Fire Resilience: Can Fish, Wildlife, and Humans Adapt to Shifts in Wildfire Disturbance? Part I

Symposium
ROOM: RSCC, A5
SESSION NUMBER: 7602
 

1:10PM Spatial Distribution of Wildfire in Australia and Known Effects on Freshwater Aquatic Systems.
  Katherine Doyle
Australia is a fire-prone country in which Aboriginal fire shaped vegetation structure, before European settlement. The south-eastern corner of the continent is known as the “great fire triangle of Australia” due to the occurrence of big fires, both in the area (affecting large areas) and frequency (high frequency). Such wildfires cause instant visual alteration on plants and terrestrial ecosystems, as well as on social components. However, the understanding of the effects of fire on freshwater ecosystems is considered to a lesser extent. This study proposed to investigate the spatial distribution of bushfires in south-eastern Australia and its proximity to waterways, as well as to discuss the current knowledge about the effects on freshwater ecosystems. Bushfires have been frequent and extensive, particularly in Victoria. Nevertheless, studies about the effects of fire on freshwater are scarce and generally focused on hydrology, soil erosion, sediment dynamics and organisms, ranging from algal assemblages to stream macroinvertebrates and fish. The effects of bushfires on freshwater can also have significant economic and social impacts, which have not been investigated yet. Increased research effort in this area deemed necessary for this Australian region to provide for best fire-management practices and protect water resources for healthy aquatic ecosystems.
1:30PM Fire and Wildlife in Southeastern Ecosystems
  Cathryn Greeenberg
Many animals require disturbances including fire to create or maintain specific forest structures. Natural fire regimes differ among Southeastern ecosystems due to differences in lightning strike frequencies and ignitibility. Historically, low-intensity fires ignited by lightning and fueled by continuous wiregrass groundcover frequently burned across longleaf pine-wiregrass landscapes, maintaining an open, pine-dominated canopy and grass-herbaceous groundcover structure required by gopher tortoises, red-cockaded woodpeckers, and other fauna. Infrequent, stand-replacing burns in the xeric “fire-fighting” sand pine scrub ecosystem created vast areas of scrubland with abundant bare sand required by endemic scrub jays, sand skinks, and other animals. In eastern hardwood forests, lightning-ignited fires are infrequent; strikes are less common and usually accompanied by rain, and fuels are generally moist. Fires in hardwood forests are usually low-intensity, and have a minimal, transient effect on forest structure. Few wildlife species rely on fire to maintain required forest conditions, suggesting it was not a predominant disturbance type, except in specific topographic positions. For millennia, humans have augmented “natural” fire frequencies by intentional burning, creating a mosaic of conditions for disturbance-dependent species and enhancing biodiversity. Today, silvicultural activities including burns can create suitable conditions for many wildlife species, but effects vary among ecosystems and disturbance levels.
1:50PM A Risk-Benefit Context for Assessing Wildfire Effects on Water Quality and Biotic Integrity
  Joe Ebersole
Wildfires can have devasting impacts on human infrastructure, watersheds, and water quality, impacting aquatic ecosystem endpoints valued by humans and regulated by federal agencies such as the USEPA. But wildfires can also have beneficial effects on aquatic ecosystems. Assessing the net risk of wildfire to aquatic ecosystem endpoints will therefore require consideration of both adverse and positive effects. Doing so requires a holistic perspective that considers the multiple pathways through which wildfire modifies watershed processes regulating the physical, chemical, and biological attributes of receiving waters. Additionally, this requires the explicit consideration of spatial and temporal variability in these processes and their companion responses. Furthermore, distinguishing between beneficial and detrimental effects of wildfire will require methods to assess both risks and benefits in a way useful to stakeholders and managers charged with making decisions about pre- and post-fire response to wildfire risks. Here, we present a research framework for assessing spatial variability in relative risk. Examples illustrate how the relative risks/benefits of wildfire to aquatic ecosystem endpoints will vary in response to watershed and catchment attributes that modify, enhance, or ameliorate wildfire effects. This approach will help identify areas likely to require differing levels and types of pre- and post-fire intervention.
