THE BENEFITS OF USING TREES FOR NATURAL STORMWATER MANAGEMENT

Natural stormwater management is an approach that utilizes natural systems to control and mitigate the effects of stormwater runoff. One highly effective and sustainable element of this approach is the use of trees. Trees offer numerous benefits for stormwater management, including reducing runoff, preventing erosion, improving water quality, and enhancing overall environmental resilience. This note explores these benefits in detail, highlighting the critical role that trees play in natural stormwater management.

Reduction of Runoff: Trees play a vital role in reducing stormwater runoff by intercepting and absorbing rainfall. Their canopies act as natural umbrellas, capturing raindrops and allowing them to evaporate or drip slowly to the ground. This reduces the volume and velocity of runoff, mitigating the risk of flooding and erosion.
Soil Stabilization and Erosion Prevention: The extensive root systems of trees help stabilize soil and prevent erosion. During heavy rain, tree roots hold the soil in place, reducing the likelihood of landslides or slope failure. The roots also create channels that facilitate water infiltration into the ground, allowing the soil to act as a natural sponge and retain stormwater.
Water Quality Improvement: Trees contribute to improved water quality by filtering stormwater runoff. As water percolates through the soil, tree roots and the associated soil microorganisms act as natural filters, removing pollutants such as sediments, nutrients, heavy metals, and chemicals. This filtration process helps protect water bodies, such as rivers, lakes, and groundwater, from contamination.
Temperature Regulation: Trees can help mitigate the urban heat island effect, which is the phenomenon of increased temperatures in urban areas due to the abundance of impervious surfaces. By providing shade and transpiring water through their leaves, trees cool the surrounding environment. This cooling effect can reduce the volume of stormwater runoff generated and alleviate strain on stormwater infrastructure during intense rainfall events.
Carbon Sequestration and Air Quality Enhancement: Trees are excellent carbon sinks, absorbing carbon dioxide (CO2) from the atmosphere and storing it in their trunks, branches, leaves, and roots. By sequestering carbon, trees help combat climate change and reduce the concentration of greenhouse gases. Additionally, trees improve air quality by absorbing air pollutants and releasing oxygen through photosynthesis, contributing to a healthier and more pleasant urban environment.
Biodiversity and Habitat Creation: Trees support biodiversity by providing habitats for various species, including birds, insects, and small mammals. Urban areas with a rich tree canopy can harbor diverse ecosystems, creating interconnected habitats and promoting wildlife movement. This ecological diversity contributes to the overall resilience of the urban ecosystem and enhances the aesthetic appeal of green spaces.

The benefits of using trees for natural stormwater management are multifaceted and far-reaching. From reducing runoff and preventing erosion to improving water quality, temperature regulation, and carbon sequestration, trees play a vital role in creating sustainable and resilient urban environments. Incorporating trees into stormwater management strategies can help cities and communities combat the adverse effects of stormwater runoff while simultaneously promoting environmental health, biodiversity, and a higher quality of life. Emphasizing the importance of trees in stormwater management is essential for sustainable urban planning and the well-being of both humans and the natural world.

Preserving natural tree canopy and the prudent use of tree plantings in urban landscapes contributes to the control of runoff through a number of mechanisms.

Trees intercept and store runoff and transfer water back to the atmosphere through evapotranspiration, reducing the volume of runoff;
the shade and tree litter beneath the canopy help promote infiltration of precipitation that reaches the ground beneath the tree, providing moisture to the tree roots (ultimately to become transpiration) and reducing the volume of runoff;
roots, tree litter, and vegetative groundcover beneath the trees can slow the travel of runoff, resulting in lower times of concentration than associated with bare earth or impervious surfaces, and thus lowering peak runoff rates;
tree roots, leaf litter, and vegetative cover stabilize the soil surface, preventing erosion and associated impacts; and
trees, associated ground litter, and groundcover provide filtration and vegetative uptake of contaminants, enhancing water quality.

These functions for control of runoff and its impacts are further discussed below.

Interception and Evapotranspiration

Through the processes of interception, evaporation, and transpiration, trees and other vegetation capture and store a portion of rainfall and release water to the atmosphere, reducing the net amount of rainfall that becomes runoff. Rain is captured (intercepted) on a plant’s leaves and stems (for trees, the leaf and stem complex is referred to as “canopy”). A portion of this captured water evaporates back into the atmosphere before reaching the ground. Larger canopies intercept greater amounts of precipitation because there is more surface area available for water molecules to adhere to.

