The Impact of Turfgrass Lawns and Non-native Ornamental Plants (2024)

Native Landscaping vs. Exotic Landscaping: WhatShould We Recommend?

Mark E.Hostetler

WildlifeSpecialist and Associate Professor

Departmentof Wildlife Ecology and Conservation

GainesvilleFL 32611-0430, hostetm@ufl.edu

MartinB. Main

WildlifeSpecialist and Professor

Departmentof Wildlife Ecology and Conservation

Immokalee,FL 34142, mmain@ufl.edu

Adaptedfrom Journal of Extension article – www.joe.org

U.S.urban populations have increased from 39% in 1900 to 75% in 1990 (U.S. CensusBureau, 1995). The threats to biodiversity are many, but habitat loss is widelyrecognized as the most important threat and the spread of non-native species isconsidered the second (Wilcove, Rothstein, Dubow, Phillips, 1998). In urbanareas, this situation is particularly acute because built areas tend to bedominated by exotic turfgrass and ornamentals.Below, we discuss 1) how turfgrass lawns and non-native plants impacturban biodiversity, and 2) how using such exotic plants can affect biodiversityin surrounding natural landscapes.

Simplyexplained, biological diversity or “biodiversity” refers to the variety of lifeand its processes. Biodiversity includesspecies diversity, habitat diversity, and genetic diversity. For the purposes of this article, we willfocus on native species biodiversity. Native species are plants and animals presentwithin a given area prior to European contact (e.g., Florida Native PlantSociety, 2003). Non-native (or exotic)plants or animals are defined as those species that were not present beforeEuropean contact. Endemic species are native organisms only found in a region and donot occur elsewhere in the world. Asexplained below, the impacts of exotics on biodiversity may warrant alteringconventional urban landscapes to emphasize native plants.

Theconventional approach of landscaping with turf and ornamentals impactsbiodiversity in two ways: 1) it limits the diversity of native species in areasdominated by turf and ornamentals, and 2) it can impact surrounding naturalenvironments, altering habitats in ways that exclude native plants andanimals. Let’s first look within thecity limits. How do turfgrass lawns andnon-native ornamental plants impact urbanbiodiversity? Simply put, landscapesdominated by turfgrass and non-native ornamental plants create an artificialenvironment that offers very little opportunity for most native species tothrive. A monoculture of turfgrass infused with non-native ornamentals excludesnative plants and provides little to no habitat for most wildlife. Think about the vast amount of land devotedto turf, both for growing the sod and the amount of sod that occurs on thelandscape as urban lawns. One estimate indicates that four million acres ofmanaged turfgrass occurs in Florida, with 75 percent of these as residentiallawns (Nagata, 2003). Such acreage limits the amount of natural habitat, thusdecreasing urban habitat diversity and ultimately native species diversity.

Withanimals, studies show that many wildlife species are not found or are in lowabundance in turfgrass/non-native, dominated habitats, particularly our mostsensitive and endemic species. Bird speciesthat were normally found in more natural areas gradually drop out along agradient of urbanization (Blair, 2008).Native insect and spider diversity declines in urban areas dominated byturf (Shochat et al., 2008; McIntyre and Hostetler, 2001). As areas become more urban, native plantspecies disappear and non-natives increase in number (Kowarik, 2008). In general, biodiversity indices decrease asone goes towards urban centers (fa*ggi, Krellenberg, Castro, Arriaga, & Endlicher, 2008).

However,biodiversity measures improve with the use of native plants. For example,native urban bird diversity increases with native vegetation (Mills, Dunning,& Bates, 1989; MacGregor-Fors, 2008),more native plants serve as host plants for butterfly larvae (Daniels,Schaefer, Huegel, & Mazzotti, 2008; Collinge, Prudic, Oliver, 2003); andnative bee diversity increases with the occurrence of native plants (McIntyreand Hostetler, 2001). Although someexotic plants, particularly trees and shrubs, can provide food and shelter forsome animals (e.g., butterfly bush, Cassiabicapsularis), it is fair to say that the negatives of a landscapedominated by non-native plants far outweigh the positives for wildlife. First, the exclusive use of non-native plantswould ultimately decrease native plant diversity because of the simple factthat native plants are absent from the area.Second, native animal diversity, in general, is correlated to nativevegetation diversity (e.g., Burghardt, Tallamy, & Shriver, 2009). Overall, the diversity of native plantsimproves urban biodiversity by simultaneously creating wildlife habitat andincreasing the presence of native plants.

Looking beyond the boundaries of cities,the use of turf and some ornamental plants can impact biodiversity ofsurrounding habitat. Non-native speciesthat invade and impact natural areas are called invasive exotics. Aninvasive exotic plant often “alters native plant communities by displacingnative species, changing community structures or ecological functions, orhybridizing with natives.” (Florida ExoticPest Plant Council, 2007) Areasdominated by invasive exotic plants can limit native animal populations; forexample, fewer small mammals were found in forests dominated by Melaleuca, Melaleuca quinquenervia, when comparedto native hammock forests and pine flatwoods in Florida (Mazzotti, Ostrenko,& Smith, 1981; Sowder and Woodall, 1985).Most invasive, non-native plants in the United States were originallyintroduced as ornamentals in urban areas and then escaped and becameestablished in surrounding natural areas (Reichard and White, 2001). We are not saying that all non-native plantsare necessarily bad, but today’s non-listed exotic could become tomorrow’sinvasive species.

