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).

Advertisements