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森林生态系统是陆地表面最大的碳库和碳汇场所,约占陆地生态系统碳储量的2/3[1],维系着全球陆地生态系统77%的植被碳库和73%的土壤碳库[2],在调节全球碳循环和减缓气候变化中起着重要作用[3]。很多学者对森林生态系统碳密度进行了研究,但多集中于某区域碳密度的分异规律以及对不同森林类型、层次以及生长阶段碳密度的比较分析等方面。如刘国华等[4]利用我国1973年至1993年间4次森林资源清查资料,推算了我国不同森林类型和不同龄级森林碳库;王效科等[5]利用全国第三次森林资源清查资料,分别估计了不同龄级森林类型植物碳储量和碳密度,并分析了中国各省市的森林植物碳密度的分布规律等。然而对某种森林生态系统从乔木层—林下植被层—凋落物层—土壤层碳密度时空分布特征的综合性研究较少,且多数学者采用含碳率为0.45或0.5估算森林生态系统碳密度[6-7],易造成估算结果偏低或偏高现象。由于某一树种生态系统碳密度的分异性具有较大的不确定性,不同地域、起源、林龄及立地条件等因素均可能影响其分异规律[8-9]。因此依据不同区域不同森林类型而采用不同的含碳率有利于提高区域碳储量估算的准确度。
马尾松(Pinus massoniana)广泛分布于我国长江流域及其以南各省区,具有适应性强、耐干旱与贫瘠的特点。不少学者对马尾松的生物量、碳储量及碳密度开展了研究[10-11],但主要集中在人工林[11-12],对天然林的研究较少[13],而且对其整个生态系统碳密度分布特征的研究更为少见。因此,笔者以江西赣南(赣州市)为研究区,以其分布面积最广、蓄积量最大的马尾松天然林为研究对象,通过标准地调查及碳含量的测定,分析其不同林龄、层次及不同组分碳密度的分配规律。这对于全面掌握其生态系统碳密度的分布特征,以及对于开展碳汇林业的科学经营管理等方面均有指导意义,同时可为区域尺度上森林碳储量的准确估算提供参考依据。
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赣州市位于江西省南部,地处24°29′~27°09′N、113°54′~116°38′E之间。地貌以山地和丘陵为主,成土母岩主要是花岗岩、千枚岩、板岩、片麻岩等,土壤以地带性红壤、黄壤为主。气候属亚热带季风气候区,年平均气温为19.1~20.8℃,年平均降水量为1580mm,无霜期平均288d,年平均日照时数为1636.3h。研究区森林资源丰富,森林覆盖率达76.23%,主要森林类型有常绿阔叶林、针叶林、针阔混交林、竹林等,其中马尾松天然林面积达92.8万hm2,占全市乔木林面积的36%。
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依据我国《森林资源规划设计调查主要技术规定》(2003),将马尾松天然林划分为幼龄林(≤20年)、中龄林(21~30年)、近熟林(31~40年)、成熟林(41~60年)4个龄组,分别龄组选择母岩(花岗岩)、坡位(中坡)、土壤(红壤、土层厚度70~100cm)等立地条件一致具有代表性的地段设置标准地,每个龄组5个重复,共设置20个标准地,标准地面积为800m2(28.28m×28.28m)。采用树木生长锥测定3株平均木的年龄,以其平均值代表林分年龄。对标准地内所有胸径≥5cm的乔木进行每木调查(胸径<5cm的乔木视为灌木),测定林分及立地等因子。并按上、中、下布设3个2m×2m的灌木样方,在所选灌木样方中各设置1个1m×1m的草本样方和1m×1m的凋落物样方,调查其种类、数量及盖度等因子。在标准地内选择代表性地块挖1m深(未达1m的挖至母岩)的土壤剖面,采用环刀法(体积为100cm3)按0~10cm、10~20cm、20~30cm、30~50cm、50~100cm土层分别取样用于测定土壤密度,同时每层取约1kg的土壤带回实验室自然风干用于测定土壤碳含量。各龄组标准地基本概况见表 1。
表 1 不同龄组标准地基本概况
Table 1. Basic situation of sample plots at different age groups
龄组
Age group平均年龄/a
Average
age/year平均林木密度/
(株·hm-2)
Average tree density/
(tree·ha-1)平均胸径
Average
DBH/cm平均树高
Average
height/m灌木盖度
Shrub
coverage/%草本盖度
Herb
coverage/%郁闭度
Canopy
density幼龄林Young forest 16 1651 8.3 6.4 5 81 0.5 中龄林Middle-aged forest 26 1113 11.3 8.9 10 58 0.6 近熟林Near-mature forest 34 886 15.7 13.5 39 60 0.6 成熟林Mature forest 46 740 20.8 15.7 11 68 0.7 -
依据实测胸径,采用高一飞等[14]模拟的异速生长方程计算乔木层各组分的生物量,并在各标准地内选择1株马尾松标准木,分干、枝、叶、根取样烘干用于测定碳含量。灌木层(含胸径<5cm的乔木)、草本层与凋落物层生物量的测定采用“样方收获法”,每个样方内的灌木分枝、叶、根,草本分地上、地下,凋落物按分解程度不同划分为未分解(凋落物保持原状,外表没有分解痕迹)和半分解(凋落物原状不完整,多分解成碎屑),分别进行收集并称取鲜质量,将样品烘干至恒质量,计算其含水率,以估算林下植被及凋落物层的生物量。
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将烘干的乔木、林下植被、凋落物样品及风干的土壤样品研磨粉碎,过0.25mm筛,所有样品均采用重铬酸钾氧化-外加热法进行测定。
