The topic of the project presented here is vegetation in cities. The project addresses the impact of climate change on vegetation and reports on the design of the school grounds in terms of vegetation and external improvement opportunities.
It focuses on the following research question:
How are the outdoor grounds designed in terms of vegetation and what suggestions for improvement can be implemented?
Keywords: Nature based solutions
Needs: –
The topic of the project presented here is vegetation in cities. The project addresses the impact of climate change on vegetation and reports on the design of the school grounds in terms of vegetation and external improvement opportunities.
It focuses on the following research question:
How are the outdoor grounds designed in terms of vegetation and what suggestions for improvement can be implemented?
Nature based solutions
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The term “vegetation” (lat. vegetatio = growth) refers to “the totality of all plants growing in an area”. This area is composed of the vegetation landscape (e.g. deciduous forest) and the plant communities growing there (e.g. deciduous trees). The terms “plant cover”, “plant growth” or “plant world” are also used as synonyms for “vegetation”.
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In times of climate change and increasing growth of cities, vegetation becomes more and more important for their inhabitants and the environment. Green structures, such as trees or hedges, have multiple functions that have a positive impact on cities.
First, plants change the microclimate, for example by helping to lower air temperatures and reduce heat. This is particularly important for cities, as they form heat islands and heat is accumulated in urban canyons and stored by streets and squares. Trees provide shade and provide cooling through evaporative effects. However, this depends on the tree species and conditions at the site.
Evaporation of water through the leaves is called transpiration. In stomatal transpiration, water evaporates through the plant’s stomata. In this process, carbon dioxide (CO2) is taken up while water and oxygen (O2) are released. The plant can control these processes by a generated internal cell pressure. In cuticular transpiration, water evaporates above a wax layer (cuticle) that lies on the outer tissue. This type of transpiration cannot be controlled by the plant and is of lesser importance. The water vapor, which is subsequently released by stomatal and cuticular transpiration, provides cooling of the surrounding air.
Furthermore, trees and hedges are an effective barrier to wind. They reduce wind speed and alter air turbulence. In a forest, for example, it can be windless, while outside the forest a strong wind blows. On the windward side of a forest, depending on the height of the plants, this windbreak causes a reduction in wind speed and a redirection of the airflow.
Another problem in urban areas is road traffic, with particulate matter being blown into the air as exhaust gases primarily from diesel vehicles. In addition, cars release so-called nitrogen oxides (NOx). Plants improve air quality by filtering dust and soot particles from the air. These stick to the leaves and are washed away with the precipitation. Gaseous pollutants are absorbed by the plants. Oxygen production by plants also helps reduce air pollution. The oxygen emitted is produced by photosynthesis. In this process, the plant forms nutrients important to it from carbon dioxide (CO2) and water through sunlight. The oxygen is produced as a by-product of this process, which is released into the environment. For example, a large beech tree supplies 50 people with oxygen in one hour.
Besides air pollution, noise is one of the most serious environmental pollutants. Plants absorb sound, which makes them a noise barrier. However, it should be noted that a single tree, for example, does not provide noise protection. The effect of a two-meter-high noise barrier corresponds to plant widths of 25- 30 meters.
Natural soil forms the basis of life not only for humans and animals, but also for plants, and fulfills important functions that are crucial for vegetation.
Soil provides a habitat for plants and thus has the necessary “habitat function”. For example, it protects plants from wind as their roots penetrate the soil and stick to it. In addition, the soil is a supplier of nutrients, as it provides substances such as phosphorus, iron, calcium and nitrogen, which plants need to grow. In addition, fertile soils absorb large amounts of rainwater, which is stored and filtered for the plants. In addition, the decomposition of organic materials such as dead animals or plant parts is of great importance. Decomposition and decomposition are carried out by small soil animals and bacteria, which convert the organic matter into valuable humus. The nutrients stored in it are made available to plants. The pores and spaces between soil particles are also essential for plants. This ensures good drainage, so that accumulations of water are avoided, which would interfere with the development of the plant.
Climate change has a significant impact on the plant kingdom, in addition to humans and animals. However, these are not exclusively negative consequences; in some cases, the changes in climate change also bring benefits to vegetation.
One negative aspect is the increasingly dry air, which causes the stomata of plants to remain closed. Among other things, the stomata is also responsible for regulating the water balance. The dry conditions in the environment cause the plant’s pores to close in the long term, reducing the uptake of carbon dioxide. This triggers negative consequences such as slower growth or lower biomass formation. This is evidenced by a study showing that dry air is a bigger problem for meadows than rainfall failures. Scientists fear that the function of forests as CO2 reservoirs will decline.
Plants are more sensitive to temperature changes than animals and have no way to move to warmer or colder areas. When temperatures rise, the plant grows taller to cool down, causing the shoot to elongate, leaves to become narrower and stick out from each other. This results in instability, which in turn causes the plants to buckle when it rains and produce less biomass. In addition, high temperatures damage the roots; the level of important constituents, such as proteins, decreases. In some cases, rapid temperature changes cause such high stress that plants fail to bear fruit or pollen becomes infertile due to extreme heat. Nevertheless, in predominantly cold regions where plants cannot thrive in freezing temperatures, the rise in temperature causes cereal crops to grow longer. This is true, for example, in Siberia or northern Europe.
