What biodiversity in the city ?

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garden plants paris - aerial view garden plants paris

Even if the urban environment imposes very strong constraints on the animals and plants that inhabit it, the biodiversity of our cities is rich in many diverse species. All these species form the urban ecosystem that provides valuable services to urban dwellers. We still need to make cities welcoming for fauna and flora.

1. The city, a place where many animal and plant species live

A city is an environment where a large human population is concentrated and which organizes its space according to needs and activities. The ecological characteristics of cities are quite particular due to the concentration of buildings of all kinds and the importance of human activities. In reality, these characteristics may vary according to the density of human populations, the geographical location and the type of activity (city centre, peri-urban districts, etc.). Nevertheless, the human presence is still more significant than in rural areas.

What are the consequences of the high human concentration in cities? Areas likely to support biodiversity are very small in size, and surrounded by buildings, streets, walls, structures that do not suit the lifestyle of a number of species because they cannot find food or shelter there… In fact, the isolation of these areas, within an inhospitable urban matrix, prevents most organisms from migrating from one area to another. The consequence of this isolation is a loss of viability of plant or animal populations through genetic impoverishment and inbreeding.

urban heat island schema
Figure 1. Schematic representation of an urban heat island. [Scheme adapted from Alexchris (Public domain)], via Wikimedia Commons]
Another particularity of the urban environment is its artificial microclimate, which is warmer and drier than its surrounding areas. This phenomenon called “urban heat island” (Figure 1) is due to human activities concentrated in cities, some of which produce a lot of heat, such as factories, vehicle engines, building heating, air conditioning, hot water circulating in sewers, etc. It is also the result of waterproofing urban soils that absorb solar radiation and then return it as heat, something that plant covered soils do not do.

young birch tree - city plant - biodiversity city
Figure 2. Plant (young birch) growing in the crevice of a street surface. [Source: gcardinal from Norway [CC BY 2.0], via Wikimedia Commons]
Finally, organisms, animals and plants, like humans, are subject to urban pollution to which they are more or less sensitive. This pollution is the result of the emissions of various gases from road traffic, industrial activities and district heating. The main pollutants encountered are nitrogen oxides (NO and NO2), carbon monoxide, volatile organic compounds, ozone formed by photochemical reaction in sunny weather and fine particles (see Air Pollution). All these molecules are absorbed by living organisms causing more or less damage (see What is the impact of air pollutants on vegetation?). Rainwater in cities is loaded with pollutants along its route, linked to car traffic and industrial activity. Polluted air and water as well as liquid or solid gaseous discharges from human activities also load the soil with toxic substances. These frequently reworked soils are a heterogeneous substrate that is not always ideal for the harmonious growth of a wide range of plants (Figure 2).

Other sources of pollution are light and noise pollution that cause serious damage to sensitive species (see What is the ecological impact of light pollution?). An example is bats, whose behaviour changes because of artificial light at night. Some very common species hunt insects attracted to the halos of streetlights. Other more rare species are very frightened and flee the cities for better preserved spaces.

In addition to the abiotic characteristics of the urban environment mentioned above, urban sites are subject to strong direct pressures due to the high concentration of urban dwellers on small areas: the soils are trampled and compacted. The concentration of animal and plant species in small areas leads them to more intense relationships, whether they are predation, competition, facilitation,… Epidemics are more violent and serious even if the microorganisms are less diversified in the city centre.

2. Why preserve biodiversity in the city?

The growing literature on the subject clearly shows that the quality of life of urban dwellers and even their health is closely linked to the quality of biodiversity in the neighbourhoods in which they live.

Through the services they provide, urban plants help to improve the quality of air, water and soil. Trees in particular absorb significant amounts of pollutants. They play a significant role in the carbon cycle and have a significant impact on neighbourhood temperatures, especially in the event of severe heat waves. Indeed, the water taken by the roots of the trees and circulating (the sap) to the leaves evaporates thanks to the stomata. This conversion of liquid water into water vapour (evapotranspiration), which uses large amounts of solar energy [1], has a particularly appreciable local cooling effect during the summer months.

Nature in the urban environment provides psychological and physical benefits for urban dwellers when they live in neighbourhoods rich in green space. This is why many cities set up many parks or squares, so that each city dweller has a public garden within walking distance. Studies show that in greener neighbourhoods, urbanites are less prone to allergies, cardiovascular disease… Indeed, these spaces improve local air quality and their pleasant landscaping encourages residents to use them for walking or playing sports. As a result, they have a positive impact on the health of city dwellers.

