Natural regeneration factors of <i>Abies georgei</i> var<i>. smithii</i> seedlings in Sejila Mountain

WANG Ruihong; PAN Gang; ZHANG Xinjun; LI Jiangrong; ZHANG Xinjian

doi:10.11833/j.issn.2095-0756.20200302

Volume 38 Issue 3

Jun. 2021

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WANG Ruihong, PAN Gang, ZHANG Xinjun, et al. Natural regeneration factors of Abies georgei var. smithii seedlings in Sejila Mountain[J]. Journal of Zhejiang A&F University, 2021, 38(3): 652-658. DOI: 10.11833/j.issn.2095-0756.20200302

Citation:

WANG Ruihong, PAN Gang, ZHANG Xinjun, et al. Natural regeneration factors of Abies georgei var. smithii seedlings in Sejila Mountain[J]. Journal of Zhejiang A&F University, 2021, 38(3): 652-658. DOI: 10.11833/j.issn.2095-0756.20200302

Natural regeneration factors of Abies georgei var. smithii seedlings in Sejila Mountain

DOI: 10.11833/j.issn.2095-0756.20200302

WANG Ruihong^{1, 2, 3
,},
PAN Gang^{1, 2, 3},
ZHANG Xinjun^{1, 2, 3},
LI Jiangrong^{1, 2, 3},
ZHANG Xinjian⁴

1.
Research Institute of Tibet Plateau Ecology, Tibet Agriculture & Animal Husbandry University, Linzhi 860000, Tibet, China
2.
National Key Station of Field Scientific Observation & Experiment, Tibet Agriculture & Animal Husbandry University, Linzhi 860000, Tibet, China
3.
Tibet Key Laboratory of Forest Ecology in Plateau Area, Ministry of Education, Tibet Agriculture & Animal Husbandry University, Linzhi 860000, Tibet, China
4.
Organization Department of CPC Tibet Agriculture & Animal Husbandry University Committee, Linzhi 860000, Tibet, China

Received Date: 2020-05-04
Rev Recd Date: 2021-03-08

Available Online: 2021-06-09

Publish Date: 2021-06-09

Abstract

Objective This paper with an analysis of the influencing factors of natural regeneration of Abies georgei var. smithii in Sejila Mountain, is aimed to provide theoretical guidance for the effective promotion of its natural regeneration. Method Based on a field sample survey as well as an analysis of the correlation between the seedlings density and the five influencing factors on shady and sunny slopes of A. georgei var. smithii in Sejila Mountain, the path analysis was carried out to find out the key factors affecting its natural regeneration. Result On both sunny and shady slopes, there was a significant positive correlation between the natural regeneration seedlings and the length of seed wing, 1000-seed weight, moss thickness, litter thickness, canopy density of sunny slope. Litter thickness was the most important factor affecting the growth of natural regeneration seedlings of A. georgei var. smithii on sunny slope and the order of contribution to seedlings density was litter thickness, 1 000-seed weight, moss thickness, winged seed length and canopy density. Moss thickness was the most important factor affecting the growth of natural regeneration seedlings of A. georgei var. smithii on shady slope and the order of contribution to seedlings density was moss thickness, litter thickness, 1000-seed weight, canopy density and winged seed length. Conclusion Litter thickness was the largest factor affecting the density seedlings of A. georgei var. smithii on sunny slope, while moss thickness on shady slope was the most critical factor. [Ch, 3 tab. 27 ref.]
- Abies georgei var. smithii,
- natural regeneration,
- correlation analysis,
- path analysis; Sejila Mountain

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天然更新是指植物或群落从种子成熟、种子扩散、种子萌发、幼苗生长，到生长为健壮个体的连续过程^[1]。森林天然更新是林木利用自身繁殖能力形成新一代幼林的过程，一般有有性更新和无性更新2种方式^[2]，是森林生态系统自我繁衍、自我恢复的手段和基础^[3]，体现森林健康状况，对森林群落的稳定性维持、森林物种多样性保护具有重要意义。目前，国内外学者对森林天然更新的研究比较多，主要集中在采伐迹地的天然更新动态研究^[4-5]、林隙与天然更新^[4]、天然更新幼苗的种群结构及空间分布格局^[6-9]等方面，其中森林天然更新影响因子的研究主要集中在土壤种子库^[10-11]和群落生境特征，如海拔与坡向^[12-13]、地被物^{[11, 13-15]}、不同采伐方式^[16-19]、林隙^[20-22]等，但在群落植物种子特性及其与环境因子综合作用的研究还鲜有报道。色季拉山急尖长苞冷杉Abies georgei var. smithii林是中国西藏东南林区暗针叶林的典型代表，为成过熟原始林，人为干扰较少，林内苔藓植物、凋落物丰富。本研究以色季拉山急尖长苞冷杉原始林为研究对象，调查林内急尖长苞冷杉幼苗，运用通径分析方法分析林分郁闭度、种子带翅长度、千粒重、苔藓厚度、凋落物厚度等因子对幼苗更新的影响，明晰影响急尖长苞冷杉幼苗生长的最重要因子，以期为有效改善急尖长苞冷杉天然更新提供理论依据，从而改变目前急尖长苞冷杉林的濒危状态，维持急尖长苞冷杉群落稳定性。

