Report: Trees for steep slopes
Sustainable Forest Solutions
Reviewed by Mike Marden, July 2018.
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Please note that the web report is regularly updated whereas the pdf download above is dated July 2018.
|Species rating *|
|Early growth rate||8|
|Root decay rate||5|
In a nutshell
Fast growing pioneering species suitable for eroded soils. Fixes nitrogen and rebuilds soil organic matter, so may be suitable for interplanting with shade-tolerant climax species such as redwood, cypress and fir. Not much is known about alder as a timber species for steeplands.
Alder species are used for erosion control in many countries, especially infertile sites (Naghdhi et al. 2013; Stokes et al. 2009 as cited in Phillips et al. 2015b).
Red alder (Alnus rubra) is easy to establish, is nitrogen fixing and relatively fast growing, reaching 40 cm diameter in 25 years on riparian margins (May, 2017).
Red alder, open ground sown and bare-rooted, was tested for early root growth and was found to be the best performing species in terms of height, lateral root spread and total root length and was therefore considered to be "a prime candidate for consideration as an erosion control species" (Phillips et al. 2015b). However, this trial was located in a sandy loam alluvial terrace near Gisborne with a seasonal water table (Phillips et al. 2015b), which may have suited the species compared with eroded and erodible hill country. However, alders have been used overseas to consolidate landslips (Phillips et al. 2015b)
Italian alder (Alnus cordata) has been successfully used as a nitrogen-fixing nurse crop for redwood in Manawatu hill country, interplanted as every second tree. The alder had faster initial growth and forced the redwood upward and with small branches. The redwood from about ten years of age began to dominate the alder and by year 13 was overtopping it, with all redwood branches remaining alive and small (P. Silcock, pers. comm).
Caucasian alder (Alnus subcordata) is one of the larger growing alders in New Zealand (T. Rose, pers. comm).
Alders can grow well in poor soils, provided these do not dry out and have been observed to grow twice as fast on southern-facing slip faces than on quality adjacent soils. (B. McNeil, pers. comm).
Red alder timber is easy to mill and season and "produces a stable, medium density, light brown timber suitable for panelling, joinery and furniture" (May, 2017).
Red alder is easily worked, glues well, takes a good finish and is increasingly being used for furniture and cabinetry. (Walton, 2009).
Clearwood red alder retails in North America for over $2,000 per cubic metre (May, 2017).
Disclaimer: The opinions and information provided in this report have been provided in good faith and on the basis that every endeavour has been made to be accurate and not misleading and to exercise reasonable care, skill and judgement in providing such opinions and information. The Author and NZFFA will not be responsible if information is inaccurate or not up to date, nor will we be responsible if you use or rely on the information in any way.