GeoLog

Field Rucksack

Imaggeo on Mondays: The unique bogs of Patagonia

Imaggeo on Mondays: The unique bogs of Patagonia

Patagonia, the region in southernmost tip of South America, is as diverse as it is vast. Divided by the Andes, the arid steppes, grasslands and deserts of Argentina give way to the temperate rainforests, fjords and glaciers of Chile. Also on the Chilean side are rolling hills and valleys of marshy topography: Patagonia’s bogs. Today, Klaus-Holger Knorr, a researcher at the University of Münster’s Institute for Landscape Ecology, tells us about what makes these peatlands so unique.

This picture shows an ombrotrophic, oceanic bog at the Seno Skyring Fjord, Patagonia, Chile. It is a view from the inner part of the peatland south toward the shore of the Fjord, in the background Isla Escapada and the Gran Campo ice field. Ombrotrophic bogs are peatlands (accumulations of more or less decomposed plant material which collect in a water-saturated environment) receiving their water and nutrients solely from the atmosphere, i.e. by rain, wet and dry deposition.

Similar to their Northern counterparts in Canada, Northern US, Fennoscandia or Siberia, these southern Patagonian peatlands  formed after the last deglaciation and accumulated huge amounts of carbon as peat.

Peatlands cover only about 3 % of the global land surface but store about a third of the soil carbon pool. Peat is formed primarily as there is excess rainfall, peat soils are water logged, oxygen gets depleted, and decomposition is limited. Pristine, undisturbed peatlands can store as much as 10-50 g carbon per square meter and year.

What makes the peatlands in Patagonia  particularly interesting  is their pristine, undisturbed conditions and extremely low input of nutrients from the atmosphere, compared to the high input into sites in densely settled or industrial regions. This allows studies of peatland functioning under natural conditions and absence of anthropogenic impacts.

Moreover, peatlands in Patagonia harbor a specific kind of vegetation, including cushion forming plants such as Astelia pumila and Donatia fascicularis. These cushion forming plants have a very low above ground biomass but an extremely large rooting system, reaching down to a depth of >2 m in case of A. pumila. As these roots act as conduits for oxygen to sustain viability of the roots in the water logged peat, they have been shown to aerate large parts even of the saturated zone, thereby impeding high methane production and emission. Oxygen supply by these roots is even hypothesized to stimulate peat decomposition and thereby lead to particularly decomposed peat under cushion plant cover.

Another plant species only occurring in peatlands of Southern Patagonia, a small conifer named Lepidothamnus fonkii, has developed a particular strategy to overcome nutrient deficiency: it has formed a close association with bacteria being able fix atmospheric nitrogen to fulfill the demand of nitrogen for growth. While such nitrogen fixation is well known for legumes and some tree species, it has rarely been found for conifers.

A further important factor for peatlands in Patagonia, leading to the term “oceanic bogs”, is the fact that these peatlands in close vicinity to the seashore receive high inputs of sea salts from sea spray, modifying availability of associated elements such as Sodium, Calcium, Magnesium, Sulphur and others.

By Klaus-Holger Knorr, researcher at the University of Münster’s Institute for Landscape Ecology

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Record-setting forest fires in 2017 – what is to blame?

Record-setting forest fires in 2017 – what is to blame?

Forest fires have once again seized the public consciousness in both Europe and North America. Extreme drought and temperatures contributed to a tinderbox in many forests, and have led to deadly fires across Europe and record-breaking, highly disruptive fires in the USA and Canada, from where I’m currently writing.

A simple way to understand fire is by thinking about the fire triangle – the three pieces that need to combine to produce fire: heat, oxygen, and fuel. While the concept of the fire triangle offers simple insights into the cause of a fire, each of the three factors are subject to a number of controls.

The availability of fuel in particular is affected by a whole range of influences, from tree species variations, to the impact of pests, to the prior history of wildfires. In many cases there will be a multitude of reasons for both the rate that a given fire spreads, and the spatial extent to which it burns. The extensive media coverage of this year’s record-breaking fire season provides a useful opportunity to explore some of these factors, and how they might have contributed to the fires that we’re seeing this year.

