人为干扰对鼎湖山马尾松林土壤细根和有机质的影响

通过处理 (根据当地习惯收割凋落物和林下层 )和保护 (无任何人为干扰 )样地的比较试验 ,1990～ 1995年期间研究了人为干扰对鼎湖山生物圈保护区马尾松 (Pinus massoniana)林土壤细根和有机质的影响。在此 5 a的研究期间 ,由于人为干扰活动而直接从处理样地取走的林下层和凋落物总量为 2 1.7t/ hm2。在保护样地 ,林下层生物量从 2 .2 t/ hm2增加至 11.10 t/ hm2 ,地表凋落物 (包括枯死的林下层 )量则从 3.0 t/ hm2 增加至 13.3t/ hm2 。收割林下层和凋落物这种人为干扰活动对林地土壤细根生物量的影响不明显 ,但却显著降低土壤轻腐殖质 (Soil lightorganic matter)量。在细根分解过程中 ,其分解速率在处理样地(试验结束时细根残存量占起始量的 4 0 .8% )显著高于在保护样地 (试验结束时细根残存量占起始量的 4 4 .3% ) ;与 Ca、Mg和K元素不同 ,N和 P两种元素的释放速率在处理样地显著高于保护样地 ,表明这种人为干扰活动不仅直接取走所收割的林下层和凋落物中的养分 ,而且还可能增加林地有效养分的流失潜力     

鼎湖山马尾松林植物养分积累动态及其对人为干扰的响应

 通过处理（根据当地习惯收割凋落物和林下层植物）和保护（无任何人为干扰）样地的比较试验,在10年时间里（1990～2000年）研究了鼎湖山生物圈保护区马尾松 (Pinus massoniana) 林群落植物养分积累动态及其对人为干扰的响应,在此基础上深入和较系统地分析讨论了不同的经营措施对马尾松林可持续性的影响,为我国目前大面积的退化马尾松林恢复和马尾松林可持续性管理提供理论依据。结果表明：1990～1995年,5年时间里由于人为干扰活动而直接从处理样地取走的各元素养分量,在林下层为（kg·hm－2）：132.72 (N)、4.72 (P)、63.32 (K)、23.51 (Ca)和7.00 (Mg),在地表凋落物为（kg·hm－2）：48.93 (N)、1.85 (P)、17.28 (K)、19.25 (Ca)和2.92 (Mg)。1990～2000年,保护样地林下层和地表凋落物各元素养分贮量分别以39%～41%和37%～38%的年平均增长速率逐年提高,至1995年达到高峰,之后各元素贮量在林下层和地表凋落物均以14%的年平均速率下降。在处理样地,1990～1995年期间各元素贮量在林下层年平均积累速率为17%,之后（1995～2000年期间）则为26%;与此同时,各元素贮量在地表凋落物年平均积累速率为22%～23%,之后（1995～2000年期间）则为28%。在整个试验过程,马尾松林乔木层养分元素总贮量随时间而增加,但其增加的速率随时间和样地不同而异。1990～1995年,保护样地乔木层养分元素总贮量增加了34.9%～38.1%,较处理样地（收获林下层和凋落物）总贮量增加的百分比（29.3%～33.5%）高。然而,1995～2000年,保护样地乔木层养分元素总贮量增加的百分比为26.3%～28.9%,较处理样地（1995～2000年也停止人为干扰）总贮量增加的百分比（28.8%～32.1%）低。可见,1990～1995年,人为干扰活动导致处理样地马尾松林乔木层养分元素年平均积累量降低约1.58%～1.72%,即年平均增长量约减少0.12～2.39 kg·hm－2（2.39 (N)、0.12 (P)、0.77 (K)、1.98 (Ca)、0.29 (Mg)）,这些量约相当于每年通过林下层和凋落物收割活动而直接从林地中取走的养分总量的6%～19%。正是由于长期以来受收割林下层和凋落物这种人为干扰的影响,鼎湖山马尾松林乔木层养分贮量较低。这种利用方式不仅直接从林地中取走大量的养分而且还对林地肥力产生间接的负面影响,其结果使该退化林地不能恢复或继续退化。作者建议的森林利用方法代替目前收割林下层和凋落物方式,既可以满足当地居民燃料的需求还有利于马尾松林的自然恢复。     

