In New Zealand, human-set fires have been responsible for irreversible changes in vegetation during the last millennium in the relative absence of strong climate variations. Fires were extremely rare in NZ prior to Māori arrival 700 years ago, occurring once every 1-2 millennia in most areas. In the absence of fire, the native flora was poorly adapted to fire’s introduction. Charcoal and pollen data from lakes in remote settings indicate near-absence of fire prior to Māori arrival followed by a few decades of high-severity fires. This "Initial Burning Period" (IBP, between 700 and 500 years ago depending on location) was a short but significant deforestation event in the history of each watershed, accompanied by a dramatic transformation in vegetation, slope stability, and limnology. At some sites, the watersheds and the native forests they supported still have not recovered. NZ falls at the far end of the spectrum of landscapes that have been altered by humans and is the rare place where we can precisely isolate human influences on fire risk and fire hazard. Tree-ring derived climate data spanning the last 2000 years in New Zealand suggest only minor climate fluctuations during the IBP that may have amplified or reinforced the success of anthropogenic burning. The relationship between changes in long-term climate, vegetation, and forest structure suggests that beech (Nothofagus) forests were generally expanding during late-Holocene cooling, prior to Māori arrival. Archeological data for the last millennia indicate that Māori presence on the South Island of NZ was generally transient except for semipermanent settlements in coastal areas, and we will determine if settlement sites and trade routes explain particular burning patterns.
In the last century, invasive non-native plant species, such as gorse (Ulex europaeus) and non-native conifer escapement from forestry plantations have influenced current fire regimes beyond the historical range of fire variability, but little is known about the feedbacks between land-use, non-native species, and fire regimes. Stand-age dynamics of native forest patches are also needed to determine whether they are remnants from European-set fires in the last few centuries, and whether they are expanding or contracting at present. The history of these forest remnants, which support much of the native biodiversity, and their relation to fire is a critical need.
In WildFIRE PIRE, lake-sediment pollen, charcoal, and geochemical records spanning the last 5000 years, dendroclimatological data of the last 2000 years, archeological data for the last 700 years, forest dynamics data spanning the last 500 years, and fire models will be used to examine:
- Changes in fire regimes in the last 1000 years at 5-6 sites that lie along a gradient in fuel types and environmental conditions from moderately dry lowland podocarp forests to wet mid- and high-elevation closed-canopy beech forests. Some records will lie in proximity to Māori settlements, trade routes, and valuable resource localities (greenstone, bracken fern, wildlife). We will model scenarios that link fire behavior to fuels and climate conditions, and compare the results with historical data to determine what burning strategies were necessary to create and maintain open landscapes.
- Recent 20th century burns in a range of beech and podocarp forests to construct a general model of post-fire vegetation dynamics needed to better interpret forest responses to past fires as well as the vulnerability of those patches to present and future disturbances.
- Interdisciplinary multi-scalar relations in three large watersheds that (1) historically supported high levels of biomass yet varied in fuel types and climate as a result of longitudinal and elevational gradients, (2) have experienced recent fires of unusual severity, and (3) are experiencing non-native plant invasion (Ulex, Pinus) and land-cover change.