The increase in the concentration of greenhouse gases causes increased evaporation and an increase in atmospheric water vapor capacity, resulting in droughts and simultaneously heavier rainfall. Increased precipitation causes flooding, which can cause great damage to plants. As a result, roots are no longer able to breathe and die. In dry regions, heavier rains without flooding create favorable effects for the vegetation there. The increase of temperatures or the distribution of precipitation can bring good and bad consequences. However, one should be much more concerned about intensity, which can have devastating effects on plant life.
General weather extremes such as heavy precipitation, hail, heat, or drought cause significant damage with respect to vegetation and are difficult to prevent. Climate variability poses the greatest threat to agricultural production.
The increase of greenhouse gases in the atmosphere also increases the concentration of carbon dioxide in the air, which plants need for their metabolism. The predominant part of cultivated plants in Germany belongs to the photosynthesis type C3 plants. The current concentration of CO2 is not yet optimal for these plants. An increase would bring about an increase in photosynthesis and ultimately an increase in yields. However, it is not yet clear whether these effects will persist in the long term.
In summary, vegetation can positively change and shape our lives in cities in many ways. The plants of our world influence their surroundings and the climate. At the same time, changes in climate also affect vegetation. It should also be noted that soil provides not only habitat functions, but also many vital functions for plants. Therefore, if we want to maintain vegetation in cities and create more green spaces, we must also protect the natural soil in cities so that its functions are not restricted, and it can thus develop freely.
At the beginning of my research, I conduct an inventory in the form of a mapping of the school grounds. The main purpose here is to find out what plants are growing on our school grounds and how large the areas covered with vegetation are in relation to the entire property. The purpose of the mapping is to document exactly what conditions can be found on the grounds. In doing so, I decided that I would create two mappings, one showing the different covered and developed areas on the site and the other illustrating in more detail the locations where different plant species grow. The first step in creating the two mappings is for me to delineate the school grounds into a specific area using a satellite image. Then I examine this area and get a first overview of the terrain and the vegetation there. In doing so, I observe which places in the schoolyard are covered with vegetation or have other ground cover/sealing. This is plotted on the printed satellite image. I also document the survey sites with photographs that will support and illustrate the mapping created. During the second walk-through of the school grounds, I explore only those areas that are covered with vegetation. To be able to name the plants growing there, I identify them using a plant recognition app called “PlantNet.” I also plot the location of the plants on a second satellite image and note which plants are growing prolifically on the school grounds. Once the surveys are complete, I evaluate the corresponding data. The differently covered areas in the schoolyard that I marked on the first mapping are digitally marked with different colors on the satellite image with the help of the computer. Then the area of the whole area and the area of the individual coverings are calculated, which is done with the program “GoogleEarth”. The proportions of the individual areas are shown in a diagram and expressed as percentages. For the areas covered with vegetation I create a table to explain the frequency of trees and plants on the outdoor area. Finally, photos of different locations are added.
It is generally true that vegetation or areas covered with plants have a lower surface temperature than sealed surfaces. In order to transfer this statement to our school grounds, I will conduct an experiment on this. The only materials needed are an infrared thermometer. First, I selected three locations with vegetation and three locations with sealed ground on the schoolyard to compare them with each other.
I also interviewed two experts who are knowledgeable in the field of “vegetation” and could answer some questions on the subject.
One of them is an employee of the OBI garden centre in Bergisch Gladbach. In this interview, the main question is what to look for when purchasing plants for the outdoor area and what suggestions for improvement can be implemented at a school. I got into conversation with Mrs. Molls about which problems arise about the vegetation of the schoolyard and collected solutions or already implemented/planned improvements. I was also allowed to look at the school gardening group.
Land use on our school grounds (blue = soil sealing, black = development, yellow = vegetation, gray = gravel/crushed stone)
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During my measurements, I was able to observe that the surfaces covered with plants sometimes have significantly lower surface temperatures than the sealed surfaces.
One reason for the higher surface temperatures over sealed soils is that they cannot evaporate water and thus do not contribute to cooling the air in summer months. In addition, sealed surfaces have only a low reflectivity (low albedo) and consequently absorb most of the solar radiation. Natural soils with vegetation, on the other hand, provide a decreasing surface temperature (see “Importance of vegetation in cities”). Therefore, the statement made at the beginning is also true for our school grounds.
OBI- Garden Centre:
To summarize, there are no specific plants for outdoors that particularly improve air quality or that cool the environment. This means that any plant that is cold-resistant can be planted on the site. The only rule here is that the larger, taller and more lush, the more suitable they are for the site. In addition, you should make sure that the selected plants are bee-attracting. The employee of the garden center recommends above all large meadow areas with wildflowers or a hedge (for example cherry laurel) to put on. In addition, one could, for example, buy plant baskets/buckets that can be placed on sealed surfaces. The idea of purchasing planter boxes is also to be supported. Vigorously green plants are particularly well suited for this, she said.