辽河源不同龄组油松天然次生林生物量及空间分配特征

油松是中国暖温带区域主要的森林植被,精确计算油松天然林生物量及准确表征空间分布特征对其在固碳释氧、林木积累营养物质等方面的生态服务功能评估具有重要意义。目前,国内基本上没有进行油松天然次生林生物量及空间分配在一个年龄序列上的研究。研究的主要目的是准确估算河北省平泉县辽河源自然保护区4个龄组油松天然次生林林分各组分的生物量,并揭示生物量在空间的分配特征。在每种林分内,林下植被层(灌木和草本)和凋落物层生物量通过样地调查和全挖取样的方法计算。基于胸径(DBH)和树高(H)的异速生长方程则用于计算乔木层生物量。结果表明:(1)林分生物量大小排序为:成熟林(397.793 t/hm2)近熟林(242.188 t/hm2)中龄林(203.801 t/hm2)幼龄林(132.894 t/hm2);(2)乔木层生物量成熟林(373.128 t/hm2)近熟林(224.991 t/hm2)中龄林(187.750 t/hm2)幼龄林(119.169 t/hm2)。地上部分各组分生物量大小关系略有差异,幼龄林和近熟林为:干根枝叶干皮球果,而中龄林和成熟林则是干根枝干皮叶球果。干生物量对于各龄组乔木层生物量来说是最大的贡献者,所占比例表现为:中龄林(66.25%)近熟林(64.38%)成熟林(62.09%)幼龄林(38.41%),而贡献较小的球果则是成熟林(1.02%)幼龄林(0.88%)近熟林(0.72%)中龄林(0.53%)。根系总生物量在18.315 t/hm2(中龄林)—44.849 t/hm2(成熟林)之间,其组分生物量大小整体上表现为:根桩粗根大根细根小细根;(3)灌木层生物量成熟林(0.861 t/hm2)近熟林(0.790 t/hm2)中龄林(0.559 t/hm2)幼龄林(0.401 t/hm2),各组分生物量大小为根茎叶;(4)草本层生物量幼龄林(3.058 t/hm2)近熟林(2.017 t/hm2)中龄林(1.220 t/hm2)成熟林(1.181 t/hm2),地下部分生物量均大于地上部分;(5)凋落物层生物量成熟林(22.623 t/hm2)近熟林(14.390 t/hm2)中龄林(14.272 t/hm2)幼龄林(10.265 t/hm2),各层生物量大小为:未分解层半分解层全分解层。(6)在各层次生物量的比较中,4个龄组均表现为乔木层凋落物层草本层灌木层。其中,幼龄林乔木层生物量占89.67%、中龄林占92.13%、近熟林占92.90%,成熟林占93.80%。     

黄土丘陵区主要林分生物量及营养元素生物循环特征

以黄土丘陵区子午岭为研究区域 ,用标准木法和收获法对暖温带森林优势群落辽东栎林、油松林及刺槐人工林的生物量、营养元素生物循环量及循环特征进行了研究。结果表明 :黄土丘陵区子午岭油松林、辽东栎林和刺槐人工林 3林分总生物量为 :86 .2 4 7、12 9.0 0 5 t/ hm2和 14 4 .795 t/ hm2 ,乔木层生物量分别为 :85 .2 2 3、12 6 .989t/ hm2和 14 2 .4 88t/ hm2 ,随群落针阔树种转化替代 ,群落总生物量呈现明显的增加趋势。年均生长量为 3.2 75～ 5 .6 99t/ hm2。生物量和年生长量排序为刺槐人工林 >辽东栎林 >油松林。 3林分林下植被层生物量、凋落物贮量表现为刺槐林 >辽东栎林 >油松林 ,林下植被层生物量的差异主要是由林分郁闭度和林下凋落物的不同引起的 ;刺槐林和辽东栎林林下植被层发达的根系和较高的凋落物量有利于提高土壤肥力、保持水土。同化器官的各种元素含量高于其它器官 ,茎中营养元素的含量最低。乔木层营养元素积累量分别为 :0 .74 5、1.378t/ hm2和 1.80 5 t/ hm2 。不同林分不同营养元素的积累量差别较大。因采伐而引起的 3林分林地养分流失量分别达 6 5 .4 5 %、5 3.76 %和 2 5 .1%。 3林分林下植被层和凋落物层的营养元素积累量排序为 :刺槐林 >辽东栎林 >油松林。凋落物营养元素贮     

