UC Berkeley experts investigating why millions of trees in California have fallen victim to sudden oak death have figured out where the infestation began: Mount Tamalpais and Santa Cruz.Link.
Scientists also now think the killer organism, which they suspect rode in on nonnative nursery plants, eventually was carried by humans to the two ground zero zones.
It must be acknowledged that for all the good gardeners do, we also bring in diseases and weeds.
Not to mention all the "gardeners" who still use copious amounts of pesticides and fertilizers. Is that even considered gardening anymore? I don't think so.