Salt-wind induced wave regeneration in coastal pine forests in New Zealand

Abstract

Strong onshore winds and airborne sea salt can gradually defoliate trees at the exposed margin of temperate pine stands in New Zealand and induce a slowly moving front of dieback and regeneration. Overcrowded mature stands are vulnerable to crown abrasion: abrasion affects trees 20 m ahead of the dieback front; suppressed trees 12 m ahead die before the front reaches them. At the stand margin, trees die from abrasion and salt wind induced dieback. The dieback zone lets sunlight enter the stand; light-demanding pine seedlings establish, but a gradient of increasing litter depth from the dieback front and summer dryness restrict successful seedling establishment to a narrow zone that moves parallel with the dieback front and 11-13 m ahead of it. Further seedlings establish for 4-10 years before the juveniles form a closed canopy; competing vegetation is partly suppressed by infrequent cattle browsing. Regenerating juvenile maritime pine (Pinus pinaster Ait.), show a strict age-related gradation from the dieback front and indicate that wind and salt deposition have been constant for 30 years. Stands further from the sea, with lower stocking rates and other pine species, did not have a clear-cut regeneration zone, because there were no strong gradients of litter depth and light intensity.