人为干扰对鼎湖山马尾松林种群动态的影响

通过处理（根据当地居民习惯收割凋落物和林下）和保护（停止人为干扰,无任何人类活动）样地的比较在五年内（9190－1995年）研究了人为干扰对鼎湖山马尾松林植物种群动态的影响。结果表明,保护样地的林下层和灌木层盖度逐年上升,而处理样地相对较稳定。保护样地的草本层盖度略上升至1992年后,呈显著下降的变化,处理样地的变化则与保护样地的相反。保护样地的林下层植物种数逐年下降（从1990年的41种降至1995年的30种,减少11种）,处理样地变化不大（从1990年的36种降至1995年的34种,仅减少2种）。小径级（≤13cm)的马尾松胸径增长速率保护样地高于处理样地,且径级越小,增长速率越大,然而,径级大于13cm的植株,则没有显示出这种规律性的变化。以上现象表明,适度的人为干扰对稀疏马尾松林的自然更新及林下植物种类多样笥具有一定的维持或促进作用,但不利于马尾松的生长。同时对稀疏马尾松－灌木－草本群落在停止人为干扰后的演替途径作了预测和探讨。     

森林演替在南亚热带森林生态系统碳吸存中的作用

研究了鼎湖山南亚热带森林同一演替系列中3个不同演替阶段(马尾松针叶林、马尾松荷木混交林和季风常绿阔叶林)生态系统碳贮量和分配格局特征,并探讨了该地区森林演替过程中生态系统碳吸存潜力和速度。结果表明:(1)针叶林各组分碳素含量高于阔叶林对应组分的碳素含量(后者是前者的72.0%～94.5%)。两个森林植物碳素含量,不同层次比较,均为乔木层>灌木层>草本层,不同器官比较,以根或干最高。(2)乔木层生物量随森林演替进展而增加。针叶林、混交林和阔叶林乔木层生物量分别为:143.5t/hm2、270.1t/hm2和407.8t/hm2,其中大部分由干和皮组成(各器官占乔木层生物量的比例平均为:叶2.8%、枝19.3%、干和皮混合57.0%、根20.9%)。林下层生物量为4.23～14.10t/hm2,是乔木层的1.0%～9.8%,随森林演替进展而减少。(3)土壤容重随深度增加而增加,但随森林演替进展而减少。与土壤容重相反,土壤有机碳含量随深度增加而明显减少,但随森林演替进展而增加。(4)3种类型森林生态系统碳总贮量分别为135.8t/hm2、215.1t/hm2和259.7t/hm2。生态系统碳贮量在各组分的格局十分相似,植被、土壤和凋落物层所占比例均分别约为67.6%、30.2%和2.2%。与其它地带森林比较,鼎湖山保护区森林植被与土壤碳贮量之比和表层(0～20cm)的土壤碳占整个     

