Increment core analysis of declining Norway maples, acer platanoides

A regression model was able to predict decline classes on the basis of crown density, small dead limbs and crown shape. The filtering of increment core data revealed three growth trends. One growth trend, termed responsive, generally followed fluctuations in climate. A second, termed nonresponsive, decreased over the time regardless of climatic fluctuations. A less common type, intermediate, showed no change in growth over the 20-year study period. The responsive growth trend was associated with the most healthy appearing trees. This early stage of decline was generally found in trees which had been subjected to root injuries following a drought stress period. Trees with advanced decline today had significantly reduced growth rates 15–20 years ago, indicating that Norway maple decline is a long-term multiple stress process.