Penguins

If ever one needed an excuse to post pictures of penguins, yesterday was World Penguin Day.

King penguins at Green Gorge
King penguins at Green Gorge
King penguins are much more graceful in the water than on land!
King penguins are much more graceful in the water than on land!

Four penguin species breed on Macquarie Island. King penguins (Aptenodytes patagonicus) can reach a metre tall and can dive to deeper than 300 metres. Royal penguins (Eudyptes schlegeli) are endemic to Macquarie Island, where they breed in colonies up to 1 km from the coast. Rockhoppers (Eudyptes chrysocome) and gentoos (Pygoscelis papua) breed in smaller numbers.

Royal penguins.
Royal penguins at Finch Creek.

What do penguins have to do with plants? Plants require nitrogen and penguins produce lots of nitrogen. Although nitrogen is an essential plant nutrient too much of it can be toxic to plants. Nitrophilous plants are well adapted to abundant nitrogen. On Macquarie Island the herbs Callitriche antarctica and Montia fontana and the grasses Poa annua and Poa cookii are frequently found in and around penguin rookeries and seal wallows where nitrogen concentrations are high. Studies on subantarctic Marion Island show that plant nutrients are derived mostly from the ocean, as aerosols and as excreta from seabirds and seals. Plants growing around penguin rookeries tend to have high concentrations of nitrogen and a characteristic bright green leaf colour. Animal-derived nitrogen is a key nutrient source for plants in the subantarctic, where nitrogen from other sources such as bedrock and nitrogen-fixing cyanobacteria is limited.

Gentoo penguin.
Gentoo penguin.

Macquarie Island’s penguin populations are still recovering from exploitation in the early 1900s when an estimated 150,000 penguins were slaughtered for oil every year. Many penguin species are listed as threatened on the IUCN Red List. A recent review of threats to penguin populations points to the need for an effective global network of marine reserves.

Penguin digestors at the Nuggets. Thousands of penguins were boiled alive in these to produce oil in the late 1800s and early 1900s. Royal penguin colony in the background.
Penguin digestors at the Nuggets. Thousands of penguins were boiled alive in these to produce oil in the late 1800s and early 1900s. High-rise royal penguin colony in the background.
Penguin city. The population of king penguins at Lusitania Bay is at least 350,000 and growing.
Penguin city. The population of king penguins at Lusitania Bay is at least 350,000 and growing.
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Four years without bunnies

Walking is getting harder on Macquarie Island. Previously short-cropped grass only centimetres tall is now a knee-deep meadow of grass matted with mosses and herbs. This is one of the initial observations from last week’s field trip to the Subantarctic island.

Short grassland at Green Gorge study site has more than doubled in height since rabbits were removed.
Short grassland at Green Gorge study site has more than doubled in height since rabbits were removed. The previous day this was under snow but after overnight rain it became possible to do a vegetation survey.

Another obvious change is a shift in the dominant species. Under the rampant rabbit regime, one grass species in particular flourished – Agrostis magellanica. Now other native grasses which were present in lower numbers are now prominent, even dominating sites where rabbits had previously kept them in check. The mat-forming herb Acaena which thrived in heavily grazed grasslands is struggling to compete with the vigorous growth of grasses and sedges.

Many of the smaller herbs which favour bare ground and occupy openings amongst the grasses appear to be less common. In the absence of rabbit diggings and overgrazing they are now abundant only on creek banks and landslides, which is perhaps their original niche in a pre-grazing era.

Boggy short grassland at Bauer Bay on the west coast. The Macquarie Island cabbage plants which have appeared here since rabbits were removed have the potential to reach over 1 metre in height.
Boggy short grassland and herbfield at Bauer Bay on the west coast. The Macquarie Island cabbage plants which have appeared here since rabbits were removed have the potential to reach over 1 metre in height. Note the tussocks on the slopes in the background, most of which have appeared in the past four years.

Tussock grass (Poa foliosa) is clearly increasing in abundance and in height, signalling a future shift in vegetation type from short grassland to tall tussock grassland. And the Macquarie Island cabbage, which was virtually eliminated from much of the island by rabbits, is popping up as young plants throughout many grasslands. In a few years time it is likely to outgrow the short grasses and take over. The tall tussock grass and Stilbocarpa vegetation described in Nineteenth Century accounts might be making a comeback. The return of the megaherbs seems imminent.

Goodbye Macca

Vegetation monitoring site with two converging landslides, covered in snow. Even with the snow cover it is obvious that tussock grasses (Poa foliosa) are colonising this site.
Vegetation monitoring site with two converging landslides, covered in snow. Even with the snow cover it is obvious that tussock grasses (Poa foliosa) are colonizing this site.

Just arrived back at the station via helicopter. Unfortunately we lost about half of our planned fieldwork time: operations on the island are winding up early due to forecast bad weather, and earlier in the week we had two days where the island was blanketed in snow – sure looked nice, but hopeless for studying plants! Nevertheless we managed to complete 4 of our 6 long term vegetation change study sites and made lots of other observations. The plants are certainly getting taller without rabbit grazing.

