Monitoring genetic diversity of Torminalis glaberrima for resilient forests in the face of population fragmentation.

Abstract

Background and aims: Torminalis glaberrima (Gand.) Sennikov & Kurtto is a European tree species currently underutilized in forestry, valued for its high-quality wood and contribution to ecosystem stability. Despite a projected range expansion as climate change progresses, current population fragmentation levels may inhibit the species' ability to migrate and stabilize fragile forest ecosystems. To investigate the relationship between structural and functional connectivity, we surveyed the genetic diversity, spatial genetic structure, and gene flow of T. glaberrima across Austria, to understand which populations should be given conservation priority.

Methods: Our sampling encompasses 21 natural and planted populations and 910 individuals of T. glaberrima covering the species' distribution in Austria. We estimated genetic diversity indices, the extent of gene dispersal, and conducted SPAGeDi, STRUCTURE, and discriminant analyses of principal components analyses using one chloroplast minisatellite and eight nuclear microsatellite markers.

Key results: Despite a highly fragmented distribution of T. glaberrima in the southern, western and central part of its range in Austria, we found high genetic diversity, low population differentiation and inbreeding, and estimated higher gene dispersal values than previous studies. Population structure analyses identified two main regions of genetic ancestry in the northwestern and southeastern part of the species' range in Austria and evidence for the usage of foreign genetic material in two planted populations.

Conclusions: Only two of the established ex situ plantations and seed orchards appear to well represent the fine-scale population structure present in Austria, and existing in situ gene conservation units (GCUs) are insufficient to conserve the current natural genetic diversity. We suggest the establishment of further in situ GCUs to maximize the conservation of extant forest genetic diversity. Additionally, we encourage corridor plantings between isolated populations, bolstering the genetic connectivity and diversity of populations.