Lantana

Article by Nick Clancy, conservation partnerships officer, Sunshine Coast Council

Lantana camara is possibly the most widespread weed in South-east Queensland (SEQ); very few rural properties can claim a lantana-free status. It covers an estimated four million hectares of eastern Australia, often to the exclusion of wildlife, people and livestock.

Despite being considered in the top ten of the world’s worst weeds and a ‘weed of national significance’, landholders don’t actually have a legal requirement to control lantana. However many landholders do feel compelled to reduce its extent.

But not everyone feels this way. I often hear the comments, ‘but it’s great habitat for birds’ or ‘it provides important cover for wildlife’. So, which is it? Great habitat? Or serious weed? Well, like many polarised debates the answer probably lies somewhere in the middle and is often site specific.

Many Land for Wildlife properties in SEQ consist of regrowth forests that have a history of logging and/or grazing, providing ideal disturbed niches for lantana to grow. Lantana is not a fussy plant, it grows in most SEQ vegetation communities. As far as plants go, it’s somewhat of a ‘shape shifter’. It adapts its growth form in response to environmental conditions. In high rainfall areas it can form impenetrable thickets that blanket entire hillsides of neglected pasture. In regrowth forests where it struggles for light it will climb up and over trees creating lantana ‘towers’, while in drier, ‘hungrier’ country it can form tough, raspy shrubs. Lantana can also send long runners out along the ground, which then shoot skywards when they find a sunny gap. This adaptability, coupled with the fact that there are hundreds of recognised varieties of this nursery manufactured ‘species’, makes generalising about Lantana camara and its control somewhat problematic.

So why is lantana considered a problem? For starters it’s highly invasive. First introduced into a Sydney garden in the 1840s it quickly spread. By 1889 the first dense stands were mapped close to the mouth of the Brisbane River. 8 years later it was described as Brisbane’s ‘most troublesome weed’ that formed ‘impenetrable thickets on the banks of stream, deserted farms and the edges of scrubs’.

Lantana seeds are dispersed by birds and mammals and germinate readily, especially in disturbed areas. While seed viability decreases with time (about a quarter will germinate after 36 months) some have been found to remain viable for up to 11 years. Lantana establishes rapidly in disturbed sites at the expense of other plants, due to its fast growth rates and allelopathic effects (toxicity to other plants).

Regenerating native seedlings are shaded out, as are groundcovers and grasses. Existing shrubs and small trees can be smothered and are eventually pulled down by sheer weight. So in essence, lantana can stall the successional process of regrowing forests and dominate the understorey of disturbed forests, especially if the canopy has been opened up through activities such as logging. Combined, these impacts can lead to a reduction in biodiversity.

Lantana provides cover for some undesirable animals; feral animals such as cats, pigs, rabbits, foxes and wild dogs have all been shown to take cover in lantana thickets. Contributing to another threatening process for wildlife, lantana can promote changes in fire regimes, in some instances it can increase wildfire intensity, while in other situations it can limit the spread of fire.

On grazing properties lantana is not just a problem because it competes with pasture, it is also toxic to livestock. The economic costs of lantana to the grazing, forestry and conservation sectors are very high. In 2005/06 it was estimated that the Australian grazing industry alone was losing $104 million per year in lost productivity as a result of lantana. So we have heard from the nay side of the debate, what about the ayes?

On the ‘great habitat’ side of the debate, lantana provides food for a range of wildlife. For example I have often observed Richmond birdwing butterflies and numerous species of honeyeaters feeding on the nectar of lantana flowers. Birds such as silvereyes, pied currawongs, satin bowerbirds and Lewin’s honeyeaters eat the small fruits. The vulnerable black-breasted button-quail utilises lantana for day-time foraging and nocturnal roosting and lantana thickets are considered a crucial component of their habitat requirements in some locations.

