Article reviewed: Fuel treatment longevity in a Sierra Nevada mixed conifer forest

By S. Stephens, B. Collins, and G. Roller. Published in the journal Forest Ecology and Management, 285: 204-212

The plot line: This study looks at how long fire hazard reduction treatments last. The researchers conducted 4 different approaches to reducing fire hazard: doing nothing, prescribed burning, mechanical thinning, and doing both a mechanical thin and a burn. They found that, while the mechanical treatment reduced fire hazard only modestly immediately following the treatment, the mechanical treatment turned out to be about as effective as the prescribed burning treatments were after seven years. All of the treatments were much better than doing nothing, which just got worse over time. They conclude that fire hazard reduction treatments could last quite a bit longer (and be more cost effective) if managers pay attention to the timing of treatments and possibly the combination of different fuel treatment methods over time.

Relevant quote: “The net effect is that fire hazard (indicated by predicted flame length and torching probability) noticeably decreased after 7 years and is similar to the two fire treatments, which was surprising.”   

Relevance to landowners and stakeholders:

It keeps getting worse…

The type of forest where this experiment was done is often called a “second-growth” forest, which in this case means that it was harvested with something similar to a clearcut about 110 years ago when we were building places like San Francisco. It took a lot of lumber to build all of these cities, so much of the Sierra Nevada was harvested at that time. One lingering result of those harvests that we are now faced with is that the forests are still growing as a response to those harvests (this is not true everywhere, but is often true in productive forests). As they grow without any disturbances such as fire or another harvest, fire hazard also tends to get worse and worse. The “control” in this experiment represents the choice that every a forest landowner has a right to make. That is, the choice to do nothing. There are serious risks that go along with making this choice, however, as this study shows. The risk of high severity fire and of the majority of the trees suddenly dying increases (what ecologists might call a “sudden and catastrophic” disturbance). This can even lead to a cycle of continued high severity fires and loss of trees as the dominant organism (i.e. no more forest).   

But there is hope…

These researchers are fire scientists. I don’t think that anyone can devote their career to studying fire unless they are, at least to some degree, pyromaniacle (can you believe that word is not in the spell-check dictionary?). So it is natural that a study like this would emphasize the benefits of using fire to manage forests. But these researchers also seem to have a healthy respect for practicality. They seem to realize that forests of the Sierra Nevada are in nearly-desperate need of treatments to reduce fire severity, and that it is not practical to be able to start burning everywhere (as much as they wish it was). Smaller landowners (who own about a third of the forests), especially have little opportunity or risk tolerance for burning. So it is important for studies like this to continue to identify the tradeoffs between the different treatment methods so that we can conduct treatments that work as soon as is possible, wherever possible.  

The finding here that mechanical treatments eventually were as effective as burning treatments (when using the limited metrics in the study) is significant on a practical level. It does not mean that any mechanical thinning or harvest will eventually reduce fire hazard. But it does mean that if a mechanical treatment is designed to reduce fire hazard then it can be beneficial from a fire hazard reduction perspective. Having options for meeting objectives is usually a good thing.

Relevance to managers:

The mechanical only treatment was characterized by the following 7-year changes:

• Little mortality
• Increased stand growth (as a response to the harvest)
• Eventual decomposition of the activity fuel that was created during the harvest

The fire only treatment was characterized by:

• Lots of immediate and delayed mortality, especially in small and medium sized trees
• A reduction in surface fuels that persisted
• A flat rate of stand growth (probably because of fire-caused mortality and possibly decreased vigor of individual trees).

The paper discusses the potential to realize the benefits of both mechanical and fire reduction treatments by doing a “staged treatment.” Specifically, they suggest conducting a mechanical treatment (including the removal or chipping of small trees in addition to medium sized trees) and then waiting for 10 years or so before conducting a prescribed fire as a way to maintain the low fire hazard.

Of course, if one likes the benefits of either mechanical treatments (the clear winner from a timber perspective), or if they like the benefits of burning (other organisms can surf in the ecological wake of a prescribed fire) then this study’s results also suggests that you can probably keep doing either thing repeatedly and get the particular benefits associated with that treatment, while also reducing fire hazard.

Critique (I always have one, no matter how good the article is):

One of the surprising results is not explained in this paper. Somehow, the height to crown base decreased in the mechanical treatment between year 1 and year 7. It is not a big deal in terms of the results, because fire hazard decreased in the mechanical treatment in spite of this odd result. But I can’t think of a way in which crown base would have decreased unless there was either lots of ingrowth or epicormic sprouting. But tree density did not increase and canopy cover did increase, which suggests that there was not much ingrowth of smaller trees. And epicormic sprouting doesn’t make much sense either, since only white fir commonly has epicormic sprouts in this forest and I haven’t seen it occur much as a response to light thinning. The method of measuring height to crown base could have changed, which would be measurement error. Or, perhaps the way in which crown base was estimated with the FVS model had something to do with it. The reader is left to make their own speculation, since one was not provided by the authors.

