Distribution and diversity of leaf-cutting ants in Northeastern Argentina: species most associated with forest plantations

Abstract

Leaf-cutting ants (LCA) are considered one of the main herbivores and one of the most destructive pest insects of the Neotropics. Northeastern Argentina harbors the greatest species richness of these ants and in turn comprises the highest surface with forest plantations. Our aim was to establish which species of leaf-cutting ants are most commonly associated with forest plantations by analyzing their geographic distribution using published and unpublished species occurrence data. Also, estimate their potential areas of distribution along a latitudinal gradient that entirely encompasses northeastern Argentina using Ecological Niche Modeling. Only seven of the 20 species recorded were strongly associated with productive systems along the gradient, but only 2–3 species in each region could be considered high-risk species for forest plantations. High-risk species composition shows a turnover between regions. Our models show the potential distribution areas where LCA could become more abundant and dominant, and possibly causing a detrimental effect on the forest plantations in the studied region. We find that ecological niche models are useful tools to assess the environmental suitability of important LCA.     

秃杉人工林施肥效应试验初报

采用不同肥料种类和施肥剂量对秃杉人工林进行施肥对比试验。观测胸径、树高和蓄积生长量,分析不同肥料种类和施肥剂量对秃杉人工幼龄林高、粗和蓄积生长量的效应。试验结果表明,合理的施肥措施对秃杉人工林生长有明显促进作用,与对照相比,年高生长增加34%,粗生长增加26%,蓄积生长增加35%。     

不同栽培模式茶园黑刺粉虱发生规律

为明确北方茶园黑刺粉虱发生规律, 2016年—2017年于山东烟台系统研究了日光温室盖保温被?日光温室及露地3种栽培模式茶园黑刺粉虱发生规律?结果表明, 3种栽培模式茶园黑刺粉虱均以若虫在叶片背面越冬, 1年发生4代, 世代重叠严重?日光温室盖保温被栽培模式越冬代成虫羽化较日光温室和露地栽培发生早28 d左右, 日光温室和露地栽培模式下黑刺粉虱发生期差异不显著?3种栽培模式茶园黑刺粉虱成虫全年均有4次发生高峰期, 第1次高峰期日光温室盖保温被栽培模式较日光温室早20 d左右, 日光温室较露地早30 d左右?黑刺粉虱发生量依次为日光温室>露地>日光温室盖保温被, 均于10月上旬陆续以3龄若虫在叶片背面越冬?     

桑天牛自然种群生命表的初步研究

毛白杨幼林地桑天牛主要死亡因子为:卵寄生蜂寄生、啄木鸟啄食和林木折断或枯死后影响其生长发育等。经过一代自然种群生命表初步研究,结果其种群趋势指效为3.84.     

Factors affecting a sheep vegetation management system in British Columbia, Canada

A silvopastoral agroforestry system involving sheep is an important silvicultural issue. We examined the factors that affect the continuation or discontinuation of sheep vegetation management (SVM) in British Columbia. A questionnaire was used to conduct interviews with a randomly selected sample of contractors and farmers who were involved in SVM in British Columbia (BC). Based on a stepwise discriminant analysis, we found that the profitability of SVM, and the practitioners' commitment (number of ewes owned by the farmer or contractor), experience (number of years the farmer or contractor has practiced SVM on public lands in BC) and trust or confidence (number of years the farmer or contractor has consistently worked for the landlord) contributed to the farmer's or contractor's continuation or discontinuation of SVM practice. The factors we defined seemed to be validated (corroborated) by a complex of determinants voiced by various experts concerning the relationship between SVM and the forestry economy in BC, the scale of sheep farming in BC, the relative absence of an agricultural infrastructure to support sheep farming in BC, and the continuity of SVM from year to year. Further investigation into these factors and others is required to advance our understanding of SVM in British Columbia. This revised version was published online in June 2006 with corrections to the Cover Date.     

