Analysis of the treated wood market for agricultural and horticultural uses in New Zealand

The forest industry contributed $1.91 billion to New Zealand’s GDP in 2019 (Infoshare, 2019), while the other primary sectors of agriculture and horticulture were also prominent in New Zealand’s economy (Westpac, 2016). Horticulture contributed $2.06 billion, while sheep and beef and other livestock farming contributed $4.21 billion in addition to dairy farming’s contribution of $6.16 billion to New Zealand’s GDP in 2019 (Infoshare, 2019). Although each of these industries has been analysed extensively, little has been published about forestry’s relationship with agriculture and horticulture. Specifically, there is little publicly available information about the treated wood market for agricultural and horticultural uses in New Zealand. Ostensibly, this market is significant, with these primary industries playing a key role in New Zealand’s economy. Roundwood is a term commonly used to define both posts and poles, including other materials such as strainers, half rounds, quarter rounds etc. There is a continuous transition in terms of production of posts to poles, with compliance to building and construction standards such as NZS3605 (2001), AS/NZS4676 (2000) or AS2209 (1994) necessary for the latter (Altaner, 2020). Generally, roundwood post and pole products differ widely across these industries (Manley & Calderon, 1982). This study looked at fence material for stock and crops, kiwifruit pergolas, vineyard posts and other horticultural supporting structures. It did not include treated wood for retaining walls, power poles, decks, sheds and so forth. As the majority of wood used in the agricultural and horticultural industries is in ground contact, there is a risk of fungal decay. Radiata pine (Pinus radiata) is the most commonly used species in these two industries and is the dominant plantation species in New Zealand (Richardson, 1993). However, it is not naturally durable and requires preservative treatments such as chromated copper arsenate (CCA) to be suitable for outdoor applications (New Zealand Timber Industry Federation, 2013). This study used three different ways to estimate the size of the treated wood market for agricultural and horticultural uses. Firstly, the market was estimated directly from an estimate of the stock of treated wood in these industries and an estimate of service life. This method is an approximation and involved reconciliation to increase accuracy. Secondly, the production of treated wood was obtained from data provided by the manufacturers who use treatment chemicals, predominately CCA. Lastly, production at the forest level referring to the volume of harvested wood that makes up the supply of treated wood provided the third estimate. This work is useful for the New Zealand forest industry as it can lead to better utilisation and an increased understanding of markets for the small diameter log resource. When producing posts, smaller diameter logs are used, leading to higher value solid wood products. There appears to be a good opportunity to use commercial thinnings or even harvesting residues for posts (Visser et al., 2018). There is also potential for new markets and products to be found for posts (Altaner, 2020). This research will aid the establishment of a naturally durable hardwood resource (Hedley, 1997) as proposed by the New Zealand Dryland Forests Initiative (NZDFI). The NZDFI project was established in 2008 and proposes eucalypts as a promising alternative to treated radiata pine (NZDFI, 2019). The focus is therefore on the agricultural and horticultural markets (Millen et al., 2018b). Manley and Calderon (1982) also noted that in terms of both the number and volume, the greatest demand in these industries is for relatively small agricultural and horticultural posts.

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