Recovery process of a mountain forest after shifting cultivation in Northwestern Vietnam

The recovery process of fallow stands in the mountainous region of Northwestern Vietnam was studied, based on a chronosequence of 1–26-year-old secondary forests after intensive shifting cultivation. The number of species present in a 26-year-old secondary forest attained 49% of the 72 species present in an old-growth forest. Total stem density decreased gradually from 172,500 ha⁻¹ in a 3-year-old forest to 24,600 ha⁻¹ in the 26-year-old stand, but stem density of larger trees (diameter at breast height (D) ≥ 5 cm) increased from 60 ha⁻¹ in a 7-year-old to 960 ha⁻¹ in the 26-year-old forests, which was similar to that of an old-growth forest. Annual biomass increment of the 26-year-old stand was 4.2 Mg ha⁻¹ year⁻¹. A saturation curve was fitted to biomass accumulation in secondary forests. After an estimated time of 60 years, a secondary forest can achieve 80% of the biomass of old-growth forests (240 Mg ha⁻¹). Species diversity expressed by Shannon Index shows that it takes 60 years for a secondary forest in fallow to achieve a plant species diversity similar to that of old-growth forests.     

Recovery of Baikiaea forest of southwestern Zambia from shifting cultivation and its implications for sustainable management

We studied the dominant species by age category of re-growth, and how subsistence forest use through shifting cultivation impacted on the floristic composition of Baikiaea forest. For re-growth stands, variable sampling method was adopted in data collection while in mature stands, a sample plot size of 50 m 9 50 m was used at each of three study sites. Distribution of species by age categories showed that shrub, herb, and grass species were abundant in young re-growth stands while woody vegetation became common with increasing age of the re-growth stand. Hierarchical clustering for common woody species showed several species associations with age categories and also with relatively undisturbed woodland. Common regeneration mechanisms of key woody species were mainly by seed(48%), coppicing(40%) and root suckers(12%). The young re-growth stands of 6–10 and 11–15 years were characterized by B. petersiana, B.massiensis, Combretum zeyheri, and Guibourtia coleosperma. Older stands(16–20 years after abandonment) were characterized by B. plurijuga, Pterocarpus antunesii, and Baphia massiensis, thus closely mimicking the relatively undisturbed forest whose dominant key woody species were B. plurijuga, P. antunesii, and G. coloesperma. There were many stems in younger stands(2–5 years) and fewer stems in older re-growth stands of 16–20 years after abandonment following shifting cultivation. Older regrowth stands(16–20 years) were similar to undisturbed stands(P \ 0.005). The similarity between re-growth stands of 16–20 years and control stands demonstrates the recovery of Baikiaea forest over time after cessation of shifting agriculture. Baikiaea forest requires some disturbance to perpetuate the dominant species and begins to show signs of recovery from shifting cultivation within16–20 years after abandonment. This is contrary to assertions that this ecosystem could take up to about 100 years for abandoned fields to begin showing signs of     

Exploitation shifted trophic ecology and habitat preferences of Mediterranean and Black Sea bluefin tuna over centuries

During recent decades, the health of ocean ecosystems and fish populations has been threatened by overexploitation, pollution and anthropogenic-driven climate change. Due to a lack of long-term ecological data, we have a poor grasp of the true impact on the diet and habitat use of fishes. This information is vital if we are to recover depleted fish populations and predict their future dynamics. Here, we trace the long-term diet and habitat use of Atlantic bluefin tuna (BFT), Thunnus thynnus, a species that has had one of the longest and most intense exploitation histories, owing to its tremendous cultural and economic importance. Using carbon, nitrogen and sulphur stable isotope analyses of modern and ancient BFT including 98 archaeological and archival bones from 11 Mediterranean locations ca. 1st century to 1941 CE, we infer a shift to increased pelagic foraging around the 16th century in Mediterranean BFT. This likely reflects the early anthropogenic exploitation of inshore coastal ecosystems, as attested by historical literature sources. Further, we reveal that BFT which migrated to the Black Sea–and that disappeared during a period of intense exploitation and ecosystem changes in the 1980s–represented a unique component, isotopically distinct from BFT of NE Atlantic and Mediterranean locations. These data suggest that anthropogenic activities had the ability to alter the diet and habitat use of fishes in conditions prior to those of recent decades. Consequently, long-term data provide novel perspectives on when marine ecosystem modification began and the responses of marine populations, with which to guide conservation policy.     

Dynamics of soil chemical properties in shifting cultivation systems in the tropics: a meta‐analysis

The forest cultivation system (slash‐and‐burn or shifting cultivation) has contributed to the transformation of social systems since the early Neolithic period. Despite being considered by conservationists and public policymakers as a system of low productivity that generates environmental degradation and contributes to the maintenance of rural poverty, the shifting cultivation system (SCS) is being declared a practice that is highly ecologically and economically efficient. Such dichotomy of opinions is the consequence of the disparate results of studies assessing the effects of SCS on soil properties of rainforests throughout the last three decades. To circumvent this apparent inconsistency, we used a systematic quantitative review method (meta‐analysis), with the objective of integrating and synthesizing the data published in the literature to assess the overall effects of SCS on soil chemical properties. Four variables traditionally assessed in primary studies were chosen for the meta‐analyses: pH, cation exchange capacity (CEC), total carbon (Total C) and total nitrogen (Total N). Our results show that pH values increase under SCS conditions, while Total N and C content are significantly reduced under SCS. No significant impacts are observed on CEC. Our results on pH and CEC support the position from researchers who argue for the sustainability of SCS and highlight the importance of evaluating the soil system as a soil/vegetation complex. Also, our results indicate that soil chemical properties under SCS scenarios are better conserved and more readily recoverable, provided there is a rather longer fallow period than has been traditionally employed.     

