Forest Inventory and New Technological Developments

Last December the second National Forest Inventory was published and the main findings were highlighted in this newspaper on the 14th January. As a national inventory it provides invaluable information about Ireland’s forest estate at the macro level, and one of the telling statistics is that 56pc of the entire estate is still less than 20 years old. That said, with every passing year many more thousands of hectares of private forest enter the harvesting stage, consequently taking stock and preparing an inventory at the micro, individual private forest level becomes a vital component of sound forest management.
Good management requires knowledge. The amount of available knowledge has a direct bearing on the quality of management, and allows informed decision making. Knowing the extent of the assets owned by and available to the owner or manager is fundamental to a successful business.
A woodland inventory should be prepared once a first thinning has been completed when it is possible to “see the wood for the trees”. A well prepared inventory gives the owner a snapshot of the stock of timber in his woodland, and is therefore an essential component of a woodland management plan. The inventory must be updated regularly to take stock of the growth in volume, and as a matter of course should be updated following each harvest. Over time the emphasis with many of our even aged and predominantly spruce plantations will be to convert them to more uneven aged forests with greater species diversity and inventories will become an increasingly important part of management planning.
The Woodland inventory
An inventory is best set out in the form of a table (an Excel spreadsheet or equivalent is ideal). Depending on the size and age structure of the woodland it should be separated into compartments, and possibly sub-compartments too, if necessary, and an example is included in the table below:


The notes column should include any pertinent points relevant to the compartment in question, for example other minor species, open areas, or a description of biodiversity, archaeological or other features that should be noted.
To get as accurate a picture as possible it is important to take sample plots throughout the plantation. The number necessary will vary, but as a guide for areas of two to ten hectares the recommendation is for eight plots for uniform crops and twelve where there is greater variability.
Of course it is also important to choose plots at random and evenly spaced throughout the plantation.
The information gathered not only gives an indication of what the woodland contains at a particular point in time but is essential in planning a thinning, and more specifically as a tool to help with thinning control. Second and subsequent thinnings need to be carefully controlled if the crop is to realise its full potential, and therefore maximum value.

Yield Class
The concept of yield class is often mentioned by foresters but not always understood by the layman. The growth of a tree may be measured in terms of height, diameter, volume or weight, but volume is the most meaningful for management purposes. In an even-aged stand the cumulative volume production divided by the age of the stand is referred to as the mean annual increment (MAI), but the growth curve of a tree is not a straight line. During the early years growth is vigorous, it reaches a maximum and then declines with increasing age. The point at which the MAI curve reaches its maximum is the maximum average rate of volume increment which the stand can achieve and this number is the yield class. Therefore a stand with a maximum MAI of 20 cubic metres per hectare has a yield class of 20.
Fortunately there is a close correlation between cumulative volume production and the top height of a stand so yield class is relatively easy to measure. In actual fact, most crops in Ireland never reach their full potential yield class as almost invariably they are harvested before the age of maximum MAI, but yield class remains an important item in the management tool box, not least because the second and subsequent thinnings should aim to remove 70 pc of the yield class. Thus, on a 5 year thinning cycle, for a plantation of yield class 20 the aim should be to harvest 70 cubic metres per hectare (YC20 x 5 years x 70pc = 70 cubic metres).

Technological developments
For much of the last 100 years forest measurement techniques changed very little, and to take accurate measurements from a sufficient number of sample plots is inevitably labour intensive. Typically the tools of the trade consist of a girthing tape to measure diameter at breast height, a hypsometer to measure tree height, and more recently electronic calipers connected to a portable computer which speeds up the recording process.
A year ago I wrote in these pages of the Cork-based forest technology company Treemetrics Ltd. Treemetrics has been developing a completely new system of forest measurement that is now gaining international recognition for its considerable accuracy. Using sophisticated laser scanning equipment, the company can measure both the volume of timber in a stand and also assess tree form, taper and stem straightness before a saw goes anywhere near it. Previously these features could only be established after the tree was cut.

Forest Mapping & Monitoring (The Forest Mapper™)
Traditionally, maintaining informative and accurate maps has presented a challenge to foresters. As the forest grows and closes canopy it is increasingly difficult to maintain a picture of productive area, and frequently the forest manager can only make an informed guess regarding the percentage that is unproductive. Treemetrics is the first system that integrates satellite imagery with aerial and terrestrial laser scanning, thus allowing accurate mapping of the forest into all categories of productivity.
Treemetrics, in partnership with the European Space Agency, have just announced the development of a new global forest mapping and monitoring product called Forest Mapper™
This has now been released in Ireland to assist private owners to understand their forests better. According to Enda Keane of Treemetrics “the Irish forest industry is entering a new exciting phase with the ever increasing emergence of private timber harvesting. Forest owners and buyers are now asking key questions about the quality, quantity and value of available timber. In addition, forest owners with younger plantations wish to know when their forests will be suitable to harvest.”
Treemetrics have developed the system to provide an independent method that also assists the valuation of a forest. Utilising the latest satellite images and global mapping technology, and image analysis software, Mr Keane says they are able to obtain new insight into the quality of the forest. The technology enables them to count the individual trees as the crop matures, providing owners, foresters and sawmillers with key planning information to assist in optimum decision making.
Mr Keane says Treemetrics can also assist with the ongoing automated monitoring of the crop. Forest disturbance caused by storms, disease and the increasing threat of theft can be monitored remotely.
While sample measurements still need to be undertaken on the ground, the system calculates the minimum number of sample plots required and their most suitable locations, thus reducing the cost associated with this operation. A phone application has been developed with accurate GPS technology to help navigate the forester to the right locations to collect the measurements and the resulting data is automatically sent to the online system where it can be stored and analysed.
Treemetrics will be announcing key partnerships to assist with the roll out of the system nationally and internationally over the coming months, and the company can be contacted at or by phone at 021 7304630.

Forest Inventory and New Technological Developments


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