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Does increased forest protection correspond to higher fire severity in frequent-fire forests of the western United States?

Authors:
  • John Muir Project of Earth Island Institute
  • Geos Institute

Abstract and Figures

There is a widespread view among land managers and others that the protected status of many forestlands in the western United States corresponds with higher fire severity levels due to historical restrictions on logging that contribute to greater amounts of biomass and fuel loading in less intensively managed areas, particularly after decades of fire suppression. This view has led to recent proposals-both administrative and legislative-to reduce or eliminate forest protections and increase some forms of logging based on the belief that restrictions on active management have increased fire severity. We investigated the relationship between protected status and fire severity using the Random Forests algorithm applied to 1500 fires affecting 9.5 million hectares between 1984 and 2014 in pine (Pinus ponderosa, Pinus jeffreyi) and mixed-conifer forests of western United States, accounting for key topographic and climate variables. We found forests with higher levels of protection had lower severity values even though they are generally identified as having the highest overall levels of biomass and fuel loading. Our results suggest a need to reconsider current overly simplistic assumptions about the relationship between forest protection and fire severity in fire management and policy.
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23
1Center for Biological Diversity, PO Box 710, Tucson, Arizona 85701 USA
2Earth Island Institute, 2150 Allston Way, Suite 460, Berkeley, California 94704 USA
3Geos Institute, 84-4th Street, Ashland, Oregon 97520 USA
Citation:
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Abstract.
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
   Pinus ponderosaPinus jereyi)
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Key words:

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
E-mail: 
IntroductIon
  
      
       
   

(Pinus ponderosa    
       


     
      
  
     


      

 





    
      
      



     
vvArticle e014922v www.esajournals.org
 

       

     

  


Study area
     
     
     
       

      
Pinus jereyi

    Quercus 
      

 

Pinus contortaPinus lambertiana
AbiesPseudotsuga menzeisii
Calocedrus decurrens
Methods


      
        
      
      

     
 
 


     
     
       

     

       

  
public communication 
      
     
   
      

     
 
       
  

    
 
      
      



       



     

   


        
     
       
       


Fires
  
  public communication 
       
   


        
       
      

     
 
     
      
      

      
vvArticle e014923v www.esajournals.org
 
  




     
      
2009a       

     





vvArticle e014924v www.esajournals.org
 
       

        








 

  
 
       

      
 

Topographic and climatic data


      
public communication
 
m2

   

     
 
    
  public communication 
  

     

        
public communication
 
      
       
    
      


 
       
      
     
       


       



Protected area status and ecoregion classification
      



  

     
   


 



     

     


      
     


     
      
       
       
       


       
    
  
 public communica-
tion 

      
       


 
vvArticle e014925v www.esajournals.org
 
       
      

      



     
       

Random Forests analysis




        
       
    
      
      


      

     
     


     
       

       
    
        
       
     
        
      
       
      
       
       


    
        
       
  
      
    

    

    

      

      

   
         

        
      
     
       

     
        
  

Mixed- effects analysis
     

        
  n  
(n


       
       
    
        

        
     
    
     
      
r        
      
      
    

Spatial autocorrelation analysis

 

    
vvArticle e014926v www.esajournals.org
 
   

       
      
  
       
x  y  



 
  
P 
 
        

     
     
    
     
     
  
P 
results
       


        

      



       
   
      
      
     

      
        
  
  

     


        


       

       
 


           
R2
vvArticle e014927v www.esajournals.org
 
        
     
      



dIscussIon
Protected forests burn at lower severities
 
    
 


       
     
    





      


      
     


      
      
  
 




       
       

    

        
 
     
       
     
       
     
   

       
         


  
     



      
     


vvArticle e01492v www.esajournals.org
 
      
        
 Results      
 
     

 
     





Prevailing forest–fire management perspectives vs.
alternative views

      
       
      
   
     
      
  b




    
      
     
      
    
  
       


      
       

  
     
       

    
       
      
     
2009b       
 
     
         
       
       


        

        
        
  Strix occidentalis caurina  
       
 



