北京八达岭地区典型林分林地土壤抗蚀性分析

2016-09-21 00:39周玮查同刚孙怀宁黄俊威杨瀚
中国水土保持科学 2016年4期
关键词:油松林灌木林阔叶林

周玮,查同刚†,孙怀宁,黄俊威,杨瀚

(1.北京林业大学水土保持学院,100083,北京; 2.林业生态工程教育部工程研究中心,100083,北京)



北京八达岭地区典型林分林地土壤抗蚀性分析

周玮1,2,查同刚1,2†,孙怀宁1,2,黄俊威1,2,杨瀚1,2

(1.北京林业大学水土保持学院,100083,北京; 2.林业生态工程教育部工程研究中心,100083,北京)

为研究八达岭地区不同森林植被对土壤抗蚀性的影响,揭示不同林分林地土壤抗蚀性特征,以该地区典型植被类型(油松林、针阔混交林、阔叶林和灌木林)为研究对象,运用主成分分析及相关分析方法,研究该区域内,不同林分类型土壤的抗蚀性。结果表明:八达岭地区林分林地土壤干筛时,团聚体主要集中于5~2 mm粒径范围内,在0.5~0.25 mm粒径范围内质量分数最少;湿筛后,<0.25 mm小粒径范围内质量分数最大,在10~5 mm大粒径范围内质量分数最少。为比较各典型林分林地土壤抗蚀性,选取土壤理化性质、土壤团聚特征等12种指标,以主成分分析方法为基础,确定评价北京八达岭地区土壤抗蚀性的最佳指标体系,同时,经相关分析选定干筛时,土壤几何平均直径(GMD)为八达岭地区各典型林分林地最佳土壤抗蚀指标。经分析,八达岭地区各典型林分土壤表层(0~10 cm)抗蚀性由强到弱依次为阔叶林>灌木林>针阔混交林>油松林;对于主要发生土壤侵蚀的0~20 cm土壤表层抗蚀性由强到弱为灌木林>油松林>阔叶林>针阔混交林;在各土层平均值综合情况下,评价结果选取抗蚀性综合指数表示,得出各林地土壤抗蚀性由强到弱依次为灌木林>油松林>针阔混交林>阔叶林。

林地土壤; 土壤团聚体; 土壤抗蚀性; 八达岭地区

土壤侵蚀不仅会引起土壤质量的下降,还会带来水体富营养化等一系列生态环境问题,如地表径流挟带土壤氮进入水体,是造成水体面源污染的主要途径之一[1-2]。地表植被通过调节凋落物输入、热量与水分分配和土壤微生物类群与活动等途径,影响林地土壤层的抗侵蚀能力和侵蚀过程。土壤抗蚀性是指土壤抵抗水分散和悬浮的能力[3],是评定土壤抵抗侵蚀能力的重要参数之一,且与土壤理化性质等内在因素密切相关[4-9];此外,土壤抗蚀性大小,还与植被类型等外部因素有关[10]。因土壤抗蚀性能受多指标影响,且时空变异性较大,故即便为同一林地,在不同时间下也有差异[11]。关于土壤抗蚀性的研究颇多:韩鲁艳等[13]通过聚类分析等方法,对黄土丘陵沟壑区人工林地土壤进行抗蚀性评价;薛萐等[14]以时空互代法,研究黄土丘陵区不同年限人工灌木林的土壤抗蚀性演变特征;王俭成等[15]在北川地区,以主成分分析方法对典型林分抗蚀性进行了研究。笔者选择作为重要景观和水源涵养功能区的北京八达岭地区为研究区,通过选择4种典型林分(油松(Pinus tabulifomis)林、针阔混交林、阔叶林和灌木林),采用主成分分析法研究不同植被类型对土壤抗蚀性影响,揭示不同林分林地土壤抗蚀性特征。研究结果对科学评价研究区不同林分的水土保持功能,具有重要实践意义,对揭示土壤抗侵蚀机理,服务区域水土流失的防治,以及协调区域土地利用具有参考价值。

1 研究区概况

研究区位于北京市西北部延庆县内八达岭林场(E 115°55′,N 40°17′)。林场总面积2 940 hm2,平均海拔780 m,相对高差788 m。属大陆性季风气候,具半湿润、半干旱暖温带气候特点,年均气温10.8 ℃,年均降雨量454 mm。土壤主要有典型褐土、碳酸盐褐土和淋溶褐土3种,典型褐土垂直和水平分布最广,土层厚30 cm左右,各海拔及坡向均有分布[16-18]。该区自20世纪50年代实施封山育林与人工造林,目前森林覆盖率达60.7%。阔叶林360 hm2,针叶林1 478 hm2,针阔混交林52.2 hm2,灌木林1 003.5 hm2,均为水源保护林,部分因沿长城分布,兼有游憩观赏功能,较好反映该区森林的多效益性,是华北地区山地森林的典型代表[17]。 在该区选取油松林、针阔混交林、阔叶林和灌木林4种典型林分,进行土壤抗蚀性研究。各林地基本情况见表1和表2。

