Fascination of trees – Why are trees so thirsty?

photo_julia  Posted by Julia Kaplick @julekap

Water is crucial for most organisms on the planet. Humans are made up of more than 50% water and everyone knows how important it is to water the plants in the garden. Trees are especially fascinating in their water use. On a hot summer day an individual tree can take up close to 2000 litres of water and transport that huge amount several 10’s of metres from the roots to the canopy. But unlike us humans trees do not have a pumping organ to achieve that. The uptake is driven by negative pressure created at the surface of the leaves when water is transpired through the stomata to the atmosphere. More than 99% of water is transpired and only a very small amount is actually used during photosynthesis or to transport metabolites within the tree.

huapai_01   haupai_02  huapai_04

Tall trees, canopy sampling and sap flow sensors at Huapai scientific reserve. Middle photo by Freddie Hjelm from The Living Tree Company

The great loss of water is necessary because at the same time carbon dioxide can diffuse into the leaf where it can be transformed into sugars and subsequently used for growth and maintenance. Water use patterns vary greatly between tree species. Some trees have a greater water use efficiency than others, which means they can gain more carbon while losing less water than other species. Some trees also have very conservative water use patterns, they control their stomata opening and lose less water, but also take up less carbon resulting in slower growth.

On a global scale trees and forested areas play a major role in the hydrological cycle due to transpiration but also because of evaporation of intercepted water. According to estimates, 41,000 cubic km of water are transpired globally every year. This is equivalent to 630 times the water volume of Lake Taupo and strongly influences rainfall patterns and the amount of water vapour (an important greenhouse gas) in the atmosphere. On a more local scale forested areas directly and indirectly influence many fresh water catchments and subsequently the supply and quality of drinking water.

Transpiration is still one of the biggest uncertainties in climate modelling, mainly due to a lack of data and the difficulty of measurement. We also know very little about the water use patterns of New Zealand trees. How much water do they use? How does that vary seasonally and annually? What effects does a rising atmospheric carbon dioxide concentration have on water use and transpiration? And how do changes in other climate variables affect the water use and related physiological processes of trees in New Zealand?

The recent global fascination of plants day highlighted the value and intrigue of plants and trees add an extra dimension to that. My research is exploring the physiology of four native tree species here in New Zealand. Stay tuned for some fascinating results!

Julia Kaplick is a PhD student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. She is researching the response of native trees to seasonal variation in climatic conditions using measurements of sap flow, water relations and carbon allocation. Julia is supervised by Cate Macinnis-Ng (University of Auckland) and Mike Clearwater (Waikato University). Julia is supported by funding from the Marsden Fund.  

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When natives go wild: New Zealand… a global supplier of invasive species

Stringer UoA photo

Posted by Lloyd Stringer

After reading Mick Clout’s post on New Zealand’s potential as an Ark for non-native species; a source of genetically diverse species, that could be used to repopulate the historically native ranges from whence they came, I got a-thinking… Is New Zealand a source of invasive species?

In my day job I work on ways to prevent adventive species establishment in New Zealand. I was heartened to discover that Aotearoa has been exporting more than vibrant young kiwis on overseas working holidays.

As a kid I dreamed of a never ending Christmas. That has potential to come into fruition with the spread of New Zealand’s Christmas tree, the pohutukawa, Metrosideros excelsa into European countries. Meanwhile, in South Africa, pohutukawa threaten the ecologically unique Fynbos, already under threat from other invasive species, via prolific seed production leading to dense seedling stands.

A Pohutukawa in full bloom. This species typically flowers from Dec-Jan. Credit: by Ed323 at en.wikipedia (Transferred from en.wikipedia) [Public domain], from Wikimedia Common.

A Pohutukawa in full bloom. This species typically flowers from Dec-Jan. Credit: by Ed323 at en.wikipedia (Transferred from en.wikipedia) [Public domain], from Wikimedia Common.

Another successful export has been the Karaka, Corynocarpus laevigatus. This New Zealand treasure provides a risky food requiring days of preparation to detoxify the seeds prior to eating. Karaka were used in reforestation efforts in Hawaii early in 20th century where it now forms dense stands potentially shading out local, rare endemic plant species.

Possibly some of the less iconic New Zealand species making their way around the globe are the mudsnail Potamopyrgus antipodarum and flatworm Arthurdendyus triangulatus. New Zealand’s mudsnail can reach densities of up to 300,000 individuals per square metre in some rivers, modifying ecosystem processes. Whereas on land, the flatworm, predates on earthworms which could lead to secondary effects such as a reduction in soil quality and a reduction of a food source for native birds.

Perhaps what we are seeing are the New Zealand-sourced winners that could have a chance at surviving in a possible future world that is less species–rich, instead dominated by a few widespread species.

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Lloyd Stringer is an invasive species entomologist at Plant & Food Research and doctoral student in the School of Biological Sciences, University of Auckland, investigating the interactions between eradication tools and Allee thresholds.

 He is supervised by Max Suckling, Jacqueline Beggs and John Kean. Here Lloyd is planning a red imported fire ant field experiment.

We need to talk about ALAN

Ellery (2)Posted by Ellery McNaughton @EJ_McNaughton

Like Santa, ALAN probably sees you when you are sleeping. ALAN will be trying to get in through your window tonight. Perhaps you haven’t noticed ALAN. But ALAN is always there. ALAN may be having serious impacts on your health. ALAN kills innocent birds and baby turtles for fun.

ALAN will be following you home tonight... and when you get there, ALAN will already be waiting for you

ALAN will be following you home tonight… and when you get there, ALAN will already be waiting for you

And yet, who doesn’t love ALAN? Who hasn’t invited ALAN into their homes and cities?

