Kauri and drought – What’s their survival strategy?

Posted by Julia Kaplick @julekap

New Zealand’s future climate is likely to be warmer and dryer and the frequency and duration of drought events is predicted to increase. Drought-induced tree mortality is increasing world-wide, with several instances also reported in New Zealand. So far we know very little about the drought vulnerability of New Zealand forest trees, but due to our research on kauri we are beginning to understand more and more about the drought survival strategy of this forest giant.



The roots are integral for trees to extract water from the soil and a good root network is crucial for drought survival. During times of water stress many trees, including kauri, invest in root growth. This allows them to keep up their normal transpiration levels for a little longer. So far it is assumed that kauri roots are very shallow, but sap flow measurements during the 2013 drought suggest otherwise. The upper soil layer during that time was extremely dry, but the trees still used water which suggests that kauri roots must reach a lot deeper than we previously thought allowing access to deeper water stores.


Kauri roots

Drought avoidance or toleration?

In general, every tree species falls somewhere on the spectrum between drought avoidance and drought toleration. Drought tolerating trees keep up transpiration as long as possible. Drought avoiding species on the other hand start closing their stomata to reduce water loss, when the soil moisture goes down. Both strategies have their downsides. Drought tolerators risk the formation of little air bubbles (xylem embolism) in their conducting tissue. This can lead to hydraulic failure if a drought lasts too long. Drought avoiders protect their hydraulic integrity but risk starvation, because the closure of the stomata also means a reduction of carbon intake. Kauri are clearly drought avoiders. Even under ideal growing conditions kauri are conservative water users, closing their stomata early in the day. They are known to be very susceptible to xylem embolism and protect their hydraulic integrity in that way.


Kauri cone in a bed of leaf litter

Leaf shedding

During the 2013 drought the kauri in our study plot lost a substantial amount of leaves and twigs. The reduction of leaf area is an effective way to reduce the water-losing surface and consequently the reduction of transpiration and the need for water uptake.


Base of a kauri stem

Water storage

All components of a tree (roots, stem, branches, leaves) can serve as water storage compartments. This is a drought survival strategy that succulents have perfected. Kauri make use of stored water on daily basis. Water is withdrawn from the stem and branches in the morning when the water starts to transpire from the leaves. During the afternoon and night these stores are refilled again. The massive stem volume paired with deep sapwood seem to make a great water store. During prolonged drought conditions kauri should be able to use the water reserves to their advantage. This is something we are investigation right now, stay tuned.


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.  

Untangling insect respiration

Posted by Jessica Devitt @Colette_Keeha


Over several millennia insects have developed physiological adaptations to their environments through the process of natural selection.  Thus, insects are one of the most diverse and widespread animal taxa.

Insects have evolved diverse respiratory responses to a wide range of environments. The mechanisms behind these differing responses are not fully understood, with some insects displaying adaptations to low O2 (hypoxic) and high CO2 (hypercarbic) atmospheres. One such adaptation is the so-called Discontinuous Gas Exchange Cycle (DGC) where the insect only releases CO2 to the external environment periodically (Figure 1).


Figure 1. Graphic showing discontinuous gas exchange phases: The flutter phase (F) where CO2 is released during a rapid opening and shutting of the spiracle, the open phase (O) where a burst of CO2 is released from the spiracle and the closed phase (C) where the spiracle is closed for a time resulting in a small release of CO2 (Hetz & Bradley, 2005, p. 517).

There is debate as to what the main function of this adaptation is: one school of thought suggests DGC might protect against desiccation. The other is that DGC allows insects to withstand hypoxic environments.

This brings us to my study species: The golden-haired bark beetle (GHBB) (Hylurgus liginperda: Curculionidae). Bark beetles predominantly attack damaged trees, stumps and fallen/felled trunks and branches. GHBB adult beetles burrow through the bark creating galleries within the cambium/phloem, in which the eggs are laid. Once the larvae have consumed the available cambium/phloem and undergone pupation, newly emerged adults take flight to the next available resource.


Figure 2. Hylurgus ligniperda (Fabricius, 1792). (Schmidt, 2014)


Figure 3. Hylurgus ligniperda adults exposed under pine bark. (Pest Alert, n.d.)

The golden-haired bark beetle is a widespread forest pest distributed throughout several continents, such as Australasia and North and South America. Although the beetle itself does not cause significant damage to the heartwood, its presence on export logs creates a market access issue.

