Introducing the kauri drought experiment

KDE logo - 300 dpi web-01

I’m super excited to reveal my new project logo designed by the amazingly talented Josie Galbraith.  Thanks Josie for creating such a beautiful visual to represent my work. And now, it’s time to science!


Exciting news! PhD scholarships coming soon

I’m super excited about my recent success in the Rutherford Discovery Fellowship scheme. The grant is worth $800K over five years and will allow me to concentrate on my research for that period of time. I will be working on a field-based drought experiment in native NZ forest. I will use throughfall exclusion (similar to this) to create artificially droughted plots and will then explore aspects of the physiology and ecology of the plants and associated biota. The funding includes two PhD scholarships. These will be open to  domestic and international students. If you are interested, please get in touch (via my University of Auckland email address).

Interested students should be specific about their expertise and interest in drought research. Skills in plant ecophysiology, modelling, soil science, forest ecology, fluxes of carbon and water and forestry are particularly desirable. At this stage, I’m hoping one of the students can start in early 2016 with another starting later in 2016 or early 2017. I will post more information as it becomes available.

The Paturoa Kauri FAQ

On Monday morning (9th March 2015) locals, conservationists and tangata whenua gathered at 40 Paturoa Road to protect a centuries old kauri tree marked for felling to make way for new dwellings on the property. Thanks to the efforts of these dedicated folk, the trees are safe (for now). So what is so special about this tree and why should we care about it being removed? Here I address several important questions about the value and significance of this tree and the surrounding vegetation.

Why are kauri trees so special?

Kauri are amongst the largest and longest-lived trees in the world. Tree enthusiasts travel from across the globe to see these majestic plants. Kauri have a special place in Maori cultural heritage because they are taonga species. They have an important role in the spiritual beliefs of tangata whenua and are viewed as chiefs of the forest and a living connection to ancestors. They produce beautiful wood that has been used to build houses, boats and carvings and kauri gum was used to make carvings, glue and other products. Sadly, their wood is so prized that around 95-97% of kauri was cleared after European settlement. Kauri are now protected but the new threat of kauri dieback is threatening the remaining individuals.

Is it really 500 years old?

The age of the tree appears to have been estimated. We can estimate the age of a tree using two approaches. The most accurate approach is to count the annual rings accumulated in the trunk as the tree grows. We can also measure the diameter of the trunk and estimate tree age. For some tree species, this has been shown to be a very effective approach but for kauri, it can be inaccurate because there is only a weak relationship between tree age and trunk girth. That said, it is highly likely that the tree is several centuries old. A tree of this size and age supports a range of epiphytes, lichens and mosses in its branches and is therefore valuable habitat for other species. It also stores vast amounts of carbon and is important for binding soil and modulating the water cycle. No matter the age of the tree, it is ecologically significant.

What about kauri dieback?

The Paturoa Road area is known to be heavily infected with kauri dieback with a number of confirmed cases of diseased trees. Reports about the tree in question suggest that it is currently healthy. A well tree in a diseased area may have some form of resistance and therefore has increased ecological value. The tree may be a vital resource for the Scion Research programme looking for resistant trees. If the tree is infected with dieback and is yet to show symptoms, the removal process and management of the site during the building process must consider biosecurity. The pathogen causing kauri dieback is transported in soils and if wood and equipment are not properly disinfected before entering and leaving the site, the pathogen will be further spread. It is not clear if biosecurity tests have been done at the site to check for kauri dieback. This is a vital step, even if the tree was removed.

What has gone wrong here?

Without knowing the internal processes in council, it’s hard to know why this tree has been approved for removal. It is clear that the current legislation is not protecting valuable trees. Where kauri are involved, there should be mandatory biosecurity checks to make sure the site is correctly managed to prevent spread of kauri dieback. Reports suggest there was no iwi consultation. This is unacceptable given the spiritual significance of kauri. Titirangi is famous for its leafy environment and local residents clearly treasure their forest and trees. There needs to be better protection of this unique and beautiful part of Auckland for everyone to enjoy.

What about the rimu?

Other trees and vegetation, including a 300 year old rimu will also be removed from the site. This is also unfortunate but rimu are not currently threatened by dieback. It would be nice to conserve the rimu too but building on bush land will always require the removal of some plants.

The final word

All kauri are living national treasures. In Europe, centuries old buildings are carefully preserved and protected. We don’t have that type of architectural heritage but we do have a rich natural and cultural heritage that forms part of our identity. This heritage must be conserved for the benefit of future generations. Tane Mahuta will not live forever and this tree may be the largest tree centuries from now. In the context of kauri dieback, this tree is particularly valuable. Surely with some clever design, this tree can be saved for future generations. If nothing else, the tree protection laws need to be reconsidered.

