Uniform drought and warming responses in Pinus nigra provenances despite specific overall performances

Abstract

Climate extremes are expected to increase in frequency and magnitude as a consequence of global warming, threatening the functioning, services and goods of forest ecosystems.The introduction of species from drier and warmer climates is one option that is discussed to adapt forest ecosystems to these adverse effects of climate change. The (sub)-mediterranean Pinus nigra is a potential candidate for such assisted migration, especially for dry sites in Central Europe. The high genetic diversity within this species and thus the potential differences in adaptive capacity, however, makes it necessary to assess the response of P. nigra provenances to climatic extremes and identify suitable populations or ecotypes which are better adapted to projected future climates than indigenous species.Here, we tested juvenile plants of 6 provenances of P. nigra for their response to different climate change scenarios (42-days drought and warming by 1.6K) in a full-factorial common-garden experiment in Bayreuth, Germany. In the second year only the warming treatment was imposed. Height, shoot quantity, mortality and needle phenology were determined for the two consecutive years.Provenances differed in absolute growth (from 6.0 to 7.4 in 2009 and from 4.4 to 5.9cm in 2010) and survival rates (from 78.6% to 97.6%), but not in terms of shoot quantity and, surprisingly, sensitivity to drought and warming. The drought treatment showed a delayed impact on height growth, as a significant growth reduction was detected for the second year (−2.6cm), but not for the first year, when the actual treatment took place. Drought decreases survival rates by 20.6%. The drought treatment had no effect on needle phenology.Warming did not impact growth performance (height, shoot quantity). However, warming in combination with the drought treatment decreased the survival rate (−13%). Plants exposed to the warming treatment showed an earlier onset of needle development (−10.6days).Our results imply that no significant local adaptation of growth and survival to drought and warming occurs in P. nigra. Performance and growth response in face of warming and drought cannot be predicted by the climate at the places of origin. We therefore recommend that an introduction of P. nigra to regions outside its natural distribution range should not aim at introducing a single best-adapted provenance but at establishing populations with a high genetic diversity, e.g. by promoting natural regeneration in native stands or by intermixing with different genotypes in order to maintain a high adaptive capacity to climate change.