Urban biodiversity also has cultural and educational virtues. It provides an opportunity to raise awareness of environmental issues among a wide audience, starting with children. A large proportion of small urban dwellers are in contact with nature only in the areas around their homes. The growing interest in associative initiatives whose objective is to show the nature of cities (nature festivals and other events around biodiversity for example) or the success of certain participatory science programmes (see focus on Participatory sciences) whose objective is to collect data on the functioning of biodiversity in cities (Sauvage de ma rue [2], Lichen go [3], garden biodiversity…) demonstrates the importance in preserving green spaces in the most central districts.

apartment garden - garden city
Figure 3. Apartment with flower and vegetable garden, in the city centre of Aretxabaleta (Spain). [Source : Vmenkov (CC BY-SA 3.0), from Wikimedia Commons]
Urban agriculture tends to be renewed in our cities. Whether for leisure or economic reasons, vegetable gardens are returning to the neighbourhoods (Figure 3). Fruit and vegetable production is based on good quality soils and water as well as pollinating or regulating organisms for crop pests.

In addition to these purely utilitarian arguments, preserving nature in cities means preserving part of the biodiversity of certain regions. Indeed, since urban territories are becoming increasingly large and urban sprawl sometimes takes place in areas rich in fauna and flora, preserving urban biodiversity is potentially a way to preserve certain species. Some examples found in the literature: very rare plants grow around Perth Airport in Australia [4] or a beautiful population of a lizard that is declining sharply throughout its range, lives on a greenway in Oklahoma City, USA [5].

Similarly, the preservation of areas dedicated to biodiversity in cities allows them to act as corridors for fauna and flora, continuous or discontinuous for species likely to cross the city from peri-urban populations. In Brisbane, Australia, this is the case of a marsupial who occupies urban sites as soon as they are connected, even episodically, to populations on the fringes of the city.

3. What species in the city?

The major taxonomic groups are almost all represented in the city. As in many other terrestrial ecosystems, aquatic species suffer most from developments that are often at the expense of wetlands. For example, amphibians are often at high risk in urban areas. Otherwise, plants, herbivores or phytophages, carnivores may be found in cities. Apart from trees that have a special status, urban animal and plant organisms are of modest size. In French metropolitan cities, the largest animals are domestic or in captivity.

3.1. Cultivated and domestic species

green wall - green roof - biodiversity city
Figure 4. Green wall and roof.. A (left), Plant wall of the Musée du Quai Branly (Paris); [Source © Patrick Blanc (CC BY 2.0), via Flickr] ; B, (right) Green roof of a building on the NIH campus (Bethesda, Maryland, USA) [Source © Djembayz (CC BY-SA 3.0), via Wikimedia Commons].
One of the characteristics of urban biodiversity is that it is composed of a large proportion of cultivated or domestic species. For the flora, we think of all the horticultural or vegetable species that populate houses, balconies, public and private gardens, flower beds in the streets… Several hundred species are mobilized to accompany us. Among the cultivated flora are species on the ground, on walls and on roofs and terraces (Figure 4). Due to the characteristics of these different structures, the plant communities are not identical: on the walls grow mainly plants that like shade and humidity. On roofs and terraces, it is the plants in upland areas that are most enjoyable.

Species come from a variety of geographical regions. Some are local, they have been part of the flora of our country for several hundred years, white stoneware (Sedum album L.) for example is used to green some roofs (Figure 5). Many others are exotic. The agapanthus (Agapanthus praecox Willd.), for example, which flowers nicely in many gardens, comes from South Africa (Figure 5).

white stonecrop - agapanthus
Figure 5. A (left), White Stone Plant [Source Photo © Franz Xaver (CC-BY-SA-3.0), via Wikimedia Commons] ; B (right), Agapanthus flower [Photo © Pierre Mirosa (CC BY-SA 4.0), via Wikimedia Commons].
The alignment trees that line avenues and boulevards – including plane trees, horse chestnut trees and silver lime trees – are of real importance in the urban environment. It has been demonstrated that a tree-lined urban environment contributes to improving the living conditions of urban dwellers. The 100,000 or so trees in the streets of Paris have many beneficial properties: they contribute to the urban green fabric by creating corridors for a number of species, regulating microclimates and influencing the water cycle. Indeed, they provide a beneficial summer shade during hot weather. Their evapotranspiration (see above, section 2) cools and hydrates the air. Their foliage modifies the air flows that contribute to aerate the city but also to reduce the force of turbulence.

