drought

Posted by Noor Rooding @noorrooding ‏

I left the Netherlands as winter was finally coming to an end. Arriving in Auckland I have been able to experience the final glimpse of summer, before it heads into the depths of winter. Coming from the Netherlands I thought I understood rain… Sadly, Auckland has taught me that there is more to rain than I had realised.

In the Netherlands I study Applied Biology at the HAS University of Applied Science in Venlo. This is a four-year bachelor’s programme and I am currently in my third year. This year I had the opportunity to go on an internship abroad. I contacted Cate Macinnis-Ng and she was happy to get some help with some ongoing projects. This is how I ended up on the other side of the world

I have done some traveling in the past but only in Europe, so going to the other side of the world was a big step. I have been in New Zealand for two months now. One of the first things that I noticed is the average size of the New Zealander is a little bit smaller than in the Netherlands. But after all Dutch people are just tall, so it shouldn’t be a surprise. Of course, there are more obvious differences like the time difference, climate and nature. One of the major differences that has struck me is how much native bush I see, even when I am in the middle of the city.

I have also enjoyed seeing other parts of New Zealand. The Netherlands is very flat and does not have amazing things like volcanoes. I had a great experience doing the Tongariro alpine crossing and met some awesome people there. Everyone is so friendly and willing to help you. Someone even took me on a road trip the day after the walk.

As well as having lots of fun checking out your beautiful country I have also been doing some work. I am working on the litterfall project, which is an ongoing project involving many people. For this I am collecting litterfall material and sorting them into different categories such as species, branches and reproductive material. My main focus is looking at the reproductive cycle of the kauri. This involves looking at the data to date and seeing if drought has any effect on the reproductive cycle. I am expecting to see that drought conditions lead to more loss of reproductive material, such as seeds.

Coming to New Zealand has been an amazing experience that I will never forget. One of my favourite parts of my internship has been getting involved in several other projects. I was lucky to be help with the 24-hour project climbing kauri trees. It gave me the chance to climb these amazing trees and see them up close and personal.

Climbing the trees for the 24-hour project

I am here to learn and enjoy my stay in the country and experience as much as possible. If anyone needs help with anything, please feel free to contact me.

noor

Noor is an intern visiting from The Netherlands, working with Cate Macinnis-Ng on ‘The Litterfall Project’. Contact details: noorrooding@hotmail.com

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.

Roots

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.