Abstract
Invasive and nuisance plants, both introduced as well as native, have negatively impacted native flora and fauna and altered hydrological processes. Economic damage estimates range from $1.4 trillion globally to as high as $120 billion in the United States. Eastern redcedar (Juniperus virginiana) is native to at least 37 states in the United States. A medium-sized tree, eastern redcedar is commonly used as a landscape ornamental given its ability to grow in a wide range of conditions and its tolerance to many environmental pollutants. A tenacious conifer, eastern redcedar is valued for its landscape value and other uses, including wildlife habitat, lumber, medicines, and more. However, with wildfires suppressed and prescribed fires often discouraged, eastern redcedar has grown outside its original habitat and is an example of the term “range change.” This species’ predisposition to be opportunistic has allowed it to encroach on both abandoned and cultivated fields as well as grasslands. When the tree exhibits nuisance tendencies, control measures are warranted including prescribed fire, mechanical control, and herbicides. Ultimately, integrated control measures culminate in the best long-term results. The objective of this article was to describe eastern redcedar’s desirable ornamental features as well as landscape and utilitarian uses for humans and animals but also outline that it can be weedy to invasive depending on several factors discussed herein.
Global economic and ecological consequences of invasive plants are documented and summarized by a number of researchers (Kettenring and Adams 2011; Pysek et al. 2012; Weidlich et al. 2020). Invasive plants often reduce crop yields and forage availability (Pimentel 2009), interfere with native plant populations and fauna (Fletcher et al. 2019), and disrupt hydrological processes (Zou et al. 2017). Invasive species (accounting for plants, pathogens, and animals) cause damage valued annually at $1.4 trillion globally, with economic ramifications in the United States alone estimated to range from $40 billion to $120 billion annually (City of Portland, OR, Bureau of Environmental Services 2021; Diagne et al. 2020a, 2020b). Many plans have been proposed to discourage introductions of harmful nonnative species. Barbier et al. (2013) suggested that an annual license fee paid by the industry would mitigate risk of potentially problematic introductions while raising funds for research, screening imported species, and promoting the education and eradication of existing invasive plants. In contrast, other researchers propose reaching consumers by educating them about invasive species, which could curb or prevent introductions and bolster support for control interventions (Cordeiro et al. 2020; Culley et al. 2022; Howard et al. 2022).
Contrary to popular belief, native plants too can sometimes become a nuisance to invasive (Gettys 2019; Gettys and Schnelle 2019; Marble 2018; Nackley et al. 2017; Schnelle 2019, 2021; Schnelle and Gettys 2021; Simberloff et al. 2012; Valery et al. 2009). It is estimated that 10% to 20% of nuisance to invasive plant species in North America are native to the United States. Whether scientists refer to this as expansion, encroachment, colonization, or regime shifts, ecological phenomena have been documented that mimic many characteristics with invasions by nonnative species. Characteristics include impacts on ecosystem structure and function, and impacts on biodiversity, ecosystem services, and regional economies (Nackley et al. 2017). The objective of this article was to describe eastern redcedar’s desirable ornamental features as well as landscape and utilitarian uses for humans and animals but also outline that it can be weedy to invasive depending on a number of factors discussed herein.
Species description
Eastern redcedar is a medium-sized tree up to 40 to 50 ft tall ×10 to 20 ft wide on average (Gilman and Watson 2014) and found growing in US Department of Agriculture Hardiness Zones 2a to 9b (North Carolina State University Extension 2021). Growth habit varies widely from broadly conical, pyramidal, to columnar in nature allowing landscapers to use the plant as a limbed landscape specimen, for vertical accent, or as a living privacy fence (Fig. 1A–C). The plant is native to the United States spanning east of the Rocky Mountains in the northern Great Plains to eastern Texas and east to northern Florida (Anderson 2003). Eastern redcedar can be found growing from sea level to 5000 ft, and most commonly in areas where annual rainfall ranges from 15 to 60 inches. The species tolerates soil pH range from 4.7 to 7.8 (Lawson 1990) with the tree still managing to grow in pH levels to at least 8.0 (Schnelle MA, personal observation). Eastern redcedar prefers full sun locations but can be found in dappled shade, thereby having the broadest range of any conifer in North America (Engle et al. 2008).
(A) Nearly mature specimen of eastern redcedar serving as an ornamental landscape tree. (B) Upright selections of eastern redcedar create vertical accent in the landscape. (C) Eastern redcedar often serves as a living privacy fence in the built environment.
