September 4, 2009

Forest carbon, from cradle to grave

Article reviewed: Forest carbon storage: ecology, management, and policy

By T.J. Fahey, P.B. Woodbury, J.J. Battles, C.L. Goodale, S. Hamburg, S. Ollinger, and C.W. Woodall, published in the journal Frontiers in Ecology and the Environment

The plot line: This is a review of the role that forests have in sequestering atmospheric carbon. They explain the general processes that make a forest either a sink or source of carbon. The authors also review the currently developing global and regional policies that may influence how forests are managed for carbon. They conclude that forests that are managed with specific goals of net carbon sequestration can indeed be net sinks of carbon, but that better models and methods for tracking how forest management decisions actually influence carbon are needed before individual landowners can confidently and legitimately take “credit” for sequestering carbon on their land. They also state that immediate benefits of forests can come from using forest wood products for either energy production or for building materials instead of using other products that consume fossil fuels (e.g. using wood instead of concrete for building, or forest biomass instead of oil for energy production).

Relevant quote: …we emphasize that it is critical to assure both policy makers and potential investors that forest C offset projects address the full range of social and environmental issues that can result from forest management activities. Although there is considerable scope [i.e. capacity] for C mitigation, the danger of encouraging mismanagement is real, and an acceptable “gold standard” for forest C offset projects should be the ultimate goal.”

Relevance to landowners and stakeholders:

Landowners who are counting on sequestering carbon from their forests in order to make money may still have to wait awhile to get paid. In California, landowners can “register” their forests and use a pre-defined method for accounting how much carbon they are sequestering. But, as the authors point out, there are several issues still to work out before a true “gold standard” method for accounting is developed. There is also an economic market reality in the way: trees are worth more dead than alive. Landowners can make more money selling their trees for sawlogs than for carbon. The good news is that these two objectives (sawlogs and carbon) are not necessarily mutually exclusive. And in California, they may actually be complementary.

To maximize forest carbon sequestration, a landowner would allow their forest to develop with very high densities and little intervention except for fire suppression. In California, however, such high densities dispose the forest to an unacceptable risk of intense wildfire. While one could develop a “fire insurance” pool to offset the risk to investors, it is clear that wildfire intensities have been increasing over time (as discussed in a previous post). Would you invest in a market where risk has steadily been increasing (because of physical, biological reasons and not for socio-economic reasons)? I wouldn’t.  

I would, however, invest in a forest that was managed to balance objectives of high carbon sequestration, resistance to wildfire, and production of wood products that went into building materials and/or energy production.

Relevance to managers:

Silviculturally, these three objectives can be managed for by paying attention to the following management activities:

1.     Controlling stand density- As density increases, stand increment (forest carbon sequestration) also increases. But when a certain density threshold is passed, tree mortality is high and there is also often a higher risk of catastrophic loss (fire or insects). So the manager’s critical decision is to define an acceptable density management zone. This zone defines the upper and lower densities (e.g. thin when a stand gets to within 75% of maximum density, down to 50% of maximum density). This maximum density measurement can be measured with local knowledge of maximum basal area/volume, with a stand density index, or with new approaches such as using leaf area index.

2.     Reducing wildfire intensity- thinning projects can be counter productive with respect to carbon if they result in conditions that will cause even more intense fires than before. But as discussed in another entry, we know the basic principles for conducting forest operations to reduce fire intensity (i.e. reduce surface fuels, reduce ladder fuels, thin canopy density from below, and prefer fire-resistant species).

3.     Keep the forest as a forest- converting trees into wood products commits the carbon to long-term storage and is a better option (carbon-wise) than using wood substitutes such as metal or concrete. But the forest that the wood products came from has to remain a forest. If it is developed into housing subdivisions, it becomes a very long-lasting source of carbon. If biomass (debris and small woody material) resulting from a project can be used for energy production, then you can really feel good about yourself since it offsets energy that would have been produced by fossil fuels (which is what got us into this mess in the first place). 

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

They did not address the role that management treatments can play in avoiding episodic loss of carbon (for example, in western forests susceptible to wildfire). They state that forest reserves (not harvested) can be beneficial because they sequester carbon and they stay as forests. But in many forests, they also become susceptible to loss from fire or insect outbreaks. Management decisions that influence carbon include intermediate treatments (like thinning), not just coarse-scale decisions like whether to harvest or not to harvest. Given the potential impact on carbon from large-scale forest losses, I think this would have been an important discussion point.