Knowledge of sexual reproduction associated with flowering behavior is essential for seed orchard establishment. For these rarer species, approved seed stands are often not available in sufficient numbers. Seed orchards play an important role in providing forest reproductive material for the rarer forest species such as Norway maple. These include the establishment of provenance and progeny tests, as well as marker-based population genetic studies. Several research projects have begun to fill the knowledge gap that exists compared to many dominant forest tree species. Since Norway maple is considered to be adaptable to climate change, it has increasingly become a focus of forestry as one of the so-called alternative tree species. Recently, a first analysis was performed in Latvian populations where SSR markers were transferred from other maple species (Ruņģis and Krivmane 2021). Initial studies were conducted in Finland to characterize intraspecific variation using isozyme markers (Rusanen et al. Nevertheless, very few population genetic studies have been carried out for this tree species. Compared to the tetraploid sycamore maple ( Acer pseudoplatanus L.), it should therefore be methodically better accessible to genetic characterization. Norway maple is a diploid species with a chromosome number of 2 n = 26 (Arohonka 1982). Very detailed studies on flowering of maple species were conducted, e. As described by Scholz ( 1960) for the floral biology of maple species, both protogynous and protandrous individuals occur, i.e., bisexual trees that flower first female or first male. The species exhibits heterodichogamy with different temporal and individual sex expressions as a feature of its sexual system. It flowers at 10–15 years in the open, but after about 25–30 years in closed forests. Norway maple is known as a monoecious, insect-pollinated tree species. Better knowledge of the adaptability and reproductive behavior of Norway maple populations may help to increase future consideration of this tree species, which is suitable as a mixed tree species, to diversify species composition in forests. To date, Norway maple has played only a minor role in forests, although the wood is similar to that of sycamore (Roloff and Pietzarka 1998). However, Norway maple is also adaptable to other conditions, such as moderately moist to very dry sites (reviewed in Caudullo and de Rigo 2016). The species prefers to grow on deep, nutrient-rich soils with sufficient water supply. It occurs in scattered or in small populations and is predominantly mixed with other tree species. The Norway maple ( Acer platanoides L.) is a tree species native to Central Europe and Germany. Conclusions are drawn for the establishment of new seed orchards and for further research. The number of ramets per clone in the seed set has a significant impact on the proportion of genetic contribution per clone to total seed yield. Four flower types were observed, with protogynous and hermaphrodite types contributing more female gametes, while the protandrous type is highly variable in its female or male contributions. The total seed had proportions of 68% outcrossed offspring between clones of the seed orchard, 11% selfing and 20% external pollination. We used a recently developed set of species-specific SSR markers to genotype the parental clones and respective seed samples. In a first step, we conducted a mating system analysis in a seed orchard. The sexual system of Norway maple is known as heterodichogamous, with male-first and female-first flowering individuals mixed in a population. However, little knowledge exists on the phenotypic variation in the natural range, and no studies on the reproductive behavior of this monoecious and insect-pollinated tree species. Since Norway maple is considered to be adaptable to climate change, it has increasingly become a focus of forestry as one of the so-called alternative tree species to diversify species composition in forests. Norway maple ( Acer platanoides L.) is a tree species native to Central Europe and occurs in scattered or in small populations mixed with other tree species.
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