In my PhD study we will investigate the respiratory responses of GHBB to a range of atmospheric conditions, such as contrasting O2/CO2 levels over different durations. I plan to use GHBB as an experimental model to understand bark beetle respiration in the presence of low O2/high COenvironments.  My experiments will manipulate atmospheric conditions with the addition of fumigants in order to ascertain the most effective conditions in which to treat export logs.


Hetz, S. K., & Bradley, T. J. (2005). Insects breathe discontinuously to avoid oxygen toxicity. Nature, 433(7025), 516-519. doi:10.1038/nature03106.

Pest Alert. (n.d.). Hylurgus ligniperda adults exposed under pine bark.  Retrieved from http://www.pestalert.org/espanol/PhotoDetail.cfm?RecordID=47

Schmidt, U.  2014. Hylurgus ligniperda. Retrieved from https://www.kaefer-der-welt.de/hylurgus_ligniperda.htm


Jessica Devitt is a PhD student at the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland and Plant and Food Research. She is researching the respiratory responses of the golden-haired bark beetle to advance fumigation techniques. She is supervised by Jacqueline Beggs from the University of Auckland, Adriana Najar-Rodriguez and Matthew Hall from Plant and Food Research

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When a blessing becomes a curse…. A case of invasive Prosopis juliflora

Posted by Tshego Chilume @tschilume

When you live in an arid environment with temperatures that can go up as high as 47oC the prospect of the introduction of any tree into your area is music to your ears. This was the case for the people of Kgalagadi Desert when Prosopis juliflora and Prosopis grandulosa were introduced into the desert to control desertification and the constant moving sand dunes. For the first time large trees were seen around the district and communities had natural shade, fodder for their livestock and kids had playgrounds covered from the scorching sun. It was all merry; what could go wrong in such a beautiful scene? You would think nothing!


Except Prosopis is one of the worst invasive plant taxa in the world, it is capable of eradicating all woody plant species in its invaded habitat. Because there wasn’t much woody vegetation in Kgalagadi District, I figured there was no need to worry, however Kgalagadi Desert is known for its shrubs, cactus and grasses that have adapted to the harsh environment of their native ecosystem and are a valuable source of water and food for the locals, their livestock and wildlife. Forty years ago, the introduction was apparently met with dancing, celebrations and slaughtering of cattle (something Batswana do a lot when they have something to be happy about). But as time went on, a massive commotion has started between the relevant government agencies and communities. The impact of Prosopis is becoming increasingly apparent and difficult to ignore and everyone needs someone to blame for this. Prosopis is perceived to have caused the loss of native grasses, shrubs, reduction in borehole water yields, poisoning livestock and causing allergies to people. The communities blame the department of forestry for the introduction, forestry blames political pressure while the politicians blame the communities for insisting on a quick solution and the department of forestry for not doing enough research prior to the introduction.

The situation is that a solution to this social unease was necessary and back then there was very little funding available for research in issues of environmental issues. Even today, funding for research in environmental issues comes from donors outside Botswana. While this bickering continues, the impacts of Prosopis in Botswana have never been quantified and the current control practices were brought about by the public outcry.

This brings me to my current research on quantifying the ecological impacts of Prosopis juliflora in Gantsi District, the most ecologically and economically valuable district of Botswana. Gantsi district is home to one of the largest wildlife management areas in the world, Central Kalahari Game Reserve and in close proximity to the Okavango Delta (a world heritage site). This research will provide the impacts associated with Prosopis juliflora on the soil chemical variables and vegetation of Gantsi District. The research will improve our understanding of the effects of Prosopis and enable government to make informed decisions on the control measures and development of Prosopis management programmes.

tshegoTshegofatso Sputnik Chilume is an MSc student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. She is supervised by Cate Macinnis-Ng and Keotshepile Kashe (Okavango Research Institute, University of Botswana) quantifying the ecological impacts of Prosopis juliflora in Gantsi District, Botswana.

Aliens in Our Backyard: Parasitoid Wasps (and How to Catch Them)

Posted by Tom Saunders.

The eponymous extra-terrestrial from the Alien film franchise struck terror into our souls –razor sharp teeth, acid for blood, and an unusual capacity for memorising the layout of ventilation shafts. But it had another interesting trait – it had a parasitoid life cycle. A parasitoid is an organism that spends its juvenile life stage feeding on the body of a host. While a parasite allows its host to live, a parasitoid does not. It emerges from its dead host in a similar way to how the alien bursts out of the chest of a helpless crew member. But while the ‘xenomorph’ was a frightful fantasy dreamt up by Hollywood, parasitoid wasps are important creatures that live all around us, and we should try to understand them.