Urban forests sequester some of the greenhouse gases, including CO2, and produce oxygen owing to photosynthesis. They purify a fraction of air pollution, particulate and gaseous (CO, NOX and NO2, and some non-biodegradable toxic substances for example). Finally, the tree enriches the soil with bacteria and fungi that degrade complex organic pollutants (some pesticides, PAHs, organochlorines, etc.). Increasing the number of urban trees, and greening cities leads to a reduction in pollution.

flowers of roses tremieres city - flowers in city - plants city - biodiversity city
Figure 6. Hollow rose flowers in the city (metro in Korea). [Source : Photo, CC0 Public Domain, via Max Pixel]
For animals, dogs and cats are extremely numerous. They have a strong impact on the urban ecosystem. Studies show that these animals are terrible predators, killing billions of birds, lizards and small mammals. They enrich the soil with their excrement.

Whether animal or plant, domesticated species are likely to establish and prosper in the urban environment. Examples include hollyhocks (Alcea rosea L., Figure 6) escaping from gardens or Florida turtles (Trachemys scripta) released into the urban wilderness, which can be found outside areas where they have been raised or cultivated.

3.2. Wild species on my street

annual skate - canada fleabane
Figure 7. A, Annual bluegrass plant [Source photo, Rasbak (CC BY-SA 3.0), from Wikimedia Commons]; B, Canada fleabane plant. [Source Photo © Phil Bendle (CC BY-SA 3.0 New Zealand License), via Kete New Plymouth]
Wild plant species are quite few wild plant species. The richness of natural communities depends on the diversity of the spaces that make up the urban ecosystem because each type of environment, which corresponds to a type of use, has its own set of species: lawns, wastelands, vegetable gardens, etc. Depending on management practices, we can move from grass to lawn, meadow, wasteland or even urban forests. Naturalist databases report annual bluegrass (Poa annua L.), dandelion (Taraxacum officinale F.H. Wigg) or Canadian fleabane (Erigeron canadensis L.) as some of the most common species (Figure 7). In general, species are very common. For many of them, they are pioneer or ruderal species. They are well adapted to the disturbances linked to the activities of city dwellers, trampling, mowing or regular uprooting. There are about 1000 plant species in Paris intramuros.

The most threatened are wetland plants that have been largely drained during the urbanization phases. Some ferns in particular are protected because they are becoming scarce in the city.

budgie
Figure 8. Necklace parakeet in the Parc de Sceaux (Paris). [Source: Vianney Tran (CC BY-SA 2.0), via Wikimedia Commons]
Among all the plants living in cities, some species come from remote areas and have significant proliferation capacities. They are called invasive alien species (see Climate change and globalization, drivers of insect invasions & When invasive plants also wander in the fields). Many of them, coming from hot countries, find in cities the conditions favourable to their proliferation. The roads give them access to the hearts of cities.

On the wildlife side, the most visible are birds. Several dozen species populate our cities. House sparrows, blue tit, common starling, blackbird and black swift are among the most common species. Some species are exotic, such as the beetle pigeon or the collared parakeet (Figure 8). In the urban environment, adapted birds find nesting places and abundant feeding resources, so the abundances observed can be very high. The house sparrow remains common in the city. Its decline is mainly documented in rural areas. The window swallow finds its main nesting habitat in Western Europe in the city. In winter, the city loses some migratory species but also gains some non-breeding species such as alder tarin, which come to seek food and heat.

fox in town
Figure 9. Fox on Ayres Street, Southwark (London borough). [Source: photo © Dun.Can (CC BY 2.0), via Flickr]

As far as urban mammals are concerned, there are only about ten species. In our highly urbanised European cities, the last references to large mammals, carnivores or herbivores, wolves, deer, etc. date back several centuries, even if wild boars are increasingly reported in some outlying districts. Hedgehogs, moles, martens, squirrels, rats and mice, rabbits or foxes (Figure 9) and some species of bats are about the only mammals found in urban centres. While most thrive thanks to a very adapted lifestyle (prolific reproduction, night life…), others suffer from too difficult conditions. Hedgehogs in particular are in sharp decline due to the increasing scarcity of insect or gastropod species on which they feed, killed by insecticides or slug pellets. Fencing between gardens in increasingly large urban areas that prevent genetic exchanges between populations, as well as deadly encounters with vehicles on the road, make them a highly threatened species.

solitary bees - species bees - bees
Figure 10. Lonely bee species. A, Carpenter bee, Xylocopa violacea [Source Photo © Jacques Joyard) ; B, Horned osmie, Osmia cornuta [Photo © Bj.schoenmakers (CC0), via Wikimedia Commons].
The warm urban environment and the high availability of food resources also attract many small invertebrates. Beetles, for example, can be observed in many gardens. Studies have shown that the more gardens are connected to each other by hedges or other vegetated structures, the more small detritus feeders they contain. In general, the city appears to be a refuge for generalist insects, adapted to varying living conditions in highly disturbed environments. Butterflies often desert city centres but can be found in large numbers in gardens when they have a few unmanaged spaces and when the floral resource is quite abundant. Other pollinating species are also found in cities, especially solitary bees (Figure 10), which are responsible for most of the pollination of entomophilic plants in cities, or are not too competitive with honeybees from the many hives placed in certain areas.

