Landscape changes
Prior to the arrival of humans 1000 years ago, 85 - 90% of New Zealand was covered by forest. Only 15% of the South Island and 1.5% of the North Island was above the timberline. A notable feature of the lowland areas was their large swamps and bogs. In the North Island especially, many of these wet areas were covered with dense forests of tall conifer or broadleafed trees such as kahikatea, rimu, silver pine, kauri, tanekaha, kaikawaka and swamp maire. The fruit of many of these species were food for kerer? and other birds.
At the beginning of the 21st century, only 18% of the country is covered by forest - an almost complete reversal of the balance. Of the pre-human-arrival lowland forests, only a very small proportion remains. Mäori cleared some areas - maybe as much as 30% of the total - for gardens, kainga, pä and other uses or by accidental fires. As food sources such as moa and other large birds were depleted, it seems that they also managed lowland forests as an abundant food source in themselves, especially the swamp forests.
But when European settlers arrived seeking farmland in the 19th century, the remaining lowland forests were doomed. A good deal of New Zealand's hill country is not well-suited to farming as it is too steep. British settlers had been promised large areas of farming land and so, when they arrived and found much of the land under forest, they set about draining and clearing it. The technologies they brought with them to achieve this - draught animals, steel axes and shovels - were highly efficient and were used both by Päkehä settlers and by Mäori who were enthusiastic traders. These new technologies allowed huge areas of forest to be destroyed between 1860 and 1890.
As the forests disappeared, so too did their bird inhabitants, including kerer? . After millions of years of evolution, some tree seeds do not germinate easily without being eaten and since the kerer? is the only remaining bird species capable of swallowing some of the larger fruit, they are very important to the maintenance of our forests. Kerer? briefly store these fruit in their crops (a pouch below the throat), and the seed, stripped of the nutritious flesh, eventually passes through the gut, including the muscular gizzard, undamaged and is deposited with its fertilizer. As a result, and because kerer? occasionally fly several kilometres between food sources, the species is very important for seed dispersal.
As kerer? numbers decline, this part of the relationship web is affected and renewal of our forests slows down. If too many such relationships are broken, the healthy functioning of the ecosystem will be put at risk.
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