Red Maple: Can this native new weed of the temperate forest make for good mushroom wood?

Red Maple is a very successful native tree that appears to be on the move, increasing its predominance across the Great Lakes states and Northeast. Also known as swamp, water or soft maple, it is tolerant to both very wet and very dry sites and everything in-between. Whether the reason for the invasive quality is from decreases in fire frequency, current forestry practices or climate change, there is a worry that Red Maple is replacing regeneration of high value oaks, chestnut and sugar maple. For the mushroom grower, red maple has some great qualities. Stumps sprout in profusion, often growing straight with multiple stems and is very plentiful. It serves as a substrate for Shiitake mushrooms, but its profitability to mushroom growers has been variable at best. At F&FP we have always believed that if we can make it grow a little it can be tweaked to make it grow better. In 2015 Field & Forest Products (FFP) and Misty Dawn Farms (MDF) teamed up on a two-year research project investigating the use of Red Maple for Shiitake mushroom production.

The short answer is Red Maple is a useful mushroom wood species if you cut in spring during sap flow, use larger diameters (5" in diameter and coarse bark) and let it age 4 weeks prior to inoculation. For more information about the study, see below.

1) Does the month in which the logs are cut make a difference on log success?

Normally we say that logs should ideally be cut during the dormant season (from approximately 1/3 leaf color change in the fall, anytime through winter up until bud swell in the spring). Logs cut during this time typically hold onto their bark longer and are less prone to contamination by other competing fungi. To test whether this is the case with Red Maple, we inoculated over 20 logs every month in a one year period with the "Night Velvet" shiitake mushroom strain and incubated them indoors at 60-70° F with 85-90% relative humidity. Mushroom production was stimulated by force fruiting logs (soaking logs in cold water for 24hrs) after 11 months incubation time, and then mushroom yield was taken for each log. We found that March logs cut during sap flow produced the highest mushroom yields and were the most successful compared to logs cut in all other months of the year. Off all the logs that fruited, larger diameter logs with thicker, coarser bark were more successful than smaller logs with smooth bark.

You can cut Red Maple when the buds are anywhere between these two stages

2) Does the amount of time between cutting Red Maple logs and inoculating influence log success?

Typically shiitake logs are cut then allowed to sit for a minimum of two weeks prior to inoculation. This time allows for cellular dieback in the log and subsequent dampening of the log's defense system against fungal invasion. Shiitake is a saprophytic fungus that invades and consumes only dead organic matter. The weedy nature of Red Maple means these logs are more prone to re-sprouting (Figure 1). This livelihood means that the log is still capable of fighting against fungal colonization and really reduces mushroom log success. To test this, we inoculated logs either 2 weeks or 4 months after cutting. We found that many of our logs inoculated after only 2 weeks rest period struggled with successful spawn run. Logs that rested four months prior to inoculating were far more successful and productive. This indicates that more than two weeks resting before inoculation is necessary.

Figure 1. The central log has re-sprouted indicating the log is still alive and capable of fighting off shiitake invasion (shown by the lack of spawn run and mycelium on the end of the log).

3) Is Red Maple a viable wood type for commercial shiitake production?

Many of the red maple logs inoculated only two weeks after felling were only moderately successful. Logs cut and inoculated four months later were far more productive yielding up to 2.3lbs shiitake/log. Unfortunately, disease presence was considerably higher in the Red Maple logs compared to other wood species used for shiitake cultivation (Red Oak, White Oak, Sugar Maple, Aspen) managed similarly.

Results from the red maple logs were compared to standard shiitake logs inoculated and managed under the same conditions. Average yields per log from other wood types during for the first fruiting year include Sugar Maple (0.68lbs/log), Red Oak (0.96lbs/log), White Oak (1.01lbs/log), Aspen (0.89lbs/log), and are comparable to Red Maple cut in December (0.80lbs/log) and Red Maple cut in February (1.02lbs/log) (Figure 2).

Figure 2. Results from the ideal larger-sized red maple logs were compared to standard shiitake logs inoculated and managed under the same conditions. NOTE: These results are from the first year of fruiting only and do not necessarily represent the overall capability of each wood type over the life of the logs. Red maple and similar softer hardwood species tend to have shorter fruiting lives than oak logs which remain the recommended log type for shiitake cultivation.

Conclusion

By selecting for log parameters (coarse bark, >5.5"/14cm diameter), allowing sufficient rest time between felling and inoculation, and controlling for competing fungal disease, red maple logs are capable of producing yields comparable to other wood species commonly used in commercial cultivation of shiitake such as Sugar Maple and Oak species.

There are abundant advantages to being able to utilize Red Maple over standard wood species including cost per log ($2.00 versus $3.00, respectively), increased availability and abundance of Red Maple, increased speed of stand regeneration after wood harvest, faster spawn run in a softer harder, and public willingness to harvest weedy wood species.

Disadvantages - the weedy nature of Red Maple means these logs are more prone to re-sprouting (Figure 1). This livelihood means that the log is still capable of fighting against fungal colonization. To reduce these chances, we recommend letting the logs rest at least 4 weeks (optimal time still being determined) from cutting until inoculation. Secondly, because Red Maple is a softer hard wood, the average life of the log is shorter than hardwoods typically used for shiitake cultivation. Lastly, softer hardwoods like Red Maple are more prone to contamination by competing fungi. Altering log management to reduce these risks may be necessary.

We at Field and Forest Products are constantly striving to improve and clarify the standards for shiitake cultivation to improve success. To do so, we are working on a follow-up to this study examining timing of cut and optimal length of rest time to increase productivity comparing Sugar Maple and Red Maple. We also believe this data will be transferable to other invasive soft maple species such as Norway Maple (Acer platanoides). We will share those results with you in the future!

This two-year research project was funded by the North Central Region of Sustainable Agriculture Research & Education (SARE) program. You can read the full report here on their website: https://projects.sare.org/sare_project/fnc15-1021/