by Lauren Hubbard — Many factors come in to play when considering what ground cover, shrubs, trees, and other landscaping elements are best suited for a campus’s exterior. A few obvious considerations are aesthetics, cost, and level of effort required to maintain these features. One factor that may be overlooked is the ongoing changes to the earth’s climate and whether the landscape will be able to adapt to new and often harsher conditions. Climate change could have a significant impact on the type of plants you will be able to maintain in your landscape. With predicted increases in temperature, precipitation, floods, droughts, and other extreme weather events, your future landscaping may look substantially different than your current landscaping.
Regrettably, even with immediate, aggressive and globally coordinated actions to mitigate greenhouse gases, the earth will still experience some level of climate disruption over the next few decades. Like many facets of everyday life, there is a coming cost for facilities and their landscapes from climate change and extreme weather. However, you can save resources and frustration by preparing for these conditions in advance while also helping the planet. This approach includes choosing plants that are suited for a changing climate and introducing sustainable landscape techniques and practices. By planning for these changes now, you can ensure you will have an aesthetically pleasing yet sustainable and resilient landscape for years to come.
Drought-tolerant Landscapes
The Dust Bowl era of the 1930’s was an extensive period of severe drought across the U.S. that had devastating effects on agriculture and the economy. While the decades since have been more stable albeit with significant yet shorter-lived droughts, a period of intense, extensive drought may be returning to the U.S. According to a 2020 study in the journal Science, western states may be entering a period of “megadrought” in which intense droughts persist for decades or longer. The research scientists attributed about half of this phenomenon to global warming. Droughts, however, are not limited to the western U.S. There are areas in the Midwest and Northeast currently experiencing moderate to extreme drought.
For facility managers in dry or drought-stricken areas, the key to successful landscaping is water conservation, proper soil, and drought-tolerant vegetation. Such vegetation typically includes plants with fleshy stems and leathery or furry leaves. Tropical and exotic plants commonly used in landscaping, such as hibiscus or plants with large, dark leaves, consume too much water to be successful in drought prone areas. The suitability of a particular drought-tolerant plant will vary by climate region and should be confirmed with experts before planting. However, plants that may be suitable across all regions include sedums, daylily’s, coneflowers, and yarrows. In general, native plants will require less care and be more successful since they are already adapted to the existing climate.
The soil plants grow in is also critical to their survival. Well-drained soil is best for drought-tolerant plants. However, mulched soil, specifically soil with organics such as compost, grass, leaves, hay, and bark, is much more effective at holding moisture for plants that are less tolerant of dry conditions.
In drought-affected areas, water should be conserved as much as possible. Rain barrels are a cost-effective way to capture rainwater from roofs, which can then be used later for irrigation during dry periods. It is important to water plants at the soil and not the leaves in order to minimize the amount of evaporation. It is also best to irrigate in the morning and avoid evaporative losses during the peak heat of the day. Best practices for watering your landscape include using a drip irrigation system, a watering wand, or a soaker hose, when possible. If area sprinklers must be used for watering, be sure that they aren’t irrigating the sidewalks and parking lots, as well.
Landscapes can be designed to require less maintenance and little or no irrigation through xeriscaping. Techniques include planting drought-tolerant plants such as cacti and agave and using rocks and mulch. This landscaping approach has been successfully implemented in dry parts of the western U.S. and has shown a significant reduction in water consumption.
Flood-resistant Landscapes
There are three major types of flooding that could impact landscaping depending on your location, including flash flooding (also known as interior flooding), riverine flooding, and coastal flooding. As extreme precipitation events increase, and as rainfall levels rise, flash floods and river floods will become more frequent and intense in many areas. Similarly, as sea levels rise, coastal flooding will become more common. According to a National Oceanic and Atmospheric Administration (NOAA) report on U.S. High Tide Flooding and Coastal Sea Levels, coastal areas in the U.S. had a median frequency of four flood days per year in 2019 (see Figure 1). This is an increase from less than one flood day per year in 1990.
Figure 1: U.S. High Tide Flooding and Coastal Sea Levels. (From NOAA, 2020)
Using select landscape features and techniques, you can protect your landscaping and help mitigate damaging stormwater flow. Redirecting stormwater can often be accomplished with modifications such as swales, which are depressions in a landscape. A vegetated swale, or bioswale, will slow the flow of water and give it more time to absorb into the ground. Relatedly, blue-green infrastructure combines drainage infrastructure with natural or man-made features to help control stormwater and flooding. For example, a city near a river could incorporate a low-lying recreational field to capture and slowly release stormwater runoff. These projects are often larger in scale and may require coordination with local government planners.
