Long-Term Effects of Mistletoe Removal on Radial Growth of Semi-Arid Aleppo Pine Forests

Abstract

Mistletoes are hemiparasites that modify how trees cope with drought by impairing the relationships between water, carbon, and nutrients within the tree. Thus, mistletoes endanger the vitality and persistence of trees in drought-prone regions, such as the Mediterranean Basin. Here, we evaluated radial growth patterns and drought sensitivity of Aleppo pine (Pinus halepensis Mill.) trees from which mistletoe was removed ca. two decades ago (MRTs) with control; currently infested trees (MCTs) from a semi-arid region in NE Spain. Growth showed negative trends in both tree classes since the 1980s concurrent with progressive aridification and aggravated by mistletoe infestation, as indicated by the positive effect of mistletoe removal on the growth of MRT trees. Water availability during the previous autumn and winter and current spring and early summer drove growth. Climate–growth correlations were similar between tree classes before treatment, but after mistletoe removal, precipitation became significant in MCT trees but not in MRT trees. Likewise, the impact of drought on growth changed through time: it increased until the late 20th century and then decreased in the MRT trees, which showed higher resistance and resilience against post-treatment droughts. This study provides evidence of the long-term positive effect of mistletoe removal on radial growth in semi-arid pine forests.

Keywords

• drought
• forest management
• Mediterranean region
• <i>Pinus halepensis</i>
• <i>Viscum album</i> spp. <i>austriacum</i>