Yangen Chen

Managing forest understory has a significant impact on soil greenhouse gas (GHG) emissions and the ecosystem’s capacity for carbon sequestration. However, its specific impacts and mechanisms within hickory (Carya cathayensis Sarg) forests remain unclear. The objective of this study was to examine the effects of different understory vegetation treatments on hickory stands with similar growth history, site conditions, and slopes: Cinnamomum chekiangense (Cinnamomum chekiangense Nakai) and strip-sown ryegrass (Lolium perenne L.) (CR1), Cinnamomum chekiangense and scattered ryegrass (CR2), Torreya grandis (Torreya grandis’ ‘Merrillii’ Hu) and strip-sown wild rapeseed (Brassica napus L.) (TW1), Torreya grandis and scattered wild rapeseed (TW2), and removal of understory vegetation (CK). Twenty experimental plots were established at the Lin’an Forestry Carbon Sink Pioneer Base, and after 12 months of monitoring, the responses of GHG emissions, vegetation, and soil organic carbon (SOC) sequestration were analyzed, revealing the differences in ecosystem carbon sequestration capacity. Compared to CK, CR1, CR2, TW1, and TW2 increased the global warming potential (GWP) by approximately 26%, 55%, 26%, and 16%, respectively. The SOC increased by approximately 76%, 102%, 51%, and 32%, respectively, while the vegetation carbon sink increased by approximately 30%, 27%, 53%, and 62%, respectively. In summary, ecosystem carbon sequestration increased by approximately 109%, 98%, 95%, and 92%, respectively. The findings indicate that managing understory vegetation in pecan forests significantly enhances ecosystem carbon sequestration but also increases soil GHG emissions. To enhance future research priorities, it is essential to focus on increasing carbon sequestration in hickory forests and managing soil GHG emissions through effective and rational understory vegetation management.

Amidst the global shift towards a low-carbon development trajectory, the hickory industry in Lin’an District is progressively embracing green, low-carbon, and sustainable practices. This study, leveraging the life cycle assessment (LCA) methodology, meticulously scrutinizes the carbon footprint of the hickory industry by segmenting its life cycle into two distinct subsystems: the plantation and the factory. Through comprehensive, year-long monitoring of soil greenhouse gas (GHG) emissions in hickory plantations, our findings underscore that while total GHG emissions from eco-complex management (ECM) surpassed those of intensive management (IM) by 10.7% (p < 0.001), ECM significantly mitigated the carbon footprint per kilogram of hickory produced, achieving a reduction of 1.0495 kgCO₂eq. This advantage is primarily attributable to ECM’s diminished reliance on chemical fertilizers. Within the factory subsystem, when processing 1 kg of hickory, the digital factory incurred a carbon footprint of 2.5923 kgCO₂eq kg⁻¹, whereas family workshops exhibited a lower footprint of 1.9544 kgCO₂eq kg⁻¹. Notably, the processing and packaging stages collectively accounted for over 90% of the factory subsystem’s carbon emissions, with natural gas being the primary contributor during processing. To estimate the carbon emission reduction potential within the hickory industry, this research draws parallels with emission reduction strategies employed by other industries and outlines tailored strategies to propel its low-carbon development. By advocating for the widespread adoption of ECM and enhancing the energy efficiency of processing enterprises, the hickory industry can effectively diminish its carbon footprint and steer towards a green, low-carbon, and high-quality development paradigm.

As an important means of near-natural management in secondary forests, thinning effectively enhances the growth status of forest trees, and increases the overall forest yield and carbon sequestration capacity of the forest floor through rational stand regulation. This study focused on subtropical secondary broadleaf forests in the mountainous regions of western Zhejiang, China, and involved three treatment groups: a high-intensity thinning group (HT) (retaining trees with a diameter greater than 8 cm and removing shrub-layer vegetation), a low-intensity thinning group (LT) (retaining trees with a diameter greater than 5 cm and removing shrub-layer vegetation), and a control plot (no thinning treatment) (CK). The study aimed to investigate the effects of different thinning intensities on forest carbon stocks, soil respiration, and soil environmental factors, as well as to assess how thinning modifications impact the carbon sequestration capacity of the forest floor. The results illustrate the following: (1) The biomass growth and carbon sequestration capacity of individual trees under HT were significantly greater compared to other treatment groups. Conversely, carbon stock growth in the arboreal layer was higher under LT than under other treatments. (2) Thinning operations increased soil carbon stocks and improved soil fertility. (3) High-intensity (HT) and low-intensity thinning (LT) increased the soil moisture in both the surface and subsurface layers, with HT showing the highest levels. (4) One year after thinning, the soil organic matter (SOM) increased significantly, rising by 30.86% in HT and 21.84% in LT compared to CK. (5) In comparison to LT and CK, HT showed a significant increase in soil respiration rates, which led to higher CO₂ and N₂O emissions from the soil while also suppressing CH₄ uptake. The study concludes that LT can enhance carbon sequestration in both the tree and soil layers, improve soil fertility, and reduce greenhouse gas emissions. This supports the sustainable development of forest ecosystems and effective carbon management.

Forest management, especially understory vegetation conversion, significantly affects soil greenhouse gas (GHG) emissions and soil C and N pools. However, it remains unclear what effect renovating understory vegetation has on GHG emissions and soil C and N pools in plantations. This study investigates the impact of renovating understory vegetation on these factors in Chinese hickory (Carya cathayensis Sarg) plantation forests. Different understory renovation modes were used in a 12-month field experiment: a safflower camellia (SC) (Camellia chekiangoleosa Hu) planting density of 600 plants ha⁻¹ and wild rape (WR) (Brassica napus L.) strip sowing (UM1); SC 600 plants ha⁻¹ and WR scatter sowing (UM2); SC 1200 plants ha⁻¹ and WR strip sowing (UM3); SC 1200 plants ha⁻¹ and WR scatter sowing (UM4); and removal of the understory vegetation layer (CK). The results showed that understory vegetation modification significantly increased soil CO₂ and emission fluxes and decreased soil CH₄ uptake fluxes (p < 0.01). The understory vegetation transformation significantly improved soil labile carbon and labile nitrogen pools (p < 0.01). This study proposes that understory vegetation conversion can bolster soil carbon sinks, preserve soil fertility, and advance sustainable development of Chinese hickory plantation forests.

In recent years, the impact of surface heat islands in urban street canyons has become increasingly apparent. However, the research on the use of trees to mitigate surface heat islands remains limited. To address this gap, this study combines experiments and simulations to analyze the cooling effect of trees on surface temperatures under varying timeframes and layouts in an east–west street canyon. The results reveal that the temperature of the road decreases by 10–15 °C, which is 2–4 times greater than that on the south side. Moreover, at 5:00 p.m. in the afternoon, the cooling effect on the south side is 10.3 °C, which is twice that of the north side. In practical planning and design, the diameter of the tree canopy should be maximized, and trees with leaf-area densities greater than 1.5 m²/m³ should be selected. Additionally, the layout of trees should be optimized to maximize the tree canopy coverage. These findings have important implications for optimizing plant selection and placement in street canyons.