中国主要农产品若干统计特征及发展趋势

选取1985～2008年以来全国主要农产品的若干指标进行统计分析，采用新型直观图法描述了一些指标的变化规律，划分了农产品指标发展的阶段。采用多因素前移回归法预测了2009年的第一产业增加值，进而从中得出若干启示和分析结论。     

Casuarina Coastal Forest Shelterbelts in Hambantota City, Sri Lanka: Assessment of Impacts

Growing of Casuarina equisetifolia as a small shelterbelt on the beach in Hambantotota City was implemented to protect the beautiful natural sand dunes, preserve visual amenity and be a barrier to seawater salt spray. The casuarina shelterbelt has become popular because it was the only undamaged area in Hambantota City after the devastating 2004 tsunami. The objective of the study was to assess the impacts of the casuarina shelterbelt in economic, social and environmental terms. A survey was conducted to elicit observations and experiences of city dwellers close to the shelterbelt. Respondents did not consider that the shelterbelt reduced wind speed. Although the belt has increased the size of the sand dunes, the casuarina trees have suppressed the growth of native species as an under-storey. The belt has improved the aesthetic value of the beach. No impact of the shelterbelt has been identified in protecting agricultural crops and reducing the corrosion of household goods from seawater salt spray. The city dwellers have not recognized the economic importance of casuarina timber but are impressed with the increase of fuelwood supply from the shelterbelt. The shelterbelt has prevented illegal settlement, but facilitated anti-social and illegal activities among lawless city dwellers. The attractiveness of the beach for tourism has been enhanced. Empirical evidence reveals that the casuarina belt in Hambantota City has greater environmental and social impacts than economic impacts.     

Extinction of a shark population in the Archipelago of Saint Paul’s Rocks (equatorial Atlantic) inferred from the historical record

Detecting and determining the validity of local extinctions is an important conservation measure in order to uncover management failures. There are quantitative and qualitative methods that estimate extinction probability based on past sighting records. However, because current baselines about species’ abundances and distributions in the sea were mostly established after humans had started affecting marine populations, researchers must often rely on historical data to elucidate past environmental conditions. We review early historical records from the Archipelago of Saint Paul’s Rocks, together with data from recent expeditions, with the aim of testing the hypothesis that reef sharks (Carcharhinus spp.) have become extinct there. Our analyses are based on non-parametric probabilistic tests for extinction and on a qualitative framework to examine and judge as objectively as possible the likelihood of local extinction. Until the mid-20th century, visitors to St. Paul’s Rocks invariably commented on the remarkable number of sharks around the Archipelago. These observations contrast with those of expeditions carried out during the last decade, which report no carcharhinid reef sharks while scuba diving in the archipelago, despite many more hours of underwater fieldwork than previous expeditions. All quantitative and qualitative methods conclude that the reef shark Carcharhinus galapagensis is locally extinct at St. Paul’s Rocks after a sharp decrease in abundance that took place following the commencement of fishing. However, the persistence of occasional individuals of the once locally common Carcharhinus falciformis in the vicinity of the Archipelago, as a result of constant immigration of this oceanic species from outside the area, suggest that the population might recover if the present fishing pressure was removed.     

Demographic response and life history of traditional forest resource tree species in a tropical mosaic landscape in Papua New Guinea

Disturbance is well known to play an important structuring role in rainforest succession and in maintaining overall diversity. However, the ecological responses arising from changes in land use such as traditional and modified shifting cultivation practices are less well known. The distribution and dynamics of plant populations may be affected by such changes in land use and often their responses are compounded by a lack of life history data. The life history traits and demographic parameters important to successional species responses to disturbance remain poorly understood beyond broad generalisations, particularly in rainforests outside of the Neotropics. We examined the life history and demography of five rainforest tree species in Papua New Guinea to investigate the effect of shifting cultivation practices on their population dynamics. The demographic parameters most successful for continued population growth were medium to high recruitment, low seedling mortality and high seedling abundance, relatively low growth rates (compared to many pioneer species) and moderate to high abundance in all life stages. Successful life history traits were high seed mass, moderate shade-tolerance and high cultural value. In accordance with their demographies and life histories, Pterocarpus indicus, Vitex cofassus and Artocarpus altilis were classified as early successional species, while Pometia pinnata and Canarium indicum were considered mid-successional. The results suggest that the earlier successional species do not necessarily have an advantage in disturbed environments; persistence is more likely to rely on the response of inherent demographic processes to external influences.     

农村剩余劳动力转移障碍分析

农村剩余劳动力转移过程中存在诸多障碍。农村经济发展滞后不利于本地转移,城市就业形势严峻阻碍了异地转移,农村劳动力综合素质限制了就业范围,制度性因素则制约了劳动力市场健康发展。     

不同防治方式下靶标农药沉积量比较

[目的]明确热雾机热雾滴的有效沉积量,分析热雾滴在作物上的有效附着量。[方法]研究了3种施药机具(喷雾器、热雾机和弥雾机)的雾滴田间分布效果,并测定了3种施药方式下油菜叶片上的多菌灵含量。[结果]热雾机的雾滴在载玻片上分布比喷雾器和弥雾机均匀,热雾机防治有效距离为25 m以上,正、背面热雾粒数量分别在204～263和83～93滴/cm2。热雾机施药叶片上多菌灵含量介于喷雾器和弥雾机,下部叶片多菌灵含量达28.569 6 mg/L,高于喷雾器和弥雾机;热雾机施药土壤中多菌灵沉积量为39 176.36mg/hm2,低于喷雾器和弥雾机。[结论]热雾机作为高效、清洁的植保施药器械有广阔的利用前景。