Silviculture can facilitate repeat prescribed burn programs with long-term strategies

A significant expansion of prescribed fire activity will be necessary to mitigate growing wildfire hazard in California forests. Forest managers can facilitate this expansion by promoting forest structures that allow for more effective implementation of prescribed fire, for both initial-entry and repeat burns. We analyzed changes in surface fuel during a series of three burns in replicated mixed-conifer stands following a period of over 100 years of fire suppression and exclusion. Total fuel load, proportion of pine present, canopy cover and basal area of live trees were relevant forest-structure components that influenced plot-scale fuel consumption. The study highlighted the importance of pre-fire fuel load and the relative proportion of pine in the overstory, which both led to greater amounts of fuel consumption. The initial-entry burn dramatically reduced all fuel categories (fine fuel, coarse wood and duff). Following each burn, fuel recovered until the next burn reduced loads enough to maintain low fuel levels. We apply the results to provide an example of how to determine the timing of prescribed fires.

Invasive Plant Relations in a Global Pandemic: Caring for a “Problematic Pesto”

In Spring 2020, amidst a COVID-19 state of emergency, the City of Toronto's Parks & Urban Forestry department posted signs in the city's remaining Black Oak Savannahs to announce the cancellation of the yearly ‘prescribed burn’ practice, citing fears it would exacerbate pandemic conditions. With this activity and other nature management events on hold, many invasive plants continued to establish and proliferate. This paper confronts dominant attitudes in invasion ecology with Indigenous epistemologies and ideas of transformative justice, asking what can be learned from building a relationship with a much-maligned invasive plant like garlic mustard. Written in isolation as the plant began to flower in the Black Oak savannahs and beyond, this paper situates the plant's abundance and gifts within pandemic-related ‘cancelled care’ and ‘cultivation activism’ as a means of exploring human-nature relations in the settler-colonial city. It also asks what transformative lessons garlic mustard can offer about precarity, non-linear temporalities, contamination, multispecies entanglements, and the impacts of colonial property regimes on possible relations. Highlighting the entanglements of historical and ongoing violences with invasion ecology, this paper presents ‘caring for invasives’ as a path toward more liveable futures.

Short-term vegetation responses to the first prescribed burn in an urban pine rockland preserve

Background Preserving fire-dependent ecosystems can mitigate biodiversity loss from urbanization, but prescribing fire is challenging near human habitation. Consequently, dereliction of fire-dependent forests is widespread in urban fragments. Natural disturbance-based management, like prescribing fire, is gaining global acceptance, yet it is unclear what affects prolonged exclusion have on the initial regeneration of isolated plant communities immediately after fire is reintroduced. We took advantage of the first prescribed low-intensity burn on a university pine rockland nature preserve in South Florida, USA, to gain insight. We measured the changes in plant community composition and vegetation cover 1 week before the prescribed burn, and again 1, 2, and 14 weeks after to assess the early and short-term stages of recovery. Results The fire consumed substantial leaf litter, surface fuels, and canopy leaves, increasing sunlight availability to the understory and exposing bare ground. Many woody plants perished within a week post-burn, particularly invasive shrubs; however, germinating and resprouting plant growth were rapid. By 14 weeks, vegetation covered more of the ground than before the burn, although the upper canopy remained relatively open. Rarefied species richness was recovered by 14 weeks but did not exceed pre-burn levels. Invasive species richness was also maintained post-burn. Despite no overall changes in the community structure, our correspondence analysis and analysis of similarity of the plant community suggest high species turnover from the pre-burn to the final community surveyed, with an intermediate turnover in between. Conclusion The endangered pine rockland ecosystem, like many fire-dependent ecosystems, is threatened by habitat loss and fire suppression. Managing urban preserves with periodic burns is essential for supporting habitat for endemic species while decreasing demands for manual and time-intensive maintenance. Our study demonstrates that seedling recruitment from early plantings of native species can contribute significantly and immediately to restoration efforts in a fire-excluded urban preserve; however, many changes were ephemeral. Supplemental burns are likely necessary to further reduce vegetation density and sustain changes to the community composition.

Fine-Scale Fire Spread in Pine Straw

Most wildland and prescribed fire spread occurs through ground fuels, and the rate of spread (RoS) in such environments is often summarized with empirical models that assume uniform environmental conditions and produce a unique RoS. On the other hand, representing the effects of local, small-scale variations of fuel and wind experienced in the field is challenging and, for landscape-scale models, impractical. Moreover, the level of uncertainty associated with characterizing RoS and flame dynamics in the presence of turbulent flow demonstrates the need for further understanding of fire dynamics at small scales in realistic settings. This work describes adapted computer vision techniques used to form fine-scale measurements of the spatially and temporally varying RoS in a natural setting. These algorithms are applied to infrared and visible images of a small-scale prescribed burn of a quasi-homogeneous pine needle bed under stationary wind conditions. A large number of distinct fire front displacements are then used statistically to analyze the fire spread. We find that the fine-scale forward RoS is characterized by an exponential distribution, suggesting a model for fire spread as a random process at this scale.