Canopy fieldwork = tree climbing fun in the kauri forest

So many things can go wrong in ecoshysiology fieldwork. The main concern is the weather, then there are equipment failures, battery issues, helpers becoming unwell, forgetting gear, the list goes on but we had a close to perfect field trip last week. Here are some photos of our adventures in the field. We were measuring leaf gas exchange (photosynthesis and stomatal conductance) and leaf water potentials of several species in the kauri forest at Huapai Scientific Reserve. We also installed some sap flow sensors at the base of the canopy in our two largest sample trees to complement the sensors at breast height.

Thanks to Dan, Sarah, Jo and Julia for their efforts throughout several long days and a big thank you to Freddie Hjelm from The Living Tree Company and his team, Scotty and Chrissy for their assistance in getting everything happening up above. Some of these photos were taken by Freddie too. Stay posted for some of the results and more photos soon.

There are climbers in each of these trees. Can you spot them?

There are climbers in each of these trees. Can you spot them?

My dirty secret about my latest paper

I have a dirty secret. Actually, it’s not a secret because it’s on twitter which is a public forum so everyone can see it. But I do feel kind of grubby about it and I’ve just worked out why. Last Thursday, I sent this tweet –

Ten lovely people obliged (thank you for playing along @benbondlamberty, @TimCurran8, @PhilJ_Rose,  @HelenWNathan, @PPUAMX, @jcusens, @jmrbrock, @SarahTheWise, @turtleandweasel, @ju*ka, you guys rock) and now my paper is ranked 3rd of 172 for the journal Plant Ecology. I think it’s an important paper because it shows litterfall increases significantly in kauri forest under severe drought. However, I am well aware that I’m completely biased and we haven’t really made any major scientific advances with this work. So now I don’t feel right about manipulating altmetrics scores. As part of this process, one of the retweeters contacted me (probably tongue-in-cheek) and suggested I should tweet about his paper. So I had a look at it and wrote this –

It’s been retweeted 13 times. So for one retweet, my friend has my tweet plus 13 retweets contributing towards his altmetric score. I’d like to think it was my witty take on his paper that scored the retweets. Reality is, it was the universal appeal of their findings. This paper was already in the to 5% of all papers with altmetrics scores so had already proven it’s worth.

I guess that’s why I feel kind of wrong about what I did. Something with wide appeal or super cool results will get attention without the author being so overt. I’m not convinced I have the 3rd best paper in this journal but I do know I have a few fun friends on twitter. I don’t think I’ll be so bold about asking for retweets again. I’d be interested to hear your thoughts on this?

For more on altmetrics and what they tell us, check out this post on the Wiley Exchanges Blog.

And find further reflections on social media stats here.

Let the litter fall! Leaf loss to safe water. Kauri and drought part 2.

During the 2013 drought, the most noticable impact on the kauri forest was the increase in litterfall. It’s well established that many tree species lose their leaves in response to drought, leading to decreased plant water loss. Deciduous trees may lose their leaves early while semi deciduous trees may lose more leaves in a dry year. By reducing leaf area, trees reduce the aarea of water-losing surfaces, thereby reducing overall water loss.

In a recently accepted paper in Plant Ecology, we report that litterfall increased 72% in 2013 compared to 2012 because of dry soil conditions (see figure). Most of the extra litter was kauri leaf and twig material.

Kauri are known to self-prune branches but the reason for branch abscission has been unclear.  It may be that this costly process occurs to protect the highly vulnerable hydraulic system of these forest giants. During dry periods, trees through off twigs to prevent failure of the water conducting system of the plant.

We are doing ongoing monitoring to determine the lag impact of this massive biomass loss to the forest floor.

Kauri and drought – part 1. Is drought an issue for these forest giants?

Kauri is one of the most iconic tree species on the planet and is particularly symbolic for New Zealand. Trees are big (with trunk diameters up to 5 m) and long-lived (possibly up to 2000 years or more). Amongst conifers, kauri is the third largest species. It’s culturally significant for Maori and Europeans for it’s place in the forest and the resources it can provide. A single tree could yield enough wood for four houses. While we don’t log native forest any more, kauri face other threats from the mould-like PTA causing kauri dieback and also drought.

My research is looking at drought vulnerability of kauri and in this series of posts, I will explain what we have discovered when the drought of early 2013 presented itself as a natural experiment. In this post, how did I get into this work and why kauri? I’m fascinated by how trees work. How does transpiration work? How do trees work out how to use carbon? And kauri are especially interesting. How do they get so big and how do they live so long?

We know kauri are responsive to climate because their tree rings record climatic conditions, leading to one of the longest proxy records of past climate in the southern hemisphere. The growth response is correlated with the El Nino Southern Oscillation (ENSO) cycle. Larger rings occur during drier spring-times and smaller rings occur during wetter periods. This counter intuitive pattern got me thinking about what the underlying physiological mechanism might be. The first step was to explore the literature and I was surprised to find that there were only snippets about this species and we know comparatively little about kauri responses to changes in climate from season to season and from year to year. As long-lived organisms, kauri must have some potential to deal with variation in environmental conditions. Yet, there are three pieces of evidence that kauri may be vulnerable to drought.

