Scots pine needle longevity and gradation of needle shedding along pollution gradients

Scots pine (Pinus sylvestris L.) needle longevity and gradation of needle s hedding (the time span with 90-10% needle survival) in the middle and north ern boreal vegetation zones were studied. The duration of the first half of gradual shedding (the time span with 90-50% needle survival) was of specia l interest, because it represents the number of youngest cohorts that have lost needle biomass. Branches of adult trees along transects with an air po llution gradient were sampled. Mean longevity (the sum of survival proporti ons) decreased 15-40% as pollution sources were approached. To rank or comp are the values of a single needle age parameter, we prefer to use mean long evity. It gives an estimate of the whole needle biomass, and it was the par ameter with the least variation. The first half of gradual shedding proved to be a valid indicator of changes in needle age structure. The most marked variation in needle age structure was seen in slightly polluted areas, whi ch continued to pose a risk of acute pollution injuries. This study confirm ed the feasibility of the needle age structure of branch samples as an obje ctive and reliable vitality indicator for Scots pine.