鼎湖山退化马尾松林、混交林和季风常绿阔叶林土壤全磷和有效磷的比较

土壤全磷和有效磷浓度的变化随林型和季节不同而异,总的来说,其大小顺序为:季风常绿阔叶林> 混交林>马尾松林(林型);夏季>冬季>春季>秋季(季节),有效磷浓度为:秋季>春季>冬季>夏季(季 节)。收割林下层和凋落物这种人为干扰活动对土壤全磷含量的影响不明显,但对土壤有效磷含量具有显著 的影响。在试验开始时(1990年5月),土壤全磷和有效磷浓度在马尾松林保护样地(停止人为干扰)和处理样 地(按当地习惯继续收割林下层和凋落物)间的差异均不显著。经七年多的试验后,土壤全磷浓度在保护样地 和处理样地间仍十分相似,但土壤有效磷浓度在保护样地显著高于处理样地,说明保护样地在停止人为干扰 后相对于继续受干扰的处理样地其林地条件得到了改善,从而使土壤有效磷含量也得到提高。只要停止人为 干扰,鼎湖山退化马尾松林土壤有效磷供应力是可以自然恢复到季风常绿阔叶林的水平。     

贵阳市区灌木林生态系统生物量及碳储量

采用直接收获法和实测数据,以贵州省贵阳市区天然灌木林内木本和草本植物、凋落物及土壤为研究对象,研究了灌木林生态系统的生物量、碳含量及碳储量。结果表明:灌木林植被层生物量为23.16 t/hm2,其中木本植物层生物量为12.46 t/hm2;草本植物层为3.74 t/hm2;凋落物层为6.96 t/hm2,分别占植被层生物量的53.08%、16.15%、30.05%。木本植物25种的碳含量范围为445.91—603.46 g/kg;草本植物6种的碳含量为408.48—523.04 g/kg;凋落物层碳含量为341.01—392.81 g/kg;土壤层碳含量为5.73—26.68 g/kg。生态系统总碳储量为88.34 t/hm2,其中植被层为8.10 t/hm2;凋落物层为2.56 t/hm2;土壤层为77.68 t/hm2,分别占系统总碳储量的9.17%、2.89%、87.94%。灌木林生态系统碳储量的空间分布格局为:土壤层植被层凋落物层。研究结果,可为喀斯特城市估算森林生态系统碳储量和碳平衡提供科学依据。     

鼎湖山马尾松林凋落物及其对人类干扰的响应研究

通过处理（根据当地习惯收割凋落物和林下层）和保护（无任何人类活动）样地的比较,在3年时间里研究了鼎湖山生物圈保护区马尾松（Pinus massoniana)林凋落物,养分动态及其对人类干扰的响应,处理和保护样地年平均凋落物总量分别为：2．388和2．342t/hm^-2.a^-1,它们主要由针叶组成（45．4％－78．8％）,皮＋枝占12．4％－14．4％,杂物8．6％－40．2％,凋落物量具有明显的年,季和月变化规律。尽管为人工起源的马尾松林,但其凋落物的空间分布很不均匀（变异系数＞22％）,凋落物中主要营养元素浓度因组分和季节不同而异,但总的趋势以杂物和春季的浓度最高。凋落物主要营养元素的归还量亦随季节和组分不同而异,其年平均归还总量为：处理样地N15.85kg.hm^-2.a^-1.P0.63kg.hm^-2.a^-1,K2.86kg.hm^-2.a^-1,Ca6.04kg.hm^-2.a^-1和Mg1.77kg.hm^-2.a^-1;保护样地N16．24kg.hm^-2.a^-1,P0.67kg.hm^-2.a^-1,k2.61kg.hm^-2.a^-1,Ca5.41kg.hm^-2.a^-1和Mg2.09kg.hm^-2.a^-1,当停止人为干扰后,凋落物产量及其养分归还量相对于继续受干扰的松林趋向逐年增加。     

海南岛北部木麻黄林凋落物与土壤养分、细根生物量的关系

通过对海口市桂林洋海岸木麻黄防护林地表凋落物进行持续清除处理,与保留凋落物层的对照样地进行比较实验,研究防护林凋落物-土壤养分-细根生物量三者之间的关系。结果表明:(1)处理样地与对照样地的年凋落物量分别是6.0162和5.9505t·hm-2,但无显著性差异。两种样地一年内凋落物量变化的时间格局较一致。凋落物组成均为小枝占比例最高,且小枝凋落物量月动态与凋落物总量月动态相似,杂物占比例次之,皮+枝占的比例最小;(2)N、P、K元素归还量的月动态变化在两样地中均较一致。两样地中小枝养分归还量的大小顺序为N>K>P;(3)处理样地在短时间无新鲜凋落物输入情况下,两样地的土壤养分含量无显著性差异;(4)两样地的细根生物量季节动态均呈现"单峰"特征,细根生物量在实验期间无显著性差异,但处理样地的细根生物量有随时间延长低于对照样地的趋势,清除凋落物的处理可能会引起细根生物量的减少。     