表1 典型林分代表性标准样地基本情况

表2 典型林分基本组成

2 材料与方法

2.1取样方法

选择具有典型性与代表性的4种林分,并分别在4种林分下,选择坡向、坡度和海拔等条件基本一致的4个调查样地(20 m×20 m),在每个样地的上、中和下3个部分,以土壤深度为标准,10 cm为一层,分3层挖掘土壤剖面,并将挖掘的3个土壤剖面作为3个重复。共开挖12个剖面,获取36个土壤层及土壤样本。

2.2土壤团聚体指标选取

多项研究表明,土壤自身性质是土壤侵蚀的内因,特别是土壤团聚体稳定性,它与土壤易蚀性间存在显著负相关性[19-20]。土壤团聚体水稳性则是评价土壤可蚀性的重要指标[21]。土壤团聚体相关指标计算方法如下:

>0.25 mm水稳性团聚体数量(Water Stable aggregates,WSA)可反映土壤结构好坏,越大结构越好[22]。

式中:WSA为>0.25 mm水稳性团聚体数量,%;i为土壤团聚体的级数,i=1,2,…,n;mi为第i级土壤团聚体质量,g;m为土壤团聚体总质量,g。

团聚体破坏率(Percentage of Aggregate Destruction,PAD)

式中:PAD为团聚体破坏率,%;Md为>0.25 mm干筛团聚体质量比例,%;Mw为>0.25 mm湿筛团聚体质量比例,%。

平均重量直径(Mean Weight Diameter,MWD)。常用评定土壤结构的指标之一,愈大结构性愈好[23]。

式中:wi为第i粒级中土壤团聚体质量分数,%;di为相邻两粒级土壤团聚体的平均粒径,mm。

团聚体平均重量直径变化(Mean Weight Diameter changes,MWDC):差值较小的,结构稳定性较好[23]。

MWDC=MWD干筛-MWD湿筛。

几何平均直径(Geometric Mean Diameter,GMD)[24]

2.3数据处理分析

主要利用统计分析软件SPSS18.0,进行相关性以及主成分分析。

3 结果与分析

3.1典型林分林地土壤理化性质

土壤有机质、氮磷钾等质量分数可反映土壤肥力状况,在一定程度上反映土壤结构的好坏(表3)。在各典型林分林地土壤中,随土层的加深,各林分土壤中有机质、全氮、速效钾及速效磷的质量分数均呈递减趋势。土壤有机质中,含有植物生长所需要的多种营养元素,是土壤肥力的物质基础。各林分中土壤有机质在土壤表层(0~10 cm)质量分数较高,各林分平均值为49.86 g/kg,质量分数最大的为阔叶林(60.58 g/kg),各典型林分林地有机质质量分数顺序为阔叶林>针阔混交林>油松林>灌木林。这可能与阔叶林枯落物较针叶林更易降解,或与不同树种间的立地条件不同有关。土壤全氮反映土壤氮素总量,0~10 cm全氮质量分数平均值为1.51 g/kg,10~20 cm为0.908 g/kg,2土层均表现为针阔混交林质量分数最高,油松林和阔叶林次之,灌木林质量分数最少。不同林分的速效钾质量分数有明显差异,针阔混交林质量分数较高,灌木林质量分数较少。0~10 cm速效钾质量分数平均值为143.3 mg/kg,10~20 cm为87.92 mg/kg,20~30 cm为66.99 mg/kg,各典型林分林地3个土壤层次中,速效钾质量分数由高到低都表现为:针阔混交林>油松林>阔叶林>灌木林。磷是植物生长所需要元素之一,0~10 cm各林分速效磷质量分数平均值为42.18 mg/kg,针阔混交林速效磷质量分数明显高于其他3种林分,油松林的速效磷质量分数最少。10~20 cm速效磷质量分数平均值为33.56 mg/kg,灌木林与针阔混交林质量分数较高,阔叶林质量分数最少。这表明各典型林分林地下,土壤有机质、氮、磷及钾等养分的质量分数,具有较明显差异。

