Introduction

In our last tree bark themed blog we discussed the value of coloured tree bark in the landscape, however colour is only one aspect of bark to provide interest.

In this blog we shall address the often underrated textural qualities of tree bark, and go into detail of how we can maximise their visual impact to elevate our landscape designs.

Textural qualities of bark

When hearing the word “tree bark” a typical person may think of a generic rough-brown surface, however there is so much more to tree bark. Bark can be smooth, rough, shiny, flaky, peeling, fissured, bumpy, rounded, hairy.

Tree bark is not always constant – it can change over time, sometimes starting smooth before developing increased roughness/fissures (e.g. Prunus sp.). Some of the amazing textural qualities of tree bark are not apparent straight away and can take years to develop (eg. Carya ovata), while in other species bark interest is apparent even in young specimens (e.g. Prunus serrula), but may lose vibrancy over time.

When selecting tree species for bark interest – consider the time factors involved. Do you want instant bark interest, with tree bark that may lose some visual interest over time, or do you want a tree with bark that improves over time?

Species lists

In the following species lists we have divided trees into the following categories – flaky/peeling tree barks, rough/fissured tree bark, hairy/fibrous tree bark and patterned tree bark. (Please note this is not an exhaustive list – there are many more unlisted species, as well as species listed which could fit into multiple categories.)

Tree bark noted as having particularly strong/exaggerated qualities are highlighted in bold.

Flaky/Peeling bark species often reveal a smooth/shiny surface beneath, providing a mosaic of textures that visually ‘break up’ the vertical structure of the tree stem. These include species such as:

• Acer buergerianum
• Acer griseum
• Acer triflorum,
• Arbutus unedo
• Betula ermanii
• Betula nigra
• Betula papyrifera
• Betula utilis sp.
• Carya ovata
• Cupressus arizonica
• Eucalyptus gunnii
• Heptacodium miconioides
• Juniperus virginiana
• Metasequoia glyptostroboides
• Prunus maackii
• Prunus serrula
• Stewartia sinensis
• Taxodium distichum
• Taxus baccata

Rough/Fissured bark includes species with an uneven surface, sometimes rounded or forming ridges and crevices within the surface. This category is more typical (or appears stronger) in older tree specimens, and these characteristics may not be apparent on younger trees as the fissures and topography of the surface can take years to develop. These include species such as:

• Acer campestre
• Acer pseudoplatanus
• Alnus glutinosa
• Araucaria araucana
• Castanea sativa 
• Catalpa sp.
• Cedrus sp.
• Celtis occidentalis
• Cercidiphyllum japonicum
• Cercis canadensis
• Cercis siliquastrum
• Chamaecyparis lawsoniana
• Corylus colurna
• Crataegus sp.
• Cupressus macrocarpa
• Ginkgo biloba
• Gleditsia triacanthos
• Juglans sp.
• Larix sp.
• Liquidambar styraciflua
• Liriodendron tulipifera
• Phellodendron amurense
• Picea sp.
• Pinus nigra
• Populus sp.
• Pseudotsuga menziesii
• Pterocarya fraxinifolia
• Pterocarya stenoptera
• Pyrus calleryana
• Quercus suber
• Quercus sp.
• Robinia pseudoacacia
• Salix sp. 
• Tilia sp.
• Tsuga sp.
• Ulmus sp.

Hairy/fibrous bark are present on primarily coniferous tree species, and are typically more subtle than the other categories, requiring closer proximity by the casual viewer to be noticed. These include species such as:

• Cryptomeria japonica
• Juniperus communis
• Sequoiadendron giganteum
• Sequoia sempervirens
• Thuja plicata

Patterned bark include species with repeated blocks of colour or fissures forming a pattern. Although this category could include many within the rough/fissured bark category, these species have a more obvious, distinctive and less chaotic pattern to the human eye. This includes species such as:

