Weedy woes and ecosystem rehabilitation – what are the biophysical consequences of woody weed management?

Harrington 3 6 15 1 (6)It is well known that invasion of ‘natural’ vegetation communities by non-indigenous plants (commonly termed ‘weeds’) significantly threatens native vegetation diversity and ecological function. It is widely assumed that restoration of native vegetation can be facilitated through weed removal, but it is clear from recent evidence that removal of a weed alone is unlikely to restore resident ecosystems. Indeed, it has been estimated that as little as 20% of management activities are quantitatively evaluated for community responses to weed removal. More often than not, ‘positive conservation outcomes’ are evaluated in terms of how much biomass of a particular weed is cleared from a particular area, with little consideration given to the degree to which the community regenerates once the weed has been removed.

At the start of this year I began an investigation on the patterns of native vegetation responses to weed management, in collaboration with ecologist Kris French and human geographers Nicholas Gill and Natalia Adan from the Australian Centre for Cultural Environmental Research (AUSCCER) at the University of Wollongong. My project is couched within and complements an overarching study on the complex social and cultural drivers of weed invasion and management systems across rural landscapes      IMG_6682(see detailed outline of this project here).

My specific project will examine whether and how native wet sclerophyll vegetation regenerates in response to removal of the thicket-forming shrub Lantana camara (lantana) by private residents across semi-rural and forested landscapes of south-eastern Australia. This will be achieved through detailed vegetation censuses across a diverse array of vegetation plots from which lantana has been removed, as well as reference invaded and relatively intact patches dominated by native forest. (I am a bush-pig at heart and have a rollicking good time when rummaging around forests, collecting data on plant communities – if you fancy being pinged with photos of a bearded boy head-deep in lantana, covered in ticks, leeches and scratches but exploring the most extraordinarily beautiful landscape, follow me on Twitter @GoodenBen…).



Does time heal all wounds, or only at some places some of the time?

Fundamentally, I expect that the plant assemblages that emerge once lantana is removed will be richer and more structural diverse than those present in lantana-dominated patches of vegetation. Indeed, I have been shocked at how rapidly native plants (grasses, sedges and forbs in particular) recruit into plots once lantana is removed (see image below, taken before and then only four months post removal)! I will survey vegetation along a chronosequence of lantana management (before removal and 1 to 20 years post removal) to determine the temporal scale over which native communities recover from invasion.

Harrington 3 6 15 1 (4)

However, it is clear from recent evidence that the patterns of community regeneration in response to weed management is moderated by at least three key attributes: (1) mechanism by which the weed is removed (see classic example here), (2) landscape context and (3) ‘resilience’ of the community to invasion. For instance, we are finding that lantana is removed either mechanically (sometimes using heavy machinery, such as tractors and slashers) or chemically, and I anticipate that the pattern of vegetation response will differ between these two control methods. Disturbance of the soil, through mechanical removal, may activate seeds stored within the soil and facilitate native plant recruitment. Alternatively, mechanically-controlled sites may become dominated by secondary weeds, as a result of soil disturbance, which inhibit recruitment of native species… we do not know what to expect, but I predict nonetheless that these two modes of weed management will have divergent trajectories of native vegetation restoration. Other methodological factors that may influence how the vegetation recovers post invasion include: how long was lantana present prior to its removal? How much lantana was removed, and how often; once only, or were follow-up treatments used to prevent it from re-establishing? How many practitioners participated in the removal programme?

Likewise, we are finding that lantana removal is conducted across a gradient of vegetation cover within the landscape matrix, and I anticipate that each managed site’s landscape context will moderate patterns of community regeneration post lantana removal. Sites embedded within a forested matrix are likely to contain a diverse and abundant suite of plant propagules within the soil seed bank and higher rates of visitation by avian frugivores than sites located in extensively cleared landscapes. Will forested sites thus experience faster rates of vegetation regeneration once lantana is removed compared to managed sites with little residual vegetation in the surrounding landscape?

