Improving small-plantation and woodlot inventories

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Small plantations and woodlots are a vital part of the New Zealand forest sector. Growers of these woodlots include an estimated 14,000 small-scale and medium-scale forest owners and much of this resource is found on New Zealand’s farms.

Accurate assessment of these forests is important for ensuring realistic valuation during forest transactions and to understand current and future wood availability at regional and national levels.

Forest inventory traditionally involves installing sufficient sample plots to estimate saleable volume separated by log grade. This may deemed to be too expensive for smaller plantations because they are sometimes highly variable, and are of low total value compared to larger forests. As a result, insufficient field plots may be measured to keep costs down.

Too few ground plots can lead to inaccurate estimates of the forest value. Precision estimates obtained in this way, such as probable limit of error (PLE), may be misleading. Potential buyers may undervalue the resource to compensate for the high degree of uncertainty. On the other hand, an over-estimation of the value could lead to unexpected results at harvest with detrimental flow-on effects for rural businesses.

Improving the methods for estimating yields is important to support the management of small-plantations and to ensure the sustainability of this important wood source. A two-year research programme initiated at Scion (NZ Forest Research Institute) aims to do just that.

This research will develop methods to integrate remotely sensed data into forest inventories at an appropriate scale and in a cost-effective manner. Remote sensing based inventory techniques have been developed for larger plantations, but these methods are not well suited to smaller forests. We intend to develop new methods to allow for more precise and cost-effective estimates of the volume and value of small to medium-scale forests.

The research programme has several distinct themes including re-using existing data where appropriate, providing methods for integrating newly collected data and focussing on developing unmanned aerial vehicles (UAVs) for forest inventory. At the end of the project we will have a set of options for small to medium-scale forest growers to assess their trees more accurately.

In recent years, statistical techniques have been developed that enable data from laser scanners on board conventional aircraft (LiDAR) to be integrated into forest inventories. These techniques are now routinely applied across major commercial forests in New Zealand and Australia with considerable success.

However, these methods are not well suited to small-plantations. This is due in part to the requirement for a large number of field sample plots to exploit the most popular statistical modelling methods.

These plots can easily be accommodated in the measurement programme of a large estate, but are prohibitively expensive for small-plantation growers. Furthermore, larger forests can access cost efficiencies in aerial data collection through acquisition over larger areas.

As part of this research Scion will investigate whether small to medium-scale forest growers can access the benefits of existing techniques by following a community-based, data sharing method. We hope to collate a database of field plots from a group of participants who are willing to share their data. Field plot data may have been installed specifically by a user for this purpose or may be acquired from pre-existing sources such as permanent sample plots (PSPs), already established forest inventory plots, or field measurement plots associated with the Emissions Trading Scheme (ETS). These data will be combined with freely available remotely sensed data frequently collected by regional or national government agencies. We hope that this will provide useful forest yield data for all participants.

The success of this approach depends on finding willing participants who will share their data. All data can be made anonymous if required. If you are interested in helping with this research and becoming part of a community of users, we would love to hear from you. Please get in touch with Jonathan.dash@scionresearch.com by e-mail. We will also be targeting small-forest growers through forest management and forest consulting companies so you may well hear from us directly.

We will be presenting our research results via seminars and articles in both scientific and industry publications in 2018. The work is being supported by AgMardt, Forest Growers Levy Trust, New Zealand Farm Forestry Association, The Neil Barr Foundation and Scion’s core funding.

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