Ancient woodlands in the limelight: delineation and genetic structure of ancient woodland species Tilia cordata and Tilia platyphyllos (Tiliaceae) in the UK

Ancient woodlands in Europe are currently subjected to fragmentation, which leads to ecological deterioration and genetic isolation. This is likely to intensify with further climate change and increased land use. Tilia are keystone, ancient woodland indicators, represented in the UK by two species (Tilia cordata and Tilia platyphyllos) and their hybrid (Tilia x europaea). For management of the species, we need to investigate genetic differentiation and population genetic structure. Morphology can usually separate the two species but the distinguishing features are not always observable, particularly in less optimum, shady, conditions. Here, we test for the first time 13 microsatellite markers to discriminate the species and hybrid, and to assess the population genetic diversity of the two species. The markers successfully distinguished the species and hybrid. The two species show significant genetic differentiation, indicating two distinct biological units. Sub-structure within both species is loosely related to geographic location. Because Tilia populations in the UK are highly fragmented, future conservation should consider provenance issues.