Florida planted Australian pine for shade, windbreaks, and storm protection; by 1993, the fast-growing tree had invaded more than 372,000 acres

Sometimes it seems obvious to make certain choices when landscaping. However, decades later, the decision is described in a government report as an ‘infestation’. This has been the case for Australian pine in Florida. The Florida House of Representatives Committee on Environmental Protection prepared a 1999 report titled “Review of Invasive Plant Management Programs.” The report states that by 1993 the Australian pine had infested over 372,000 acres. This is a great example of well-meaning intentions gone wrong, and a reminder that tree species matters as much as the reason you’re planting one.

Planting with good intentions

As stated in the report produced by the Committee on Environmental Protection, Australian pines are native to Malaysia, Southern Asia and Australia. They were introduced to areas surrounding Miami and Palm Beach in the late 1800s as ornamental trees. They were often planted as a windbreak around canals, fields, homes and roads. During the 1960s, they were planted along shorelines as protection against damage caused by hurricanes.

However, the Australian pine grew at an explosive rate, and by 1993 it had infested over 372,000 acres of land, stretching from just north of Okeechobee to Florida Bay. The Australian pines were found growing in mangroves, rocky shorelines, beach dunes, and terrestrial areas. This creates a thick monoculture, and the needles fall, creating piles of leaf litter. These figures are from 1993.

The storm test

Ironically, the tree that was meant to reduce damage caused by hurricanes was causing problems due to wind damage. A survey was carried out by Duryea and others (scientists from the University of Florida) after Hurricane Andrew hit Dade County on the 24th of August 1992. According to their 1996 research article titled “Wind and Trees: A Survey of Homeowners After Hurricane Andrew,” published in the journal Arboriculture & Urban Forestry, only 4% of the Australian pines remained standing. The survey reached 128 homeowners across Dade County, who between them reported on 1,947 individual trees on their properties, giving researchers a large enough sample to compare how different species fared.

The study also found that native tree species, including Sabal palm, Gumbo Limbo, and Live Oak, were amongst the most resilient. Although this survey was completed following one storm and in one county, and data was collected from homeowners, it does give an insight into the issues with this tree species. The report also mentions that the tree has a shallow root system, meaning it can easily blow over in high winds.

A more complicated turtle story

Additionally, the committee’s report mentions complications with wildlife. Due to the shallow roots, sea turtles and American crocodiles can be harmed whilst nesting; the trees are prone to toppling and blocking nesting beaches. Jill Schmid and colleagues in their 2008 paper titled “The Effect of Australian Pine (Casuarina equisetifolia) Removal on Loggerhead Sea Turtle (Caretta caretta) Incubation Temperatures on Keewaydin Island, Florida,” published in the Journal of Coastal Research, looked at a separate question: whether the shade from the pines was changing nest temperatures enough to skew hatchling sex ratios. Researchers placed 274 temperature data loggers in nests over 5 nesting seasons between 2001 and 2006, and found that the shade provided by Australian pines did not alter incubation temperatures any differently from native species.

In other words, the pines weren’t quietly protecting turtle nests through shade; they just posed a different, more direct threat through their unstable roots. Overall, the research shows that the Australian pine was initially well received as a solution; however, it struggled during the type of storms it was supposed to reduce damage from. It also shows that there are complications with making the tree the bad guy. When considering climate-friendly actions such as planting trees in your garden or in cities, tree species compatibility deserves careful thought.