Conifer regeneration poor after high-severity fire

Some “best available sound science” to inform forest managers….

Key finding: “Across all fires, 43% of all plots had no conifer regeneration.”

But this comes as no surprise to foresters….

From “Predicting conifer establishment post wildfire in mixed conifer forests of the North American Mediterranean-climate zone,” by Kevin R. Welch et al, Ecosphere, December 2016. Link to full text.

Here’s the abstract.

Abstract. Due to fire suppression policies, timber harvest, and other management practices over the last century, many low- to mid-elevation forests in semiarid parts of the western United States have accumulated high fuel loads and dense, multi-layered canopies that are dominated by shade-tolerant and firesensitive conifers. To a great extent, the future status of western US forests will depend on tree species’ responses to patterns and trends in fire activity and fire behavior and postfire management decisions. This is especially the case in the North American Mediterranean-climate zone (NAMCZ), which supports the highest precipitation variability in North America and a 4- to 6-month annual drought, and has seen greater-than-average increases in air temperature and fire activity over the last three decades. We established 1490 survey plots in 14 burned areas on 10 National Forests across a range of elevations, forest types, and fire severities in the central and northern NAMCZ to provide insight into factors that promote natural tree regeneration after wildfires and the differences in postfire responses of the most common conifer species. We measured site characteristics, seedling densities, woody shrub, and tree growth. We specified a zero-inflated negative binomial mixed model with random effects to understand the importance of each measured variable in predicting conifer regeneration. Across all fires, 43% of all plots had no conifer regeneration. Ten of the 14 fires had median conifer seedling densities that did not meet Forest Service stocking density thresholds for mixed conifer forests. When regeneration did occur, it was dominated by shadetolerant but fire-sensitive firs (Abies spp.), Douglas-fir (Pseudotsuga menziesii) and incense cedar (Calocedrus decurrens). Seedling densities of conifer species were lowest in sites that burned at high severity, principally due to the biotic consequences of high severity fire, for example, increased distances to live seed trees and competition with fire-following shrubs. We developed a second model specifically for forest managers and restoration practitioners who work in yellow pine and mixed conifer forests in the central NAMCZ to assess potential natural regeneration in the years immediately following a fire, allowing them to prioritize which areas may need active postfire forest restoration and supplemental planting.

11 Comments

  1. Steve – Good Post

    Unless people have studied fire, soil and forest silvicultural science, they have no comprehension that fire baked soils are impenetrable for seeds whether the seeds were already in place underground or fell shortly after the soil was baked. They have no comprehension that where this baked soil exists, it will take erosion or a planting tool to make the soil suitable for regeneration.

  2. Additionally, such fires lead to salvage clearcutting on private lands. The “wildfires are good” people never seem to mention THOSE impacts, do they? We’ve seen these unfortunate activities happen in the Sierra Nevada, especially in the checkerboarded lands where the King Fire and others burned. We’ve also seen that on the Rim Fire, where about 20,000 acres were clearcut, on SPI land.

  3. Alternate Headline: Benefits of Complex Early Seral Habitat Extended by Delayed Conifer Regeneration.

    The study period for this study was far too short to say that conifer regeneration is a problem. It is not unusual for conifer regeneration to take up to 30 years. Why not appreciate the benefits of these natural processes?

    • Well, in the Rim Fire, only about 15% of the burned acreage was salvaged. AND, remember, pine seeds do not travel very far and are subject to a limited amount of ‘good cone years’. If that does not happen within a a couple of years, those saplings will be ‘shaded-out’ by the faster growing brush. Additionally, we have seen areas of Yosemite where regeneration might be impossible, especially in areas that have or will re-burn. Granitic soils are also subject to a catastrophic loss of water-holding capacity, which will severely impact regeneration of ANY kind. We’ve already seen it happening in the Foresta area of Yosemite National Park.