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植被碳密度的计算是各组分生物量乘以相对应的碳含量,其中乔木层、林下植被层、凋落物层碳密度为各组分碳密度之和。土壤剖面的碳密度计算基于各土层碳含量、土壤密度、土层厚度,土壤碳密度Dsoc(t/hm2)计算公式[15]为:
$$ {D_{{\rm{soc}}}}{\rm{ = }}\sum\limits_{i = 1}^{\rm{k}} {{C_i}{D_i}{E_i}} \left( {1 - {G_i}} \right)/10 $$ 式中:Ci为土壤碳含量,g/kg;Di为土壤密度,g/cm3;Ei为土层厚度,cm;Gi为直径大于2mm的石砾所占体积百分比,%;k为土层数。
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运用SPSS17.0软件对不同龄组的马尾松天然林各层碳密度进行单因素方差分析(one-way ANOVA),并使用LSD法进行多重比较分析,差异显著性以α=0.05为基准。统计数据及图表的绘制采用Excel 2010。
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由表 2可知,乔木层、灌木层、草本层和凋落物层各组分碳含量随林龄的变化均未表现出明显的规律性,而土壤各土层碳含量均随林龄的增大而增加。不同龄组间的乔木层、草本层和凋落物层碳含量均无显著差异(P>0.05);灌木层碳含量幼龄林显著高于其他龄组(P < 0.05),其他龄组间无显著差异(P>0.05);土壤碳含量在不同龄组间存在显著差异(P < 0.05)。对于不同层次各组分的平均碳含量,乔木层表现为树叶>树干>树枝>树根,但差异不显著(P>0.05);灌木层各组分平均碳含量差异显著(P < 0.05),表现为叶>枝>根;草本层则表现为地上部分显著高于地下部分(P < 0.05);凋落层总体表现为未分解层>半分解层;土壤各层的碳含量均表现为成熟林>近熟林>中龄林>幼龄林,且不同土层的平均碳含量间存在显著差异(P < 0.05),随着土层深度的增加碳含量逐渐减小,且同一龄组各土层碳含量呈现同样规律。
表 2 不同龄组各层次碳含量
Table 2. Carbon content of each layer at different age groups
g·kg-1 层次
Layer组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean乔木层
Arbor layer树干Trunk 484.70±34.63 474.62±8.96 481.91±29.33 461.34±10.45 475.64±10.44A 树枝Branch 461.62±29.57 469.67±16.95 452.81±8.98 463.90±22.80 462.00±7.00A 树叶Tree leaf 468.89±37.10 497.85±13.14 494.36±13.53 499.86±48.29 490.24±14.41A 树根Tree root 454.65±45.43 433.70±11.38 452.15±26.70 430.22±13.29 442.68±12.50A 平均值Mean 467.47±14.23a 468.96±21.25a 470.31±23.77a 463.83±21.67a 467.64±18.54 灌木层
Shrub layer叶Leaf 440.21±21.13 377.70±49.30 363.69±69.77 426.18±29.54 401.95±36.98A 枝Branch twig 441.02±35.79 363.93±36.64 389.91±39.53 389.55±56.05 396.10±32.32B 根Root 422.01±25.06 323.47±35.25 358.91±35.06 366.91±64.59 367.82±40.76C 平均值Mean 434.41±16.26a 355.03±23.84b 370.84±17.92b 394.21±22.34b 388.62±17.69 草本层
Herb layer地上Aboveground 462.67±74.29 501.77±26.97 462.96±45.69 430.43±13.07 464.46±29.19A 地下Underground 357.04±20.52 337.15±17.13 320.70±17.77 344.72±45.37 339.90±15.20B 平均值Mean 409.86±26.45a 419.46±13.66a 391.83±22.84a 387.58±18.23a 402.18±16.53 凋落物层
Litter layer半分解层Half-decomposed layer 394.22±17.35 423.41±45.43 386.02±12.12 404.54±18.26 402.05±16.13B 未分解层Undecomposed layer 453.46±36.25 397.23±16.61 420.17±59.36 405.06±28.85 418.98±24.88A 平均值Mean 423.84±19.45a 410.32±28.74a 403.10±15.43a 404.80±21.18a 410.51±16.64 土壤层
