Factors affecting the establishment of natural regeneration of Sitka spruce (Picea sitchensis (Bong.) Carr.) in Ireland.

Abstract

In Ireland, natural regeneration of Sitka spruce (Picea sitchensis (Bong.) Carr.) is becoming common on reforestation sites, especially in the eastern part of the country. The management of this phenomenon is relatively new to many foresters here, as its occurrence is often sporadic and difficult to predict accurately. Due to this novelty, its management can often be difficult. The main objective of this study was to examine the influence of various site factors on the establishment of natural regeneration, in order to make it more predictable for forest managers. It was also intended to examine the extent of natural regeneration in the study area, which was confined to State owned forests in Counties Wicklow and Dublin. Results showed extensive regeneration on sites with a previous crop of Sitka spruce. Over 50% of planted sites had an adequate cover of natural regeneration. It was found that poor soils, especially those with a peat layer which only sustain a thin cover of ground vegetation, regenerated more readily than richer soils such as brown earths or gleys. Good seed years were also shown to have a significant impact on the establishment of natural regeneration, especially on sites which are recolonized quickly by very dense vegetation. Some shade appears to favour the development of natural regeneration, probably by protecting seedlings from environmental extremes. An examination of ground cover types showed that Sitka spruce regenerates most readily on low moss and litter and that regeneration generally does not occur in areas with dense grass, rush or brash. The main conclusion of this study is that, while there are many factors which influence the establishment of natural regeneration, it can be predicted with a fair degree of accuracy if all important variables are taken into account.