Elsevier

Dendrochronologia

Volume 64, December 2020, 125763
Dendrochronologia

Original article
Climatic responses of Pinus brutia along the Black Sea coast of Crimea and the Caucasus

https://doi.org/10.1016/j.dendro.2020.125763Get rights and content

Abstract

Pinus brutia var. pityusa (Steven) Silba (Calabrian pine) is considered a vulnerable species because of reductions in its population sizes linked to habitat decline in recent decades. Global warming alongside the collateral modification of precipitation regimes may markedly affect the distribution ranges of this species.

In this dendroecological study, we identified the most influential climatic factors affecting the radial growth of P. brutia on the northern and eastern coasts of the Black Sea among the northern refugia of this species. Chronologies from five sites located on the Crimea Peninsula and the Caucasian coast and exposed to varying climatic conditions were used in this analysis. The study of environmental factors controlling the growth of P. brutia trees in the coastal populations of Crimea and the Caucasus revealed that within the longitudinal transect, which encompasses a specific range of climatic conditions, correlations between climate and the growth of P. brutia under analogous orographic conditions are similar.

Aridisation of the dry Crimean climate in 1981–2012 led to an increase in the tree growth response. In the same period, populations of P. brutia trees growing in the subtropical climate of the Black Sea coast exhibited a weakened growth response to the point of disappearance. The northern populations of P. brutia, which are at the climatic limit of the species’ distribution, are exposed to a high risk of increasing climate aridisation. Our findings could provide useful information for further research on the effects of climate change on Black Sea coastal forest ecosystems.

Introduction

P. brutia is a drought-tolerant, fast-growing, and widely distributed coniferous species native to the eastern coast of the Mediterranean region, extending from Greece to Syria (Boydak, 2004). Several pine species growing along the northern and northeastern coasts of the Black Sea, including Pinus pithyusa Stev., Pinus stankewiczii Sukac., and Pinus eldarica Medwed., were categorised as subspecies of P. brutia by Nahal (1983) and as varieties of P. brutia by Critchfield and Little (1966) and Vidaković (1991). However, these species are now classified as being among the same species and populations despite their phenotypic differences (Semerikova and Semerikov, 2020).

Trees growing on steep sea-facing slopes usually have wide crowns, curved stems, and long and coarse branches, whereas those growing on flat slopes usually have narrow and dense crowns and long, straight stems with small branches (Alemdag, 1962; Arbez, 1974; Isik and Isik, 1999). P. brutia forests provide important environmental benefits and services, including soil protection, biodiversity conservation and climate change mitigation and adaptation. Small refugia of this species have been preserved on the eastern and northern shores of the Black Sea (Conkle et al., 1988; Yena et al., 2005), where this species grows at the limit of its resistance to low winter temperatures. P. brutia is a thermophilous species that prefers lowland semihumid and humid sites with mean annual temperatures of 12–20 °C (Boydak, 2004; Quézel and Barbero, 1992). In addition, it is highly drought resistant, has a deep rooting zone, and can grow in areas with mean annual rainfall as low as 400 mm (Nahal, 1983). The unique growth characteristics of P. brutia make it one of the most promising pine species in arid regions.

In Crimea, P. brutia grows under the drought-prone conditions of the Mediterranean climate and can be found on steep slopes with poor soil horizons and low water-holding capacities. The habitats along the Caucasian coast are less stressful (Bebia, 1987). Tree-ring data of P. brutia can provide accurate information about the relationship between tree growth and climate. Most dendroclimatic studies of P. brutia have focused on the centre of this species’ distribution (Griggs et al., 2014; Sarris et al., 2007; Touchan et al., 2005). The present study was the first to measure the climatic response of P. brutia based on discrete populations in its northernmost refugia along the northern and eastern Black Sea coasts. The specific objectives of this study were to (1) identify the climatic variables that most strongly correlate with the tree-ring width of P. brutia growing under Mediterranean and subtropical conditions, (2) determine whether climatic signals in tree-ring chronologies change with longitudinal shifts, and (3) examine the dynamics of radial growth response under climatic changes.

Section snippets

Methods

We analysed the effect of climate on the radial growth of P. brutia from five site chronologies. The sampling sites were located along a longitudinal gradient on the Black Sea coast and presented different environmental conditions (Fig. 1 and Table 1). All five areas are botanical reserves for the conservation of P. brutia populations. Two sites, namely, Mys Ayia (AYIA) and Novy Svet (NSVT), were located along the southern coast of the Crimean Peninsula; the other three sites, namely, Dzhanhot

Tree-ring chronologies

The oldest trees were in the NSVT site and the youngest were in the GAGR site. The chronological ranges were as follows: 153–275 years in the AYIA site, 122–297 years in the NSVT site, 89–145 years in the DZHA site, 45–115 years in the GAGR site, and 116–172 years in the PITS site. The SSS value for each site was above the minimum threshold of 0.85 as far back as the years 1752, 1805, 1857, 1878, and 1956 for the AYIA, NSVT, PITS, DZHA, and GAGR sites, respectively (Fig. 3 and Table 3). The

Discussion

The tree growth–climate correlations of P. brutia demonstrated considerable variation among the different sites. Regarding the difference in responses between the two population groups growing in different climates, the Crimean populations are more sensitive to climate; growing in more arid conditions, these populations are more heavily influenced by the conditions of the growth period. In contrast, the Caucasian coastal populations are most responsive to the pre-growth period conditions.

The

Conclusion

This study of the climatic factors that control the growth of P. brutia trees in coastal populations in Crimea and the Caucasus revealed that within a longitudinal transect that encompasses a specific range of climatic conditions, correlations between climate and the growth of P. brutia under analogous orographic conditions are fairly consistent. However, under more arid conditions (Crimea), the association between radial growth and summer precipitation is more clearly expressed. During the

Declaration of Competing Interest

None declared.

Acknowledgements

We extend our thanks to Svetlana Semerikova, PhD, Roman Dbar, PhD, and Mr Ivan Surkov for their assistance in accessing dendrochronological data.

This research was funded by RFBR project numbers 18-05-01110 and 11-04-90301.

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