3.2土壤团聚体

3.2.1土壤团聚体分布特征干筛时,各林分土壤团聚体主要集中在5~2 mm粒径范围内,各层质量分数分别为:0~10 cm土壤层团聚体质量分数平均值为31.14%,10~20 cm为34.57%,20~30 cm为34.31%。土壤团聚体在0.5~0.25 mm粒径范围内最少,在10~5 mm和2~1 mm内,分布较相似,几乎都分布于10%~15%内。湿筛后,各林分土壤团聚体主要集中在<0.25 mm粒径内,各林分0~10 cm质量分数平均值为28.27%,10~20 cm为30.03%,20~30 cm为33.3%。在10~5 mm粒径范围内,质量分数最少,在0~10 cm土层团聚体质量分数为7.44%,10~20 cm为11.95%,20~30 cm为6.07%。湿筛时,5~2 mm粒径范围内,团聚体质量分数相对于干筛时明显减少,减少量达16%左右。可见湿筛后,大团聚体数量明显减少,而小团聚体数量明显增加,即土壤团聚体具有干筛时大团聚体数量多,而湿筛时小团聚体数量多的特点,这是干燥的土壤团聚体遇水分散的原因(图1)。

表3 典型林分林地土壤有机质及氮磷钾质量分数

3.2.2土壤团聚体稳定性特征MWD与GMD是土壤团聚体稳定性重要指标[24]。研究表明,MWD与GMD能较好反映团聚体及水稳性团聚体分布和稳定性特征,其值越大,团聚体平均直径团聚度越高,稳定性也就越强[25]。如图2所示,MWD与GMD在各林分土壤层的分布趋势具有一致性。油松林中,10~20 cm土壤层的团聚度最高、稳定性最好,20~30 cm次之,0~10 cm最低;针阔混交林中,20~30 cm土壤团聚体稳定性最好,0~10 cm土壤稳定性最低;阔叶林中,土壤团聚体的稳定性随深度增加而降低,0~10 cm土层团聚体稳定性最好,可能与该层有机质质量分数较高(60.58 g/kg)有关;灌木林10~20 cm层土壤稳定性最好,0~10 cm土壤稳定性最差。总体来说,各典型林分中,10~20 cm土壤团聚体的稳定性最好,0~10 cm土层团聚体稳定性最差。土壤可蚀性与土壤团聚体水稳定性关系密切,WSA可在一定程度上反映出土壤结构的好坏。PAD反映土壤团聚体遇水的破坏程度,其值越小团聚体稳定性越好。图2中WSA在各典型林分各土壤层的分布趋势,与MWD和GMD一致,PAD值大小的分布情况与MWD、GMD和WSA值大小的分布情况正好相反;故PAD与WSA所反映的土壤团聚体稳定性与其他2个指标相同。

MWD:mean weight diameter; GMD:geometric mean diameter; PAD:percentage of aggregate destruction; WSA:water-stable aggregate.The same below.图2 各典型林分下不同稳定性指标大小分布图Fig.2 Distribution diagram of each stability index of four typical forest stands

3.3土壤抗蚀性能

3.3.1抗蚀指标的选定经主成分分析确定,该区典型林分林地土壤抗蚀性的最佳指标体系。3个主成分Y1、Y2和Y3的特征根累积贡献率为85.882%>85%,可满足主成分分析对信息损失量的要求;故可用第1、第2及第3主成分作为评价综合指标,且评价可信度为85.882%。第1主成分贡献率为47.080%,特征值为5.650;第2主成分贡献率为24.628%,特征值为2.955;第3主成分贡献率为14.173%,特征值为1.701(表4)。

表4 典型林分林地土壤抗蚀性指标PCA分析的因子负荷量、特征值和贡献率

注:X1:土壤密度;X2:有机质质量分数;X3:全氮质量分数;X4:速效钾质量分数;X5:速效磷质量分数;X6:MWD干筛;X7:MWD湿筛;X8:MWDC;X7:GMD干筛;X8:GMD湿筛;X11:PAD;X12:WSA; Y1:第1主成分;Y2:第2主成分;Y3:第3主成分。Note:X1:soil bulk density; X2:organic matter; X3:total nitrogen; X4:available potassium; X5:available phosphorus; X6:MWDDry seived; X7:MWDWet seived; X8:MWDWet sleved; Y1:the first principal component; Y2:the second principal component; Y3:the third principal component.

