Soil Science in the New Zealand Forestry Sector
The predominant production system followed by the New Zealand forestry sector is a low input, short rotation model. This results in significant disturbance to forest soils on a much more frequent basis than occurs in other countries, e.g. rotation lengths of 30 years compared with 60 years. This increased pressure placed on soil resources has the potential to degrade the ability of the soil to support forest establishment and growth, resulting in reduced yield over multiple rotations.
In response, Crown Research Institute for forestry, Scion, has conducted extensive research into the factors that affect the ability of soil to support productive forests. This research has extended over time from simple assessments of soil nutrient pools to assessments of the stability of soil processes that determine the flux and availability of those nutrients, the activity of the soil microbial communities that influence forest health and growth, and the importance of the physical structure of soil to the sustainability of forestry operations.
Although this research has identified a range of opportunities to develop improved forest management systems, to date it has resulted in only limited changes to silvicultural practices. A key reason for this is unfamiliarity with soil itself as an indicator of site productivity. Analysis of foliar tissue has long been considered the simplest method to determine if a forest stand is deficient in key nutrients. To further explore issues in the use of soil-based data in forest management, we surveyed opinions on the role of soil research across the forestry sector.
The survey collected information from 130 respondents, including farm foresters, small-block owners, corporate foresters, and independent forestry consultants across most regions of New Zealand. Survey information indicated that the vast majority of respondents regarded soils as relevant to forest productivity and were interested in making use of soil data. However, it was equally apparent that most respondents considered themselves unable to conduct soil sampling effectively, or to take soil data and translate it into practical actions that could be incorporated into their forest management strategies.
To address this lack of confidence, Scion has instigated a series of forest soil sampling workshops to provide the sector with greater understanding of methods for soil sampling (Fig. 1). Issues discussed included the use of mapping systems and sufficient replication to ensure soil samples are representative of the area in question, the timing of sampling efforts within the life of the forest stand, and the level of resolution in sampling across the landscape – balanced against the cost-effectiveness of investment in soil collection and analysis. The workshops comprised a field component, allowing the attendees to become familiar with the various tools and techniques used to obtain the different kinds of soil samples, which is a critical element in understanding the time required to conduct such sampling (Fig. 2).
Through the “Growing confidence in forestry’s future” (GCFF) research programme, Scion works closely with the sector to address the successful use of soil data to inform forest management. This spans a diverse range of projects, including issues of precision nutrient management, enhancing the activity of beneficial soil microbes, and maintaining license to operate through assessment of the environmental sustainability of management.