yew is a native evergreen tree that grows best in the high humidity of mild oceanic climates, which makes killarney a very suitable location. the soil in the wood is mostly thin and in many places the trees are rooted to fissures in the bare limestone. yew has an extensive horizontal root system. in the killarney woods, the roots spread out over the rock surface and penetrate deeply into fissures in the limestone. the wood has a low canopy of 6–14 m (20–46 ft). yew's extreme tolerance of the dense shade its canopy creates has allowed it to out compete other species to create the pure yew woodland present today. this dense shade prevents flowering plants from establishing themselves in these woods and prevents the herb layer from developing. bryophytes are however abundant and thrive in the humid and cool conditions. in some parts of the wood there are continuous dense blankets of moss that can be up to deep. the moss species present are primarily "thamnium alopecurum" with "eurhynchium striatum" and "thuidium tamariscinum".