Abstract
Under global warming,drought will reduce productivity of Pinus halepensis s.l.(subspecies halepensis and brutia)and cause a retreat from its rear edge distribu-tion(latitudinal/elevational)in the Mediterranean.To test whether topography can influence this scenario,we studied for approximately 40 years the growth of six natural pine stands in water-limited habitats on the islands of Zakinthos and Samos(eastern Mediterranean Greece),and determined the critical moisture sources that drove pine growth.Domi-nant pines were selected with no permanent water sources under contrasting moisture conditions created by topogra-phy("wet"-gulley/valley vs."dry"-upslope habitats).The responses of P.halepensis s.l.to drought under a moderate and a worst case scenario were tested,projected under global warming(approx.-25％and 40％in annual precipitation compared to 1961-1990 average).Our results show that"wet"habitat pines had higher productivity under normal to wet climate.However,the more precipitation declined,"wet"habitat tree growth was reduced at a significantly faster rate,but also showed a faster recovery,once rainfall returned.Thus,Pinus halepensis s.l.populations in gullies/valleys,may be more drought resilient and less likely to retreat towards higher elevation/latitudes under global warm-ing,compared to pines on dry upslope sites.Under moderate drought,both ecosystems relied on deeper moisture pools supplied by rainfall of the previous 3-6 years(including the year of growth).However,valley/gully habitat pines on significantly deeper soils(and probably on deeper heavily weathered bedrock),appeared to utilize surface moisture from winter/spring rainfall more efficiently for survival and recovery.Thus,deep soils may provide the key"buffer"for pine survival in such ecosystems that could act as potential refugia for P.halepensis s.l.under climate change.
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