An official website of the United States government
Abstract Detailed information about the historical range of variability in wildfire activity informs adaptation to future climate and disturbance regimes. Here, we describe one of the first annually resolved reconstructions of historical (1500–1900 ce) fire occurrence in coast Douglas‐fir dominated forests of the west slope of the Cascade Range in western Oregon. Mean fire return intervals (MFRIs) across 16 sites within our study area ranged from 6 to 165 years. Variability in MFRIs was strongly associated with average maximum summer vapor pressure deficit. Fire occurred infrequently in Douglas‐fir forest stands seral to mountain hemlock or silver fir, but fire frequency was much shorter than predicted by theory in other forest types. MFRIs within Douglas‐fir stands seral to western hemlock or grand fir ranged from 19 to 45 years, and MFRIs in stands seral to Douglas‐fir ranged from 6 to 11 years. There was little synchrony in fire occurrence or tree establishment across 16 sites separated by 4 km. The lack of synchrony in fire suggests that large, wind‐driven fire events that are often considered to be characteristic of coast Douglas‐fir forests were not an important driver of succession in our study area during the last ~400–500 years. Climate was more arid than normal during fire years in most forest types, but historical fire in stands seral to Douglas‐fir was strongly associated with antecedent moisture and less strongly associated with drought. We interpret the extraordinary tempo of fire we observed in stands seral to Douglas‐fir and the unique climate pattern associated with fire in these stands to be indicative of Indigenous fire stewardship. This study provides evidence of far more frequent historical fire in coast Douglas‐fir forests than assumed by managers or scientists—including some of the most frequent fire return intervals documented in the Pacific Northwest. We recommend additional research across the western Cascades to create a comprehensive account of historical fire in highly productive forests with significant cultural, economic, and ecological importance.
more »
« less
Legacies of Indigenous land use shaped past wildfire regimes in the Basin-Plateau Region, USA
Abstract Climatic conditions exert an important influence on wildfire activity in the western United States; however, Indigenous farming activity may have also shaped the local fire regimes for millennia. The Fish Lake Plateau is located on the Great Basin–Colorado Plateau boundary, the only region in western North America where maize farming was adopted then suddenly abandoned. Here we integrate sedimentary archives, tree rings, and archeological data to reconstruct the past 1200 years of fire, climate, and human activity. We identify a period of high fire activity during the apex of prehistoric farming between 900 and 1400 CE, and suggest that farming likely obscured the role of climate on the fire regime through the use of frequent low-severity burning. Climatic conditions again became the dominant driver of wildfire when prehistoric populations abandoned farming around 1400 CE. We conclude that Indigenous populations shaped high-elevation mixed-conifer fire regimes on the Fish Lake Plateau through land-use practices.
more »
« less
- Award ID(s):
- 1749059
- PAR ID:
- 10221781
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 2
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)We review science-based adaptation strategies for western North American (wNA) forests that include restoring active fire regimes and fostering resilient structure and composition of forested landscapes. As part of the review, we address common questions associated with climate adaptation and realignment treatments that run counter to a broad consensus in the literature. These include: (1) Are the effects of fire exclusion overstated? If so, are treatments unwarranted and even counterproductive? (2) Is forest thinning alone sufficient to mitigate wildfire hazard? (3) Can forest thinning and prescribed burning solve the problem? (4) Should active forest management, including forest thinning, be concentrated in the wildland urban interface (WUI)? (5) Can wildfires on their own do the work of fuel treatments? (6) Is the primary objective of fuel reduction treatments to assist in future firefighting response and containment? (7) Do fuel treatments work under extreme fire weather? (8) Is the scale of the problem too great – can we ever catch up? (9) Will planting more trees mitigate climate change in wNA forests? and (10) Is post-fire management needed or even ecologically justified? Based on our review of the scientific evidence, a range of proactive management actions are justified and necessary to keep pace with changing climatic and wildfire regimes and declining forest successional heterogeneity after severe wildfires. Science-based adaptation options include the use of managed wildfire, prescribed burning, and coupled mechanical thinning and prescribed burning as is consistent with land management allocations and forest conditions. Although some current models of fire management in wNA are averse to short-term risks and uncertainties, the long-term environmental, social, and cultural consequences of wildfire management primarily grounded in fire suppression are well documented, highlighting an urgency to invest in intentional forest management and restoration of active fire regimes.more » « less
