This week for Flora and Fauna Friday, we have a pair of tree species that help define some of our most iconic Lowcountry ecosystems, the Bays of genus Persea.
Here on Edisto Island we have two species of Bay, Redbay (Persea borbonia) and Swamp Bay (Persea palustris). Both species share many similar physical characteristics. However, the two species differ most notably in their habitats. Redbay is predominantly found in maritime forests on barrier islands and sparsely in maritime fringe forests on our sea islands on the wet but well-drained soils possible with our unique geology. Swamp Bay is found in stagnant, freshwater wetlands on acidic, poorly-drained soils. They are particularly abundant in Carolina bays and are the source that lent these isolated wetlands the “bay” name. They can also be differentiated by their twigs, with Redbay having smooth twigs and Swamp Bay having fuzzy twigs. Both teeter somewhere between a small tree and a large shrub, Swamp Bay tends to be more tree-like and Redbay shrubbier. Yet the two are more similar than different, in fact they were lumped together as one species until recent decades. Our Bays have somewhat blocky, light-gray bark and usually a gnarled or kinked stem. Their evergreen leaves are narrow but close to hand length with a glossy, dark-green upper surface. Both bloom in mid-spring with small pale yellow-green flowers and bear an egg-shaped dark-blue drupe. Both of our Bays are also the primary host plants for the Palamedes Swallowtail and can host the Spicebush Swallowtail too. The Avocado (P. americana) is a tropical member of the Bay genus but not native to the United States.
Our Bay trees are in trouble, particularly Redbay. Redbay has long been feeling the impacts of coastal development, as its barrier island and maritime fringe habitats have been rapidly developed over the last century. Swamp Bay has a much wider distribution and has been secure from such pressures. However, early in the 2000s an exotic pest carrying a pathogenic fungus was introduced from Asia and has been ravaging native populations of Bay trees since. A miniscule female Redbay Ambrosia Beetle locates a healthy Bay tree and bores a hole into its living wood. This beetle carries a pathogenic fungus called Laurel Wilt which is deposited by the beetle during the wood boring process. The beetle and the fungus have a symbiotic relationship. The beetle and its larvae feed on the fungus as it spreads throughout the tree and, in exchange, the fungus inoculates the beetles with spores and is spread deliberately and directly to the sapwood of new host trees by dispersing female beetles. The life cycle of the Redbay Ambrosia Beetle is fascinating but ultimately spells doom for infected Redbay and Swamp Bay trees, with infected stems dying within a matter of months. Infected trees can be identified by fine tubes of sawdust emerging from the trunk and dying trees are easily recognized by sudden wilting and browning of foliage across entire limbs or whole crowns. This disease affects not only our native Bay species but also other members of the Laurel family, including Sassafras, Spicebush, and Avocados. It is now becoming a serious economic threat to Avocado orchards in south Florida.
