SAEON in LTER workshop to analyse grassland data

A view of the Sevilleta National Wildlife Refuge within which the research projects of the Sevilleta LTER are located. The Sevilleta Field Station, which provides laboratories, offices and accommodation for researchers is in the bottom right corner (Picture © Dr Tony Swemmer) Searching for inspiration - scientists work on ways to analyse the available long-term data, They are (clockwise from left) Prof Judy Cushing, Dr Kristin Vanderbilt, Dr Lee Zeman, Prof Alan Knapp, Doug Moore, Dr Esteban Muldavin and Prof Miki Kertesz (Picture © Dr Tony Swemmer)

- Dr Tony Swemmer, Manager, SAEON Ndlovu Node

Net primary productivity is a key process in all ecosystems that involve the capture of energy from the sun, and the conversion of this energy into live matter (or biomass).

The energy ultimately sustains all living organisms within an ecosystem, and plays an important role in regulating the earth’s climate.

Despite the importance of net primary productivity, the factors that determine just how much biomass is produced by an ecosystem in a particular year are not well understood.

In grassland ecosystems, net primary productivity of the above-ground parts of plants (or ANPP) has been particularly well studied, as ANPP is relatively easy to measure in these systems. The USA Long Term Ecological Research network (LTER) has the best ANPP data, having accumulated decades worth of ANPP data at various grassland and desert sites.

Grasslands Data Integration database

Information managers and ecologists from these LTER sites recently partnered with computer scientists to create a database to integrate ANPP data from all these sites. To promote the International Long Term Ecological Research Network (ILTER), scientists working at long-term research sites in other countries were also invited to participate.

This led to the creation of a Grasslands Data Integration (GDI) database, and in January this year, a workshop was held to add more data to the database, as well as test the utility of the database. The idea was to bring together ecologists from sites around the world to formulate research questions based on the availability of the various long-term datasets, and then to extract the data needed directly from the GDI database and analyse it.

South African contribution

Dr Tony Swemmer from the SAEON Ndlovu Node participated in the workshop, and contributed two datasets from long-term grassland sites in South Africa, namely a veld condition experiment run by Prof Hennie Snyman at the University of the Free State, and a veld fertilisation experiment previously conducted at the Towoomba Agricultural Research Station in South Africa’s Limpopo Province.

Both these datasets are impressive in their length, encompassing 31 years and 27 years respectively – a longer time series than any of the USA LTER sites have produced to date.

Other participants included scientists from USA LTER sites, including the Konza LTER (situated in tallgrass prairie), the Shortgrass Steppe LTER (shortgrass prairie), the Sevilleta LTER (desert grassland), the Jornada LTER (desert grassland and shrubland), and a grassland LTER site recently established in Hungary.

The main research question put forward was whether the different ecosystems respond similarly to extreme climate events, specifically years of drought or flood.

Having the datasets readily available facilitated some rapid analysis during the four-day workshop, but unfortunately the data were not very co-operative. Preliminary analyses were rather disappointing, as no common trend was found in terms of the importance of cumulative effects of multiple years of below- or above-average precipitation on producing exceptionally low, or high, ANPP.

It appears that the role of climate in determining ANPP is more complex than previously thought, and more focused analyses were proposed to untangle the influence of climate on ANPP at each site. Preliminary analyses of how individual plant species respond to climate were also undertaken.

The workshop was organised by Dr Kristin Vanderbilt (Sevilleta LTER, University of New Mexico).

Other participants were:

• Dr Lee Zeman (Evergreen State College, Olympia),
• Prof Judy Cushing (Evergreen State College, Olympia),
• Prof Miklós Kertész (Institute of Ecology and Botany, Hungarian Academy of Sciences),
• John Anderson (Jornada LTER, New Mexico State University),
• Dr Esteban Muldavin (Sevilleta LTER, University of New Mexico),
• Doug Moore (Sevilleta LTER, University of New Mexico),
• Prof Alan Knapp (Shortgrass Steppe and Konza LTER, Colorado State University),