    • More like perpetual brushfields, in some cases. This part of the Rim Fire was also part of the early 70’s Granite Fire. This patch was left out of salvage plans, to ‘let it recover on its own’. Well, before the Rim Fire, it was a nasty mess of manzanita and whitethorn. You can see how there wasn’t much pine regeneration since the first fire. The aspect and elevation prevented shade tolerant trees from seeding in, too.

      • Can we call conifer regeneration good in plantations that don’t reach maturity (i.e. those in the Granite, Rogge, Ackerson, and 87 Complex that subsequently burned in the Rim Fire)? Does it make fiscal sense to reforest all that, only to have it burn before it actually resembles a functioning, real forest? I don’t claim to know the answer, but these are important questions in an age of declining funding and increasing temperatures.

        • In many areas, it just isn’t worthwhile to replant an unsalvaged area. When such an area, like in the picture I provided, has lots of logs covered by 6-8 foot tall brush, the soils are going to be severely damaged (when it re-burns), with many seed sources eliminated. In these fire prone areas, we should be focusing on resilience to man-caused fires. If we don’t, we’re not looking at the big picture. Giant site-specific pictures, ready to burn at high intensity with any type of ignition. Important questions and important answers, indeed.

        • Roy

          A) Re: “Can we call conifer regeneration good in plantations that don’t reach maturity”
          – Yes, we are looking for the root cause when studying and classifying the cause of mortality so that we can use continuous process improvement to make better decisions in the future. Nothing would be learned if we called a 15 year old stand that was eaten by bugs or burned by fire a regeneration failure.

          B) Re: “Does it make fiscal sense to reforest all that, only to have it burn before it actually resembles a functioning, real forest?” Assuming that the “post fire” landscape level adjusted goal for the burned area was to remain as a forest:
          – If we could predict when and where lightning, arsonists, and irresponsible campers were going to strike then you have a point. However, since we can’t, the post fire analysis should determine where natural regeneration had a reasonable chance of succeeding and where artificial regeneration was more appropriate. Then the budget, goals and priorities based on the relative probabilities of success will determine the answer to your question.

          – C) Re: “increasing temperatures”
          – Global warming makes controlling stand density (competition) through sustainable forest management practices all the more important. “increasing temperatures” lowers the availability of water and the nutrients needed by each tree. So competition between trees for those limited resources must be decreased in order to keep the remaining trees as healthy as possible. Where compensation can not be achieved the forest will eventually fail and succession will move to a more sustainable ecosystem and if the heat increases too greatly then desertification is a possibility. However, since forest ecosystems make their own micro-climates, the smaller the acreage destroyed the better the chance of regenerating the stand as warming and drought increase.

          So when we get through all of that we quickly see that there is no simple financial formula that can take all of the subjective potential outcomes, their probability of occurrence, spatial and temporal relationships, cost, revenue and compliance constraints and say that this is what you should do. Where we can make a reasonable assessment to quantify the outcomes and their probabilities, we can use linear programing or other mathematical techniques to suggest the best approach over the landscape. But even there, the existence of contradictory constraints in a non-commercial public forest will, more often than not, require a subjective compromise between conflicting constraints.

          Playing God is pretty tough but He did put us in charge of all of this so: the budget, goals and priorities based on the relative probabilities of success will determine what gets done and what is left undone. What make sense will be done until we run out of cents. That is the answer to your question. Hopefully, what makes sense will eventually be based on established science rather than on the unproven theory, speculation, emotion and wishful thinking which seems to drive a lot of federal forest policy currently.

    • 2ndLaw

      No problem as long as the natural process doesn’t lead to a transition to a whole new ecosystem contrary to the integrated, landscape level goals for a specific site as dictated by sustainability issues.

      I don’t often agree with George Wuerthner but, subject to my caveat in the preceding paragraph, he explains some forest management options that may fit in some specific situations in this article which he published as a repudiation of the findings cited in the opening post at the top of this thread. His problem is that his headline and some other claims are an attempt to make a one size fits all claim that can’t be supported in many cases.

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