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The influence of soil quality and tree quality on regeneration of juniper (Juniperus communis) in Drenthe

Kromkamp, N. (2014) The influence of soil quality and tree quality on regeneration of juniper (Juniperus communis) in Drenthe. Master's Thesis / Essay, Biology.

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There is limited regeneration of the common juniper (Juniperus communis L.) in Western Europe, mostly in Belgium, Germany, the UK and the Netherlands. If the juniper were to go extinct, several associated species of lichens and fungi would also disappear, as well as unique habitat types. The decline is thought to be caused by changes in environment and land use, but empirical evidence is thus far scarce. To determine the importance of grazing and soil conditions, 16 areas within the Dutch province of Drenthe were investigated. These areas differ in management, grazing and regeneration levels. In each area, soil samples were taken inside a juniper thicket and in a site with juniper seedlings, and the pH, acidity, concentrations of phosphate, sodium, calcium, potassium and magnesium, carbon, nitrogen and C:N ratio, water content, dry matter ratio, organic content and cation exchange capacity were measured in the lab. Current data on grazing was gathered from an existing inventory of juniper seedlings in Drenthe, and information on grazing regimes was collected from area managers. We used linear models and generalised linear models to analyse the data. Linear models containing the parent tree quality and either the dry matter ratio or the C:N ratio explained most of the variation in seedling density between areas. Tree quality and C:N ratio were positively correlated with seedling density, while dry matter ratio was negatively correlated. The quality of the parent trees was positively affected only by Na+ content of the soil, but even this relationship was not very strong. No effect was found of grazing by sheep or cattle on seedling density. These results suggest that juniper regeneration is most successful if water holding capacity of the soil is high, but due to strong correlations with other factors such as acidity and organic content ratio, a more correct conclusion would be that juniper seedling density is positively influenced by soil richness. While the soil in old heathlands is generally dry, sandy and poor in organic compounds, heather fields in recently deforested areas were found to contain more organic compounds and retain more water, enabling a higher seedling density. In conclusion, this means that, for the sake of juniper regeneration, it might be good to enrich heathland soils. This could be done by temporarily allowing succession to forest to occur, because current heathland management is aimed at maintaining nutrient-poor conditions in favour of purple heather.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:02
Last Modified: 15 Feb 2018 08:02

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