A High-Resolution Chronology of Rapid Forest Transitions following Polynesian Arrival in New Zealand

Abstract

Human-caused forest transitions are documented worldwide, especially during periods when land use by dense agriculturally-based populations intensified. However, the rate at which prehistoric human activities led to permanent deforestation is poorly resolved. In the South Island, New Zealand, the arrival of Polynesians c. 750 years ago resulted in dramatic forest loss and conversion of nearly half of native forests to open vegetation. This transformation, termed the Initial Burning Period, is documented in pollen and charcoal records, but its speed has been poorly constrained. High-resolution chronologies developed with a series of AMS radiocarbon dates from two lake sediment cores suggest the shift from forest to shrubland occurred within decades rather than centuries at drier sites. We examine two sites representing extreme examples of the magnitude of human impacts: a drier site that was inherently more vulnerable to human-set fires and a wetter, less burnable site. The astonishing rate of deforestation at the hands of small transient populations resulted from the intrinsic vulnerability of the native flora to fire and from positive feedbacks in post-fire vegetation recovery that increased landscape flammability. Spatially targeting burning in highly-flammable seral vegetation in forests rarely experiencing fire was sufficient to create an alternate fire-prone stable state. The New Zealand example illustrates how seemingly stable forest ecosystems can experience rapid and permanent conversions. Forest loss in New Zealand is among the fastest ecological transitions documented in the Holocene; yet equally rapid transitions can be expected in present-day regions wherever positive feedbacks support alternate fire-inhibiting, fire-prone stable states.

Ecological consequences of human niche construction: Examining long-term anthropogenic shaping of global species distributions

“…1. Case studies in the application of archaeological science methods to understand past human-mediated biological translocations and transformations relating to the following: global colonization, origins and spread of food production, island colonization, and trade and urbanization (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18).…”

First human impacts and responses of aquatic systems: A review of palaeolimnological records from around the world

“…Despite low initial numbers (it is estimated that between 50 and 100 founding females account for the modern Māori population; Penny and Murray-McIntosh, 2002), their impact on the landscape was quick, significant and long-lasting. The first detectable impact of the Māori on aquatic ecosystems is traceable only 200 years following their arrival (McWethy et al, 2010), through shifts in diatom and chironomid community structure in several small South Island lakes, concomitant with deforestation proxies linked to burning (inferred from the abundance and size of charcoals) and replacement of forests with shrubland (inferred from changes in pollen assemblages) that is still in place today (McWethy et al, 2014).…”

A quantitative assessment of shoot flammability for 60 tree and shrub species supports rankings based on expert opinion

“…The first arrival of humans in NZ ,1280 AD (Wilmshurst et al 2008) resulted in considerable changes in fire regimes. The initial burning period that followed Polynesian settlement caused rapid and extensive forest loss (likely .40%) and the transition from closed-canopy forests to early-successional Bracken (Pteridium esculentum), shrub and grassland communities (McWethy et al 2009;McWethy et al 2014;Perry et al 2014). Further anthropogenic fire converted forest and secondary shrubland to pasture following European settlement ,1840 AD (McWethy et al 2009;Perry et al 2014).…”