The Combined Influences of Canopy Openness, Browsing Protection, and Low Intensity Fire on the Natural Regeneration of Oak in Southern Sweden

Abstract: Whilst oak was historically prevalent in the landscape of temperate Europe, changes in the disturbance regime of forests have led to limited regeneration across its distribution. In this study, the fire oak hypothesis is tested to assess the tolerance of Quercus robur and Quercus petraea recruits (seedlings and saplings) to a low intensity burn, and how this response may differ depending on the presence of browsing and canopy openness. In five oak dominated forests, the use of a replicated field experiment, with a randomized block design revealed distinct differences in the conditions that favour the regeneration of oak. After the initially raised mortality of recruits in a burning treatment in the first two years, low levels of mortality were observed across treatments. For unburned recruits, growth was largely absent with lower light conditions, whilst under a canopy gap, a dramatic increase in growth was observed, heavily favouring the larger recruits. Most recruits survived a burning treatment by resprouting, after the above ground portion of the tree was killed (top-kill). However, the largest recruits measured (≈25 mm diameter) were found to survive without top-kill, but only in conjunction with a canopy gap. For burned recruits, growth was dramatically higher under a canopy gap, however, the elevated levels of browsing with this treatment point to benefits from fencing recruits. The results of this experiment highlight the importance of different treatment conditions on the successful regeneration of oak and suggest low intensity burns may allow the successful natural regeneration of oak, if complemented with browsing protection, and improved light conditions.