Last week I examined and re-photographed a hillside of sick oaks in Toro Canyon, near Santa Barbara, that received fire mimicry treatment in January of 2009. By January of 2010 the oaks were responding very well (see Toro Canyon oaks). Due to the good results the property owner decided to hold off on additional treatments, despite my recommendations to treat the oaks again.
The results below indicate that the oaks showed very good improvement up to two years following the treatment, but by the third year, many of the oaks began showing a marked decline in health, due, I believe, to the lack of any follow up treatments. As can be seen in the photos, the oaks after three years are still notably healthier than they were initially, but many have shown a decline in canopy health compared to one year ago. Other property owners have similarly been fooled into thinking that, given the good initial response of their trees, further treatments were no longer necessary.
The lesson here is that a single fire mimicry treatment is not sufficient to reverse the many years of poor soil fertility and oak health.
However, some oaks on the same property (below) have remaining healthy in appearance after three years despite receiving only one treatment: