Forest Transition in Xishuangbanna,Yunnan

Forest transition is a process of overall forest cover from net loss to net gain over time. Forest transition especially the process after turning point from deforestation to reforestation has inspired lots of researches for its potential to improve environmental services. China has undergone forest transition since the 1980s. However, in tropical China, deforestation was still existed, while the overall forest cover increased greatly. To investigate this issue, we conducted this research by classifying overall forest into natural forest and plantation in Xishuangbanna, which has undergone forest transition and deforestation and overall forest cover increasing. We found that natural forest continues decreasing while overall forest cover increasing and plantation expansion in forest transition. The forest transition in Xishuangbanna was found to be a tree cover transition, which was mainly contributed by large plantation expansion. In Xishuangbanna, deforestation is still undergoing after its overall forest cover transition occurred in 1988. The general overall forest definition used by forest transition will not be able to recognize deforestation when natural forests are displaced by plantations because the overall forest cover remains unchanged or even increasing. We therefore recommended to classify forest types in forest transition researches.     

Glacial bottleneck and postglacial recolonization of a seed parasitic weevil, Curculio hilgendorfi, inferred from mitochondrial DNA variation

Climatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in the warm temperate zone. We investigated phylogeographical patterns of a weevil Curculio hilgendorfi (Curculionidae), a host-specific seed predator of Castanopsis (Fagaceae) growing in the broadleaved evergreen forests in Japan. We examined 2709 bp of mitochondrial DNA for 204 individuals collected from 62 populations of the weevil. Four major haplogroups were detected, in southwestern and northeastern parts of the main islands and in central and southern parts of the Ryukyu Islands. The demographic population expansion was detected for the two groups in the main islands but not for the Ryukyu groups. The beginning time of the expansion was dated to 39 000–59 000 years ago, which is consistent with the end of the last glacial period. Our data also demonstrated that the southwestern population of the main islands has experienced a more severe bottleneck and more rapid population growth after glacial ages than the northeastern population. At least three refugial areas in the main islands were likely to have existed during the last glacial periods, one of which had not previously been recognized by analyses of intraspecific chloroplast DNA variation of several plant species growing in the broadleaved evergreen forests. Our results represent the first phylogeographical and population demographic analysis of an insect species associated with the broadleaved evergreen forests in Japan, and reveal more detailed postglacial history of the forests.     

不同龄级速生杨人工林土壤微生物数量与养分动态变化

通过稀释平板法和常规化学分析法, 对伊犁河谷地区3种龄级(5年、10年、15年)的速生杨欧美黑杨(Populus × euramericana)人工林的土壤微生物数量、组成和土壤养分变化进行了研究。结果表明, 3种不同林龄林地土壤微生物集中分布在10-40 cm土层, 数量和种类组成随季节变化有明显差异。随着林龄的增长, 土壤微生物总数、细菌数量减少, 真菌和放线菌数量在10年生人工林最高, 这一规律随季节变化。三大类土壤微生物的组成比例相对稳定, 不随季节变化而变化。土壤有机碳、氮含量主要集中在0-20 cm土层, 随土壤深度的增加逐渐减少, 其含量及分布受季节和土壤深度不同程度的影响。土壤有机碳含量随林龄的增长而逐渐增高, 有机氮则先减后增。相关分析表明, 土壤微生物总数与土壤有机碳呈负相关, 真菌数量与土壤有机氮呈正相关。3种林地土壤有机C/N比与土壤细菌数量/真菌数量比例一致, 说明速生杨人工林在一定生长年龄内能提高土壤的固碳能力, 改善土壤肥力。     

利用氮同位素技术探讨天津地表水氮污染

地表水的氮污染状况与水质、区域景观等密切相连。本文分析了天津地表水的三氮(NO3-N、NH4+-N、NO2-N)组成,以及部分水样NO3-N和NH4+-N的N同位素组成。结果显示:NO3-N的含量为0.01～16.51mg.L-1,均值为2.25mg.L-1,部分样品NO3-的含量超过50mg.L-1(以NO3-N计为11.29mg.L-1);NH4+-N的含量为0～10.60mg.L-1,均值为1.15mg.L-1,有1/4水样超过1.5mg.L-1;另外,在所有样品中有1/12水样有较高的NO2-N。NO3-N为大部分水样无机氮的主要形态,污水等部分水样以NH4+-N为主要形态。NO3-N同位素值的变化范围为-5.5‰～+28.6‰,均值为+9.0‰(n=49),中值为+8.5‰;NH4+-N同位素值的变化范围为-8.8‰～+34.3‰,均值+11.6‰(n=11),中值为+13.6‰。水化学和同位素结果分析表明,该区地表水的氮主要来源为生活污水,而且氮形态转化受硝化作用、挥发作用以及可能的反硝化作用影响明显。     

