Historically, most timber harvesting in New Hampshire occurred during the winter.
Before logging machinery was invented, trees were felled with an ax and moved, or skid, by a team of draft animals, either horses or oxen. The friction-less, snow-blanketed ground made it easier for the animals to drag the logs to the “rollways” along the riverbanks. When the river ice thawed in late spring, the meltwaters would carry the rafts of logs to the mills.
Snow cover protects the undergrowth from being damaged, insulates the frozen ground, keeping it solid until mud season, and protects the soil from compaction and erosion. As more and more logging machinery was introduced to the region, conducting a timber harvest in winter became the most reliable way to minimize soil compaction from the heavy equipment.
With our winters warming due to climate change, however, temperature and precipitation fluctuations have decreased the longevity of the once reliable snowpack and frozen ground.
Over the last 50 years, New England’s average air temperature in winter has risen by more than 3° F, more than any other season. An increase of a few degrees does not sound like much, but it can greatly influence whether it rains or snows. Overall, researchers are seeing our winters trending warmer with less snowpack and fewer days with frozen ground, resulting in a shorter season that’s suitable for harvesting. The variability of our winters year to year has also increased, leading to increased uncertainty.
For example, in December 2024, New Hampshire saw a well-developed snowpack disappear following heavy rainstorms. This phenomenon, called a rain-on-snow event, has become increasingly more common as the climate warms.
Rain-on-snow events accelerate the melting of the snowpack, which in turn can rapidly thaw the soil. If proper measures are not in place, this influx of rainwater may be washed down the skid trails, causing gully erosion in the tracks from the logging machinery and permanently scarring the landscape.
Additionally, the increased flow of water in streams can cause flooding at trail and road crossings, or in extreme cases, wash them away. Early winter rain-on-snow events, as seen this year, can delay operations until the ground freezes again. In the case of late winter rain-on-snow events, an operation may be halted until the spring mud season is over or until the following winter, as was the case for some of the Forest Society’s 2024 harvests, which are being completed this winter.
Currently, the Mount Washington Observatory is researching the impacts of these events within the high-elevation alpine zone and has identified that the number of occurrences of rain-on-snow events continues to increase, with annual fluctuations. These weather patterns not only impact the alpine zone and lower elevations, but they have also caused a shift in winter logging operations, often leading to the pause or even termination of harvests.
To mitigate the soil compaction and erosion associated with rain-on-snow events and thaws, foresters and loggers employ best management practices. Some examples include ensuring skid trails freeze better at the start of an operation by removing the insulating leaf duff and snow, allowing the trails to solidify and stabilize. Furthermore, the slash from cut trees can be used to protect the soil on skid trails by acting as a barrier between the logging equipment and the ground beneath. In wet areas, where the ground will not reliably freeze, logs can be laid perpendicularly across the trail, utilizing a technique called “corduroy” that prevents logging equipment from impacting the landscape and avoiding direct contact with the soil. Operators also create dips in the skid trails, called water bars, to divert water off the trails and prevent runoff from eroding soil and puddling.
While equipment choice plays an important role in every winter operation, each method of harvesting has its own advantages and disadvantages while operating on sensitive sites. Regardless of the equipment choice, foresters and loggers should work to install preventative measures prior to rain-on-snow events. Forest products markets have shifted significantly over the past 10 years, with markets for low-grade wood and chips becoming scarcer. This has allowed slash and low-grade logs to be utilized in trail infrastructure to minimize erosion.
Foresters and loggers are continuing to adapt to our unpredictable winters by employing best management practices, utilizing slash and low-grade wood to build resilient trails, and writing plans that have contingencies for changes in the weather.
Only time will tell when a new form of adaptation will have to be tested and rolled out to mitigate the effects of our changing climate, but rest assured, the Forest Society will be at the forefront of these practices for generations to come.