        












       
  a       
 b
       

      
      

        
     




    

   





2015a      
vvArticle e014929v www.esajournals.org
 


  

 
         

2015a      

     
    


Limitations
   
     
   


    
    
      
    
        







       
       
       
       


       
     
      
        
 



 

      
       


    
   


conclusIons



      
    


     
     
      
 


     

      



 
    
b
      


      
 
     
 
      
       


  

 
 
     
     
       
     


vvArticle e0149210v www.esajournals.org
 

     
       
 
      
     


AcknowledgMents


      
       

lIterAture cIted
    


          

      


       



         
       

 


    

      
 

         
      
      



  
 

       a 
   
in         
     
    

b

    

        
  
      
     in  

     


  
    



   
        


     


   
    
 Pseudotsuga     


       
        
      


     

 
     


       


      


     


       
     

vvArticle e0149211v www.esajournals.org
 
      


        


     


      
 

       


         
      
  in  
      
  






    



       
 

     

        

in
   
 

 

 
     
       


           
a
      
      

    

      



          
b

     


        
       
     

  

       
     

         

        

  
      

  

        
     


    

        


     
      


       
     


   
      

   
  



   

vvArticle e0149212v www.esajournals.org
 
        
     
      

  

     
  

        
   

         
      

      


       



      



       



      
      





   
        
   


 
      

       
   
      


       

          
      
      



    
    


 
      

      

   

          

     



 

       

         



        
        





      
    in    

      
 








     

         
     
       


vvArticle e0149213v www.esajournals.org
 

      
      

   

      

 

  


   

 

      

    


       
      


     
     
     
     

      
       
     


       
       
      
      

         
    
     
in   

 

       a 
   

    

 b




        
 
      

