Darling Range Branch, April 2012 Meeting Report
Dr Natasha Pauli from UWA presented the talk for the meeting on a subject that explored some of the relationships between soil fauna and vegetation. In her illustrated talk she developed on the poser: ‘are plants really the architects for below ground diversity?’
Aspects of the complex interactions among insects, soil and vegetation were presented with using PowerPoint, presentation and we followed some of Natasha’s field work that was the basis of her PhD thesis research carried out over a number of seasons in Honduras.
To begin, the makeup of the soil was explained as a diverse world containing life that covered sizes from macro- to micro-organisms; the visible macro-organisms being easiest to observe, some of which are isopods, millipedes, centipedes, spiders and earthworms. Mesofauna included springtails, and ants and bacteria are the most important microfauna. Together all these life forms affect the porosity and nutrient content of the soil, with bacteria being especially important. Their numbers are high and many hundreds of life forms are involved; per square metre (to depths of 30 cm), microarthropods for example may number 300 000 individuals and earthworms, which comprise the majority of soil/animal biomass, may number 400 to 500 individuals. Soil fauna are poorly known, difficult to observe and have attracted relatively little research due to lack of funding. Aspects of the work demonstrated that certain principles that apply above ground do not necessarily follow on below ground.
The Candelaria research area in the west of Honduras is hilly, very dissected and remote. It is accessed by unpaved roads in constant need of repair. Geologically the area is a zone of instability where three crustal plates converge. Aerial views of the small farms showed a mix of small cropping fields with some trees preserved within the fields. These views were made by a camera suspended from a helium balloon, a practise that is apparently not always easy, unsecured balloons being the main problem. The main crops are maize, sorghum and beans, alternated with periods of fallow. The area is distinguished by having changed from a ‘slash and burn’ system to a ‘slash and mulch’ one. Farming is diverse and the hill slopes are steep. Seasonal rains, being heavy, prevent work continuing throughout the year. Natasha was hosted within the local community, speaking Spanish (of necessity) and found the local people co-operative. There is a technical college in the area.
Much of the field work concentrated on a study of the relationships between the tree cover and soil macrofauna with populations and activities of worms and ants being especially important. Worm numbers were assessed by the number of casts, and it was shown from statistical work that more trees relate to more casts. There is a clear benefit between trees being preserved within fields: clearing trees leads to poorer microfauna and poorer soil. Plant life, especially trees, provides organic matter as leaves, imparts shade and retains moisture within the soil. Photographs showing the ants carrying off cut leaves provided us with the evidence of ‘workers in action’ in the important world of small creatures and soil improvement.
Susan Stocklmayer