Spatial dynamics of forest decline: the role of neighbouring trees

. Changes in horizontal structure and the influence of neighbours on tree vitality were studied in a spruce forest under air pollution stress. Five permanent plots along an altitudinal gradient in the Krkonoše Mts., Czech Republic, were monitored for 18 years. Digitized maps of each plot were used for the analysis: the health of each tree, expressed by the defoliation degree was recorded each year, the biometrical characteristics were measured at five‐year intervals. Various indices of neighbourhood competition were used to evaluate the interference with neighbours. The results show that the suppressed trees are most susceptible to other environmental stresses, particularly to the air pollution stress. Similarly, tree damage is more severe in plots near the natural timberline, where the trees are close to their natural environmental limits. The spatial pattern of surviving trees changes towards regularity at a scale of 2–5 m ( K ‐function analysis) when the suppressed trees, usually those with close neighbours, die.