Response of Pine Trees to Chlorine in the Atmosphere

"Three species of pine trees--Pinus echinata, P. elliottii, and P. taeda-- were exposed to various time-concentration doses of atmospheric chlorine in an experimental chamber. The needles of all species were visibly injured by a 3-hour fumigation at 1.00 ppm chlorine. As the gas concentration was increased, damage to the needles became more extensive, but there was no tendency toward defoliation. Even when damage encompassed almost the entire complement of needles, the shoot was not killed, as evidenced by the subsequent appearance of new growth. The presence of moisture on the needles during chlorine exposures did not intensify the tissue damage as it does during sulfur dioxide and hydrogen fluoride fumigations. When pine trees in a hardened condition were exposed to chlorine they were less sensitive than those in an actively growing condition. The chloride content of pine needles generally increased following a chlorine fumigation, but the increment was proportional neither to the level of fumigation, nor the extent of damage." [Abstract]