Adapting to Climate Change: How Forestry and Cropping Systems Differ

By Chris Schnepf

Many westerners presume any forest they drive by is managed by the U.S. Forest Service. But nationally the largest portion of forests are owned privately. Even in the West, key regions have a very high percentage of private forests. For example, over half of the forests in the Idaho Panhandle are private.

Some people debate whether forestry should be considered part of agriculture. Like farmers, forest owners and managers are discerning how to adapt their management to a changing climate. But forestry in North America starts from a different point than most cropping systems. While farmers generally focus on single-species crops, often brought in from other parts of the world—be they annual, like cereals, or perennial, like cherries—forestry in North America has usually focused on managing diverse native species and ecosystems in ways that mimic the natural patterns of forest growth and development. This difference leads to some unique climate change adaptation implications for Pacific Northwest forestry:

• Long time frames. Foresters were among the first to take climate projections seriously, because planting a tree is a long-term decision. Cereal producers can usually switch to a new variety next year if necessary; an enviable degree of flexibility. Northwest forests are grown on 40-year regeneration cycles on the most productive sites, and much longer on drier sites or where wood production is not the most important objective.

• Native seed sources. Foresters have focused primarily on regeneration from adapted seed sources—often through natural regeneration from trees on or near the site—because their genetics have been selected by the range of environmental conditions that hit that site historically. If trees are planted, seed must be from an adapted latitude and elevation, which varies greatly by species. To the extent the future won’t look like the past, that strategy weakens. On some sites, the best seed source may be from a location where the past looks more like our future (e.g., seed from a site where the growing season starts sooner). But such “assisted migration” can be problematic. Just because a seed source looks better adapted 40 years from now doesn’t mean it can handle environmental conditions on a site for the next 10 years (e.g. it may still face frost in its new location, even if frost days are projected to almost disappear in 40 years). Researchers in Oregon recently developed a useful online GIS tool to help foresters think about matching seed sources to future climate scenarios. Annual (and even perennial) crops can have more flexibility: you could wait to change variety—or even change crop—until frosts have mostly disappeared.

• Lack of extra water sources. Some agricultural producers can supplement water for crops through irrigation. That is almost never an option in native forests. We manage forests to be resilient in the face of likely drought years by favoring tree species that are adapted to drought extremes for the site, and thinning stands to reduce the number of trees competing for limited moisture.
• Insects and disease. The primary focus of strategies to manage forest insects and diseases is favoring tree species and spacing which tolerate native insects and diseases. This also means forest management places more emphasis on native biological controls of problem insects and diseases. How will climate change affect these natural biological controls and their hosts? We’ve discussed insects in cropping systems, and there may be useful lessons to be learned from how farmers and foresters are, respectively, tackling these issues.
• Fire. Drought, floods, wind events and other natural disasters affect both forests and crops. But regarding one kind of natural disaster-fire-forests are different. Northwest forest management since 1910 has emphasized extinguishing all forest fires immediately. In recent years, this has become more difficult, especially in forests that historically had frequent surface fires, reducing understory fuels. Fire seasons are projected to become longer and more intense. We will likely see more discussion of ways to allow fire, when manageable, back into these forests.
• It’s not just about the trees. Forests are valued for many benefits. Even where some timber is harvested, some forests’ primary value may be for water storage (as snow), fisheries, recreation, wildlife, or other benefits. Therefore, forest management must often consider those values just as much, and in some cases more, than harvested commodities. This may also be the case in cropping systems, though the balance may be more heavily weighted towards the harvest commodities there.

As with agriculture, a variety of groups are researching ways to adapt forestry to changing climates. If you would like to learn more, start with the Climate Forests and Woodlands Community of Practice or the U.S. Forest Service Climate Change Resource Center. And keep an eye on AgClimate: we do consider forestry within the Agriculture and Climate umbrella, so we will continue to discuss forestry-relevant topics in the future.