There is some minor conflation between tree and stand growth in the discussion. They state that tree growth “stagnated” following the fire treatments, but mortality is not taken into account. And as far as I can tell, the fire only treatment actually caused a reduction in density (from fire-caused mortality) without a corresponding decrease in basal area. This would actually represent a growing stand in my mind (or at least not a “stagnating” one). Individual trees obviously aren’t all healthy since some are dying, but on balance the stand is growing. This would suggest that the survivors are growing. A more accurate analysis of stand or tree level growth would include a more detailed profiling of diameter distributions as well as ingrowth and mortality.

Some silvicultural terms used could have been chosen better. They say that the mechanical treatment was a thin from below followed by a crown thinning. This might suggest to some that the second thing done was a harvest of the largest trees. But in fact the second treatment was also a thin from below to a basal area threshold. It involved some medium sized trees, but it was never a large tree harvest.   

Article reviewed: Arbuscular mycorrhizal colonization of giant sequoia (Sequoiadendron giganteum) in response to restoration practices

By C. Fahey, R.A. York, and T.E. Pawlowska. 2012. Published in the journal Mycologia, 104: 988-007. DOI: 10.3852/11-289

The plot line: This study looked at the way that roots of giant sequoia seedlings interact with a fungus (together forming what is known as mycorrhizae). They found that when they planted giant sequoia seedlings, beneficial fungi would attach on to the seedling’s roots mainly when the seedlings were planted in open sunny conditions. While it was hypothesized that the fungi would not be as common on roots in areas that had been burned, there was no difference between burned and unburned locations. Also interestingly, the beneficial fungi actually seemed to outcompete the harmful fungi, thus possibly helping seedlings to avoid other diseases. They make the inference that this mycorrizal interaction between tree and fungus is a potentially important process in giant sequoia growing fast as a seedling and may be a key ingredient in how it eventually becomes the world’s largest organism.

Relevant quote: “This [rapid seedling growth in sunny locations] suggests that the symbiosis as a whole has improved function at the centers of gaps because both partners have improved growth.” 

Relevance to landowners and stakeholders:

Nature is dominated by individualistic, chaotic, and brutal selfishness. Organisms are hard wired to have a primary goal- to reproduce. Often, plants achieve this goal at the expense of other organisms via a fierce competition for the triple-crown of resources: light, water, and nutrients (it’s a baseball theme today). But sometimes it is in an organism’s best interest to be of assistance to another. Such is the case with mycorrhizae, which is a combination of plant roots and fungi attached to each other (“myco” = fungi; “rhizae” = roots).

Giant sequoia is an interesting species because it is so different than any other in so many ways. The most obvious difference that people know about is its tremendous size- larger than any other tree on earth. But the way that it reaches this size, and in fact its entire “life history strategy” is somewhat of an outlier when you compare it to other tree species. It’s mycorrizal interactions are no different. It forms what are known as “arbuscular mycorrizae,” which is uncommon in conifer trees. Beyond that, not much is known about this plant-fungus interaction in giant sequoia, but this study offers a little insight.

The primary relevance to landowners and stakeholders might be that this paper reminds us that planting a tree and getting it to survive and grow is a complex, ecological process. Planting is something we might be doing a lot more of in forests, as climate change and wildfires become forces that hinder natural regeneration. Successfully planting a tree, where the measure of success is getting the tree to complete its life cycle, involves much more than planting a tree and walking away. It involves understanding the resource requirements for that species, and how that particular tree will be able to make its way up into the canopy to become mature. For giant sequoia, and most other trees, the mutualistic interaction that seedlings will have with root colonizing fungi is key information. This study suggests that planted giant sequoia seedlings have the best chance of success when they are placed in distinct canopy openings in sunny conditions, in part because this is where the mutualistic relationship with fungi can benefit giant sequoia growing quickly into the tall canopy above.

By the way, I think most green campaigns that ask you to pay a little extra so that you can sponsor the planting of tree seedings are scams. I would not advise believing or certainly not paying for such “plant-a-tree campaigns” unless you knew the species that was being planted, the location, and the method used for tracking survival.