Ecological indicators for assessing ecological success of forest restoration: a world review

Restoration is increasingly being used to reverse degradation and destruction of forest ecosystems. With increasing investment in restoration, there is an urgent need to develop effective programs to assess treatment efficacy and effects. We conducted a global review of forest restoration assessments, in order to identify geographic trends in the locations where assessments have been implemented and the specific ecological attributes (ecosystem composition, structure, and function) and indicators being used to measure effects. We found that the number of forest restoration assessments varied by region and was not related to degree of degradation or restoration need. Some regions, like Africa, which have experienced high rates of forest loss and degradation, had few assessments. The majority (43%) of assessments included indicators for only two of three key ecological attributes (composition‐structure or composition‐function) and assessments on average used fewer than three indicators per attribute. The most commonly employed indicators for composition were richness and abundance of plant species and for structure were height and diameter of trees, variables that are generally relatively easy to measure. The use of functional indicators has been increasing over time and they are now more commonly used than structural indicators. The most common functional indicators were soil functions. Most investigators evaluated treatment effects for 6–10 years after implementation. Our findings related to gaps in analysis of ecological indicators can serve as a guide for developing monitoring and assessment protocols for current global forest restoration initiatives by 2020–2030.     

土地退化过程、机制与影响——以土地退化与恢复专题评估报告为基础

土地退化已成为威胁32亿人口福祉的全球性重大环境问题之一,近年来受到UN、IPBES、IPCC等组织的广泛关注。然而,当前的土地退化研究中,还存在概念不清、过程和机理不明、影响认识不彻底等问题,因此,厘清土地退化的概念、过程和机制是防止土地退化和恢复退化土地的关键。以生物多样性和生态系统服务政府间科学-政策平台（IPBES）土地退化与恢复专题评估报告为基础,剖析了土地退化的概念、过程、机制及影响：土地退化过程受自然环境和人类活动两大因素驱动,退化过程包括疑似退化、历史退化、敏感退化、弹性退化、持续退化和永久退化6种状态;土地退化类型可根据土地利用类型分为城市土地退化、农田退化、森林与草地退化、湿地退化等;土地退化具有多重影响,包括威胁食物和水安全,影响生物多样性及生态系统服务,引发地区冲突、大规模人口迁徙和疾病传播,加剧贫困及全球气候变化。土地退化过程、机制及影响的审视将为我国沙漠化、石漠化等土地退化的进一步研究提供理论指导,并为我国"山水林田湖草"土地系统的统筹治理和"美丽中国"、"生态文明"建设提供决策支持。     

Trend analysis of vegetation dynamics in Qinghai-Tibet Plateau using Hurst Exponent

As one of the most sensitive areas responding to global environmental change, especially global climate change, Qinghai-Tibet Plateau has been recognized as a hotspot for coupled studies on global terrestrial ecosystem change and global climate change. As an important component of terrestrial ecosystems, vegetation dynamic has become one of the key issues in global environmental change, and numerous case studies have been conducted on vegetation dynamic trend in different study periods. However, few are focused on the quantitative analysis of the consistency of vegetation dynamic trends after the study periods. In the study, taking Qinghai-Tibet Plateau as a case, vegetation dynamic trend during 1982-2003 were analyzed, with the application of the method of linear regression analysis. The results showed that, vegetation dynamics in Qinghai-Tibet Plateau experienced a significant increasing as a whole, with nearly 50% forest degradation in the study period. And among the 7 kinds of vegetation types, the change of forest was the most fluctuant with desert the least one. Furthermore, the consistency of vegetation dynamic trends after the study period, was quantified using Hurst Exponent and the method of R/S analysis. The results showed high consistency of future vegetation dynamic trends for the whole plateau, and inconsistent areas were mainly meadow and steppe distributed in the middle or east of the plateau. It was also convinced that, vegetation dynamic trends in the study area were significantly influenced by topography, especially the elevation.     

