Tribute to the fallen: urban trees

Posted by Ellery McNaughton @EJ_McNaughton

Every month for the past 15 months I have stood on the streets at my study sites and conducted 10-minute bird counts. Somewhere along the line, I inadvertently began counting trees. Every site has at least one tree that birds seem to favour perching in over others, a sort of bird-version of the cushy chairs that granddads can always be found in. I often find myself focussing on these trees during my bird counts (while also not forgetting the other, less favoured bird-versions of church pews and university-seminar chairs). It makes it particularly noticeable when I turn up for the next month’s count, and that tree is gone.

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Of my 27 sites, 14 of them have had at least one tree cut down in the past year. Some were natives. Some were over 10 metres tall. Sometimes they were replaced with other trees. Sometimes they were replaced with houses. Mostly they weren’t replaced with anything.

Urban trees are at risk. In places like central Auckland, where the majority of urban tree cover is on private land, it is important to have policies in place that can be used to protect and maintain the urban forest. Unfortunately, governmental policy reforms meant that in 2015 blanket urban tree protection was removed in Auckland, leaving an inadequate individual-based tree protection policy behind. With the exception of registered ‘notable’ trees and those in certain ecological areas, homeowners have free rein with regards to chopping down trees on their property.

Yes, a man’s home is his castle. The problem is, we live in a community of castles. Trees provide communal benefits. They increase health, mental wellbeing and air quality. They create additional opportunities for connection with nature by providing habitat to urban wildlife. People need to start looking past the boundaries of their property and their present time. When decades of growth can be cut down in minutes, the least one can do is consider the bigger picture. If nothing else, at least consider that it is jolly difficult to conduct a bird count over the noise of a chainsaw.

Ellery (2)Ellery McNaughton is a PhD student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. Her project investigates 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 Darryl Jones (Griffith University, Australia).

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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.

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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.

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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.

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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.

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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.

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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.  

Thanks, volunteers!

Posted by Carolina Lara @carislaris

A quick summary of some of the amazing things achieved in the second year of my PhD: leaf samples of 350 trees collected, processed and stored at -80˚C, 500 hours of birds´ visitations to New Zealand native plants video recordings analysed and 162 hours in the field mistnetting – 232 birds so far. If you think I have done it myself, you´re wrong. Throughout this PhD-year I have worked with great volunteers who have helped me achieved all these things. A special mention to Manon Pulliat, our French intern from Agrocampus Ouest, who spent five months at the Centre of Biodiversity and Biosecurity getting to know how scientific research is conducted in other parts of the world.

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Manon after a hard day in the field collecting leaf samples

All of those whose PhD projects involve some sort of fieldwork will agree with me on this: WE NEED VOLUNTEERS. A volunteer is defined as a person who is willing to provide a service without expecting any sort of monetary compensation (quite important if your project is money-limited). They can be classified in three types: 1) casual volunteers whose activity targets specific needs, 2) volunteers who perform more formal types of volunteer service – having a personal commitment and gaining a sense of accomplishment, and 3) volunteers who are required to volunteer by a specific organization. More specifically in the ecology field, there is a relatively new term to refer to those volunteers who participate as field assistants gathering information in scientific studies: “citizen scientists”. Citizen scientists are not necessarily directly involved in the scientific community, some of them are members of the public with a strong desire to understand ecological processes and most importantly, to connect with nature.carola

No volunteer can resist holding a bird while mist netting

Our job as scientists is to provide volunteers with the necessary tools to collect reliable data in the field. This takes time but the end-product will be definitely worth it. Thanks, volunteers for all the help and good moments in the field!

 

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Carolina Lara M. is a PhD Candidate within the Centre for Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. Her research interests focus on seed dispersal networks within fragmented landscapes. She is supervised by Margaret Stanley,Jason Tylianakis, Karine David, and Anna Santure.

An Ode To Possums and other Pests

Posted by Robert Vennell @RobertVennell

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Conservation in New Zealand often involves killing things. Especially cute and fluffy things, like bunnies, mice, hedgehogs, ferrets and possums. We’ve got a good reason for it – these creatures are decimating our native ecosystems and wildlife and would cause untold destruction if left unchecked. But our obsession with killing things sometimes boggles overseas observers who struggle to understand why we would dress up dead possums in wedding gowns and bikinis.  Come to think of it, I struggle to understand that one as well.

Growing up in New Zealand I think it can be really easy to hate our introduced mammals for all the damage they cause. But its nice from time to time to reflect on how neat these creatures really are. They are incredibly intelligent, curious and fascinating little beasties – It’s just a shame they are in the wrong place and need to go.

One of the things I’ve really enjoyed about using camera-traps for my research – is getting to observe all sorts of cryptic creatures and behaviours that we rarely get a chance to see.

For example, if you head along to the Ecology Ngatahi Youtube Channel you can check out this great video of a playful possum getting up to all sorts of mischief. The final image is a rat falling out of the tree – perhaps it was pushed? Or how about this somewhat spooky montage of rats scuttling up a tree at rapid speed.

The nature of conservation in New Zealand means that to protect our native species from extinction, we have to remove the invasive ones – but that doesn’t mean we can’t appreciate these pests for being amazing little critters in their own right.

 

Robert VennellRobert Vennell is an MSc student in the Centre of Biodiversity and Biosecurity, University of Auckland studying the impacts of wild pigs on native forests. He is supervised by Margaret Stanley, Mark Mitchell (Hawkes Bay Regional Council),Cheryl Krull (AUT) and Al Glen (Landcare Research). He also writes about the history, meaning and significance of New Zealand’s native tree species at www.meaningoftrees.com