Coprosma wallii is a shrub or small tree, endemic to Aotearoa / New Zealand, where there are records from Te Ika a Maui / North Island (Erua, Paengaroa, Eastern Wairarapa), Te Wai Pounamu / South Island – from southern Nelson / North Westland south to Southland, Rakiura / Stewart Island. The estimated population size is 6,000–8,000 mature individuals left in situ, with a maximum 300–600 mature individuals occurring in a subpopulation. There is a decline in the population size, suspected at 10–30% over the next three generations. Currently about one third of the total population is believed full functional and secure. The species is assessed as Vulnerable.

This species is endemic to Aotearoa / New Zealand, where there are records from Te Ika a Maui / North Island (Erua, Paengaroa, Eastern Wairarapa), Te Wai Pounamu / South Island – numerous locations from southern Nelson / North Westland south to Southland (though scarce in Central Otago), and Rakiura / Stewart Island – one location only. Distribution map is generalised.

There are 90 subpopulations ranging from scattered trees through to sites with 300–600 individuals. Collectively it is estimated that there are between 6,000 and 8,000 mature individuals of this species. At some locations single specimens are known (as this species is dioecious – these sites are not included in this overall figure).

The most vulnerable populations are those in the Wairarapa (Te Ika a Maui) where there are many isolated trees or moribund stands of 3–10 trees. Some of the northern and central Otago Te Wai Pounamu / South Island sites also comprise isolated stands of fewer than 20 mature individuals. The largest populations are in Westland and the eastern Southland. At many sites only mature trees are known and recruitment is often an issue. The population trend, although directly unknown, has been suspected to be declining at a rate to cause a decline of 10–30% over the next three generations (estimated at 50 years per generation) (Criteria ‘Declining’ A1 (S1, T1) (Townsend et al. 2008) – see also de Lange et al. 2018).

Coprosma wallii occupies a diverse range of habitats from flood prone alluvial forest, valley floors and the margins of frost flats to rubble slopes and the summits of exposed rock outcrops. However, the preferred habitat appears to be riparian forest and based on the associated geology this species seems to require or follow base-rich substrates such as basalt, limestone, calcareous mud and siltstones and chlorite schists. Coprosma wallii often associates with a range of other similarly threatened or uncommon plants notable examples of which include Coprosma obconica, C. pedicellata, Melicytus flexuosus, Olearia gardneri, Teucrium parvifolium, Pittosporum obcordatum, P. turneri and Mazus novaezeelandiae.

Coprosma wallii probably underwent a major and unnoticed (the species was described in 1925) decline during the initial European settlement of Aotearoa / New Zealand, when riparian forests were cleared for agriculture. Since its formal description in 1925 Coprosma wallii has been found in a wide range of localities suggesting it was formerly more widespread. Until recently the species was poorly known and so undoubtedly overlooked. There are now more localities known for the species because of dedicated surveys and more are being found each year. Nevertheless, despite being a distinct species, the fact that Coprosma wallii is often overlooked (even in well-known sites) has meant that some populations have been partially destroyed by tracking and amenity buildings erected, ironically, within reserves. Most populations are found on private land, and these typically comprise mature or moribund adults with little or no recruitment, in depleted indigenous forest remnants or worse, occur as isolated trees. As this species is dioecious many of these sites are no longer reproductively functional. The species is palatable, especially seedlings and saplings, while the bark of mature trees is often stripped and so it is at risk wherever populations are accessible to livestock as well as feral goats (Capra hircus), deer (Cervidae) and possums (Trichosurus vulpecula); and it faces competition from weeds, which inhibit regeneration. In the eastern part of its range the species is also vulnerable to summer drought and fires.

This species is occasionally cultivated in Aotearoa / New Zealand.

Coprosma wallii needs a nationwide survey to accurately determine population size, along with a monitoring regime in key sites throughout its range to ascertain trends. While fencing of forest remnants has been undertaken at some sites and this helps secure the species in the short-term, the subsequent increase in swarding weed species such as grasses otherwise suppressed by browsing animals inhibits regeneration of C. wallii. 

Long-term security of this species will only be assured when a management regime is determined that ensures successful recruitment without loss from browsing animals or weed competition. At this stage management has tended to rely on collecting fruits from depleted populations and replanting seedlings derived from these into ‘secure’ sites. Otherwise, animal control in the larger more intact and functional populations is either underway or proposed. A critical need is to better understand the remaining genetic diversity of the species to help guide management, to prevent ad hoc decisions potentially wasting critical resources on those more accessible, severely fragmented populations at the expense of others. None of these issues are unique to Coprosma wallii, resolute and innovative research into determining how best to manage highly fragmented, often scarcely functional taxa in riparian habitats subjected to intense browsing pressure and weed issues will be of benefit to numerous other co-associated threatened or uncommon species (plant and animal). Further there is an urgent need to better understand the genetic diversity and gene-flow within widespread, highly fragmented species of plant.

New Zealand Threat Classification System assessed this species as ‘At Risk / Declining’ Qualified ‘CD’ [Conservation Dependent], ‘RF’ [Recruitment Failure] (de Lange et al. 2018).