间伐对杉木人工林生态系统碳储量的短期影响

【目的】研究不同间伐强度下杉木人工林生态系统碳储量及其分配格局,进一步优化林分经营管理措施,准确评估间伐对杉木人工林生物量和碳储量的短期影响,为提高人工林的碳汇能力提供依据。【方法】以福建省三明市官庄国有林场11年生杉木人工林为研究对象,选择坡度、坡位、土壤条件相对一致的林分,按照完全随机区组试验设计,设置弱度间伐(31%,伐后林分2 250株/hm²,LIT)、中度间伐(45%,伐后林分1 800株/hm²,MIT)、强度间伐(63%,伐后林分1 200株/hm²,HIT)等3种间伐强度;共设置9块20 m×20 m样地,采集深度为1 m剖面内不同土层的土壤;并在样地内每木检尺,利用生物量回归方程对乔木层生物量进行估算,同时实测林下植被和凋落物生物量;通过元素分析仪测定植被和土壤碳含量,并根据碳含量估算碳储量。【结果】间伐后3年,杉木人工林乔木层碳储量随着间伐强度的增加而减小,LIT、MIT、HIT处理样地乔木层碳储量依次为66.16、58.78、49.71 t/hm²;杉木人工林灌木层和草本层的碳储量随着间伐强度的增加而显著增加,分别占生态系统碳储量的0.03%~0.19%和0.01%~0.67%;凋落物层碳储量占生态系统碳储量的2.87%~4.32%,间伐对凋落物层碳储量无显著影响;土壤有机碳储量在不同间伐处理间差异显著(P<0.05),杉木人工林土壤层碳储量随着间伐强度的增加而降低,HIT处理土壤层碳储量较LIT和MIT处理降低了32.07%和1.03%。间伐后3年,杉木人工林生态系统碳储量随着间伐强度增加而显著降低(P<0.05),LIT、MIT和HIT处理样地总碳储量依次为173.85、161.12、121.73 t/hm²。乔木层和土壤层碳储量之和占比超过90.00%,表明乔木层和土壤层是巨大的碳库,且间伐短期降低生态系统总碳储量。【结论】间伐后短期内杉木人工林乔木层、凋落物层和土壤层碳储量随着间伐强度的增加而下降,而灌木层和草本层的碳储量则随着间伐强度的增加而增加,表明间伐3年后试验林地还处于恢复期,杉木人工林间伐短期内会降低生态系统总碳储量。研究结果可部分解释间伐后短期内杉木人工林生态系统各组分碳储量的分布格局,并为研究区的人工林碳汇增加和可持续经营提供科学依据。

Short-term effects of thinning on carbon storage in Chinese fir plantation ecosystems

【Objective】 Thinning is an important management measure in plantation forest management, which can change the growth environment and affect the growth, productivity and carbon storage of the forest stands. As an important tree species for afforestation in southern China, Chinese fir occupies an indispensable position in forestry production. Therefore, studying the short-term impact of different thinning intensities on carbon storage in Chinese fir plantations helps to optimize forest management measures, and accurately evaluate the short-term effects of thinning on the biomass and carbon storage, which is important in the development of carbon sink forestry, and can provide a basis for improving carbon sink capacity.【Method】 The 11-year-old Chinese fir plantations in Guanzhuang State Forest Farm in Sanming City, Fujian Province, with consistent slopes, slope positions and soil conditions were selected for research. The experiment was designed according to a random block design with three levels of thinning intensity with light thinning (31%, LIT, 2 250 plants/hm² in post-cutting stand), moderately intensive thinning (45%, MIT, 1 800 plants/hm² in post-cutting stand),and highly intensive thinning (63%, HIT, 1 200 plants/hm² in post-cutting stand). A total of nine 20 m×20 m sample plots were set up, and soils from different soil layers in a 1 m section were collected. In the sample plot, the biomass of the tree layer was estimated using the biomass regression equation, and the biomass of the understory vegetation and litter were measured. The carbon content of the vegetation and soil was measured using an element analyzer, and the carbon storage was estimated based on the carbon content. The carbon storage and distribution pattern of each component in the ecosystem were examined after three thinning treatments. The carbon storage of each component of the ecosystem during the growth of the Chinese fir after three thinning treatments was analyzed to evaluate the effects of thinning on the carbon storage of the Chinese fir plantation.【Result】 Three years after thinning, the carbon storage of the tree layer and the soil layer decreased with the increase in thinning intensity. The carbon storage of the tree layer for the LIT, MIT, and HIT plots was 66.16, 58.77, and 49.71 t/hm², respectively. The carbon storage of the shrub layer and herb layer significantly increased with the increase in thinning intensity, accounting for 0.03%-0.19% and 0.01%-0.67% of the carbon storage of the ecosystem, respectively. There was no significant effect on the carbon storage of the litter layer, and the litter layer carbon storage accounted for 2.87%-4.32% of the ecosystem carbon storage. The soil carbon storage decreased with the increase in thinning intensity, and the soil organic carbon storage was significantly different between different thinning treatments (P < 0.05). The soil carbon storage from the HIT treatment reduced 32.07% and 1.03% compared with LIT and MIT treatments. Three years after thinning, the carbon storage significantly decreased with the increase in thinning intensity (P < 0.05). The total carbon storage of the LIT, MIT and HIT plots was 173.85, 161.12 and 121.73 t/hm², with the sum of the carbon storage of the tree layer and soil layer accounting for more than 90.00%. It indicates that the tree layer and soil layer are huge carbon pools, and thinning will reduce the total carbon storage in short-term in the ecosystem.【Conclusion】The carbon storage of the arbor, litter layer and soil layer in the Chinese fir plantation short-term decreased with the increase in thinning intensity after thinning, while the carbon storage of the shrub and herb layer increased with the increase in thinning intensity, indicating that the intensity of thinning increased after three years, and that the experimental forest land is still in the recovery period. The research revealed that thinning of Chinese fir plantations will reduce the total carbon storage of the ecosystem in short-term, provide a scientific basis for the carbon sink and sustainable management of plantations in the study area.