When we encounter the extensive tussocklands of the eastern South Island [see below right], it is hard to imagine any other landscape in that place – so much a part of the “natural” New Zealand landscape have they become. Yet, as explored in a previous post What is natural? The tussocklands of Lindis Pass, this is in fact a human-induced landscape; the tussocklands have replaced podocarp and beech forest [see left] that once covered the South Island. However, this occurred long before any written history was established, and this environmental history has had to be pieced together through painstaking paleoenvironmental research.
New ground-breaking research, undertaken by an team of both New Zealand and international scientists, has determined how, to what extent, and over what time-frame large tracts of South Island forest were destroyed.
Their recently published paper, “Rapid landscape transformation in South Island, New Zealand, following initial Polynesian settlement“, explains that although the vanishing of a large portion of South Island forests has long been accepted as established fact, there has been ongoing debate as to whether people or climate changes were responsible.
Pollen records show that before Polynesian arrival in New Zealand, 85 to 95% of the country was heavily forested, with low scrub and herbaceous plants above the treeline. The South Island supported beech (Nothofagus) forest at wetter, higher elevations, and podocarp forest (rimu, miro, matai, kahikatea, totara etc) at drier, lower elevations.
However, between the arrival of the first settlers from the Polynesian Islands 700 – 800 years ago to the European settlement of New Zealand in the 19th century, 40% of this forest had disappeared from the South Island, mainly on the eastern side [see forest cover maps below left]. What makes this remarkable is that this extensive deforestation was achieved by small, largely transient, non-agricultural populations in places remote from any settlement, and occurred throughout the relatively large South Island in only a few decades.
The question remained – was this rapid and extensive deforestation the result of solely human factors, or was climate change also a factor. By examining the climate, fire, and environmental changes of the last 1000 years across gradients of topography and precipitation, the researchers have concluded that the deforestation was the result of human influence alone – i.e., human-set fires.
The paper also seeks to answer another “burning” question (pardon the pun!): why did these early settlers burn such large tracts of forest? There is no evidence that these forests were cleared to facilitate the hunting of birds; rather, birds were snared or speared along forest tracks. However, in the case of the cooler South Island, archaeological evidence suggests that the cultivation of introduced crops such as kumara and taro was not possible in the montane interior nor along the coast south of Banks Peninsula. In these regions, the rhizomes of postfire-induced bracken and other starch-rich plants, such as the cabbage tree (ti kouka), were an important source of carbohydrates in Maori diets. In addition to increasing productivity from a human sustenance perspective, the fern-shrubland environments that replaced burnt forest also made travel easier.
Evidence shows that while in some wetter, higher elevations sites registered less impact from fires, and one higher-elevation site even shows forest recovery during the Late Maori period (1600 – 1840AD), most forests never recovered from these repeated and sustained burnings.
To read more about this research, or to find out how to obtain a copy of the published paper, go to the Landcare Research website. A related article, also published in the Proceedings of the National Academy of Sciences, is “Paradise burnt: How colonizing humans transform landscapes by fire”. Click here for abstract.
Photo top: Oxford Forest, one of the last areas of beech forest in Canterbury which escaped both fire and the European settler’s axe, click here for approximate location. (Photo: Rainer Kant). Next right: The tussocklands of Lindis Pass. While many people regard these as “natural”, they are in fact the product of human-induced environmental transformation (Photo: Rainer Kant). Above left: forest distribution maps showing pre-human and pre-European forest cover. Above right: Soil profile showing dark charcoal horizon from the time of forest clearance. (Photo: Landcare Research).