The influence of two wildfires and biological control agents on the population dynamics of Melaleuca quinquenervia in a seasonally inundated wetland

Abstract

The potential of Melaleuca quinquenervia (Cav.) S.T. Blake to re-invade cleared areas was evaluated over a 13 y period that included two wildfires and the introduction of biological control agents. The first wildfire occurred in 1998 and was followed by a mean of 591.5 recruited seedlings m-2. Recruits from that fire were cleared seven years later in July 2005 for a second experiment to evaluate seedling recruitment into cleared areas. Seed rain, seedling recruitment and mortality, and sapling growth rates were measured in four plots located around individual large reproductive trees. A second natural wildfire in 2007 burned through those plots leading to increases in seed rain followed by a pulse in recruitment of 21.04 seedlings m-2, 96.5% fewer than after the 1998 fire. Recruits in half of the plots around each tree were then treated with regular applications of an insecticide to restrict herbivory by biological control agents, while herbivory was not restricted in the other half. There was no difference in seedling mortality between treatments 1083 days post fire (2007) with 96.6% seedling mortality in the unrestricted herbivory treatment and 89.4% mortality in the restricted herbivory treatment. Recruits subjected to the restricted herbivory treatment grew taller than those in the unrestricted herbivory treatment, 101.3 cm vs. 37.4 cm. Many of the recruits were attacked by the biological control agents that slowed their growth. Although solitary M. quinquenervia trees retain some capacity to re-invade areas under specific circumstances, there was a downward trend in their overall invasiveness at this site with progressively smaller recruitment cohorts due to biological control agents. Land managers should prioritize removing large reproductive trees over treating recently recruited populations which can be left for many years to the biological control agents to suppress before any additional treatment would be needed.

Recruitment of Melaleuca quinquenervia (Myrtaceae) in the fringing forests of the Myall Lakes, NSW, Australia

“…S.T.Blake (broad-leaved paperbark tree) is a weed of global significance (Global Invasive Species Database 2021). Listed as noxious in Asia, Central and South America, South Africa and the Pacific (Dray et al 2006;van Kleunen et al 2015;van Wyk and Jacobs 2015), the species has proven to be an invasive coloniser and difficult to eradicate (Bodle et al 1994;Tipping et al 2016;Martin et al 2019;Tipping et al 2021). In the Florida Everglades, for example, where M. quinquenervia was first introduced from Sydney in 1886 to drain swamps and increase agricultural land (Turner et al 1997;Dray et al 2006), it now infests and outcompetes native plants due to its ability to release seeds in high numbers (Myers 1983), to resprout following fire (Cronk and Siobhan-Fenessey 2001) and to tolerate submergence following flooding (Serbesoff-King 2003).…”