Growth Response of mature longleaf pine to drought and thinning at the Harrison Experimental Forest in south MississippiThis article is part of a larger document. View the larger document here.
We explored the diameter growth of longleaf pine (Pinus palustris) planted in 1961, during the years following disturbances from Hurricane Katrina (2005) and thinning (2011) at the Harrison Experimental Forest in southern Mississippi. Winds from Hurricane Katrina destroyed 7 percent of the longleaf pine and damaged much more, while the thinning was variable based on existing density, with 29 percent of trees being removed. In April 2017, a total of 180 trees were sampled with an increment borer and analyzed to quantify basal area increment (BAI). After Hurricane Katrina impacted the site in 2005, BAI declined an average of 23 percent during the next 6 years. Immediately after thinning, growth markedly increased in 2012 (50 percent) and 2013 (30 percent). Without any other context, the interannual variation in BAI could be interpreted as being driven primarily by disturbance. However, the site had experienced prolonged drought during the years following Hurricane Katrina which was eventually alleviated in 2012. Using a suite of climate variables (monthly precipitation, air temperature, solar radiation, and vapor pressure deficit), we found that 79 percent of the annual variation in BAI could be explained by the amount of precipitation during the growing season (partial R2 = 0.59) and warm winter nights in January (partial R2 = 0.05) and February (partial R2 = 0.15). The 50-year-old longleaf pine trees were unresponsive to thinning, and variation in interannual growth rates was primarily dependent on climate. It seems the trees of that age have limited ability to exploit additional light, moisture, and nutrient resources. If the goal of thinning is to increase the growth rate of residual trees, it should be implemented at an earlier age or perhaps be combined with fertilization