Tag Archives: Kerguelen cabbage

Azorella Peninsula Gigapan

Processing the Azorella Peninsula gigapan.  Image credit: Bill Mitchell (CC-BY).
Processing the Azorella Peninsula gigapan. Image credit: Bill Mitchell (CC-BY).

This is the second in a series of three posts about the gigapan images taken on Heard Island (1: Big Ben, 3: Windy City), with more information about the Azorella Peninsula gigapan.

The Azorella Peninsula is on the northern edge of the main part of Heard Island, east of the Laurens Peninsula. It forms the eastern boundary of Atlas Cove (Laurens Peninsula forms the western boundary; see map below). At the west end of the Azorella Peninsula’s southern margin is the heritage zone around the ANARE campsite, two water-tank shelters, a green “apple” shelter, and the area where our expedition made camp. That many of the camps are all in the same area is no accident: Atlas Cove is probably the best harbor on the island (though still not sheltered from a northerly swell), there is a convenient beach for boat landings, and a small step up of elevation from the lava flows of the Azorella Peninsula provides higher ground than the sometimes-inundated Nullarbor.

Heard Island Map, 1985. Image credit: excerpt from the Division of National Mapping.
Heard Island Map, 1985. Image credit: excerpt from the Division of National Mapping.

Getting a gigapan here was not as straightforward as I had hoped. Although there were plenty of pahoehoe flow tops, cracks where a flow had deflated and collapsed in on itself, and other lava flow features, few of them were of a scale and in a location which enabled them to be nicely gigapanned with the tripod I had. With another 3–5 m of elevation, the gigapan would be spectacular.

As it was, there were some additional features besides the lava flows which I wanted to include. For one, the landscape has significant erosional processes happening, and there are sandy areas which get washed when it rains. Even more than the rain, though, the wind creates eolian features. Many of the small rocks have a little dune in their lee, and often the Kerguelen cabbage and Azorella moss grow on the leeward side of rock barriers as well. Some of this organization is visible in the gigapan.

At the top right of the Gigapan image, and lost to the fog and overexposure of the image, is a strongly layered prominence: Corinth Head. Although I would have liked to go see this outcrop up close, our permit did not allow that—the area is a major nesting site for burrowing seabirds, and in places there are lava tubes with thin ceilings which may give way underfoot.

Corinth Head, Heard Island, viewed from the south (further east than the Gigapan was taken).  Layering is clearly visible, and is likely of igneous origin.  Image credit: Bill Mitchell (CC-BY).
Corinth Head, Heard Island, viewed from the south (further east than the Gigapan was taken). Layering is clearly visible, and is likely of igneous origin. Image credit: Bill Mitchell (CC-BY).

Where the Azorella Peninsula lava flow field meets the Nullarbor, there was a little flow which caught my eye. There, one flow clearly traveled through an older channel or tube. Weathering has removed some of the older flow, giving a cross-sectional view of the dark vesicular rock.

Lava flows of the Azorella Peninsula meet the Nullarbor.  An older, grey unit is visible with a redder unit in the middle.  Notebook is 19 cm wide.  Image credit: Bill Mitchell (CC-BY).
Lava flows of the Azorella Peninsula meet the Nullarbor. An older, grey unit is visible with a redder unit in the middle. Notebook is 19 cm wide. Image credit: Bill Mitchell (CC-BY).

Some lava tubes showed obvious signs of deflation or lava tube collapse. The one seen below had eolian features nearby, and the Kerguelen cabbage and Azorella moss can be seen growing on the leeward side of the rocks. An elephant seal is also present.

Deflated lava flow beside the Nullarbor on the Azorella Peninsula, Heard Island.  Some eolian features are present.  Note the Azorella moss and Kerguelen cabbage at right, in the lee of the solid rocks.  The tan mass at right is an elephant seal.  Notebook is 12x19 cm.  Image credit: Bill Mitchell (CC-BY).
Deflated lava flow beside the Nullarbor on the Azorella Peninsula, Heard Island. Some eolian features are present. Note the Azorella moss and Kerguelen cabbage at right, in the lee of the solid rocks. The tan mass at right is an elephant seal. Notebook is 12×19 cm. Image credit: Bill Mitchell (CC-BY).

Finally, here is another example of a collapsed lava tube, which shows off a cross-section of the top of the lava tube as well as some pahoehoe flow tops.