Vegetation monitoring plot at Brothers Point under snow. Toe of landslide has flattened grass but not the marker stake.
Vegetation monitoring plot at Brothers Point under snow. Toe of landslide has flattened grass but not the corner marker stake.

Another unfortunate but interesting thing is that a few of the 35 year old monitoring plots have been impacted by some of the numerous landslides and debris flows which occurred during the unprecedented heavy rains in January this year. Getting on the ship and heading back to Hobart soon. Full report and pictures to come…

Into the field!

We landed on Macquarie Island yesterday and spent a few hours setting up and testing an automatic weather station. Now it is ready to be airlifted to over 300 m elevation on the plateau, ready for installation. We’ll find out just how windy it is up there!

The station is hectic with resupply activity. But we’re heading off for a few days to look at the vegetation. Already from the ship we could see the bright green tussocks of Poa foliosa creeping up the previously rabbit-grazed hillsides.

My colleague Micah and I are kitted out with warm waterproof clothing and ready to get out there.

First clear glimpse of Macca on Friday morning. It was a shadow in the mist when we arrived Thursday afternoon.
First clear glimpse of Macca on Friday morning. It was a shadow in the mist when we arrived Thursday afternoon.

Ferrying people ashore from the ship, 60 seconds by air.
Ferrying people ashore from the ship, 60 seconds by air.

Electronics 101. Luckily Micah knows about electronics because I don't!
Electronics 101. Luckily Micah knows about electronics because I don’t!

Weather station datalogger, wired up and wateprroofed, ready to face the elements.
Weather station datalogger, wired up and waterproofed, ready to face the elements.

Expedition begins

Helicopter landing on the Aurora prior to departing Hobart.
Helicopter landing on the Aurora prior to departing Hobart.

How much has the vegetation changed in the past two years? We’ll soon see.

Finally it’s time to do some field work. The Aurora Australis is loaded up and heading south. In 3 days time we will be at Macquarie Island. The main aim of my fieldwork is to revisit the vegetation monitoring sites which were established at six locations in the early 1980s. We will record the abundance of all the vascular plant species in these plots to determine which are the winners and losers in this new era of rabbit-free ecosystem.

Hope we don't need these...
Hope we don’t need these…
Departing Hobart on a grey autumn afternoon.
Departing Hobart on a grey autumn afternoon.

The Project

My research project is looking at vegetation change on Macquarie Island. Since rabbits were eradicated from the island in 2012 the plants which had been subject to intensive grazing by these pest animals are now growing back. Nobody knows what the original vegetation of the island looked like before rabbits were introduced int he late 1800s. What will it look like in 5 years, 10 years, 100 years?

To manage the island in the future we need to understand the vegetation. What grows where and why? What are the key factors determining which plants dominate in different environments?

IMG_7489 sml

The Subantarctic – where 43 plant species is a lot

Macquarie Island’s total of 43 native vascular plant species is low by most standards – some Tasmanian National Parks of similar size have more than ten times this diversity.* But amongst the Subantarctic islands, none come close to Macca’s species richness. The Kerguelen islands (7,215 km2 of which 6,450 km2 is ice-free) in the southern Indian Ocean have a land area around 50 times the size of Macca (128 km2), yet only 30 native plants. Other Subantarctic islands support even fewer species – Australia’s Heard Island for example has just eight. Further south, in the Antarctic proper, only two vascular plants survive in the harsh climate.

A water fern, Blechnum penna-marina ssp. alpina, one of five pteridophytes found on Macquarie Island. This widespread fern also occurs elsewhere in the Subantarctic, in Australia, New Zealand and South America.
The water fern Blechnum penna-marina ssp. alpina, one of five pteridophytes found on Macquarie Island, also occurs elsewhere in the Subantarctic, in Australia, New Zealand and South America. The fern is growing with one of the many moss species found on Macca.

The theory of island biogeography suggests that species richness on an island is a function of island size (land area) and isolation (distance from nearest major landmass). Amongst the Subantarctic islands, area does predict  plant species richness, but isolation does not. However temperature is as important or more so – the plant species richness declines with temperature. A third factor that may also be influential is glacial history, because it seems that vascular plants were wiped out during glaciations on some of the more southerly islands, such as South Georgia, and therefore needed to recolonise those islands following each glacial period. Isolation is perhaps not so important in the Subantarctic where every island is very isolated and the typical plant species are not limited by dispersal ability.

Macquarie Island, having no history of glaciation and a slightly milder climate than other Subantarctic islands, therefore has a relatively high richness of vascular plants, despite its modest size.

Not surprisingly, definitions come into play here: if we are to generously include New Zealand’s so-called ‘Subantarctic’ islands (arguably not Subantarctic because they support trees), then the numbers rocket up to 188 for the Auckland Islands.

