Incomplete Stand-scale Disturbances

Incomplete stand-scale disturbances are smaller in scale than stand replacing events, but impact larger spatial areas than canopy gaps. Incomplete stand-scale events may be caused by ice storms, insect outbreaks, pathogens, or high wind events, among other mechanisms. Not all trees in the disturbed area are killed by events of this scale. For most incomplete stand-scale events, residual trees are left both in the overstory and understory. These disturbances allow for an increase in growing space as well as availability and quality of light, water, and nutrients. Residual individuals in the understory are often released following incomplete stand-scale events because some overstory trees are removed. Events of this scale may provide the opportunity for seeds either in the seedbed at the time of the disturbance, or seeds that arrive on site immediately following the disturbance to germinate and become established. Some incomplete-scale disturbances may free enough growing space and resources to allow germinants and sprouts to reach dominant positions in the stand before canopy closure, especially for pioneer species such as shortleaf pine, Virginia pine, sweetgum, and yellow-poplar. Fast growing, pioneer species may be able to occupy the newly available growing space before they are outcompeted by other individuals. Seed germination of some species is initiated by disturbances, such as fire or light regime changes after partial removal of the canopy. Incomplete stand-scale disturbances do not always create conditions required for the establishment of newly colonized individuals, and understory trees present at the time of the disturbance are often recruited to the canopy.