Soil layer0~10cm 8.15±3.10 10.47±3.07 12.80±6.55 14.40±4.65 11.46±2.73A 10~20cm 5.54±2.33 7.55±2.75 8.40±5.44 9.23±2.47 7.68±1.58B 20~30cm 4.91±3.16 4.92±2.09 6.50±4.47 6.52±0.49 5.71±0.92C 30~50cm 3.70±2.46 3.89±0.56 5.41±3.19 6.00±0.34 4.75±1.13D 50~100cm 2.97±3.27 3.04±1.33 4.70±1.65 4.75±2.89 3.86±0.99E 平均值Mean 5.06±1.34d 5.88±2.14c 7.58±1.94b 8.23±1.67a 6.69±1.26 注:数值为平均值±标准误。不同大写字母表示相同层次不同组分差异显著(P < 0.05),同一行不同小写字母为差异显著(P < 0.05)。下同。
Notes:data is mean value ± standard error. Different capital letters show the significant differences among different components with same level(P < 0.05),different lowercase letters in the same line show significant differences(P < 0.05). The same below. -
由表 3可以看出,乔木层平均碳密度为43.81t/hm2,表现为树干>树枝>树根>树叶,其中树干所占比最高,约为65.51%,树叶所占比最小,为6.87%。乔木各组分及总的碳密度均随着林龄的增大而增加,成熟林总的碳密度最大,为83.55t/hm2,且其各组分碳密度均显著高于其他龄组(P < 0.05)。
表 3 不同龄组乔木层碳密度 t·hm-2
Table 3. Carbon density of arbor layer at different age groups t·ha-1
组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean树干Trunk 6.82±5.76c 24.57±17.02b 28.10±3.72b 55.30±27.07a 28.70±19.68 树枝Branch 1.39±1.07c 5.63±3.98b 6.40±1.22b 12.66±5.62a 6.52±4.60 树叶Tree leaf 0.83±0.52c 2.77±1.88b 3.00±0.57b 5.44±1.88a 3.01±1.77 树根Tree root 1.31±0.73c 4.94±3.23b 5.95±1.18b 10.15±3.73a 5.58±3.33 合计Total 10.35 37.91 43.45 83.55 43.81 -
随林龄的增大,灌木叶、枝及其总的碳密度均呈先减少后增加再减少趋势,灌木根的碳密度则表现出先增加后减少趋势,草本层地上部分的碳密度呈先增加后减少再增加趋势。而草本层及其地下部分、林下植被层碳密度随林龄变化表现出先减少后增加趋势(见表 4)。方差分析表明,不同龄组间的灌木层、草本层及其各组分碳密度均有显著差异(P < 0.05),其中灌木层碳密度以近熟林最大,草本层碳密度以成熟林最大,而林下植被层碳密度最大为幼龄林。林下植被层的平均碳密度为4.60t/hm2,草本层碳密度远大于灌木层,且草本层地上部分、地下部分各占整个林下植被层的44.35%、26.09%;灌木层中枝、根分别占整个林下植被层的13.04%、10.87%,叶仅占5.43%。
表 4 不同龄组林下植被层碳密度 t·hm-2
Table 4. Carbon density of understory vegetation layer at different age groups t·ha-1
层次
Layer组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean灌木层Shrub layer 叶Leaf 0.24±0.14b 0.19±0.14c 0.43±0.34a 0.15±0.12d 0.25±0.13 枝Branch twig 0.82±0.17a 0.44±0.34c 0.78±0.58b 0.37±0.36d 0.60±0.18 根Root 0.37±0.20b 0.41±0.52d 0.86±0.63a 0.36±0.36c 0.50±0.32 小计Subtotal 1.43b 1.04c 2.07a 0.88d 1.35 草本层Herb layer 地上Aboveground 2.11±0.48b 2.59±1.04a 1.48±1.41d 1.96±1.26c 2.04±0.46 地下Underground 1.55±0.81b 0.88±0.39c 0.68±0.74d 1.71±1.03a 1.20±0.50 小计Subtotal 3.66b 3.47c 2.16d 3.67a 3.24 合计Total 5.09 4.51 4.23 4.55 4.60 -
凋落物层各组分及总的碳密度均随着林龄的增大呈先增加后减少趋势(见表 5)。未分解层及凋落物层总的碳密度以近熟林最大,而半分解层碳密度则中龄林最大。方差分析表明,各龄组间半分解层的碳密度差异不显著(P>0.05),近熟林未分解层的碳密度显著高于其他龄组(P < 0.05)。凋落物层的平均碳密度为0.57t/hm2,半分解层、未分解层各占整个凋落物层的57.89%、42.11%。
表 5 不同龄组凋落物层碳密度 t·hm-2
Table 5. Carbon density of litter layer at different age groups t·ha-1