Shrubby vegetation on Enderby Island, 50° 31' South, considered Subantarctic by some definitions. The red flowers are Southern Rata, Metrosideros umbellata.
Shrubby vegetation 2-3 m tall on Enderby Island, 50° 31′ South, considered Subantarctic by some definitions. The red flowers are Southern Rata, Metrosideros umbellata.

But that’s just vascular plants; like the temperate rainforests of Tasmania, Macca’s non-vascular flora dwarfs the angiosperms and ferns in species richness. There are at least 75 mosses, 60 liverworts and 55 lichens known from the island.

Macquarie Island’s native vascular plants – 22 dicots, 16 monocots and 5 pteridophytes – along with 3 introduced species are all illustrated in an online key.

* Tasmania’s Maria Island National Park has over 470 native vascular plants in an area slightly smaller than Macquarie Island; Douglas-Apsley National Park, a little larger than Macquarie Island at 160 km2, has over 270 native vascular plants, while the 169 km2 Freycinet NP has over 500 species.

Land of the Megaherbs

There are no trees. No shrubs even. The tallest plants are  ‘megaherbs’, which can just reach over head height. This is the unusual assemblage of plants which inhabit Macquarie Island.

In contrast to the Northern Hemisphere tundra where low-growing shrubs are prominent, the megaherbs and tussocks are king here.

Stilbocarpa polaris
Stilbocarpa polaris can grow to 2 metres tall with leaves up to half a metre across.

Macca’s most well known and most prominent plants are the tussock grass Poa foliosa with masses of long leaves sprouting from a root pedestal; Stilbocarpa polaris, Macquarie Island Cabbage (which looks more like a hairy rhubarb but is not related to either food plant); and Pleurophyllum hookeri, a rosette daisy with silvery leaves.

IMG_1297
Pleurophyllum hookeri has underground rhizomes from which these silver rosettes grow. The leaves can grow to 60 cm long in summer but are replaced by shorter leaves over winter.
Tussock grass Poa foliosa forms pedestals composed of peat, roots and old shoots which elevates the living foliage to over head height on sheltered sites.

‘Megaherb’ is a poorly defined term in botany and is generally only applied to plants from the Subantarctic. It essentially refers to non-woody plants which attain unusually large sizes, often appearing as giant versions of their more modestly proportioned relatives. There are several potential benefits to the megaherb form which may explain why they are so prominent on the Subantarctic islands: the large leaves may help trap sunlight and reduce wind speeds, creating a leaf microclimate with relatively high temperature and low evapotranspiration which would aid growth in a cool windy environment; their greater height and leaf area means they can outcompete smaller plants for precious sunlight; and the large leaves are likely to collect airborne nutrients which would be an advantage on the infertile peat soils of Macquarie Island’s plateau (these are discussed in a study of Campbell Island megaherbs).

Although the term ‘megaherb’ is rarely used beyond the far southern latitudes, the growth form does occur in a few other places. Large-leaved herbs are quite rare globally and tend to occur where there are few or no shrubs, such as in the equatorial montane vegetation of Mt Kilimanjaro where tree groundsels and giant lobelias occur.

Dendrosenecio kiliminjari is a giant herb (it's stem is not made of wood) from high elevations on Mt Kilimanjaro.
Giant groundsel Dendrosenecio kiliminjari is a giant herb (its stem is not made of wood) from high elevations on Mt Kilimanjaro.

Finally, I kinda lied about there being no shrubs – to be technically correct there is a ‘shrub’ on Macca. Coprosma perpusilla has wiry stems which creep through the moss, giving it the appearance of a herb (botanically described as a ‘subshrub’, it must be amongst the smallest even of this dwarf subset of shrubs).

Coprosma perpusilla ssp. subantarctica2 is a miniature creeping shrub whose tiny woody stems are hidden. It is a fraction of the size of the dominant megaherbs on Macqaurie Island, and of its more temperate relatives.
Coprosma perpusilla ssp. subantarctica is a miniature creeping shrub whose tiny woody stems are hidden. It is a fraction of the size of the dominant megaherbs on Macquarie Island, and of its more temperate relatives.

Who? What? Where? Why? How?

An exclosure plot showing effects of rabbit grazing on Macquarie Island.
An exclosure plot showing effects of rabbit grazing on Macquarie Island.

I’m a postgrad student at the University of Tasmania, studying plant ecology in alpine and Subantarctic environments. My studies focus on Macquarie Island, half way between Australia and Antarctica. (More about me here).

Why travel for days across the notorious Southern Ocean to then tramp around a soggy, windy and cold island looking at herbs and grasses? Well, ‘Macca’ is one of the wildest places on Earth – and is becoming increasingly wild as the ecosystem rebounds following the eradication of pest animals such as cats and rabbits – making it an ideal natural laboratory for studying ecosystem recovery and climate change impacts.

My other study sites are not so far south: alpine vegetation on the peaks of southern Tasmania. Evidently I like cold, windy, damp places. Or at least the plants which inhabit such places.

How to study vegetation change in these remote and wild environments? Read on…