Multi-tiered fires

Not all forest fires are equal. The forestry service in British Columbia defines 6 different levels of fire, ranging from slow burning of peat below the surface of a forest (a ground fire), through the burning of scrub and ground level debris (surface fire), to far harder to control conflagrations that consume the canopy of the trees (a crown fire).

Each type of fire consumes fuel from different levels of the forest, and a transition from a lower to higher level requires at a minimum that there is enough flammable material in the upper layers of the forest. As such, the history of fire in a given stand of woodland will have a significant effect on the potential for future fires; a prior surface fire could remove the under-brush and limit the future fire risk.

Many older trees in a forest can have fire scars from previous, smaller fires that have not burnt them entirely, demonstrating that not all fires make the transition to crown fires. In the US, the largest 2-3% of wildfires contribute 95% of the total area burned annually, and these are generally the largest crown fires. For these large fires, the conditions must be optimal to reach the canopy, but once they make this transition they can be very difficult to stop.

Although the largest fires require a specific set of conditions, the transition to large fire can lag for a long time behind the initial trigger of a fire:

“Once ignited, decaying logs are capable of smouldering for weeks, or even months, waiting the time when prevailing conditions (hot, windy, and dry) are conducive for expansion into a full-blown forest fire,” write Logan & Powell in 2001.

The initial trigger in natural settings for the fire is generally lightning, or in rare cases the intense heat from lava flows. However, a recent study has shown that in the continental US, 84% of fires are started by humans. This can range from discarded cigarettes to prescribed fires that have raged out of control.

So, we now have a simplified understanding of the requirements for a fire, but perhaps the more important question remains: why do they spread?

What fans the flames?

So what are the processes that control the strength and spread of a fire? Certain aspects, like climatic conditions, tend to set a long-term propensity for wildfire, while other short term effects define the local, immediate cause for a fire.

The long-term role of climate is quite diverse. Flannigan and co-authors, in their 2008 paper, summarise the importance of temperature in setting the conditions for fire:

“First, warmer temperatures will increase evapotranspiration, as the ability for the atmosphere to hold moisture increases rapidly with higher temperatures… (Roulet et al. 1992) and decreasing fuel moisture unless there are significant increases in precipitation. Second, warmer temperatures translate into more lightning activity that generally leads to increased ignitions (Price and Rind 1994). Third, warmer temperatures maylead to a lengthening of the fire season (Westerling et al. 2006).”

The importance of temperature at a global scale is demonstrated by studies suggesting that fire outbreaks have systematically increased since the last glacial maximum 21,000 years ago, when average temperatures were several degrees colder.

So once the climatic conditions set a long term likelihood for a fire to break out, as well as the distribution of tree species (and therefore the amount of fuel), short term disturbances can act to further increase susceptibility. We can divide these more immediate factors into weather, ecological, and human influences.

Unsurprisingly, weather conditions that bring hot, dry weather with the chance of thunderstorms will be highly likely to drive fires. A number of studies have shown that this kind of weather is often linked to persistent high pressure systems in the atmosphere, which push away rainfall, and can last for weeks at a time.

This kind of atmospheric conditions can often be linked to longer term weather patterns, in particular El Niño, and the effects can be long-lived. For example, El Niño brings warm, dry weather to the North-western part of North America, driving increased fire. In the South-west, El Niño brings wetter weather, but the increased vegetation growth provides a larger amount of fuel that can then burn in subsequent drier conditions.

Caption: Healthy pines mix with red, decaying trees afflicted with pine beetle infestation in Jasper National Park, Canada (Aug 2017). Credit: Robert Emberson

The growth of plants is just one way that the forest ecosystem can affect the availability of fuel for fire. Many trees are affected by pests. The classic example is the pine beetle, which can kill so many trees that whole swathes of pine forest are left characteristically red as they decay in the aftermath of an infestation. While some studies have shown that this can reduce the chance of a crown fire (since less fuel is available in the canopy), the dead and decaying trees provide a source of drier fuel at ground level that is a concern in many regions.