组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean半分解层Half-decomposed layer 0.30±0.12a 0.39±0.14a 0.36±0.25a 0.28±0.07a 0.33±0.05 未分解层Undecomposed layer 0.20±0.09b 0.21±0.06b 0.34±0.16a 0.21±0.03b 0.24±0.07 合计Total 0.50 0.59 0.70 0.49 0.57 -
由图 1A可知,幼龄林、中龄林、近熟林和成熟林土壤碳密度分别为59.89、71.20、92.16和96.82t/hm2。各土层碳密度随林龄的增大呈增加趋势,且不同龄组间差异均达显著水平(P < 0.05)。此外,由于各土层厚度不同,为了直观的反映土壤碳密度的垂直分布特征,将各层土壤碳密度换算成以10cm为单位厚度的平均碳密度(见图 1B)。可以看出,不同龄组土壤各层单位厚度的平均碳密度均随土层深度的增加而逐渐降低,以0~10cm土层的碳密度最大,且0~50cm土层下降幅度最大,50cm以下各土层碳密度下降过程较为平缓。
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由表 6可知,赣南马尾松天然林林分总碳密度为129.00t/hm2,从林龄来看,林分总碳密度表现为成熟林(185.41t/hm2)>近熟林(140.54t/hm2)>中龄林(114.21t/hm2)>幼龄林(75.83t/hm2);而从层次上,土壤层(80.02t/hm2)>乔木层(43.81t/hm2)>林下植被层(4.60t/hm2)>凋落物层(0.57t/hm2),分别占总碳密度的62.03%、33.96%、3.57%、0.44%。方差分析表明,林分各层次及总碳密度均在不同龄组间差异达显著水平(P < 0.05)。乔木层、土壤层碳密度占林分总碳密度的比重随林龄的变化均未表现出明显的规律性,而林下植被层、凋落物层碳密度占林分总碳密度的比重随林龄的增大而减小。
表 6 林分总碳密度分析 t·hm-2
Table 6. Analysis of the total carbon density of forest stand t·ha-1
层次
Layer幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest总平均值
Total mean乔木层Arbor layer 10.35d 37.91c 43.45b 83.55a 43.81 (13.64%) (33.19%) (30.91%) (45.06%) (33.96%) 林下植被层Understory vegetation layer 5.09a 4.51c 4.23d 4.55b 4.60 (6.70%) (3.95%) (3.01%) (2.45%) (3.57%) 凋落物层Litter layer 0.50c 0.59b 0.70a 0.49d 0.57 (0.66%) (0.52%) (0.50%) (0.26%) (0.44%) 土壤层Soil layer 59.89d 71.20c 92.16b 96.82a 80.02 (79.00%) (62.34%) (65.58%) (52.22%) (62.03%) 合计Total 75.83d 114.21c 140.54b 185.41a 129.00 注:括号中数据为占林分总碳密度的百分比。Note:date in brackets are percentages of the total carbon density of forest stand. -
本研究表明,马尾松天然林乔木层碳密度表现为树干>树枝>树根>树叶,林下植被层表现为草本层>灌木层,凋落物层为半分解层>未分解层。与此相比,曹小玉等[16]对湖南马尾松林碳密度研究得出的乔木层、林下植被层碳密度的分配规律与本研究结果完全一致;张治军等[17]研究得出重庆铁山坪马尾松次生林乔木层碳密度也表现为树干>树枝>树根>树叶,但凋落物层为未分解层>半分解,林下植被层则为灌木层>草本层;而方运霆等[18]对鼎湖山马尾松人工林研究得出的乔木层碳密度为树干>树根>树枝>树叶,凋落物层则为半分解层>未分解层。显然,不同区域马尾松林植被层各组分碳密度的分配规律不尽相同,究其原因可能是植被各组分碳密度的分配不仅受区域水热条件的影响,同时也受林分起源、林分密度、林龄、林木空间分布格局等林分结构以及坡位、坡度等立地因子的综合影响。在土壤碳密度的垂直分布上,土壤各层单位厚度的平均碳密度随土层深度的增加而逐渐降低,以表层(0~10cm)土壤碳密度最大,这与目前大部分研究结果相同[19-20],这主要由于植物根系分布于表层土壤,而凋落物与根系分解后的养分首先进入表层土壤,且随土壤深度的增加土壤碳的积累逐渐降低。
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随着林分年龄的增长,林分各层次碳密度的变化规律不尽相同。其中,乔木层碳密度表现为随林龄的增大而增加,这与许多学者的研究结果一致[21-22],表明乔木层碳是随着林龄的增大而不断累积的过程。林下植被层碳密度随林龄增大表现出减少后增加趋势,与潘鹏等[21]的研究结果一致,但陶玉华等[23]对广西罗城马尾松林的研究得出林下植被层碳密度随林龄增大呈减少的趋势,而蔚海东等[24]研究得出福建马尾松林下植被层碳密度随林龄增大呈先增加后减少趋势,这可能是林下植被的种类及盖度受林冠结构、土壤、微地形等因子的综合影响不同所致。凋落物层碳密度表现为随林龄增大呈先增加后减少趋势,由于凋落物数量、质量及其分解速率与树种组成、林龄、林分密度等林分因子以及林下植被类型、气候、人为活动等因素有关,所以相关研究结果不尽一致。如庞洪东等[13]对湖北省马尾松天然林碳储量及碳密度特征的研究得到凋落物层碳密度随林龄增大而增加,徐慧芳等[25]对广西不同林龄马尾松人工林碳储量的研究得到凋落物层碳密度随林龄增大呈“M”型变化趋势,等等。土壤层碳密度随林龄的增大而增加,肖欣等[26]、秦晓佳等[27]很多学者得出相同结论;但也有不同的结果,如潘忠松等[28]对黔南马尾松林土壤碳密度的研究结果为中龄林>成熟林>近熟林>幼龄林,究其原因可能受土壤类型、厚度、理化性质以及林下植被与凋落物层盖度、林分密度、根系周转率等复杂因素的影响所致。