Artificial Light At Night (ALAN) is a global issue. If you live in an urban area you cannot escape it. Streets, buildings, sports fields, parks, monuments – all are lit up come night time, and it’s easy to see why. Light enables us to see better, feel safer and do more at night. Plus it looks pretty. Bonus!

Sydney - an example of cities' typical love of ALAN. When has pollution ever looked so fetching?

Sydney – an example of cities’ typical love of ALAN. When has pollution ever looked so fetching?

Light pollution doesn’t get the same attention that water or air pollution does. Perhaps this is because it doesn’t add a physical pollutant to the environment. Perhaps it is because it is seen as transient – once the lights are switched off in the morning, problem solved. Or perhaps it is because we have forgotten what the night sky should look like, so we fail to realise just how polluted our skies are. Whatever the reason, traditionally light pollution has only been an issue of concern among astronomers.

Recently however, there is light on the horizon in addition to light in our skies. There has been a surge of research into the myriad effects of ALAN on the environment (e.g. this special issue in Proc. R. Soc. B). Citizen science is being used to better understand variations in the levels of light pollution. The United Nations proclaimed 2015 to be the International Year of Light and Light-based Technologies, while the Nobel Prize in Physics for 2014 was awarded to the inventors of the blue light-emitting diode. This recent focus on light, light technologies and ALAN in particular opens up opportunities for discussion and thought on these issues. And really, this needs to happen. Because ALAN is most definitely on the naughty list, and we need to talk about it.

Ellery McNaughton is a PhD student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. Her project will investigate the effects of a city-wide changeover in streetlight technology on urban bird behaviour and ecosystem function. She is supervised by Margaret Stanley, Jacqueline Beggs, Kevin Gaston (University of Exeter, UK) and Daryl Jones (Griffith University, Australia).

Teenage mutant ninja ecological research

Posted by Josie Galbraith

Pizza!What does it take to pull off a successful project in the urban jungle? The short answer is courage and people… pizza helps too. Last week I (along with my PhD supervisors) had a paper published in the Proceedings of the National Academy of Sciences (PNAS) – Supplementary feeding restructures urban bird communities. This was a big milestone for me, but also hugely important for getting urban ecological research and the practice of bird feeding into the spotlight. Urban ecology has only relatively recently become a thing – before then it was just a clandestine notion, whispered in dark corridors and laughed at at meetings of ‘real’ ecologists. Now though, the urban environment is a place where real ecological science happens. Bold, brave, big science! It certainly takes a great deal of courage to plunge into the ocean of urban ecological research. It is awash with houses, high-rises, industry, roads, gardens, parks, and of course people. As such, there are a myriad of challenges and barriers associated with working in these areas that just don’t exist in more natural habitats.

Native silvereye at experimental feeding station

Native silvereye (Zosterops lateralis) at an experimental feeding station.

One of our experimental bird feeding stations, complete with radio antenna for scanning PIT-tagged birds, in the garden of a volunteer household

One of our experimental feeding stations, complete with antenna, in the garden of a volunteer household.

So how can we meet the challenges urban research presents, and make the most of inevitable time and funding constraints? Urban areas hold the greatest human resource of any habitat an ecologist will encounter – make use of it!  There are plenty of keen folk willing and ready to get involved. In our study we recruited 24 householders purely through word-of-mouth and emails asking people to forward on our request.  We had many more people respond than we needed, so could be more choosy with our property selection. What we were asking of these householders was pretty major – a 2-year commitment to an experimental feeding study, with those selected as “feeding properties” having to put out food for the birds every morning. We expected over the course of the project a number would find the study too onerous and drop-out. In fact, only one did. Our volunteer householders were brilliant to work with, and, while I did the key data collection, they provided plenty of additional observational information, which has been really valuable.

Urban areas are also fantastic fountains of goods and equipment, from pizza to nunchuks. We ecologists often need the weirdest things for our projects – we’ve all had those looks before at our local hardware store…

Ask and you shall receive! We found exactly what we needed for our study (a mountain of bread) by asking around.

Ask and you shall receive! We found exactly what we needed for our study (a mountain of bread) by asking around.

Them: “Why do you need such a small piece of piping?”

Me: “I’m making an aspirator to suck up ants…”

Them: “Uhhhhh…*you’re so weird*…”

Local companies or businesses may be willing to donate materials support to the project, particularly if the things you need are someone else’s trash – off-cuts, end of lines, seconds. You never know what you’ll find, so it pays to ask. Our study required a mountain of bread (1580 loaves to be exact) – and we found one. Literally. A staggering amount of food gets wasted these days, and I didn’t want our study to be using food that could’ve been on someone’s plate. After a few phone calls we found what happens to our cities’ bread waste – it gets trucked to a food recycling factory before being turned into stock feed. The manager happily let us collect the bread we needed for the study each month – it was such a tiny fraction of the volumes that they process. Thanks Ecostock!

There are fascinating ecological things happening in our cities, and they are crying out for ecologist heroes to come and study them. Heroes that will boldly go where there are plenty of other humans. Heroes who will remember to involve their fellow humans and make use of all the resources cities have to offer. Heroes who are willing to push the boundaries, to redefine ecological science. Heroes that have the number for pizza delivery on speed-dial ‘cos you just never know when you might discover mutant turtles in the sewers…

Josie Galbraith is a PhD student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. She is supervised by Margaret Stanley, Jacqueline Beggs and Daryl Jones (Griffith University, Australia).