Radial growth responses to gap creation in large, old Sequoiadendron giganteumYork, Robert A. et al. S. giganteum radial growth response

Questions: Do large, old Sequoiadondron giganteum trees respond to the creation of adjacent canopy gaps? Do other co-occurring tree species and younger S. giganteum adjacent to gaps also respond? What are the likely factors affecting growth responses? Location: Mixed-conifer forests of the southern Sierra Nevada, California, USA. Methods: We measured the growth response of large, old S. giganteum trees (mean DBH5 164 cm; ages estimated 41000 yr) to gap creation by coring trees and comparing growth after gap creation to growth before gap creation. We also measured young Abies concolor, Pinus lambertiana, and young S. giganteum. Gap-adjacent trees were compared with non-adjacent reference trees. Tree rings were analysed for carbon isotope discrimination and for longer-term growth trend correlations with climate. Results: Following gap creation gap-adjacent old S. giganteum grew more than reference trees. Abies concolor trees also exhibited a growth response to gap creation. No response was detected for young S. giganteum or P. lambertiana, although detection power was lower for these groups. There was no difference in carbon isotope discrimination response to gap creation between gap-adjacent and reference trees for old S. giganteum and radial growth was positively correlated with winter precipitation, but not growing season temperature. Conclusion: It is unclear what caused the growth release in old S. giganteum trees, although liberation of below-ground resources following removal of competing vegetation appears to be a significant contributor. Sequoiadondron giganteum, the thirdlongest lived and the largest of all species, remains sensitive to local environmental changes even after canopy emergence. Management activities that reduce vegetation surrounding individual specimen trees can be expected to result in increased vigor of even these very old and large trees.