Some water flows down the plant stem to the ground as “stemflow”, and some rainfall infiltrates the ground around the plant, entering the root zone where the plant withdraws moisture to sustain itself. In this process, water taken up through its roots is then released through the plant’s vegetative structures as water vapor, a process known as transpiration. The combination of these two mechanisms – evaporation and transpiration – whereby a plant transfers moisture to the atmosphere is referred to as evapotranspiration. In both processes the water is diverted before ever becoming runoff.

Mature tree canopies are of particular value in the interception of rainfall. For example, in a New Hampshire hardwood forest at the Hubbard Brook LTER site, deciduous trees were observed to intercept 13% of the total rainfall during the leaf period and 12% of the total rainfall during the leafless period (Leonard, 1961).

Individual mature trees also provide significant rainfall interception. An illustration of this potential stormwater benefit using the National Tree Benefit Calculator was cited in Chapter 1 of this report (i.e., greater than 9% annual rainfall capture over the “footprint” of the tree). The significant volumes of interception shown in that example and in the Hubbard Brook study cited above are consistent with findings of other studies throughout the United States.

The amount of rainfall intercepted by vegetation varies depending on the type of species, time of year, and intensity and duration of the rainfall event. Species characteristics like leaf surface area and specific tree architecture contribute to the variation in total water intercepted. Also, trees typically intercept more rain during a storm of longer duration than a short storm with equal total rainfall accumulation (CUFR, 2002). In areas where rainfall is highest in the fall, winter, and spring, broadleaf evergreens and conifers intercept more rainfall than deciduous species (Xiao and McPherson 2002).

Promotion of Infiltration

Another crucial role plants have in reducing landscape runoff is facilitating ground water infiltration. Plants provide suitable conditions for water to infiltrate through several mechanisms. Decomposing plant material on the ground captures and temporarily stores runoff. Root systems create large pores in the soil called macropores that facilitate infiltration. Tree roots provide pathways for stormwater infiltration to enter soils compacted by development activity (e.g., see Bartens, et.al., 2008). The uptake of water from the soil by plants between rainfall events frees pore space that then becomes available for storage during a subsequent storm.

Note, however, that in the case of trees, much of the infiltrated water will ultimately be taken up by the trees themselves, so that in areas with extensive tree cover, deep groundwater recharge may actually be less than in areas with little or no tree cover.

Vegetative Retardance of Runoff

Vegetation not only reduces the volume of runoff, but can also reduce runoff velocity compared to flow over an un-vegetated surface (an effect referred to as vegetative retardance). This results in longer times of concentration. Natural surface roughness associated with vegetation contributes to lower peak rates of discharge than would occur on an un-vegetated landscape. Maintaining and restoring vegetated landscapes thus can contribute to the control of the rate runoff is transported through a drainage basin.

Surface Stabilization

Trees and other vegetation throughout the landscape stabilize slopes and channels and prevent soil erosion. Trees protect soil from direct exposure to falling rain by intercepting rain, absorbing the impact of rainfall that does drip from the leaf surface to the ground, and providing leaf litter that absorbs the impact of rainfall as it hits the ground. Each of these mechanisms helps prevent dislodgement of soil particles by rainfall. Additionally, the tree’s root system keeps soils intact, stabilizing slopes against displacement by runoff flowing over and through the surface soils. Reduced erosion rates from vegetated landscapes protect the quality of receiving waters by minimizing transport of sediments and associated pollutants.

Water Quality Enhancement

Not only can trees reduce the total amount and rate of stormwater runoff, they can also improve the water quality of runoff. The forest litter associated with woody plants (as well as groundcovers that may thrive beneath trees) can filter runoff as it passes over the ground. Woody plants in particular can uptake nutrients, contaminants, and metals from water or soil. A study showed that within one growing season a maple removed 60 mg of cadmium, 140 mg of chromium, 820 mg of nickel, and 5200 mg of lead (Coder, 1996). Vegetative pollutant uptake improves the surrounding soil and water quality, resulting in less contamination in runoff reaching the stormwater system from tree covered landscapes and from stormwater treatment practices that include tree plantings.

