%0 Research article
%T Survival and early seedling growth of conifers with different shade tolerance in a Sitka spruce spacing trial and relationship to understorey light climate
%A Mason, William L.
%A Edwards, Colin
%A Hale, Sophie E.
%D 2004
%J Silva Fennica
%V 38
%N 4
%R doi:10.14214/sf.404
%U https://silvafennica.fi/article/404
%X Alternative silvicultural systems to clearfelling are being adopted in  Great Britain as a means of increasing the species and structural  diversity of conifer plantation forests. One area where knowledge is  lacking is the critical level of below-canopy light for survival and  growth of young seedlings. This was investigated by planting seedlings  of European larch Larix decidua (Mill.), Scots pine Pinus sylvestris L.,  Sitka spruce Picea sitchensis (Bong.(Carr.)), Douglas fir Pseudotsuga  menziesii (Mirb.(Franco.)), and western hemlock Tsuga heterophylla (Raf.  (Sarg.)) in a Sitka spruce plantation thinned to 3 different spacings.  The incident light intensity beneath the canopy ranged from about 2 to  over 60 per cent of full light. Planting in an adjoining open area  provided an indication of growth under full light. Growth and survival  of these seedlings were followed for 4 growing seasons. The highest  seedling survival was found under the widest spacing and declined with  closer spacing and lower light intensity. Only Douglas fir and western  hemlock seedlings survived at the closest spacing, and in low  percentages. The tallest seedlings of each species were found in the  open grown conditions but survival was variable due to increased weed  competition. Species-specific growth responses showed little difference  under high light conditions but performance at low light was generally  consistent with shade tolerance rankings in the literature except that  Sitka spruce shade tolerance was slightly lower than expected. Minimum  light requirements for these species increased from 10 to 30 per cent of  full light with decreasing shade tolerance. Other studies of incident  light in Sitka spruce plantations indicated that target basal areas in  the range 25–30 m2 ha–1 are required if these light conditions are to be  met, which suggests an irregular shelterwood system with frequent  interventions should be favoured.