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本研究表明,赣南马尾松天然林林分平均总碳密度为129.00t/hm2,高于庞宏东等[13]研究得出的湖北省马尾松天然林碳密度(121.16t/hm2)。究其原因主要是本研究得出的土壤层平均碳密度(80.02t/hm2)高于湖北省的土壤层碳密度(71.87t/hm2),虽然土壤取样深度均为100cm,但本研究将土壤分为5层,而庞宏东等分为3层取样,由于土壤碳密度通常是随着土层的加深而减少[19],在气候及生物等因素相似条件下,土壤分层的不同可能是导致其差异的主要原因。林分总碳密度表现为随林龄的增大而增加,这与许多学者的研究结果一致[24, 29]。而徐慧芳等[25]对广西5种年龄的马尾松人工林碳密度研究表明60年>32年>21年>5年>15年,并不完全表现为随林分年龄的增大而增加,其总碳密度15年的小于5年的;主要原因是由于其土壤层、灌木层碳密度更小所导致,这与立地条件差异等有关。林分各层碳密度大小顺序为土壤层>乔木层>林下植被层>凋落物层,这与张治军等[17]、Xiao等[22]对马尾松林碳密度研究得出的结果一致。而巫涛等[30]对长沙市区13年生马尾松人工林碳密度研究则表明土壤层>乔木层>凋落物层>林下植被层,这可能是林下植被层与凋落物层碳密度大小主要与森林抚育等人为干扰强度有关,如砍杂等抚育措施使林下植被层的生物量减少而凋落物层生物量增加。此外本研究及大量研究表明,土壤碳库与乔木层碳库是森林生态系统中极重要的组分,而林下植被层、凋落物层碳密度所占比例均很小[31-32];但其在维持土壤肥力和生态系统稳定性等方面[33]以及在森林生态系统碳循环过程中发挥着极为重要的作用[34],因此在碳汇林业经营中同样不容忽视。
Distribution characteristics of carbon density of natural Pinus massoniana forest at different stand growing stages in southern Jiangxi Province, eastern China
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摘要:
目的通过对赣南马尾松天然林碳密度的分析, 为其区域尺度上森林碳储量的准确估算以及开展碳汇林业的科学经营提供参考依据。 方法基于标准地调查与碳含量的测定, 采用单因素方差分析和LSD多重比较法, 分析不同林龄、层次及不同组分碳密度的分布特征。 结果(1) 林分总碳密度为129.00 t/hm2, 表现为成熟林(185.41 t/hm2)>近熟林(140.54 t/hm2)>中龄林(114.21 t/hm2)>幼龄林(75.83 t/hm2); 各层碳密度为土壤层(80.02 t/hm2)>乔木层(43.81 t/hm2)>林下植被层(4.60 t/hm2)>凋落物层(0.57 t/hm2), 分别占总碳密度的62.03%、33.96%、3.57%和0.44%;每层碳密度的分配规律表现为:乔木层为树干>树枝>树根>树叶, 林下植被为草本层>灌木层, 凋落物为半分解层>未分解层, 土壤各层单位厚度的碳密度随土层深度的增加而逐渐降低。(2)随林龄的增大, 各层碳密度的变化规律不尽相同。其中, 乔木层、土壤层的碳密度均呈增加趋势, 且均以成熟林最大, 成熟林的林木各组分碳密度均显著高于其他龄组(P < 0.05), 而土壤层碳密度在不同龄组间均存在显著差异(P < 0.05);林下植被层碳密度随林龄变化表现出先减后增趋势, 但以幼龄林最大。不同龄组间的灌木层、草本层及其各组分碳密度均有显著差异(P < 0.05), 其中灌木层碳密度以近熟林最大, 草本层碳密度以成熟林最大; 凋落物层碳密度随林龄增大表现为先增后减的趋势, 近熟林未分解层碳密度显著高于其他龄组(P < 0.05), 而半分解层碳密度各龄组间差异不显著(P>0.05)。 结论土壤层和乔木层是马尾松天然林整个生态系统碳密度的主体; 随着林龄的增大, 乔木层及其各组分和土壤层的碳密度均呈增加趋势, 而林下植被层、凋落物层及其各组分碳密度的变化并未表现出相同规律。 Abstract:ObjectiveTo analyze the carbon density of natural Pinus massoniana in southern Jiangxi Province of eastern China was to provide references for accurate estimation of forest carbon stocks in regional scale, and to develop scientific management of carbon sequestration forest. MethodBased on the investigation of standard plots and the determination of carbon content, the distribution characteristics of carbon density of different stand