Ponderosa pines are not adapted to high-severity fire

And this type of fire is increasingly common in the Southwest

Regenerating Ponderosa Pine
Regenerating ponderosa pine in a high-severity burn patch, 13 years after the 2000 Pumpkin Fire. (From the Fact Sheet)

The increasing size and severity of wildfires in the Western United States may have long term effects on species composition. A Fact Sheet published this month by Northern Arizona University and the U.S. Forest Service looks at ponderosa pine regeneration in patches of high-severity areas of the 2000 Pumpkin and the 2002 Rodeo-Chediski wildfires in the Southwest. Below are excerpts from the document written by Suzanne Owen, PhD student, School of Forestry, Northern Arizona University:


Introduction

Over the past three decades, wildfires in southwestern U.S. ponderosa pine (Pinus ponderosa) forests have increased in size and severity, leaving large, contiguous patches of tree mortality. Ponderosa pines evolved under fire regimes dominated by low- to moderate-severity wildfires. They are poorly adapted to regenerate in large patches of high-severity fire because they are not a sprouting species and do not have serotinous cones or long-lived soil seedbanks. Consequently, the lack of seed-producing trees in high-severity burn patches may prevent or significantly delay ponderosa pine regeneration. Previous studies have documented low ponderosa pine regeneration densities in large high-severity burn patches, but less is known about the spatial patterns of ponderosa pine regeneration and interactions with sprouting species near residual live forest edges or the interiors of high-severity burn patches.

[…]

Results

  • Ponderosa pines were re-establishing in all of our study plots, however regeneration densities were lower farther from forest edges.
  • Ponderosa pines seedlings were found in areas more than 980 feet from potential parent trees on all interior study plots.
  • Regenerating ponderosa pines displayed patterns of small-scale spatial aggregation in all plots, except one edge and one interior plot on the Pumpkin Fire, which displayed random distributions.
  • Dense resprouting trees dominated tree regeneration on the Rodeo-Chediski Fire, but did not influence the spatial location or height of regenerating ponderosa pine.
  • Regenerating ponderosa pine height was positively correlated with neighboring ponderosa pine densities and height.

Implications

  • Tree regeneration densities and species composition in high-severity burn patches are highly variable in different geographic locations.
  • Regeneration patterns suggest both short- and long-distance dispersal may play important roles in ponderosa pine regeneration in high-severity burn patches.
  • Ponderosa pine regeneration could be more strongly influenced by intraspecific facilitation than interspecific competition from dense sprouting species.
  • Future forest spatial patterns and composition are still unclear, but at this stage of development, these heterogeneous patches, characterized by drought-tolerant sprouting species or low pine densities, could be more resilient to climate change and severe wildfires than the overly dense ponderosa pine forests that were present before the wildfires.
  • Managers may want to use a “wait and see” approach before replanting in some areas to monitor natural regeneration over time.

Author: Bill Gabbert

After working full time in wildland fire for 33 years, Bill Gabbert now writes about it from the Black Hills. Google+

6 thoughts on “Ponderosa pines are not adapted to high-severity fire”

  1. Aren’t high-severity burn areas increasing through out all of western north America.

    Perhaps I’m missing a definition of “high severity” here. Are high-severity burn areas those areas where mature trees are simply killed by the fire? Or, are they the areas where sustained crown runs destroyed cones/seeds on branches and so inhibited natural reseeding to a greater extent? It seems like mature cones still on trees killed by heat intensity at the base would would affect reseeding densities. Of course, this would be affected by the time of year and maturity of the seed cones on the trees when the fire occurred.

    1. From Fire Words:

      Fire severity is a continuous variable ranging from low to high. It can be expressed at various scales, from fire affecting the individual tree to fires ranging up to 500,000 acres or more, such as the 2002 Biscuit Fire in Oregon and California. A high-severity fire occurs at the extreme end of this continuum and is expressed by complete fuel consumption and extensive soil heating, and usually more than 70 percent top-kill of vegetation. When patches of vegetation that have experienced high-severity fire are interspersed with patches that have experienced low severity in a single fire, the event may instead be considered a mixed-severity event.

      And if you want to get into it in more detail, read this: “Fire intensity, fire severity and burn severity: a brief review and suggested usage”

  2. With all due respect, how many tree species are adapted to high-severity fires anyway? These modern fires have been vicious. Seeds that could handle a fast brush fire end up as cinder powder, just like everything else.
    Isn’t this the take-away?: “overly dense ponderosa pine forests that were present before the wildfires.”
    Translation: There was over-crowding of pine forests (i.e. not thinned.) Over-crowding of any trees, including ponderosas sets the stage for out-of-control infernos. Why bother with a study? Replant, with good spacing and where possible, restore mixed populations of grazing wild animals to naturally prune what’s growing. Just a thought.

  3. Thanks for providing a summary. I’ll have to read the whole thesis, but the last bullet point is so typical of the regeneration research lately – it does not take Forest Plan Objectives or the law into account. It also shows an ignorance of the effect of all that sprouting vegetation in a dry environment on conifer establishment. It also seems that the author has disproved her hypothesis that there is no adaptation- given the long distance dispersal, which is presumably from animals – my take is that the big seeds ARE an adaptation to allow long distance dispersal that can facilitate regeneration after a big disturbance. Given the age class of much of the Pine in some areas, it is obvious there were large scale severe disturbances in the past – and in AZ there was large scale harvest with subsequent natural regeneration.

  4. Thoughts… If a forest was wiped out in a super-charged fire thanks to decades of no-touch management, then replant with the native mix of trees and bushes and grasses. Otherwise, it’ll be nasty thorns and weeds for a long time – they bounce back faster than anything. Not all trees either – plant scattered stands of trees with meadows and edge – the mix that animals love.

    It may not be noticeable to many Americans, but a trip to Africa to see the massive herds is an eye-opener… that is upon returning to realize how sterile and devoid of life the American wilderness is. There’s something very wrong and it’s been wrong for a long while. The U.S. bison and antelope herds today are nothing compared to what they were – yet proof it’s possible for the American landscape to support herds of a mix of animals which all graze and browse differently. Yet, today bears seem to do quite well… usually predators should be few, the prey many.
    But after a very disappointing day in the tree-choked Rocky Mountain park (mostly dead trees piled like pick-up sticks, almost impossible to move through), seeing all of one deer, one squirrel and six elk dots at 2 miles distance, we drove back to our motel and parked only to discover four huge elk eating out of the motel dumpster. We got some drinks and chips and enjoyed the rest of the daylight on the balcony watching elk nonchalantly chow down fifteen feet from us. Quite magnificent beasts actually. In the morning, they were down the street at 6 a.m. nibbling at the two tender green saplings helpfully put out by Taco Bell landscaping meant to decorate their customer parking. All that park, hundreds of thousands of acres set aside and the wild animals had to go to Taco Bell for a bite to eat. Something’s seriously out of whack.

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