Understanding urban trees: form, function and vulnerability

背景全球一半以上的人口已经生活在城市地区，到2020年，这一数字将上升到66%。因此，城市地区生态系统服务的提供对人们的生活质量和更广泛的环境正变得越来越重要，而城市树木对此做出了不成比例的贡献。这些服务包括城市热岛缓解、空气污染物过滤、雨水调节和碳固存，但人们对不同树种的生态系统服务提供的差异知之甚少。此外，虽然大多数城市森林研究侧重于树木改善城市环境的能力，但较少关注城市环境(如污染加剧、城市热岛效应、干旱胁迫)对树木本身的影响。在不了解现有城市森林对这些压力的弹性的情况下，种植树木的人，从地方当局到个人，都面临着选择适合城市环境的树种的挑战，特别是在面临气候变化等未来威胁的情况下。这篇博士论文将解决以下三个问题：1)在典型的英国城市中，最常见的城市树木是什么？它们是如何分布在整个城市结构中的？2)常见树种的分布、大小和生态系统服务提供之间的关系？3)在特定的生命阶段，哪些城市树种，是否容易受到典型城市压力的影响？目标本项目将以谢菲尔德为例，通过为常见的城市树种安装原位生长监测设备，在城市范围内建立长期监测点。这个现场监测网络将与定期实地工作相结合，测量生理变量和生态系统服务提供的关键指标，实验室分析，地理信息系统和遥感，以探索城市树木的分布、物种和大小如何影响树木功能，从而影响生态系统服务提供，以及这些树木如何受到城市压力的影响。它将涉及以下目标：1.确定城市范围内不同土地覆盖范围内常见城市树种和大小的分布情况。评估城市树木对关键生态系统服务的贡献，包括空气温度、污染物清除和不同城市土地覆盖的碳储存。3.确定城市压力因素，包括污染、高温和干旱，对城市景观中树种的形态和功能的影响。4.与地方当局共同设计植树指南，以确保城市森林在未来的复原力。该项目将与谢菲尔德市议会合作管理。谢菲尔德市议会的数据科学家尼古拉·麦克休博士将共同指导这项博士研究。她在基于地理信息系统的城市森林分析方面拥有特殊的专业知识。此外，该学生将与树木和林地经理曾傑瑞·冈顿合作。他们将为学生提供实物支持，包括获得i-Tree生态调查数据(实物价值20,000 GB)和工作人员时间(实物价值2,000 GB)。新颖性和时效性政府的25年环境计划(2018年发布)的目标是到2020年种植100万棵城市树木。这项研究将更好地为决策提供“更多和更好质量的绿色基础设施，包括树木”，并帮助发展国家框架的绿色基础设施标准在25年计划中提出。它将帮助地方当局了解如何在正确的地方种植正确的树，以便最大化树木的存活机会，并在特定位置提供所需的生态系统服务。了解这些问题是确保未来可持续和有弹性的城市森林的关键。

BackgroundMore than half the global population already live in urban areas and that figure will rise to 66% by 2020. Ecosystem service provision in urban areas is therefore becoming increasingly important for people's quality of life and the wider environment, to which urban trees make a disproportionate contribution. These services include urban heat island mitigation, air pollutant filtration, storm water regulation and carbon sequestration, but there is little understanding of how ecosystem service provision varies among tree species. In addition, whilst the majority of urban forest research focuses on the ability of trees to improve the urban environment, less attention is paid to the effects of the urban environment (e.g. increased pollution, urban heat island effect, drought stress) on the trees themselves. Without understanding the resilience of the existing urban forest to these pressures, it is challenging for people planting trees, from both a local authority level down to an individual, to select species suitable for the urban environment, particularly in the face of future threats such as climate change.This PhD will address the three following questions:1) What are the most common urban trees in a typical UK city and how are they distributed throughout the urban fabric?2) What is the relationship between the distribution of common tree species, size and ecosystem service provision?3) Which urban tree species, at specific life-stages, are vulnerable to typical urban stresses?ObjectivesThis project will use Sheffield as a case-study to establish long-term monitoring sites at a city-scale by fitting common urban tree species with in-situ growth monitoring devices. This in-situ monitoring network will be combined with regular fieldwork, to measure physiological variables and key indicators of ecosystem service provision, lab analysis, GIS and remote sensing to explore how urban tree distribution, species and size affects tree function and therefore ecosystem service provision and how these trees are affected by urban stresses. It will address the following objectives:1. Determine the distribution of common urban tree species and sizes within different land-covers at a city-scale.2. Assess the contribution of urban trees to key ecosystem services, including air temperature, pollutant removal and carbon storage in different urban land-covers. 3. Determine the effects of urban stressors, including pollution, heat and drought, on the form and function of tree species across the urban landscape. 4. Co-design with the local authority tree planting guidelines to ensure the resilience of the urban forest in the future.This project will be managed in partnership with Sheffield City Council. Dr Nicola McHugh, a Data Scientist at Sheffield City Council, will co-supervise the PhD. She has particular expertise in GIS based analyses of the urban forest. In addition, the student will work with Jerry Gunton, the Trees and Woodlands Manager. They will provide in-kind support to the student including access to the i-Tree Eco survey data (in-kind value £20,000) and staff time (in-kind value £2,000). Novelty and timelinessThe Governments' 25 Year Environment Plan (published in 2018), aims to plant 1 million urban trees by 2020. This research will better inform decision making on providing 'more and better quality green infrastructure, including trees', and aid development of the national framework of green infrastructure standards proposed in the 25 Year Plan. It will help local authorities to understand how to plant the 'right tree for the right place' in order to both maximise the trees chance of survival and to provide the ecosystem service required at that specific location. Understanding these questions is key to ensuring a sustainable and resilient urban forest into the future.