Growth, spring phenology and stem quality of four broadleaved species assessed in provenance trials in the Netherlands - Implications for seed sourcing

Local seed sourcing from autochthonous tree populations is widely practiced for biodiversity conservation, as they are presumed to be adapted to local environmental conditions. Yet, autochthonous seed sources are not registered in the Netherlands for timber production, as these stands often exhibit poor stem quality due to their coppice history. Here, we study whether the performance of registered local seed sources from autochthonous origin (category “Source identified”) differs from local seed sources selected or improved for forestry purposes. We analyzed survival, growth, spring phenology, and stem form in four single-site provenance trials. In total, seeds from 74 provenances of four broadleaved species (Alnus glutinosa, Betula pubescens, Fagus sylvatica, and Quercus robur) were collected and planted in four provenance trials between 2008 and 2010. Provenance effects were consistently significant for budburst, whereas the effects on survival, growth, and stem form varied by species. Betula pubescens showed a 169% height difference between provenances at age 12, with several autochthonous provenances outperforming seed orchard material. In the other species, several autochthonous provenances performed equally well in terms of growth compared to seed sources in the “Tested” category. Differences in budburst timing were particularly evident in Fagus sylvatica and Quercus robur. In these trials, the autochthonous provenances were among the latest in flushing compared to the other local seed sources. Principal component analysis revealed strong correlations between growth and budburst, especially in Fagus sylvatica and Quercus robur, where earlier flushing was linked to greater height. This highlights potential trade-offs in selecting for both growth and late budburst. Overall, the study demonstrated that even within the ecologically uniform Dutch environment, genetic differences are present between local seed sources. We conclude that autochthonous provenances, despite exhibiting inferior phenotypic characteristics in situ due to past intensive silvicultural practice, can possess good growth and form characteristics, which makes them suitable for seed collection for both ecological and production purposes.