Spruce woods thrive in the highest locations from about 800 m to the tree line at around 1,000 m above sea level. These woods are also home to some deciduous trees such as rowan, silver and downy birches (Betula pendula and Betula pubescens) and willows (Salix spec.). Conditions of high humidity foster an environment rich in mosses and lichens. In spite of the near-natural habitat there are only a few, indigenous, genetically adapted (autochthonous) spruce trees. Wood-reed spruce woods dominate. A well developed ground vegetation thrives on their moderately rocky and fresh, but certainly not wet, soils, characterised in appearance especially by grasses such as shaggy wood-reed (Calamagrostis villosa) and wavy hair-grass (Avenella flexuosa). The soils in the higher regions are, as in most of the Harz, comparatively poor in nutrients and bases, so that only a few herbaceous plants occur here, such as heath bedstraw (Galium saxatile). For that reason it is more the ferns, mosses, lichens and fungi that, in addition to spruce trees, characterise these woods. Boulders and stone runs occur in the areas of weather-resistant rock in the high (alti-)montane and montane zones - these are extreme habitats for vegetation. Due to the lack of soil material, only weak, straggly, very open spruce woods thrive here. They have an especially high variety of trees and allow more room of light-loving species such as silver birch, rowan, sycamore, willow and dwarf bushes such as the blueberry (Vaccinium myrtillus). Mosses and ferns are also common here. One unusual species is the Carpathian birch (Betula pubescens subsp. carpatica). Bog-spruce woods are found around the raised bogs on marshy and boggy soils. In these sorts of places spruce woods can, in exceptional cases, also form the natural woodland in lower down the mountains. These wet, moorland woods have a high proportion of peat mosses (Sphagnum spec.). The ground vegetation may also have a rich proliferation of low bushes such as cowberry (Vaccinium vitis-idaea). Clumps of purple moor grass (Molinia caerulea) are also typical of this type of woodland habitat. The characteristic species of fungi in natural spruce woods are Phellinus viticola and prunes and custard (Tricholomopsis decora).