By Holly R. Prendeville, Coordinator for the USDA Northwest Climate Hub
Weather in the Northwest has gotten more variable. We have recently experienced drought for two years followed by flooding in 2017. The 2015 drought coincides with future climate projections for the Northwest: warmer temperatures leading to lower and earlier melting of snowpacks. Though trees are locally adapted to climate and can tolerate moderate changes, rapid and large changes in climate may be beyond the capacity of some species. As we saw in 2015, longer and drier growing seasons affect tree regeneration, growth, and mortality. This poses challenges for foresters, which Chris Schnepf discussed in a recent article.
After timber harvest, reforestation is essential to return to a productive forest and healthy ecosystem. However, forest productivity and health are affected if seedlings from natural regeneration or plantings are not also suitable for future climates. Until recently, choosing which seedlings (seedlots) match a local climate was accomplished by using defined zones or seed transfer rules that specify an area by geography or climate from which seeds can be moved and are likely to grow well. An assumption of these zones is that climate will not change over the long-term, which is not likely given predictions by climate scientists. So how can foresters bring in climate change considerations to improve their chances of selecting seedlings that are—and will be—suitable? An online tool has recently been developed to do just that.
The Seedlot Selection Tool is a web-based mapping application developed by the USDA Forest Service, Oregon State University, and the Conservation Biology Institute, that helps foresters and land managers determine if natural regeneration or replanting seedlings from a particular source will result in a forest adapted to current and to future climates. This tool uses climate models to define areas based on historical and projected climate rather than geography alone. With this tool, foresters can explore whether natural regeneration is appropriate, or from where seedlings should be sourced so that they are suited to thrive in both current and future climates. The Seedlot Selection Tool allows the user to control which climate variables to display, and it can be customized for management practices, climate change assumptions, and risk tolerance of the user.
Here is an example. As a landowner of a 50-year old stand of Douglas-fir in southeastern Washington that you plan on harvesting, you visit the Seedlot Selection Tool to help you include climate information in your reforestation plan. You enter your coordinates (46.28, -117.47). You choose the climate from 1961-1990, since the current stand was established under this climate. You then choose Zone, to view the climate information along with the seed zone. You select Douglas-fir as the species of interest and mean coldest month temperature as the climate variable, since chilling hours are important to tree development. You run the tool and save the output that shows areas with similar climate in dark orange (Figure 1A). You then choose 2041-2070 for “When should trees be best adapted to the planting site?” to see the future climate. There are two climate scenarios: RCP4.5 represents the future climate with a reduction in greenhouse gas emissions, whereas RCP8.5 represents the climate with an increase in emissions. You choose RCP8.5 as it is more likely, and rerun the tool. Comparing the two outputs you find no suitable source within your seed zone (no orange inside the green boundary; Figure 1B) indicating that natural regeneration alone will likely not yield a productive stand in 50 years considering the future climate. You may need to obtain seedlings from the western slopes of the Cascades.
The Seedlot Selection Tool synthesizes existing research and allows you to explore alternatives before testing something out on your land. Combined with your expertise, you can use the Tool output to incorporate climate information into your management decisions, and to find appropriate sources for reforestation. The Tool can provide climate information as you consider a variety of options such as how climate will change across different rotation lengths, sourcing seedlings from a mix of sources that are adapted to the local and future climates (e.g., WA (2002) Zone 16 4200’-4900’ and the Columbia River’s WA (2002) Zone 6 1000’-2000’) or planting a species that is more tolerant to future climate change and will still be profitable.
It can take years if not decades to see negative effects of seedlings planted in the wrong climate, so planting a mixture of seed source or a species more tolerant of climate change can reduce the risk of poor harvest in the future. Exploring options using the Seed Selection Tool is cheaper than a 30-100 year trial-and-error option. To try it out for yourself, see these additional instructions and a webinar to help you get started.
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