Growing mushrooms on wood versus oats (or other grain substrates) can make a difference in terms of nutritional content, medicinal quality, and environmental sustainability. Here are reasons why one might prefer wood-grown mushrooms:

1. Natural Habitat: Many medicinal mushrooms, especially species like Reishi and Maitake, naturally grow on hardwood trees in the wild. Growing them on wood replicates their natural environment, which can lead to a product that's more true to its wild counterpart in terms of nutrient and medicinal compound profiles.

2. Medicinal Compounds: Some studies suggest that mushrooms grown on wood may have higher concentrations of beneficial compounds, such as beta-glucans and triterpenes. This might be due to the complex compounds present in wood, which mushrooms break down, absorbing beneficial nutrients in the process.

3. Environmental Sustainability: Using logs or wood chips can be more sustainable, especially if sourced from local tree thinning or sustainable forestry practices. In contrast, grain substrates often come from large-scale agricultural processes that might be less environmentally friendly.

4. Fewer Contaminants: Wood, especially when sourced sustainably and without chemicals, can lead to fewer contaminants in the final mushroom product. Grains, on the other hand, might be treated with pesticides or other chemicals unless they're specifically organic.