Citation: HortTechnology 33, 6; 10.21273/HORTTECH05264-23
Prized for its showy evergreen foliage, eastern redcedar has prickly triangular needled foliage (awls) the first 3 to 4 years of growth followed by smooth flattened needles with leaf blades less than 2 inches long (Gilman and Watson 2014). However, awl-like juvenile growth may continue on terminal tips of new growth and through a tree’s lifespan, particularly in shady areas. Opposite to whorled in arrangement, needles are simple, green to blue green, closely appressed, and overlapping the leaf above (like shingles). The species is blue green through summer but bronze to light brown during winter months (Stevens et al. 2005). Foliage is pleasingly aromatic, reminiscent of true cedar (Cedrus sp.) and thus the common name. Eastern redcedar has reddish-brown branches with comparable color on the main trunk with bark peeling off in narrow strips (Gilman and Watson 2014).
Dioecious in nature, the species is found as separate male or female plants that sexually mature within 10 years (Stevens et al. 2005). Female flowers, technically cones, do not open and contain one to four elliptically shaped seeds (Lawson 1990). Attractive one-tenth- to one-third-inch berry-like fruit, cones begin green but then mature to dark blue to purple with an attractive blush (Stevens et al. 2005). Yellow pollen cones (male “flowers”), 0.2 to 0.4 cm long, are yellowish brown, papery, and profusely arranged at tips of branches with wind pollination occurring December through May (Stevens et al. 2005).
Horticultural purposes
In addition to serving as a windbreak or privacy screen, eastern redcedar is often promoted to serve various landscape themes including native gardens, winter gardens, butterfly gardens, and pollinator gardens (North Carolina State University Extension 2021). Because it tolerates pruning, it is also useful as a hedge or topiary. In addition, eastern redcedar is a viable streetscape candidate when lower branches are pruned to satisfy line-of-site requirements and to provide adequate space for pedestrians. This conifer serves as a potential candidate in the built environment such as on southern and western faces of dark buildings that reflect significant heat (Keefe 2019). Many commercially available cultivars in the trade provide versatility ranging from shrub-like forms such as Royo (Scioto Gardens 2022) that matures to 3 ft tall × 6 ft wide to Taylor maturing to 20 ft tall but only 4 ft wide (Monrovia Nursery Company 2023). Smaller, more prostrate or dwarf cultivars are quite versatile and suitable for large architectural containers. Cultivars are often grafted on the species’ rootstock (Breen 2023). The naturally widespread conifer has been trialed and found suitable as an alternative nursery crop in the southern Rocky Mountains as well as an interim crop for Christmas tree growers in the region (Harrington and Fisher 1999). Besides grafting, vegetative propagation can also be achieved by stem cuttings. Henry et al. (1992) achieved up to 87% rooting success from hardwood cuttings secured in December, from trees at 4 years old. Researchers found that the ideal rooting compound determined was 5000 ppm indole-3-butyric acid. However, treated cuttings can be obtained from older trees but with varying and lower degrees of rooting success (Henry et al. 1992; Schnelle MA, personal observation). Last, the species can also be propagated by seed. Fruit are collected in early fall with pulp removed to expose seeds. Warm stratification at 70 to 85 °F for 6 weeks is then followed by 10 weeks of cold stratification at 40 °F. Growers can also simply sow seed in the fall and expect germination to commence the next spring. Germination rates can be as low as ∼50% (Schnelle MA, personal observation; Stevens et al. 2005).
Landscapers and consumers enjoy the species’ ability to withstand moderate to severe drought, compacted soils, and wind-swept areas. It is often free of any significant diseases or insects and related pests (Gilman and Watson 2014). Tolerant of average temperatures ranging from −40 to 115 °F (Anderson 2003; Lawson 1990), it is a candidate in virtually any US landscape. Twelve months of ornamental appeal is provided via its durable evergreen foliage, showy fruit, and variable but pleasing growth habits. Likewise, it also tolerates drought, airborne salt, and other pollutants such as hydrogen fluoride and sulfur dioxide (Keefe 2019). A resilient species, eastern redcedar is known for its hurricane-wind resistance in coastal locations (Florida Native Plant Society 2021). Couple the hardy nature of the species with the fact that it can be purchased in several growth habits, and it quickly becomes apparent why eastern redcedar is sought out and used for many landscape applications. A long-lived species, a 1300-year-old specimen is reportedly growing from a cliff in Wisconsin (Mentzer 2019).