-
Abstract Increasing area burned across western North America raises questions about the precedence and magnitude of changes in fire activity, relative to the historical range of variability (HRV) that ecosystems experienced over recent centuries and millennia. Paleoecological records of past fire occurrence provide context for contemporary changes in ecosystems characterized by infrequent, high-severity fire regimes. Here we present a network of 12 fire-history records derived from macroscopic charcoal preserved in sediments of small subalpine lakes within a c. 10 000 km2landscape in the U.S. northern Rocky Mountains (Northern Rockies). We used this network to characterize landscape-scale burning over the past 2500 yr, and to evaluate the precedence of widespread regional burning experienced in the early 20th and 21st centuries. We further compare the Northern Rockies fire history to a previously published network of fire-history records in the Southern Rockies. In Northern Rockies subalpine forests, widespread fire activity was strongly linked to seasonal climate conditions, in contemporary, historical, and paleo records. The average estimated fire rotation period (FRP) over the past 2500 yr was 164 yr (HRV: 127–225 yr), while the contemporary FRP from 1900 to 2021 CE was 215 yr. Thus, extensive regional burning in the early 20th century (e.g. 1910 CE) and in recent decades remains within the HRV of recent millennia. Results from the Northern Rockies contrast with the Southern Rockies, which burned with less frequency on average over the past 2500 yr, and where 21st-century burning has exceeded the HRV. Our results support expectations that Northern Rockies fire activity will continue to increase with climatic warming, surpassing historical burning if more than one exceptional fire year akin to 1910 occurs within the next several decades. The ecological consequences of climatic warming in subalpine forests will depend, in large part, on the magnitude of fire-regime changes relative to the past.more » « less
-
Human activity and climate change are altering natural rates and intensities of wildfire, but the scale and extent of burning prior to the modern era are poorly understood. Prehistoric fire activity can be reconstructed using a variety of records including charcoal deposited along with sediment at the bottom of lakes and burn scars on tree rings, but these are not available in all environmental settings. We are developing a new paleofire proxy: polycyclic aromatic hydrocarbons (PAHs) in stalagmites. PAHs are produced by the burning of vegetation, with molecular weights reflecting combustion conditions. After being formed in a fire, PAHs are transported downward by infiltrating rainwater and in cave areas can become incorporated into stalagmites as they crystallize from drip water in underlying caves (Perrette et al., 2008; Denniston et al., 2018). Thus, the potential exists for PAHs in stalagmites to preserve evidence of the presence and intensity of fire through time. Because this is a new method, several important tests need to be performed to evaluate its veracity. I assessed how well PAH abundances, ratios, and trends replicate between two coeval stalagmites from cave KNI-51 located in the tropics of Western Australia. Stalagmite KNI-51-F was previously analyzed and I analyzed the overlapping portion of stalagmite KNl-51-G: overlap in age from CE 1310-1630. This work was done at Ca' Foscari University, Venice, in the fall of 2022, under the direction of Dr. Elena Argiriadis. The results show similarities between the area of overlap in the G and F stalagmites. The commonalities of the concentrations of PAH in the stalagmites indicate confidence in the developed method in assessing pyrogenic compounds in coeval stalagmites.more » « less
-
null (Ed.)Characterizing wildfire regimes where wildfires are uncommon is challenged by a lack of empirical information. Moreover, climate change is projected to lead to increasingly frequent wildfires and additional annual area burned in forests historically characterized by long fire return intervals. Western Oregon and Washington, USA (westside) have experienced few large wildfires (fires greater than 100 hectares) the past century and are characterized to infrequent large fires with return intervals greater than 500 years. We evaluated impacts of climate change on wildfire hazard in a major urban watershed outside Portland, OR, USA. We simulated wildfire occurrence and fire regime characteristics under contemporary conditions (1992–2015) and four mid-century (2040–2069) scenarios using Representative Concentration Pathway (RCP) 8.5. Simulated mid-century fire seasons expanded in most scenarios, in some cases by nearly two months. In all scenarios, average fire size and frequency projections increased significantly. Fire regime characteristics under the hottest and driest mid-century scenarios illustrate novel disturbance regimes which could result in permanent changes to forest structure and composition and the provision of ecosystem services. Managers and planners can use the range of modeled outputs and simulation results to inform robust strategies for climate adaptation and risk mitigation.more » « less
