Over the past two years, our winters have been long and cold, sometimes plunging to less than 10 degrees Celsius. In August, we note changes. Increases in temperature, new leaves appearing on our fruit trees in the orchard and with the arrival of the new leaves, the hatching out of the stick insects, but only on the early leafing trees. How is it, we asked, that the stick insects remain on the first trees, while the later leafing trees are allowed to flourish without stick insects?
The answer to this question lies with the amazing inter-relationships that exist in nature. When the stick insects start munching on the leaves, they stimulate a reaction from the tree. The tree sends out a chemical message, a pheromone that informs the surrounding trees of the invasion. Somehow this pheromone triggers a response from the recipient tree to protect the new leaves. A tannin is inserted into the new formative leaves that is not palatable to the stick insects. The early leafing trees become the sacrificial trees that allow the later leafing trees to remain free of pests. How’s that for co-operation?
So what happens with climate change? We noted last year that the long cold winter interfered with the careful timing of the new leaves and the hatching of the stick insects. Most of the trees shed the old leaves and grew their new leaves before the stick insects hatched out. Seems that temperature is critical in the timing of this operation. Delayed warmth resulted in a later hatching of strong stick insects infesting most trees. Continuance of changing temperature patterns could affect the balance of stick insects to ancestral custard apple trees (Annonaceae) in the rainforest.
At this stage, we cannot say that there is a clear pattern of change. We could say that change is within normal limits, but where those limits are breached remains a mystery to us. By recording events in our weblog, we can compare the dates and comment on changes.
We have also noted that Boyd’s Forest Dragons position themselves close to the fruit trees when the stick insects mature, so that the dragons can munch on their favourite delicacy, large female stick insects.
With weather patterns changing each year, and no clearly defined direction, I cannot point out changes that may be occurring because of climate change. One thing I do know is that Australia’s tropical rainforests are enduring. Their complexity and biodiversity is something to be marvelled at – and protected.