To Weed or not to weed, that is the Question.

 
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 groups of birds can be an inspiring sight for many. However when I mentioned that the large number of Topknot’s also coincided with a particularly good fruiting of the exotic camphor laurel’s Cinnamomum camphora the joy tends to evaporate and is replaced with a look of concern.
What a confusing situation! 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 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 possibly 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 the devils 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? 
Weeds such as 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. 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 thus have the perfect conditions for weed establishment, large tracts of cleared land and the birds capable of spreading weed seed. Most remnant rainforest is highly fragmented in small patches throughout the range. Much 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, the areas are just too small to sustain them. However the spread of many weeds such as camphor, privet and lantana has created vital links between many forest fragments and also created buffers to protect the edges of 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 wide 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 for one like nothing better than a good bit of lantana smashing or privet and camphor felling. But when undertaking these activities we should also be giving due consideration to habitat values for native wildlife?
In my particular reveg plot when we started 90+% of the habitat was exotic. We left the majority of thecamphor laurels and planted the grassed areas. We also left 50% of the lantana patches but as the replacement habitat has developed from the planting’s, the exotic weeds are now being cut out or being out competed.
Thank goodness we now have projects such as the Corridors of Green projects and other reveg activities both private and public that are establishing corridors of native vegetation through planting or regen’. But also let’s not underestimate nature’s capacity to create its own corridors out of whatever is left available. The good news is that the more native vegetation we plant or regenerate the greater will be the future seed production of these species and maybe one day we will see as many native seedlings popping up as 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 crassirostris *.
*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.