风景园林碳汇能力建设的基本逻辑

根据政府间气候变化专门委员会（IPCC）第六次评估报告显示，2011年至2020年平均气温较工业化前增高1.09℃。“双碳”行动是应对全球气候变暖的重要举措，截至2021年4月，已有130多个国家和地区拟议了“零碳”或“碳中和”气候目标。碳中和一般从碳源（碳排放）和碳汇（碳固定）的角度进行理解，包含了自然过程和人为过程。生态系统在固碳中发挥重要作用，国内的森林大都处于幼年期，在树木的适龄期内，固碳作用可持续进行，同时，还有不少可造林面积，加之草地、湿地、农田土壤的碳大都处于不饱和状态，因此，生态系统的固碳潜力巨大。而风景园林作为城市生态系统的重要构成，是城市中唯一有生命的具有碳汇功能的基础设施，也是实现人口高密区碳中和的主要组成部分。

广义的风景园林，是城市区域内包含森林、湿地、绿地、水体等要素的生态系统，其助力碳中和的途径主要通过植被、土壤和水体的减源和增汇来实现。植物配置以适应性、抗性、固碳能力较强的地带性乡土植物为主，综合考虑植物寿命、规格、常绿与落叶配比、幼龄与老龄配比、群落相生相克、落地与架空等因素；土壤碳汇能力显著强于植被碳汇，通过改良土壤肥力、生物活性和物理结构，可充分发挥土壤的碳固持能力；水体质量、水生植物配置、水下土壤等是水体碳汇需重点关注的内容。从风景园林空间布局而言，在“双碳”政策和公园城市建设理念下，以生态建设目标为引领，推进绿地、林地、湿地等融合发展，优化布局体系，持续增强生态系统的碳汇能力。从管控的角度，风景园林建设和管理养护过程中要控制碳排放、降低能源消耗，以达到“低维护”目标，寻求碳平衡；以科学表征为基础，尊重自然规律，遵循高碳汇的作用机理。

本期专题“科技创新助力碳中和”，涵盖宏观规划到微观实践的研讨，进一步厘清了碳中和目标下风景园林减碳增汇的基本逻辑以及技术需求。提出“双碳”战略是换跑道，而不是原道超车，需通过一系列颠覆性变革，在新一轮产业革命中获得主角地位等革新思考；剖析碳中和背景下全球11个国家的30项相关规划行动，构建城市绿地适应性规划“目标—策略—指标”总体技术框架，提出“市域—城区—街区—地块”四级管控层级，并差异化制定了多尺度精准增效规划策略和多层级评估管控指标；基于自然的解决方案的绿色空间韧性—降碳协同范式与设计策略，提出全周期迭代演进的动态适应性范式和七项原则性策略；抽样城市街道的行道树，运用i-Tree Streets模型对街道空间的碳储效益比、CO2吸收效益、节能效益等构成的低碳综合效益进行评估测算，提出街道空间精细化改造提升建议。

实现碳中和是一项极具挑战性的系统工程。从“达峰”到“中和”，控碳、减碳、低碳、中和是必经的过程阶段。“达峰”与“中和”之间是有鸿沟的，没有系统性的社会变革，没有颠覆性的技术革命，很难实现从量变到质变的跃迁。当前，“双碳”目标依赖自上而下的制度牵引已成为共识，如何切实推进法律法规充分发挥其保障作用，任重而道远。

主编

2022年12月20日

The Basic Logic of Carbon Sink Capacity Construction of Landscape Architecture

According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), the average temperature from 2011 to 2020 increased by 1.09℃ compared with pre-industrial period.The “double carbon” action is an important measure to deal with global warming.As of April 2021, more than 130 countries and regions have proposed “zero carbon” or “carbon neutrality” climate goals.Carbon neutrality is generally understood from the perspective of carbon sources (carbon emissions) and carbon sinks (carbon sequestration), including natural and man-made processes.Ecosystems play an important role in carbon sequestration.Most forests in China are in their infancy, and carbon sequestration can be carried out continuously in the right age of trees.At the same time, there is still a lot of afforestation area, and the carbon of grassland, wetland and farmland soil is mostly in the unsaturated state,so the carbon sequestration potential of the ecosystem is huge.As an important component of urban ecosystem, landscape architecture is the only living infrastructure with carbon sink function in the city, and also the main component of carbon neutrality in high-density population area.

Broadly speaking, landscape architecture is an ecosystem containing forest,wetland, green space, water and other elements in an urban area.Its contribution to carbon neutrality is mainly achieved through reducing the source and increasing the sink of vegetation, soil and water.The plant configuration is dominated by zonal native plants with strong adaptability, resistance and carbon sequestration ability.Factors such as plant life, size, ratio of evergreen to deciduous, ratio of young to old, community interaction and conflict, ground and aerial are considered comprehensively.Soil carbon sequestration capacity is significantly stronger than vegetation carbon sequestration capacity.Soil carbon sequestration capacity can be fully exerted by improving soil fertility, biological activity and physical structure.Water quality, aquatic plant configuration,underwater soil and so on are the key contents of water carbon sink.In terms of the spatial layout of landscape architecture, under the “double carbon” policy and the concept of urban park construction, the integrated development of green space, woodland and wetland should be promoted, the layout system should be optimized, and the carbon sink capacity of the ecosystem should be continuously enhanced.From the perspective of management and control, carbon emissions and energy consumption should be controlled and reduced during the construction, management and maintenance of landscape architecture, so as to achieve the goal of “low maintenance” and seek carbon balance.

The topic of this issue, “Scientific and Technology Innovation Promotes Carbon Neutrality”, covers the discussion from macro planning to micro practice, and further clarifies the basic logic and technical requirements of landscape architecture for carbon reduction and sink increase of landscape architecture under the goal of carbon neutrality.It was proposed that the “double carbon” strategy is to change the runway instead of overtaking the original road, and it needs to obtain the leading role in the new round of industrial revolution through a series of subversive changes.30 relevant planning actions in 11 countries were analyzed, and multi-scale precise efficiency planning strategies and multi-level evaluation and control indicators were differentiated.Based on the green space resilience and carbon reduction collaborative paradigm and design strategy of natural solutions, the dynamic adaptability paradigm and seven principle strategies of the whole cycle iterative evolution were proposed.Besides, the i-Tree Streets model was used to evaluate and calculate the comprehensive benefit of low carbon of street space by sampling street trees of urban streets, and the suggestions on refinement and improvement of street space were put forward.

Achieving carbon neutrality is a very challenging systematic engineering.From “peak” to “neutralization”, carbon control, carbon reduction, low-carbon and neutralization is the necessary process stage.There is a gap between “peak” and“neutralization”.Without systematic social change and subversive technological revolution, it is difficult to realize the transition from quantitative change to qualitative change.At present, it has become a consensus that the goal of “double carbon” relies on top-down institutional traction.It is still a long way to go to effectively promote laws and regulations to give full play to their safeguarding role.

Editor-in-Chief

December 20th, 2022