Effects of large-scale Amazon forest degradation on climate and air quality through fluxes of carbon dioxide, water, energy, mineral dust and isoprene

Loss of large areas of Amazonian forest, through either direct human impact or climate change, could exert a number of influences on the regional and global climates. In the Met Office Hadley Centre coupled climate-carbon cycle model, a severe drying of this region initiates forest loss that exerts a number of feedbacks on global and regional climates, which magnify the drying and the forest degradation. This paper provides an overview of the multiple feedback process in the Hadley Centre model and discusses the implications of the results for the case of direct human-induced deforestation. It also examines additional potential effects of forest loss through changes in the emissions of mineral dust and biogenic volatile organic compounds. The implications of ecosystem-climate feedbacks for climate change mitigation and adaptation policies are also discussed.     

Accelerating forest loss in Southeast Asian Massif in the 21st century: A case study in Nan Province,Thailand

Farmers are carving a new agricultural frontier from the forests in the Southeast Asian Massif (SAM) in the 21st century, triggering significant environment degradation at the local scale; however, this frontier has been missed by existing global land use and forest loss analyses. In this paper, we chose Thailand's Nan Province, which is located in the geometric center of SAM, as a case study, and combined high resolution forest cover change product with a fine‐scale land cover map to investigate land use dynamics with respect to topography in this region. Our results show that total forest loss in Nan Province during 2001–2016 was 66,072 ha (9.1% of the forest cover in 2000), and that the majority of this lost forest (92%) had been converted into crop (mainly corn) fields by 2017. Annual forest loss is significantly correlated with global corn price (p < 0.01), re‐confirming agricultural expansion as a key driver of forest loss in Nan Province. Along with the increasing global corn price, forest loss in Nan Province has accelerated at a rate of 2,616 ± 730 ha per decade (p < 0.01). Global corn price peaked in 2012, in which year annual forest loss also reached its peak (7,523 ha); since then, the location of forest loss has moved to steeper land at higher elevations. Spatially, forest loss driven by this smallholder agricultural expansion emerges as many small patches that are not recognizable even at a moderate spatial resolution (e.g. 300 m). It explains how existing global land use/cover change products have missed the widespread and rapid forest loss in SAM. It also highlights the importance of high‐resolution observations to evaluate the environmental impacts of agricultural expansion and forest loss in SAM, including, but not limited to, the impacts on the global carbon cycle, regional hydrology, and local environmental degradation.     

森林退化/衰退的研究与实践

森林退化可以理解为森林面积减少、结构丧失、质量降低、功能下降;森林衰退则是森林退化的一种形式,指森林（树木）在生长发育过程中出现的生理机能下降、生长发育滞缓、生产力降低甚至死亡,以及地力衰退等状态.国内外研究表明,森林采伐/毁林是造成森林面积减少的最主要原因,有关森林采伐/毁林引起的森林退化研究主要集中在森林退化的后果、国家/国际政策的影响、加强全球性合作以及寻求解决途径等方面.森林衰退原因可归纳为：工、农业污染,自然胁迫/致衰因子,林分动态发生变化,森林衰退病或生态病,人工纯林以及纯林连栽导致的地力、生产力衰退等.中国的森林退化/衰退现状与世界各地森林退化基本一致,但由于历史原因,中国森林退化又有其自身特点：近一个世纪的强烈人为干扰,使大部分原始天然林退化为次生林;中国拥有世界上最多的人工林,且多数人工林均具有质量差、功能低等衰退特征.本文在综述森林退化/衰退研究与实践基础上,提出中国现代森林退化/衰退的的主要原因,给出中国森林退化/衰退的基本对策.     

