Types of introduced hollows & cavities

Our team of arborists and ecologists can assist on any canopy access project from arboreal research to the installation of species targeted cavities and hollows.

Types of introduced hollows & cavities

There are a range of methods for introducing a cavity or hollow into a tree or log, there is no right or wrong way however there are some key considerations.

Hollows can be fully created or they can be accelerated.  Acceleration of hollow formation has been explored around the world with tools such as fire and water some methods are faster (e.g. explosives), or slow (fungal inoculation), we continue to experiment in this area.  The information below relates to the introduction of completed usable hollows.

Many types of tools can be used, particularly hole boring and wood cutting tools attached to grinders, currently in the industry there are three primary methods being used for mechanically introduced hollows in trees:

Treetec door / Narrow door

Our team developed this methodology over some years of experimentation.  It provides a range of advantages and eliminates a few problems but it’s still a work in progress.  The narrow width reduces wound impact whilst allowing generous internal dimensions, these doors reduce issues related to ventilation, drainage and longevity.

A narrow slot is cut into the tree, the wider internal cavity is then created with a chainsaw or other tools and then a pre-made door is fitted.  This methodology allows enough access for internal excavation but keeps the wound narrow which is a key issue for protecting tree structural integrity. We’ve installed thousands of these cavities.

In partnership with ARI (DELWP) as part of a research project we’ve installed over 100 Treetec Doors into fast growing Mountain Ash of the Central Highlands Victoria, these hollows were designed to suit Leadbeater’s Possums.  The research on occupancy, cavity microclimate and tree response is ongoing.

Hollow Hog

The HollowHog is a tool invented by Matt Stephens out of NSW Australia. It is powered by a typical angle grinder and a portable generator, and in most cases requires an external vacuum to remove debris. It allows an internal cavity to be created through a 50mm or larger opening. This method has been designed to minimise the overall wounding in live trees, however wound wood formation is an issue that has resulted in most users adding entry modifiers such as spouts to combat wound closure. Correct installation of these entry modifiers requires a greater surface area of wounding (~90mm diameter) but does allow control of specific entry sizes smaller than 50mm.

From our experience using the hollow hog, it excels where:

  • larger tree options are limited,
  • site access is good for movement of vehicles & equipment,  and
  • target species requirements are small (entry holes 40mm diameter or less).

We have found that for larger internal hollows with entry requirements 50mm diameter or greater, the narrow door method  (discussed above) is the most efficient and cost effective. Treetec utilise both methods on many projects.

Faceplate method

Using a chainsaw a large ‘faceplate’ is cut from the tree, a cavity is created within the internal trunk behind that cut, then the faceplate is reattached, usually with an entrance hole bored through it, or through the trunk to meet the internal cavity.

This is a versatile method but is not suitable for live trees; the wound is far too wide, thus greatly impacting tree health and structure. Additionally, the faceplate of live wood will more than likely split over time due to shrinkage.

The Faceplate method is best used on dead trees that have been pruned to reduce the crown above the wound.

Nest boxes vs introduced cavities

Key considerations related to introduced cavities & hollows

Melbourne Arborist