2:10PM Wildfire’s Impacts on Water Quality and Aquatic Life: A Case Study from the Upper Rio Grande
  Ashley Rust
Wildfire size and frequency are increasing across the Rocky Mountain West, creating short-term and long-term impacts on aquatic life and water supplies. The West Fork Complex (WFC) fire surrounded the Rio Grande, in the Colorado Rockies, affecting water quality and habitat critical to insects and fish. We investigated the impacts of the WFC on the river’s ecosystem and water quality in the mainstem of the Rio Grande (above and below the burn) as well as several effected tributaries for three years after the fire. Precipitation and flow data revealed monsoon rain events delivered sediments into the Rio Grande and its tributaries from steep, severely burned hillslopes which led to elevated turbidity and localized fish kills. The ecosystem appears to be recovered, results indicate insect and fish populations impacted by the fire are similar to pre-fire levels after three years. We then researched 159 wildfires across the western United States from 1984-2012 and found significant increases in nutrient flux (different forms of nitrogen and phosphorus), major-ion flux, and metal concentrations are the most common changes in stream water quality within the first five years after fire. Results provide critical information on water quality behavior and ecosystem recovery.
2:30PM Landscape-Scale Responses to Wildfire in Pacific Northwest Streams
  Elliot Koontz
Recent wildfire seasons in the Pacific Northwest have emphasized the need for understanding the impact of these disturbances on freshwater ecosystems of the region. The abiotic and biotic responses to wildfire in stream ecosystems has been documented for individual watersheds and burn events, but landscape-scale investigations of wildfire and stream ecosystem dynamics are limited. In this talk, we will discuss our research quantifying responses in stream thermal regimes and macroinvertebrate communities following wildfire activity across the Pacific Northwest. We used a non-parametric multivariate approach to compare pre- and post-fire stream temperature time series and identify patterns and drivers of stream thermal response in burned watersheds. We also utilized community-level generalized linear modelling techniques to explain patterns of functional diversity in macroinvertebrate communities along a gradient of wildfire disturbance over 15 years and 14 different basins. Our results suggest that 30-55% of variation in stream thermal regime metrics is constrained by variability in hydrological and pyrological predictors, and that functional diversity can be largely resilient to wildfire effects across large spatial gradients. Ultimately, our work demonstrates how combining vital long-term stream monitoring networks with wildfire occurrence data in a statistical framework can provide much-needed nuance to our understanding of fire-watershed interactions.
2:50PM Refreshment Break
3:20PM Wildfire Smoke Cools Summer River and Stream Water Temperature
  Eli Asarian
To test whether wildfire smoke can cool summer river and stream water temperatures by attenuating solar radiation and air temperature, we analyzed data on summer wildfire smoke, solar radiation, air temperatures, precipitation, river discharge, and water temperatures in the lower Klamath River Basin in Northern California. We used a newly available daily high‐resolution (1 km) dataset of aerosol optical thickness (AOT) derived from satellite imagery to represent smoke density during six years with extensive wildfire activity. Smoke reduced solar radiation by 121 W m−2 per 1.0 AOT relative to clear‐sky conditions. Linear mixed‐effects models showed that on average, smoke cooled daily maximum and mean air temperatures by 0.98 °C and 0.47 °C per 1.0 AOT, respectively, across 19 remote automated weather stations. Smoke had a cooling effect on water temperatures at all 12 river and stream locations analyzed. On average, smoke cooled daily maximum and mean water temperatures by 1.32 °C and 0.74 °C per 1.0 AOT, respectively. This is the first study to evaluate this phenomenon with rigorous statistical analysis of long-term datasets. Smoke‐induced cooling has the potential to benefit cold‐water adapted species, particularly because wildfires are more likely to occur during the warmest and driest years and seasons.
3:40PM Bottom-up Trophic Cascade after Wildfire and Post-Fire Salvage Logging in Canadian Rocky Mountain Streams
  Uldis Silins
Ecohydrological linkages between stream water quality, periphyton growth, macroinvertebrate community composition, and trout were studied for 11 years after severe wildfire in the south-west Rocky Mountains of Alberta, Canada. Post-wildfire production of sediment (TSS) and phosphorus (P) were 2-13 times greater in burned and post-fire salvage-logged streams than in unburned reference streams (p<0.001). Unlike other nutrients regulating aquatic productivity in oligotrophic mountain streams (e.g. nitrogen), elevated P production persisted for 11 years after the wildfire which was associated with persistence of 2-100 times greater periphyton production in fire affected compared to reference streams. Elevated periphyton growth was strongly associated with greater benthic macroinvertebrate abundance and diversity in fire affected streams 4 years after the fire (Silins et al. 2014), however while differences in invertebrate composition persisted 8 years after fire in burned streams, chronic sediment loading in salvage-logged streams was associated with notable dominance by disturbance or sediment tolerant taxa (Martens et al. 2019). Wildfire effects at lower trophic levels were, in turn, associated with greater weight, length, and growth rate of Westslope Cutthroat trout (Oncorhynchus clarkii lewisi) 2 years after the fire, but these effects were no longer evident an additional 6 years later.
