Abstract
Background and aims – Common juniper (Juniperus communis L.) is one of the most widespread woody species on the planet. Over recent decades, however, common juniper populations are decreasing in size and number in different regions. Lack of recruitment, caused by extremely low seed viability and the absence of suitable microsites for recruitment, is the key reason for this decline. For successful germination, the seeds need gaps in the existing vegetation and a soil with a relatively high base saturation. The aim of this study was therefore to assess how management actions such as sod cutting, rotavation and liming (alone or in various combinations) influence soil characteristics, seed germination and seedling survival of common juniper.Methods – We installed a sowing experiment across 104 1-m2 plots in four different sites in Belgium and the Netherlands using treatments with different combinations of fencing, sod cutting, rotavation, litter addition and liming. We determined how these treatments affected soil characteristics and how they influenced seed germination and seedling survival.Key results and conclusions – Across the whole experiment, germination rates of juniper seeds were very low (almost always < 1%). Our results confirm that bare ground promotes the germination of juniper seeds. Secondly, higher silt and lutum (clay) proportions in the soil and higher soil organic matter content seemed to have a positive impact on recruitment, possibly due to drought reduction. Management actions that negatively affect those soil characteristics, such as deep sod cutting, should thus be avoided in heathlands on sandy soils. Our results reveal a complex relationship between seedling recruitment success, soil conditions and management of common juniper populations. Overall, combinations of fencing, (superficial) sod cutting and liming or rotavation were most successful.
Highlights
With a distribution range that covers most of the northern hemisphere (Adams 2008), common juniper Juniperus communis L. (further referred to as ‘(common) juniper’) is one of most widespread plant species on earth
We studied the effects of the different management actions in heathlands on seedling recruitment of common juniper
The main goal of our research was to assess the effects of heathland management on germination and seedling establishment of common juniper on sandy soils
Summary
With a distribution range that covers most of the northern hemisphere (Adams 2008), common juniper Juniperus communis L. (further referred to as ‘(common) juniper’) is one of most widespread plant species on earth. Together with European yew (Taxus baccata) and Scots pine (Pinus sylvestris), juniper is one of the only three native conifers in Belgium and the Netherlands. In these regions, the species mainly occurs on nutrient poor, acid, sandy soils, typical for heaths and drift sands. Verheyen et al (2009) revealed a triangular relationship between the fraction of recently recruited individuals and the percentage of viable seeds in a population. The lack of recruitment is due to low seed viability (Ward 1973, 1982; Fitter & Jennings 1975; Gilbert 1980; García 2001; Broome et al 2017)
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