Abstract
AbstractLocal climate and ungulate browsing are two major factors that affect tree regeneration and genetic adaptation in Central European forests. Owing to climate change and increasing ungulate numbers, the abiotic and biotic environments of trees are changing remarkably, making it necessary to investigate the separate and joint effects of seed source (i.e., location of tree population origin) and ungulate herbivory. We used a common garden experiment to study the growth and morphology of Fagus sylvatica saplings from 77 Swiss seed sources. The experiment was set up at two sites and included a clipping treatment (i.e., terminal shoot clipped at two intensities) applied before budburst to simulate winter ungulate browsing. We studied F. sylvatica sapling growth and morphology before and two years after clipping. Measured growth traits included sapling height, stem diameter, and biomass. Morphological traits included multi‐stemming, stem and crown form, stem quality, and reaction to clipping. Seed source, test site, and simulated leader browsing were all important in determining the growth and quality of F. sylvatica saplings. The effects of seed source on growth and quality indicate that F. sylvatica possesses a large pool of diverse genotypes across Switzerland and thus has the potential to adapt to local conditions through gene flow. Growth and morphology differed significantly between the two test sites, indicating that local environments should be considered carefully when a new plantation is established. The effect of the single simulated browsing event disappeared over time for the growth traits, owing to growth compensation. However, sapling quality decreased after clipping, suggesting that browsing may lead to persistent quality losses in production forests. Neither the growth nor the morphological reaction after clipping depended on the effect of population, meaning that resilience to browsing was independent of seed source. Consequently, interactions with ungulate browsing do not have to be taken into account when selecting F. sylvatica populations for particular climatic and site conditions.
Highlights
Browsing by ungulates such as red deer (Cervus elaphus L.), roe deer (Capreolus capreolus L.), and chamois (Rupicapra rupicapra L.) has increased over the last decades in many parts of the world (Apollonio et al 2010)
Population differences We found a significant effect of population (p < 0.05) for 12 out of 21 growth traits and 4 out of 18 morphological traits (Fig. 2)
Are the population differences shown in this study sufficient to guide seed source selection, for example, for establishing new plantations? The notably high population differentiation values show that the choice of population is important, in particular for sapling quality, since we found highest Qst values for these traits
Summary
Browsing by ungulates such as red deer (Cervus elaphus L.), roe deer (Capreolus capreolus L.), and chamois (Rupicapra rupicapra L.) has increased over the last decades in many parts of the world (Apollonio et al 2010). Growth and morphology are key traits of forest trees They determine (1) the period in which tree saplings are susceptible to browsing (Vacek et al 2014), (2) the time span during which saplings are not effective in protecting against snow avalanches in winter because of complete snow coverage (Kupferschmid et al 2006), (3) the time needed for wood production (rotation time), and (4) the quality of timber (Mitscherlich and Weise 1982). Saplings with a straight growth form provide timber of higher quality than saplings with a crooked growth form (e.g., forked, twisted, spiraled; see Fischer 2000) It is highly useful for forest managers to know the growth traits and morphological traits of sapling when selecting them as future timber trees. Three main factors are known to influence the growth and morphology of tree saplings: the genetic pre-conditions of populations (Matyas 1996), abiotic site conditions such as climate and soil properties (Gould et al 2012), and biotic site conditions such as ungulate browsing intensity (Gill 1992, Wallgren et al 2014)
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