ages, layers and components were analyzed by one-way ANOVA and LSD multiple comparison methods. Result(1) the total carbon density of stand was 129.00 t/ha. The carbon density of different age groups ranked as mature forest (185.41 t/ha)>near-mature forest (140.54 t/ha)>middle-aged forest (114.21 t/ha)>young forest (75.83 t/ha). The carbon density of different layers followed a sequence of soil layer (80.02 t/ha)>arbor layer (43.81 t/ha)>understory vegetation layer (4.60 t/ha)>litter layer (0.57 t/ha), accounted for 62.03%, 33.96%, 3.57% and 0.44% of total carbon density, respectively. The distribution law of carbon density in different layers performed as follows: the arbor layer was trunk>branch>tree root>tree leaf, the understory vegetation layer was herb layer>shrub layer, the litter layer was half-decomposed layer>undecomposed layer, the carbon density of unit thickness at each soil layer decreased with the increase of soil depth. (2) The variation law of carbon density in different layers differed with the increase of stand age. The carbon density of arbor and soil layer increased along forest development, and in mature forest was the largest. The carbon density of different components of arbor layer in mature forest was significantly higher than in other age groups (P < 0.05), but there were significant differences in the carbon density of soil layer among different age groups (P < 0.05). The carbon density of understory vegetation layer decreased firstly and then increased with the increase of stand age, but in young forest was the largest. There were significant differences in the carbon density of shrub layer, herb layer and their components among different age groups (P < 0.05), the largest carbon density of shrub and herb layers was respectively in near-mature forest and mature forest. The carbon density of litter layer increased firstly and then decreased with the increase of stand age, the carbon density of undecomposed layer in near-mature forest was significantly higher than in other age groups (P < 0.05), and there were no significant differences in the carbon density of half-decomposed layer among different age groups (P>0.05). ConclusionThe majority of carbon density of the natural Pinus massoniana ecosystem was stored in the arbor layer and soil layer. The carbon density of arbor layer and its components, and soil layer increased along forest development, but the changes in carbon density of understory vegetation layer, litter layer and their components did not display such a pattern. -
