Tree Health

The physiological state of a tree characterised by robust cellular function, structural integrity, and resilience against environmental stresses, pests, and pathogens.

Tree health represents the holistic physiological and structural state that allows a tree to fulfill its biological functions, from photosynthesis to mechanical support. It is governed by a delicate balance between internal vitality and external pressures, most notably tree pests and pathogens.

In a balanced forest ecosystem, native insects, fungi, and bacteria act as natural evolutionary drivers, clearing weakened individuals and creating vital deadwood niches. However, anthropogenic factors—including the globalisation of trade and climate change—have accelerated the spread of devastating non-native pathogens, such as ash dieback and acute oak decline, alongside destructive pests like the oak processionary moth. Because these organisms frequently encounter host species with no evolutionary immunity, they pose existential threats to entire forest populations.

Managing tree health requires moving beyond individual treatments to landscape-scale silvicultural strategies. Cultivating multi-species, uneven-aged woodlands fosters natural ecological resilience, preventing single-species outbreaks from causing catastrophic canopy collapse while securing the forest's long-term environmental and economic viability.

Tree and Woodland managers should adopt a tree health plan.