Pittosporum tenuifolium ‘Little Kiwi’

Globular crowns have a rounded form with vertical and horizontal dimensions being approximately equal. Ovoid crowns are somewhat elliptic, broader at the base than they are at the top, with the vertical axis greatly exceeding the horizontal axis. Obovoid crowns are also somewhat elliptic, with the vertical axis greatly exceeding the horizontal axis but are broader in the upper part of the crown. Conical crowns are approximately triangular in their outline and are broadest at their base. Columnar crowns have a vertical axis that greatly exceeds the horizontal axis but the proportions of the upper and lower crown are similar. Irregular crowns have an asymmetrical and uneven outline. Weeping crowns have strongly pendulous branches. Vase crowns are much broader in the upper crown, which is often relatively flat rather than rounded.

Information sourced from the Tree Species Selection for Green Infrastructure guide produced by the Trees & Design Action Group. Find the guide here: https://www.tdag.org.uk/tree-species-selection-for-green-infrastructure.html

Healthy crowns differ in their density as a function of leaf and branching characteristics. Three categories are used: dense, moderate and open. In some cases, it has been possible to underpin these categories with leaf area index (LAI: leaf area per unit ground area (m² m^-2) data. Dense crowns typically have a LAI of >6m² m^-2, moderate crowns 3-6m² m^-2 and open crowns <3m² m^-2.

Information sourced from the Tree Species Selection for Green Infrastructure guide produced by the Trees & Design Action Group. Find the guide here: https://www.tdag.org.uk/tree-species-selection-for-green-infrastructure.html

The four-level scale, tolerant to drought; moderately tolerant to drought; moderately sensitive to drought; and sensitive to drought, makes use of a number of sources of information. The Niinemets and Valladares (2006) scale integrates a range of climatic factors and the physiological potential to survive with <50% of foliage damage or dieback to create a continuous five-level scale (see table below).

Scale used by Niinemets and Valladares (2006) to rank 806 temperate woody species according to their drought tolerance. Trees were allocated a ranking based on their ability to survive on a site, with <50% foliage damage and dieback. P : PET is the ratio of precipitation to potential evapotranspiration.

Information sourced from the Tree Species Selection for Green Infrastructure guide produced by the Trees & Design Action Group. Find the guide here: https://www.tdag.org.uk/tree-species-selection-for-green-infrastructure.html

Most temperate deciduous trees can cope with several weeks, waterlogging during the period of winter dormancy as metabolic activity is minimal. However, waterlogging during active growth is more serious because roots are more active and require aerobic soils. In general, the more active the growth, the more rapidly the effects of waterlogging can be seen. Factors such as the water oxygenation status and temperature will also affect how acutely waterlogging stress develops so there can be a great deal of variation around how trees experience waterlogging stress.

For this scale, tolerant species can survive consistent waterlogging for the duration of the growing season. Moderately tolerant species can survive consistent waterlogging for approximately one month during the growing season. Moderately sensitive species are only likely to survive if the waterlogging event is less than two weeks during the growing season and sensitive species are only likely to survive if the waterlogging event is less than a few days during the growing season. However, it is important to note that as this scale relates to the likely time-course to tree mortality, symptoms of waterlogging (and associated dysfunction) will be apparent within a shorter period of time.

Information sourced from the Tree Species Selection for Green Infrastructure guide produced by the Trees & Design Action Group. Find the guide here: https://www.tdag.org.uk/tree-species-selection-for-green-infrastructure.html

A species is allocated its shade tolerance rating based on whether they can grow satisfactorily at a certain light availability. The four-level scale used relates approximately to the following light conditions, expressed as a percentage of full sunlight: tolerant (<10% full sunlight); moderately tolerant (10-25% full sunlight); partially tolerant (25-50% full sunlight) and intolerant (>50% full sunlight).

It should be noted that many species towards the more tolerant end of the spectrum often perform better in slightly higher light levels than their tolerance rating suggests, however, it is generally unrewarding to plant moderately tolerant or tolerant trees in fully open (high-light) environments. It should also be acknowledged that, for many larger species, shade tolerance diminishes somewhat with age. This is because a tree’s need for shade tolerance is typically reduced as it becomes established within the forest canopy. Therefore, the allocated ratings are most closely related to young trees of the species and not fully mature specimens.

Information sourced from the Tree Species Selection for Green Infrastructure guide produced by the Trees & Design Action Group. Find the guide here: https://www.tdag.org.uk/tree-species-selection-for-green-infrastructure.html