PARENT SESSION
Oral Session # 93: Vegetation Change and Response.
Presiding: B Parry Hecht
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 105.
Impact of saline intrusion upon growth of loblolly pines, Blackwater National Wildlife Refuge, Maryland USA.
Yanosky, Thomas*,1, Kroes, Daniel1, 1 US Geological Survey, Reston, VA, USA
ABSTRACT- Rings of loblolly pines (Pinus taeda L.) were studied to determine the effects of saline intrusion upon radial growth and survivability within parts of the Blackwater National Wildlife Refuge, and to estimate the approximate onset of intrusion. The sparse forest is even-aged and began to grow about 1940. Increment cores were collected at breast height from 24 living trees along an intrusion gradient; cross sections also were cut from 11 dead trees. Surface elevations were determined near the trunk of each pine. Each ring was crossdated, measured to the nearest 0.01 mm, and converted to area (in cm2). Mean-annual sensitivity (MAS) values (a measure of ring-to-ring variability and thus of growth responses to environmental variables) of all 35 trees ranged from 0.18 to 0.29 for 13 unimpacted trees, and from 0.34 to 0.72 for 22 impacted living and dead trees. MAS values for unimpacted trees from 1960-1980 generally were greater or did not differ from those from 1980-present; for most impacted trees, however, MAS values were significantly greater after 1980 than during 1960-1980, suggesting that a variable other than climate (presumably saline intrusion) became an important factor controlling tree growth after 1980. Although the radial growth of all study trees declined during droughts of the mid 1990s, unimpacted trees subsequently resumed prior growth trajectories and continue to grow vigorously at present; impacted living trees, however, have not recovered and growth since the mid 1990s remains suppressed. The 11 dead trees died between 1994 and 2002 following declines in 2-7 consecutive years during which ring areas were less than approximately 1.0 cm2. Based on these findings, it seems likely that surviving trees will die in the near future as the forest continues to convert to marshland.
Key words: tree growth, saline intrusion, sea level rise, tree rings