My overall aspiration, therefore, is to determine optimal regimes of woody weed management with regards to promoting native vegetation regeneration across invaded landscapes. Through extensive vegetation surveys, coupled with complex general linear mixed models, I will attempt to develop a model of vegetation regeneration, based on where, when and how lantana has been removed, as well as landscape attributes and functional traits of the native plants themselves.

People, place and entangled ontologies

Weed management is as much a function of the people who engage with the weed as the native vegetation that are impacted by the weeds. I wish to acknowledge the fabulous work that my colleagues Nick Gill and Natalia Adan are doing on working with local land managers and private custodians on weed management systems and landscape change. I’m a bush boy who is still grappling with objective realities versus entangled ontologies, but I am learning to be more open to understanding how ecological and human cultural systems  are entangled, not separate – and I thank them for this opportunity to play a part in their research.

The lost art of scientific illustration

DodoIf it were not for the work of scientific illustrators, we would have very little documentary evidence for the existence of dodos and several other now extinct, bizarre and charismatic species (Hume 2003). Indeed, the image on the right is purportedly the earliest depiction of the dodo, sketched by Joris Joostenz Laerle during a voyage to Mauritius in 1602, (housed within the Nationaal Archief, Den Haag).

Remarkably, physical evidence for the dodo is restricted to a dried head and a couple of feet, which hardly gives us an insight into the unique life history and ecology of this bizarre bird. Contemporary studies of this species’ ecology and life history depend largely upon illustrations made three to four hundred years ago.


Milly_PP_1Imagine how natural history and modern science could have progressed without such images being created and curated for posterity? Banks’ botanical expedition to eastern Australia and Darwin’s work aboard the Beagle were enriched by such illustrations and captured the imaginations of their contemporaries.

I recently joined the Twitterverse and have discovered a rich community of Milly_PP_2scientific illustrators in Australia. Their work invokes the romance of naturalist explorers hunched over parchment on rolling ships, deep in thought, brows furrowed, pencils in hand, trying to capture the essence of unique, alien specimens, aided only by the light of a flickering candle.

My favourite illustrator at the moment is Milly Formby, zoologist and artist, based in Victoria. Over the past two weeks I’ve been captivated by her illustration of the platypus (images reproduced with permission), by far the weirdest animal in Australia. Her other work on birds and fishes is equally phenomenal! Anyone interested in scientific illustration should definitely look her work up (millyformby.com)


The climate change charade

Sitting here, head in hands, all I can think is what a terrible day for Australia.

Only minutes ago the Senate voted to repeal the Carbon Tax. Sure, it might not have been the best option available to limit future greenhouse gas emissions, but it was a start and it seemed to be working! Even Big Business admits that very little, if any, of the financial ‘burden’ was passed on to energy consumers! The tax seemed to be absorbed pretty well by the economy and has been linked to a boost in the renewable energies sector and the creation of new manufacturing jobs… and god knows we need it! For all its faults, the Tax at least sent a message to humanity that, yes, Australia is serious about climate change and a ready, willing and valuable player on the World stage when it comes to climate policy and global action. As a Nation, we deserve to be shunned by the rest of the world over this farce.

And for all those who think that climate action falls along party lines, please explain to me why some of the most conservative governments in the world, including UK and Germany, are able to deal with climate change effectively whilst maintaining their conservative ideologies and solid economic growth?

What makes me sad is that the Senate’s decision today sends a clear and powerful message to the rest of the world that, in Australia, Science is simply considered to be another system of dogma, belief or ‘opinion’ by serious policy-makers, rather than a philosophy of objectivity and evidence-based consensus and decision making. I suppose it explains why the Government is continuing to take the advice of a teaching ‘expert’ who thinks that physically assaulting and abusing a child is fine, if done in the ‘correct way’, despite the wealth of scientific evidence to the contrary, and why we’re slowly dismantling the CSIRO. Oh yeah, we don’t have a Science Minister either… forgot about that bit.

To those who think that climate change is ‘crap’ and simply someone’s ‘opinion’, please answer these questions: do you trust your car mechanic to test your brake-pads, doctor when checking up on your STIs, electrician when installing the wiring on your granny-flat extension, phone when making an electronic funds transfer? If so, you should trust and believe a climate change scientists. It’s all the bloody same philosophy!

