Abstract
Key messageThis literature review identified the main factors for the success of different silvicultural approaches to regenerate sessile oak naturally and unveiled at the same time important knowledge gaps. Most previous studies were only short-term and restricted to a few factors and single locations. Hence, the findings of these studies are of limited explanatory power and do not allow to develop general, widely applicable management recommendations.ContextSuccessful natural regeneration of sessile oak (Quercus petraea (Matt.) Liebl.) through silvicultural actions depends on a number of biotic, abiotic and management factors and their interactions. However, owing to a limited understanding about the influence of these critical factors, there is great uncertainty about suitable silvicultural approaches for natural oak regeneration, in particular regarding the size of canopy openings and speed of canopy removal.AimsThis study aimed at critically evaluating documented information on natural regeneration of sessile oak. Specifically, we identified (i) the factors that determine the success of approaches for natural regeneration and (ii) evaluated the evidence base associated with different silvicultural approaches.MethodsA comprehensive literature search was done considering relevant peer-reviewed publications of ISI-listed journals as well as non-ISI listed published papers and reports by practitioners. Out of more than 260 collected references, a set of 53 silvicultural ‘core publications’ was identified and analyzed using a catalogue of numeric and categorical evaluation criteria.ResultsThe most important factors determining regeneration success extracted from the literature were light availability, presence of competing vegetation, initial oak seedling density, browsing of seedlings and intensity of stand tending measures. However, the review revealed also great uncertainty regarding the interactions between these factors and the magnitude of their influence. Most studies were of short duration and restricted to single locations. In only 20% of the experimental studies, the observation period exceeded five years. Total costs of regeneration efforts were quantified and reported in only two studies. This lack of data on the expenses of different approaches to natural oak regeneration appears to be one of the most crucial knowledge deficits revealed in this literature review.ConclusionNatural regeneration of sessile oak may be achieved under a wide range of canopy openings, if competing vegetation and browsing is negligible, seedling density is high and tending to remove competing vegetation is carried out consistently. However, since the silvicultural regeneration success depends on the interactions among these factors, which have often not been adequately considered, we caution against general recommendations for silvicultural systems developed from case studies and call for new long-term studies with comprehensive experimental designs.
Highlights
Sessile oak (Quercus petraea (Matt.) Liebl.) and pedunculate oak (Q. robur L.) are among the ecologically and economically most valuable hardwood tree species in Central Europe (Brändle and Brandl 2001; Löf et al 2016; Mölder et al 2019a)
Height increment differences between sessile oak and European beech diminish and eventually vanish with increasing light intensity (Ligot et al 2013; von Lüpke and Hauskeller-Bullerjahn 2004). These findings indicate that successful natural regeneration of oak requires associated silvicultural measures to control competition by accompanying species at least under the site conditions of the reviewed studies
This literature review focussed on important aspects associated with the process of naturally regenerating sessile oak
Summary
Sessile oak (Quercus petraea (Matt.) Liebl.) and pedunculate oak (Q. robur L.) are among the ecologically and economically most valuable hardwood tree species in Central Europe (Brändle and Brandl 2001; Löf et al 2016; Mölder et al 2019a). Since the species are rather drought-tolerant and more storm-resistant compared with other common tree species of the region (Albrecht et al 2012; Kunz et al 2018; Schmidt et al 2010; Zang et al 2011), their absolute and relative shares in forest cover are expected to increase in Central Europe (Bolte et al 2009; Hanewinkel et al 2013). Oaks form the second most abundant broadleaved tree species group in Germany (Thünen-Institut 2014). In oak forests managed for quality timber, an understorey of shade-tolerant tree species is usually employed to shade the oak stems and reduce epicormic sprouting (von Lüpke 1998). A second purpose of this understorey is to inhibit the development of ground vegetation and advance regeneration of shade-tolerant tree species which could be an impediment to the regeneration of oak (Röhrig et al 2006)
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