Needle and stem injuries of Picea rubens (Pinaceae) in the Adirondack Mountains, USA

During the past several decades, red spruce (Picea rubens) in the northeastern US has undergone a large decline in both number and vigor. The purpose of this study was to determine quantitative relationships between visible and histological characteristics of both stems and needles of first-year shoots of red spruce trees from four high elevation mountain sites in the Adirondack Mountains, New York, before, during, and after an overwintering period, 1994-1995. Most shoot elongation was completed and phellem formation began by September 1994. In samples of November/December 1994, needles of current-year stems exhibited between 3 and 50% dead mesophyll cells, there was a nearly full complement of needles and 1.2-2.0 phellem layers were present within current-year stems. Anatomical injuries to mesophyll cells of autumn (November/December) 1994 needle samples were identical to ozone injuries to conifers from published reports. None of the stem and needle samples in the forest (in situ) and none of the preserved stem and needle samples from 1994 showed any visible symptoms of injury. However, preserved samples of needles and stems from March and May 1995 exhibited extensive visible injuries. For March and May samples, most visible injuries on needles were located near shoot terminals and most visible injuries to stems occurred near needle bases. For March needle samples between 38 and 94% of all mesophyll cells were dead. By May 1995, only about 66% of all needles were present on shoots. The mean numbers of phellem layers were 3.6 and 4.0, for March and May 1995 samples, respectively. In March and May samples, percentages of discolored needles were negatively correlated with numbers of phellem layers. Stem segments exhibited between two and six localized areas of internal tissue injury per twig. The two to six areas of injury in stem segments may have resulted because only 1.2-2.0 (mean = 1.6) phellem layers were present in November/December samples. These extensive injuries occurred in needles and stems during a winter in which temperatures were not unusual for the region. These results suggest that visible injuries to foliage of red spruce so predominant during and after winter may occur prior to overwintering and that the overall damages may be attributed to cellular injuries that are not visible in needles and/or stems.