{{Short description|Fast-growing non-indigenous trees used as a nurse crop}} {{Use dmy dates|date=April 2024}} {{Use New Zealand English|date=April 2024}} [[File:Milnthorpe Park MRD 01.jpg|thumb|Exotics and natives combine to make a popular recreational ecosystem]] The '''Milnthorpe Model''' describes a situation where fast-growing [[Introduced species|non-indigenous]] trees such as [[Eucalyptus|eucalypts]], are used to [[Colonisation (biology)|colonise]] ex-pasture in order to establish a forested environment where indigenous canopy species can thrive.
The expression was coined in 2010 during a nationwide MAF ([[Ministry of Agriculture and Forestry (New Zealand)|Ministry of Agriculture and Forestry]]) roadshow on carbon forestry and derives from a {{convert|162|ha|adj=on}} property<ref>{{cite web |title=Property Details |url= https://ce.tasman.govt.nz/rates/properties/1862014200 |publisher=[[Tasman District Council]] |access-date=1 April 2024}}</ref> near [[Parapara Inlet]] in [[Golden Bay / Mohua|Golden Bay]], New Zealand. This marginal land was progressively planted from 1973 to create what is now a [[Scenic reserves of New Zealand|scenic reserve]] and an [[arboretum]]. It has an abundance of [[Understory|understorey]] species, predominantly natives, and is a popular location for recreational walks.<ref>{{cite book |last1=Gaffney |first1=Sally |title=Man, slasher, wheelbarrow: The story of Milnthorpe Park Arboretum |date=2020 |publisher=Sally Gaffney |isbn=9780473526290}}</ref>
==Importance of the Milnthorpe Model== Recent years have been particularly tough for sheep and beef farmers in New Zealand. A report from [[Beef + Lamb New Zealand]] in 2023 forecast farm profitability to fall by 31% for the 2023–24 year, following a decline of 32% in 2022.<ref>{{cite web |title=New Season Outlook 2023–24 |url= https://beeflambnz.com/sites/default/files/2023-10/New-Season-Outlook-23-summary.pdf |publisher=[[Beef + Lamb New Zealand]] |access-date=1 April 2024 |date=October 2023}}</ref> This means profits for farmers have more than halved in two years. For example, it is now common for sheep farmers to spend more money on shearing their sheep than the return from their wool-clip.
There are several motives for seeking to afforest marginal farmland. First, it is often profitable to do so. The returns from wood can exceed the returns from livestock. In addition, there are payments from the sale of [[Carbon offsets and credits|carbon offsetting]]. Lastly, there can be environmental benefits compared to pastoral farmland, in terms of reduced soil erosion, water quality, and buffering of flood peaks.<ref>{{cite book |last1=Maclaren |first1=J. Piers |title=Environmental Effects of Planted Forests in New Zealand |date=1996 |publisher=[[New Zealand Forest Research Institute]]}}</ref>
===Benefit of eucalyptus trees=== [[File:Milnthorpe Park ADW 005.jpg|thumb|Indigenous species under a cover of mixed eucalypts]] [[Carbon sequestration]] is about the conversion of a low-carbon ground cover such as pasture of short scrub to a forest with more biomass, and therefore carbon.<ref>{{cite book |last1=Maclaren |first1=J. Piers |title=Trees in the Greenhouse: Forest Research Bulletin No. 219 |date=2000 |publisher=[[New Zealand Forest Research Institute]] |location=[[Rotorua]]}}</ref> Eucalypts, in particular, can create a huge volume of wood and in a short time, although this will depend on the exact species of eucalyptus and the growing conditions of the site.
===Importance of native trees=== There is a widespread backlash, particularly from the farming community, against large conversions of farmland to forestry. In New Zealand, pine trees receive the most opprobrium, but in several other countries the target is eucalyptus plantations. Natives, on the other hand, have a favourable image everywhere. In New Zealand, this is accentuated because indigenous forest occupied nearly all suitable land in the fairly recent past,<ref>{{cite journal |last1=McGlone |first1=Matt S. |last2=Bellingham |first2=Peter J. |last3=Richardson |first3=Sarah J. |title=Science, policy, and sustainable indigenous forestry in New Zealand |journal=New Zealand Journal of Forestry Science |date=2022 |volume=52 |issue=8|doi=10.33494/nzjfs522022x182x |doi-access=free }}</ref> and because New Zealanders have a great love for their own flora, much of which is endemic.
