Influences of planting stocktype and simulated browse on northern red oak seedling development
Artificial regeneration represents a potential means to augment natural forest regeneration. Success of tree plantings, however, is often negatively affected by herbivory from high populations of white-tailed deer ( Odocoileus virginianus Zimmerman). Container seedlings may have higher resistance to stress and herbivory than conventional bare-root stock, thereby improving regeneration success of planted oaks. In the first study (CHAPTER 2), northern red oak (Quercus rubra L.) seedlings of four stocktypes (1+0 bare-root and 164-ml, 336-ml, and 520-ml containers) were planted at three reforestation sites across Indiana and subjected to three simulated browse treatments (control, dormant browsed, and summer browsed). The second study (CHAPTER 3) further investigated the physiological responses of 1+0 bare-root and 164 ml container seedlings subjected to the same simulated browse treatments as in CHAPTER 2. Container seedlings exhibited higher relative growth rates than bare-root seedlings on all sites. At one site, control 336 ml container seedlings had relative height growth of 165% in the first year and 144% in the second year, compared to 30% for the first year and 39% in the second year for bare-root seedlings. Summer-browsed seedlings had negligible height growth on all sites for all stocktypes, and survival of summer-browsed seedlings for all stocktypes was reduced by 23% and 31% at two of the sites. Container seedlings had greater percent increases in biomass and total non-structural carbohydrates than bareroot seedlings. Container seedlings had consistently higher gas exchange (i.e., rates of transpiration, stomatal conductance, and photosynthesis) than bare-root seedlings, but lower whole tree photosynthetic assimilation rates due to reduced leaf areas. Summer browsed seedlings had significantly higher gas exchange for both stocktypes, but whole tree photosynthetic rates did not differ across browse treatments. Summer browsed seedlings had lower percent increases in biomass and total non-structural carbohydrates. Results from these two studies suggest that container seedlings are more resistant to transplant stress, likely associated with more fibrous root systems. Although summer browsing increased gas exchange, it did not compensate for the decreased leaf area, which was illustrated by the significantly lower growth of these seedlings. Unlike summer browse, dormant browse did not significantly affect growth or physiology of seedlings. These results illustrate the potential for container seedlings to help improve oak regeneration success, and the negative impacts of summer browse.
Jacobs, Purdue University.
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