Adaptive responses to thinning: growth and sensitivity to hydric and thermal stress in four widely planted pine species

In seasonally dry areas, thinning has been proposed as a measure of adaptive forest management to enhance growth and increase drought resistance and resilience. However, long-term growth data on different tree species and site conditions remain scarce for investigating the interactions between thinning and climatic stressors. To fill that research gap, we examined radial growth and its sensitivity to climatic conditions in 19 experimental sites of the four most planted pine species in Spain (Pinus halepensis, P. pinaster, P. nigra, and P. sylvestris). We also assessed the influence of thinning at varying intensities on growth responsiveness to climate stress. To quantify how climate impacts growth, we used seasonal temperature and water balance anomalies expressed as temperature and drought indices.

Thinning consistently enhanced tree growth for 8–20 years, with the magnitude of this effect modulated by hydric conditions. While drought reduced growth, wetter conditions promoted it—particularly in mesic species such as P. sylvestris and P. nigra. Importantly, thinning increased trees’ sensitivity to climate: thinned stands—especially those of P. halepensis and P. sylvestris—became more responsive to water availability, exhibiting stronger growth increases during wet years following thinning.

Temperature also played a key role, with high spring and autumn temperature anomalies enhancing growth, comparable in magnitude to favorable hydric conditions. However, in the post-thinning period, spring temperature effects were lower than prior to thinning in species from xeric sites (P. halepensis and P. pinaster). High summer temperature anomalies negatively affected growth, though more weakly and only in species from xeric sites. Thinning, however, aggravated the negative effects of summer temperatures on growth in xeric sites and induced negative effects on growth in mesic sites.

These findings highlight the species-specific interactions between thinning, water availability, and temperature stress, emphasizing the need for tailored, species- and site-specific adaptive management strategies of planted forests in response to climate change.