Relevance to managers:

OK, here’s where the baseball analogy suggested by the title finally comes into play. Stay with me here…

Giant sequoia is a base runner, where rounding third means going home, which in terms of a tree is equivalent to reaching the canopy and reproducing (and for a person on a date, this is of course equivalent to something similar).

The fungus that forms the mycorrhizae is the third-base coach, hoping to be of some assistance to the base runner but hoping to get something in return (a job).

A base runner doesn’t really need the third base coach, but the third base coach definitely needs the base runner to have a job and make a living. Often the third base coach can be helpful to the runner, but only when things are already going pretty well for the runner. When they are rounding third base, the runner is in pretty good position to score, and the third base coach can help them score. Sometimes, however, the third base can be a hindrance if they get in the way or if they give the runner some bad advice. But usually they are a help. And of course no championship team (such as the Giants) would be without a third base coach.

Get it? Giant sequoia seedlings are happy to have this relationship with fungi, but only when things are already going well. Mycorrhizae were more common on seedlings when they were planted in the open, so there was plenty of carbon for the seedling to spare. It is carbon that is the currency paid by the tree, in return for nutrients like Phosphorous from the fungus. And fungus can also keep the plant out of trouble by fighting off pathogenic fungi, kind of how a third base coach can tell the runner to get back when the pitcher tries to pick them off.

Implications? If you plant giant sequoia, do so in distinct canopy openings and pay attention to how the nursery either sterilized or inoculated the soil. In this case, the nursery had sterilized the soil so the mycorrhizae developed on roots after the seedlings were planted in the field. When you plant far away from a mature forest edge, don’t worry about it taking a long time for fungus to colonize the area- they are probably already there because of lateral roots from surrounding trees.

Critique (I always have one, no matter how good the article is):

The authors set this study up as a hypothesis-testing experiment, but there is so little known about mycorrhizae in giant sequoia that doing so sets up an easy claim of “surprising” or “unexpected results.” In fact, some information in the discussion that is presented would actually suggest that the hypothesis should have been the opposite of the one proposed in the introduction. It’s not a big deal with this study, but more of a critique of studies in general that tend to set themselves up so that they can easily say that they got a “surprising result…”

September 21, 2012

Forest scientists bet on the trifecta SWEEP in the Sierra Nevada

Article reviewed: Forests and water in the Sierra Nevada: Sierra Nevada Watershed Ecosystem Enhancement Project (SWEEP)

By R.C. Bales, J.J. Battles, Y. Chen, M.H. Conklin, E. Holst, K.L. O’Hara, P. Saksa, and W. Stewart

The plot line: [Note that this is a “white paper” (self-published), so I am straying from my typical format of reviewing only peer reviewed articles. Given the relevance for management and the quality of this particular paper, it seems worth making an exception]. This group of forest scientists quite aggressively makes the argument that forests in the Sierra Nevada can be managed for improving both the quantity and quality of water to benefit the commonwealth of California, and that there should be monetary incentives for the landowners who do such management. Their case is built upon the notion that water is of very high value and that several studies done in other similar forests clearly document that lower density forests (i.e. recently harvested) do increase water yield and potentially increase snow pack persistence. They make the case for large-scale studies that can be used in the future to help foresters and landowners meet the triad objectives of water, fire severity reduction, and species restoration (the trifecta SWEEP).

Relevant quote: “The perspective that forest management for water supply is not worth the trouble is ingrained in both upstream and downstream resource managers. The SWEEP team contends that forest management for water supply is worth the trouble…”

Relevance to landowners and stakeholders:

Forest landowners pay attention any time a scientist or economist suggests that they should be paid more for the “ecosystem services” that they provide to society. Forests support wildlife, clean air, and natural beauty that people from the city enjoy. So why shouldn’t the folks that own these forests get paid for it? There is of course a way in which landowners can be paid for protecting their forests. That is, through a conservation easement. But what these scientists are suggesting is something quite different than a conservation easement. Instead of a forest landowner getting paid to do nothing with an easement, they are suggesting that they get paid to do something! Doesn’t that sound more feasible as an economic model?

We are of course a ways away from this actually happening, but this team of scientists is trying to conduct research that will help such a system to develop. Rigorous experiments will have to be done in order to measure with accuracy how much more water can actually come from a forest managed for water quantity and quality (when I say quality, I am referring mainly to the timing of snow melt- if snow melts later in the spring/summer, then it is of higher quality in terms of value).

You can find the arguments for why forest management could be managed for water in any forest ecology text book. A simplified version of it is this:

1. All plants have leaves.
2. Leaves do photosynthesis, which pulls water from the soil and transpires some of it into the air
3. Leaves intercept snow and rain, some of which evaporates directly back into the atmosphere
4. The fewer leaves that are present, the less water will be sent into the air, and the more water will leave the site and go into reservoirs or hydro-electric facilities.