Conversation with Ms. Molls:
First, I asked Ms. Molls to evaluate the results of my mapping. In her opinion, the proportion of vegetation (about 19%) in relation to the sealed areas in our schoolyard is far too low, so this needs to be counteracted. In addition, plants have positive effects on the environment and microclimate, such as the cooling effect by evaporation of water above the leaves (see Importance of Vegetation in Cities). In addition to these benefits, however, trees and plants in the schoolyard are also very important to students and teachers. Most spend time in shaded places (under trees, etc.) in green spaces. More vegetation on the school grounds would therefore provide more pleasant retreats in summer as well as increase human well-being.
From the method carried out, the main problem is that only a small area is covered with vegetation. The largest part of the surface, which is almost half of the total outdoor area, is sealed. This results in high surface temperatures as well as an increase in heat storage and a significant increase in heat in summer in the schoolyard, which is also evident from the experiment conducted by the school itself. Due to the sealing, a cooling effect, a habitat for plants, the donation of shade or the infiltration of rainwater as well as numerous functions of the natural soil (see “Importance of the soil in relation to vegetation”) are not possible.
In the following I present several possible solutions or already planned projects, which deal with the creation of more vegetation on the school grounds and their design forms.
It is common knowledge that trees help mitigate climate change. Planting trees would bring many benefits to our school grounds such as purifying the air or absorbing pollutants. This also creates natural soil, allowing rainwater to infiltrate and be absorbed in these locations. In addition, the trees are excellent for providing shade and protection from the wind. The individual trees are surrounded by round beds. For this purpose, however, the pavement or paving stones would have to be broken up at the respective locations in order to be able to create the beds there. The first step in unsealing a surface is to remove the layers that have a sealing effect. After that, base layers and fills (e.g. gravel) must be completely settled. Finally, soil compaction is removed and the soil is loosened. Since this is a major project, it is advisable to hire a company that specializes in this. Locations that could be considered in our schoolyard would be, for example, the large slabbed area in front of the Mediterana entrance next to the gymnasiums. Several such beds could also be created in front of the gymnasiums. Originally, a project was already planned at this location, which involved the implementation of an avenue. The beds with trees would therefore be a good alternative. Planting trees on the west side of the site would also definitely be worthwhile. Especially in summer, the surface temperature rises above the pavers there (see experiment). However, this is difficult to implement on this side of the site because the fire access road there must be kept clear. In addition, wooden benches could be built around the trunks of the trees to provide more shaded retreats in the schoolyard during breaks.
These problems existing in our schoolyard can be solved by creating more green structures and possibly by unsealing surfaces.
The alternative of placing planters is proving to be a quicker and easier method to implement on our school grounds. However, it is important to remember that when making a purchase, a selection should not be made based solely on the appearance of the planters. Several factors play a large role in the purchase. The so-called “outdoor buckets” must withstand appropriate weather conditions. These include, for example, heat, cold, frost or temperature changes, and no cracks must form. In addition, the material of the buckets must not become soft during prolonged exposure to sunlight. It is also necessary that the buckets are waterproof. If they absorb water, it could freeze into ice, thereby “cracking” the bucket (forming cracks). They should also have a robust surface from rain, snow and wind and be UV resistant. Materials such as stainless steel, fiberglass, zinc or even wood are well suited for this purpose. But not only the tubs, but also the plants inside them must be able to withstand outdoor weather conditions. Plants that can tolerate drought and heat could be purchased for the outdoor area. These include, for example, verbena, blue rue, sage or rosemary. A good location for the tubs would be the flagstone-covered “plateau” in front of the entrance to the building.
Another design option, which is already planned and will be implemented at our school, is the construction of a plant wall. For this purpose, the wall with graffiti at the south entrance will be used. Such a wall is the arrangement of plants growing on a vertical support, which in turn is attached to the wall itself. For this project, climbing plants such as honeysuckle are particularly suitable. Trellis fruit would also be a good idea for our school. This refers to fruit trees that grow on a framework (trellis). For example, apricots and apples could thrive on said wall. The advantage of this is that the fruit trees take up less space on the fixture and their fruit quality is higher due to optimal exposure to light. In addition, the risk of late frost decreases and fertilization rates from the flowers are higher, as bees like to be on the south side. The heat given off by the wall helps the plants produce energy sources for their growth. The wall greening also makes insect hotels possible at the planned location.
In some respects, my expectations were reflected and confirmed in my research and methods used. These include the assumption that plants improve ambient air quality and lower surface temperatures, which the experiment also supports. However, I initially assumed that vegetation was a large contributor to the overall plot. However, it has been shown that the areas covered with plants only account for about 19%. The evaluation of the mapping also showed that the percentage of sealed surfaces is the highest, which is in line with my expectations.