Lemon tree borer parasite (Xanthocryptus novozealandicus), a native New Zealand parasitoid wasp. Image © by Pete McGregor. Image licensed under Creative Commons Attribution-NonCommercial 4.0. .


Parasitoid wasps are potentially the most diverse group of organisms in the world (sorry beetle fans). They are abundant, they are crucial to the functioning of ecosystems, and they can be used by humans to control pests which damage food and other crops. Despite all this, they are incredibly understudied and there is still much that we don’t know about them on a global, regional, or even local scale. As with any species, the first step in collecting information on parasitoid wasps is to sample their diversity, in order to construct an inventory of species and to monitor how their diversity changes over time. The problem is:

  • How many samples should you take?
  • How many traps should you use?
  • How long should you leave the traps out for?
  • How much diversity can you expect to catch?
  • How many traps are required to achieve the level of diversity you want?



Netelia sp., a native New Zealand parasitoid wasp. Image © by Pete McGregor. Image licensed under Creative Commons Attribution-NonCommercial 4.0. .


By employing some of the concepts from optimal sampling theory, we can analyse the results from preliminary sampling and incorporate them into a new program that can tell us the answers to these questions. My master’s is tackling how this issue relates to New Zealand’s parasitoid wasps. I’ve collected my insect samples, and now I’m identifying the parasitoid wasps. Once that is complete, I’ll prepare some analyses which will help to build a foundation for the future study of these amazing insects.


Me setting up a malaise trap at the Oratia field site.


Once we know how to sample efficiently for parasitoid wasps, future work can look at some other interesting questions related to this group. For example, someone could look at how useful the NZ fauna would be as indicators of environmental quality, or surrogates for the diversity of other groups. This would help immensely in the selection of species and habitats to include in conservation planning. Who knows, you could be the one!



Tom Saunders is a Master’s student at the Centre for Biodiversity and Biosecurity, within the School of Biological Sciences, at The University of Auckland. He is supervised by Dr Darren Ward (Landcare Research). You can find out more about Tom and his research at TomSaunders.co.nz

Play time – Scientific toys

Posted by Julia Kaplick @julekap

My research focuses on trees, but when I look at the equipment I fill my car with when I go out to my field site, it looks more like I am an electrician. There are car batteries, cables, a bag full of tools, a laptop and lots more. Only a field notebook to record observations like Darwin or Humboldt have done it, is just not enough anymore. Nowadays most research involves specialised equipment to gather data or samples and advanced technology to physically or chemically analyse all sorts of sample materials. That can be daunting, but mostly it is just great to have so many toys to play with as a researcher.

kauri sapflow

Kauri tree with sap flow sensor – nicely wrapped (for sun protection) like toys for christmas

I rely on sensors to gather most of my data. A meteorological station records environmental data for me, sap flow sensors (that I partly built myself) measure how much water my trees are using and I use a little thing called Trephor to collect wood samples (see how in this little video). The newest additions to our toy collection are called radius dendrometers. They will very soon record the expansion and contraction of my study trees’ stems on an extremely fine scale. That will give me an idea about daily patterns of water storage and growth. When the parcel with that equipment arrived I was excited like a little child at Christmas, but very soon the daunting part started. I needed to figure out how to get them working, how to install them and there is always that little bit of anxiety, because all that equipment is ridiculously expensive since it is so specialised and only few people in the world use it.


Some of the toys I get to play with: Trephor micro corer to collect wood samples, our meteorological station, sap flow sensors (that is how it looks like under the wrapping paper) and data loggers to record measurements (with lots of fun coloured cables)

All these toys are great and playing with them is mostly fun, the harder part is the interpretation of the data they gather. Even though there have been many advances in how to get data the part where you have to make sense out of it to generate knowledge has not actually changed much since Darwin and Humboldt.


#girlswithtoys, specifically #ecologytoys: Measuring water potential with a pressure bomb and (attempt to) shooting down leaves

To have a look at some cool toys scientists are using check out #girlswithtoys on twitter.


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.  

Taken for granted: New Zealand’s looming freshwater crisis

Posted by Cate Macinnis-Ng @LoraxCate

Water, water, every where,

And all the boards did shrink;Riparian vegetation

Water, water, every where,

Nor any drop to drink.