1. 研究区概况

研究区位于西藏自治区林芝县鲁朗境内的色季拉山(29°10′~30°15′N，93°12′~95°35′E)，海拔为2 100~5 300 m，大致呈西北—东南走向，面积约2 300 km²；受印度洋暖湿季风气候影响，为典型的亚高山温带半湿润气候，冬温夏凉，干湿季节比较分明，降水多集中在每年的4−10月，年降水量为875~1 350 mm，约全年降水量的80.0%；年平均气温−0.7 ℃，7月为最暖月，平均气温9.2 ℃，1月为最冷月，平均气温−14.0 ℃。色季拉山遍布原始森林，乔木层中原始暗针叶林急尖长苞冷杉林占绝对优势，属于过熟林，此外还有林芝云杉Picea likiangensis var. linzhiensis、高山松Pinus densata、方枝柏Sabina saltuaria^[20]等，林下灌木层生长繁茂，主要有林芝杜鹃Rhododendron nyingchiense、西南花楸Sorbus rehderiana、柳叶忍冬Lonicera lanceolata等，草本主要有红景天Rhodiola rosea、委陵菜Potentilla chinensis、西南草莓Fragaria moupinensis、卷叶黄精Polygonatum cirrhifolium等；地被层主要有枯枝落叶、苔藓Bryophyte等，部分区域苔藓厚度达到10 cm以上，盖度约80%。

2. 研究方法

2.1. 样地设置

在色季拉山阴坡与阳坡沿海拔3 700~4 200 m，隔100 m设1个梯度，共设置12个10 m×10 m样地，记录样地的海拔、坡向、郁闭度。在样地中设置5个2 m×2 m样方调查灌木的种类、郁闭度，在各样方中分别设置5个1 m×1 m小样方调查草本盖度、苔藓植物厚度、凋落物厚度及急尖长苞冷杉幼苗数量。

2.2. 测量方法

对12个样地内的急尖长苞冷杉每木检尺，选取标准木。于急尖长苞冷杉种子成熟初期，分别在树冠上、中、下层用高枝剪取下5个球果，标记装袋带回实验室。待球果裂开后，剥出种子，待其自然风干；各样地随机选取100粒种子，测量种子带翅长度，称量种子千粒重；测量小样方内苔藓层厚度及凋落物厚度。各重复5次，取平均值。

2.3. 数据分析

通过SPSS 19.0双变量Pearson检验进行相关性分析，通过SPSS 19.0进行多元回归计算通径系数。

3. 结果与分析

3.1. 不同海拔高度影响因子对急尖长苞冷杉天然更新幼苗的影响

由表1可知：阳坡不同海拔高度下千粒重均为极显著差异(P＜0.01)；3 700~3 900、4 000~4 200 m海拔高度林分郁闭度及凋落物厚度差异性均不显著(P＞0.05)，3 700~3 900 m种子带翅长度差异不显著，3 700与3 900 m海拔高度苔藓厚度差异不显著，其他海拔之间差异显著，3 700与3800 m海拔高度下幼苗数量差异不显著，其他海拔之间差异显著；其中海拔3 700 m处郁闭度最高，达75.12 %，4 200 m处最低，只有40.05 %。随海拔升高，千粒重、苔藓厚度、凋落物厚度均呈现先增加后减小的趋势；单位面积内幼苗数量海拔3900 m处最多，4 200 m处极少，主要是由于土壤贫瘠，沙石较多，不能为种子发芽与幼苗定居提供必需的营养与水分。在阴坡，3 700~4 100 m海拔高度下林分郁闭度差异均不显著；3 700~4 000 m海拔高度下种子带翅长度差异不显著；海拔3800与3 900 m千粒重差异不显著，其他海拔之间差异显著；海拔3 700与3 800 m苔藓厚度差异不显著，其他海拔之间差异显著；凋落物厚度亦同阳坡；3 700~4 000 m海拔高度下幼苗数量差异不显著，其他海拔之间差异显著。