Of the numerous native species that utilise lantana thickets as habitat, it is the dense growth structure that makes it attractive. Whipbirds, scrubwrens, pheasant coucals and fairy wrens all utilise the dense structure provided by lantana. Bandicoots, wallabies and pythons will use lantana as a refuge during daylight hours. Its habit of occupying forest edges is also useful for species such as red-necked pademelons as it provides dense cover from predators immediately adjacent to more open foraging areas. Prior to 1840 all of these native animals thrived in an environment without lantana, and in the absence of their pre-European habitat they have adapted to utilise lantana in various ways. So there is no doubt that lantana provides habitat opportunities for a range of wildlife. But does this mean that we should simply leave lantana wherever it grows and assume that everything is hunky-dory in downtown lantana land?

Well, in some instances the answer is probably yes. For example where there is an absence of alternative cover for lantana dwelling native wildlife. Also, where lantana forms a fringing thicket along forest margins, then it can function well as an ‘edge’ plant. As an edge plant it can help to exclude livestock from natural areas or waterways. The buffer provided can be beneficial, preventing spread of other weeds into the forest. However in this context lantana is not providing anything that structurally-similar natives such as native raspberry (Rubus spp.) can’t also provide.

In many cases I would suggest that we can do better than simply leaving lantana, especially in the mosaic of remnant, regrowth and open country that occurs on many Land for Wildlife properties.

Where lantana forms a mono-cultural land blanket it offers a very simplified habitat. By this I not only mean structurally, but it only provides one variety of flower, fruit and foliage. When the dominant lantana is not flowering or fruiting, alternative food sources are limited. If, as ‘Land for Wildlifers’, it is our objective to expand and improve the habitat resources available to native wildlife on our properties, then we should aim to replace lantana with the suite of endemic plants. This doesn’t always mean that you need to plant trees either, often when lantana is removed we release the brakes on natural regeneration, stimulating a flush of germinating native plants from all strata including herbs, ferns, grasses, shrubs, trees and vines.

With assistance, this regenerating pulse of plants can provide a greater variety of both structure and feeding opportunities, offering a range of foliage, flowers, seeds and fruits throughout the year. Over time the subsequent increase in plant and invertebrate diversity will likely result in an increase in the diversity of wildlife.

Of course there is a lag effect. For a time there will be limited cover available in the cleared area. For this reason it is often recommended to stage your lantana control so you are not removing large areas all at once. This is not only better for the wildlife but it also means you are more likely to keep up with the required maintenance. Regardless of the method employed, the key to successful control is follow-up weeding. Manual control can be done in autumn outside the usual breeding season for most small birds and when the weather is mild. Chemical control is best done in the summer growing season. While the clumps will lose their foliage after spraying they will maintain a dense structure of canes through to autumn when the brittle frame can be knocked down manually.

Try to assess your lantana patches objectively. Take some time to determine the beneficial habitat roles that a patch may be providing but also assess what’s being smothered and/or suppressed. Consider the potential diversity of plants that may be locked up in the soil seed bank. Look around and see what alternative dense thickets are available and also check what other weeds may be waiting to move in once the lantana is removed. Other invasive species such as Broad-leaved Paspalum are best controlled prior to tackling lantana, otherwise you will end up with one weed replacing another.

For better or worse, lantana is here to stay as an entrenched component of SEQ ecosystems. Many properties will have lantana patches that may never reach the top of their owners’ priority list; they will remain for the next generation of land managers to consider. Wherever lantana grows a range of native animals will continue to take advantage of its resources and some observant landholders will choose to keep some patches of lantana for dependant species such as whipbirds and the black-breasted button-quail. Other landholders will choose to remove lantana patches and restore native forest cover to the benefit of other animal species and some will choose to have a bet each way.

References and further reading:

• Stock D (2009) Lantana: Best practice manual and decision support tool. Dept of Employment, Economic Development & Innovation Qld
• Low T (1999) Feral Future: The untold story of Australia’s exotic invaders. Penguin
• Low T (2017) The New Nature: Winners and losers in wild Australia. Penguin.