A collapsed lava tube on the Azorella Peninsula, Heard Island, gives a cross-sectional view of the roof of the lava tube.  Kerguelen cabbage plants in foreground are roughly 25 cm across.  Several pahoehoe flow tops are visible: small-scale in the foreground, and large-scale in the center toward the top of the image.  Image credit: Bill Mitchell (CC-BY).
A collapsed lava tube on the Azorella Peninsula, Heard Island, gives a cross-sectional view of the roof of the lava tube. Kerguelen cabbage plants in foreground are roughly 25 cm across. Several pahoehoe flow tops are visible: small-scale in the foreground, and large-scale in the center toward the top of the image. Image credit: Bill Mitchell (CC-BY).
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Peer-Reviewed Research: Terrestrial Vegetation and Environments on Heard Island

Kerguelen cabbage (Pringlea antiscorbutica).  Image credit: B.navez, CC-BY-SA, via Wikimedia commons.
Kerguelen cabbage (Pringlea antiscorbutica). Image credit: B.navez, CC-BY-SA, via Wikimedia commons.

Previously I’ve mentioned rocks, glaciers, a volcano, penguins, and elephant seals, but what about plants on Heard Island? That has been well-covered (pardon the pun) by Bergstrom and Selkirk (2000), who published their findings in an open-access journal.[1]*

Vegetation on Heard Island is generally categorized into six groups (“communities”), which reflect the general microhabitats and species makeups of the area. Here are a couple of brief descriptions:

Poa cookii maritime grassland” is characteristic of nutrient-enriched, animal influenced environments (Hughes 1987, Scott 1988). This community is dominated by the small tussock grass Poa cookii (Hughes 1987), with the nitrophiles Callitriche antarctica and Montia fontana also common.

“Feldmark communities” are characterised by less than 50% vegetation cover. Hughes (1987) described feldmark as having high relative vasular plant diversity but low species abundance, with predominant plants being Azorella selago, Poa kerguelensis, Colobanthus kerguelensis, Pringlea antiscorbutica, bryophytes and lichens. Scott (1988) recorded feldmark on well-drained areas of high altitude/high wind exposure, areas of recent glacial retreat, flat valleys likely to be subject to cold air drainage, and geologically recent lava flows.

After establishing some terminology about what types of communities are there, the authors move into the environmental factors that influence the plants on Heard Island.

Animal-derived nutrients are one factor. “A nutrient gradient is apparent, diminishing away from coastal seal and bird-breeding, resting, and hauling-out areas. Areas affected by direct manuring by seals, penguins, cormorants and giant petrels are generally devoid of vegetation, reflecting toxic nutrient levels and physical damage to plants.”

The types of rocks present, and the geochemistry of those rocks, could control what plants will thrive there. However, that has not been studied in detail on Heard Island (yet! [as of 2000]).

Salt spray from the ocean can make life difficult for plants, as can debris blowing in the wind. The depth to which roots can be sunk varies greatly, from almost nothing on the lava flows to more than 50 cm on moraines and other areas of loose sediment. Water availability also is important; some areas with poor drainage form pools, while other areas of loose rocky material drain very quickly. Snowmelt provides water throughout the summer, although precipitation is frequent throughout the year.

Movement of the rock/soil surface, such as through landslides, frost-heaving, and sediment accumulation can disrupt plant activity. Animals can trample (and eat!) plants, in addition to “adding nutrients”. Of course, the general climate influences, such as temperature (warmer toward sea level) and sunlight (more clouds on west side, more sun on east side) also play a role.

Bergstrom surveyed the plant diversity and abundance quantitatively during the 1986/1987 Australian National Antarctic Research Expedition to Heard Island. Almost 500 quadrats (1×1 m squares) were surveyed, and included three main vegetated areas of the island: Laurens Peninsula (northwest), Spit Bay (southeast), and Long Beach (south-southwest). By placing these quadrats on random (or as random as practical) ice-free locations, representative population statistics can be tabulated. Some species occur primarily clustered with certain other species, and others (e.g. Azorella selago) are widespread.

This survey of terrestrial flora provides an excellent baseline from which to study the changes in populations as the climate warms and glaciers recede on Heard Island. Through this kind of work, scientists can find how the plants are responding to changing conditions and new areas to colonize.

Beyond this research are some big questions: how did plants first arrive on Heard Island? Where did they come from? Which species were first to arrive? When did they arrive, and how long had Heard Island been above the ocean when they came?

[1] Bergstrom, DM and Selkirk, PM (2000) Terrestrial vegetation and environments on Heard Island. Papers and Proceedings of the Royal Society of Tasmania, 133 (2). pp. 33-46. ISSN 0080-4703

* Open access journals are a great way to ensure that research is widely accessible. I am considering outlining my views on academic publishing in a later post (this footnote is only so large).