Although typically problem-free in the landscape, there are a few challenges with this species. Eastern redcedar serves as alternate host for cedar (Juniperus sp.), apple (Malus sp.) rust, hawthorn (Crataegus sp.) rust, and quince (Chaenomeles sp.) rust. These rusts are incited by several species of Gymnosporangium. These diseases are more challenging for tree fruit species than for eastern redcedar. Special care must be taken to not plant this species any closer than 1 mile regarding nearby homeowner fruit gardens or apple orchards (Olson 2017). Also, because this evergreen can become flammable under intense heat and drought, landscape siting should be planned accordingly around homes and other structures (North Carolina State University Extension 2021). Last, although male trees “flower” in January through May, some people have an allergic reaction from the windborne pollen (Bunderson et al. 2013).
Historical use
More than 106 uses have been reported across 19 Native American tribes. Fruit and leaves were made into tea to treat colds, coughs, worms, and rheumatism and to induce sweating. Chewed fruit were used for relief from canker sores and leaf smoke or steam treated bronchitis, rheumatism, and incense for purification and rituals (Foster and Duke 2014; Moerman 1998).
Eastern redcedar was purposeful and sacred to Native American tribes and thus populations were carefully managed (Moore 2020). Colonists used wood for coffins, log cabins, and furniture (Chadwick 2017). Medicinal value of young leafy twigs as a diuretic was listed in US pharmacopoeia from 1820 to 1894 (Kindscher 1992). Settlers’ fear of loss of life and property resulted in fire suppression, which led to the species not being kept in check (Smith 2011). In addition, eastern redcedar began to be used extensively in windbreaks starting with the dustbowl in the 1930s (Chadwick 2017).
Wildlife value
In addition to benefits for people, at least 42 different species of moth, butterfly, and other insects feed on the species. In turn, resulting caterpillars serve as a food source for a variety of birds throughout the growing season (Lawson 1990). At least 71 vertebrate species (birds and small mammals) use the evergreen and consequently the species is inadvertently spread by seed (Van Dersal 1938).
Miscellaneous value
Added value from eastern redcedar includes fenceposts, boats, pencils, mulch, and timber, as well as the wood used for cabinet paneling and indoor and outdoor furniture, particularly for wooden chests. Its deep red heartwood has chemical properties known to deter moths (Hiziroglu 2018; Keefe 2019). Currently, cytotoxic juniper leaf extracts have been determined to yield podophyllotoxin, a precursor for the synthesis of efficient anticancer drugs (Ivanova et al. 2021; Stenmark 2021).
Invasive factors
Even though eastern redcedar can be a valuable asset in the built environment, it can become weedy to invasive outside of regularly manicured landscapes. Eastern redcedar’s weediness is typically not an issue within the built environment given that regular mowing and cultivation practices intercept any potentially unwanted seedlings [Schnelle MA, personal observation (Fig. 2)]. Before European colonization, fires were not suppressed and consequently eastern redcedar was confined to drainages, ridges, deep canyons, rocky bluffs, and other areas (Smith 2011) where fire could not easily reach populations. However, seedlings outside these protected areas were killed by fire long before reaching sexual maturity. Because the frequency of wildfires has increased, fire officials have decreased the number of annual burn permits (Extension Foundation 2019). Much of the biogeographical distribution of this species has remained within its range but its sheer density and tendency to invade deciduous forests and grasslands within its range has increased dramatically (Bidwell et al. 2016; Brooke 2019; Iannone et al. 2020; Meneguzzo and Liknes 2015). Its sheer tenacity to grow in difficult areas coupled with anthropogenic disturbances has led to this native species becoming weedy to invasive under certain conditions. A pioneer species, eastern redcedar is one of the first species to grow in barren clearings, eroded areas, open woods thinned by timber harvest, abandoned fields, and disrupted habitats (Carignan 2022). Currently, eastern redcedar ranges from rocky uplands to swampy bottomlands with well-drained and sunny sites preferred (Lancaster et al. 2023). Despite its native status, abandoned fields can be dominated by this native tree in as few as 40 years or less without human intervention [Schnelle MA, personal observation (Fig. 2)]. Loss of forage for livestock can range as high as 80% within 20 years (Helzer 2020).