马尾松人工林施肥试验初报

本文通过对马尾松人工林施肥试验，表明在Ⅲ类地，适量施尿素和过磷酸钙可促进幼林树高、胸径生长。     

A Study on the Effects of Insect Pests and Diseases on Intensively Managed Plantations

Basedon the results of monitoring the environment of China National Afforestation Project (NAP) and the investigation on insect pests and diseases in 1.2 million ha of plantations, the author elaborates the areas, species and causes of insect pests and diseases occurring in the project's areas and provides fundamental theory for guiding environmental protection and plantation establishment in a sound way. Since the project's activities strictly follovved the guideline of environmental protection in past five years, little losses were caused by some commonly insect pests and diseases.     

Shade-based control of Imperata cylindrica: tree fallows and cover crops

Imperata is shade-intolerant, although little is known of the relative roles of competition for light, water and nutrients in suppressing its growth. Shading of Imperata results in reduced carbohydrate storage, reduced rhizome and tuber-bulb production, reduced shoot dry weight, increased susceptibility to competition, increased susceptibility to herbicides and decreased vigor/regeneration. Herbaceous cover crops in the genera Calapogonium, Crotoleria, Mucuna and Pueraria have been shown to effectively suppress Imperata growth and can be used to prevent and in some cases eradicate Imperata. Tree fallows with fast-growing species such as Sesbania sesban, Acacia nilotica and Leucaena leucocephala can improve soil physical and chemical properties and suppress weed growth. Forest plantations have been successfully used, particularly with the use of moderate to high tillage, weeding and fertilizer inputs to suppress Imperata growth. These plantations produce marketable wood and reclaim the site for other uses. Additional research is needed to evaluate the specific nature of competition and allelopathic effects from Imperata. Continued evaluation of tree species and provenances for Imperata suppression, forms of tillage after woody fallow crops and the constraints to adoption of cover crops and trees as Imperata control measures are also needed.     

Root exposure effects on water relations of Eucalyptus nitens nursery stock

Bare-root seedlings of Eucalyptus nitens frequently exhibit water stress after planting resulting in leaf lamina damage and reduced leaf area. Two trials examined effects of root exposure and desiccation between lifting and transplanting on post-planting water relations, leaf retention and root growth. Plants with roots exposed on a glasshouse bench initially lost water rapidly. In one trial ₁ declined to around –2.0 MPa within 2.5 h, after which there was no further change with exposure up to 7.5 h. In the second trial, the initial decline in ₁ was more rapid, reaching below –2.0 MPa in the first hour, before remaining stable with continuing exposure up to 4.5 h. A further decline then continued to –4.0 MPa after 7.5 h.Two days after transplanting into potting mix, day – time leaf water potentials in all desiccation treatments had declined to near –2.0 MPa. Hydraulic resistivity, measured as leaf specific resistivity two days after transplanting, increased following exposure for greater than 2.5 h, but there was no further increase between 4.5 and 7.5 h. The increase in resistivity corresponded with leaf water potential declining below –2.0 MPa during exposure.In the second trial, increasing root exposure time resulted in decreased leaf area due to lamina necrosis. Root growth, measured three weeks after planting, was also reduced. and there was also a positive curvilinear relationship between leaf area remaining at three weeks and new root growth. The results are discussed in terms of hardiness and the management of E. nitens seedlings from nursery to plantation.     

杉木人工林林分直径结构预测影响因子的研究

林分直径结构预测能为科学地进行人工林的定向培育提供可靠的理论依据。本文从生长方程等 4方面探讨了产生杉木人工林林分直径结构预测效果好坏的原因 ,并对两种参数估计方法作了实证比较研究 ,对影响预测适合度高低的原因从林分因子的角度进行了进一步的探索 ,得到如下实验结果 :不同的回收模型、建模材料、检验材料、生长方程对检验适合度的影响程度分别为具有极显著影响、显著影响、呈显著影响或极显著影响、无显著影响 ,当回收模型采用最简幂函数时 ,适合度均在 5 0 %以上 ,Richards生长方程预测效果较好 ,其 6种情形下的适合度仅有 1种低于 6 0 % ;参数预测法和参数回收法用于预测时检验适合度均较高 ,此 2种方法各有优劣 ,均具有很好的应用前景 ;林分初植密度不同于年龄、立地指数、间伐等因子 ,不同密度范围下的预测适合度大小总体上存在一定的规律 ,且对适合度具有显著影响 ,按密度因子作分类预测时 ,应考虑密度的这种突出效应。