The first piece of evidence is that kauri are highly vulnerable to xylem embolism. Xylem embolism is the formation of air bubbles in the water conducting system of a plant. This can happen when water is scarce or during the freeze-thaw cycle. If too many air bubbles form, the water system can fail completely and the plant dies due to lack of water, or hydraulic failure. Embolism occurs in kauri with only minimal reductions in water availability.

Second, the literature suggests that kauri have shallow roots. Trees with deeper roots have access to deeper water stores which can sustain them during drier periods. During dry periods, shallow soil layers are the first to dry out so plants with shallow roots will run out of soil water first. Reports of fallen trees indicate that deep peg roots are for anchoring only as they do not have any fine roots attached (but more on this on a later post). Furthermore, remaining kauri are often found on ridge-tops which can be the first areas to dry out during drought as water flows downhill.

Finally, there have been reports of groups of dead kauri trees in early timber appraisal reports that have been linked to the extensive 1917 drought. New Zealand’s climate is generally considered to be moist and mild. However, climate projections indicate droughts will become more severe and more frequent. My research is exploring whether kauri can survive dry conditions year after year.

Stay tuned for results in coming weeks.

Ecohydrology in New Zealand. Water supply issues and the threat of drought for forests

Under a changing climate, parts of New Zealand will become warmer and drier. As yet, we know very little about the impact this will have on vegetation. In a recent post on the Waiology blog, I explain the importance of understanding responses of evapotranspiration (ET) to climatic conditions because ET is a major component of water budgets. It is particularly vital to quantify how much water is returning to the atmosphere as through this pathway in water supply catchments. In future climates, overseas studies indicate that water yield will decline, reducing water available for human consumption.

A further reason to explore the impact of future climates on forests is the potential for increased tree mortality. Several instances of drought-induced tree mortality in New Zealand were included in a global review in 2010. Such events are likely to become more common in all biomes because trees across the world operate close to their safety margins and even slight changes in climate can be catastrophic for trees. The combination of increased temperatures and lower rainfall leads to particularly challenging conditions for tress because both the soil and the atmosphere are drier, putting the plant’s water system under stress. This lethal formula has been implicated in California recently and was discussed as a global issue at the Tree Mortality Workshop in Jena, Germany last week. In addition to changing climate, attacks from insects, fungi and other pathogens will further weaken trees and impact on forest ecosystem services. With so many unique plants and ecosystems in New Zealand, there is an urgent need to improve our understanding of drought in the local context.

The two body problem – the biggest issue for advancement of women in science and academia?

I discovered something today. The ‘two-body problem’ has its own page on Wikipedia. I’ve been thinking for a long time now that the two-body problem is the biggest issue I face in the advancement of my career and if it’s on Wikipedia, it must be big, right? Maybe it’s not just me.

Women in science and academia face a number of additional challenges in their day-to-day activities. First, science is sexist since both men and women are biased against female colleagues and students. This discrimination leads to inequalities in pay and less funding for women of equal competency. There is also evidence that papers with a female lead author are more likely to be rejected than those with a male first author. Women with children suffer the motherhood penalty while men benefit from the fatherhood bonus. Processes of appointment and advancement overwhelmingly favour men. All of these factors (and more) make science and academia a tough career choice for women. It’s no wonder the pipeline is leaky. These barriers pose a huge challenges but they can be overcome with enormous effort and a supportive network.

So why is the two-body problem the stand-out issue for women? Working couples managing career progression for both parties face a dilemma as each partner becomes more successful. In order to chase highly specialised positions, there will come a time when one of the pair is offered a position in another city, state or country. Traditionally the couple would move for the male’s job while a working partner follows, settling for whatever position they can find. In a progressive world, we would hope to see some balance in movement with some couples choosing to move for the female’s career. However, in all of my friends and acquaintances in science, I don’t know of any families who have moved for the woman’s career progression. I think it’s because of the motherhood penalty. For the best financial outcome for a family, it makes sense to favour the career of the more successful partner and as soon as children come into the picture, the woman has already taken a career hit that slows (and sometimes ends) her career. I’ve been offered several positions in different cities that I have turned down because of the negative impact a move would have on my husband’s career. I  wonder how many other women in science and academia have faced the same choice? Without being able to take the best opportunities, it is difficult for me to maintain career momentum.  Don’t get me wrong, I’m proud of my husband’s success but we’ve both worked hard for my career success too.

What’s the solution?

In an isolated part of the world such as New Zealand, academics moving from elsewhere are more likely to be men than women (personal observation but it would be great to know about any data on this) so the gender imbalance becomes more pronounced. It therefore becomes particularly important for selection committees to seek out good women who are available. There are two strategies that could and should be used in appointment processes; gender quotas and broadly defined areas of research in calls for applicants. Affirmative action attracts more highly qualified women while non-specific calls for applicants will have a larger talent pool, allowing more women the opportunity to apply and both strategies will enhance the quality of women applying for a given role. This approach is a win for women, a win for institutions with enhanced productivity and a win for students with more female role models.