An additional water quality benefit provided by tree canopy comprises moderation of the thermal impacts of stormwater runoff. For discharges to temperature-sensitive water resources such as coldwater fisheries, prudent preservation or enhancement of tree cover to shade impervious surfaces (where runoff originates), outlet channels (where runoff discharges), and stream banks can moderate temperatures of stormwater discharges.

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ENCOURAGING NATIVE TREE SPECIES FOR UTAH LANDSCAPES

The use of native tree species in landscaping offers a wide range of benefits that go beyond aesthetics. Native trees are those that naturally occur and have evolved in a specific region or ecosystem over a long period of time. When incorporated into landscaping projects, these trees provide numerous advantages that contribute to the health, sustainability, and overall quality of the environment. Here’s why native tree species are important in landscaping:

Adaptation to Local Conditions:

Native trees are already adapted to the specific climate, soil types, and environmental conditions of the region. This makes them well-suited to thrive without excessive maintenance or resources.
They can withstand temperature extremes, drought, and other challenges commonly found in their native habitat.

Reduced Maintenance Requirements:

Native trees have evolved to thrive in local conditions, reducing the need for extensive irrigation, fertilization, and pest control.
Their natural resistance to local pests and diseases further minimizes the need for chemical interventions.

Water Conservation:

Native trees are often drought-tolerant, requiring less water once established compared to non-native species.
Planting native trees helps conserve water resources, making them valuable for water-scarce regions.

Biodiversity Support:

Native trees are essential components of local ecosystems, providing habitats, food sources, and nesting sites for native wildlife.
They support a diverse range of insects, birds, and mammals that rely on them for survival.

Soil Health and Erosion Control:

Native trees’ root systems help stabilize soil, preventing erosion and improving soil structure over time.
They contribute to soil health by enhancing nutrient cycling and organic matter accumulation.

Preservation of Local Identity:

Using native trees in landscaping helps maintain a sense of place and connection to the local environment and history.
These trees can hold cultural and ecological significance for communities.

Lower Carbon Footprint:

Native trees require less transportation and energy-intensive care due to their adaptation to local conditions, resulting in a lower carbon footprint.

Wildlife Habitat Creation:

Native trees provide essential habitats for local wildlife, promoting biodiversity and supporting the balance of local ecosystems.

Pollinator Support:

Native trees often have co-evolved with native pollinators, providing them with suitable nectar sources and contributing to pollination services.

Resistance to Invasive Species:

Native trees are less likely to be invasive and outcompete local vegetation, reducing the risk of introducing harmful species to the ecosystem.

Resilience to Climate Change:

Native trees have a better chance of adapting to changing climate conditions because of their evolutionary history in the region.

Educational and Recreational Value:

Native trees offer opportunities for education about local ecosystems and natural history.
They create inviting spaces for outdoor activities and recreational use.

Incorporating native tree species into landscaping projects promotes ecological integrity, conserves resources, and enhances the overall health of the environment. By embracing the unique characteristics of native trees, individuals and communities can contribute to the long-term sustainability and resilience of their local ecosystems.

Benefits Of Using Native Trees For Utah’s Unique Environment

Using native trees for Utah’s unique environment offers a host of benefits that are specifically tailored to the region’s climate, soil conditions, and ecosystems. Utah’s diverse landscapes, from deserts to mountains, present unique challenges and opportunities for landscaping. Native trees have evolved to thrive in these conditions, making them ideal choices for enhancing the environment and supporting local ecosystems. Here are the benefits of using native trees for Utah’s unique environment:

Adaptation to Arid Conditions:

Utah’s arid and semi-arid climate requires trees that can withstand drought and limited water availability. Native trees are naturally adapted to these conditions, requiring less irrigation once established.

Water Efficiency:

Native trees have evolved to use water efficiently, making them well-suited for Utah’s water-scarce environment.
Using native trees helps conserve water resources and supports sustainable landscaping practices.

Resistance to Temperature Extremes:

Utah experiences a wide range of temperatures, from hot summers to cold winters. Native trees are adapted to these extremes and can tolerate temperature fluctuations.

Soil Compatibility:

Native trees are suited to Utah’s varied soil types, including rocky soils and alkaline soils commonly found in the state.
Their root systems help improve soil structure, reducing erosion and promoting soil health.

Biodiversity Support:

Using native trees enhances local biodiversity by providing habitats and food sources for native wildlife, including insects, birds, and mammals.
This contributes to the overall health and balance of Utah’s ecosystems.