Many insect species are poorly perceived by urban dwellers, such as bed bugs, food mites or cockroaches. These species find in the human way of life the ideal conditions for proliferation.

4. Welcoming more effectively biodiversity in cities?

The most important factor that governs the quality of biodiversity is the place it is given: vast green spaces, many gardens, connected to each other by vegetalized structures within the urban matrix. Buildings and other artificial surfaces can support vegetation as long as the planting was planned at the time of construction.

Management must be diversified according to spaces and uses. Pesticides must be banned for their toxicity to biodiversity and dangerous to the health of urban dwellers. Mowing and pulling up must be spaced out over time to allow the species to complete their life cycle.

bercy park paris france
Figure 11. Garden in Bercy Park (Paris) [Source: Patrick GIRAUD (photo) Original uploaded by Calips (Transfered by Tangopaso) (CC BY-SA 1.0), via Wikimedia Commons]
In conclusion, preserving fauna and flora is necessary even in cities. Nevertheless, it is up to city dwellers to choose the species with which they want to live. Often it is a question of finding the best compromise between what is desirable for biodiversity, what is economically possible and what is compatible with the way of life and perception of urban dwellers.

Nevertheless, as part of climate change, our regions are increasingly subject to catastrophic events, floods, storms or heat waves (see Extreme Weather Events and Climate Change). It is by implementing effective urban renaturation policies that cities will have a chance to escape the worst. The abandonment of chemicals in public spaces is already beginning to yield results, since at the beginning of the 21st century, the urban environment is the only terrestrial environment that is seeing its biodiversity increase (Figure 11).

5. Messages to remember

  • The ecological characteristics of cities are quite particular due to the concentration of buildings of all kinds and the importance of human activities.
  • In cities, the areas likely to host biodiversity are very small in area, and isolated from each other by buildings. It is hot and dry. The air, water and soil are more polluted than elsewhere.
  • Nevertheless, there is sometimes an abundant biodiversity in the city, depending on the quality of the management and configuration of the city. Cultivated or domesticated animals and plants live alongside wild species.
  • The quality of biodiversity depends on the place it is given and the management applied to it. But in return, it provides city dwellers with many services and benefits that are essential to their quality of life and health.

References and notes

Cover image. Aerial view of Paris above the “Jardin des Plantes”. Urban green spaces contain a large part of the biodiversity of cities. Waterways or tree lines can provide ecological corridors for some animal and plant species. [Source: screenshot Géoportail © IGN]

[1] A large tree can evaporate hundreds of litres of water vapour, using 0.7 kWh/L of energy to convert liquid water into vapour.

[2] http://sauvagesdemarue.mnhn.fr/

[3] http://www.particitae.upmc.fr/fr/participez/suivez-les-lichens.html

[4] Close DC, Messina G, Krauss SL, Rokich DP, Stritzke J & Dixon KW (2006) Conservation biology of the rare species Conospermum undulatum and Macarthuria keigheryi in an urban bushland remnant. Australian Journal of Botany 54(6) 583-593

[5] Endriss DA, Hellgren EC, Fox SF & Moody RW (2007) Demography of an urban population of the Texas horned lizard (Phrynosoma cohnutum) in central Oklahoma. Herpetologica 63:320-331


The Encyclopedia of the Environment by the Association des Encyclopédies de l'Environnement et de l'Énergie (www.a3e.fr), contractually linked to the University of Grenoble Alpes and Grenoble INP, and sponsored by the French Academy of Sciences.

To cite this article: MACHON Nathalie (August 15, 2019), What biodiversity in the city ?, Encyclopedia of the Environment, Accessed November 1, 2024 [online ISSN 2555-0950] url : https://www.encyclopedie-environnement.org/en/life/what-biodiversity-in-the-city/.

The articles in the Encyclopedia of the Environment are made available under the terms of the Creative Commons BY-NC-SA license, which authorizes reproduction subject to: citing the source, not making commercial use of them, sharing identical initial conditions, reproducing at each reuse or distribution the mention of this Creative Commons BY-NC-SA license.

城市里有哪些生物多样性?