Just because you don’t understand how something operates, doesn’t mean that it’s not TRUE! I don’t know how quantum mechanics works, for instance, but my mobile phone operates regardless of my ignorance. Likewise, I’d be hard-pressed to explain how vaccines enable disease resistance in my body, but I know that they do and that’s enough for me to get the jab! Again, just because I don’t understand it, doesn’t mean that it’s not an accurate model to explain how the physical world operates.

Trust a scientist and the scientific process – it’s the best system we have to weed out the loads of crap in this world that make our lives difficult. Fundamentally, an attack on climate scientists and the philosophy that has driven their discoveries over the past two decades or so is an attack on all who hold Science as fundamental to human enterprise.

I thought we finished fighting this corner 400 years ago or so…

Differential effects of chemical and non-chemical control of a woody weed (Lantana camara) on native tree seedling regeneration

Lantana camara is undoubtedly one of Australia’s (and arguably the world’s) most destructive invasive plants. Research that I did during my honours found a clear negative association between lantana abundance and native plant recruitment and species richness within wet sclerophyll along the southern coastline of New South Wales (see publications in Biol Cons and FEM).Image

There’s a huge amount of research out there now on the mechanisms by which lantana impacts native plant community diversity (for example, see work by Gentle and Duggin). There is very little research available, however, on the capacity for the vegetation community to recover following lantana control.

I conducted a weed-removal experiment in 2007 within lantana-invaded turpentine forest at Macquarie Park National Park, to examine the effects of lantana invasion and two methods for its control on rates of tree seedling establishment and growth. There were two lantana-removal treatments used in this study: (1) mechanical removal of above-ground lantana biomass ONLY and (2) mechanical removal followed by the application of herbicide (Glyphosate) to cut lantana stems. This second removal treatment is the standard, intensive control measure used by bush regenerators when restoring sclerophyll forest infested with lantana. However, many bush regenerators (myself included!) are averse to using chemicals, prefering to instead mechanically remove lantana only from sensitive sites.

A single native tree seedling (nine species in total) was planted in the centre of 2 m x 2 m plots from which lantana was removed and their establishment and growth monitored monthly for one year. I also examined whether native seedling responses to lantana invasion and removal treatments varied across native tree functional groups: (1) upper canopy sclerophyllous trees of the genera Eucalyptus and Syncarpia, (2) subcanopy mesophyllous trees, such as Syzygium and Synoum and (3) species typically recorded in disturbed canopy openings or along forest edges (e.g. Trema and Acacia species).Image

I found that lantana invasion and removal had no effect on rates of seedling mortality. However, upper canopy species were significantly less likely to survive overall than subcanopy or disturbance-adapted species. Importantly, seedlings which survived the growing season were significantly larger (measured by height, basal stem width and number of leaves) in both plots dominated by native vegetation (i.e. without lantana) and where lantana’s canopy was removed and its basal shoots poisoned than in lantana-dominated plots. Furthermore, seedling growth was inhibited in plots where lantana canopy was removed but where herbicide was NOT applied to its cut basal shoots!!!

Overall, my results are not surprising and confirm the wealth of experimental evidence that already exists on the impacts of lantana and other woody invasive plants on the regeneration of native vegetation. However, my results clearly show that mechanical removal of lantana alone is unlikely to promote the regeneration of native vegetation without the application of appropriate herbicides to cut stemsIMG_0461[1]

Many bush regenerators, myself included, are hesistant to use herbicides to control weeds in ‘sensitive’ bushland, and prefer to mechanically remove both above-ground shoots and below-ground roots to control woody weeds, such as lantana. It is highly probable that mechanical removal of both lantana shoots and roots would indeed lead to a similar positive outcome for seedling recruitment as the herbicide treatment used in my experiment. However, mechanical removal of lantana roots probably disturbs the soil and promotes vigorous secondary invasion by other weeds present within the soil seed bank. Many of these are benign and transient opportunists (e.g. Conyza, Bidens and Sonchus species), but others are often more difficult to control than lantana.

