Thirsty forests

1 02 2019

Climate change is one ingredient of a cocktail of factors driving the ongoing destruction of pristine forests on Earth. We here highlight the main physiological challenges trees must face to deal with increasing drought and heat.

Forests experiencing embolism after a hot drought. The upper-left pic shows Scots (Pinus sylvestris) and black (P. nigra) pines in Montaña de Salvador (Espuñola, Barcelona, Spain) during a hot Autumn in 2015 favouring a massive infestation by pine processionary caterpillars (Thaumetopoea pityocampa) and tree mortality the following year (Lluís Brotons/CSIC in InForest-CREAF-CTFC). To the right, an individual holm oak (Quercus ilex) bearing necrotic branches in Plasencia (Extremadura, Spain) during extreme climates from 2016 to 2017, impacting more than a third of the local oak forests (Alicia Forner/CSIC). The lower-left pic shows widespread die-off of trembling aspen (Populus tremuloides) from ‘Aspen Parkland’ (Saskatchewan, Canada) in 2004 following extreme climates in western North America from 2001 to 2002 (Mike Michaelian/Canadian Forest Service). To the right, several dead aspens near Mancos (Colorado, USA) where the same events hit forests up to one-century old (William Anderegg).

A common scene when we return from a long trip overseas is to find our indoor plants wilting if no one has watered them in our absence. But … what does a thirsty plant experience internally?

Like animals, plants have their own circulatory system and a kind of plant blood known as sap. Unlike the phloem (peripheral tissue underneath the bark of trunks and branches, and made up of arteries layered by live cells that transport sap laden with the products of photosynthesis, along with hormones and minerals — see videos here and here), the xylem is a network of conduits flanked by dead cells that transport water from the roots to the leaves through the core of the trunk of a tree (see animation here). They are like the pipes of a building within which small pressure differences make water move from a collective reservoir to every neighbours’ kitchen tap.

Water relations in tree physiology have been subject to a wealth of research in the last half a decade due to the ongoing die-off of trees in all continents in response to episodes of drought associated with temperature extremes, which are gradually becoming more frequent and lasting longer at a planetary scale (1). 

Embolised trees

During a hot drought, trees must cope with a sequence of two major physiological challenges (2, 3, 4). More heat and less internal water increase sap tension within the xylem and force trees to close their stomata (5). Stomata are small holes scattered over the green parts of a plant through which gas and water exchanges take place. Closing stomata means that a tree is able to reduce water losses by transpiration by two to three orders of magnitude. However, this happens at the expense of halting photosynthesis, because the main photosynthetic substrate, carbon dioxide (CO2), uses the same path as water vapour to enter and leave the tissues of a tree.

If drought and heat persist, sap tension reaches a threshold leading to cavitation or formation of air bubbles (6). Those bubbles block the conduits of the xylem such that a severe cavitation will ultimately cause overall hydraulic failure. Under those conditions, the sap does not flow, many parts of the tree dry out gradually, structural tissues loose turgor and functionality, and their cells end up dying. Thus, the aerial photographs showing a leafy blanket of forest canopies profusely coloured with greys and yellows are in fact capturing a Dantesque situation: trees in photosynthetic arrest suffering from embolism (the plant counterpart of a blood clot leading to brain, heart or pulmonary infarction), which affects the peripheral parts of the trees in the first place (forest dieback).

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We need a Revegetation Council

14 01 2019
planting trees

As I have discussed before, the greatest threatening process to biodiversity in South Australia today is past and ongoing clearing of native vegetation. So, arresting further vegetation clearing, and restoring previously cleared land to functional native-vegetation communities are easily the highest priorities across the entire State.

Despite some valiant attempts across South Australia to revegetate previously cleared areas1, the haphazard approach to reforestation in South Australia means that we are unlikely to be maximising ecological function and providing the best habitats for native biodiversity. Several improvements in this regard can be made:

(i) Establish a State Register of past, ongoing, and planned revegetation projects, including data on the proponents, area revegetated, species planted, number of individuals planted for each species, monitoring in place (e.g., plant survival, other species using the restored habitat, etc.), and costs (actual or projected). Such a State Register would allow for a more regional coordination of future revegetation projects to suggest potentially more ecologically useful approaches. This could include identifying the most locally suitable species to plant, maximising the area of existing native habitat or restored fragments by planting adjacent to these, joining isolated islands of habitat to increase connectivity, or even to create more efficient projects by combining otherwise independent proponents (e.g., adjacent landholders).

