粤港澳大湾区不同恢复模式植物群落结构与生态系统健康的动态变化

基于长期定位监测数据，量化揭示了红锥纯林（Castanopsis hystrix）、10种与30种乡土树种混交林等3种乡土人工林植物群落的生物量、物种多样性、生物热力学健康水平（eco-exergy）和土壤理化性状在种植后13年内的发展动态，并与尾叶桉（Eucalyptus urophylla）纯林，以及自然恢复系统（灌草坡）进行了比较。结果表明：（1）研究期间，5种恢复模式的植物群落生物量均呈现波动上升趋势，但在发展节率上有所差异。13龄时的尾叶桉纯林与两种乡土树种混交林生物量显著高于其各自1龄时的水平，且显著高于自然恢复灌草坡；相较于其他人工林，红锥纯林生物量增长缓慢，但快于灌草坡；（2）5种恢复模式植物群落的物种多样性（物种丰富度、Shannon-Wiener指数、Pielou均匀度指数）在6至13龄间均呈下降趋势，且30种乡土树种混交林下降趋势最为显著。13龄时，两种混交林Shannon-Wiener指数略高于两种纯林，显著高于灌草坡；10种乡土树种混交林的Pielou均匀度指数略高于红锥纯林与30种乡土树种混交林，显著高于尾叶桉纯林与灌草坡。（3）4种人工林的植物群落生物热力学健康水平皆在6至13龄间显著增加；13龄时两种乡土混交林群落生态显著高于两种纯林，两种纯林显著高于灌草坡，且该差异主要源自于乔木层生态的差异。（4）不同植被恢复模式中，10种乡土树种混交林土壤养分的累积效果最佳，13龄时其土壤总氮含量显著高于红锥纯林和自然恢复灌草坡，但与30种乡土树种混交林和尾叶桉纯林无显著差异。（5）冗余分析结果显示，研究期间植被与土壤间的相关关系逐步建立，土壤理化性状对地上植被结构变化的解释度由1龄时的73.3%逐步上升至13龄时的82.0%，但只有土壤有机碳含量在13龄时与地上植被结构的相关性达到显著水平。上述结果表明，乡土种人工林与外来种人工纯林群落结构、生物热力学健康水平、及植被与土壤间关系的发展规律相似，且相对而言，混交林优于纯林，纯林优于自然恢复灌草坡。植被恢复的起始物种丰富度并不是越高越好；发展到13龄时，10种乡土树种混交林在植被结构与土壤改良方面均优于30种乡土树种混交林。植被与土壤间相关关系的建立是一个长期的过程，不同植被恢复模式对土壤理化性状的差异性影响难以在短期内有所显现。

Plant community structure and health development dynamics of different restoration modes in Guangdong-Hong Kong-Macao Bay Area

Based on long-term monitoring data, the dynamics of plant community biomass, species diversity, bio-thermodynamic health state (eco-exergy) and soil properties of Castanopsis hystrix monoculture, 10 native species and 30 native species mixed forest plantations after planting 13 years were quantitatively revealed, and compared with Eucalyptus urophylla monoculture and the naturally recovered shrub and herb (SH) ecosystem. The results showed that:(1) the plant community biomasses of all five restoration modes exhibited a fluctuating increase tendency during the study period, but with different development rates. The biomasses of the E. urophylla monoculture and the two mixed-native species forest plantations at 13 years old were significantly higher than their own states at 1 year old respectively, besides significantly higher than that of the SH ecosystem. The biomass of the C. hystrix monoculture developed slowly than that of other forest plantations but quickly than that of the SH. (2) The plant species diversity (species richness, Shannon-Wiener index, and Pielou index) decreased progressively in the five restoration modes from age 6 to 13, and the downtrends of the 30 native species mixed forest plantation were most significant. At 13 years old, the Shannon-Wiener index of the two mixed-native species plantations was slightly higher than that of the two monocultures and the SH. The Pielou index of the 10 native species mixed forest plantation was slightly higher than that of the C. hystrix monoculture and the 30 native species mixed forest plantation, but was significantly higher than that of the E. urophylla monoculture and the SH. (3) The community bio-thermodynamic heath states of the four forest plantations significantly increased from age 6 to 13. Up to 13 years old, the plant community eco-exergies of the two mixed-native species forest plantations were significantly higher than those of the two monocultures which were significantly higher than that of the SH. (4) Among the five vegetation restoration modes, it was the 10 native species mixed forest plantation that had the superior characteristic at soil nutrient accumulation, with its soil total nitrogen content significantly higher than that of the C. hystrix monoculture and the SH at 13 years old, but not significantly different with that of the 30 native species mixed forest plantation and the E. urophylla monoculture. (5) The results of redundancy analysis showed that the correlation between vegetation and soil was gradually established during this study period, and the explanatory degree of soil properties to the change of aboveground vegetation structure gradually increased from 73.3% at age 1 to 82.0% at age 13. However, only the correlation between the soil organic carbon content and the aboveground vegetation structure indices reached a significant level at age 13. The results showed that the development of the native species forest plantations followed the same laws with the exotic species monoculture and the natural recovery ecosystem in the pant community structure, the bio-thermodynamic health state and the relationship between plant community and soil properties. Comparatively, the mixed-native forest plantations were superior to the monoculture plantations in plant community development and soil nutrient accumulation, while the monoculture plantations were better than the natural recovery ecosystem. However, the initiative plant species richness was not the higher the better. After 13 years development, the 10 native species mixed forest plantation performed better than the 30 native species mixed forest plantation in both vegetation structures and soil properties. The establishment of the relationship between vegetation and soil is a long-term process, and the effects of different vegetation restoration modes on soil properties is hard to emerge in a decade.