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The hunt for the lost exclosure

Way back in 1967, the NZ Forest Service had the foresight to build an animal “exclosure” in Waingake Waterworks Bush. It was well known even then, that browsing ungulates (deer, goats and pigs) were causing severe damage to the forest understory, resulting in a reduction in the population of some highly palatable species within the forest. The purpose of building a fence to exclude these animals from a small plot within the forest was to show the difference in understory vegetation when there is no pressure from browsing. Quite how they achieved this feat of construction, using wire, netting and warratah standards in densely forested, remote and rugged terrain is unknown, as was the exact location of the plot- until March of this year.

As part of the Waingake Waterworks Bush restoration project, it was decided by the project team that the exclosure plot needed to be re-visited and its status assessed. But there was one problem- where in the 1100ha bush reserve would we find the plot? There was no GPS in 1967. Some historic information about the plot was available, but maps were vague and inaccurate. The plot had been located and re-measured in 1981 and the report produced from this visit included a description of the altitude and aspect of the site, along with a description of the vegetation. A big clue from this was the description of a canopy of black beech. Black beech is clearly distinguishable in forest canopy in modern aerial photography.

A few long-serving GDC staff members also had a general indication of where they had encountered the site years previously, but with recent intensive work in the reserve (including the camera trap survey in 2017 and the internal possum bait laying operation of 2020) not having yielded any encounters with the plot, the information was sketchy. Despite this a probable location was identified, and in February 2021 a small expedition party set off in search of the plot.

Needless to say this first expedition was unsuccessful, so it was back to the drawing board. Armed with some new information, a second search party in March successfully located the site and found the 54 year old fence to be largely intact and still ungulate-proof, but it had sustained some minor damage. Several of the waratahs were either broken or rusted through on the damaged edge.  In general the netting was in good condition and intact.  Several of the corner stays had broken.  A small roll of netting was also found near the plot to allow for repairs. Some wire was also found on site which allowed the fence to be stood up properly. Unfortunately the fence is under threat long-term from a large rotten beech tree just outside the perimeter which is expected to eventually fall on the exclosure.

Inside the fence

The vegetation inside the fence was found to be very different to the outside.  The ground cover contained a greater range of highly palatable plant species including hangehange, kanono and shining karamu. Other plants with medium palatability were also much more common inside the fence, including kawakawa, sickle and shining spleenwort and hound’s tongue fern.  The litter layer was much deeper inside the fence.

A few trees of large leaved coprosma were present inside the fence.  Most obvious on these large individuals was the presence of leaves from ground level upwards.  There were no exotic species noted in the plot.  The sapling layer inside the fence didn’t appear to be very dense and instead there were few large individuals.  This contrasted with comments made in the 1981 report which suggested a very dense sapling layer.  It is possible that the original cohort (plants of same age) self-thinned.  The process of self-thinning involves a few saplings surviving through to older age classes.

It is likely that light levels in the exclosure were relatively low (due to a thick beech canopy) over the last few decades resulting in a slow regeneration response in the understory.  In more recent times some large branches have fallen off nearby trees which may change the future lighting dynamics of the vegetation in the exclosure.

Outside the fence

The vegetation outside the exclosure was very different in composition.  The ground cover was dominated by bush rice grass and hook sedge.  Seedlings of kohuhu were noted.  Lots of animal tracking was observed outside the plot.  The soil and litter was much more compacted.  Coprosma rhamnoides was the most common shrub outside the fence.

One of the most notable differences was the absence of Astelia and hound’s tongue fern outside the fence.  These species are not highly palatable but high animal numbers at the site have probably reduced the abundance in the understory.  The gentle topography of the site may have encouraged ungulates to camp in the area.  A number of large grassy clearings are present nearby and are probably favoured by ungulates.

What next?

Now that the exclosure plot has been located, GPS co-ordinates logged and in-house knowledge of how to get there is cemented- we can work on using the exclosure plot to help us better understand the dynamic of the forest and what we are aiming for in its restoration. The project team plans to find out if any original data sheets from the 1981 survey still exist to allow re-measurement to occur, and data to be entered into Landcare Research’s NVS database. Other plans for the site include;

  • Revisit exclosure with a team to re measure the internal and external plots
  • Photograph again the corner photo points accurately
  • Photograph again the other photo points in the QEII block at a similar stage to allow the same time sequence
  • Ensure the fence is ungulate proof with existing materials onsite for as long as possible. Replacement of the fence is not worthwhile due to the large rotten beech tree nearby
  • Provide NVS with data and information.

Lost exclosure