Abstract
Tree growth in boreal regions and at high elevations, where low temperatures limit growth, has generally benefited from recent climate warming. However, since the late 20th century, a reduced sensitivity of tree growth to temperature has been observed, primarily at high-latitude forest sites in the Northern Hemisphere. This phenomenon, termed the divergence problem, has been linked to temperature-induced drought stress and increased competition for resources in densifying stands. Here, we investigate how stand density influences radial growth of European larch (Larix decidua Mill.) in subalpine larch grasslands of the Central-Eastern Alps. Increment cores from 140 larch trees across seven sites were analyzed. Each site comprised a pair of stands with comparable environmental conditions but contrasting management history and stand density: an abandoned larch grassland that developed into a closed stand and a continuously managed larch grassland that remained open. Response function analyses indicated that May-August temperature significantly promoted radial growth in both open and closed stands. However, after 2000, climate warming did not translate into increased basal area increment (BAI). Instead, BAI trends in both managed and abandoned larch grasslands became decoupled from temperature trends, likely reflecting increasing nutrient or water limitation, as suggested by stronger growth declines with increasing stand density. These findings highlight the role of traditional land-use practices by reducing competition among existing trees. We conclude that stand density is a key constraint on larch growth and should be explicitly considered in areas where land-use changes alter stand structure.