Past, present and future suitable areas for the relict tree Pterocarya fraxinifolia (Juglandaceae): Integrating fossil records, niche modeling, and phylogeography for conservation

Abstract

Pterocarya fraxinifolia, native to the southern Caucasus and adjacent areas, has been widely introduced in Europe. In this study, we investigate the following: (1) How did its current distribution form? (2) What are the past, current, and future suitable habitats of P. fraxinifolia? (3) What is the best conservation approach? Ecological niche modeling was applied to determine its climatic demands and project the distribution of climatically suitable areas during three periods of past, current, and future (2070) time. Then, an integrated analysis of fossil data was performed. Massive expansion of Pterocarya species between the Miocene and Pliocene facilitated the arrival of P. fraxinifolia to the southern Caucasus. The Last Glacial Maximum played a vital role in its current fragmented spatial distribution in the Euxinian and Hyrcanian regions with lower elevations, and Caucasian and Irano-Turanian regions with higher elevations. Climatic limiting factors were very different across these four regions. Future climate change will create conditions for the expansion of this species in Europe. Human activities significantly decreased the suitable area for P. fraxinifolia, especially in the Euxinian, Hyrcanian, and Irano-Turanian regions. Considering genetic diversity, climate vulnerability, and land utilization, the Euxinian, Hyrcanian, and Irano-Turanian regions have been recognized as conservation priority areas for P. fraxinifolia.

Adaptive divergence and genetic vulnerability of relict species under climate change: a case study of Pterocarya macroptera

“…The top three environmental variables explaining genetic variation were temperature-related, especially for the NWY and QDT lineages. Pterocarya is a typical riparian relict tree genus ( Song et al ., 2020 , 2021 ). Compared with other Pterocarya species, P. macroptera occupies the highest elevations, with the largest change in elevational range, along mountain streams and water-rich slopes ( Kozlowski et al ., 2018 ; Song et al ., 2019 ).…”

Pleistocene-Holocene sedaDNA reconstruction of Southern Doggerland reveals early colonization before inundation consistent with northern refugia.

“…It would therefore have been suited to the ecology of the Southern River had temperature conditions been mild enough. Pollen records indicate it was common in Northern Europe in the Early Pleistocene and became rare in the Middle Pleistocene (770-120 ka) prior to the last glaciation, after which time it has not been detected 30 . Pterocarya pollen has been recovered from Hoxnian Stage (424-324 ka) sites nearby the study area 31 .…”

Evolutionary history ofCastanea sativaMill. in the Caucasus driven by Middle and Late Pleistocene paleoenvironmental changes

“…Increased climatic variability during the Pleistocene undoubtedly reinforced these patterns (Lisiecki & Raymo, 2005). Indeed, pollen records in west Georgia (Mahler, Shatilova & Bruch, 2022) indicate that the Colchis and Hyrcania became major refugia for the Caucasian biota, especially during the last glacial period, hosting some Neogene relicts (Arpe et al ., 2011; Shatilova et al ., 2011; Connor & Kvavadze, 2009; Tarkhnishvili et al ., 2012; Song et al ., 2021).…”