Effects of overstorey dieback on understorey light environment and seedling photosynthesis in Nothofagus solandri var. cliffortioides

Dieback of Nothofagus solandri var. cliffortioides (mountain beech) in the Craigieburn Range associated with Platypus beetle and fungal invasions has produced a forest with a very heterogeneous canopy. The understorey light environment was quantified in six stands of mountain beech experiencing a range of dieback. Not only did the total quantity of light reaching the forest floor increase with a decrease in canopy cover, but the temporal characteristics (duration and frequency) of understorey sun flecks also varied in a regular manner as coverage decreased. The change in light environment due to dieback results in increases in seedling photosynthetic carbon gain. Carbon gain increases because of a direct photosynthetic response (increased light), more favourable light dynamics (longer sunflecks with shorter intervals between), and long-term increase in seedling photosynthetic capacity.