A four-year study evaluated Missouri floodplains performance of RPM seedlings. Researchers studied mast production, growth and early field performance. Natural disturbances affected outcomes as expected.
This article explains which natural factors impact native plant growth. The Smoky Waters/Plowboy Bend study also shows other forces which affect the growth of oaks.
Flooding and Rabbit Impact on Oak Growth
In two of the four years (2001, 2002), the study site at Smoky Waters flooded. Also, every winter after the first year, cottontail rabbits girdled and shoot clipped oak seedlings and oak sprouts. Both factors affected oak survival and growth. The amount and severity of rabbit damage to planted oaks varied considerably between the cover crop treatments (i.e., redtop grass versus natural vegetation fields).
Rabbit Density and Associated Damage
In the natural vegetation fields at the study site, there were more rabbits. Further, winter forbs cover promoted higher rabbit densities than in the redtop grass fields. The difference was significant, with 7.4 rabbits per hectare in the former environment and 2.5 rabbits per hectare in the latter.
The difference can be attributed to the amount of cover from predators provided by each type of grass. For example, in the winter, the dead tops of forbs and clumps of Johnsongrass remained upright, providing cover almost one meter in height. In contrast, the redtop grass was matted down to only 0.20 meters. This left rabbits exposed to predators in the area.
Rabbits with more cover caused damage to most of the seedlings each winter. They clipped the shoots of all bareroot seedlings and severely girdled 90% or more of the RPM seedlings that were in the natural vegetation fields by the end of the second winter. For comparison, only 8% of bareroot seedlings and 26% of RPM seedlings in the redtop grass field at Plowboy Bend Conservation Area had herbivory damage from rabbits.
The data reveals direct correlation between cover and severity of seedling damage.
Flooding was also a factor in healthy oak growth and survival.
In 2001 and 2002, the Smoky Waters site experienced flooding for up to three weeks in June. To prevent future inundation, researchers used soil mounding. Forrest Keeling developed this technique, called the Walk-A-Way system. This improved drainage and reduced effects of flooding on the trees. This also helped improve soil environments for root growth. Improved drainage also yielded higher growth and survival of bareroot and RPM seedlings.
The results of the study revealed various environmental disturbances can inhibit seedling growth. It also showed these disturbances impact both RPM and bareroot seedlings.
Rabbit damage was greater when there was adequate cover from predators.
RPM seedlings proved to have more resilience to flooding than their bareroot counterparts. RPM seedlings were also impacted by the effects of the flood. Improving drainage helped mitigate some of these issues. It was an effective remedy during years when flooding was most prevalent. More research may show drainage impact on different types of soils.