尾巨桉-红锥混交复合生态营林模式下尾巨桉采伐强度对林下植物多样性的影响

Effects of Cutting Intensity on Understory Plant Diversity in the Mixed Eucalyptus urophylla × E. grandis and Castanopsis hystrix Plantations under Eco-silviculture Regime

关键词:  尾巨桉-红锥混交林，短中长周期复合经营，采伐强度，林下植被，物种多样性

Key words:  mixed E. urophylla × E. grandis and C. hystrix plantation  short-, medium- and long-term cycle compound management  cutting intensity  understory vegetation, species diversity

摘要:

在桉树（Ecalyptus spp.）与乡土珍贵树种短中长周期复合经营中，短周期桉树采伐强度的确定对林分结构调整和林下植物多样性维持至关重要。为合理选择桉树采伐强度、优化林分结构、提高林下植物多样性，实现可持续经营，以尾巨桉（E. urophylla × E. grandis）-红锥（Castanopsis hystrix）混交林为研究对象，对林龄7 a的尾巨桉进行不同强度采伐 [LC（轻度采伐，25%）、MC（中度采伐，50%）、HC（重度采伐，75%）和CC（皆伐，100%）]，以未采伐的林分为对照，研究尾巨桉不同采伐强度对林下植物多样性的影响，结果表明：（1）采伐尾巨桉改变了灌草层优势种的组成；灌木层中，林下植物多样性无显著差异；草本层中，MC和CC显著提高物种丰富度和Simpson指数，MC显著提高Shannon-Wiener指数。；（2）轻度至重度采伐显著降低0-20 cm土层土壤有效氮含量，皆伐对土壤有效氮含量影响不显著；而中度采伐和皆伐显著提高土壤0-20 cm、20-40 cm土层有机碳、全氮、全磷含量；（3）随采伐强度增加，林分叶面积指数表现为MC(4.58)>CC(4.23)>HC(4.20)>LC(3.86)>CK(3.79)，但各采伐强度间差异不显著；（4）影响林下植物多样性的主控因子为土壤有机碳、有效氮、土壤碳氮比、叶面积指数，其中土壤有机碳、叶面积指数与灌木层物种丰富度呈显著正相关，有效氮、土壤碳氮比与草本层物种丰富度呈显著正相关。综上所述，不同尾巨桉采伐强度对其与红锥混交林林下植物群落物种多样性的影响不同，以中度采伐（50%）提升林下植物群落物种多样性、土壤养分含量的效果最佳。

Abstract:

Eucalyptus (Eucalyptus spp.) plantations play a crucial role in ensuring national timber security and addressing global climate change. Therefore, studying the impact of harvesting intensity on understory plant diversity in Eucalyptus plantations, specifically in the case of Eucalyptus urophylla × Eucalyptus grandis hybrids, is of great significance. To provide scientific basis for rational selection of cutting intensity, optimization of stand structure of mixed Eucalyptus and precious tree species plantations, and realization of short-, medium- and long-term combined management, the effects of different cutting intensities [LC (light cutting, 25%), MC (moderate cutting, 50%), HC (heavy cutting, 75%), and CC (clear-cutting, 100%)] of E. urophylla × E. grandis on understory plant species diversity and its main controlling factors in mixed E. urophylla× E. grandis and Castanopsis hystrix plantation were investigated. The results showed that: (1) The harvesting of Eucalyptus urophylla × E. grandis altered the composition of dominant species in the shrub-herb layer; within the shrub layer, there was no significant difference in plant diversity beneath the canopy. In the herb layer, both monoculture (MC) and close-canopy (CC) treatments significantly increased species richness and the Simpson index, with MC also significantly enhancing the Shannon-Wiener index. (2) MC and HC significantly decreased soil available nitrogen content in 0-20 cm soil layer, while CC had no significant effect on soil available nitrogen content. MC and CC significantly increased the contents of organic carbon, total nitrogen and total phosphorus in 0-20 cm and 20-40 cm soil layers. (3) The stand leaf area index with cutting intensity were MC (4.58) > CC (4.23) > HC (4.20) > LC (3.86) > CK (3.79), although no significant differences were observed among the LAI values across different cutting intensities. (4) The primary controlling factors influencing understory plant diversity are soil organic carbon, available nitrogen, soil carbon-to-nitrogen ratio, and leaf area index. Notably, soil organic carbon and leaf area index exhibit significant positive correlations with species richness in the shrub layer. Conversely, available nitrogen and soil carbon-to-nitrogen ratio show significant positive correlations with species richness in the herbaceous layer. In conclusion, different cutting intensities of E. urophylla × E. grandis had varying effects on the understory plant species diversity in mixed E. urophylla × E. grandis and C. hystrix plantation. Moderate cutting (50%) had the best effects on understory plant species diversity and soil nutrient content.