If a tree falls in the forest, and no one hears it…

The demise of long-term population monitoring

Posted by Margaret Stanley @mc_stanley1

“Is there any evidence that an introduced insect – other than a social insect – has caused the decline of a native species in New Zealand?”

A feeling of total frustration and helplessness came over me when I heard those words – while standing before an EPA panel deciding whether to allow a generalist insect predator into New Zealand for biocontrol of a crop pest.

The answer to this is “no”. The frustration comes from the fact that we have no evidence, because there is no long-term monitoring of native insect populations in New Zealand. The Dept. of Conservation (DoC) may have data for a few threatened species (perhaps wetapunga?), but not for common insect species – those that might follow the fate of the passenger pigeon if an additional invasive predator is the thing that tips the balance for that population. The example I gave the EPA in answer to that question was anecdotal – the decline of our native mantis as a result of the invasive South African mantis. There’s certainly no long-term population monitoring that has picked up the demise of the native mantis.

The lack of long-term monitoring for non-charismatic species (e.g. bees) has also been lamented in Europe lately, where a massive decline of insects in Germany over the last few decades has been detected by the Krefeld Entomological Society: a group of mostly amateur entomologists, recording insects since 1905. They have recorded declines of up to 80% since the early 1980s – that’s a lot of bird food (if you care only for vertebrates!).

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Plans for long-term biodiversity monitoring in Germany (Vogel 2007)

Changes in science funding over the last few decades, and the vagaries of politics, means that long-term population monitoring is no longer ‘sexy’ and not worthy of funding (‘Cinderella Science’: unloved and underpaid). These types of datasets are difficult to maintain because they exceed cycles of funding and government administration. In New Zealand we now lament the loss of amazing datasets that have provided the foundation and impetus for some amazing science around ecology, conservation and pest control: e.g. the Orongorongo Valley dataset, and the long term monitoring of wasps, pests and birds in Nelson.

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Seedfall of hinau and hard beech trees in the Orongorongo Valley 1968-1991 (Fitzgerald & Gibb 2001)

DoC and some councils do undertake regular biodiversity monitoring where they can, but on a reduced number of taxa (usually birds and vegetation), not often at a population level (except for threatened species), and the data are often held within these organisations, rather than open access sites. Some scientists also try to sneak in a long-term monitoring project where their (often unfunded) time and resources allow.

Instead, community groups in New Zealand, those groups undertaking pest control and restoring ecosystems, are taking up the slack in long-term ecological monitoring. At least for vegetation and birds, they are the ones undertaking regular and long-term monitoring via vegetation plots and bird counts. There is also the rise of citizen science – with large numbers of people recording biodiversity: counting kereru and garden birds. Although scientists are doing what they can to give community groups technical advice, and make citizen science more robust, will the data being collected be robust enough to understand how disturbance, invasion, and climate change are affecting biodiversity? Community restoration often takes place primarily where people are (close to urban centres), and restoration projects are dominated by lowland coastal forest ecosystems. Hardly representative of New Zealand’s ecosystems.

Needless to say, there was great excitement within the ecological/entomological community with the initiation of NZ’s National Science Challenges. The idea was mooted that we could have a Long Term Ecological Research network (LETR) like that funded by the National Science Foundation (NSF) in the USA. This network of sites provides the research platforms and long-term datasets necessary to document and analyse environmental change. There are numerous papers that summarise the benefits of long-term ecological datasets, such as: (1) quantifying and understanding how ecosystems respond to change; (2) understanding complex ecosystem processes that occur over long time periods; (3) providing core ecological data to develop, parameterise and validate theoretical and simulation models; (4) acting as platforms for collaborative, transdisciplinary research; and (5) providing data and understanding at scales relevant to management (Lindenmayer et al. 2012). Surely gaining an in-depth understanding of New Zealand populations and ecosystems over time would allow us to understand their resilience to the effects of long-term and large-scale drivers like climate change, and even the effects of new invasive species, such as myrtle rust?

However, it was not to be. And although citizen science and community monitoring is valuable in its own right for specific purposes, it doesn’t allow us to respond to the opening salvo.

If an insect goes extinct in the forest, will anyone know?

Postscript: The EPA decided not to allow import of the predatory insect – not so much because the ecological risk was perceived to be particularly high – but the industry benefits were seen as too low relative to the risk.

 

MargaretDr Margaret Stanley is a Senior Lecturer in Ecology, School of Biological Sciences, University of Auckland and is the programme director of the Masters in Biosecurity and Conservation. Her interests in terrestrial community ecology are diverse, but can be grouped into three main research strands: urban ecology; invasion ecology; and plant-animal interactions.

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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.