(ii) Establish a State Revegetation Council that uses data from the Register to prioritise projects, enhance collaboration, and suggest improvements in design and placement according to the principles mentioned above. The Council could also help to coordinate monitoring of progress and ecological outcomes at the landscape scale. A similar State Register for Wetland Restoration and a relevant Council could be established in a similar manner, emphasising the conservation and restoration of smaller wetlands with more unique, endemic plant species. Likewise, both Councils could ideally assist in coordinating non-profit and private organisations in terms of their revegetation priorities, as well as coordinate with conservation covenants(see below) for private landholders.

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Influential conservation ecology papers of 2018

17 12 2018

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For the last five years I’ve published a retrospective list of the ‘top’ 20 influential papers of the year as assessed by experts in F1000 Prime — so, I’m doing so again for 2018 (interesting side note: six of the twenty papers highlighted here for 2018 appear in Science magazine). See previous years’ posts here: 2017, 20162015, 2014, and 2013.

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Ecophysiological feedbacks under climate change

29 10 2018

Variability in heat tolerance among populations modifies the climate-driven periods of diurnal activity expected for ectotherm species. We illustrate this phenomenon for Iberian lizards in a paper we have just published in the Journal of Animal Ecology (blog post reproduced with permission by the Journal; see related blog).

Common wall lizard (Podarcis muralis, male) and three localities where the species is abundant in Spain, left to right including Valdesquí/Madrid (Central System), Peñagolosa/Castellón (Iberian System) and El Portalet/Huesca (The Pyrenees).

Iberia is a wonderful natural laboratory, with a complex blend of flat/hilly, open/woody and coastal/continental terrain, swept by climatic gradients of temperature and moisture. In 2013, I launched a BES-supported project about the thermal ecology of Iberian lizards and managed to drive over much of the Iberian Peninsula in fairly little time. Not being a reptile specialist myself, I was confronted by the consistent observation that lizard populations occupied very different habitats across the known distribution of each of the ~ 25 known Iberian species belonging to the family Lacertidae.

For instance, the common wall lizard (Podarcis muralis) likes water, rocks and mountains, but you can find this pencil-long reptile at the top of a summit, along the slopes or riversides of shallow and deep ravines, on little stones barely surfacing above peatland grasslands, or among the bricks of buildings. These animals must experience different local climates conditional on where they live, and adapt their thermal physiology accordingly.

Having then started a postdoc in Miguel Araújo’s lab — a world-class site for global change ecology and ‘big’ biodiversity patterns — I reviewed a sizeable body of literature looking into large-scale gradients of thermal tolerance. Most of those papers had collated (mostly) one estimate of tolerance from each of tens to thousands of species, then mapped them against regional and global metrics of climate change through sophisticated mathematical frameworks. But these studies rarely accounted for population-level thermal tolerance.

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Save a jaguar by eating less meat

8 10 2018

Kaayana

My encounter with Kaayana in Kaa-Iya National Park in the Bolivian Chaco. Her cub was around but cannot be seen in the photo

I was trapped. Or so I thought.

The jaguar came towards me on the dirt road, calmly but attentively in the dusky light, her nearly full grown cub behind her. Nervous and with only a torch as defence, I held the light high above my head as she approached, trying to look taller. But she was merely curious; and, after 20 minutes, they left. I walked home in the thickening darkness, amazed at having come so close to South America’s top predator. We later named this mother jaguar ‘Kaayana’, because she lives inside Kaa-Iya National Park in the Bolivian Chaco. My fascination with jaguars has only grown since then, but the chances of encountering this incredible animal in the wild have shrunk even since that night.

A few years after that encounter, I’m back to study jaguars in the same forest, only now at the scale of the whole South American Gran Chaco. Jaguars are the third largest cats in the world and the top predators across Latin America. This means that they are essential for keeping ecosystems healthy. However, they are disappearing rapidly in parts of their range.

Understanding how and where the jaguar’s main threats — habitat destruction and hunting — affect them is fundamental to set appropriate strategies to save them. These threats are not only damaging on their own, but they sometimes act simultaneously in an area, potentially having impacts that are larger than their simple sum. For instance, a new road doesn’t only promote deforestation, it also increases hunters’ ability to get into previously inaccessible forests. Similarly, when the forest is cut for cattle ranching, ranchers often kill jaguars for fears of stock loss.

