To weed or not to weed, that is the question
  • Last updated:
  • 27 Mar 2019

A year ago on the Blackall Range, we were treated to the sight of big flocks of topknot pigeons Lopholaimus antarcticus cruising around the skies. To witness these big flocks of birds can be an inspiring sight. However, when I mentioned that the large number of topknots also coincided with a particularly good fruiting of the exotic camphor laurel Cinnamomum camphora, the joy tends to evaporate and is replaced by concern. 

On one hand an inspiring, immense and beautiful flock of native birds. On the other hand we have an insidious, noxious and invasive weed tree. Unfortunately the two are quite firmly entwined in their lifecycles. General consensus is that we should be getting rid of all weeds, right? However, if we get rid of all the lantana, privet, tobacco and camphor, are we then depriving the native birds and animals that spread them, of habitat that could be crucial to their survival? It is often said that weeds are damaging the local ecology, invading native ecosystems and reducing biodiversity but is this true of all weeds in all situations?

The question I wish to pose is, “can weeds actually increase biodiversity”? I’m going to play devil’s advocate here and say “yes”. What’s that I hear you say? He’s finally gone mad – perhaps spent a little too much time out in the sun or taste tested one too many funny looking mushrooms.

Camphor laurel, privet and lantana

Weeds like camphor laurel, privet and lantana are spreading in our local environment because of the relationship they have with our native fauna. Weeds most often thrive in disturbed ecosystems or ecosystems in a state of change. A mature rainforest is very stable and one of the most resilient of ecosystems to weed invasion. However, areas that have been cleared of rainforest are highly susceptible to weed invasion. In an area like the Blackall Range we have the perfect conditions for weed establishment – large tracts of cleared land and the birds capable of spreading weed seed.

Majority of the remnant rainforest on the Blackall Range is small in size and highly fragmented. Less than 10% of the landscape on the red soil areas of the range is home to remnant rainforest ecosystems. These fragments are so small and isolated that many species will die out in these remnants. However, the spread of many weeds such as camphor laurel, privet and lantana has created vital links between many forest fragments and also created buffers to protect the edges of many of the remnants.

What we must remember when we view these weeds as a problem, is that the weeds didn’t arrive in this area independently of us, create large scale ecological imbalance and then plant themselves. We created the situation and exotic plants are exploiting that situation. What’s left of the native fauna are also exploiting whatever resources are available. They certainly don’t pause to consider whether a fruit is of an exotic tree or not, they are just hungry! I’m not for one second suggesting that weeds don’t require management. I like nothing better than a good bit of lantana smashing or privet and camphor felling. But when undertaking these activities should we also be giving due consideration to habitat values for native wildlife?

Revegetation

In my revegetation plot, more than 90% of the habitat was initially exotic. We left the majority of the camphor laurels and planted the grassed areas. We also left 50% of the lantana patches but as the replacement habitat has developed from the plantings, the exotic weeds are now being cut out or out-competed.

Thank goodness we now have projects such as the Corridors of Green and other revegetation activities, both private and public, that are establishing corridors of native vegetation through planting or regeneration. Let’s also not underestimate nature’s capacity to create its own corridors from whatever is left. The good news is the more native vegetation we plant or regenerate the greater will be the future seed production of these species. Maybe one day we’ll see more native seedlings popping up than exotics.

Solanum mauritianum fruit are a valuable food resource for birds such as Macropygia amboinensis the brown cuckoo-dove.

Ligustrum lucidum fruit are a valuable food resource and corridor tree for many birds such as satin bowerbirds Ptilonorhynchus violaceus and catbirds Ailuroedus crassirostris.

Lantana camara fruit is a delicacy for the Superb Fairy-wren Malurus cyaneus.

If you think botanists have made the scientific names for plants complicated, then you will soon realise that zoologists have taken the art of complicated names to a whole new level.

Article — Spencer Shaw, Brushturkey Enterprises.