Informed conservation management of rare tree species needs knowledge of species composition, their genetic characteristics and ecological niche
Here we assess Tilia species in the Bavarian Forest National Park (BFNP), a large mixed coniferous and deciduous forest in South-Eastern Germany. Tilia occurs here at low density, as in many other mixed forests in Central and Northern Europe. Therefore, results are not only relevant to BFNP but also to other areas. Exhaustive sampling resulted in the collection of 113 mature trees that were genotyped using 20 microsatellite markers, derived from both T. cordata and T. platyphyllos. For the first time, size and aspect of trees, and their community association were contrasted between the species. The data presented here contain the genotypes of the trees as well as size measurements and ecological data of their location. Genotyping confirmed that T. platyphyllos, T. cordata and their hybrid (T. x europaea) were present in the BFNP and both species deserve conservation. T. platyphyllos has a higher genetic diversity for both sets of markers than T. cordata, confirming earlier work. Both species showed genetic diversity comparable to other populations in Central Europe, which is likely to be sufficient for the maintenance of the species in the short term. However, increasing the number of trees, ensuring local sources are used, and gene flow from surrounding forests over the next decennia may be crucial for long-term survival. Further, within the T. platyphyllos group there was a set of 11 trees that were distinct from the others: they had a lower genetic diversity and were shorter. We hypothesise that these were planted and should not be used for propagation and augmentation. Most saplings analysed appeared to derive from asexual propagation (36 out of 41), although a few (five out of 41) were novel genotypes. This means that, currently, there is some, but rather limited, regeneration. T. cordata was found at a lower altitude and less steep terrain than T. platyphyllos and the hybrid. The hybrid was taller than the two species, while the diameter at breast height was smallest in T. cordata. T. cordata shows a preference for mixed and coniferous forests, while T. platyphyllos occurs mostly in deciduous forests. Our results indicate that biodiversity at the species and genetic level as well as species’ ecology have to be considered in order to guide informed conservation management. These results form the basis to recommend conservation management improving the long-term viability of Tilia in the BFNP and other mixed forests.