• Ailanthus altissima
• Acer capillipes 
• Acer davidii 
• Carpinus betulus
• Cornus sp.
• Cydonia oblonga
• Diospyros kaki 
• Eucalyptus aggregate
• Eucalyptus deglupta (unfortunately not hardy enough for outdoor use in the UK)
• Eucalyptus pauciflora
• Halesia Carolina
• Maytenus boaria
• Parrotia persica 
• Picea abies
• Picea orientalis
• Platanus orientalis
• Platanus x hispanica 
• Populus alba 
• Pyrus communis
• Stewartia pseudocamellia 
• Stewartia sinensis
• Syringa vulgaris

Bark design principles

So it’s all well and good understanding what trees have what bark, but how can we use this information to inform our landscape design?

Through repetition of complimentary textures, trees can be grouped together in the landscape to accentuate their characteristics. For example, using a palette of exclusively peeling bark trees will provide a pleasantly obvious, but unique sense of cohesion within the landscape.

Using a polyculture of species with similar characteristics provides the benefits that could be obtained from a monoculture of species i.e. a sense of unity/cohesion, but without the drawbacks of increased risk of landscape damage from pests/diseases; as well as overall having greater biodiversity.

‘Birch monoculture: Should one of these birches become infected with pests or disease, the whole area of tree planting is at risk’ (Photo: Monoculture, Martyn Ferry, 2016)

This concept is not only limited to tree bark, it can apply to foliage, flower colour or even plant habit to create cohesive palettes of plants.

Alternatively through contrast, such as proposing a Prunus serrula tree with its smooth shiny red bark, next to a tree with one of the rough/fissured bark species, the relative smoothness and roughness of the trees are accentuated for added interest.

Amongst trees with unexciting tree bark, consider using a specimen tree with exceptional bark interest (see trees in bold in the species lists) to pull focus towards it – especially within the winter months when bark is exposed.

Specification of trees with unique bark

There are a few ways to specify trees with bark interest to maximise the visual impact of the bark:

• Avoid specifying as feathers, as the foliage will obscure the trunk for a large portion of the year (if not all for evergreen species).
• If planting as a single-stem tree, specify it as having at least 175cm (if not 200cm) of clear stem, for a clear view of the trunk for pedestrians.
• Maximise bark visibility by specifying as a multi-stem tree, as more stems = more bark impact.
• Ideally specify a deciduous species, so that within the winter months the bark is exposed and not overshadowed by foliage.
• If planting shrubs around the base of the stem, make sure they are relatively small and do not obscure too much of the trunk.
• Avoid planting ivy or other vigorous self-clinging climbers nearby, as they could completely obscure the bark.

Optimal positioning

So where can we position trees with interesting bark to get the most out of their visual interest?

As the trunk of a tree occupies a much smaller area of the human eye compared to the foliage of the canopy, human proximity to the tree needs to be much closer in comparison to get the visual impact of tree bark.

For this reason, it is better to specify trees with textural bark in pedestrian/static/slow moving spaces, such as near seating, or within play areas where people will be in close proximity to the trees in question, and have the time to notice and appreciate the surrounding landscape. This is in contrast to a dynamic/fast moving space like a roundabout, where drivers and car passengers will have less time to take in these detailed characteristics. In this case species selection for aesthetic qualities might be better selected by foliage interest instead.

As a general rule, trees with peeling barks generally have a larger detail scale (as the peeled bark is larger in size), meaning the detail can be viewed from further away compared to patterned trees, or trees with rough/fissured bark. As such peeling barks could be considered the preferable bark texture in dynamic/car dominated spaces where the distance to the tree trunk is greater, and there is less time to view the texture.

On the opposite end of the scale hairy/fibrous barks have a much smaller texture scale and as such require very close proximity to the trunk (preferably touching distance) to clearly see the fine hair-like strands of bark.

Patterned barks, and rough/fissured barks textures are more variable in scale, and as such need to be considered on a more species by species basis.

For definitive values and calculations, refer to our next blog, which goes further into depth considering factors such as visual acuity and the scale of tree bark textures, to provide optimum viewing distances.

Joseph D’Ambrogio