Bothwithin and beyond city boundaries, the maintenance of lawns and exotic plantswith an array of insecticides, fertilizers, and herbicides can also impactbiodiversity. With insecticides and herbicides, most people use these chemicalsto keep other plants out and to keep turf and ornamentals healthy andalive. The end result is usually theeradication of native plants and insects.For example, many insecticides are not specific to the pest insect andkill many of our native pollinators such as bees, beetles, wasps, andbutterflies (Kunkel, Held, & Potter, 2001; Gels, Held, & Potter, 2002). Applying herbicides to get rid of “weeds”reduces biodiversity simply because the weeds can be native plants embeddedwithin landscaped and turf areas. Forexample, many herbicide applications are used for the removal of FloridaBetony, Stachys floridana, which is anative plant (Unruh, Partridge-Telenko, & and Brecke, 2009). Roundup, and its active ingredient isopropylamine,was found to be toxic to native freshwater mussels (Bringolf, Cope, Mosher,Barnhart, & Shea, 2007) and lethal to both aquatic and terrestrialamphibians (Relyea, 2005a). The end result is a net native biodiversity loss aslocal native plants and animals can be eradicated from a yard or neighborhood,a nearby waterbody (Relyea, 2005b), and even surrounding natural habitat.

Howdo fertilizers impact biodiversity?Excess fertilizers (e.g., phosphate and nitrate that is not taken up by yardplants) end up in local wetlands and waterbodies when nutrients run off the landscapeafter a storm event. In one study on theFlorida Wekiva River Basin, it was estimated that 20% of the nitrate load wasfrom residential properties (See report at - http://www.dep.state.fl.us/water/wekiva/). Rivers, streams, and lakes that have highlevels of nitrates and phosphates cause algal blooms (Lin, He, Yang, Stoffella,Phlips, & Powell, 2008), fish kills (Gannon et al., 2009), and the growthof invasive exotic plants (e.g., Sutton, Van, & Portier, 1992). Near major population centers, even thedisturbing appearances of “dead zones” in our coastal waters have been linkedto nutrient runoff from the land (Diaz and Rosenberg, 2008).

Biodiversityloss can even affect important ecosystem services, such as removal of carbondioxide (CO₂) and pollination services. More biodiverse ecosystems can uptake more CO₂,a greenhouse gas, than ecosystems with less species diversity (Reich et al.,2001). Furthermore,the maintenance of turf and ornamentals can actually cause a net increase in CO₂ and othergreenhouse gases (Townsend-Small and Czimczik, 2010). This is due to the use of fertilizers andmowing of a manicured landscape, which takes fossil fuels, thus releasing CO₂into theatmosphere. Greenhouse gas emissions from fertilizers, mowing, leaf blowing andother lawn management practices are four times greater than the amount ofcarbon stored by lawns (Townsend-Small and Czimczik, 2010).

Somewill argue that evidence of impacts by exotics is not conclusive and exceptionsoccur. Further, if homeowners and thelandscaping industry managed lawns and ornamentals appropriately, we couldminimize our impact on natural environments.However, the risk is great and thus the precautionary principle may be most appropriate here. Essentially the precautionary principlestates that “where there are threats of serious or irreversible damage, theabsence of full scientific certainty should not be used as a reason forpostponing measures to prevent environmental degradation.” (Untaru, Gu,Ramanitrarivo, 2008) Certainly, non-nativesdo have their place (e.g., vegetable gardens, turfgrass for recreation, andexotic flowers for show) but the dominance of exotic vegetation is at theexpense of our natural heritage. Alternatives do exist (Hostetler and Main,2010), and people are increasingly interested in sustainable options (Moravec,2006). The challenge is to increase the amount of native plants in urban yards,and each person that uses native plants will help to further connections to ournatural heritage.

References

Blair, R. B. (2008). Creating a hom*ogenous Avifauna. In Urban Ecology: An InternationalPerspective on the Interaction Between Humans and Nature. (editors: Mazluff, J.M., Shulenberger, E., Endlicher, W., Alberti, M., Bradley, G., Ryan, C., Simon,U., & C. ZumBrunnen). pp. 405 – 424. Springer, New York.

Burghardt, K. T., Tallamy, D. W.,& Shriver, W. G. (2009). Impact of native plants on bird and butterflybiodiversity in suburban landscapes. ConservationBiology. 23 (1): 219-224.

Bringolf, R. B., Cope, W. G., Mosher, S.,Barnhart, M. C., &Shea, D. (2007). Acute and chronic toxicity of glyphosatecompounds to glochidia and juveniles of LampsilisSiliquoidea (Unionidae). EnvironmentalToxicology and Chemistry. 26 (10): 2094-2100.

Buchmann, S. L., &Nabhan, G.P. (1996). The Forgotten Pollinators.Island Press, Washington, D.C.

Collinge, S. K.,Prudic, K. L., Oliver, J. C. (2003).Effects of local habitat characteristics and landscape context ongrassland butterfly diversity. ConservationBiology. 17(1): 178-187.

Diaz, R. J. &Rosenberg,R. (2008). Spreading dead zones and consequences for marine ecosystems. Science 321 (5891): 926 – 929.

Daniels,J. C., Schaefer, J., Huegel, C. N., &Mazzotti, F. J. (2008). Butterfly gardeningin Florida. Retrieved January 27, 2010 fromhttp://edis.ifas.ufl.edu/document_uw057