For buildings and other roofed structures, green roofs can slow runoff and allow time for plants to absorb a large percentage of the rainfall. In 2005, researchers at Pennsylvania State University found 3.5-4” deep sedum green roofs captured up to 80% of rainfall during rainstorms, while standard roofs captured only 24%. Down at ground level, heavy mulching of vegetation can be used to help stabilize riskier areas. Heavy mulch will require lower maintenance than lighter mulch, which can be more easily washed away and clog drains.
Rain gardens are another approach to controlling stormwater and reducing flooding on a campus. The concept involves modifying soil to allow rainfall to be absorbed more quickly. Soils with high filtration rates are optimal, and you can have your soil tested to determine its infiltration rate. Adding compost and sand will make existing soil more porous whereas high clay content will slow infiltration. The vegetation that is added to a rain garden will also help absorb moisture. The best plants to use in a rain garden are native plants because they are already adapted to regional conditions and require less maintenance (see Figure 2).
Figure 2: Rain Garden at the VA Central Western Massachusetts Healthcare System Facility in Leeds, MA (From USAF)
Heat-tolerant Landscapes
The ten warmest years on record have occurred since 1998. According to the NOAA 2019 Global Climate Summary, land and ocean temperature combined have increased at an average rate of 0.32°F per decade since 1981 (see Figure 3). There are several regional effects that increasing temperatures have on vegetation including unpredictable growing seasons, reduction of native plant species, and expansion of invasive species.
Figure 3: 1988-2017 Global Temperature Trends. (From NOAA, 2020)
Temperature plays a vital role in the development of plants. Extreme heat can reduce photosynthetic capacity and impact productivity and root development. As in drought-affected climates, native plants should be the first choice with heat-affected climates since they are already acclimated to those conditions and can help to fight off invasive species. Using native species will also help maintain important pollinator connections.
In regions like the Midwest, plants commonly endure high temperatures and excess precipitation. St. John’s wort, Lilac shrubs, and green ash trees are suitable for these conditions. St. John’s Wort and green ash can be used for ground cover and shade while lilac shrubs can improve aesthetics. Lantana is native to the tropics and thrives in the sun, while marigolds and geraniums are also suitable for high heat conditions. There are many heat-resilient plant options to consider, but you should seek advice from experts, such as your local county extension office, before making any permanent changes to your landscape.
During both heat waves and droughts, it is critical to reduce water consumption throughout your landscape. A thin layer of mulch helps maintain moisture in the soil and keeps plant roots cool. Shade cloths can be used to cover plants, keeping them cool and well ventilated. If you have turf or other grasses, allowing them to grow a few inches higher than usual can shade the soil and lessen the amount of evaporation. Lastly, keeping plants away from asphalt, concrete, brick, and other heat-absorbing materials will help keep vegetation cooler and healthier.
Wind-resistant landscapes
As tropical storms and hurricanes become more intense due to climate change, their maximum sustained winds are expected to increase, potentially impacting coastal landscapes through wind-generated forces. Many plants with coastal origins are tolerant of salt spray and high winds, but other landscaped vegetation may not be well-adapted to higher wind forces. Specialized fencing, windbreak netting, and hedges can be added as temporary or permanent windbreaks to help mitigate wind effects.
Trees are common casualties of tropical storm generated winds, but root development plays a vital role in their susceptibility (see Figure 4). Conifers typically contain more compact root structure whereas deciduous trees have a more lateral root spread. In the South, where tropical weather is common, live (or evergreen) oak, magnolia, and bald cypress trees are more wind-resilient than species such as Australian Pine, elm, maple, and most oak trees, which are also common in the South.
Figure 4: Impacts of Hurricane Sandy. (From USDA, 2017)
Landscaping Solutions for Climate Change
It is important to remember every climate region has its own unique growing characteristics and will respond differently to climate disturbances. There are plants, shrubs, trees, and ground cover that may be suitable for one climate area today but not suitable for its future climate. Conserving water and planting drought-resistant vegetation will be key to sustaining a lively landscape in drought-affected areas, while incorporating vegetated features such as green roofs, bioswales, and rain gardens can help mitigate stormwater risk to your facility. While trees can be effective for shading and climate change mitigation via carbon capture, they can also create vulnerabilities in areas where extreme winds are expected, so they must be selected wisely. In most cases, native vegetation is a wise choice because it requires low maintenance and is already adapted to the climate. Contact an expert for advice before making any permanent changes to your landscape.
Lauren Hubbard is a staff professional for FEA where she has developed experience in site and facility condition assessments, physical security assessments, emergency preparedness planning, and IWMS implementation consulting services. Prior to FEA, Lauren worked at Salisbury University’s Physical Plant Service Center, where she gained experience working with Facilities Management Software (FMS) and Computerized Maintenance Management Systems (CMMS).