坡向	海拔/m	X₁	X₂	X₃	X₄	X₅	Y
阳坡	3700	75.12±2.79 a	12.45±0.50 a	10.38±0.14 c	5.50±0.21 b	8.38±0.46 a	8.80±0.30 b
	3800	64.96±4.59 a	12.36±0.33 a	12.37±0.11 a	8.05±0.31 a	8.57±0.44 a	6.20±0.64 b
	3900	69.65±3.16 a	13.27±0.29 a	11.25±0.14 b	5.90±0.36 b	8.52±0.43 a	14.24±1.32 a
	4000	49.74±5.00 b	11.06±0.42 c	9.69±0.07 d	3.74±0.20 c	4.73±0.21 b	5.40±0.83 c
	4100	49.52±3.42 b	11.54±0.40 b	8.60±0.20 e	2.20±0.16 d	4.38±0.37 b	5.60±0.92 c
	4200	40.05±2.98 b	11.11±0.24 c	8.02±0.13 f	1.28±0.13 e	3.41±0.29 b	0.83±0.11 d

阴坡	3700	65.16±1.05 a	12.01±1.06 a	8.72±0.21 b	10.62±0.27 b	9.31±0.18 a	13.44±0.58 a
	3800	64.83±1.97 a	12.04±0.44 a	10.38±0.11 a	10.06±0.18 b	9.33±0.18 a	11.61±1.54 a
	3900	60.16±2.11 a	12.74±1.11 a	10.46±0.14 a	12.27±0.19 a	9.54±0.16 a	15.19±1.62 a
	4000	59.62±1.05 a	11.99±0.79 a	8.31±0.20 b	4.30±0.14 d	4.66±0.15 b	11.40±0.75 a
	4100	59.25±1.29 a	11.17±0.63 b	7.58±0.21 c	5.25±0.15 c	4.55±0.15 b	9.69±0.68 b
	4200	49.41±1.05 b	10.68±0.51 c	6.72±0.32 d	2.51±0.13 e	4.34±0.18 b	5.00±0.90 c
说明：X₁为林分郁闭度(%)；X₂为种子带翅长度(mm)；X₃为种子千粒重(g)；X₄为苔藓厚度(cm)；X₅为凋落物厚度(cm)；Y为幼苗密度　　　　　(株·m⁻²)。小写字母表示不同海拔间差异显著(P＜0.05)

Table 1. Each influencing factor of natural regeneration and seedings density

3.2. 急尖长苞冷杉天然更新影响因子相关性分析

由相关性分析可知(表2)：阳坡种子带翅长度、种子千粒重、苔藓厚度、凋落物厚度、林分郁闭度等因子均与急尖长苞冷杉天然更新幼苗密度呈极显著正相关(P＜0.01))，说明这些因子可能有利于阳坡急尖长苞冷杉天然更新；同时各影响因子之间均存在极显著相关(P＜0.01)。阴坡林分郁闭度与急尖长苞冷杉幼苗密度相关性不显著，可能是阴坡光照较弱，相对比较湿润，林分郁闭度大小对急尖长苞冷杉天然更新影响较小；其他各因子与急尖长苞冷杉幼苗密度呈极显著正相关(P＜0.01)；阴坡林分郁闭度与种子带翅长度、种子千粒重之间相关性不显著，与苔藓厚度、凋落物厚度之间存在显著相关(P＜0.05)，其他各因子之间均存在极显著相关(P＜0.01)。阴坡林分郁闭度与种子带翅长度、种子千粒重之间相关性不显著，与苔藓厚度、凋落物厚度之间存在显著相关(P＜0.05)，其他各因子之间均存在极显著相关(P＜0.01)。

坡向	因子	X₁	X₂	X₃	X₄	X₅	Y
阳坡	X₁	1.000	0.464**	0.603**	0.551**	0.605**	0.467**
	X₂		1.000	0.414**	0.346**	0.450**	0.438**
	X₃			1.000	0.763**	0.774**	0.543**
	X₄				1.000	0.638**	0.344**
	X₅					1.000	0.586**

