Wednesday, 14 August 2013

Vegetation survey in sunny Spain

by Michelle Farrell (@DrM_Farrell)

In my last blog post a few weeks ago, I gave a brief introduction to the science of palynology, or pollen analysis. Essentially, palynologists analyse the pollen grains preserved in ‘environmental archives’ such as peat bogs or lakes where sediments have accumulated in order to build up a picture of how the surrounding vegetation has changed over time. However, the interpretation of these pollen assemblages is far from straightforward, since pollen grains from different species vary in terms of size, shape and therefore dispersability, and there are also differences in the amount of pollen per unit plant produced by different species due to variation in plant reproductive strategies. For example, wind-pollinated plants need to produce much greater amounts of pollen than insect-pollinated species in order to increase their chances of reproductive success.
A key goal since the earliest days of palynology has been the quantitative reconstruction of past vegetation abundance from pollen assemblages. Models of pollen dispersal and deposition have now been developed, and estimation of Relative Pollen Productivity (RPP) is an essential for applying these models to reconstruction of vegetation from pollen records. Empirical estimates of RPP can be extracted from measurements of modern pollen assemblages and vegetation cover, and over the last 10-15 years considerable research effort has been invested in obtaining RPP estimates for key taxa. A recent review reported a wide range of RPP values for individual pollen taxa from different studies across Europe (Broström et al. 2008)‚ but since a standard methodology was not used to record vegetation cover it is not possible to determine whether these differences are due to variation in taxonomic groups (pollen grains can often only be identified to family or genus level, so in different regions a different assemblage of species may make up the palynological equivalent taxon Betula or Poaceae)‚ variations in environmental factors between study sites (e.g. climate‚ management)‚ or reflect the variations in methodology (Bunting and Hjelle 2010).

In May 2010, we held a workshop at the University of Hull which brought together several key researchers in the field of quantitative vegetation reconstruction from pollen records. At this workshop we came up with a standardised method of vegetation survey for obtaining RPP estimates. As part of the Crackles Bequest Project Jane Bunting and I, along with a team of European project partners, have applied this method to compare estimates of RPP within individual species across a wide climatic range and in different habitats. We’ll write more about the results of this project in future blog posts.

The majority of researchers who are interested in using models of pollen dispersal and deposition to quantitatively reconstruct past vegetation cover are based in north-west Europe, and as a result this is where most research activity to date has been focussed. The approach is now beginning to be adopted worldwide, and we are now collaborating with groups working in India, South Africa and South America to obtain estimates of RPP for common taxa in their regions. A little closer to home, research groups based in southern Europe are using the standardised vegetation survey protocol developed for the Crackles Bequest Project to taxa of interest for reconstructing Mediterranean environments. 

In June 2013 I was invited to join a team from the Pyrenean Institute of Ecology in Zaragoza, Spain on their fieldwork near the town of Teruel in the east of the country. Their research project is focused on the palaeolake at Villarquemado, from which they have recovered a 74m long sequence for pollen analysis. The group are now working towards estimating RPP for six key taxa in this sequence to enable them to quantitatively reconstruct the former vegetation in this area. I joined the group for a week to demonstrate the standardised vegetation survey methodology and to learn more about their research.

The palaeolake at Villarquemado, now mostly infilled and supporting fen-type vegetation

After a false start (I arrived at Leeds-Bradford airport on the day I was due to fly to Barcelona to find that all flights were cancelled due to a French air traffic control strike!), I eventually arrived in Zaragoza two days later than originally planned. I was met at the railway station in Zaragoza by my colleague’s husband, and we then drove for approximately two hours to the village that we would be staying in. Incidentally, if anyone is planning a holiday in this region you could do worse than to stay at the house we rented for the week – it was absolutely beautiful!

The following day we made an early start to avoid the worst of the heat (although I have to say that 30oC was still a bit of a shock to my system, coming as I had straight from the miserable British summer that we had been having at that point!) and headed to one of the group's sampling locations. There are some differences between working in north-west Europe and in the Mediterranean region - for example in our fieldwork areas we normally collect a moss polster as our pollen 'trap', but since moss is pretty hard to come by in semi-arid Mediterranean environments 'Tauber traps' had to be used by the Spanish research group. These are essentially plastic containers sunk into the ground so that the top is at ground level, with a hole in the lid to allow the pollen rain to be collected. The team will return to empty the traps at the end of the flowering season to ensure that a full year of pollen rain is collected, so for now our task was to survey the surrounding vegetation.
The view from one of our sampling sites - very different to the lush green landscapes that I am used to working in in north-west Europe. Although I'm told that this is an unusually wet year and that everything is much more green than usual...

View from another sampling site, with the Tauber trap visible in the foreground
Once we had all got to grips with the intricacies of the survey method, the team worked incredibly efficiently, and we managed to survey all 12 sites in five days. We also had fantastic logistical support from the husbands of two members of the survey team, who arrived to meet us every lunch time with hampers full of goodies to fuel us through the afternoon! For me, there were huge benefits to joining my Spanish colleagues for a week – I got to know people that I had previously met only at conferences much better, I made new friends, I got to experience fieldwork in a totally different environment to that which I am used to working in, and I learned a lot about Mediterranean plants and environments. I’m really looking forward to seeing the results once Edu has processed all the pollen and vegetation data from this field season!

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