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garden plants paris - aerial view garden plants paris

  尽管城市环境极大程度上限制了动植物的生长,但我们城市的生物多样性仍较为丰富,种类繁多。这些动植物构成了城市生态系统,为城市居民提供美化城市、改善环境等服务,所以我们的城市依然需要引入和接纳动植物。

1. 城市是许多动植物生活的地方

  城市中人口高度集中,根据实际需求和人类活动来分配空间。由于城市中各类建筑集中、人类活动活跃,城市的生态特征尤为独特。因人口密度、活动类型和地理位置(城市中心、城郊区等)的差异,这些特征可能有所不同。相对于农业地区,人类存在对于城市更为重要。

  城市人口高度集中的后果是什么?特点之一是能支持生物多样性的空间面积非常小,并被建筑、街道、墙壁等构筑物包围,许多动植物无法在这些区域中找到食物或栖息地,其生长受到限制……事实上,这些区域被隔离在城市空间中不适宜居住的地区,阻止了大多数生物的迁移。这种隔离会导致动植物种群因遗传缺失和近交繁殖而丧失生存能力。

环境百科全书-城市里有哪些生物多样性-城市热岛
图1 城市热岛的示意图。[图片改编自Alexchris(公开资源), 来自维基共享]

       城市环境的另一个特点是其人工小气候,比周围地区更温暖干燥,这也被称为“城市热岛”现象(图1)。由于人类活动主要集中在城市,工厂运转、汽车发动机运行、建筑或空调供暖、污水中的热水循环等活动产生大量热量,从而形成“城市热岛”。与此同时,城市里不透水的地表也吸收太阳辐射并将其转化为热量,也会产生这种效果。但植物覆盖的土壤则没有这种现象。

环境百科全书-城市里有哪些生物多样性-缝隙中生长的植物(
图2 在街道的缝隙中生长的植物(小桦树)。[图片来源:挪威[CC BY 2.0], 来自维基共享]

  最后,动植物等生物体与人类一样,或多或少都会受到城市污染的影响。城市污染是由道路交通、工业活动和地区供暖排放的气体造成的,主要污染物是氮氧化物(NO和NO2)、一氧化碳、挥发性有机化合物、晴朗天气下光化学反应形成的臭氧和细颗粒物(见关于空气污染的介绍)。这些污染物分子都会被生物体吸收,并造成一定损害(见“空气污染物对植被的影响)。城市降雨都含有污染物,主要来源于汽车交通或工业活动;此外,人类活动排放的固液气体废物,都会给土壤带来有毒物质。同时,城市中的土壤由于频繁重复使用,是一种非均匀的基质,并不适合各种植物的生长(图2)。

  其他污染源包括光污染和噪声污染,都会对敏感物种造成严重危害(见“光污染的生态影响)。例如,蝙蝠的行为常因夜间人造光源而改变。此外,一些常见的物种会捕猎被路灯光晕吸引的昆虫。还有一部分稀有的物种非常抗拒强光环境,因此纷纷逃离城市去寻找更好的生存空间。

  除了上述城市环境的非生物因素外,由于城市居民在小范围内高度集中,城市中的场地承受强烈压力,例如土壤被挤压和压实;动植物在小范围内高度集中,导致它们之间的关系更加激烈,无论它们是捕食、竞争还是相互促进关系……虽然城市中的微生物种类较少,但由此引发的流行病更为猛烈和严重。

2. 为什么要保护城市的生物多样性?

       越来越多的相关文献表明,城市居民的生活质量甚至健康,都与他们居住环境的生物多样性质量密切相关。

  城市植物有助于改善空气、水和土壤质量,尤其是树木能够吸收大量污染物。城市植物在碳循环中也起着重要作用,并且在发生严重热浪的情况下,能够对附近环境的温度进行调控。树根吸收的水分通过气孔蒸发到树叶。这种将液态水转化为水蒸气的过程(蒸腾作用)需要消耗大量的太阳能[1],在夏季对当地的降温效果尤为明显。

  当城市居民生活在植被覆盖丰富的社区时,城市种的自然环境会给他们带来心理和生理上的益处。这就是为什么城市建立了很多公园或广场,使每个城市居民在步行范围内都有公共花园。研究表明,在绿化更丰富的社区,城市居民不易过敏或患心血管疾病等……此外,这些区域改善了当地的空气质量,其宜人的景观也鼓励居民至此散步或运动。由此来看,公共绿化区域能够对城市居民的健康产生积极影响。

