Lowland native forests under threat
THIS year, the extensive sudden death of native trees in a rare lowland forest reserve in southern Wairarapa has been widely reported. In a 1.9ha forest, 249 trees, including 300yearold kahikatea, died simultaneously. This swamp forest is in the Whakatomotomo Valley, near the small Turanganui River.
The first sign that the trees were dangerously stressed was when kiekie and supplejack in the southern end of the reserve died out completely in 2015. Later that summer, rimu outside the reserve were in serious stress — one tree dying this year, while the others are now moribund. Dieback within the reserve continues unabated.
Causes of the dieback are being investigated, but are thought to include global climate change in concert with more local human activities over the past 100 years, such as draining paddocks to make them more amenable for farming.
A local man who had dug ditches, drained paddocks, channelled the river and converted swampland to farms, said that in 1987 he had proposed that his lattice of ditches should connect to a natural waterway that entered the southern corner of the forest, but that was not carried out, to the detriment of the forest. Groundwater in the narrow valley is now being used for domestic water supply, general farm use, and for agricultural irrigation. Together, this human activity is killing the forest.
Attention is drawn to this dying forest reserve because I have visited numerous, very valuable, small isolated lowland native forest remnants throughout New Zealand that are similarly affected — including forest reserves in Canterbury, Otago and Southland.
In most of these dying native forest reserves, native insects such as ground beetles (Carabidae), stag beetles (Lucanidae) and even spider wasps (Pompilidae) are in much lower numbers this century than they were in the 1970s and 1980s.
In some reserves, many grounddwelling insects have been wiped out completely by introduced mammals, particularly rodents and hedgehogs, and large grazing mammals such as sheep and cattle, whose hooves have compacted the soil and broken up rotting logs where beetles and their larvae once lived and sheltered.
Throughout New Zealand most species of our beautiful native birds are declining rapidly in stressed and deteriorating native forests.
All humans depend ultimately on a healthy environment. A wise vote on Saturday can help save the environment and rescue nature, which is in crisis.