Elsewhere, we can see cases where trees encourage fire. Eucalyptus trees contain oil that burns strongly; the fire that this produces is suggested to remove the other tree species competing with the Eucalyptus. A strange method, but no doubt effective! The Eucalyptus, introduced to Portugal by humans in the 18th century, has been linked to many of the deadly fires that occurred there this summer. The lodgepole pine, too, has pinecones that require the heat of fire to open and release their seeds.
As such, fire is a natural part of the ecosystem, and in most areas of the boreal forest fire management is limited, with attempts at suppression only made where human settlement is at risk.

Where humans do step in, their actions can have an important role in setting the overall susceptibility to fire. Creating ‘fire breaks’ by felling or controlled burning of woodland in the path of a fire removes fuel and limits the growth of a fire, and a program of controlled burns is an important part of forest management to limit the potential for future fire by clearing scrub vegetation at the surface.

On the other hand, continual suppression of fires can lead to build up of fuel – which can then form a significantly more dangerous fire on a long term basis.

Ken Lertzman, Professor of Forest Ecology and Management at Simon Fraser University, told me that in general, control mechanisms are only useful for smaller surface fires; once the fire reaches the canopy, fire suppression is extremely difficult.

“It’s a combination of a statistical and philosophical problem”, he says. Fire control is expensive, so unless it’s financed by profits from felled lumber, cost benefit analysis is necessary, based in part on the statistical probability of a huge fire breaking out in a given location. Philosophically, though, “management forest stand structure at the boundary conditions [between surface and canopy fires] may be able to keep small fires becoming extreme.” and thus perhaps it’s worth trying to use control mechanisms even if giant canopy fires would ignore them, just to avoid that transition to the canopy.

As with most natural systems, the factors discussed above don’t necessarily act independently. Many can amplify other effects. For example, the geographical range of pine beetle outbreaks could increase under a warming climate. At a smaller scale, giant fires can create their own weather patterns, acting to dry out the surrounding forest even before it ignites. So, is the greater incidence of fire this year down to this kind of combination of factors?

What’s happening in 2017?

The sun at 10.15 in the morning in Chilliwack, BC, 3rd August 2017 – more than 50km from the nearest fire. Credit: Megan Reich.

The summer of 2017 has been brutal for wildfire in many locations. Europe has been hit hard with more fires in one day in Portugal than any previous on record. In British Columbia (BC), the largest single fire on record is currently burning, contributing to the largest total area burned in historical record. The fires released so much particulate matter and haze that the sun was obscured in large parts of BC.

According to Professor Lertzman, in British Columbia at least, this is “a fire year different in degree, not in kind”. The same processes are at play as always, but in overdrive. An early spring thaw combined with a long, hot and dry summer created the ideal antecedent conditions for fire.

Linking individual intense ‘fire years’ to long term climate change in challenging, but it is likely that these kind of conditions would be more likely to occur in a world influenced by anthropogenic climate change. Years like this one, which are clearly exceptional compared to the long term trend for fire, might begin to occur more often; every 5-10 years rather than every 30-50, for example.

In the short term, fire damage and suppression is expensive, both financially and in terms of lives affected. Smoke is a health risk to wide areas in the face of such intense fire, but ecological damage can be more difficult for humans to see.

Mature forest is a different niche for organisms to fill in comparison to fresh surfaces stripped bare by fire. While each ecosystem has its place in the natural forest, an increased prevalence of fire reduces the mature forest available for the species that prefer that ecological zone. These can range from recognisable mammal species such as bears, deer and caribou, to less well-known but still important canopy lichen species, says Professor Lertzman.

While this year’s fire season is beginning to ease off, it is clear that the range of factors, both natural and those driven by humans, will continue to play a role in years to come. More build-up of infrastructure in developed countries puts more human settlement at risk, so a clear understanding of how fire interacts with the climate, weather, and forest management strategies will be vital to allow us to live alongside fire in the future with fewer problems.

