宁夏引黄新灌区的开垦与昆虫类群的演替

1989～1991年对中宁县大战场和灵武县狼皮子梁的荒漠草原和垦后不久(约1～5年)的农田昆虫类群进行系统调查结果,鉴定出各类昆虫11目77科260种,其中属荒漠草原原生种88种、与农业共有种85种、农田继生种87种,其中荒漠区优势类群有伪步(虫甲)科、象(虫甲)科;荒漠垦殖后原生类群68.2%的种类消失,其余残存于田埂、渠岸、沟岸和较高的小片荒地上。     

浙江海岛砂生植被研究（Ⅰ）植被的基本特征

砂生植被在浙江海岛见于部分岛屿的砂质海岸，由砂生植物和部分耐砂植物组成。植物区系组成简单，约有野生维管植物２７１种，隶属于６７科１９１属。地理成分复杂，热带亲缘性明显。植被外貌整齐、低矮，季相变化明显，层次结构简单。植被分布因地区、岛屿、沙滩和立地而差异较大，具有明显的条带性。虽属隐域植被但地带性烙印清晰。植被演替外因于土壤质地、水分、盐分和有机质含量的变化，属外因生态演替。     

四川棉花病虫害发生及防治演替

根据四川棉花的特殊生态条件，通过对棉花主要病良生发展和动态防治技术进展分析，提出以推广良种，做好监测，科学用药，统防统治为重点的综合治理对策。     

Factors Responsible for the Co-occurrence of Forested and Unforested Rock Outcrops in the Boreal Forest

Rock outcrops in the boreal forest of Québec can show either of two different states: a forested state with >25% tree cover, and an unforested state (<25% tree cover). We tested three different hypotheses that might explain the co-occurrence of forested and unforested rock outcrops: (1) differences in bedrock geology, with unforested outcrops associated to bedrock types inimical to tree growth; (2) unforested outcrops as recently disturbed sites undergoing secondary succession towards a forested state; (3) unforested outcrops as an alternative stable state to forested outcrops, induced by post-fire regeneration failure. Digitized forest inventory maps were used along with bedrock geology maps and time-since-fire maps to compare forested and unforested outcrops for bedrock geology type and date of the last fire. Field surveys were conducted on 28 outcrops (14 forested, 14 unforested) to gather information regarding tree species composition and site characteristics (thickness of the organic matter layer, percent cover of lichens, mosses and ericaceous shrubs). None of the three hypotheses explain the co-occurrence of forested and unforested rock outcrops in the boreal forest of Québec. Both outcrop types occur on the same bedrock geology types. Unforested outcrops are not recently disturbed sites in early-successional states, as no clear distinction could be made in tree species composition and date of the last fire between the two outcrop types. Forested and unforested outcrops are not alternative stable states, as unforested outcrops are unstable and cannot maintain themselves through time in the prolonged absence of fire. Hence, unforested rock outcrops could be viewed as degraded, diverging post-fire types maintained by the late Holocene disturbance regime, characterized by high fire frequencies.     

小胡杨对滨海苏打盐渍土改良效果研究

滨海苏打盐渍土修筑台田后种植小胡杨可以成活,18年后小胡杨林分基本郁闭。以未种植树木的台田作为对照(CK),对小胡杨林地内植被演替规律、土壤水分物理性质进行研究。结果表明,小胡杨成林后,林地内植被向良性方向发展,群落生态型由中度耐盐群落演替成轻度耐盐群落,群落高度也由0.2～0.6 m增加到0.5～0.8m,盖度则达到80%～90%,土壤也由苏打盐渍土转变成轻盐碱土;小胡杨可显著降低土壤容重,改善土壤孔隙状况,增加土壤持水性能,使土壤水分物理性质得到显著改良,其中,对0～10 cm土层的改良效果要好于10～30 cm土层。     

退耕还林工程对米脂县农业生态经济演替过程的影响

"退耕还林工程"对区域农业生态经济系统演替过程产生了重要影响.通过对高人口密度区的米脂县退耕还林工程实施效果的分析,发现米脂县实施退耕还林工程10 a来,植被恢复明显,森林覆盖率较退耕前提高了13.85%;水土流失得到了有效治理,水土流失治理程度较退耕前提高了12. 73%;农民收人增加,思想观念、生产生活方式变化显著,区域产业结构优化,取得了明显的生态效益、经济效益和社会效益.这一实施效果也证明黄土丘陵区可以实现生态与经济的协调发展.     

