Recent Drought-Induced Vitality Decline of Black Pine (Pinus nigra Arn.) in South-West Hungary—Is This Drought-Resistant Species under Threat by Climate Change?

: This paper analyses the recent recurring dieback and growth decline of Black pine
(P. nigra Arn. var austriaca) in the Keszthely mountains of south-west Hungary, and their relations
to water deficits due to droughts. These relations were studied in five stands with low soil water
storage capacity for the period 1981–2016. The vitality was assessed using 60 tree-ring samples and
changes in remotely sensed vegetation activity indices, i.e., the normalized difference vegetation
index (NDVI) and the normalized difference infrared index (NDII). Water deficit was estimated by
using meteorological drought indices such the standardized precipitation–evapotranspiration index
(SPEI) and the forestry aridity index (FAI), as well as the relative extractable water (REW), calculated
by the Brook90 hydrological model. Results revealed a strong dependency of annual tree ring width
on the amount of water deficit as measured by all the above estimators, with the highest correlation shown by the summer REW. Droughts also showed a long-term superimposed effect on tree growth. NDII seemed to be more sensitive to drought conditions than NDVI. The robust dependency of tree growth on the summer water availability combined with the projected increasing aridity might lead to decreasing growth of Black pine in Hungary towards the end of the century. We thus argue that the suggestion by several papers that Black pine can be a possible substitute species in the Alpine and Mediterranean region in the future should be revisited