阴坡	X₁	1.000	0.198	0.228	0.298*	0.296*	0.210
	X₂		1.000	0.547**	0.541**	0.492**	0.390**
	X₃			1.000	0.787**	0.755**	0.579**
	X₄				1.000	0.945**	0.612**
	X5					1.000	0.509**
说明：X₁为林分郁闭度(%)；X₂为种子带翅长度(mm)；X₃为种子千粒重(g)；X₄为苔藓厚度(cm)；X₅为凋落物厚度(cm)；Y为幼苗密度 (株·m⁻²)。P＜0.05，*P＜0.01

Table 2. Correlation coefficients between each influencing factor of natural regeneration and seedings density

3.3. 急尖长苞冷杉天然更新影响因子通径分析

通径分析可进一步明确各影响因子对急尖长苞冷杉天然更新幼苗效应的直接和间接作用。由表3可知：阳坡林分郁闭度对幼苗密度产生直接正效应，但贡献较小，决定系数仅为0.014。种子带翅长度与幼苗密度极显著正相关(P＜0.01)，即种子带翅长度对幼苗密度产生直接正效应，原因是急尖长苞冷杉种子带翅，有利于种子传播，可为幼苗繁育提供更多生存空间。种子千粒重与幼苗密度极显著正相关，通径分析认为其对幼苗密度产生显著的直接正效应，相对其他影响因子直接效应较大。原因是种子千粒重可以为天然更新提供丰富的种子库储备，有利于天然更新幼苗的发生。苔藓厚度与急尖长苞冷杉幼苗密度极显著相关，通径分析发现其对幼苗密度产生显著的直接负效应，但通过其他影响因子产生的间接正效应较大，因此总体表现为正效应。凋落物厚度对幼苗密度产生显著的直接正效应和间接效应，是影响阳坡急尖长苞冷杉天然更新幼苗生长的最关键因子。通过直接作用来看，阳坡各影响因子对幼苗密度发生的贡献大小依次为凋落物厚度、种子千粒重、苔藓厚度、种子带翅长度、林分郁闭度。利用SPSS统计分析软件进行多元回归分析，得到最优拟合回归方程：Y=−14.617+0.033X₁+0.622X₂+0.964X₃−0.394X₄+0.654X₅ (R²=0.424)。

坡向	因子	直接作用	决定系数	相关系数	间接作用
坡向	因子	直接作用	决定系数	相关系数	X₁→Y	X₂→Y	X₃→Y	X₄→Y	X₅→Y	合计
阳坡	X₁	0.118	0.014	0.467**		0.084	0.191	−0.135	0.208	0.348
	X₂	0.182	0.033	0.438**	0.055		0.131	−0.085	0.154	0.255
	X₃	0.317*	0.100	0.543**	0.071	0.075		−0.187	0.262	0.221
	X₄	−0.245*	0.060	0.344**	0.065	0.064	0.242		0.219	0.590
	X₅	0.343*	0.118	0.586**	0.071	0.082	0.245	−0.156		0.242

阴坡	X₁	0.042	0.002	0.210		0.003	0.062	0.301	−0.198	0.168
	X₂	0.016	0.000	0.390**	0.008		0.148	0.546	−0.329	0.197
	X₃	0.270	0.073	0.579**	0.010	0.009		0.795	−0.505	0.309
	X₄	1.010**	1.020	0.612**	0.013	0.009	0.212		−0.632	−0.398
	X₅	−0.669*	0.448	0.509**	0.012	0.008	0.204	0.954		1.178
说明：X₁为林分郁闭度(%)；X₂为种子带翅长度(mm)；X₃为种子千粒重(g)；X₄为苔藓厚度(cm)；X₅为凋落物厚度(cm)；Y为幼苗　　　　　密度(株·m⁻²)。P＜0.05，*P＜0.01

Table 3. Path analysis between each influencing factor of natural regeneration and seedings density