氮添加和采脂对湿地松林土壤酶活性及酶化学计量比的影响

大气氮沉降和采脂会引起树木生长和代谢的变化,从而影响土壤养分循环和酶活性.土壤酶和酶化学计量可以揭示土壤碳、氮循环和微生物生长代谢过程的养分限制,但目前亚热带湿地松人工林土壤酶和酶化学计量对氮添加和采脂的响应还不清楚.以亚热带北缘的湿地松人工林为研究对象,设置采脂(resin tapping,RT)和未采脂(no re...     

剔除灌草和添加翅荚决明对厚荚相思林土壤温室气体排放的影响

森林土壤是CO₂、CH₄和N₂O等温室气体的主要排放源.本研究采用静态箱/色谱分析技术,对中国科学院鹤山丘陵综合开放试验站内厚荚相思林土壤CO₂、CH₄和N₂O通量进行原位测定,研究剔除林下灌草和添加翅荚决明对土壤温室气体排放的影响.结果表明：厚荚相思林土壤CO₂通量在湿季维持较高水平,在旱季则明显降低.CH₄和N₂O在9-11月波动幅度较大,峰值出现在10月.在不同处理下,厚荚相思林土壤可能是CH₄的源也可能是CH₄的汇,而于CO₂和N₂O则是源.林下剔除灌草能显著增大土壤CO₂排放(P<0.05),而添加翅荚决明能加快土壤CH₄的排放(P<0.05).林下剔除灌草及添加翅荚决明两种处理都能够加大N₂O的排放通量.表层土壤温度、湿度、NO₃^--N和微生物生物量碳都是影响土壤温室气体排放的重要因子.     

The importance of pre-thicket conifer plantations for nesting Hen Harriers Circus cyaneus in Ireland

Hen Harriers Circus cyaneus are threatened across much of their range and their conservation requires appropriate habitat management. The locations of 148 Hen Harrier nests found in the Republic of Ireland during national breeding surveys in 2000 and 2005 were used to assess nest-site selection. The distribution of these nests was compared to distributions of randomly located points to investigate selection at the scale of the nest-site and landscape. The main nesting habitats selected were pre-thicket stage of first and, particularly, second rotation plantations, mostly of exotic conifers. There was no evidence that the area of post-closure plantations negatively affected Hen Harrier nest distribution. There was a positive correlation across study areas between changes in numbers of Hen Harrier nests between 2000 and 2005 and changes in the area of pre-thicket second rotation plantations over the same period. The overall effect of plantation forests on breeding Hen Harriers in Ireland therefore appears to be positive. However, this study did not consider the effects of plantation habitats on breeding success. Improved grassland was strongly avoided as a nesting habitat. Furthermore, after controlling for the influence of nesting habitat on nest location, landscapes with a high percentage cover of improved grassland were also avoided. Further agricultural intensification of grassland in areas where Hen Harriers breed is likely to have a negative impact on this species. These results are required for the development of management strategies for the conservation of this species.     

Increased Litter Build Up and Soil Organic Matter Stabilization in a Poplar Plantation After 6 Years of Atmospheric CO2 Enrichment (FACE): Final Results of POP-EuroFACE Compared to Other Forest FACE Experiments

Free air CO₂ enrichment (FACE) experiments in aggrading temperate forests and plantations have been initiated to test whether temperate forest ecosystems act as sinks for anthropogenic emissions of CO₂. These FACE experiments have demonstrated increases in net primary production and carbon (C) storage in forest vegetation due to increased atmospheric CO₂ concentrations. However, the fate of this extra biomass in the forest floor or mineral soil is less clear. After 6 years of FACE treatment in a short-rotation poplar plantation, we observed an additional sink of 32 g C m⁻² y⁻¹ in the forest floor. Mineral soil C content increased equally under ambient and increased CO₂ treatment during the 6-year experiment. However, during the first half of the experiment the increase in soil C was suppressed under FACE due to a priming effect, that is, the additional labile C increased the mineralization of older SOM, whereas during the second half of the experiment the increase in soil C was larger under FACE. An additional sink of 54 g C m⁻² y⁻¹ in the top 10 cm of the mineral soil was created under FACE during the second half of the experiment. Although, this FACE effect was not significant due to a combination of soil spatial variability and the low number of replicates that are inherent to the present generation of forest stand FACE experiments. Physical fractionation by wet sieving revealed an increase in the C and nitrogen (N) content of macro-aggregates due to FACE. Further fractionation by density showed that FACE increased C and N contents of the light iPOM and mineral associated intra-macro-aggregate fractions. Isolation of micro-aggregates from macro-aggregates and subsequent fractionation by density revealed that FACE increased C and N contents of the light iPOM, C content of the fine iPOM and C and N contents of the mineral associated intra-micro-aggregate fractions. From this we infer that the amount of stabilized C and N increased under FACE treatment. We compared our data with published results of other forest FACE experiments and infer that the type of vegetation and soil base saturation, as a proxy for bioturbation, are important factors related to the size of the additional C sinks of the forest floor–soil system under FACE. Author Contribution: MRH conceived of and designed the study, performed research, analyzed data, and wrote the paper; GES conceived of and designed the study and performed research.     