Kaayana & kittens

Kaayana was seen years later by Daniel Alarcón, who took much better photos of her and her new cubs

However, the interactions between these threats are still not fully understood. In our new study, just published in the journal Diversity and Distributions, we developed a new framework to quantify how and where habitat destruction and hunting risk acted together over three decades, at the expense of highly suitable jaguar habitat in the Gran Chaco. We also analyzed how well the different Chaco countries — Bolivia, Paraguay and Argentina — and their protected areas maintained key jaguar habitat. Read the rest of this entry »





South Australia’s broken biodiversity legislation

24 09 2018

It might come as a bit of shock to some who might give more than a shit about our State’s environmental integrity that there is no dedicated legislation to protect biodiversity in South Australia today.

What? Well, ok, we do have the Native Vegetation Act that is supposed to restrict the clearing of existing native vegetation (of which there is precious little left), and the National Parks and Wildlife Act 1972 to legislate protected areas and species endangerment. We also have the Wilderness Protection Act 1992 that addresses wilderness protection and land restoration, and the Natural Resource Management Act 2004 that is designed to promote sustainable and integrated management of the State’s natural resources. Finally, the South Australia Environment Protection Authority operates under various acts1 to limit environmental damage.

However, South Australia has no act specifically focussed on biodiversity conservation, and the legislation that does exist does not even consider invertebrates (like insects) as animals — because most animals are in fact invertebrates, this means that most of South Australia’s species are ineligible for official threat listing, even if they have a high risk of extinction.

If you recall, I reported in July this year that in 2017 we had a Parliamentary Inquiry into Biodiversity2, which concluded that existing environmental legislation in South Australia “… lacks cohesion and consistency, particularly regarding enforcement and compliance provisions”.

In my judgement, therefore, an entirely new, biodiversity-focussed act would add legislative teeth to biodiversity conservation in South Australia. As it turns out, that very same Parliamentary Inquiry into Biodiversity I mentioned above recommended3 the creation of a Biodiversity Expert Panel to reform the legislative framework of environmental protection. Thus, the new Government of South Australia has the perfect opportunity to do so under their proposed changes to natural resource management legislation. Following these calls for reform and the new direction of Nature of SA, there is a real opportunity here for statutory reform that includes integrated biodiversity legislation analogous to the New South Wales Biodiversity Conservation Act 2016.

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The European Union just made bioenergy worse for biodiversity

21 08 2018

bioenergy2While some complain that the European Union (EU) is an enormous, cumbersome beast (just ask the self-harming Brexiteers), it generally has some rather laudable legislative checks and balances for nature conservation. While far from perfect, the rules applying to all Member States have arguably improved the state of both European environments, and those from which Europeans source their materials.

But legislation gets updated from time to time, and not always in the ways that benefit biodiversity (and therefore, us) the most. This is exactly what’s just happened with the new EU Renewable Energy Directive (RED) released in June this year.

Now, this is the point where most readers’ eyes glaze over. EU policy discussions are exceedingly dry and boring (I’ve dabbled a bit in this arena before, and struggled to stay awake myself). But I’ll try to lighten your required concentration load somewhat by being as brief and explanatory as possible, but please stay with me — this shit is important.

In fact, it’s so important that I joined forces with some German colleagues with particular expertise in greenhouse-gas accounting and EU policy — Klaus Hennenberg and Hannes Böttcher1 of Öko-Institut (Institute of Applied Ecology) in Darmstadt — to publish an article available today in Nature Ecology and Evolution.

bioenergy4So back to the RED legislation. The original ‘RED 2009‘ covered reductions of greenhouse-gas emissions and the mitigation of negative impacts on areas of high biodiversity value, such as primary forests, protected areas, and highly biodiverse grasslands, and for areas of high carbon stock like wetlands, forests, and peatlands.

But RED 2009 was far from what we might call ‘ambitious’, because globally mandatory criteria on water, soil and social aspects for agriculture and forestry production were excluded to avoid conflicts with rules of the World Trade Organization.

Nor did RED 2009 apply to all bioenergy types, and only included biofuels used in transport, including gaseous and solid fuels, and bioliquids used for electricity, heating, and cooling. But RED 2009 requirements also applied to all raw materials sourced from agriculture and forestry, especially as forest biomass is explicitly mentioned as a raw material for the production of advanced biofuels in the RED 2009 extension from 2015.

Thus, one could conceivably call RED 2009 criteria ‘minimum safeguards’.

But as of June this year, the EU accepted a 2016 proposal to recast RED 2009 into what is now called ‘RED II’. While the revisions might look good on paper by setting new incentives in transport (advanced biofuels) and in heating and cooling that will likely increase the use of biomass sourced from forests, and by extending the directive on solid and gaseous biomass, the amendments unfortunately take some huge leaps backwards in terms of sustainability requirements.

These include the following stuff-ups: Read the rest of this entry »