林下植被对半干旱区不同密度刺槐林地土壤水分环境的指示作用

 研究林下植被对不同密度林地土壤水分环境的指示作用,可以为造林营林中的密度调控、提高林分生产力和林分稳定性等,提供理论根据。为此,对山西黄土丘陵沟壑区的14年生人工刺槐(Robiniapseudoacacia)林6种造林密度(1.5m×2m、1.5m×3m、1.5m×4m、1.5m×5m、1.5m×6m、1.5m×7m)林分的土壤水分、林下光照强度等环境因子进行观测,同时,采用样方调查法,对不同密度林内的树木生长情况和林下植物的类型、数量、分布及发育状况进行了研究。结果表明:密度小的林分内,各小环境指标均优于密度大的林分,其中土壤水分、光照强度有显著的随林分密度增大而减小的趋势,刺槐林地内随着林分密度的增大,渐渐出现干旱、半干旱地区成龄人工林土壤干化的现象,林下植被的种类和数量相应减少,物种丰富度和物种多样性指数也降低,且逐步由以鹅观草(Roegneriakamoji),小菅草(Themedaminor)为典型的中生植物,向以角蒿(Incarvilleasinensis),灰绿藜(Chenopodiumglaucum)为典型的旱生植物过渡,反映出林分内的小环境条件随林分密度变化的特征。因此,在半干旱区造林和营林中,密度不可过大,以便提高林分生产力和林分稳定性。     

Mobile and readily available C and N fractions and their relationship to microbial biomass and selected enzyme activities in a sandy soil under different management systems

Within different land‐use systems such as agriculture, forestry, and fallow, the different morphology and physiology of the plants, together with their specific management, lead to a system‐typical set of ecological conditions in the soil. The response of total, mobile, and easily available C and N fractions, microbial biomass, and enzyme activities involved in C and N cycling to different soil management was investigated in a sandy soil at a field study at Riesa, Northeastern Germany. The management systems included agricultural management (AM), succession fallow (SF), and forest management (FM). Samples of the mineral soil (0—5, 5—10, and 10—30 cm) were taken in spring 1999 and analyzed for their contents on organic C, total N, NH₄⁺‐N and NO₃^—‐N, KCl‐extractable organic C and N fractions (Corg_(KCl) and Norg_(KCl)), microbial biomass C and N, and activities of β‐glucosidase and L‐asparaginase. With the exception of Norg_(KCl), all investigated C and N pools showed a clear relationship to the land‐use system that was most pronounced in the 0—5 cm profile increment. SF resulted in greater contents of readily available C (Corg_(KCl)), NH₄⁺‐N, microbial biomass C and N, and enzyme activities in the uppermost 5 cm of the soil compared to all other systems studied. These differences were significant at P ≤ 0.05 to P ≤ 0.001. Comparably high C_mic:C_org ratios of 2.4 to 3.9 % in the SF plot imply a faster C and N turnover than in AM and FM plots. Forest management led to 1.5‐ to 2‐fold larger organic C contents compared to SF and AM plots, respectively. High organic C contents were coupled with low microbial biomass C (78 μg g^—1) and N contents (10.7 μg g^—1), extremely low C_mic : C_org ratios (0.2—0.6 %) and low β‐glucosidase (81 μg PN g^—1 h^—1) and L‐asparaginase (7.3 μg NH₄‐N g^—1 2 h^—1) activities. These results indicate a severe inhibition of mineralization processes in soils under locust stands. Under agricultural management, chemical and biological parameters expressed medium values with exception for NO₃^—‐N contents which were significantly higher than in SF and FM plots (P ≤ 0.005) and increased with increasing soil depth. Nevertheless, the depth gradient found for all studied parameters was most pronounced in soils under SF. Microbial biomass C and N were correlated to β‐glucosidase and L‐asparaginase activity (r ≥ 0.63; P ≤ 0.001). Furthermore, microbial biomass and enzyme activities were related to the amounts of readily mineralizable organic C (i.e. Corg_(KCl)) with r ≥ 0.41 (P ≤ 0.01), suggesting that (1) KCl‐extractable organic C compounds from field‐fresh prepared soils represent an important C source for soil microbial populations, and (2) that microbial biomass is an important source for enzymes in soil. The Norg_(KCl) pool is not necessarily related to the size of microbial biomass C and N and enzyme activities in soil.<?show $6#>     

赤河上游森林植物群落物种多样性研究

赤水河流域上游国酒特殊水源保护区是水源涵养林工程重点地区之一.根据样地调查资料,运用4种常用的物种多样性指数对调查林分乔木层、灌木层和草本层的物种多样性进行研究,分析了该地区森林植物群落物种多样性的特征.结果表明:随着灌草群落阶段Ⅰ、灌丛群落阶段Ⅱ、灌木群落阶段Ⅲ、乔林群落阶段Ⅳ和次顶极群落阶段V的演替进展,群落高度逐渐增加,同时结构趋于复杂;各阶段灌木层较乔木层和草本层物种组成丰富、多样性高.Shannon-Wiener多样性指数、Margalef指数、Pielou指数的排序与物种数量的排序一致,Simpson指数则相反.乔林群落阶段Ⅳ的物种组成最复杂,适宜灌木和草本生长,为森林群落结构调整提供依据.总体而言,该区植物多样性指数不高,应采取合理森林经营及适度人为干扰措施,提高森林群落植物多样性,促进水源涵养和水土保持等功能的恢复.     

