PARENT SESSION
Poster Session 6: Arctic and Alpine Ecology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Radial-growth trends of Pinus uncinata treelines and forests in the Pyrenees indicate a positive response to climate warming.

Camarero, J. Julio^*,1, Batllori, Enric^*,2, Gutiérrez, Emilia^*,2, ¹ Unidad de Recursos Forestales, Zaragoza, Spain² Departament d’Ecologia, Barcelona, Spain

ABSTRACT- Radial growth of trees at alpine treelines is supposed to respond positively to increasing temperatures. However, several studies have not detected positive growth responses to climate warming, or even a recent growth reduction has been described due to increasing drought stress. We assess if the temperature rise recorded at the Pyrenees is inducing a negative growth response at alpine Pinus uncinata treelines and nearby forests. Dendrochronological methods were used to quantify radial-growth changes and to detect growth releases between consecutive 10-yr. periods. Radial-growth trends for the two halves of the 20th century were explored using time-growth correlations. Correlation analyses were applied to quantify the relationships between radial growth and climate (temperature, precipitation). Forests showed the main events of growth release (e.g., 1948-1951, 1986) in similar periods that nearby treelines (e.g. 1945-1948, 1985). Radial-growth releases in older trees (100-300 yrs.) were mainly observed in the 1940s, whereas younger trees (30-100 yrs.) located above the forest showed most releases in the 1980s. These were two of the warmest decades of the past two centuries. Most young trees (71-80%) showed positive trends in radial growth during the last half of the 20th century, but older trees showed a lower frequency of positive trends (10-57 %). Radial growth was positively correlated with November temperature during the year previous to ring formation and with current May temperature, whereas September temperatures of the previous year were negatively correlated with growth. In the easternmost forests, radial growth was negatively correlated with January precipitation and positively correlated with July precipitation during the year the tree-ring formed. We suggest that drought stress may constrain growth in the easternmost forests due to the greater Mediterranean influence in these sites. We found firm evidence of enhanced radial growth of young trees at alpine treelines, where there has been a recent increase in tree density.

Key words: treeline, tree-ring width, Pinus uncinata, Pyrenees