I like to encourage moss on the substrate.
The bull did not delicate far from this post. Most Yamadori from the mountains are found growing in a pile of their own needles and duff.
I think it depends on air circulation bad air circulation with outdoor mature pines might invite unwanted types of fungi that could transfer from the ground cover to the tree but overall I think its an evolutionary tactic from the trees to minimize competition from grass and weeds while continuously creating fertile ground for mycorrhizal fungi that the tree forms a symptomatic relationship with. My knowledge comes only from conservation of pines in the wild not in bonsai pot culture. In pot culture I imagine you would like to keep things fertile
I saw a semi commercial operation out here in the countryside. they grow them from seed in a plastic green house potted in crappy clay topsoil/sand mix and mulch with pine needles. I found it to be bizarre so I asked why and they told me to increase acidity. Anyway the jade I bought from them didnt have any needles on top but was planted in a tiny brick of cracked up clay (didnt look good but I wanted to help them out). Hopefully it will have time to repot it soon, maybe make a bonsai
and also the differences in climate and many other factors that can make our pot grown plants more or less susceptible to pest and disease.
Making horticultural decisions is often about risk assessment.
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