Detecting critical nodes in forest landscape networks to reduce wildfire spread

Although wildfires are an important ecological process in forested regions worldwide, they can cause significant economic damage and frequently create widespread health impacts. We propose a network optimization approach to plan wildfire fuel treatments that minimize the risk of fire spread in forested landscapes under an upper bound for total treated area. We used simulation modeling to estimate the probability of fire spread between pairs of forest sites and formulated a modified Critical Node Detection (CND) model that uses these estimated probabilities to find a pattern of fuel reduction treatments that minimizes the likely spread of fires across a landscape. We also present a problem formulation that includes control of the size and spatial contiguity of fuel treatments. We demonstrate the approach with a case study in Kootenay National Park, British Columbia, Canada, where we investigated prescribed burn options for reducing the risk of wildfire spread in the park area. Our results provide new insights into cost-effective planning to mitigate wildfire risk in forest landscapes. The approach should be applicable to other ecosystems with frequent wildfires.

Long-Term Effects of Fuel Reduction Treatments on Surface Fuel Loading in the Blue Mountains of Oregon

Fire exclusion and a lengthening fire season has resulted in an era of megafires. Fuel reduction treatments in forested ecosystems are designed to guard against future extreme wildfire behavior. Treatments create a heterogenous landscape and facilitate ecosystem function and resilience in fire-adapted forests of the western United States. Despite widespread recognition that repeated fuel treatments are needed to maintain desired stand characteristics over time, few field studies have evaluated treatment longevity. The Blue Mountains Fire and Fire Surrogate site in northeastern Oregon presented an opportunity to investigate woody fuel loading 15–17 years after four treatments: mechanical thin, prescribed burn, both thin and burn, and no treatment control. The principal findings were: (1) fine fuel load 15 years post-burn remained slightly below pre-treatment values; (2) rotten coarse fuel load was reduced post-burn, but sound coarse fuel was not altered by any active treatment; and (3) total woody fuel load 15–17 years post-treatment was similar to pre-treatment values. Understanding surface fuel loading is essential for predicting fire behavior. Overall, the effects of fuel reduction treatments on woody surface fuels were transitory in dry mixed conifer forests. Frequent maintenance treatments are recommended to protect values at risk in areas with high fire hazards. Quantifying the persistence of changes in forest conditions aids in the planning and analysis of future fuel treatments, along with scheduling maintenance of existing treated areas.

Facilitating Prescribed Fire in Northern California through Indigenous Governance and Interagency Partnerships

Prescribed burning by Indigenous people was once ubiquitous throughout California. Settler colonialism brought immense investments in fire suppression by the United States Forest Service and the California Department of Forestry and Fire Prevention (CAL FIRE) to protect timber and structures, effectively limiting prescribed burning in California. Despite this, fire-dependent American Indian communities such as the Karuk and Yurok peoples, stalwartly advocate for expanding prescribed burning as a part of their efforts to revitalize their culture and sovereignty. To examine the political ecology of prescribed burning in Northern California, we coupled participant observation of prescribed burning in Karuk and Yurok territories (2015–2019) with 75 surveys and 18 interviews with Indigenous and non-Indigenous fire managers to identify political structures and material conditions that facilitate and constrain prescribed fire expansion. Managers report that interagency partnerships have provided supplemental funding and personnel to enable burning, and that decentralized prescribed burn associations facilitate prescribed fire. However, land dispossession and centralized state regulations undermine Indigenous and local fire governance. Excessive investment in suppression and the underfunding of prescribed fire produces a scarcity of personnel to implement and plan burns. Where Tribes and local communities have established burning infrastructure, authorities should consider the devolution of decision-making and land repatriation to accelerate prescribed fire expansion.

Quantitative Analysis of Forest Fires in Southeastern Australia Using SAR Data

Prescribed burning is a common strategy for minimizing forest fire risk. Fire is introduced under specific environmental conditions, with explicit duration, intensity, and rate of spread. Such conditions deviate from those encountered during the fire season. Prescribed burns mostly affect surface fuels and understory vegetation, an outcome markedly different when compared to wildfires. Data on prescribed burning are crucial for evaluating whether land management targets have been reached. This research developed a methodology to quantify the effects of prescribed burns using multi-temporal Sentinel-1 Synthetic Aperture Radar (SAR) imagery in the forests of southeastern Australia. C-band SAR datasets were specifically used to statistically explore changes in radar backscatter coefficients with the intensity of prescribed burns. Two modeling approaches based on pre- and post-fire ratios were applied for evaluating prescribed burn impacts. The effects of prescribed burns were documented with an overall accuracy of 82.3% using cross-polarized backscatter (VH) SAR data under dry conditions. The VV polarization indicated some potential to detect burned areas under wet conditions. The findings in this study indicate that the C-band SAR backscatter coefficient has the potential to evaluate the effectiveness of prescribed burns due to its sensitivity to changes in vegetation structure.