A survey method for evaluating drought-sensitive bryophytes in fragmented forests: A bryophyte life-form based approach

Drought-sensitive bryophytes are especially vulnerable to edge effects caused by forest fragmentation. Because of increased forest fragmentation, these bryophyte species are declining and are in need of conservation. Considering that a field survey including all bryophyte species is very time consuming, methods that make identification less difficult should be tested for their usefulness in conservation. This paper describes an alternative survey method that utilizes the correlation between bryophyte life-forms and microclimates for evaluating drought-sensitive bryophytes. This survey method was examined using epiphytic bryophyte flora on tree trunks in 27 fragmented forests of Kyoto city, in the western part of Japan. The usefulness of life-forms for this evaluation was discussed based on the correlation of life-forms with species richness and microclimates. The results indicated that, while life-from richness was considered to reflect the heterogeneity of moisture availability and light intensity in bryophyte habitats, a certain life-form category (for example, fans and dendroids) seemed to correlate with drought sensitivity of bryophytes. Considering this correlation, an alternative survey method was proposed that utilizes the richness of hygrophilous life-forms. This survey method seems to be more cost-effective than a traditional all-species survey, and provides an important step toward the conservation of drought-sensitive species.     

Linking past land use, recent disturbance, and dispersal mechanism to forest composition

Many areas in north-eastern North America were historically cleared for agriculture and subsequently abandoned. The resulting woodlots are exposed to varying degrees of recent disturbance. This paper examines the contributions of land use history and recent disturbance on the species richness and community composition of wooded areas in an agricultural landscape. Woodlots were categorized according to land clearance history, past grazing, and recent disturbance, such as the presence of roads or selective cutting. Vegetation surveys resulted in the identification of 250 herbaceous plant species, 44 of which were classified as exotic. While no influence of recent disturbance on community composition was detected, past land use influenced species richness for all plant groups examined. General linear models indicated that herbaceous, native, and forest species richness was highest in historically partially cleared sites; while exotic and invasive species richness was greatest in historically cleared sites. Non-metric multi-dimensional scaling (NMS) ordination was used to identify associations between community assemblage, land use history, and dispersal mechanism. The two axes of the NMS ordination explained 79.2% of the variation in the data, and indicated that woodlots completely cleared in the past were associated with wind dispersed species indicative of disturbed habitats. In contrast, historically uncleared sites contained short-distance dispersed species indicative of rich woods. Although no effects of recent disturbance were detected, the long lived impacts of past land use and the increase of exotic and invasive species in historically cleared indicate that undisturbed woodlots should be considered of highest conservation importance.