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.

中文翻译：

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是什么影响英国森林中混合物的长期发展？

在1955年至1962年之间，在英国北部和西部的不同地区建立了六个实验，这些实验使用重复的随机区组设计比较了两种物种的50:50混合物与纯种组成的混合物的性能。涉及的物种有以下几种：松木（Pinus contorta Dougl。），日本落叶松（Larix kaempferi Lamb.Carr。），苏格兰松木（Pinus sylvestris L.），白桦树（Betula pendula Roth。），锡特卡云杉（Picea sitchensis Bong。 Carr。）和西铁杉（Tsuga heterophylla拉夫 Sarg。）。前四个物种对光线的需求很高，而锡特卡云杉具有中等的阴影耐受性，西部铁杉具有很高的阴影耐受性：只有苏格兰松树和白桦树才是英国本土。在三个实验（Bickley，Ceannacroc，Hambleton）中，混合物为两种对光有要求的物种，而在其他三个位置，所测试的混合物则包含了不同的耐荫性的物种。进行了大约50年的实验，类似于英国均匀老化的针叶树林的完整旋转。五个实验表明一种物种在混合物中占主导地位的趋势，可能反映出组分物种的耐荫性或其他功能性状上的差异。在这三个实验中 在最后一次评估中，混合物的基础面积显着高于基于纯林的性能所预测的水平（即，混合物“产量过高”）。在其中两种情况下，该混合物的基础面积比生产效率更高的纯林中的基础面积高，表明“过度入侵”。较大的基础面积差异通常在以后的评估日期更为明显。唯一的例外是苏格兰樟子松：西部铁杉混合物，其中较早的收成更高表明具有护理（“促进”）作用。在其余的实验中，混合物的性能符合纯林中各组分物种的生长所做出的预测。总的来说，