Relevance to managers:

I think the relevant quote above says it all for managers. These authors are right- water can no longer be ignored. I have personally heard other scientists and mangers state that forest management simply cannot make a significant difference when it comes to water yield or the timing of runoff. But the large amount of evidence presented in this paper suggests the contrary. And it is no secret that water is becoming a more valuable resource every year, so even small increases in yield can be meaningful. It is only a matter of time before markets force us managers to more explicitly manage forests with water as the objective. If the research these and other scientists propose comes to fruition, then we’ll be more ready for the challenge.

The UC Center for Forestry has been managing for what we call a “water efficient forest” for the past decade. It is at a slightly lower elevation than what these authors say will be optimal for increasing water yield and runoff timing, but they also provide some logic in this paper that suggests these lower elevations could increase yield as well. The easy part was thinning the forest down to a level where one could reasonably expect an increase in throughfall and runoff. In this particular case, we have harvested to a density at about 50% of the maximum that we observe on nearby stands. The density then fluctuates between about 50 and 75% of maximum over time in between harvests. Based on the estimates from this paper, this level of density reduction might result in somewhere between a 9 and 18% increase in water yield and it should mean snow persisting for a little while longer (although for low elevation forests, it is likely more about water yield than the timing of snow melt).

In my experience, the easy part in managing for water has been conducting the commercial thins. After all, it is a productive forest so we can generate revenue from the thins by harvesting commercial sized trees. We have been able to, concurrently or immediately following harvests, reduce the small tree cover and surface fuels to make the forest resistant to high severity fires. According to this paper, this action has resulted in what should be a structure that yields more water (somewhere between 9 and 18% increase). The challenge over time has been in managing the understory vegetation in order to prevent it from developing a significant amount of leaf area that would defeat the purpose of increasing water yield. It is challenging because this means conducting treatments that are not paid for with a commercial harvest. Theoretically, one could save the revenue from the commercial thin and apply it to understory treatments in between thins. This is indeed what we have done in this particular case (in the form of mastication and broadcast burn treatments), but without a financial incentive to do these treatments, I can see the situation occurring where these follow-up treatments simply aren’t done. So the authors make a good point in this paper that a water efficient forest needs to be maintained over time. It is not a one-and-done situation.

Critique (I always have one, no matter how good the article is):

They say that many of the upper watershed forests are zoned as wilderness areas, the implication being that these areas cannot be managed for increased water yield. I would argue that these areas can also be managed for water quality with fire being the mechanism for maintaining low density. Without fire in these areas, they will burn with higher severity fire that could input massive amounts of sediment into downstream watercourses, thus countering any positive effect of water quantity and quality treatments that are done in non-wilderness areas.

They make an excellent point that, if runoff is delayed because of forest management activity, then hydro-electric energy production can occur later in the summer, when demands are high. I think they missed out on a point to make about the further potential for these treatments to benefit energy production during the summer. If the treatments are done in the summer and involves a biomass harvest of small trees and tops/limbs, then this would also potentially result in energy production during a time when it is most needed. Perhaps this is too speculative, but it is interesting to think about the potential for biomass harvests to by synergistic with water yield treatments from an energy production perspective.

They focus on forests between 5,000 and 12,000 feet elevation as having the most potential for increasing water yield and runoff timing, because they are productive and warm (above freezing). 12,000 feet… really? Any time I’ve been at 12,000 feet in the Sierra Nevada, I have not noticed many trees. At 12,000 feet, I’m catching my breath and enjoying the view because there aren’t many trees, if any at all. And lots of the winter period is cold at this elevation. Given their logic, it seems like this elevation should be shifted downward, perhaps between 4000 and 9000 feet. 4000-5000 foot elevation forests may not be dominated by snow, so the potential to delay runoff timing is less. But based on their logic and points scattered throughout the paper, forests in this elevation could increase yield substantially. The paper could use some clarity in reconciling all of the different factors of water yield and runoff timing in order to justify the 5 to 12,000 foot elevation target.

They report an average basal area in one of their targeted study areas of 400ft2/acre, with an average canopy cover of only 51% and an average canopy height of only 60 feet in a forest dominated by 100 year old trees. These numbers are not adding up in my head. That basal area seems very high for a forest that does not appear to be highly productive (trees growing 60 feet in 100 years). On the other hand, the LAI they report is also exceptionally high. A high LAI is the only way that I can visualize a forest like this having such a high basal area, so perhaps the numbers are good. But their statement about this forest being typical of much of the northern Sierra Nevada is a stretch- especially considering the 5000 to 12000 foot elevation range that they are talking about.

