Growth Response of Endemic Black Pine Trees to Meteorological Variations and Drought Episodes in a Mediterranean Region

Nikolaos Proutsos,Dimitris Tigkas

doi:10.3390/atmos11060554

Abstract

Weather variations affect natural ecosystems, while in regions where climate change is anticipated to intensify extreme events such as droughts, the vitality of vulnerable species may be reduced. The sensitivity of key-species to the climatic conditions may illustrate their adjustability in specific areas and assist decision making towards proper mitigation and adaptation measures. Pinus nigra, commonly known as black pine, is an endemic species, forming many protected habitats in the Mediterranean. In this study, black pine tree-ring data from Greece are used to assess the response of tree growth to specific temperature-related (mean, max. and min. temperature and diurnal temperature range) and water-related (precipitation, evapotranspiration, relative humidity and vapor pressure deficit) meteorological parameters. Additionally, the effect of drought episodes is estimated using indices, including the well-established standardised precipitation index (SPI) and reconnaissance drought index (RDI), as well as two recently proposed modifications, namely, the agricultural SPI (aSPI) and the effective RDI (eRDI). The outcomes reveal several seasonal patterns, emphasising the sensitivity of black pine principally to water-related meteorological parameters, with winter and early spring conditions having a primary role on annual tree growth. Black pine seems to be tolerant to drought in the study region, in terms of its resilience; however, there are indications that multiyear droughts may have prolonged effects on tree growth, which may last approximately three years after drought ends. Additionally, it is derived that both aSPI and eRDI illustrate more efficiently tree growth response to drought, indicating that these modifications provide increased accuracy regarding drought characterisation in the forest environment.

Highlights

The Mediterranean region is considered as a climate change and biodiversity hotspot and is expected to face increased challenges due to climate shifts [1,2]
The decreasing tree growth of specific species is associated with the warming climate and decreasing precipitation trends observed in the Mediterranean [4,5,6], while reduced water availability and drought have been identified as the main factors limiting tree growth in the region [7,8]
Precipitation and other water-related parameters, such as relative humidity (RH), vapor pressure deficit (VPD) and ETo, seem to have a greater influence on tree-ring width, compared to temperature-related parameters. It is noteworthy the small value of TRWI during the year 1989–1990, which is characterised as a year of extreme drought, corresponding to a significantly low amount of precipitation

Summary

Introduction

The Mediterranean region is considered as a climate change and biodiversity hotspot and is expected to face increased challenges due to climate shifts [1,2]. The unique Mediterranean-type ecosystems and several species with distinctive Mediterranean features may be highly affected by extreme climatological events such as droughts, which are anticipated to be intensified in the forthcoming period [3]. The decreasing tree growth of specific species is associated with the warming climate and decreasing precipitation trends observed in the Mediterranean [4,5,6], while reduced water availability and drought have been identified as the main factors limiting tree growth in the region [7,8]. Understanding the response of ecosystems and specific forest species to meteorological factors and drought events may provide essential information regarding the anticipated stress that they may undergo due to adverse climatic conditions, while appropriate mitigation or adaptation measures may be taken. Precipitation is of major importance, with a positive effect on radial growth of pines, indicating specific species as dendroclimatically sensitive [9,10,11]

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