I am in the process of preparing this paper for submission to Ecological Management & Restoration. Please get in touch (bgooden@uow.edu.au) if you would like further information about this project and my research on invasive plants in general.

Urbanisation impacts abundance (but not richness) of salt marsh molluscs

salt marsh impactThe preliminary results are now in: urbanisation at the landward boundary of coastal salt marshes is associated with a two-fold reduction in the density of molluscs inhabiting adjacent coastal salt marsh. Our results found, however, that despite this reduction in overall molluscan abundance, urbanisation had no effect on the number of different mollusc species (i.e. richness) present in adjacent salt marshes.

The overall aim of this project was to examine effects of shoreline urbanisation on the unique molluscan fauna within endangered salt marsh of south-eastern Australia. My student, Geoff Clarke did a stellar job with this project, counting and identifying over 7,500 individual snails from six species, most of which are restricted to salt marsh or similar vegetation that borders estuaries and coastal embayments.

Geoff surveyed 9 ‘urbanised’ and 9 ‘forested’ (which he termed natural) reference sites across three embayments (see accompanying satellite images). Each site consisted of a 40 m x 10 m quadrat at the landward boundary between marsh and casuarina forest. Molluscs were sampled from within 15 50 cm x 50 cm subplots that were randomly distributed throughout each site.Geoff also recorded the number and abundance of resident plant species and litter cover.Gastropod.PNG

Interestingly, salt marsh patches adjacent to urbanised and forested landscapes were similar in terms of number and abundance of plant species, litter cover, bare ground cover and extent of tidal inundation.

What, then, is the mechanism by which urbanisation drives a reduction in molluscan community productivity? We are exploring the following ideas in out next field season:2014-03-05 10.11.08

(1) Chemical pollutants in urban storm-water runoff limits growth of algal soil crusts upon which gastropods graze, thus indirectly limiting population sizes.

(2) Urbanisation inhibits the fecundity and recruitment of resident molluscs, perhaps through chemical disruption of embryo development and recruit establishment.

(3) Urbanisation increases rates of predation of resident gastropods (Phallomedusa and Ophicardelus) by fishes and birds.

It would be great to hear from like-minded benthic ecologists interested in these and other interactions and getting involved with future projects at University of Wollongong!

It is muddy work but immensely enjoyable!!! This project was cosupervised by Matt Rees, member of FishThinkers research hub (http://fishthinkers.wordpress.com/)IMG_4240


New publications out now….

Gooden, B. & French, K. (2014) Non-interactive effects of plant invasion and landscape modification on native communities. Diversity and Distributions 20, 626-632.

Gooden, B. & French, K. (2014) Impacts of alien grass invasion in coastal seed banks vary amongst native growth forms and dispersal strategies. Biological Conservation 171, 114–126.

Gooden, B., French, K. & Robinson, S.A. (2014) Alien grass disrupts reproduction and post-settlement recruitment of co-occurring native vegetation: a mechanism for diversity decline in invaded forest? Plant Ecology 215, 567-580.

Gooden, B. & French, K. (2014) Impacts of alien plant invasion on native plant communities are mediated by functional identity of resident species, not resource availability. Oikos 10.1111/oik.01724.

Gooden, B., French, K., Turner, P. and Downey, P. O. 2009. Impact threshold for an alien plant invader, Lantana camara L., on native plant communities. Biological Conservation 142, 2631–2641

Gooden, B., French, K., Turner, P. 2009. Invasion and management of a woody plant, Lantana camara L., alters vegetation diversity within wet sclerophyll forest in southP1090156eastern Australia. Forest Ecology and Management 257, 960–967

Please get in touch if you would like me to send pdf copies of these papers to you (bgooden@uow.edu.au)









Educational history

  • 2007: Bachelor of Science (Biology) Honours – Advanced, First Class (90 %), University of Wollongong. Thesis title: The Effect of the Woody Plant Invader Lantana camara on Vascular Plant Diversity in Wet Sclerophyll Forest.
  • 2004-2006: Bachelor of Science (Geoscience and Biology), University of Wollongong.
  • 2003: HSC Broken Hill (Willyama High School), UAI 98.7.