supportIng InforMAtIon
        

... These initial results, which provide indirect but important information regarding fuel-reduction management in Spotted Owl habitats, do not support the fuel reduction hypothesis. Other recent research indicates that forests with less environmental protection and more tree removal tend to burn more severely [27], and there is research concluding that forests with post-fire logging and artificial tree planting burn more severely than burned forests with no post-fire logging and no tree planting [28]. ...
... In 1996, a large team of university and agency scientists, commissioned by the U.S. Congress, released the conclusions of the Sierra Nevada Ecosystem Project Report, finding the following: "Timber harvest, through its effects on forest structure, local microclimate, and fuel accumulation, has increased fire severity more than any other recent human activity" [29]. Logging, conducted under the rubric of fuel reduction, reduces the cooling shade of the forest canopy, creating a hotter, drier microclimate and reducing the buffering effect that denser stands have against the winds that drive flames, while leaving behind some amount of kindling-like slash debris and spreading combustible invasive grasses such as cheatgrass [27,30]. Post-fire logging also reduces shade and nearly eliminates large, downed logs that retain soil moisture [31] while spreading slash debris and ignitable invasive grasses [27], and the homogenous tree plantations that are planted after post-fire logging may often burn more severely [28]. ...
... Logging, conducted under the rubric of fuel reduction, reduces the cooling shade of the forest canopy, creating a hotter, drier microclimate and reducing the buffering effect that denser stands have against the winds that drive flames, while leaving behind some amount of kindling-like slash debris and spreading combustible invasive grasses such as cheatgrass [27,30]. Post-fire logging also reduces shade and nearly eliminates large, downed logs that retain soil moisture [31] while spreading slash debris and ignitable invasive grasses [27], and the homogenous tree plantations that are planted after post-fire logging may often burn more severely [28]. ...
Article
Full-text available
The California spotted owl is an imperiled species that selects mature conifer forests for nesting and roosting while actively foraging in the “snag forest habitat” created when fire or drought kills most of the trees in patches. Federal agencies believe there are excess surface fuels in both of these habitat conditions in many of California’s forests due to fuel accumulation from decades of fire suppression and recent drought-related tree mortality. Accordingly, agencies such as the U.S. Forest Service are implementing widespread logging in spotted owl territories. While they acknowledge habitat degradation from such logging, and risks to the conservation of declining spotted owl populations, agencies hypothesize that such active forest management equates to effective fuel reduction that is needed to curb fire severity for the overall benefit of this at-risk species. In an initial investigation, I analyzed this issue in a large 2020 fire, the Creek Fire (153,738 ha), in the southern Sierra Nevada mountains of California. I found that pre-fire snag density was not correlated with burn severity. I also found that more intensive forest management was correlated to higher fire severity. My results suggest the fuel reduction approach is not justified and provide indirect evidence that such management represents a threat to spotted owls.
... Often it is claimed that protected areas like Late-Successional Reserves (i.e., Northwest Forest Plan -NWFP), wilderness, national parks, and roadless areas are contributing to greater risks of high severity fires and should be actively managed with some forms of logging (e.g., see Bradley et al., 2016vs. Spies et al., 2018. ...
... Spies et al., 2018. Research that has accounted for forest type concludes that protected forests have far lower fire severity levels than logged lands showing the highest proportions of high severity fire effects (Bradley et al., 2016). Absent forestry reforms, and in a rapidly changing climate, we expect this trend toward more intense fire in heavily logged areas to continue (e.g., see Zald and Dunn, 2018). ...
Article
Full-text available
Debate remains about the effectiveness of commercial thinning as a wildfire management strategy, with some studies reporting somewhat lower severity in thinned forests, and some reporting higher severity, during wildfires. However, while vegetation severity is a measure of basal area tree mortality, research on this question generally omits tree mortality from thinning itself. We investigated whether cumulative tree mortality, or cumulative severity, from commercial thinning and wildfire was different between thinned and unthinned forests in the Caldor Fire of 2021 in the northern Sierra Nevada mountains of California, USA. We found significantly higher cumulative severity in commercial thinning areas compared to unthinned forests. More research is needed to determine whether cumulative severity is higher in commercially thinned forests in other large western US wildfires.
... Often it is claimed that protected areas like Late-Successional Reserves (i.e., Northwest Forest Plan -NWFP), wilderness, national parks, and roadless areas are contributing to greater risks of high severity fires and should be actively managed with some forms of logging (e.g., see Bradley et al., 2016vs. Spies et al., 2018. ...
... Spies et al., 2018. Research that has accounted for forest type concludes that protected forests have far lower fire severity levels than logged lands showing the highest proportions of high severity fire effects (Bradley et al., 2016). Absent forestry reforms, and in a rapidly changing climate, we expect this trend toward more intense fire in heavily logged areas to continue (e.g., see Zald and Dunn, 2018). ...
