Timber Stand Improvement in its most elemental form is a forestry management practice intended to remove trees with less potential for timber production so that the remainder can achieve greater height, width, and straightness, as well as spurred growth. In larger more aggressive contexts this may be referred to as pre-commercial thinning. In the context of savannas, a grassland ecosystem with scatterings of oak, non-oak tree species are removed to increase sunlight penetration to the ground floor. Without this sunlight penetration the grassland species die off and succession leads to woodland characteristics and ultimately the replacement of oaks with other tree species. Maintenance of savannas is important since many animal species are adapted to this now extremely rare ecosystem. It is estimated that in Wisconsin only 0.01% of the prairies present at the time of settlement remain, and even a much smaller percentage of the origianl savannas.