阴坡林分郁闭度对幼苗密度产生直接的正效应，但较其他影响因子贡献小。种子带翅长度对幼苗密度产生的直接正效应较小，但通过种子千粒重、苔藓厚度产生的间接正效应较大。种子千粒重与幼苗密度极显著正相关，说明阴坡种子千粒重同样有利于急尖长苞冷杉的天然更新。阴坡苔藓厚度对幼苗密度产生极显著的直接正效应，但通过其他影响因子产生间接负作用，总体表现为阻碍急尖长苞冷杉天然更新，因此在阴坡可以通过降低苔藓厚度来改善天然更新效果。凋落物厚度对幼苗密度有显著的直接负效应，但通过其他影响因子产生较大的间接正效应。原因在于凋落物阻碍了种子到达土壤，不利于种子的萌发，凋落物分解后可为种子萌发、幼苗建成提供必需的养分。通过直接作用来看，阴坡各影响因子对幼苗密度发生的贡献大小依次为苔藓厚度、凋落物厚度、种子千粒重、林分郁闭度、种子带翅长度，回归方程为：Y=1.309+0.015X₁+0.074X₂+0.819X₃+1.254X₄−1.229X₅ (R²=0.448)。

4. 讨论与结论

天然更新是森林生态系统的重要组成部分，是多个因子相互综合作用的结果。本研究利用通径分析分解各影响因子作用，寻找影响急尖长苞冷杉幼苗天然更新的关键因子。研究发现：千粒重、苔藓厚度及凋落物厚度随海拔升高均呈现先增加后减小的趋势，阴坡与阳坡幼苗数量均先增大后减少，天然更新幼苗状况较好。川西高山林区云杉P. asperata、冷杉A. faxoniana的天然更新普遍不良，冷杉幼苗存活率不高，幼苗向幼树阶段过渡很难^[23]。本研究中色季拉山急尖长苞冷杉天然更新幼苗较丰富，为其向幼树阶段过渡提供了数量储备。马姜明等^[1]发现：川西亚高山暗针叶林恢复过程中，不同恢复阶段岷江冷杉幼苗、幼树及小树的整体变化规律趋于一致，林分环境对川西亚高山岷江冷杉尤其是藓类林的天然更新影响更加复杂。

对5个影响因子的相关性研究发现：阴坡林分郁闭度与其他影响因子间为显著或不显著相关，其他影响因子之间无论在阴坡还是阳坡均呈现极显著相关，说明种子带翅长度、种子千粒重、苔藓厚度与凋落物厚度对幼苗密度的发生影响较大。阴坡林分郁闭度与幼苗密度相关性不显著，主要是阴坡光照不足，相对潮湿，有利于种子的萌发。阳坡林分郁闭度对幼苗密度产生直接正效应，但较其他影响因子贡献小；种子带翅长度对幼苗密度产生直接正效应；种子千粒重为显著直接正效应，且大于其他影响因子的直接效应；苔藓厚度对幼苗密度产生显著直接负效应，但通过其他影响因子产生总的间接正效应较大，因此一定程度抵消了其负效应；凋落物厚度与幼苗密度产生的显著直接正效应较大。因此阳坡各因子对幼苗密度发生的贡献大小依次为凋落物厚度、种子千粒重、苔藓厚度、种子带翅长度、林分郁闭度。阴坡林分郁闭度对幼苗密度产生直接正效应；种子带翅长度产生的直接正效应相对较小，但通过种子千粒重、苔藓厚度产生的间接正效应较大；种子千粒重与幼苗密度呈极显著正相关；苔藓厚度对幼苗密度产生极显著直接正效应，但通过其他影响因子产生间接的负作用较大，因此表现为较厚苔藓层阻碍急尖长苞冷杉天然更新作用。阴坡各因子对幼苗密度发生的贡献大小依次为苔藓厚度、凋落物厚度、种子千粒重、林分郁闭度、种子带翅长度。马姜明等^[1]证实：过厚苔藓层对岷江冷杉天然更新有显著的抑制作用，降低苔藓厚度可有效改善其天然更新效果。原因在于林下植被的存在或阻碍种子到达土壤，或阻止幼苗向幼树的发生^[24-25]。同时蔺菲等^[26]也发现：没有苔藓层或苔藓层较厚均不利于植物的早期生长。过厚的苔藓层导致幼苗的成活率较低^[27]。本研究中，阳坡苔藓层厚度为1.28~8.05 cm，阴坡为2.51~12.27 cm，阴坡苔藓层厚度普遍较高，因此总负效应也较大。

色季拉山急尖长苞冷杉天然更新受多个影响因子共同作用；利用通径分析可找到影响阳坡与阴坡幼苗天然更新的关键因子，为全面研究色季拉山急尖长苞冷杉天然更新奠定基础。后续可深入研究各影响因子的作用机制，为进一步研究急尖长苞冷杉种群更新及其种质资源的保护提供理论依据。

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