Article
Fire suppression policies and “active management” in response to wildfires are being carried out by land managers globally, including millions of hectares of mixed conifer and dry ponderosa pine (Pinus ponderosa) forests of the western USA that periodically burn in mixed severity fires. Federal managers pour billions of dollars into command-and-control fire suppression and the MegaFire (landscape scale) Active Management Approach (MFAMA) in an attempt to contain wildfires increasingly influenced by top down climate forcings. Wildfire suppression activities aimed at stopping or slowing fires include expansive dozerlines, chemical retardants and igniters, backburns, and cutting trees (live and dead), including within roadless and wilderness areas. MFAMA involves logging of large, fire-resistant live trees and snags; mastication of beneficial shrubs; degradation of wildlife habitat, including endangered species habitat; aquatic impacts from an expansive road system; and logging-related carbon emissions. Such impacts are routinely dismissed with minimal environmental review and defiance of the precautionary principle in environmental planning. Placing restrictive bounds on these activities, deemed increasingly ineffective in a change climate, is urgently needed to overcome their contributions to the global biodiversity and climate crises. We urge land managers and decision makers to address the root cause of recent fire increases by reducing greenhouse gas emissions across all sectors, reforming industrial forestry and fire suppression practices, protecting carbon stores in large trees and recently burned forests, working with wildfire for ecosystem benefits using minimum suppression tactics when fire is not threatening towns, and surgical application of thinning and prescribed fire nearest homes.
... The decision did not mention post-fire logging as a threat, and encouraged increased logging of all types ostensibly to curb high-severity fire. The decision also did not address research that found increased logging, including post-fire logging, is often associated with higher, not lower, fire severity in subsequent wildland fires [25][26][27][28]. ...
... In this context, federal wildlife and land managers are using existing confounded studies to promote the view that only highseverity fire, not post-fire logging, is a threat to Spotted Owls and, ironically, are promoting increased post-fire logging and tree plantation establishment in Spotted Owl habitat on public lands ostensibly to curb future fires [12,57]. This is in stark contrast to research finding that such management not only harms Spotted Owls [22,23] but also tends to increase future fire severity [25,27]. This suggests a need for more rigorous efforts to be made in future research and forest management decisions to disentangle the impacts of post-fire logging from the effects of high-severity fire. ...
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The Spotted Owl is a rare and declining raptor inhabiting low/middle-elevation forests of the Pacific Northwest, California, and the Southwest in the USA. It is well established that Spotted Owls select dense, mature, or old forests for nesting and roosting. High-severity fire transforms such forests into a unique forest type known as “snag forest habitat”, which the owls select for foraging. This habitat is disproportionately targeted by post-fire logging projects. Numerous recent articles have explored the influence of high-severity fire and post-fire logging on this species. Studies have shown that post-fire logging significantly reduces Spotted Owl occupancy, but efforts have generally not been made to disentangle the effects of such logging from the influence of high-severity fire alone on Spotted Owls. We conducted an assessment of published, peer-reviewed articles reporting adverse impacts of high-severity fire on Spotted Owls, exploring the extent to which there may have been confounding factors, such as post-fire logging. We found that articles reporting adverse impacts of high-severity fire on Spotted Owls were pervasively confounded by post-fire logging, and in some cases by a methodological bias. Our results indicate a need to approach analyses of high-severity fire and Spotted Owls differently in future research.
... In the western U.S., the MTBS information is available through 2019 for fires greater than 1,000 acres. Burn severity from MTBS has been used in other studies that examined patterns and impacts of burn severity on the landscape (Arkle et al., 2012;Baker, 2015;Bradley et al., 2016). For our study, the categorical burn severity (i.e., low, moderate, and high) was used, which is based on threshold values of the differenced Normalized Burn Ratio (dNBR) (Eidenshink et al., 2007). ...
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Snowpack in the western U.S. is critical for water supply and is threatened by wildfires, which are becoming larger and more common. Numerous studies have examined impacts of wildfire on snow water equivalent (SWE), but many of these studies are limited in the number of observation locations, and they have sometimes produced conflicting results. The objective of this study is to distinguish the net effects of wildfires on snowpack from those of climate. We consider 45 burned sites from the Snow Telemetry network. For each burned site, unburned control sites are identified from the same level III ecoregion. Impacts of climate changes on snowpack are analyzed by comparing pre‐fire and post‐fire snow water equivalent at the unburned sites. Combined climate and wildfire effects are considered by comparing pre‐fire and post‐fire SWE at the burned sites. Wildfire impacts are then isolated by taking the difference between the burned and unburned sites. The wildfire‐induced changes in SWE are also compared to several possible controlling variables including burn severity, leaf‐area index change, dominant pre‐fire tree genus, years since the fire, and site elevation. On average, wildfires have advanced melt‐out dates 9 days and maximum SWE dates 6 days and reduced annual maximum SWE by 10% across the sites considered. On average, the combined effects of climate and wildfire have advanced melt‐out and maximum SWE dates approximately 14 and 10 days, respectively, while decreasing annual maximum SWE by approximately 10%.
