Before humans arrived in the Otago drylands, fire was a feature of the landscape, but only on a small scale. Natural lightning-induced fires swept through patches of the woody shrubland, but widespread fires were uncommon. With thunderstorms being relatively infrequent and highly localised, and with plenty of natural fire barriers in the landscape, they never picked up great momentum. Barriers were provided by areas of rock and cliff, by scree slopes and water courses, and by the mixed nature of the vegetation cover. The areas of taller forest that lay along watercourses, in shadier moist gullies, and on the range slopes above 700 metres, were largely resistant to fire.
With the arrival of humans about 800 years ago, all of this changed. Charcoal and pollen records in the soil show a distinct change occurred between 800 and 550 years before the present. Considerable and widespread charcoal sediments show that large fires burned across whole landscapes, and the pollen records show an accompanying sudden change in vegetation. There was an abrupt drop in trees and shrubs, with an expansion of grasses, bracken, Celmisia and Aciphylla (Spaniard).
Some of the fires were probably accidental, while others were deliberate. The Polynesian settlers used fire as part of their moa hunting strategy. They probably also used it as a way to create a clearer route of travel to the Southern Alps and the West Coast, on their journeys to collect the highly valued pounamu, greenstone.
Fire made little impact in the western mountain ranges. In the lowlands of the south and west, it led to partial forest loss. In the eastern areas where rainfall was 1000 millimetres or less, it completely decimated both lowland and montane forests. Fire sensitive species were eliminated from the landscape. In small dry refuges on cliff faces, the grasses survived the fires, and from here they spread to recolonise the burnt land. Grassland became the dominant vegetation type, bracken and short tussocks first, followed by the larger snow tussocks (Chionochloa).
Grassland became the dominant vegetation type, bracken and short tussocks first, followed by the larger snow tussocks.
Bush fire. Image: Public domain.
As fires destroyed large areas of their habitat, native fauna were also experiencing pressure from hunting. The moa were an important food source for early Maori, and were hunted so intensively that within two or three centuries of human arrival, all moa species were extinct. We had other less famous flightless birds that also created a good meal, two species of giant goose, two adzebills, and six duck species, and all were gone over 500 years before present.
We had other less famous flightless birds that also created a good meal, two species of giant goose, two adzebills, and six duck species, and all were gone over 500 years before present.
When the first boat loads of European settlers arrived in Otago in the 1840s, they found grassland extending from the flanks of the Southern Alps out to the east coast. Dotting the grasslands were areas of fernland and scrub, and patches of taller forest, especially nearer the coast. While still wild and difficult country, it was a far cry from its original state. The arrivals stepping off the boats were here with a purpose, to farm this new land. The era of pastoralism had begun.
With pastoralism, the drylands with their associated flora and fauna came under increasing and multiple pressures. Fires became even more common as areas of land were burnt, and re-burnt, to establish pasture and cropland. The grazing animals, especially sheep and to a lesser degree feral goats, put further pressure on low and regenerating vegetation. With repeated burning the complex soil biota was decimated, and the soil lost its carrying capacity. Now poorly vegetated, the land was vulnerable to rabbits, whose style of intensive and close grazing made the situation still worse. With the land so stripped, it was vulnerable to erosion, and particularly on our steep hillsides, soil loss became a major problem.
With repeated burning the complex soil biota was decimated, and the soil lost its carrying capacity.
When the first wave of humans arrived, they brought two mammals with them in their waka, the Maori dog Kurī and the kiore rat. Even these two mammals brought massive change to our virtually mammal-less ecosystems, and the kiore is attributed with the extinction of several frogs, lizards and smaller bird species.
Six hundred years later, this was dwarfed by the plethora of species that accompanied the Europeans. Most devastating among these have been the cats, stoats, hedgehogs, ferrets, weasels, rabbits, Norwegian rats and possums. Our diverse fauna is ill-adapted to deal with mammalian predators, and most of our frogs, lizards, birds and invertebrates have made heartbreakingly easy picking.
McGlone, M. S. (2001). The origin of the indigenous grasslands of southeastern South island in relation to pre-human woody ecosystems. New Zealand Journal of Ecology. 25 (1): 1-15.
Morrell, V. (Mar 2014). Why did New Zealand’s moas go extinct? Science. Retrieved from: https://www.sciencemag.org/news/2014/03/why-did-new-zealands-moas-go-extinct
Phillips, C. and Fenemor, A. (2006). Pasture, present and future – A brief history of pastoralism in New Zealand. RM Update, 18. Retrieved from: https://icm.landcareresearch.co.nz/knowledgebase/publications/public/rmupdate-april-2006.pdf
Richard Holdaway (2007). Extinctions - Extinctions since human arrival. Te Ara - the Encyclopedia of New Zealand. Retrieved from: https://teara.govt.nz/en/extinctions/page-4
Wodzicki, K. and Wright, S. (1984). Introduced birds and mammals in New Zealand and their effect on the environment. Tuatara, 27 (2). Retrieved from: http://nzetc.victoria.ac.nz/tm/scholarly/tei-Bio27Tuat02-t1-body-d1.html