On the trail of early photographs of the Halfmens

Kirsti Nghidinwa and Plant Conservation Unit (PCU) Research Assistant Sam Jack recently undertook a field trip to Namaqualand as part of Kirsti’s PhD quest to determine the population trends and growth rates of the iconic Halfmens (Pachypodium namaquanum) using repeat photography. Illegal collection for ornamental use is often cited as one of the threats to the species, but natural die-offs probably also contribute to changing the age class structure of populations. Getting hold of old landscape photos of the Halfmens was the initial challenge, but thankfully the considerable historical photograph collection housed at the PCU aided in this regard, supplemented by many old photographs independently sourced by Kirsti in preparation for the trip.

Locating sites presented its own difficulty as often only the district, nearest settlement or farm name was available to work with. But with a little patience and a lot of help from farmers and, where possible, the original photographers, Kirsti and Sam managed to track down some of the historical sites and take good repeats. The search for old photos continues as more repeats are needed in order to more accurately establish how population structure is changing, and to feed in to more reliable estimates of growth rates. Following are some highlights from the trip.

 

In the footsteps of W. Giess

W. Giess was a prominent botanist in Namibia who collected profusely in his heyday. The team was on the trail of his Halfmens photographs taken in 1963 at a farm in southern Namibia, obtained from the National Herbarium of Namibia. It turned out that there were two farms in southern Namibia going by same name, but located some 200 km apart, both of which Giess might well have visited on his expedition. Between Sam’s ability to read landscapes, an enthusiastic farmers directions received via intermittent cell phone signal, and farm labourers’ knowledge of the farm, the team came upon the little kopje that looked as if time had stood still for it since Giess’ visit, except for the missing Halfmens. A couple of dead skeletons (or what was left of them) were found scattered on the ground among the rocks and no seedlings were seen at the site. However, further down the ephemeral riverbed where we made camp that night some individuals were found on a rocky slope and seemed to be in reasonable health.

W. Giess took a photograph of a cluster of Halfmens on this koppie on the farm Witputs in 1963. By 2016 all the Halfmens had died.

 

Avenue of the giants

Arguably the biggest Halfmens colony that we encountered, both in terms of density and size of individual plants, was located in the vicinity of Aggeneys on the eastern edge of the species’ distribution. The area in which the population occurs receives very little traffic and attention these days as the main district road that once ran through this part of the country was shifted to the south many years ago. One can imagine that all sorts of travellers would’ve stopped on the original route to marvel at the towering plants. And those fortunate enough to own a camera would have stopped to take a snap or two.  Featured here is a photo from the Bolus Herbarium contributed by Rev. R. F. Ridgill of Pella, estimated to have been taken in the 1920s, and a repeat taken by the team. A second photo taken by the local school headmaster at Springbok, Piet van Heerde, was captured between 1926-1979. In the photograph, the bank manager (also from Springbok) poses beside a particularly tall individual for good measure.

Rev. R.F. Ridgill captured a dense stand of Halfmens near Aggeneys in the ca. 1920s. Today the population is much thinned with only a handful of the original plants still alive.

The bank manager (name unknown) at Springbok in the mid-1900s posing for Piet van Heeerde, who took many photographs of Halfmens in Namaqualand. This individual is far taller than any specimen we encountered on our fieldtrip.

 

Uranoep - third edition

The perplexing significant reduction in plant abundance at this site - as can be observed in the repeat photo taken by Hoffman in 2003 - inspired the photographic exercise currently being undertaken throughout the species’ range. Team 2016 was glad that GPS coordinates were available to lead them to the site without much hassle. We were happy to find that not much additional mortality had occurred since 2003, although no recruitment was observed.

The series of 3 images of the population at Uranoep illustrating the dramatic decline between 1956 and 2003, and the relative stability thereafter.

 

Down in four years

The decline of the Halfmens population at Lorelei, a site in the mountains on the northern bank of the Gariep River, was a bit of a surprise. The plants did not appear old or dying only four years ago, but several individuals were dead upon inspection of the site in 2016. All dead plants were found in situ as dead skeletons on the ground, hence no foul play was suspected. Some skeletons were still quite intact and may prove useful in isotope analysis of the spines to determine plant age.

Halfmens population on the steep and loose slope at Lorelei on the Namibian side of the Gariep River. While hard to discern from the photo, several individuals died during the four years between original and repeat photo.

 

A view above C13

The original photograph for this site was taken by the well-known botanist Tony Rebelo in 1987, but no other locational information was available to find the original site. Luckily the view included a section of the Gariep River, the characteristic northward nod of the Halfmens, and some mountains in the background. Using this information Sam could, with the aid of Google Earth, reason that the site was located on the northern bank of the Gariep. And by using the distinctive colours of the mountains and shape of the river channel, he could pinpoint the locality. This technique of pre-locating the historical image served the team very well in minimising time wasted looking for historical photo sites and thereby making the most of the short duration of the fieldwork outing.

Halfmens captured on rocky slope overlooking the Gariep River. While there has been some mortality at this population, several individuals remain and appear to be healthy.

 

Worm in the Richtersveld

Initially reported by concerned tourists and tour guides as vandalism to Halfmens plants at Halfmens Pass in the Richtersveld, the decimation observed earlier this year is now attributed to a boring worm, suspected to be the larval stage of a moth. Kirsti is working with Richtersveld Park staff to get this insect identified and to assess the extent and seriousness of the damage to other Halfmens populations in the reserve.

Pieter Mier, Nursery Manager at the Richtersveld National Park and excellent botanist explaining how the worm causes the Halfmens plants to collapse and die. Insert photo of the offending worm courtesy of Pieter Mier (www.ispotnature.org).

 

~ Article and images supplied by Kirsti Nghidinwa