New Zealand's native flora evolved without ungulates (deer, chamois, tahr, goats, merinos) and did not develop many of the defensive mechanisms that are present in plants in other parts of the world.

Ungulates have well documented adverse impacts on New Zealand's native vegetation, especially when at high densities. Exclusion of ungulates, including tahr, has led to marked recovery of vegetation in the subalpine and alpine zone.

Tahr are often the dominant browsing animal in the subalpine and alpine zone of the central Southern Alps/Kā Tiritiri o te Moana, although other browsers include deer, chamois, hares, possums and merinos are also present.

Read more: Tahr cull sets conservationists against hunters

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A strong recovery in subalpine and alpine vegetation was apparent when tahr numbers were reduced significantly by aerial hunting from the 1960s-1980s.

The Himalayan Thar Control Plan was published in 1993 and sought to balance biodiversity conservation and recreational values by setting density limits for tahr in seven management units, defining northern and southern tahr exclusion zones, and allowing commercial and recreational hunting.

A strong recovery in subalpine and alpine vegetation was apparent when tahr numbers were reduced significantly by aerial hunting from the 1960s to the 1980s.
A strong recovery in subalpine and alpine vegetation was apparent when tahr numbers were reduced significantly by aerial hunting from the 1960s to the 1980s.

This plan was intended to be reviewed after five years and its successful implementation required a proactive approach and cooperation between a number of groups (government agencies, NGOs, commercial interests).

A mix of government-funded and recreational hunting was seen as the optimum way to manage tahr numbers to meet the objectives of this plan. Unfortunately, the Himalayan Thar Control Plan has never been properly implemented and the five-year review never undertaken.

Tahr numbers have increased substantially since 1993 and the only study of vegetation change over this period (Cruz et al. 2017) shows that tahr have significantly impacted vegetation cover and tussock height through until 2013, when their final field assessments were made.

Read more: Proposed tahr cull 'will go ahead'

This and other studies suggest that tahr impact both overall vegetation cover (and tussock height) and the abundance of individual palatable species (e.g. species of Ranunculus, Ourisia, Anisotome and Celmisia).

Conservation of these communities and species is only possible in New Zealand and tahr are one of the key factors constraining our ability to do this. Notwithstanding this, tahr continue to be a valued recreational hunting resource and are also important for commercial guided hunting.

Tahr also occur on a variety of land tenures whose management can have different priorities.

Eradication of tahr was probably not possible in the 1980s when numbers were at their lowest and is certainly not possible today (as tahr are now widely dispersed through West Coast forests within their range).

Therefore, in order to balance the biodiversity conservation and recreational/commercial values of the central Southern Alps/Kā Tiritiri o te Moana, the same approach that was advocated in the 1993 Himalayan Thar Control Plan is appropriate today – a mix of density targets for specific management units, exclusion zones where tahr are eliminated from, and genuine co-operative management of tahr.

There also needs to be adequate funding for tahr management, including biodiversity monitoring – current gaps in our knowledge around tahr appear to be in part a legacy of the underfunding of the Department of Conservation over the last couple of decades.

Managing tahr to levels that balances biodiversity conservation and recreational/commercial values requires good information on the distribution and population structure of tahr across their range, ongoing and detailed information on the impact of tahr on biodiversity conservation values (cf. Cruz et al. 2017), and genuine consultation and cooperation amongst the different parties interested in the subalpine and alpine ecosystems of the central Southern Alps/Kā Tiritiri o te Moana.

A science-based review of the Himalayan Thar Control Plan would seem long overdue and an urgent priority. Without the approach outlined here, there is a real risk of perverse outcomes for biodiversity conservation. Conservation is as much a social issue as a scientific one and while there are very clear ecological bottom lines, we also need to consider social issues.

•Professor Norton works in the School of Forestry at the University of Canterbury. He has 40 years of experience with the ecosystems in the central Southern Alps/ Kā Tiritiri o te Moana through research and tramping. He receives no funding from DOC or hunting groups.

Reference
Cruz J, Thomson C, Parkes JP, Gruner I, Forsyth DM 2017. Long-term impacts of an introduced ungulate in native grasslands: Himalayan tahr (Hemitragus jemlahicus) in New Zealand's Southern Alps. Biological Invasions 19: 339-349.

•This piece originally ran on Sciblogs.