第1主成分与X6(MWD干筛)、X9(GMD干筛)、X8(MWDC)关系较密切,其中,X6因子负荷量最大(0.921),即MWD干筛是所有指标中最重要的指标;第2主成分中负荷量较大的为X12(WSA)、X5(速效磷)、X7(MWD湿筛)、X11(PAD)与X10(GMD湿筛)。可见,WSA所占比例越大速效磷质量分数越多,MWD湿筛和GMD湿筛越大,PAD越小,土壤抗蚀性就越强;第3主成分中X11(PAD)与X2(有机质)指标负荷量较大。以各因子负荷量主成分线性函数,确定各典型林分林地土壤的第1、2、3主成分值,再根据各主成分提供信息量所占权重,得到各典型林分林地土壤抗蚀性综合指数的计算方法:Y=0.548 2Y1+0.286 8Y2+0.165 0Y3,见表5。

表5 典型林分林地土壤抗蚀性综合指数

经相关分析土壤综合抗蚀指数(Y)与GMD干筛(x)间存在较明显线性关系(R2=0.928 6,n=12,P<0.01)。说明GMD干筛可代表该区典型林分的土壤抗蚀性能,故可选择GMD干筛为该区最佳抗蚀指标(表6)。

表6 典型林分林地土壤抗蚀性参数与土壤抗蚀性综合指数之间的相关系数

注:MWDC=平均质量直径变化。Note:MWDC=mean weight cliameter changes.

3.3.2土壤抗蚀性能经相关分析,GMD干筛可较好代表该区土壤抗蚀情况。表7中各林分土壤0~10 cm层GMD干筛较小,其余2层基本随土层深度增加,GMD干筛逐渐递减。灌木林变异系数(CV)最小(0.18),说明灌木林各层土壤间的抗蚀性差异最小;油松林的CV值最大(0.35),说明油松林各土壤层间抗蚀性差异较大。各林分林地土壤抗蚀性,在0~10 cm层具显著差异,CV值最大(0.18),说明该地区土壤抗蚀性的差异主要体现在0~10 cm层。

0~10 cm层土壤抗蚀性表现为阔叶林(2.09 mm)>灌木林(1.53 mm)>针阔混交林(1.31 mm)>油松林(0.99 mm)。这可能与阔叶林表层有机质质量分数较高有关。油松林的枯落物虽较厚,但较难分解,抗蚀性最差。生长多种灌木类型的灌木林有相对较多的枯落物,形成较厚的腐殖质层,抗蚀性好于针阔混交林。在较深的土壤层中,除针阔混交林外,由10~20 cm土壤层至20~30 cm土壤层,随着土层加深,土壤抗蚀性减弱。

表7 典型林分林地土壤干筛GMD

注:CV为变异系数。Note:CV:coefficient of variation.

0~10 cm土壤层,土壤抗蚀性综合指数与最佳抗蚀指标GMD干筛均表现为阔叶林>灌木林>针阔混交林>油松林,即0~10 cm的表层土壤,阔叶林的抗蚀性最好,其次为灌木林,油松林的抗蚀性最差;但在各层次平均值评价时,两者出现了差异,土壤抗蚀性综合指数表现为灌木林(1.705)>油松林(0.291)>针阔混交林(-0.707)>阔叶林(-1.300),而最佳土壤抗蚀指标GMD干筛表现为灌木林(2.10)>针阔混交叶林(1.96)>油松林(1.92)>阔叶林(1.60)。二者均表现为灌木林抗蚀性最好,阔叶林抗蚀性最差。二者评价不同的关键在于油松林与针阔混交林;但因抗蚀性综合指数受多因子制约,携带更多信息量,故更具可信度,因而以其平均为准。考虑土壤侵蚀多发生于0~20 cm土层,两者评价表现为灌木林(2.04)>油松林(1.95)>阔叶林(1.81)>针阔混交林(1.74);故GMD干筛可较好地反映各典型林地的土壤抗蚀性。

4 结论

1)在各典型林地土壤中,随土层加深,各林地的土壤有机质、全氮、速效钾及速效磷质量分数均呈递减趋势,养分物质在不同的土壤层次表现不同的林分排列顺序。干筛时,各林分林地土壤团聚体主要分布在5~2 mm粒径范围内,在0.5~0.25 mm粒径范围内最少;湿筛后,土壤团聚体主要集中在<0.25 mm粒径内,在10~5 mm粒径范围内的质量分数最小。湿筛后大团聚体数量明显减少,小团聚体数量明显增加。除阔叶林外,各典型林分的MWD、GMD、WSA与PAD均反映10~20 cm土层的土壤团聚体稳定性最好,0~10 cm土层的稳定性最差。

