Longleaf pine (Pinus palustris, LLP) forests in the southeastern United States have lost 96% of the original 37 million ha due to unsustainable harvest, fragmentation, and conversion to other land uses and vegetation types. Since 2013, more than 100 million LLP seedlings have been produced annually in southern nurseries with 90% of these seedlings grown as container stock. Sapling toppling in high sustained winds is sighted in LLP plantations originated from container stock. Two companion experiments were established in December, 2009 to evaluate the effect of planting stock type on LLP field performance and root system architecture. The Palustris Experimental Forest (PEF) site in Louisiana has Malbis, Ruston, and Smithdale sandy loam and the Escambia Experimental Forest (EEF) site in Alabama has Troup fine sand and Wagram loamy sand. Six planting stock types were tested: direct seeded, bareroot (BR), SuperblockTM with cavity volumes of 108 ml (M) and 164 ml (L), and CopperblockTM with copper hydroxide lined cavities of comparable volumes to M (Cu-M) and L (Cu-L). Seedlings grown in 120 ml Jiffy PelletTM (JP) were tested at the PEF only. The study is a randomized complete block design with 4 blocks. Each plot has 10 rows by 10 trees planted at a 2- by 2-m spacing.
Results/Conclusions
The direct seeded treatment was deleted because all sown seeds disappeared within one week of sowing. Both study sites experienced prolonged, severe drought in 2010 and 2011. Seedling mortality occurred mainly in the first year. Eighty-four and 54% of BR seedlings died on the PEF and EEF sites, respectively. Containerized seedlings had much better survival compared to the BR seedlings. Between 12 and 22% of containerized seedlings died, independent of cavity volume or Cu treatment. The JP seedlings had 43% mortality in year 1. Two years after planting, 66 to 77% and 8 to 26% of seedlings emerged from the grass stage (> 12 cm in height) on EEF and PEF, respectively. In general, the PEF seedlings lagged in height and diameter growth by one year compared to the EEF seedlings. Two seedlings were randomly selected from each plot of each treatment for root excavation in the fifth year. The Cu seedlings generally had less lateral root deformity than the non-Cu seedlings indicating less potential root system failure in severe wind.