Erosion Control:

Native trees’ root systems stabilize soil on slopes and hillsides, reducing erosion caused by heavy rainfall or runoff.

Wildfire Resilience:

Some native trees, such as certain pine species, have adaptations that make them more resistant to wildfires, which can be a concern in Utah’s drier regions.

Conservation of Endemic Species:

Native trees often include species that are unique to Utah and play a role in preserving the state’s natural heritage.

Reduced Pest and Disease Risks:

Native trees have natural defenses against local pests and diseases, reducing the need for chemical interventions in landscaping.

Cultural and Aesthetic Value:

Using native trees connects landscapes to the region’s natural history and cultural identity.
Native trees contribute to the aesthetic beauty of Utah’s diverse environments.

Low Maintenance Requirements:

Native trees are adapted to the local environment, requiring less maintenance and care once established.
This reduces the need for excessive fertilization, irrigation, and pruning.

Educational Opportunities:

Incorporating native trees provides educational value by showcasing Utah’s native flora and ecosystems.
Native landscapes can serve as educational tools for residents, students, and visitors.

By utilizing native trees in Utah’s landscaping, individuals, communities, and organizations can create sustainable, resilient, and ecologically harmonious environments that contribute to the overall well-being of the state’s unique ecosystems and its inhabitants.

Understanding Utah’s Ecosystem

Utah’s ecosystem is characterized by a diverse range of landscapes, including deserts, mountains, forests, wetlands, and plateaus. The state’s geography and varying elevations give rise to distinct ecosystems with unique plant and animal species adapted to different conditions. Understanding Utah’s ecosystem involves recognizing its key features, biodiversity, and ecological dynamics. Here’s an overview:

Desert Ecosystems:

A significant portion of Utah consists of desert ecosystems, particularly in the western and southern regions.
Arid conditions and limited water availability define these ecosystems, where plants and animals have evolved to survive in harsh environments.
Iconic desert plants like sagebrush, juniper, yucca, and various cacti are adapted to conserve water and withstand high temperatures.

Mountain Ecosystems:

The Rocky Mountains traverse Utah from north to south, creating diverse mountain ecosystems.
As elevation increases, temperatures drop, and vegetation transitions from desert shrubs to coniferous forests. Pine, fir, and aspen trees dominate higher elevations.

Riparian Ecosystems:

Riparian areas, found along waterways, provide critical habitats with higher moisture levels.
These ecosystems support a variety of plant and animal species, including willows, cottonwoods, amphibians, and waterfowl.

Wetland Ecosystems:

Utah’s wetlands encompass marshes, ponds, and shallow water bodies.
These areas are important for waterfowl nesting, migration stopovers, and provide habitat for species such as muskrats and various bird species.

Alpine Ecosystems:

Above treeline, alpine ecosystems consist of rocky terrain, snowfields, and hardy vegetation.
These ecosystems are home to specialized species adapted to extreme cold and short growing seasons.

Great Salt Lake Ecosystem:

The Great Salt Lake is a unique ecosystem with fluctuating water levels and highly saline conditions.
It serves as a critical stopover for migratory birds, such as shorebirds and waterfowl.

Endangered and Sensitive Species:

Utah is home to several endangered or sensitive species, including the Utah prairie dog, Gunnison sage-grouse, and various fish species.
Conservation efforts are underway to protect and restore these species and their habitats.

Fire Ecology:

Fire is a natural part of Utah’s ecosystem dynamics, influencing plant succession and promoting habitat diversity.
Some plant species, like lodgepole pine, rely on fire to trigger seed release and regeneration.

Human Impact and Land Use:

Agriculture, urban development, and recreational activities have altered Utah’s ecosystems.
Balancing human needs with ecological preservation is a challenge, especially in the face of water scarcity and climate change.

Invasive Species:

Invasive species like cheatgrass and Russian olive threaten native plants and wildlife, disrupting natural ecosystem balance.

Climate Diversity:

Utah’s varying elevations contribute to a wide range of microclimates, influencing the distribution of plants and animals.

Biodiversity and Conservation:

Utah’s ecosystems support a diverse array of flora and fauna, contributing to its biodiversity.
Conservation efforts aim to protect and restore habitats, manage invasive species, and ensure sustainable land use.

Understanding Utah’s ecosystem requires appreciating its complexity, recognizing the interconnectedness of its components, and acknowledging the importance of responsible stewardship to preserve its ecological integrity for future generations.