An example of automated detection of dead trees. Here imagery taken with a digital airborne Leica ADS40 camera over a radiata pine plantation in Green Hills State Forest was processed and identifies the number and location of trees killed by drought and the bark beetle, Ips grandicollis.

Modern timber plantation management demands a high level of information on just how well plantation stands are doing, in order to accurately predict timber yields, establish harvesting programs and to develop strategies to combat pests.

Balancing these pressing demands with the time-consuming, expensive and labour-intensive technique of on-ground inventory has been an ongoing challenge for all plantation managers.

Recent advances in remote sensing technologies may soon alleviate this pressure.

Collaboration between NSW Department of Industry and Investment forest health researchers, Dr Christine Stone and Dr Russell Turner, and Forests NSW Hume Region planning manager, Duncan Watt, has reached the stage where they can distinguish unhealthy trees, on a computer screen, crown by crown.

Commercial softwood growers in Australia are keen to improve the efficiency and precision of resource inventory underpinning timber supply commitments, Christine Stone said.

At the same time they also need to implement forest health strategies which contribute to their environmental management systems and certification process.

For example, the Australian Forestry Standard requires forest managers to identify, assess and prioritise any potential damage agents that may impact on forest ecosystem health and vitality.

There are a number of remote sensing options available.

Christine said new multi-spectral, digital cameras are helping to shift data collection from manual mapping and aerial photographic interpretation to automated pixel and object-based techniques, suitable for both crown and stand-level inventory and canopy health assessment.

According to Christine, the two major canopy or crown damage symptoms commonly assessed in ground-based assessments are foliar discolouration (or loss of chlorophyll) and defoliation. Both had successfully been mapped and classified using remote high-resolution sensors.

Spectral analysis is a useful tool for canopy and tree health assessment, as reflectance is influenced by properties of the vegetation including foliar biochemistry (such as discolouration) and the amount of green biomass present in the canopy (defoliation), she said.

Airborne laser systems (LiDAR) are particularly good at measuring the three-dimensional arrangement of the vegetation and ground surfaces from which precise estimates of tree height and stem density can be derived, offering a powerful tool for wood resource assessments.

Any damaging agent or process that directly alters these vegetative attributes can be quantified through the fusion and analysis of data from both types of remote sensors.

In addition, the low resolution imaging satellite MODIS acquires data daily and is available free of charge, providing a low-cost option for frequent monitoring of forest plantations at broad scales, showing areas of major change that can be targeted for more detailed investigation.

Remote sensing data are quantifiable, spatially accurate and fully compatible with commercial GIS software used by forest managers, Christine said.

These remote sensing products need to be cost-competitive with current assessment methods, provide equivalent or improved estimates of tree or stand inventory and health and integrate with existing planning and resource assessment programs.

Recent advances in the capacity and range of airborne and satellite sensors and improved image processing means much of this is a realistic possibility.

This article appears in the Spring/Summer 2009 edition of Bush Telegraph Magazine.