4:00PM Linking Post-Fire Stream Responses to Watershed Characteristics across the Pacific Northwest
  Vance Almquist
Wildfire can have dramatic effects on stream ecosystems. These changes may be beneficial or detrimental to human uses of streams. The inherent variability in watershed controls on stream properties can complicate efforts to generalize the net effects of wildfire on stream ecosystems. We have developed a watershed classification with the express goal of characterizing and leveraging variability in post-fire responses of aquatic systems. The classification approach assigns all sub-catchments in Oregon, Washington, and Idaho to a biophysical sensitivity class. The assignments are made using more than 350 biophysical watershed-scale metrics. In addition to the biophysical classification, watersheds are further stratified according to their burn characteristics. Burned watersheds from each biophysical class were then compared to a regional dataset of compiled stream quality measurements to quantify hypothesized variability in watershed responses. This spatially explicit classification is intended to provide a useful tool for tailoring post-fire interventions and monitoring approaches for assessing intervention efficacy. Additionally, by explicitly accounting for nuances in watershed-level drivers of stream response to wildfire, this framework should enable improved flexibility in the decision-making process facing those tasked with overseeing post-fire recovery.
4:20PM Gaging the Importance: Hydrologic Regime Characterization for Wildfire-Impacted Streams in Changing Boreal Ecosystems
  Deanna Klobucar
Understanding how wildfire influences hydrologic patterns (e.g., timing, magnitude) in boreal streams is important for effective aquatic habitat and species management under a rapidly changing climate. In this study we: 1) used field observations to quantify and characterize hydrologic regimes in a subsample of headwater streams (drainage basins ≤ 150 km2) with different fire histories (no burn, historic burn, recent burn) in interior Alaska; and 2) calculated the “Magnificent Seven” hydrologic descriptors to classify contemporary and historic hydrologic regimes from existing stream gage data (n = 74) across the Northwestern Boreal Ecosystem. We classified streams into three size classes based on mean daily discharge (m3/s; small <17, mid-sized = 18-85, large >86); ten distinct subclasses resulted from model-based cluster analysis. We found streamflow varied with stream size (coefficient of variation; small=0.37—0.71, mid-sized=0.57—0.58, large=0.42—0.65), and instances of extreme flow events differed seven-fold between two large stream subclasses (L-kurtosis=0.03 and 0.23). Our hydrologic regime characterization will provide a benchmark with which to detect potential regime shifts that may result from continued climate warming and increased fire disturbance across the Northwest Boreal Ecosystem, and provide valuable information toward management and conservation of important boreal fish species.
4:40PM Fo’real Changes in Boreal Streams: A Multifaceted Modeling Approach to Predict the Effects of Forest Fire on Aquatic Habitat Vulnerability in Interior Alaska
  Stephen Klobucar
In light of current and expected climate driven shifts of fire regimes (e.g., increased frequency, severity) across interior Alaska, understanding future impacts of fire to stream regulating biological, chemical, and physical processes are critical for managing fire, aquatic habitats, and fish populations. In this project, we integrated dynamic predictions from spatially- and temporally-explicit climate, fire, vegetation, hydrologic, and thermal models to assess aquatic habitat and population vulnerability across a ~20,000 km2 boreal stream network. We predicted stream temperatures using remotely-sensed land surface temperatures with high precision (R2 > 0.80). We coupled these predictions with dynamically-downscaled climate projections (2000 – 2100) and riverscape bioenergetics to quantify habitat and growth potential under fire scenarios for spawning and rearing Chinook Salmon Oncorhynchus tshawytscha. Warming stream temperatures, associated with warming air temperatures, increased suitable habitats in headwater reaches two-fold by 2050 and three-fold by 2100, while summer temperatures approached thermal limits (> 20 °C) in downstream reaches. Further, throughout our study area, reaches affected by fire warmed more, with spatially-explicit positive or negative changes to habitat potential until/if vegetation regenerated. Our results will provide valuable insight for fire management decisions with respect to one of Alaska’s most valuable commercial, sport, and subsistence fish species.

 
Organizers: Mark D. Bowen, Ph.D., Henriette Jager, Luiz Silva, Serra Hoagland, Ph.D., Tracy Melvin, Jeff Thomas
 

Symposium
Location: Reno-Sparks CC Date: September 30, 2019 Time: 1:10 pm - 5:00 pm