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.

Good news for early to mid-career female researchers in New Zealand

In light of the recent awkward results of the Royal Society’s University Research Fellowships in the UK where only 2 of the 43 successful candidates where women, it was encouraging to find in the announcement earlier this week that of the ten 2014 Rutherford Discovery Fellows, five were women.  However, analysis of gender balance in previous years shows it hasn’t always been so promising for females and numbers of women are still well behind those of men (see table).

Gender success rates in the Rutherford Discovery Fellowship Scheme 2010-2014. Data from the Royal Society of New Zealand website.

Gender success rates in the Rutherford Discovery Fellowship Scheme 2010-2014. Data from the Royal Society of New Zealand website. Click for a larger image.

The overal success rate is currently 11.5% (range: 8.7-15.2%). Gender breakdown has not been released on the Royal Society of New Zealand website for 2014. For years when gender data are available (2010-13), females are consistently making up 40% of the total applications.  Yet, in two years (2010 and 2011), just two of the ten positions were awarded to women. For the 2010-13 period, 11 of the available 40 positions (27.5%) were filled by women, well below the 40% application rate of wormen. The low numbers of women fellows caused lower success rates for women in all years except 2012. In 2010, the success rates for men and women were 11.3% and 4.5% respectively with an overall success rate of 8.7%. The 2011 numbers were similarly low for women. While the fact that 50% of fellowships were awarded to women this year, women still only hold 16 (or 32%) of the 50 fellowships awarded over the five years of the scheme, still somewhat below the application rate of women. Let’s hope the upward trend for women continues.

Some good advice for applicatants and mentors can be found here. Raw data for each year can be found here (2010, 2011, 2012, 2013, 2014).

The value of trees – our Wynyard Quarter project

What do urban trees do for us and how much are they worth? Trees provide a variety of ecological services. They store carbon, improve air quality, control stormwater and make us feel happier. Find out more in an interview with Simon Morton on This Way Up (click on the Value of Trees podcast link) from 16th August at Auckland’s Wynyard Quarter urban renewal area. Our microclimate project appears at about the 9.50 mark.

Willis Bond appointed as residential developer for Wynyard Central

Image from http://www.wynyard-quarter.co.nz/


This is the website of Cate Macinnis-Ng’s lab in the School of Environment at the University of Auckland.

New Zealand’s vegetation is unique with 80% of plant species occuring nowhere else in the world. We are looking at the impacts of climatic conditions on plant functional processes like water use and carbon cycling. We use field, experimental and modelling approaches to explore how plants respond to environmental conditions like soil moisture, rainfall, light availablilty and atmospheric evaporative demand.

You can find Cate’s university website here.