Dendrochronology of pedunculate oak (Quercus robur L.) in an old-growth pollarded woodland in northern Spain: establishment patterns and the management history

摘要

Long-term patterns of tree establishment and past management practices, in an old-growth pollarded woodland in northern Spain, were studied using dendrochronological techniques. Age distribution revealed three main cohorts of pedunculate oak (Quercusrobur L.): < 50 years, 150-200 years old, and 250-500 years old. Juveniles and trees 200-299 years were found to be clumped and spatially segregated from older trees. Oaks older than 300 years showed a random spatial distribution. Mean pollarding intervals had increased through time, and the mean number of suppressions per year had decreased significantly. Pollarding frequency and intensity had decreased since 1917 in mature trees, and since 1905 in old-growths, suggesting a decline of the pollarding practice in the early 20th century. A delay of 6 years in growth releases, with respect to growth suppressions, was common. This resulted from both strong growth recovery after pollarding, and the release of growing space in the canopy. Mature oaks mainlyshowed 1-3 pollarding signals, while in old-growths between 4—7 growth suppressions per tree were more frequent. In 1774, 1792, 1806, 1839 and 1859, small groups of trees and scattered trees were pollarded, while in 1905 a generalised reduction of treegrowth was noted. The results obtained from this study have significant connotations regarding the preservation and management of formerly pollarded woodlands.