Activity Point 2 - Trees
In this section, we are joined by Bronagh Gallager from the Woodland Trust. The videos below cover a range of topics including the importance of planting trees, how we can grow our own trees from simple seeds and how to survey and measure trees in the park. At the end of the section there is an ecosystem analysis of Warrenpoint Park.
Bronagh Gallager from The Woodland Trust explains the importance of planting trees.
Bronagh Gallager from The Woodland Trust talks about seedlings and shows you how you can grow your own tree.
Bronagh Gallager from The Woodland Trust demonstrates how to measure the height and circumference of a tree.
Extracts from an Ecosystem Analysis of Warrenpoint Park, March 2022.
Summary
Understanding an urban forest's structure, function and value can promote management decisions that will improve human health and environmental quality. An assessment of the vegetation structure, function, and value of the Warrenpoint Park urban forest was conducted during 2022. Data from 142 trees located throughout Warrenpoint Park were analyzed and found the following: -
• Number of trees: 142
• Tree Cover: 1.188 acres
• Most common species of trees: Holly oak, Littleleaf linden, Norway maple
• Percentage of trees less than 6" (15.2 cm) diameter: 46.5%
• Pollution Removal: 21.4 pounds/year (£112/year)
• Carbon Storage: 132 tons (£30.3 thousand)
• Carbon Sequestration: 1.829 tons (£420/year)
• Oxygen Production: 4.877 tons/year
• Avoided Runoff: 0 cubic feet/year (£0/year)
• Building energy savings: N/A – data not collected
• Avoided carbon emissions: N/A – data not collected
• Replacement values: £307 thousand
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Tree Characteristics of the Urban Forest
The urban forest of Warrenpoint Park has 142 trees with a tree cover of Holly oak. The three most common species are Holly oak (11.3 percent), Littleleaf linden (9.2 percent), and Norway maple (7.7 percent).
Urban Forest Cover and Leaf Area
Many tree benefits equate directly to the amount of healthy leaf surface area of the plant. Trees cover about 1.188 acres of Warrenpoint Park and provide 0.9426 acres of leaf area.
In Warrenpoint Park, the most dominant species in terms of leaf area are Sweet chestnut, European beech, and Holly oak. The 10 species with the greatest importance values are listed in Table 1. Importance values (IV) are calculated as the sum of percent population and percent leaf area. High importance values do not mean that these trees should necessarily be encouraged in the future; rather these species currently dominate the urban forest structure.
Air Pollution Removal by Urban Trees
Poor air quality is a common problem in many urban areas. It can lead to decreased human health, damage to landscape materials and ecosystem processes, and reduced visibility.
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The urban forest can help improve air quality by reducing air temperature, directly removing pollutants from the air, and reducing energy consumption in buildings, which consequently reduces air pollutant emissions from the power sources. Trees also emit volatile organic compounds that can contribute to ozone formation. However, integrative studies have revealed that an increase in tree cover leads to reduced ozone formation (Nowak and Dwyer 2000).
Pollution removal (1) by trees in Warrenpoint Park was estimated using field data and recent available pollution and weather data available. Pollution removal was greatest for ozone (Figure 7). It is estimated that trees remove 21.4 pounds of air pollution (ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), particulate matter less than 2.5 microns (PM2.5), particulate matter less than 10 microns and greater than 2.5 microns (PM10*) (2), and sulfur dioxide (SO2)) per year with an associated value of £112.
In 2022, trees in Warrenpoint Park emitted an estimated 5.965 pounds of volatile organic compounds (VOCs) (1.303 pounds of isoprene and 4.662 pounds of monoterpenes). Emissions vary among species based on species characteristics (e.g. some genera such as oaks are high isoprene emitters) and amount of leaf biomass. Eightyone percent of the urban forest's VOC emissions were from Sweet chestnut and Holly oak. These VOCs are precursor chemicals to ozone formation. (3)
(1) PM10* is particulate matter less than 10 microns and greater than 2.5 microns. PM2.5 is particulate matter less than 2.5 microns. If PM2.5 is not monitored, PM10* represents particulate matter less than 10 microns. PM2.5 is generally more relevant in discussions concerning air pollution effects on human health.
(2) Trees remove PM2.5 and PM10* when particulate matter is deposited on leaf surfaces. This deposited PM2.5 and PM10* can be resuspended to the atmosphere or removed during rain events and dissolved or transferred to the soil. This combination of events can lead to positive or negative pollution removal and value depending on various atmospheric factors.
(3) Some economic studies have estimated VOC emission costs. These costs are not included here as there is a tendency to add positive dollar estimates of ozone removal effects with negative dollar values of VOC emission effects to determine whether tree effects are positive or negative in relation to ozone. This combining of dollar values to determine tree effects should not be done, rather estimates of VOC effects on ozone formation (e.g., via hotochemical models) should be conducted and directly contrasted with ozone removal by trees (i.e., ozone effects should be directly compared, not dollar estimates). In addition, air temperature reductions by trees have been shown to significantly reduce ozone concentrations (Cardelino and Chameides 1990; Nowak et al 2000), but are not considered in this analysis. Photochemical modeling that integrates tree effects on air temperature, pollution removal, VOC emissions, and emissions from power plants can be used to determine the overall effect of trees on ozone concentrations.
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Oxygen Production
Oxygen production is one of the most commonly cited benefits of urban trees. The annual oxygen production of a tree is directly related to the amount of carbon sequestered by the tree, which is tied to the accumulation of tree biomass.
Trees in Warrenpoint Park are estimated to produce 4.877 tons of oxygen per year. However, this tree benefit is relatively insignificant because of the large and relatively stable amount of oxygen in the atmosphere and extensive production by aquatic systems. Our atmosphere has an enormous reserve of oxygen. If all fossil fuel reserves, all trees, and all organic matter in soils were burned, atmospheric oxygen would only drop a few percent (Broecker 1970).
The historic value of the mature planting belts and specimen trees such as beech, ash, lime and oak are of regional importance. The park is protected by virtue of being on the Register of Parks Gardens and Demesnes of Special Historic Interest NI.
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