Biotic factor that contributes to oak decline

Several Phytophthora species are now considered to be involved in the oak decline (for both Quercus robur and Q. petraea) that is reported as widespread across central and northern Europe. A number of studies have shown that decline is accelerated or exacerbated when Phytophthoras are present.

In England, sites with declining oaks have frequencies of Phytophthora which are three times greater than those found on sites where oaks are free from visible signs of dieback or decline.

Studies across Europe also show that one of the most frequently found Phytophthoras associated with oak is Phytophthora quercina, and it is capable of causing extensive damage to the fine roots of oak on acid soils with a mesic water regime (i.e., in the absence of flooding).