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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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 »





Legacy of human migration on the diversity of languages in the Americas

12 09 2018

quechua-foto-ale-glogsterThis might seem a little left-of-centre for CB.com subject matter, but hang in there, this does have some pretty important conservation implications.

In our quest to be as transdisciplinary as possible, I’ve team up with a few people outside my discipline to put together a PhD modelling project that could really help us understand how human colonisation shaped not only ancient ecosystems, but also our own ancient cultures.

Thanks largely to the efforts of Dr Frédérik Saltré here in the Global Ecology Laboratory, at Flinders University, and in collaboration with Dr Bastien Llamas (Australian Centre for Ancient DNA), Joshua Birchall (Museu Paraense Emílio Goeldi, Brazil), and Lars Fehren-Schmitz (University of California at Santa Cruz, USA), I think the student could break down a few disciplinary boundaries here and provide real insights into the causes and consequences of human expansion into novel environments.

Interested? See below for more details?

Languages are ‘documents of history’ and historical linguists have developed comparative methods to infer patterns of human prehistory and cultural evolution. The Americas present a more substantive diversity of indigenous language stock than any other continent; however, whether such a diversity arose from initial human migration pathways across the continent is still unknown, because the primary proxy used (i.e., archaeological evidence) to study modern human migration is both too incomplete and biased to inform any regional inference of colonisation trajectories. Read the rest of this entry »





Minister, why is the dingo no longer ‘fauna’?

7 09 2018

dead dingoSo, a few of us have just submitted a letter contesting the Western Australia Government’s recent decision to delist dingoes as ‘fauna’ (I know — what the hell else could they be?). The letter was organised brilliantly by Dr Kylie Cairns (University of New South Wales), and she and the rest of the signatories have agreed to reproduce the letter in full here on ConservationBytes.com. If you feel so compelled, please voice your distaste of this decision officially by contacting the Minister (details below).

CJA Bradshaw

Honourable Stephen Dawson MLC
Minister for Environment; Disability Services
Address: 12th Floor, Dumas House
2 Havelock Street, WEST PERTH WA 6005
(minister.dawson@dpc.wa.gov.au)

cc: Department of Biodiversity, Conservation and Attractions (biodiversity@dbca.wa.gov.au)
cc: Brendan Dooley (brendan.dooley@dpc.wa.gov.au)

Dear Minister,

The undersigned welcome the opportunity to comment on and recommend alteration of the proposed section (9)(2) order of the Biodiversity Conservation Act 2016 (BC Act) that changes the listing of the dingo from “fauna” to “non-fauna” in Western Australia. Removing the “fauna” status from dingoes has serious consequences for the management and conservation of this species and other native biota it benefits. Currently, dingoes are classed as A7, or fauna that requires a management policy. The proposed section (9)(2) order will move dingoes (as “non-fauna”) to the A5 class, meaning that dingoes must be (lethally) controlled and there will be no obligation for the Department of Biodiversity, Conservation and Attractions to have an appropriate management policy (or approval).

Currently, under the Wildlife Conservation Act 1950 (WC Act) the dingo is considered “unprotected” fauna allowing management under a Department of Biodiversity, Conservation and Attractions management policy. A section (9)(2) order demoting dingoes to “non-fauna” will remove the need for Department of Biodiversity, Conservation and Attractions management policy and instead mandate the lethal control of dingoes throughout Western Australia.

As prominent researchers in top predator ecology, biology, cultural value and genetics, we emphasise the importance of dingoes within Australian, and particularly Western Australia’s ecosystems. Dingoes are indisputably native based on the legislative definition of “any animal present in Australia prior to 1400 AD” from the BC Act. Dingoes have been present in Australia for at least 5000 years. On the Australian mainland they are now the sole non-human land-based top predator. Their importance to the ecological health and resilience of Australian ecosystems cannot be overstated. Read the rest of this entry »





Greater death rates for invasive rabbits from interacting diseases

30 05 2018

When it comes to death rates for invasive European rabbits (Oryctolagus cuniculus) in Australia, it appears that 1 + 1 = 2.1.

Pt tagged rab with RHD+myxo 1 10-08

Tagged European rabbit kitten infected with myxoma virus, but that died from rabbit haemorrhagic virus disease (RHDV). Photo by David Peacock, Biosecurity South Australia.

“Canberra, we have a problem” — Sure, it’s an old problem and much less of one than it used to be back in the 1950s, but invasive rabbits are nonetheless an ecological, conservation, and financial catastrophe across Australia.

relative rabbit abundance South Australia

Semi-schematic diagram, redrawn using data from Saunders and others and extended to include the recent spread of RHDV2, showing changes in rabbit abundance in relation to the introduction of biological control agents into north-eastern South Australia. Dotted lines indicate uncertainty due to lack of continuous annual data. The broken line indicates a level of about 0.5 rabbits ha-1, below which rabbits must be held to ensure recovery of native pastures and shrubs (from B. Cooke 2018 Vet Rec doi:10.1136/vr.k2105)

Rabbits used to reach plague numbers in much of agricultural and outback Australia, but the introduction and clever manipulation of two rather effective rabbit-specific viruses and insect vectors — first, myxoma virus in 1950, European rabbit fleas in the 1960s to help spread the virus, then Spanish rabbit fleas in the 1990s to increase spread into arid areas, and then rabbit haemorrhagic disease virus (RHDV) in 1995 — have been effective in dropping rabbit abundances by an estimated 75-80% in South Australia alone since the 1950s.

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