Plant diversity can be defined as having two or more plant species established in a landscape. Having a single species is referred to as a monoculture. The practice of monoculture is very common in housing development and street tree establishment.
The disadvantage of having only one or only a few species is that diseases and insects can be species-specific; plants from the same species are susceptible to the same diseases and insects. Therefore, an entire landscape established with a single species can be wiped out with a single outbreak. Over the past few decades, a growing number of plant pathogens have invaded a variety of forest communities (Aukema et al., 2010). In recent years the redbay ambrosia beetle, which transmits the causal pathogen of laurel wilt disease to plants that are from the Laurel family (Mayfield and Thomas 2006, Fraedrich et al. 2009), caused havoc to the Florida avocado industry (Mann et al. 2011). In 2002, the emerald ash borer killed millions of ash trees in the United States. Also, not to mention the Dutch Elm Disease, which wiped out many American Elm trees. Many other pests are species-specific; azalea lace bugs feed on azaleas, avocado lace bug is a pest of avocados, and crepe myrtle scales feed on crepe myrtles. Insects have favorite plants but will feed on others if their favorites are unavailable. It is important to promote a landscape with diverse species.
When considering landscape diversity, always keep the 5:10:15 rule in mind. The rule states that never establish a landscape with more than 5% from the same species, no more than 10% from the same genus, and no more than 15% from the same family. Landscapers and homeowners often ignore this basic plant diversity rule, which often devastates monoculture landscapes. Landscape diversity may save your landscape from a complete wipeout by one type of pest. For more information on lawn and landscape, contact Grantly Ricketts, UF/IFAS Extension/St Lucie County Commercial Horticulture Agent, at firstname.lastname@example.org or by phone at 772-462-1660.