ecolonaught

Chronicles of a 21st century naturalist.


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brewing up good science

One of the great things about being co-supervised by people at Landcare Research is that I get to engage to top notch scientists, ask them about their research, and sometimes help them in the field!

From May 8th – 10th I was able to lend a hand to Barbara Anderson and her Master’s student Rob with their field work at Mt. Cardrona.

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The view from Mt Cardrona Summit. Fiordlands are seen snowcapped in the distance.

Rob’s research is on soil decomposition. When large organisms like trees and other plants die their organic matter become incorporated in to the soil. In areas with lots of vegetation the plant debris and litter that covers the ground is called the “O Horizon”. After awhile the plant material becomes partly decomposed and mixed with the next layer down, forming a nutrient rich environment called the “A layer”. It is here that most microbes reside and respire.

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Dead plant material gathering on the soil surface, forcing the litter layer. As particles decrease in size they are incorporated into the soil, forming the A horizon.

Understanding the metabolic action of these microbes is important because they are vital to nutrient cycles. They decompose previously living tissue and extract bound carbon, nitrogen, and other nutrients to be released into the environment once again so that other organisms may reuse these resources to grow.

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The snowy summit of Cardrona. Field work isn’t all fun and games!

Global soils store 3-4 times the amount of carbon than what is stored in global plant biomass. Therefore, understanding what, and how, factors influence soil nutrient cycling is paramount, especially in light of climate change. Two factors that are likely to have a major influence over soil microbial activity are temperature and humidity.

To elucidate the influence of these factors, Rob will be using the tea index across elevation and aspect gradients. The sites are positioned every 100m from the summit (~2000m) to the paddock (500m) spanning a ridge that has a sunny side and a shaded side. This range of elevation and ridge aspect encompasses a range of environmental conditions constrain microbial activity.

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Rob exhuming the first tea bag from the summit.

But how can we measure the metabolism of microscopic organisms on the top of a mountain? Cue the tea bag index. Microbes digest dead plant material. The rate at which they digest can be estimated by measuring the rate of weight loss in the dead plant material they eat. If we were able to develop a  unit of recoverable plant mass that could sit in ground for long times and have standardized weights, we could use these units to estimate soil decomposition rates across locations. This is what the tea bag index does.

Two flavors of tea are used – green and rooibos. Green tea is made of young leaves and roobios has mature leaves that are more lignified. The two break down at different rates, which allows Rob to estimate both the steep and shallow slope of the mass exponential decay function.

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Science is exciting!

By burying mass produced tea bags in the ground at different locations we can gain information about the factors that influence decomposition rates by comparing weight losses. There’s nothing better than science with a strong cup of tea! I’ll be following up this post with results when they are in.

 

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Takahe Valley

My most recent field expedition was to Takahe Valley; a place with an interesting conservation narrative, beautiful scenery, and a fantastic place to do research.

I went to Takahe Valley March 7th – March 10th with along with two Landcare colleagues and another PhD student. Our purpose was to assist with end of the summer field data collection.

The  crew grabbing lunch.

The crew grabbing lunch.

Those of you well versed in your New Zealand native birds will recognize the name takahe (Porphyrio hochstetteri). The species was thought extinct when the last 4 known individuals were captured and killed in 1898. However, Geoffrey Orbell rediscovered a remnant population of the birds in a place isolated from human activities near Lake Te Anu (Takahe Valley) in 1948. Concerted conservation efforts since rediscovery have resulted in relatively successful recovery. The Fiordland National Park was created to ensure them a safe home, and deer control is carried out within the park to reduce competition for food. The wild population estimate as of 2013 is 263.

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A takahe in captivity. Phtoto by New Zealand Department of Conservation (http://blog.doc.govt.nz/2014/12/01/takahe-finds-love-te-anau/)

I wasn’t able to see any of these beautiful birds (locally “blue chickens”), but I was able to see signs of their presence including well traveled tracks, digestive remains, freshly munched tussock grass, and tracks. Hopefully next time I will be able to sneak a peak!

I was able to see some other charismatic birds though including a Kea (Nestor notabilis), NZ rock wren (Xenicus gilviventris), rifleman (Acanthisitta chloris), and tomtit (Petroica macrocephala).

A Kea investigating our campsite, as well as me, to see if it can get an easy feed.

A Kea investigating our campsite, as well as me, to see if it can get an free feed.

The Fiordland foothills are composed of gneiss (metamorphosed from mostly granite and diorite). Apparently this is some of the oldest rock in NZ, originating from the Ordovocian period. The valleys and basins were etched through glacial erosion during the last ice age. Alpine areas have exposed rock or scree substrate, while basins soil is composed of podzolised gley and organic soils. The vegetation in our valley ranged from sub-alpine herbs up on the exposed rock and scree at the valley ridges to wetland species down in the basin. Beech forests and tussock grasses can be seen covering and deferentially partitioning large swaths of the valley.

The basin has a river flowing through it. This area is dominated by wetland vegetation.

The basin has a river flowing through it. This area is dominated by wetland vegetation.

Tussock grass vegetation dominates portions of the basin, as well as some portions of the lower and upper walls, of the valley. Forest dominates most of the midsection.

Tussock grass vegetation dominates portions of the basin, as well as some portions of the lower and upper walls, of the valley. Forest dominates most of the midsection.

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We camped partially up the valley, at the head wall. This area has some tussocks but also some sub-alpine herbs due to the higher elevation and some wetland plants from the the head water flow.

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The head wall ridge. This area has exposed rock and screes, mostly dominated by sub-alpine plants with some small tussocks.

The main purpose of our trip was research. There are transects of tussock grasses here that have been measured for over a decade, investigation the masting events of the tussocks (Chionochloa sp.). Masting is the phenomena of some plants to usually not produce many flowers/seeds most years, but every few years they will all create massive amounts of flowers/seeds. In North America most oak trees (Quercus sp.) display some level of masting.

A feather’s fate; only to drift on the low breeze; never to fly again

Another component of the research is to investigate the interacting influences of anticipated climate change, increasing soil N, and increasing soil C on tussock growth as well as reproduction. Climate change is simulated by putting translucent plastic around the bases of the tussock (creating a mini green house gas effect). Soil N is increased by adding fertilizer. Soil C is increased by sprinkling sugar on the plots. We had to count the number of tillers (stems) on every experimental plant (counts ranged from ~30 to ~800). The cages are to protect the tussocks from takahe, as this is their favorite food.

These are the experimental plots on the red tussock (C. rubra).

These are the experimental plots on the red tussock (C. rubra).

We also collected invertebrate data for each plot to see if the treatments (temperature * N * C) had an influence on invertebrate diversity or community composition.

Me emptying invertebrates from pitfall traps. These traps passively capture insects by trapping them in a cup filled with death liquid.

It was a fantastic trip filled with good company, good weather and goo food. I eagerly await my next expedition into Takahe Valley!

-Greg