  城市生物多样性还具有文化和教育价值。它给广大民众尤其是儿童提供机会来加深对环境问题的认知,因为大部分居民只在自家附近与大自然接触。人们对旨在展示城市自然风光的联合倡议越来越感兴趣,如围绕生物多样性的自然节日和其他活动,或对收集城市生物多样性数据的某些参与式的科学活动(见“参与性科学),例如“我居住街道的自然环境”[2], “苔藓加油”[3],“花园生物多样性”……这些案例都说明了在城市中心地区保持绿色空间的重要性。

环境百科全书-城市里有哪些生物多样性-有花园和蔬菜的公寓
图3 位于西班牙阿雷沙巴莱塔市中心的有花园和蔬菜的公寓[图片来源:Vmenkov (CC BY-SA 3.0),维基共享]。

  都市农业正在城市中复兴起来。无论是出于休闲还是经济目的,菜园在社区中“东山再起”(图3)。而水果和蔬菜产量的基础是优质的土壤、充足的水份以及为农作物授粉及防治害虫的生物。

  除了上述纯实用主义论点,保护城市中的自然环境也意味着保护这些地区的生物多样性。由于城市面积不断扩大,且有时会侵占动植物丰富的地区,保护城市生物多样性可能也是保存一些物种的方式。文献中提到,在澳大利亚珀斯机场周围生长着非常罕见的植物[4];美国俄克拉何马城的一条绿道上生活着一种蜥蜴,数量不少,但这种蜥蜴在其整个分布范围内的数量正急剧下降[5]

        同样,城市中保护生物多样性的区域能够作为动植物的走廊,为可能从边缘地带穿越城市的物种提供连续或不连续的通道。在澳大利亚布里斯班,一种有袋类动物一旦与城市边缘的种群相联系,甚至偶然间联系起来,它们会一起占据城市中的某些场地,增加城市的生物多样性。

3. 城市里有什么物种?

  城市里几乎涵盖了主要的动植物分类群。与其他很多陆地生态系统一样,水生物种最容易受城市发展的影响,而城市发展往往以损失湿地为代价。比如,在城市地区两栖动物往往处于高风险中,而城市中的植物、植食动物和食肉动物相对较多。除了具有特殊地位(如历史地位或较高生态价值)的树木外,城市动植物生物体型都大小适中。在法国大都市,最大的动物是家养或圈养的。

3.1. 栽培和家养品种

环境百科全书-城市里有哪些生物多样性-Quai Branly博物馆长满植物的墙和房顶
图4 法国巴黎Quai Branly博物馆长满植物的墙和房顶(A:左图)[来源:Partrick Blanc网络相册];美国国家卫生研究院(马里兰州贝塞斯达市)一个建筑物的绿色屋顶(B,右图)[来源:维基共享]

  栽培或家养物种占比较大,这是城市生物多样性的特征之一。我们能想到的植物种群包括了所有园艺和蔬菜物种,这些物种生长在房屋、阳台、公共或私人花园以及街道上的花床……成千上百种植物与我们相伴。栽培植物包含地面、墙壁、屋顶和露台上的物种(图4)。由于栽培地的结构特点不同,植物群落也不尽相同:墙体上生长的主要是喜阴喜湿的植物,屋顶和露台上主要生长适应干燥环境的植物。

  不同物种来自不同的地区。有些物种是本地的,几百年来它们一直是本地植物种群的一部分,例如,玉米石(Sedum Album L.)被用来绿化屋顶(图5)。还有很多植物体现了异国风情,例如来自南非的早花百子莲(Agapanthus praecox Willd.)(图5)。

环境百科全书-城市里有哪些生物多样性-玉米石
图5 A(左),玉米石[照片来源:Franz Xaver (CC-BY-SA-3.0),维基百科];B(右),早花百子莲[照片来源:Pierre Mirosa (CC BY-SA 4.0),维基百科]。

  城市要道和林荫大道两侧的梧桐树、栗树和椴树等在城市环境中非常重要。有证据表明,绿树成荫的城市环境有助于改善城市居民的生活质量,如巴黎街头种植的十多万棵的树有许多益处:它们为一定数量的物种构建走廊、形成城市的绿色网络,对调节小气候和促进水循环起到良性作用。此外,这些树木能在炎热天气中提供遮阳。它们的蒸散作用能够使空气(见上文第2节)降温、更加湿润。树叶改变了气流流动,有助于城市通风,同时也减少了空气湍流的强度。

  城市森林汇集储存了一些包含二氧化碳的温室气体,并通过光合作用产生氧气。它们能够净化一部分空气污染、微粒和有害气体,例如CO、NOX和NO2,以及一些不可生物降解的有毒物质。树木使土壤中有更多细菌和真菌,从而能降解一些杀虫剂、多环芳烃、有机氯等复杂有机污染物。由此可见,增加城市绿化可以减少污染。