Eastern redcedar quickly forming a monoculture in an unattended field.
Citation: HortTechnology 33, 6; 10.21273/HORTTECH05264-23
The Great Plains grasslands of the central United States is being invaded by this conifer, particularly in Kansas, Oklahoma, Missouri, and Nebraska (Fogarty et al. 2021; Galgamuwa et al. 2020; Hanberry 2022; Morford et al. 2022; Yang et al. 2023). This in turn has caused a shift from grasslands to woodlands in central North America resulting in less endemic diversity, heightened wildfire risk, and crashes in grazing land profitability (Roberts et al. 2018). Eastern redcedar is invading prairie grasslands because of the absence of fire and often exacerbated by grazing practices (Briggs et al. 2002; Fogarty et al. 2022). Considerable drought tolerance of eastern redcedar enables it to invade tallgrass prairie in the absence of fire. Afforestation (woody plant encroachment) poses the greatest threat to grasslands (Brooke 2019), as this conifer shades herbaceous species, alters species composition, and raises soil pH. Established plants compete directly with grassland species for nutrients and moisture (Converse 1983). Last, studies have indicated eastern redcedar may be allelopathic inhibiting growth and establishment of some prairie species (Bennion and Ward 2022; Xu et al. 2023).
Besides flora, fauna too can be negatively impacted with reductions in diversity and abundance of birds (Coppedge et al. 2001) and small mammals (Horncastle et al. 2005). Besides the potential to displace native flora and fauna, eastern redcedar monocultures also result in potentially reducing streamflow and water supply when encroachment increases evapotranspiration. Researchers believe potential increases in evapotranspiration could occur because it is evergreen and thus might transpire more soil water than herbaceous species because it potentially transpires year-round, and evaporation might increase because rainfall intercepted by this species’ crown exceeds rainfall intercepted by herbaceous plants (Zou et al. 2017). In addition, watershed quality is at risk when eastern redcedar increases the amount of bare soil and thus increases the potential for erosion (Thurow and Carlson 1994).
Control strategies and solutions
The key to preventing or mitigating the spread of eastern redcedar is active surveillance of vulnerable areas (grasslands, abandoned or even cultivated fields) and then taking proactive steps or corrective actions described in the following (Schnelle MA, personal observation). Once areas have been cleared of nuisance to invasive trees, to lessen future problems with eastern redcedar, producers should scout their fields and pastures, annually, to control the growth of any newly emerging trees using the method that is appropriate to their situation (Extension Foundation 2019).
Fire
Prescribed burning is the most economical means of control because the native conifer has no natural asexual regeneration and will not resprout (Anderson 2003; Jeffries et al. 2023; Weir and Engle 2017). Fire destroys thin bark and foliage given that both are combustible (Wade et al. 2000). In an Oklahoma study, eastern redcedar mortality for small (2 to 5 ft), medium (5 to 8 ft), and large (8 to 16 ft) trees was 82%, 54%, and 39%, respectively. Fuel loads varied from 1300 to 6100 lb/acre with tree mortality increasing with increasing fuel load (Engle and Kulbeth 1992). Degree of control not only is contingent on tree height and amount of fuel load (herbaceous vegetation) but also weather conditions favoring ignition of tree crowns (Bidwell et al. 2013; Launchbaugh and Owensby 1978; Weir and Scasta 2014). However, reclamation fires were shown to sometimes be short-lived, less than 20 years, with the need for follow-up treatments to maintain restored grasslands (Fogarty et al. 2021).
Mechanical
Control of smaller stands, less than 2.0 m tall, can be achieved by physically removing them with lopping shears, axes, or bow saws or mowing them, particularly when blades are near the soil surface or below the tree’s lowest branches (Extension Foundation 2019). A single cut close to ground level that removes all green foliage (cuts made below the lowest green branch) kills the species (Launchbaugh and Owensby 1978). Girdling trunks also has been reported effective in killing the evergreen. Two circular cuts clear around the diameter, 12 inches apart and below the lowest live branch is effective given the species does not have dormant buds (Lieshout 2023). In fields with many trees and in larger acreage, larger equipment such as bulldozers or mechanical tree harvesters (skid steer with a shear or cutting attachment) may be necessary. Last, a more automated approach was proposed by researchers Badgujar et al. (2023) who developed and evaluated a pasture tree-cutting robot using a tracked autonomous ground vehicle equipped with a chainsaw bar to mitigate pasture tree encroachment. Mechanical control is ideal when prescribed fire is not an option given the presence of mature trees or insufficient fuel load.
