Multiscale perspectives of fire, climate and humans in western North America and the Jemez Mountains, USA

Abstract

Interannual climate variations have been important drivers of wildfire occurrence in ponderosa pine forests across western North America for at least 400 years, but at finer scales of mountain ranges and landscapes human land uses sometimes over-rode climate influences. We reconstruct and analyse effects of high human population densities in forests of the Jemez Mountains, New Mexico from ca 1300 CE to Present. Prior to the 1680 Pueblo Revolt, human land uses reduced the occurrence of widespread fires while simultaneously adding more ignitions resulting in many small-extent fires. During the 18th and 19th centuries, wet/dry oscillations and their effects on fuels dynamics controlled widespread fire occurrence. In the late 19th century, intensive livestock grazing disrupted fuels continuity and fire spread and then active fire suppression maintained the absence of widespread surface fires during most of the 20th century. The abundance and continuity of fuels is the most important controlling variable in fire regimes of these semi-arid forests. Reduction of widespread fires owing to reduction of fuel continuity emerges as a hallmark of extensive human impacts on past forests and fire regimes.This article is part of the themed issue ‘The interaction of fire and mankind’.

Living on a flammable planet: interdisciplinary, cross-scalar and varied cultural lessons, prospects and challenges

“…They may reduce the frequency or spread of unintended lightning fires, and may increase landscape diversity by creating smaller-scale vegetation mosaics through pyric succession [12,29,[57][58][59][60][61]. Anthropogenic fire regimes also may buffer against unpredictable climate-driven changes in fire behaviour and create ecological stability in the face of non-equilibrium vegetation dynamics [38,60].…”

“…These challenges cut across particular geographical, social and temporal scales that require equivalent scientific and policy emphasis. From transnational Earth system impacts [1], to domestic impacts on sovereign nations [2], to impacts on local communities [3] and the individuals who make up communities, the perceptions, decisionmaking and prioritization of policy goals are built upon cultural and historical experiences [4][5][6] that have legacy effects, lags and feedbacks across temporal scales [7][8][9][10][11][12]. Although there is a growing literature on building fire-adapted communities [13,14], it is important to recognize that there is both heterogeneity and variability in the historical, technological, cultural and environmental contexts in which humans perceive and respond to fire challenges [15], and that in turn these have cross-scalar feedbacks through sociopolitical structures [2,16], intergenerational cultural transmission [5], historical ecology of landscapes and biomes [12,17,18], and even fire-atmosphere-climate feedbacks [19][20][21].…”

Fire effects on soils: the human dimension

“…These fires have distinct characteristics compared to 'natural' wildfires: (i) In seasonal climates, they can occur at almost any time, but are often ignited prior to, or early in, the fire season(s), whereas natural fire occurrence peaks in the dry (hot) periods [7]. (ii) Their frequency is often higher than that of natural fires [8,9]. (iii) The area burnt by a single fire is usually smaller than for wildfires [10,11].…”

Can Land Management Buffer Impacts of Climate Changes and Altered Fire Regimes on Ecosystems of the Southwestern United States?

“…A hundred-plus years of livestock grazing, logging, and fire exclusion have altered pre-European era fire frequencies, creating increased surface fuel loads, dense, fuel-rich forests, and reduced structural and spatial heterogeneity of vegetation, especially in dry conifer forests with frequent-fire regimes (typically, those with fire return intervals <35 years) [16][17][18]. Fires in these forests are likely to be more intense with larger patches of high-severity fire than occurred historically [19][20][21][22][23], reducing biodiversity, ecological function, and resilience [12,17]. Observed 20th and 21st century anthropogenic climate changes of warming temperatures and an earlier onset of snowmelt have increased the length of fire seasons and lowered fuel moistures, making large portions of the landscape flammable for longer periods of time [21,24], and widespread, regional fire years have been associated with prolonged droughts [13,25,26].…”