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.     

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.     

浙江舟山岛松材线虫入侵后松林群落的自然演替和特征

对舟山岛21个松材线虫病入侵前的马尾松林、黑松林进行典型样地调查,根据更新层树种的重要值采用模糊聚类结果划分为7种演替类群,与17年后对不同演替类群具代表性样地的复查结果比较分析,并综合群落的组成结构、动态特征、树种生态生物学特性、更新树种植株结构以及立地条件、海拔等因子,确定舟山岛松林近阶段的演替结果分别为白栎、枫香占优势的落叶阔叶林,枫香、白栎、苦槠或石栎、四川山矾、栓皮栎占优势的常绿落叶阔叶混交林,马尾松、黄檀、山合欢占优势的针阔混交林,枫香或朴树占优势的落叶阔叶林(疏林),白栎占优势的萌生灌丛和柃木占优势的常绿灌丛。研究结果说明松材线虫病发生迹地的植物群落自然演替具有一定的方向性和确定性。可针对松材线虫病为害后林分不同的演替趋势、立地条件和培育目的,应用本文的预测和林相修复技术及早采取封育、人工造林等措施恢复植被;同时,依据本文总结的演替规律,通过前期的调查和分类,可以较快推测和诊断出演替的过程和结果,从而及早在松材线虫病大面积发生后,根据不同的演替方向进行人工干预和规划。     

作物连作障碍的产生及防治

阐述作物连作障碍的定义,总结了作物连作障碍的发生原因和防治措施,并展望了今后的研究方向。     

滇东北铅锌矿区废弃地的自然演替特征研究

为探究矿区废弃地的自然演替特征,于2020年10月对滇东北两铅锌矿区废弃地进行植物群落调查和群落土样采集分析。结果表明:两区均受到较严重的重金属污染,土壤Pb、Mn、Zn、Cu和Cd的含量均超过相关背景值。其中,两区土壤Pb和Zn以及富乐镇矿区土壤Mn和Cd的有效态占比大体上都呈现随演替进行而降低的趋势,富乐镇矿区土壤Cu的有效态占比呈现随演替发生而先增后减的趋势,矿山镇矿区土壤Mn、Cu和Cd的有效态占比在不同演替阶段呈现不规则波动。两区土壤全氮随着演替的发生均呈现先增后减的趋势;两区土壤全磷含量变化趋势不同,矿山镇矿区呈现持续增加,富乐镇矿区则呈现先减后增;两区土壤有机质含量都呈现持续增加的趋势。在矿山镇矿区中,Pb和Zn、Pb和SOM呈极显著正相关性,Pb和TP、Mn和TN、Cd和TN、Zn和SOM、SOM和TN呈显著正相关性,Pb和Cu、Zn和Cu、Cu和SOM、Cu和TP呈显著负相关性。在富乐镇矿区中,Pb和Zn呈极显著正相关性,Zn和Mn、Zn和Cu、Zn和SOM、Pb和TP、SOM和TN呈显著正相关性,Pb和Cu、Zn和Cd、Cu和Cd呈显著负相关性。研究表明,矿区次生演替过程与废弃农田和灾后森林等生境的次生演替过程相似,土壤重金属元素的有效态会随演替发生而降低。研究结果可为矿区废弃地的自然恢复提供参考借鉴。     

森林生态系统研究进展

本文着重介绍近年来国外森林生态系统研究的动态和进展。对生物量积累及净生产量和它们的分配、生态系统的营养循环、生态系统的发育和演替三个主要方面的研究动态作了较详细的叙述。     

海南中部山区植被演变阶段植物物种多样性与群落结构多样性变化规律

以海南中部山区的草地、灌丛、次生林和原始林为演替系列,研究植被演替过程中群落结构多样性与物种多样性的变化规律。结果表明,群落演替过程中植物科属种数、总体Shannon-Wiener指数和Margalef指数、乔灌木层的Shannon-Wiener指数和Margalef指数及垂直结构多样性指数都显著增大;群落结构多样性指数分别与群落植物科属种数、总体alpha物种多样性指数、灌木层和乔木层物种alpha多样性指数都显著正相关。通过恢复演替,植被复杂性和质量都呈增大趋势。