Herbicides
Soil application
Seventy-five percent hexazinone [3-cyclohexyl-6-(dimethylamine)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione (Pronone Power Pellets; Pro-Serve, Inc., Memphis, TN, USA)], can provide eastern redcedar control. Use one to two pellets (0.0011 to 0.0022 a.i. hexazinone) per every inch of stem diameter applying to the soil surface within 3 ft of root collar. Another product available for soil application is picloram [4-amino-3,5,6-trichloropyridine-2-carboxylic acid (Tordon 22K; Corteva Agriscience LLC, Indianapolis, IN, USA)]. Apply as spot treatments using undiluted picloram at 0.73 to 0.98 mL a.i. per 3 ft of plant height. Apply directly to soil within the dripline and within 3 ft of stem base (Oklahoma State University Extension 2023). Soil-applied herbicides are often more effective as follow-up treatments to broadcast burning (Ortmann 1995). In general, soil-applied herbicides work best when applied in March through May when adequate rainfall facilitates movement of the herbicide into the root zone for uptake during the species’ rapid growth of May through June.
Foliar application
Broadcast foliar sprays are often ineffective given the dense nature of the species’ crown and its waxy foliage. Their effectiveness, however, can be enhanced with trees exposed to fire earlier and thus weakened (Schnelle MA, personal observation). Picloram (Tordon 22K) can be applied at 0.33 fl oz a.i./gal water. However, trees should be less than 3 ft tall. Spray to wet, but not to the point of runoff (Oklahoma State University Extension 2023). Herbicide treatments are best for trees less than 15 ft tall, with the very best control for trees under 9 ft tall (Goodman LE, personal communication). The preceding herbicides are intended for rangeland and pastures and not for landscape settings. Applicators should consult the manufacturer’s label, as the approved herbicides are weather-sensitive with runoff (water contamination) and nontarget plant injury possible if not applied with caution and consideration of current climatic conditions (Goodman LE, personal communication; Oklahoma State University Extension 2023; Schnelle MA, personal observation).
Gender
In heavily infested areas, producers can prioritize the removal of female trees, which should be considered before and if removing any male trees in high-density populations. Male trees could then be removed later, if at all, depending on severity of infestation and vulnerability of grass/forb species in the vicinity (Helzer 2020).
Conclusions
Even with the negative impacts on certain ecosystems, eastern redcedar is reported to be an essential species in windbreaks for the protection of crops, livestock shelter, reduction in wind erosion, and in some cases has been found to provide crop-yield benefits (Galgamuwa et al. 2020; Smith 2011). Furthermore, eastern redcedar is a valuable ornamental that will grow and thrive under climatic conditions where other trees would fail. In controlled environments (built environment), the species and its cultivars are an asset in landscapes for their ornamental and utilitarian purposes (Schnelle MA, personal observation).
This native evergreen’s ability to grow in difficult areas has led to it becoming invasive under certain conditions outside the built environment when not kept in check by natural or prescribed fires, cultivation practices, mechanical control, or herbicides. Eastern redcedar, like other native and nonnative species, can be opportunistic. Responsibility lies with both homeowners and producers to monitor their landscapes and fields, respectively, and then take corrective action if warranted. Ultimately, integrated management practices will help curb nuisance to invasive behavior of the tree. Native invaders, like eastern redcedar, for example, are known to have impacts that rival nonnative invaders but also have traits that make them valuable in specific contexts (Ganguli et al. 2008; Nackley et al. 2017; Roberts et al. 2018).
Climate change may ultimately affect rates of eastern redcedar encroachment. Globally, woody species have a competitive edge over herbaceous species as carbon dioxide increases and growth rates increase (Bond and Midgley 2001). Another challenge is the dearth of new herbicide chemistries because of commercial research and development operations shifting from agrichemical development to the development of genetically modified crops (Phillips 2020). Researchers note that it is imperative to acknowledge the importance of eastern redcedar in the landscape, while actively monitoring and managing the species to prevent its encroachment into surrounding areas (Armbrust et al. 2018). Researchers as well as citizen scientists using smartphone apps can all play a role in monitoring this species and other plants with invasive tendencies (Howard et al. 2022).
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