Written by Chris Schnepf, University of Idaho
Climate change questions are especially important for tree planters to consider. Gardeners and farmers usually only have to anticipate climate over the coming months. However, tree planters must anticipate climate over the next 30 years or more and consider not only the average anticipated climate conditions but, more critically, extremes of temperature, drought, and other environmental conditions the trees may have to endure. This is difficult enough for a given site assuming past climatic conditions, but is even more challenging in the face of uncertain future climate. Strategies to consider include:
- Seed source. Normally it is best to plant trees from seed sources from nearby latitudes and elevations (how near varies by species). One strategy to adapt to climate change would be to plant trees from seed sources that have evolved in response to conditions more like those anticipatef (e.g., Ponderosa pine from lower elevations or more southern latitudes if the growing season is likely to be longer). These seed sources would eventually migrate naturally, but this could take hundreds or thousands of years. Planting from alternative seed sources earlier is sometimes described as “assisted migration.” Given the uncertainty about local climate changes, another option is to plant from several seed sources that represent potential climate scenarios. Varying seed sources may be sensible if there are expectations for wider weather event extremes, such as a cold snaps or extended drought periods, warmer daytime or nighttime average temperatures, or other changes.
- Non-native species. North American forestry has always focused on managing for native species. Where anticipated climate change effects are fairly dramatic, landowners may be interested in experimenting with non-native species (even if only a small half-acre planting) to start collecting data on their suitability for planting on a larger scale if appropriate. Consult with state forestry or Cooperative Extension Service foresters before experimenting with non-natives, to avoid tree species that could be weedy or invasive.
- Seedling survival. Moisture competition, animals, seedling care, and other factors all influence the success of a tree-planting effort. Depending on how climate changes, seedling survival tools, such as tree shelters, herbicides, and shade cards, and how they are used might need to be modified as well. Always monitor plantings and make adjustments as needed (e.g., providing more intensive protection from animal damage). If mortality is high after a few years, and climate seems to be the culprit, consider replanting understocked patches with seedlings from another seed source or species that might survive better given changes in temperatures and moisture conditions.
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