Change in CO2 balance under a series of forestry activities in a cool-temperate mixed forest with dense undergrowth

To evaluate the effects on CO₂ exchange of clearcutting a mixed forest and replacing it with a plantation, 4.5 years of continuous eddy covariance measurements of CO₂ fluxes and soil respiration measurements were conducted in a conifer-broadleaf mixed forest in Hokkaido, Japan. The mixed forest was a weak carbon sink (net ecosystem exchange, −44 g C m⁻² yr⁻¹), and it became a large carbon source (569 g C m⁻² yr⁻¹) after clearcutting. However, the large emission in the harvest year rapidly decreased in the following 2 years (495 and 153 g C m⁻² yr⁻¹, respectively) as the gross primary production (GPP) increased, while the total ecosystem respiration (RE) remained relatively stable. The rapid increase in GPP was attributed to an increase in biomass and photosynthetic activity of Sasa dwarf bamboo, an understory species. Soil respiration increased in the 3 years following clearcutting, in the first year mainly owing to the change in the gap ratio of the forest, and in the following years because of increased root respiration by the bamboo. The ratio of soil respiration to RE increased from 44% in the forest to nearly 100% after clearcutting, and aboveground parts of the vegetation contributed little to the RE although the respiration chamber measurements showed heterogeneous soil condition after clearcutting.     

不同林龄杉木人工林土壤团聚体磷素分布特征

探究不同林龄杉木人工林土壤团聚体各形态磷素的分布特征有利于提升杉木人工林土壤磷素有效性。本研究选取位于广西融水县的幼龄(9 a)、中龄(17 a)、成熟(26 a)杉木人工林和邻近撂荒地(CK),利用干筛法将采集到的表层(0～20 cm)原状土壤分为4个粒级团聚体(>2、1～2、0.25～1和<0.25 mm),测定各粒级团聚体中不同形态磷组分。结果表明: 1)不同林龄杉木人工林土壤团聚体组成差异显著,CK和各林龄杉木人工林中>2 mm粒级团聚体含量显著较高,随林龄的增长先增后减,在17 a时最高;土壤平均重量直径(MWD)和几何平均直径(GMD)的变化趋势与>2 mm粒级团聚体一致。2)CK和各林龄杉木人工林中各粒级土壤团聚体全磷、无机磷和有机磷含量差异均不显著,而土壤有效磷含量在>2 mm粒级团聚体中显著较高,达1.23～7.33 mg·kg^-1;不同林龄杉木人工林土壤团聚体及全土全磷、有效磷和无机磷含量均显著高于CK,并随杉木林龄的增长先增后减,全土总磷和有效磷含量在9 a时最高,分别为322.40和7.33 mg·kg^-1,全土无机磷含量在17 a时最高,为114.05 mg·kg^-1;全土有机磷含量随杉木林龄的增长先增再减再增,在9 a时最高,为210.00 mg·kg^-1。3)不同粒级土壤团聚体磷储量与土壤团聚体组成比例显著相关。CK和各林龄杉木人工林中>2 mm粒级团聚体各形态磷储量较高。除有机磷外,各形态土壤磷储量均随杉木林龄的增长先增后减。综上,林龄17 a之前,杉木人工林的种植有利于提升土壤团聚体稳定性,促进土壤磷素水平的提升;林龄17 a后,>2 mm粒级团聚体的破碎导致土壤团聚体稳定性和土壤磷素供应水平逐渐下降。因此,在杉木人工林培育栽种17 a以后应重视土壤中>2 mm粒级团聚体的保护,以保障土壤质量,维持土壤供磷水平。