===Desirability of fast-growing introduced species=== [[File:Milnthorpe Park ADW 011.jpg|thumb|Indigenous epiphytes colonising a wilding radiata pine]] It is desirable to plant eucalypts or other fast growing introduced species in New Zealand, in order to create a native forest. It is prohibitively expensive, in most cases, to directly plant natives (particularly with some of the preferred canopy species, such as [[Podocarpus|podocarps]]). These expensive seedlings do not readily tolerate competition from grass or introduced woody weeds, and have a high mortality rate. The natural succession of native forest growth from a cleared area, such as a slip, would involve several stages, taking several hundred years altogether to reach their climax cover. On the other hand, planting eucalypts is relatively cheap, and the grass and other problematic weeds are soon shaded out. Seeds of a range of native species are brought in by birds and grow readily on the forest floor. It is thus usually quicker and cheaper to use non-indigenous trees as a [[nurse crop]] rather than directly establishing natives.<ref name="Forbes 2019">{{cite journal |last1=Forbes |first1=Adam S. |last2=Norton |first2=David A. |last3=Carswell |first3=Fiona E. |author2-link=David Norton (botanist) |author3-link=Fiona Carswell |title=Opportunities and limitations of exotic Pinus radiata as a facilitative nurse for New Zealand indigenous forest restoration |journal=New Zealand Journal of Forestry Science |date=6 July 2019 |volume=49 |issue=6 |doi=10.33494/nzjfs492019x45x |url= https://nzjforestryscience.nz/index.php/nzjfs/article/download/45/11/527 |issn=1179-5395|doi-access=free }}</ref><ref name="Forbes 2020">{{cite journal |last1=Forbes |first1=Adam S. |last2=Wallace |first2=Kiri J. |last3=Buckley |first3=Hannah L. |last4=Case |first4=Brad S. |last5=Clarkson |first5=Bruce D. |last6=Norton |first6=David A. |author3-link=Hannah Buckley |author5-link=Bruce Clarkson |author6-link=David Norton (botanist) |title=Restoring mature-phase forest tree species through enrichment planting in New Zealand's lowland landscapes |journal=[[New Zealand Journal of Ecology]] |date=2020 |volume=44 |issue=1|doi=10.20417/nzjecol.44.10 |doi-access=free }}</ref>
==Lessons from Milnthorpe Arboretum for native establishment== There is a pleasant mix of native understory species in the at Milnthorpe, such as [[tree fern]]s, [[Melicytus ramiflorus|māhoe]] (whiteywood) and [[coprosma]]. Occasionally, there are examples of self-sown [[Dacrycarpus dacrydioides|kahikatea]] or [[Podocarpus totara|tōtara]], but most other canopy species such as [[Dacrydium cupressinum|rimu]] needed to be planted by humans. In the light shade that eucalypts provide, and in the weed-free forest floor, their rate of survival and growth is excellent.<ref name="Forbes 2019" /><ref name="Forbes 2020" />
==Nationwide applicability== In Milnthorpe, prior to planting there were large areas of [[Ulex europaeus|gorse]], [[blackberry]] (on better soils), [[Hakea amplexicaulis|prickly hakea]], post-fire [[Kunzea ericoides|kanuka]], and a few [[Neopanax arboreus|five finger]]. In the wetland areas, there were masses of stunted [[Leptospermum scoparium|mānuka]].
Milnthorpe Arboretum lies at sea-level in a warm, wet, fairly wind-free microclimate. Examples of similar plantings from other regions and microclimates must be examined before a useful generalisation could be made. A study of three such situations – including Milnthorpe – was undertaken by Forbes in 2021.<ref>{{cite report |author1=Te Uru Rākau |author-link=Te Uru Rākau |author2=Forbes, Adam S. |date=August 2021 |title=Transitioning Exotic Plantations to Native Forest: A Report on the State of Knowledge |url= |publisher=[[Ministry for Primary Industries]] |page= |docket= |access-date= |quote=}}</ref>
==References== {{Reflist}}
{{Tasman District}}
[[Category:Forestry in New Zealand]] [[Category:Forestry initiatives]] [[Category:Carbon finance]] [[Category:Golden Bay]]