Die invloed van bemesting op die spesiesamestelling en basale bedekking van beweide veld in die Potchefstroom‐omgewing

The impact of fertilization on veld in the Potchefstroom area was investigated. Nitrogen and phosphorus were applied annually from 1972/73 until 1981/82. The control plots and the fertilized plots were grazed with year‐old steers. Species composition and basal cover were recorded using the wheelpoint technique. The results clearly indicated the formation of a soil fertility gradient as a result of the fertilization. Although there was a decrease in the ecological status of the fertilized plots, the production and palatability of the sward increased and thus also animal performance.     

Pattern and Composition of Secondary Succession Beneath Caribbean Pine Plantations of Southwest Sri Lanka

This study examined the vegetation growing beneath Caribbean pine (Pinus caribaea) plantations established within previously abandoned tea lands adjacent to intact rain forest in southwest Sri Lanka. To examine the pattern and composition of secondary succession and factors affecting it, vegetation was sampled in different relative locations (interior and edge conditions) within plantations. Results demonstrated that more vegetation was found near the plantation edges than in the interior, and this pattern was prominent for both wind- and bird- dispersed species. The vegetation represented a mixture of species belonging to a range of successional guilds representing early (17 species, 42.4% in stem count) and late-successional species (52 species, 40.6%), although native long-lived canopy tree species were mostly absent. Bird-dispersed species dominated the flora (80 species, 86.7% in stem count). Abundance of an exotic shrub Clidemia hirta (Melastomataceae) showed a negative correlation with that of other species, indicating its impact on native flora. Underplanting of native canopy species may be effective in assisting secondary succession and control C. hirta in the plantations.     

Species Interactions in the Dynamics of Even- and Uneven-Aged Boreal Forests

Many boreal tree stands are neither clearly even-aged nor clearly uneven-aged. The stands may undergo a series of stages, during which an even-aged stand is transformed into two-storied mixed stand, and finally to multistoried or uneven-aged stand structure. The species composition often changes during the succession of stand stages. This study developed models for stand dynamics that can be used in different stand structures and species compositions. The model set consists of species-specific individual-tree diameter increment and survival models, and models for ingrowth. Separate models were developed for Scots pine, Norway spruce, and hardwood species. The models were used in a growth simulator, to give illustrative examples on species influences and stand dynamics. Methods to simulate residual variation around diameter increment and ingrowth models are also presented. The results suggest that mixed stands are more productive than one-species stands. Spruce in particular benefits from an admixture of other species. Mixed species improve diameter increment, decrease mortality, and increase ingrowth. Pine is a more beneficial admixture than birch. Simulations showed that uneven-aged management of spruce forests is sustainable and productive, and even-aged conifer stands growing on medium sites can be converted into uneven-aged mixed stands by a series of strong high thinnings.     

菌根真菌菌种的更替与其可持续性的研究

巨尾桉菌根化组培苗试验林中所接种的彩色豆马勃,已持续生存达10a之久;而接种的西澳粘滑菇、漆蜡蘑仅生存2～6a,之后则被其它菌根菌种所更替。自然条件下未经接种的的蓝桉人工林,造林后2～4a的林中以硬皮马勃、漆蜡蘑等菌根真菌为主;之后则先后由鸡油菌和牛肝菌所取代。松茸菌在适合的自然条件下可在林中生存达数十年之久,其持续性十分明显;人工接种松茸菌的云南松幼苗上,经6a的连续观察,菌丝体仍然生长旺盛。菌根真菌的菌种更替现象及可持续性与菌种本身的生长特性有关。若菌种能适应其环境条件,则生长可持续下去;反之则可能被其它菌种所更替,因此,菌根技术的推广应用,应坚持“适地适菌”和“适树适菌”的原则,方可取得持久的接种效果。