We now have a reliable method to distinguish between small-leaved and large-leaved linden tree species
One adaptation measure to ensure the ecological stability of forest ecosystems and to protect the gene pool of native forest tree populations threatened by climate change is to promote the use of minority species that occur naturally but only sporadically. Lindens are interesting tree species whose increased presence could enhance the stability of our forests.
Photo: Group of small-leaved linden tree species in a forest stand located in the Pelhřimov region, author Jaroslav Dostál
Scientists from the Forestry and Game Management Research Institute (VÚLHM), in collaboration with Mendel University in Brno, are currently studying significant local populations of both small-leaved and large-leaved linden tree species. As part of the project titled “Using DNA Analyses for the Preservation of Desired Genetic Diversity in Recognised Sources of Qualified Reproductive Material and Genetic Characterisation of Populations of Less Common Autochthonous Forest Tree Species“ (Využití analýz DNA pro účely zachování žádoucí genetické diverzity uznaných zdrojů kvalifikovaného reprodukčního materiálu a pro genetickou charakterizaci populacı́ méně běžných autochtonních druhů lesních dřevin) they are exploring how to identify and differentiate between these species using genetic methods.
The genetic diversity of populations is crucial for ensuring that species can withstand various biotic and abiotic stresses in changing environmental conditions. Notably, genetic research on linden forest stands in the Czech Republic has not been conducted to date.
Photo: Habit of small-leaved linden, author Václav Buriánek
The understanding of genetic diversity among forest tree populations in the Czech Republic is still lacking. Given the need to adjust the species composition of forest stands, it is essential to pay attention to underrepresented forest tree species.
To obtain high-quality reproductive material, accurately identifying species is crucial, although this can be challenging based on morphological characteristics alone. Differentiating between various linden tree species is particularly difficult due to significant variability in distinguishing traits and the presence of numerous hybrids.
In contrast to the small-leaved linden, which exhibits low variability and minimal differences between populations, the large-leaved linden is highly variable. This variability can manifest in the existence of several subspecies that lack sharp morphological distinctions, making their differentiation problematic. Furthermore, confusion may arise between the rare reddish subspecies of the large-leaved linden and the small-leaved linden.
Identifying transitional types between two native species can be challenging, as individual trees may not clearly belong to one specific species. In such instances, these trees are often natural hybrids of the heart-shaped linden and the large-leaved linden, exhibiting characteristics that are intermediate between both parent species.
Photo: Linden tree species forest, author Jan Řezáč
To address this issue, scientists from the VÚLHM conducted microsatellite marker analyses to determine species affiliation, identify potential hybrids, and assess the genetic diversity of selected populations of heart-shaped linden and large-leaved linden. For their study, they collected genetic material from 250 trees of both species across eight different locations.
After completing the genetic analysis, the researchers verified the species identification of the individuals in the field and confirmed that the identification based on morphological characteristics was accurate. They included only 240 individuals that were precisely identified both genetically and morphologically in the overall evaluation of the DNA analyses. This comprised 122 individuals of the small-leaved linden and 108 individuals of the large-leaved linden tree species.
The scientists made a significant discovery: unlike previous foreign studies that used the Tc918 marker solely for the large-leaved linden tree species, they found that the Tc918 marker can also be effectively utilised in genetic analyses of the small-leaved linden tree species. As a result, they identified two suitable diagnostic SSR markers, Tc8 and Tc918, to distinguish between the small-linden and large-leaved linden tree species.
Photo: Habit of large-leaved linden, author Václav Buriánek
The representation of small-leaved linden trees in forest stands has significantly declined over the past three centuries due to the widespread introduction of spruce and pine monocultures. Increasing the presence of small-leaved linden could enhance the diversity and stability of forest ecosystems.
Large-leaved linden, even less common in forests, tends to grow at higher altitudes compared to its smaller counterpart, where it can effectively complement the existing species composition. It is frequently found in warmer, sunnier habitats with more alkaline soils, making it a viable option for restoring degraded and unstable conifer stands.
The lack of attention given to these less common forest tree species is evident in the limited recognition of high-quality sources of reproductive material, which restricts their broader use in forest restoration efforts. When certifying forest stands, it is essential to comply with European legislation, which stipulates that only seeds with at least 99% species purity can be circulated. However, conducting genetic analyses on a larger scale within local populations of these sparsely represented forest tree species could lead to changes in this requirement.
Contact for more information: Ing. Pavlína Máchová, Ph.D., e-mail: machova@vulhm.cz
Prepared by: Ing. Jan Řezáč, e-mail: rezac@vulhm.cz