2)选取土壤理化性质、土壤团聚特征等12种指标,基于主成分分析,筛选出评价八达岭地区土壤抗蚀性的最佳指标体系:Y=0.548 2Y1+0.286 8Y2+0.165 0Y3,再经相关分析,选定干筛条件下,GMD是该地区典型林分林地最佳土壤抗蚀指标。在2种评价中,各典型林分0~10 cm土壤层抗蚀性由强到弱为阔叶林>灌木林>针阔混交林>油松林;易发生土壤侵蚀的0~20 cm土壤层,土壤抗蚀性强度为灌木林>油松林>阔叶林>针阔混交林;在各土壤层平均值综合情况下,评价结果以抗蚀性综合指数表示,抗蚀性由强到弱依次为灌木林>油松林>针阔混交林>阔叶林。

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Analysis of anti-erodibility of forest soil at 4 typical forest stands in Beijing Badaling area

Zhou Wei1,2,Zha Tonggang1,2,Sun Huaining1,2,Huang Junwei1,2,Yang Han1,2

(1.School of Soil and Water Conservation,Beijing Forestry University,100083,Beijing,China;2.Forestry Ecological Engineering Research Center,Ministry of Education,100083,Beijing,China)

[Background] In order to study the impacts of different vegetation types in Badaling area on the soil anti-erodibility and further reveal the soil anti-erodibility under different vegetation types,researches were conducted on 4 forest stands of Pinus tabuliformis,mixed conifer and broadleaf,broadleaf and shrub.[Methods] Based on the data from adequate field investigation as well as sampling and laboratory analysis,principal components analysis (PCA) along with relevant analytical methods were adopted in the study.[Results] After dry sieving,the particle size of aggregates in Badaling area was mostly found in 5-2 mm and the least in 0.5-0.25 mm.By contrast,after wet sieving,most aggregates were in small particle size (<0.25 mm) while large-size (10-5 mm) aggregates accounted for the smallest proportion.The geometric mean diameter (GMD),mean weight diameter (MWD),percentage of aggregate destruction (PAD) as well as the content of soil water-stable aggregate (WSA) > 0.25 mm of P.tabuliformis forest,mixed conifer and broadleaf forest and shrub forest all showed that aggregates in 10-20 cm layer of the forestland were the most stable,while in 0-10 cm layer they were in the worst stability,however this was not applied to broadleaf forest.To make better comparisons about the capacity of soil anti-erodibility in the 4 types of forestland,12 indexes were defined,including the physical and chemical features of soil and aggregate characteristics.And based on the method of PCA,the best and most suitable index system was established for evaluating the soil anti-erodibility in Badaling area.Among all the indexes,the GMD of dry-sieved soil was then selected via analysis as the best one to describe the soil anti-erodibility of the different typical forestland.Analytically,in Badaling area,the topsoil (0-10 cm) of broadleaf forest showed the greatest resistance to soil erosion,followed by shrub forest,mixed conifer and broadleaf forest and P.tabulifomis forest.Analysis also showed the anti-erodibility of 0-20 cm layer,where erosion was most likely to take place,with the figures for the different types of vegetation,was shrub forest > P.tabulifomis forest > broadleaf forest > mixed conifer and broadleaf forest.Synthetically,considering the average conditions for each layer,the final result of the soil evaluation was presented in the form of comprehensive soil anti-erodibility index.And the comprehensive soil anti-erodibility of the 4 types of forestland was shrub forest > P.tabulifomis forest > mixed conifer and broadleaf forest > broadleaf forest.[Conclusions] The result has practical significance to the scientific evaluation of the soil and water conservation function of the different forest stand in the research area.Meanwhile,the results of the study has certain reference value for both regional soil and water conservation and the further study on the mechanism of soil erosion.Therefore,the research may contribute to the prevention and control of regional soil and water loss and the coordination of regional land use.

forest soil; soil aggregate; soil anti-erodibility; Badaling area

2015-06-12

2016-01-25

项目名称:中央高校基本科研业务费专项资金资助“北京八达岭地区典型林分土壤团聚体稳定性特征对土壤侵蚀过程的影响”(xs201404)

周玮(1994—),女,本科生。主要研究方向:水土保持与荒漠化防治。E-mail:18310233068@163.com

简介:查同刚(1972—),男,副教授,硕士研究生导师。主要研究方向:土壤退化与生态修复。E-mail:zhtg73@bifu.edu.cn

S157.1

A

1672-3007(2016)04-0084-10

10.16843/j.sswc.2016.04.011

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