Numerous publications on forest genetic monitoring (FGM) and related topics in genetics and gene conservation have been published over the past three decades. This paper reviews the methods used in FGM and, more broadly, related scientific findings published to date, of which general conclusions can be applied worldwide in FGM. In the strict sense, long-term FGM projects have been established only in a few regions in Europe. The methodological basis (guidelines) for FGM has already been developed, specifically for European tree species and forest communities. In genetic analyses, traditional SSR markers are predominantly used, but SNP markers from new-generation sequencing are increasingly available. Nonetheless, there is a high level of variation in monitoring activities such as biodiversity, forest health, and forest genetics, likely due to the efforts of national (governmental) and international professional organizations. Early evaluation of the first FGM projects has already been published. Scientific evidence for FGM has been limited because of the low number of projects that represent a few geographic regions and species.

Forests in the Tolna region (Hungary) are distributed at the xeric limit of broadleaved forest zones and adapted to the arid ecological conditions of the wood-steppe climate. An 85-year-old in situ gene conservation stand of Quercus virgiliana mixed with other taxa of section Quercus was studied, which was regenerated naturally by both seedlings and coppicing. To analyze the phenotypes growing within the stand and the genetic structure of the population, a total of 138 trees were sampled. For taxonomic classification, a complex of morphological traits of oak taxa growing naturally in the region was used. Out of the 12 morphotype groups, only a few trees were classified as Q. virgiliana (eight individuals) or Q. robur (nine individuals), and the majority of the trees (121 individuals) were hybrid or introgressed phenotypes of Q. virgiliana adapted to xeric conditions by its xeromorphic traits. Despite the high number of coppiced trees (89 pcs vegetatively regenerated), the genetic variation was relatively high based on 16 nSSR markers used for analyses. Some of the trees were classified as non-autochthonous with Slavonian oak origin, both by morphological traits and SSR structure. Despite some alleles being lost, the allelic diversity of the seedling trees’ group was similar to that of the group of parent generation (coppiced trees). The spatial structure of trees supported the results of morphologic classification, and Q. virgiliana and hybrid phenotypes were growing on xeric microhabitats of the stand, mostly on southeast-facing slopes or ridges of hills. Consequently, the stand might fulfill all the in situ gene conservation requirements based on the high genetic diversity measured and the high number of xeromorphic phenotypes in the context of climate change as well.

In the framework of an ongoing gene conservation programme in the Tolna Hills Region, Hungary, a total of 41 site plots were selected on agricultural land that had recently been used as grassland, meadow or vineyard. Aims of our study were (i) to test the taxonomic status of relic oak trees growing out of forested lands; (ii) to verify the origin of relic trees whether they regenerated by sprouts and suckers or by seeds in order to estimate their age and origin (nativeness); (iii) to test their microhabitats to see if forest-specific plant and fungal species were presented; (iv) and to test species to see if their presence linked to any forest vegetation in the past. Furthermore, the land-use type did not show a significant effect on the abundance of woody, dicot herbaceous, or monocot herbaceous plants recorded on sites based on maps from 1941 or earlier. The follow-up univariate ANOVA revealed a significant direct effect of recent land-use type (of 2022) on monocot herbaceous plants (F(3,33) = 5.21, p < 0.01). Additionally, a significant but weaker effect was observed on woody plants (F(3,33) = 3.22, p < 0.05). The overall past effect of land-use type showed a significantly high positive correlation between the abundance of woody plants and the number of times the maps showed forest or forest boundary land-use types (R = 0.46, p < 0.01). The plots have likely preserved and sustained the microhabitats of the native forest vegetation that was once distributed in the region. The site plots of relic oak trees, considered as flagstone habitats, create opportunities for gene flow, not only for the species with dispersal or discontinuous distribution, but also for the Vergilius oak populations. Therefore, relic trees and their microhabitats might have an important role in the mating system of various species and might also be valuable resources for genetic conservation programmes.