... Mixed-severity fires in landscapes with extensive northern spotted owl habitat result in diffuse forest edges that are preferentially selected for foraging and thus potentially beneficial to populations (Comfort et al. 2016). In a relatively coarsescale analysis throughout the western USA, Bradley et al. (2016) found that fire severity was lower on lands with less active management which generally corresponded to more mature forests and higher biomass and fuel loading. For one mixed-severity wildfire that burned in a mixed-ownership landscape during a drought year and with severe fire weather conditions, younger forests (mean age 52.2 years) that were intensively managed for timber production burned at higher severity than older forests (mean age 108.8 years) with complex structure and designated as late-successional reserves under the NWFP (Zald and Dunn 2018). ...
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Background The northern spotted owl ( Strix occidentalis caurina ) is an Endangered Species Act-listed subspecies that requires coniferous forests with structurally complex and closed-canopy old-growth characteristics for nesting. With climate change, large wildfires are expected to become more common within the subspecies’ range and an increasing threat to these types of forests. Understanding fire severity patterns related to suitable nesting forest will be important to inform forest management that affects conservation and recovery. We examined the relationship between fire severity and suitable nesting forest in 472 large wildfires (> 200 ha) that occurred in the northern spotted owl range during 1987–2017. We mapped fire severities (unburned-low, moderate, high) within each fire using relative differenced normalized burn ratios and quantified differences in severity between pre-fire suitable nesting forest (edge and interior) and non-nesting forest. We also quantified these relationships within areas of three fire regimes (low severity, very frequent; mixed severity, frequent; high severity, infrequent). Results Averaged over all fires, the interior nesting forest burned at lower severity than edge or non-nesting forest. These relationships were consistent within the low severity, very frequent, and mixed severity, frequent fire regime areas. All forest types burned at similar severity within the high severity, infrequent fire regime. During two of the most active wildfire years that also had the largest wildfires occurring in rare and extreme weather conditions, we found a bimodal distribution of fire severity in all forest types. In those years, a higher amount—and proportion—of all forest types burned at high severity. Over the 30-year study, we found a strong positive trend in the proportion of wildfires that burned at high severity in the non-nesting forests, but not in the suitable nesting forest types. Conclusions Under most wildfire conditions, the microclimate of interior patches of suitable nesting forests likely mitigated fire severity and thus functioned as fire refugia (i.e., burning at lower severity than the surrounding landscape). With changing climate, the future of interior forest as fire refugia is unknown, but trends suggest older forests can dampen the effect of increased wildfire activity and be an important component of landscapes with fire resiliency.
... Although the need to increase the pace and scale of fuel treatments is broadly discussed in scientific and policy arenas (Franklin and Johnson 2012, Kolden 2019, there is still confusion and disagreement about the appropriateness of forest and fuel treatments. For example, recent publications have questioned whether large, high-severity fires are outside of the historical range of variability for seasonally dry forests, and whether the risk of high-severity fire warrants large-scale treatment of fire-prone forests (Bradley et al. 2016, Del-laSala et al. 2017. Others have questioned whether ...
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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.
... Whilst there is a widely held belief that logging reduces fuel loads thereby resulting in less severe and less frequent fires (Bradley et al. 2016), studies in boreal regions have found that managed forests experience more fires (Achard et al. 2008;Kukavskaya et al. 2013). This increase has been attributed to two main causes: firstly that logging debris can lead to much higher surface and ground fuel loads (Kukavskaya et al. 2013). ...
Chapter
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In a recent PLOS ONE paper, we conducted an evidence-based analysis of current versus historical fire regimes and concluded that traditionally defined reference conditions of low-severity fire regimes for ponderosa pine (Pinus ponderosa) and mixed-conifer forests were incomplete, missing considerable variability in forest structure and fire regimes. Stevens et al. (this issue) agree that high-severity fire was a component of these forests, but disagree that one of the several sources of evidence, stand age from a large number of forest inventory and analysis (FIA) plots across the western USA, support our findings that severe fire played more than a minor role ecologically in these forests. Here we highlight areas of agreement and disagreement about past fire, and analyze the methods Stevens et al. used to assess the FIA stand-age data. We found a major problem with a calculation they used to conclude that the FIA data were not useful for evaluating fire regimes. Their calculation, as well as a narrowing of the definition of high-severity fire from the one we used, leads to a large underestimate of conditions consistent with historical high-severity fire. The FIA stand age data do have limitations but they are consistent with other landscape-inference data sources in supporting a broader paradigm about historical variability of fire in ponderosa and mixed-conifer forests than had been traditionally recognized, as described in our previous PLOS paper.
