Today we begin a three part article by well known expert on ecosystem modification in New Zealand, Bill Benfield. Bill is the author of “The Third Wave: Poisoning the Land” and regularly features in the “Tasmania Times”. This article was first published in that paper on 5 March 2016.
Forest modification over millions of years
By Bill Benfield
The forests of ancient Gondwana, New Zealand (shared with Tasmania), have been suffering die back and hillsides collapsing in great slips which have scarred the land for millions of years. If this is the case, what was the cause of these disasters before possum and deer came along?
Firstly, it is because much of the land is geologically young and unstable.Secondly, it is under the strong influence of a maritime climate and subject to cyclical extremes, of periods of storms which are often followed by periods of droughts.
We also know that pre-human forests were subject to intensive browse by birds, ranging from giant moa to bush pigeon, as well, by insects ranging from stick insects to the many grubs of moths and beetles. Browse shaped the forests. This changed with the coming of the Maori, which brought about the first mass extinction and a consequent major change to the forest ecology.
Observations on natural processes bringing change
New Zealand’s written records start at forests modified by Maori, but as yet unmodified by European arrivals. The journals of the first botanists and explorers such as William Colenso prove interesting, because he actually travelled through untracked forests, mainly in the Ruahine Ranges, in the 1840’s.
His journals chronicled a forest in a state of change, mainly from climatic factors. Before any effects from introduced browsers, he found massive slips and fallen forests from storms.
Drought which can be correlated actual records is also noted by the hydrologist Dr Patrick Grant as a cause of die back which can result in permanent forest changes, such as changing the height of the bush line. An interesting feature is the delayed impact of the real effects of drought. Though Waipawa records show severe drought in the years 1914 – 15, it was not till 1917, several years later that the full damage was obvious.
The impact of extreme weather
So too today, weather events that can affect forests are occurring, and can be verified by both observation and their impact. A case in point is Northland, where drought has been declared in both January and December 2010 and again in 2013.
It was no surprise then, that meteorologist Dr Jim Sallinger was reported in the New Zealand Herald of 3/4/13 that forest was at risk of die back over a wide area from Wairarapa to Northland. Without significant rain, he predicted century old native trees were at risk of dying due to drought. The accompanying photo showed dying trees.
A later paper quoting Salinger on Sciblogs of 14/10/14 chronicles events, ranging from global climate change, residual effects from ozone depletion and changing wind patterns from the Southern Annular Mode (SAM) as being current drivers of increasing drought.
Higher temperatures from the drought have a multiplier effect as plant evapo-transpiration increases with heat, it exacerbates the damage to both forests and farms.
( In the second part of the article, Bill examines the hysterical campaign by Forest and Bird and others, to solve the perceived Northland forest “problems” with poison.)