SAMUEL TAYLOR COLERIDGE The Rime of the Ancient Mariner 1798

In his recent contribution to the Infrequently Asked Questions Blog series, the President of The Royal Society of New Zealand Prof Richard Bedford touched on the influence of climate change on migration to New Zealand. He mentioned that the impact of climate change will be more severe in Australia because droughts and heat waves will be more extreme and more widely distributed. While it is true that the projections indicate that climate change impacts will be greater in Australia, New Zealand is ill-prepared for a changing climate and could therefore be equally vulnerable to the impacts of droughts and rising temperatures, even if they are less intense.

As a nation surrounded by water, we take our water resources for granted. Groundwater has been allowed to become contaminated and the quality of our surface freshwaters has continued to decline with excess nutrients causing algal blooms and other problems. Extraction of groundwater for irrigation is intensive in the Canterbury region, particularly during dry periods. Our rivers are dying, our groundwater is dirty and drying up. Prof Bedford points out that droughts will become more frequent and severe in several parts of the country. We already know about the impact this can have on the dairy industry and other agricultural outputs, resulting in economic declines but the impact on native systems is not as clear. We do know that droughts can be a real problem for native fish like mudfish and mast seeding events can be triggered by warmer temperatures, causing population explosions of introduced mammals, leading to declines in native birds. Further details of current knowledge can be found here but in comparison to other countries, the research effort on the ecological and physiological responses of native species to climate change is lacking.

We can’t just assume that because New Zealand has a mild maritime climate, everything will be alright. We need more research on our unique biota and the water culture in New Zealand needs to change urgently before there really is not a drop to drink.

Dr Cate Macinnis-Ng is a Lecturer in Ecology, School of Biological Sciences, University of Auckland.  She is a plant ecophysiologist and ecohydrologist working on plant-climate interactions. In 2016, Cate will be starting a Rutherford Discovery Fellowship exploring the impact of drought on native forest.

A little ode to field work

Posted by Julia Kaplick @julekap

Julia takes aim!Spring is on our doorstep here in Auckland and nature is visibly getting busy. It is the start of the growing season for many plants and the most active time of the year for many animals. For many ecologists it also means that field work season is starting.

I am lucky enough to do my research in a more applied area of ecology. I get to go out into the forest and collect the data that forms the basis of my research myself. It is in fact the part that I enjoy the most and the main reason why I chose to work in ecology. During more than a year of field work in New Zealand, I have been soaking wet, freezing cold and muddy from head to toe, but at the end of the day I went home happy and with pages full of data. I have been hanging 15 metres high in the kauri forest canopy and freezing my feet off while taking predawn measurements in the mangroves.

The view from above.

The view from above.

Field work is challenging and fun. It teaches you to plan and organise, to improvise and to find creative solutions, as things do not always go as originally planned. Who knew that the party supply store around the corner would turn into one of the best sources for field equipment? What else could you possibly do with these metre long party straws than put wood samples into them and there cannot be any other proper use for Styrofoam cups than to use them as a radiation cover for temperature sensors. I also learned that a pressure bomb is a good thing and have significantly increased my electrical skills by building and connecting sensors. You also know that you are working with pretty cool instruments when your supervisor seems to be more worried about the machine dropping out of than canopy than about the PhD student who holds it. All this I have to admit came at a price. I probably lost several litres of blood to mosquitos and a scar on my middle finger will always remind me that soldering irons are extremely hot, not that I really needed that reminder.

Mud pie anyone?

Mud pie anyone?

Field work lets you see the world with different sometimes slightly nerdy eyes. It is exciting and rewarding to see theory come to life, even if it is sometimes unexpected. Someone recently told me that field work can become a little addictive and I can already see why.

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).


Auckland Kereru Project

The Auckland Kereru Project: Following the movements and diets of urban kererū (NZ pigeon) in Auckland. 

Joint Graduate School in Biodiversity and Biosecurity PhD candidate Alice Baranyovits is investigating how kererū move around fragmented landscapes and more specifically how they utilise the urban environment. In particular she is interested in their diet, particularly where and when they are eating introduced plants. In order to do this she needs your help!

There are two ways to contribute as a one-off; by recording your garden plants and/or by recording urban kererū sightings (although you can enter as many kererū sightings as you like).

If you would prefer to have a more continual involvement you can register to take part in the phenology study (recording when your plants fruit) or the quarterly kererū count or both!

To sign up, please visit the Auckland Kereru Project website