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Fire regime characteristics in North America are expected to change over the next several decades as a result of anthropogenic climate change. Although some fire regime characteristics (e.g., area burned and fire season length) are relatively well-studied in the context of a changing climate, fire severity has received less attention. In this study, we used observed data from 1984 to 2012 for the western United States (US) to build a statistical model of fire severity as a function of climate. We then applied this model to several (n = 20) climate change projections representing mid-century (2040–2069) conditions under the RCP 8.5 scenario. Model predictions suggest widespread reduction in fire severity for large portions of the western US. However, our model implicitly incorporates climate-induced changes in vegetation type, fuel load, and fire frequency. As such, our predictions are best interpreted as a potential reduction in fire severity, a potential that may not be realized due human-induced disequilibrium between plant communities and climate. Consequently, to realize the reductions in fire severity predicted in this study, land managers in the western US could facilitate the transition of plant communities towards a state of equilibrium with the emerging climate through means such as active restoration treatments (e.g., mechanical thinning and prescribed fire) and passive restoration strategies like managed natural fire (under suitable weather conditions). Resisting changes in vegetation composition and fuel load via activities such as aggressive fire suppression will amplify disequilibrium conditions and will likely result in increased fire severity in future decades because fuel loads will increase as the climate warms and fire danger becomes more extreme. The results of our study provide insights to the pros and cons of resisting or facilitating change in vegetation composition and fuel load in the context of a changing climate.
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The prevailing paradigm in the western U.S. is that the increase in stand-replacing wildfires in historically frequent-fire dry forests is due to unnatural fuel loads that have resulted from management activities including fire suppression, logging, and grazing, combined with more severe drought conditions and increasing temperatures. To counteract unnaturally high fuel loads, fuel reduction treatments which are designed to reduce fire hazard and improve overall ecosystem functioning have been increasing over the last decade. However, until recently much of what we knew about treatment effectiveness was based on modeling and predictive studies. Now, there are many examples of wildfires burning through both treated and untreated areas, and the effectiveness of treatments versus no action can be evaluated empirically. We carried out a systematic review to address the question: Are fuel treatments effective at achieving ecological and social (saving human lives and property) objectives? We found 56 studies addressing fuel treatment effectiveness in 8 states in the western US. There was general agreement that thin + burn treatments had positive effects in terms of reducing fire severity, tree mortality, and crown scorch. In contrast, burning or thinning alone had either less of an effect or none at all, compared to untreated sites. Most studies focused on carbon storage agreed that treatments do not necessarily store more carbon after wildfire, but result in less post-wildfire emissions and less carbon loss in a wildfire due to tree mortality. Understory responses are mixed across all treatments, and the response of other ecological attributes (e.g., soil, wildlife, water, insects) to treatment post-wildfire represents an important data gap; we provide a detailed agenda for future research. Overall, evidence is strong that thin + burn treatments meet the goal of reducing fire severity, and more research is needed to augment the few studies that indicate treatments protect human lives and property.
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Burn severity products created by the Monitoring Trends in Burn Severity (MTBS) project were used to analyse historical trends in burn severity. Using a severity metric calculated by modelling the cumulative distribution of differenced Normalized Burn Ratio (dNBR) and Relativized dNBR (RdNBR) data, we examined burn area and burn severity of 4893 historical fires (1984-2010) distributed across the conterminous US (CONUS) and mapped by MTBS. Yearly mean burn severity values (weighted by area), maximum burn severity metric values, mean area of burn, maximum burn area and total burn area were evaluated within 27 US National Vegetation Classification macrogroups. Time series assessments of burned area and severity were performed using Mann-Kendall tests. Burned area and severity varied by vegetation classification, but most vegetation groups showed no detectable change during the 1984-2010 period. Of the 27 analysed vegetation groups, trend analysis revealed burned area increased in eight, and burn severity has increased in seven. This study suggests that burned area and severity, as measured by the severity metric based on dNBR or RdNBR, have not changed substantially for most vegetation groups evaluated within CONUS.