They could not have made Bladesover they cannot replace it; they just happen to break out over it—saprophytically.
saprophyte sap·ro·phyte (sāp'rə-fīt')
An organism, especially a fungus or bacterium, that grows on and derives its nourishment from dead or decaying organic matter.
An organism, especially a fungus or bacterium, that lives on and gets its nourishment from dead organisms or decaying organic material. Saprophytes recycle organic material in the soil, breaking it down into in simpler compounds that can be taken up by other organisms.
saprophytic adjective (sāp'rə-fĭt'ĭk)