See the link below.
While the report isn't dated, the field study was conducted in 2015. The report is about 25 pages long. A couple of interesting points. 1. The report was limited to Class 1 ebikes, ie pedal assist, no throttle, with assist available up to 20 mph. Most, if not all, purpose built eMTBs fit that description, although some ebikes, generally not marketed as eMTBs, have a top assisted speed of 28 mph and/or have a throttle. There are also ebikes with used added kits that can exceed 28 mph. Most user built ebikes also have a throttle. 2. The IMBA was worried enough about objections from mountain bikers that it those concerns made it into the report. 3. The report call for additional testing. 4. Based on the testing performed, generally there isn't a significant difference between Class 1 eMTBs and MTBs on trail erosion.



https://b.3cdn.net/bikes/c3fe8a28f1a..._g3m6bdt7g.pdf

Conclusion
This study found that the impacts from Class 1 eMTBs and traditional mountain bicycles were
not significantly different, while motorcycles led to much greater soil displacement and erosion.
Observations suggest that Class 1 eMTBs may lead to more displacement under certain trail
conditions. More research is needed before conclusions can be drawn regarding the
environmental impacts of Class 1 eMTBs as compared with traditional mountain bicycles.
Understanding the potential resource impacts of Class 1 eMTBs is a necessary and important
first step for formulating management strategies. Additional research is needed to further assess
the range of environmental and social impacts for successful Class 1 eMTB use on public lands.
IMBA’s initial study suggests that, with conscientious management and attention to trail design,
Class 1 eMTBs may have the potential to offer a beneficial use of public lands with acceptable
impacts.