Nitrogen dynamics in humus and soil beneath Sitka spruce (Picea sitchensis (Bong.) Carr.) planted in pure stands and in mixture with Scots pine (Pinus sylvestris L.)

1992 ◽  
Vol 144 (1) ◽  
pp. 77-84 ◽  
Author(s):  
B. L. Williams
Keyword(s):  
Pinus Sylvestris ◽  
Scots Pine ◽  
Sitka Spruce ◽  
Nitrogen Dynamics ◽  
Picea Sitchensis

Strength properties of wind- and snow-damaged stems of Picea sitchensis and Pinus sylvestris in comparison with undamaged trees

1999 ◽  
Vol 29 (5) ◽  
pp. 595-599 ◽  
Author(s):  
A D Cameron ◽  
R A Dunham
Keyword(s):  
Pinus Sylvestris ◽  
Scots Pine ◽  
Compression Wood ◽  
Outer Part ◽  
Sitka Spruce ◽  
Strength Properties ◽  
Picea Sitchensis ◽  
Modulus Of Rupture ◽  
Clear Wood ◽  
Pine Trees

This study compared the strength properties of wood taken from Sitka spruce (Picea sitchensis (Bong.) Carr.) and Scots pine (Pinus sylvestris L.) trees damaged as a result of wind and snow. The spruce trees were located in triplets of stems of similar diameter that had snapped, overturned (i.e., uprooted), or remained undamaged as a result of wind and snow. The pine trees were located in pairs of similar-sized stems that had snapped or remained undamaged. None of the pine trees overturned. Clear wood (wood without knots and sloping grain) from the outer part of the stem of snapped Sitka spruce and Scots pine trees was less stiff (lower modulus of elasticity (MOE)) than wood taken from the same location from overturned (spruce only) or standing trees. Modulus of rupture and density were unaffected. Damaged trees of both species were found to have significantly more compression wood within the test samples in comparison with undamaged trees. These findings suggest that trees that either overturn or snap are bending more than undamaged trees (because of their low MOE) thereby introducing a greater component of crown weight to the overall forces acting on the stem, and that this may be associated with compression wood.

What influences the long-term development of mixtures in British forests?

2020 ◽  
Vol 93 (4) ◽  
pp. 545-556 ◽  
Author(s):  
W L Mason ◽  
T Connolly
Keyword(s):  
Functional Traits ◽  
Scots Pine ◽  
Shade Tolerance ◽  
Basal Area ◽  
Sitka Spruce ◽  
Picea Sitchensis ◽  
Silver Birch ◽  
Western Hemlock ◽  
Larix Kaempferi ◽  
Pure Stand

Abstract Six experiments were established between 1955 and 1962 in different parts of northern and western Britain which used replicated randomized block designs to compare the performance of two species 50:50 mixtures with pure stands of the component species. The species involved were variously lodgepole pine (Pinus contorta Dougl.), Japanese larch (Larix kaempferi Lamb. Carr.), Scots pine (Pinus sylvestris L.), silver birch (Betula pendula Roth.), Sitka spruce (Picea sitchensis Bong. Carr.) and western hemlock (Tsuga heterophylla Raf. Sarg.). The first four species are light demanding, while Sitka spruce is of intermediate shade tolerance and western hemlock is very shade tolerant: only Scots pine and silver birch are native to Great Britain. In three experiments (Bickley, Ceannacroc, Hambleton), the mixtures were of two light-demanding species, while at the other three sites, the mixture tested contained species of different shade tolerance. The experiments were followed for around 50 years, similar to a full rotation of even-aged conifer stands in Britain. Five experiments showed a tendency for one species to dominate in mixture, possibly reflecting differences in the shade tolerance or other functional traits of the component species. In the three experiments, the basal area of the mixtures at the last assessment was significantly higher than predicted based on the performance of the pure stands (i.e. the mixture ‘overyielded’). In two of these cases, the mixture had had a higher basal area than found in the more productive pure stand indicating ‘transgressive overyielding’. Significant basal area differences were generally more evident at the later assessment date. The exception was in a Scots pine: western hemlock mixture where greater overyielding at the earlier date indicated a nursing (‘facilitation’) effect. In the remaining experiments, the performance of the mixture conformed to predictions from the growth of the component species in pure stands. Taken overall, the results suggest that functional traits can be used to interpret the performance of mixtures but prediction of the outcome will require better understanding of the interplay between species and site characteristics plus the influence of silvicultural interventions.

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