By Robert Emberson, freelance science writer

 

Further reading and resources

Imaggeo on Mondays: Isolated atoll

Imaggeo on Mondays: Isolated atoll

Covering a total area of 298 km², the idylic natural atolls and reefs of the Maldives stretch across the Indian Ocean. The tropical nation is famous for it’s crystal clear waters and picture perfect white sand beaches, but how did the 26 ring-shaped atolls and over 1000 coral islands form?

Coral reefs commonly form immediately around an island, creating a fringe which projects seawards from the shore. If the island is of volcaninc origin and slowly subsides below sea level, while the coral continues to grow growing outwards and upwards, an atoll is formed. They are usually roughly circular in shape and have a central lagoon. If the coral reef grows high enough, it will emerge from the sea waters and start to form a  tiny island.

“I took this photo while flying over the Maldives, south of Malè, from a small seaplane,” describes Favaro, who took this stunning aerial image of an atoll above the Indian Ocean.

Pictured, goes on to explain Favaro,

“[is] part of the ring-shaped coral reef bounding the atoll. On the right side of the image there is the lagoon and on the left side the open ocean. The coral reef is interrupted twice by ‘Kandu’ (water passages in Dhivehi [the language spoken in the Maldives]), which are the places where water flows in and out of the atoll when the tides changes”.

Two small harbours and antennas suggest the two small islands are occupied by local people, not by a resort or hotels.

“What always strikes me is how they can live so isolated, in a place which doesn’t offer basic resources, such as drinkable water,” says Favaro.

Fresh water is scarce in this archipelago nation. Rainwater harvesting is unreliable; poor rainfall means depleted collection tanks and groundwater tables. The problem is being exacerbated by climate change which is altering the monsoon cycle and rainfall patters over the Indian Ocean. As a result, the country relies heavily on desalination plants (and imported bottled water) to sustain the nation and the 1 million tourists who visit annually.

This animation shows the dynamic process of how a coral atoll forms. Corals (represented in tan and purple) begin to settle and grow around an oceanic island forming a fringing reef. It can take as long as 10,000 years for a fringing reef to form. Over the next 100,000 years, if conditions are favorable, the reef will continue to expand. As the reef expands, the interior island usually begins to subside and the fringing reef turns into a barrier reef. When the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its center, it is called an atoll. The process of atoll formation may take as long as 30,000,000 years to occur. Caption and figure credit: National Oceanographic and Atmospheric Administration (NOAA).

References and further reading

How Do Coral Reefs Form? An educational resource by NOAA

Amazing atolls of the Maldives – a feature on NASA’s Earth Observatory.

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Imaggeo on Mondays: A lava layer cake

Imaggeo on Mondays: A lava layer cake

Brekkuselslækur, a small river, carves its way across Iceland’s ancient volcanic landscape. At Hengifoss, Iceland’s third-highest waterfall, it tumbles fiercely down thick, dark layers of lavas erupted from volcanoes some 18 to 2.58 million years ago, during a period of geological time known as the Tertiary.

Eruptions are rarely continuous; during hiatuses in the extrusion of lavas, ash is able to settle atop the smoldering layers. If the pauses are long enough and the conditions just right (a warm and humid climate is needed) the ashes, through the addition of clay and iron minerals, slowly turn to soil . When new lavas are layered over the top of the ash-rich soils, a chemical reaction takes place between the iron trapped in the soil and the oxygen transported by the lavas, to form iron oxide. In essence, the soils rust and turn a distinctive red colour.

As the process is repeated time and time again, layers of alternating black lavas and red soils are built up to form a giant ‘mille feuilles’ cake.

In the summer months, tourists flock to this popular site. An unspoilt view of the 188m high torrent means an early morning hike to beat the crowds. For a bird’s eye view of Hengifoss, the adventurous can even scarmble to the cliff tops too.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.