Evaluating the impacts of wood production and trade on bird extinction risks

Biodiversity loss can be accelerated by human consumption in regions that are far removed from habitat degradation because of economic globalization, but no study has directly quantified the effects of global trade on extinction risks at a global scale with consideration for species differences. We propose a novel biodiversity footprint index based on bird extinction risks to evaluate the effects of global wood production and trade on biodiversity. Using 536 endangered bird species threatened by wood harvesting and logging, we calculated the “quasi-extinction” probabilities, that is, the probabilities that population sizes become lower than an extinction threshold after habitat loss based on initial population sizes and forest habitat loss rates. We then used bilateral wood trade data to link the biodiversity impacts in wood exporters to wood importers. We found that if recent trends in forest cover loss continue until 2100, bird species in Brazil would be the most rapidly and heavily affected by wood production and trade, followed by those in Indonesia; these two countries alone would account for about half of all global bird extinctions. Large-scale wood importers (i.e., China, Japan, and the United States) significantly elevate overseas extinction risks and, simultaneously, reduce domestic impacts, indicating a heavy responsibility of these countries for global biodiversity loss. We also conducted a scenario analysis, which showed that the total projected number of extinct species would not decrease if each country produced the amount of wood materials necessary to meet current consumption levels. This is because bird extinction risks in tropical wood importers, such as Mexico and the Philippines, as well as Japan and China will increase if these countries increase domestic wood production. Our biodiversity footprint index is useful to identify countries whose bird species are highly affected by wood production and trade, and to quantify the role of wood trade in bird species extinctions. Additional scenario analyses are needed to establish effective patterns of wood production and consumption for bird biodiversity conservation.     

The structure and status of forest fragments outside protected areas in central Uganda

Given the extent of tropical forest deforestation and as a number of conservation programmes and local communities rely on forest fragments, it has become important to understand how fragment exploitation by local communities affects forest structure and function. The effects of forest exploitation on forest structure and status of forest fragments were investigated in 20 nonreserved forest fragments in central Uganda. Enumeration of plots showed that tree species composition of the forest fragments was 60.0%, 23.7% and 6.3% for under‐storey, middle and top canopy trees respectively. The major activity was fuel wood extraction (65%), followed by brick making (10%), cultivation and livestock paddocks (10%), charcoal burning (5%), local brew distillation and others (5%). These extractive processes caused drastic structural changes, habitat degradation and destruction. Tree stumps enumeration indicated that under storey trees formed the highest proportion for wood extraction. There was no significant difference in the level of forest exploitation (basal area loss) among forest patches of varying sizes.     

南亚热带森林不同演替阶段植物与土壤中N、P的化学计量特征

选择南亚热带森林演替过程3个阶段(初期、中期和后期)的典型森林生态系统为研究对象, 在测定植物与土壤中全N、全P含量的基础上, 阐明了森林演替过程中植物与土壤的N、P化学计量特征。结果显示: 1)土壤中全N含量随演替进行而增加, 马尾松(Pinus massoniana)林(初期)、混交林(中期)和季风林(后期) 0-10 cm土层中全N含量分别为0.440、0.843和1.023 g·kg^-1; 混交林0-10 cm土层中全P的含量最为丰富, 为0.337 g·kg^-1, 马尾松林和季风林土壤全P含量分别为0.190和0.283 g·kg^-1。2)植物叶片中全N、全P的含量随演替呈减少的趋势, 但根系中全N、全P的含量都以马尾松林为最多, 混交林和季风林含量彼此相当。3)各土层中N:P随演替的进行呈现明显增加趋势, 马尾松林、混交林和季风林0-10 cm土层中N:P分别为2.3、2.5和3.6; 植物各器官中N:P随演替的进行也呈增加趋势, 且叶片和根系中的N:P相近, 马尾松林、混交林和季风林叶片中N:P分别为22.7、25.3和29.6。基于上述结果, 探讨了南亚热带森林生态系统植物与土壤中N:P特征、森林演替过程中植物与土壤中N:P变化规律以及P对南亚热带森林生态系统的限制作用。结果表明, P已经成为南亚热带森林生态系统生物生长和重要生态过程的限制因子。