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Planning your treescape Part 2: Species Selection and Placement

The main considerations when planning your treescape are:
 |  Andrew Noakes  |  ,

Mature Kanuka too close to a shed, requiring crown lift away from building.

• Purpose of the planting area: native or exotic species; fruiting trees; wildlife habitat; resource production (ie timber, firewood); or problem solving (ie pollution, water retention).

• Available Resources: light, water, soil structure and nutrients.

• Space Limitations and Access: for the tree, the root system, as well as yourself.

• Desire or ability to undertake ongoing maintenance.

There are several factors to consider to achieve long-term results when planning your treescape. It is important to consider that you are really developing an ecosystem/microclimate. There are both biotic (living) and abiotic (non-living) influences on a treescape:

• Biotic Factors: The players in the food chain: producers, consumers and decomposers; all plant matter: trees, shrubs, mosses, grasses, fungi; all animal influences: insects, worms, animal inhabitants; and competition from all living beings for the limited resources in the area.

• Abiotic Factors: Availability of exposure to sunlight (too much or too little) effecting photosynthesis and growth potential; availability to water (too much or too little); inanimate factors of the area (ie soil, rocks, water); and temperature and climate factors.

Tree root systems are also worth consideration when planning a treescape as they are an unseen, but necessary and sprawling part of tree health. The top root structure works as part of the vascular system (absorbing nutrients), and the deeper roots provide structural support. What is often the case with trees is that what you see above the ground is mirrored below; so a large tree has a large root system.

When contemplating the distribution of tree roots, these factors must be assessed:

• Resource Availability: The dynamic vascular system of plants enables the roots to grow towards needed resources like water, nutrients, oxygen available in the soil.

• Soil Type: Soil composition can encourage or inhibit the ways in which the roots grow; they often cannot easily grow through dense soils, but can easily move through loamy soils.

• Soil Compaction: Physical compression (ie buildings, boulders, vehicles), soil structure and water retention can inhibit the ability of the roots to move towards needed resources.

• Tree Species: Varied tree species have different root systems which determine whether the roots grow laterally, vertically, together or separate. This is a major consideration when planting; for example, planting a large, broad leafed species near the house is not a good choice as the roots can interfere with utility structures and foundations.

However, some species have the ability to actually improve the soil structure through their roots (ie clay soil becoming more loamy). The roots of some species also act as a nitrogen fixer and can improve the resources available (this can be beneficial around fruit trees and vegetable gardens). For example, Gladitsia triacanthos (Honey Locust) is a species that improves nitrogen in the soil. A word of warning though, this species has the potential to be a large tree so formative pruning and ongoing maintenance is often required.

When thought is put in to planning prior to planting, the benefits are multi-fold and can be abundant and enjoyed for years to come. So think before you dig.

Next Month… Planning Your Treescape – Part 3: Specific Species Recommendations

Andrew Noakes, of NZ Arb Consultancy, is a local Qualified Arborist and TRAQ Certified Assessor with over 30 years experience caring for trees in a variety of situations. 0204 163 5486