Key words:
- Pinus massoniana /
- natural forest /
- carbon density /
- distribution characteristics
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表 1 不同龄组标准地基本概况
Table 1. Basic situation of sample plots at different age groups
龄组
Age group平均年龄/a
Average
age/year平均林木密度/
(株·hm-2)
Average tree density/
(tree·ha-1)平均胸径
Average
DBH/cm平均树高
Average
height/m灌木盖度
Shrub
coverage/%草本盖度
Herb
coverage/%郁闭度
Canopy
density幼龄林Young forest 16 1651 8.3 6.4 5 81 0.5 中龄林Middle-aged forest 26 1113 11.3 8.9 10 58 0.6 近熟林Near-mature forest 34 886 15.7 13.5 39 60 0.6 成熟林Mature forest 46 740 20.8 15.7 11 68 0.7 表 2 不同龄组各层次碳含量
Table 2. Carbon content of each layer at different age groups
g·kg-1 层次
Layer组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean乔木层
Arbor layer树干Trunk 484.70±34.63 474.62±8.96 481.91±29.33 461.34±10.45 475.64±10.44A 树枝Branch 461.62±29.57 469.67±16.95 452.81±8.98 463.90±22.80 462.00±7.00A 树叶Tree leaf 468.89±37.10 497.85±13.14 494.36±13.53 499.86±48.29 490.24±14.41A 树根Tree root 454.65±45.43 433.70±11.38 452.15±26.70 430.22±13.29 442.68±12.50A 平均值Mean 467.47±14.23a 468.96±21.25a 470.31±23.77a 463.83±21.67a 467.64±18.54 灌木层
Shrub layer叶Leaf 440.21±21.13 377.70±49.30 363.69±69.77 426.18±29.54 401.95±36.98A 枝Branch twig 441.02±35.79 363.93±36.64 389.91±39.53 389.55±56.05 396.10±32.32B 根Root 422.01±25.06 323.47±35.25 358.91±35.06 366.91±64.59 367.82±40.76C 平均值Mean 434.41±16.26a 355.03±23.84b 370.84±17.92b 394.21±22.34b 388.62±17.69 草本层
Herb layer地上Aboveground 462.67±74.29 501.77±26.97 462.96±45.69 430.43±13.07 464.46±29.19A 地下Underground 357.04±20.52 337.15±17.13 320.70±17.77 344.72±45.37 339.90±15.20B 平均值Mean 409.86±26.45a 419.46±13.66a 391.83±22.84a 387.58±18.23a 402.18±16.53 凋落物层
Litter layer半分解层Half-decomposed layer 394.22±17.35 423.41±45.43 386.02±12.12 404.54±18.26 402.05±16.13B 未分解层Undecomposed layer 453.46±36.25 397.23±16.61 420.17±59.36 405.06±28.85 418.98±24.88A 平均值Mean 423.84±19.45a 410.32±28.74a 403.10±15.43a 404.80±21.18a 410.51±16.64 土壤层
Soil layer0~10cm 8.15±3.10 10.47±3.07 12.80±6.55 14.40±4.65 11.46±2.73A 10~20cm 5.54±2.33 7.55±2.75 8.40±5.44 9.23±2.47 7.68±1.58B 20~30cm 4.91±3.16 4.92±2.09 6.50±4.47 6.52±0.49 5.71±0.92C 30~50cm 3.70±2.46 3.89±0.56 5.41±3.19 6.00±0.34 4.75±1.13D 50~100cm 2.97±3.27 3.04±1.33 4.70±1.65 4.75±2.89 3.86±0.99E 平均值Mean 5.06±1.34d 5.88±2.14c 7.58±1.94b 8.23±1.67a 6.69±1.26 注:数值为平均值±标准误。不同大写字母表示相同层次不同组分差异显著(P < 0.05),同一行不同小写字母为差异显著(P < 0.05)。下同。