Adapting to climate change: Forests will try, but they can’t do it on their own

Article reviewed: Forest responses to climate change in the northwestern United States: Ecophysiological foundations for adaptive management

By D.J. Chmura, P.D. Anderson, G.T. Howe, C.A. Harrington, J.E. Halofsky, D.L. Peterson, D.C. Shaw, and J.B. St. Clair Published in the journal, Forest Ecology and Management (Vol. 261: 1121-1142).

The plot line: This is a review of the likely and potential effects that climate change will have on the physiology of trees in the western US. The authors discuss how these effects might influence forests at larger scales and also discuss the degree to which forests might be able to adapt to a changing climate. They focus on a changing snowpack and drought stress as important stresses that may lead to changing fire regimes and forest pest interactions. While significant impacts appear certain, they also note the tremendous uncertainty in predicting the details of how impacts will play out. They conclude that forests will not be able to adapt without management intervention. The recommended management actions that may help vulnerable forests adapt to climate change include density management, planting, and assisted migration.  

Relevant quote: “Overall, density management should be the most effective [silvicultural] approach because of its ability to lessen drought stress, fire risk, and predisposition to insects and disease.”

Relevance to landowners and stakeholders:

If forest landowners are anything like me, they go through ups and downs when it comes to worrying about how climate change might influence their forest. For forest managers, it is arguably their responsibility to think in long time frames so it is therefore their responsibility to think about how climate change might influence the forests they manage. But landowners may not have that same incentive to think longer-term. I admit that sometimes my time frame only extends to the time at which I think I am going to sell the land or when I will no longer be able to physically work on it. This tends to make me rather blasé when it comes to worrying about climate change effects. But even for those like me that suffer this periodic short-sightedness, this review reminds readers that it is wise to address climate change impacts now. The uncertainty and complexity of how climate change will affect forests are frankly overwhelming. This review includes how climate change might influence factors of how forests grow:

• Carbon dioxide concentration (going to go up)
• Temperature (going to go up)
• Precipitation (not sure where it’s going)
• Drought (going to be more common and longer)
• Wildfire (going to be more frequent and severe, but might go down after a while)
• Insects and diseases (going to emerge in new locations and intensities)

Those are just 6 factors that we know are going to change (in uncertain ways), but there are probably more. Sometimes we can consider one factor individually and make a scientific guess about how it will affect forests. But the reality is that these factors will be interacting with each other to affect forests in completely uncertain ways. We really have no clue what the exact effects will be or how long they will take to occur. But we do know they will be a big deal socially, economically, and ecologically. As I’ve reviewed in previous posts, active adaptive management is really the only realistic management response to such a foreboding reality.

Relevance to managers:

True to the title of the paper, the review focused on the foundations for adaptive management so there are not many actual management recommendations. I think these are the primary foundations which can be drawn upon from this review with respect to constructing adaptive management plans:

• Inter-breeding populations are the scale at which plants can adapt, so management decisions are ideally done at a fairly local level
• The regeneration phase of trees is the most vulnerable to the impacts of climate change
• The abiotic changes that will most likely either directly or indirectly influence forests are drought stress, a shrinking snowpack, and an earlier timing of snow melt (I am thinking mostly of dry montane forests here)
• We have already seen climate change interact with existing pests to result in unpredicted epidemics (i.e. mountain pine beetles). Expect more of the same.

The authors very briefly suggest the following as possible management responses:

• Density management. Thinning forests makes individual trees more resistant to drought stress
• Planting. Because the regeneration phase is most vulnerable to failure
• Assisted migration. It was confusing, but I believe their emphasis was on within-species range migration
• Forest stand triage. Foresters should think of the different seral stages and structures that they manage for, and then consider which of these might be most vulnerable to climate change. For example, forests that have reserves where density is very high and fuel is also very high could be the most vulnerable. Because of the vulnerability of the seedling stage to changes in climate, young stands (or those in an understory re-initiation phase) might also be especially vulnerable.  

Critique (I always have one, no matter how good the article is):

The management recommendations were not as thorough as I was hoping. They provided very detailed reviews of how climate change might influence forests differently in different parts of the western states. But management recommendations were not given with anywhere near the same level of detail. Assisted migration, molecular and genetic breeding, and gene conservation were mentioned as possible strategies. Given that many folks are very skeptical of these types of intervention (in my experience, some people think assisted migration is a capital offense), it would have been useful to provide some examples or perhaps bounds on how they should be used given the range of plausible ecophysiological responses to climate change.