Air Pollution Reduction

"The researchers found that roadsides that only had hedges were the most effective at reducing pollution exposure, cutting black carbon by up to 63 percent. Ultrafine and sub-micron particles followed this reduction trend, with fine particles (less than 2.5 micrometres in diameter) showing the least reduction among all the measured pollutants. The maximum reduction in concentrations was observed when the winds were parallel to the road due to a sweeping effect, followed by winds across the road. The elemental composition of particles indicated an appreciable reduction in harmful heavy metals originating from traffic behind the vegetation.

The hedges only - and a combination of hedges and trees - emerged as the most effective green infrastructure in improving air quality behind them under different wind directions.

Roadsides with only trees showed no positive influence on pollution reduction at breathing height (usually between 1.5 and 1.7m), as the tree canopy was too high to provide a barrier/filtering effect for road-level tailpipe emissions.

According to the United Nations, more than half of the global population live in urban areas – this number increases to almost two thirds in the European Union where, according to the European Environmental Agency, air pollution levels in many cities are above permissible levels, making air pollution a primary environmental health risk." - University of Surrey: Plant Hedges Combat Near Road Pollution Exposure 

 Carbon Dioxide

"The CPRE argue that a 40% increase in the UK’s hedgerow cover could provide a net CO₂ sequestration potential of 18.5 million tonnes. That may be a fraction of current UK CO₂ emissions 354 million tonnes in 2019, but the potential contribution to the climate problem is significant."

"In England alone, epidemiological studies estimate that 26,000 to 38,000 deaths and thousands of NHS hospital admissions are linked to dust-like particles carried in air pollution — much of which is generated by heavy traffic in urban environments.

This particle pollution — or particulate matter — is made up of a variety of chemical compounds, metals and other materials, some of which are toxic. The bigger particles (which are still tiny) measure less than 10 microns in diameter (called PM10) and are easily inhaled. Finer particles of less than 2.5 microns across (PM2.5) can penetrate deeper into the lungs and are small enough to enter the bloodstream.

Children attending schools next to busy roads are especially vulnerable to the effects of air pollution because their airways are still developing and they breath faster than adults."

"In the school playground, 30 metres from the road, they measured a 78% decrease in PM10 relative to roadside air.

They noticed that this removal was even more efficient for ultrafine PM2.5 particles. “What was remarkable was just how efficiently the tredge hoovered up the very finest particles,” said senior author Professor Richard Harrison, also from Cambridge’s Department of Earth Sciences. They measured an 80% reduction in the ultrafine particles just behind the tredge.

They think the ultrafine particles are preferentially filtered out by the tredge because they have a higher likelihood of being captured on the ridged surfaces of the red cedar leaves than coarser particles.

However, they did note a slight uptick in levels of magnetic PM2.5 in the playground, although they were still 63% below roadside air. “The ultrafine particles were very effectively removed, but this shows that some air still goes over or around the tredge,” said Sheikh. Less is currently known about how particulate matter moves and disperses at this higher level, where air mixes around buildings and trees.

“That means the design and placement of tredges near playgrounds and schools should be carefully considered so that their ability to soak up particles can be used to maximum effect,” said Harrison." - Roadside Hedges Can Reduce Harmful Ultrafine Particle Pollution Around Schools

Increased Biodiversity

Native bushes, and especially hedgerows can provide a big ecological boost as they provide food, shelter, and more for species throughout the food web. The following are just a few of the species who can benefit from hedges.

Provide Safe Passage

Fences and walls can dissect a habitat until many of the shorter and medium-sized animals can't pass through them any more. Hedgehogs for example face extinction from Europe and Asia and down into Africa for many reasons including the increasing loss and dissection of their habitats. Hedges provide hiding spaces, food sources, and are permeable enough for many at-risk species to move through, allowing them to mate and forage without hinderance.

Food Source

Hedges made from a variety of native species provide an array of food for different species throughout the year. The more diverse the selection the more likely it will be able to provide flowers for pollinators year round, fruits and berries for birds (or even humans!), or maybe even nuts! In the winter, birds and other species may still be able to find insects around the roots.

Flood Control

Noise Pollution

Vegetation can help reduce noise pollution, but hedges can work especially well at creating a barrier.

Soil Protection & Erosion Control

Fiels with hedges were found to suffer less from wind and water-driven erosion. This meant less watering and fertilization was needed to keep the fields healthy. When livestock are in these fields, the bushes also provide them with shade from harsh sunlight as well as shelter from wind and rain.

Problems with Hedges

Invasive Species

When invasive species get into hedgerows they can be difficult to eradicate. Certain popular bush species have been imported and used for hedgerows but have turned out to cause various problems, including growing too tall and blocking out sunlight, or pushing our native species toward extinction by outcompeting them.

Other invasives that may hide in hedgerows include certain species of lizards, insects, and birds.

Landscaping Pollution

Certain methods of maintenance can create noise or chemical pollution. 

Motor-powered equipment generally tears at the bushes and does a lot of damage while producing dangerous levels of noise pollution that can cause hearing loss to humans, as well as terrify animals who may suffer heart attacks or abandon their nests. Using traditional methods instead of modern equipment types will eliminate this issue.

Chemical pollutants can include fertilizer, pesticides, fungicides, and anything else people might apply to or around hedgerows, that can seep into our soils or wash into bodies of water.

Resources

Use the Plant Natives button to find resources that can help you determine what species belong in your area.