Notes:data is mean value ± standard error. Different capital letters show the significant differences among different components with same level(P < 0.05),different lowercase letters in the same line show significant differences(P < 0.05). The same below.表 3 不同龄组乔木层碳密度 t·hm-2
Table 3. Carbon density of arbor layer at different age groups t·ha-1
组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean树干Trunk 6.82±5.76c 24.57±17.02b 28.10±3.72b 55.30±27.07a 28.70±19.68 树枝Branch 1.39±1.07c 5.63±3.98b 6.40±1.22b 12.66±5.62a 6.52±4.60 树叶Tree leaf 0.83±0.52c 2.77±1.88b 3.00±0.57b 5.44±1.88a 3.01±1.77 树根Tree root 1.31±0.73c 4.94±3.23b 5.95±1.18b 10.15±3.73a 5.58±3.33 合计Total 10.35 37.91 43.45 83.55 43.81 表 4 不同龄组林下植被层碳密度 t·hm-2
Table 4. Carbon density of understory vegetation layer at different age groups t·ha-1
层次
Layer组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean灌木层Shrub layer 叶Leaf 0.24±0.14b 0.19±0.14c 0.43±0.34a 0.15±0.12d 0.25±0.13 枝Branch twig 0.82±0.17a 0.44±0.34c 0.78±0.58b 0.37±0.36d 0.60±0.18 根Root 0.37±0.20b 0.41±0.52d 0.86±0.63a 0.36±0.36c 0.50±0.32 小计Subtotal 1.43b 1.04c 2.07a 0.88d 1.35 草本层Herb layer 地上Aboveground 2.11±0.48b 2.59±1.04a 1.48±1.41d 1.96±1.26c 2.04±0.46 地下Underground 1.55±0.81b 0.88±0.39c 0.68±0.74d 1.71±1.03a 1.20±0.50 小计Subtotal 3.66b 3.47c 2.16d 3.67a 3.24 合计Total 5.09 4.51 4.23 4.55 4.60 表 5 不同龄组凋落物层碳密度 t·hm-2
Table 5. Carbon density of litter layer at different age groups t·ha-1
组分
Component幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest平均值
Mean半分解层Half-decomposed layer 0.30±0.12a 0.39±0.14a 0.36±0.25a 0.28±0.07a 0.33±0.05 未分解层Undecomposed layer 0.20±0.09b 0.21±0.06b 0.34±0.16a 0.21±0.03b 0.24±0.07 合计Total 0.50 0.59 0.70 0.49 0.57 表 6 林分总碳密度分析 t·hm-2
Table 6. Analysis of the total carbon density of forest stand t·ha-1
层次
Layer幼龄林
Young forest中龄林
Middle-aged forest近熟林
Near-mature forest成熟林
Mature forest总平均值
Total mean乔木层Arbor layer 10.35d 37.91c 43.45b 83.55a 43.81 (13.64%) (33.19%) (30.91%) (45.06%) (33.96%) 林下植被层Understory vegetation layer 5.09a 4.51c 4.23d 4.55b 4.60 (6.70%) (3.95%) (3.01%) (2.45%) (3.57%) 凋落物层Litter layer 0.50c 0.59b 0.70a 0.49d 0.57 (0.66%) (0.52%) (0.50%) (0.26%) (0.44%) 土壤层Soil layer 59.89d 71.20c 92.16b 96.82a 80.02 (79.00%) (62.34%) (65.58%) (52.22%) (62.03%) 合计Total 75.83d 114.21c 140.54b 185.41a 129.00 注:括号中数据为占林分总碳密度的百分比。Note:date in brackets are percentages of the total carbon density of forest stand. -
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