The Problem With Florida Palm Trees: Native vs. Non-Native Palms

Like everywhere else in the world, Florida faces the twin crises of biodiversity loss and climate change. In that context, Florida's palm trees are a mixed blessing: Native palms in their natural habitats play vital roles in preserving biodiversity and mitigating climate change.

Outside those habitats, however, palms do less to preserve Florida's biodiversity and nearly nothing to protect the state from catastrophic climate change. This is why cities like Miami Beach and West Palm Beach are planting alternatives to palms—such as shade trees—to make the city more climate-resilient and sequester carbon at the same time.

Here, we explore Florida's palm tree issue, the good and the bad palms, and climate change mitigation strategies.

Benefits of Native Palms

In the coastal ecosystems of Florida, native palm trees are keystone species. They support a wide range of animal life with their fruit and flowers. Their canopies provide an over-story for smaller trees and shrubs and are critical bird perching and nesting sites, with, for example, the native Royal palm (Roystonea regia) being by far the most frequent nesting home of Florida's woodpeckers. And their dense, shallow root systems play a key role in supporting microbial biodiversity, including nitrogen-fixing bacteria, important for almost all plant growth.

The Problem With Non-Native Palms

Outside those natural settings, however, palms play only a small role in supporting biodiversity, as their fallen fronds are often removed from urban and residential environments, depriving the soil of nutrients as they decompose. In those settings, the number of non-native palm species outnumbers the natives, while human development has led to the disappearance of some species and the endangerment of numerous others.

Of the 20 non-native species of palm trees on the University of Florida's Assessment of Non-Native Plants in Florida's Natural Areas and Florida Invasive Species Council's List of Invasive Plant Species, these are the top concerns:

• Coconut palms (Cocos nucifera)
• Queen palms (Syagrus romanzoffiana)
• Washington palms (Washingtonia robusta)
• Solitary palms (Ptychosperma elegans)
• Senegal date palms (Phoenix reclinata)
• Chinese fan palm (Livistona chinensi)
  

Non-native species do little to preserve Florida's native habitat, as they create “novel ecosystems” that can have far-reaching ecological effects, even if the tree species themselves are not considered invasive.

Florida's Vital Native Palms

There are 12 palms native to Florida, both trees and shrubs, which will do a better job than non-natives in supporting native ecosystems.

South Florida and the Florida Keys are home to the most fragile of Florida's palms, those that cannot withstand cold or have been threatened by the region's heavy development.

• The shaggy-trunked Everglades palm (Acoelorrhaphe wrightii), grows up to 30 feet high in colonies in marshy wetlands.
• The feather-leaved buccaneer palm (Pseudophoenix sargentii) grows to 10 feet high in sandy soil or limestone only in extreme southern Florida, and is considered endangered.
• The Miami palm (sabal miamiensis) is believed to be extinct in the wild, the victim of human development, but is still cultivated as an ornamental shrub.
• The Key thatch palm (Leucothrinax morrisii) is native to Florida Keys, grows 20 to 25 feet tall, and is considered endangered.
  

Other native palms can grow throughout most of Florida, as they are more cold-tolerant.

• The cabbage palm (Sabal palmetto) is Florida's state tree and needs little encouragement to grow to 40 feet tall.
• The saw palmetto (Serenoa repens) is one of the most abundant of the native palms, forming dense colonies along sandy shorelines throughout the state and beyond.
• The Florida silver palm (coccothrinax argentata) grows up to 20 feet tall in forests, rocky environments, and in the Keys.
• As its name suggests, the Florida royal palm (Roystonea regia) is a giant, growing 50 to 70 feet tall.
• And the 20-foot Florida thatch palm (Thrinax radiata) is used for landscaping and to build tiki huts.
  

There is also a small group of native palms that are more like shrubs than trees. The native needle palm (Rhapidophyllum hystrix) has stems that emerge from a single base; the scrub palmetto (sabal etonia) grows in colonies in Florida's lake region; while leaves of the stemless dwarf palmetto (sabal minor) emerge from an underground stock and grow to a height of 5 to 10 feet.

Palms and Climate Change

Sea level rise, drought, and extreme weather all threaten Florida's vital coastal ecosystems and freshwater forests—and the palms that anchor them.

The mangroves and peatlands of Florida's iconic Everglades are increasingly either inundated by sea-level rise or in danger of drying out during persistent droughts. Peatlands and mangroves are among the most important carbon sinks on Earth, with peatlands absorbing more carbon per area than land-based forests and mangroves absorbing carbon at a rate three to four times faster. When peatlands dry out or mangroves are destroyed, they release significant amounts of greenhouse gases.

Palms are vital to preserving Florida's wetlands and coastal ecosystems, which offer resilience against extreme weather events, including their ability to protect coastlines from erosion control and to act as buffers during storm surges. Cabbage palms dominate Florida's island wetlands, and is the sole tree species on the most saline islands. Yet despite their high salt tolerance, saltwater intrusion has led to a substantial decline in their numbers since the 1990s, devastating entire island ecosystems. Losing these buffers against hurricanes and storm surges increases the damage to human shoreline communities as well.

Mitigation

Yet planted in urban and residential settings, especially in lieu of other Florida natives, native palms do little to mitigate the existential threat that climate change poses to Florida.

Cut down a palm tree and you won't find annual tree rings. Palm trees are monocots of the Arecaceae family, so-called because palms have only one embryonic leaf (or cotyledon). Palms have more in common with grasses than with trees that have two cotyledons (dicots). From a botanical perspective, they are the tallest grasses to ever grow on Earth.

Because they lack secondary growth (tree rings), palm trees do a poor job sequestering carbon dioxide. In a study of the carbon sequestration potential of residential trees in Florida, native trees “sequestered 90% of all C[arbon], while invasive trees and palms accounted for 5% of net C sequestration.” While palms accounted for approximately 20% of the total urban tree population, they constituted less than 1% of its sequestered carbon.

The trees that Florida cities will plant instead of palms must be Florida natives that are salt-tolerant, drought-tolerant, and high wind-tolerant. They should also act as both heat and carbon sinks. Nothing is gained by removing Florida's iconic palms, but much is lost by not increasing Florida's tree diversity.

Planting Native Alternatives

Planting palms as ornamentals in residential environments does little to preserve biodiversity or mitigate climate change. Protecting native palms in their natural habitats means supporting their role as keystone species in carbon-rich swamps and coastal ecosystems.

In urban and residential settings, planting a greater diversity of trees alongside existing palms is necessary to preserve Florida's natural heritage, protect endangered species, and help prevent the state from being inundated by catastrophic sea-level rise.

Correction—March 29, 2021: This article was corrected from a previous version that incorrectly listed crape myrtle (Lagerstroemia indica) and royal poinciana (Delonix regia) as native to Florida.