环境百科全书-城市里有哪些生物多样性-蜀葵花
图6 城市中(韩国地铁)的蜀葵花。[图片来源:Max Pixel工作室的公开照片]

  在动物方面,城市中猫和狗的数量非常多,对城市生态系统会产生严重影响。研究表明,猫狗是可怕的捕食者,杀死了数十亿只鸟类、蜥蜴和小型哺乳动物,但他们的日常排泄物可以使土壤肥沃。

  动植物的驯化物种都有可能在城市环境中生存繁衍。例如,可以在种植或饲养区域之外找到离开花园的蜀葵(Alcea rosea L.,图6)或被释放到郊野的佛罗里达海龟(Trachemys scripta)。

3.2. 街边的野生物种

环境百科全书-城市里有哪些生物多样性-一年生蓝草植物
图7 A.一年生蓝草植物[照片来源:Rasbak (CC BY-SA 3.0),维基百科];B.加拿大飞蓬。[照片来源:菲尔·本德尔(Phil Bendle) (CC BY-SA 3.0新西兰许可),凯特新普利茅斯(Kete New Plymouth)]

  野生植物的种类较少。自然群落的丰富性取决于构成城市生态系统的空间的生物多样性,因为草坪、荒地、菜园等每一种类型的空间用途不同,其物种也有差异。经过人为管理,草地可以变为草坪、牧场、荒地甚至城市森林。另外,根据自然数据库的统计,一年生蓝草(Poa annua L.)、蒲公英(Taraxacum officinale F.H. Wigg)和加拿大飞蓬(Erigeron canadensis L.)是日常生活中最常见的物种(图7)。一般来说,野生物种常见是因为它们中相当大一部分是先驱物种或原始物种,这些物种能够很好地适应与城市居民有关的干扰活动(如践踏、除草或连根拔起等)。巴黎市大约有1000种植物。

  最受威胁的是湿地植物,这些植物在城市化进程中已基本枯竭。此外,还有一些蕨类植物因为在城市中变得稀缺而受到保护。

环境百科全书-城市里有哪些生物多样性-国玺公园的项链鹦鹉
图8国玺公园的项链鹦鹉(巴黎)。[来源:Vianney Tran (CC BY-SA 2.0),维基共享]

  生活在城市里的所有植物中,有些物种来自偏远地区,并且有强大的繁殖能力。它们被称为外来入侵物种(参见气候变化和全球气候变化和全球化,昆虫入侵的驱动力昆虫入侵的驱动力和在野外游荡的入侵植物)。其中许多外来入侵物种来自气候温暖的国家,在城市里找到了有利于其繁衍壮大的生存环境。与此同时,畅通的道路使它们能够顺利进入城市的中心地带。

  在野生动物方面,最常见的是鸟类。我们的城市中栖息者几十种鸟类,如家麻雀、蓝山雀、紫翅椋鸟、乌鸫和黑雨燕等。有些物种是外来物种,例如甲虫鸽或领长尾小鹦鹉(图8)。在城市环境中,适应环境的鸟类呢个找到合适的筑巢地以及丰富的觅食资源,因此观察到的鸟类数量可能非常多。家雀在大多数城市仍然很常见,但在农村地区却出现了数量下降的情况。窗燕则在西欧的部分城市找到了适合它们生存的主要筑巢栖息地。冬天,一些需要迁徙的鸟类离开了城市,但还能看到一些非繁殖鸟类,例如来寻找食物和热量的桤木黄雀。

环境百科全书-城市里有哪些生物多样性-艾尔斯街上的狐狸
图9 艾尔斯街上的狐狸,索斯沃克(伦敦区)。[照片来源: Dun.Can (CC BY 2.0), 维基百科]

       城市中的哺乳动物种类较少,只有大约十种。尽管一些偏远地区也有越来越多关于野猪的报道,但在高度城市化的欧洲城市中,最近一次观察到大型哺乳动物、食肉动物或食草动物,已经是几个世纪以前了。刺猬、鼹鼠、貂、松鼠、老鼠、兔子、狐狸(图9)或某些种类的蝙蝠应该是城市中为数不多的哺乳动物。虽然大多物种适应了城市的生活方式(如多产繁殖、夜间活动……)而能够存活,但其余物种面临着艰难的生存环境问题。特别是刺猬的数量急剧减少,原因是它们赖以生存的昆虫或腹足动物被杀虫剂或除蛞蝓药杀死,食物来源变得日益稀缺。城区日渐扩大的同时,花园之间竖立的围栏阻碍了部分种群之间的基因交流,并加上在路上与车辆发生致命碰撞的威胁,刺猬已成为一个高危物种。

环境百科全书-城市里有哪些生物多样性-离群的蜜蜂
图10 离群的蜜蜂。A.木蜂,木蜂属[照片来源:雅克·乔亚德(Jacques Joyard)];B.角蜂[图片来源:Schoenmakers (CC0),维基共享]。

  城市中环境温暖,食物资源丰富,吸引了许多小型无脊椎动物。例如,在许多花园中都可以观察到甲虫。有研究表明,花园之间用树篱或其他植被结构连接地越多,其中的小型碎屑取食者就越多。总的来说,城市是杂食性昆虫的避难所,它们容易适应高度干扰环境中不同的生活条件。而蝴蝶则经常远离城市中心,但但当花园中有一些无人照管的空间,且花卉资源相当丰富时,就会发现大量蝴蝶。另外,在城市中也发现了其他授粉物种,比如独居蜜蜂(图10),它们能够为城市中大部分虫媒植物提供授粉,并且不会对某些地区蜂巢中的蜜蜂造成太大的影响。

  城市居民对臭虫、食物螨或蟑螂等昆虫嗤之以鼻。但这些昆虫却在人类的生活环境中找到了理想的生存环境和繁殖条件。

4. 更有效地提升城市的生物多样性?

  决定生物多样性质量的最重要因素是其所处的环境,例如广阔的绿地、众多的花园通过城市内的植被结构相互连接。因而只要在建造时做好规划,建筑物和其他人造场所就可以支持植被生长。

  必须根据空间和用途进行多样化管理。同时,必须禁用杀虫剂,因为它们对生物多样性有极大威胁,而且危害居民健康。此外,为使物种完成其生命周期,割草和种植必须间隔一段时间。

环境百科全书-城市里有哪些生物多样性-贝西花园
图11 贝西花园(巴黎)[来源:帕特里克·吉罗(Patrick GIRAUD),原创由Calips上传(CC BY-SA 1.0),维基共享]。

  总之,即使在城市中,保护动植物也是必要的。但是,城市居民可以选择他们想要与之共存的物种。通常,这需要在生物多样性、经济效益、城市居民的生活方式和观念之间找到最佳折衷方案。

  然而,在气候变化的背景下,我们的地区越来越多地受到洪水、风暴或热浪等灾难性事件的影响(参见极端天气和气候变化)。只有通过实施有效的城市“回归自然”政策,城市才能摆脱厄运。在公共空间禁用化学品已经初见成效,因为自21世纪初以来,城市环境是唯一一个生物多样性不断增加的陆地环境(图11)。

5. 本文要点

  • 由于城市中各类建筑高度集中、人类活动频繁,城市的生态特征十分特殊。
  • 城市中,可拥有生物多样性的区域面积很小,并且被建筑物相互隔离。此外,城市中天气炎热干燥,空气、水和土壤污染相比其他地方更为严重。
  • 不过,城市中也有丰富的生物多样性,取决于城市管理和配置的质量。栽培或驯养的动植物与野生物种共存。
  • 生物多样性的质量取决于其所处的空间及管理配置。但作为回馈,它也为城市居民提供了许多功能和益处,对他们的生活质量和居民健康至关重要。

 


参考资料及说明

封面照片:从“植物花园”上方的巴黎鸟瞰图。城市绿地包含了城市生物多样性的很大一部分。水道或行道树可以构成某些动植物物种的生态廊道。【来源: Geoportal 截图 © IGN]

[1] A large tree can evaporate hundreds of litres of water vapour, using 0.7 kWh/L of energy to convert liquid water into vapour.

[2] http://sauvagesdemarue.mnhn.fr/

[3] http://www.particitae.upmc.fr/fr/participez/suivez-les-lichens.html

[4] Close DC, Messina G, Krauss SL, Rokich DP, Stritzke J & Dixon KW (2006) Conservation biology of the rare species Conospermum undulatum and Macarthuria keigheryi in an urban bushland remnant.Australian Journal of Botany 54(6) 583-593

[5] Endriss DA, Hellgren EC, Fox SF & Moody RW (2007) Demography of an urban population of the Texas horned lizard(Phrynosoma cohnutum) in central Oklahoma. Herpetologica 63:320-331


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To cite this article: MACHON Nathalie (March 13, 2024), 城市里有哪些生物多样性?, Encyclopedia of the Environment, Accessed November 1, 2024 [online ISSN 2555-0950] url : https://www.encyclopedie-environnement.org/zh/vivant-zh/what-biodiversity-in-the-city/.

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