Volcanic fertilisation of tropical forest biomes

Tropical rainforest biomes are some of the most diverse and productive ecosystems on the planet, but are also projected to be vulnerable to changing climatic and environmental conditions. These susceptibilities are exacerbated as tropical forest biomes often inhabit very nutrient limited soils. In most tropical soils phosphorus (P) is considered the key limiting nutrient and periods of high soil P concentration are linked to enhanced forest development. Recent research has hinted at the role that volcanism may play in fertilizing large areas of tropical forest with P-rich ash during volcanic events. However, these ashfalls have a complex temporal impact on soil P concentration and vegetation response. This relationship needs further investigation using a number of biological and geochemical tracers. One with great potential is phosphate oxygen isotopes, which can distinguish between soil P sources through the palaeorecord.

This studentship will focus on the Dipterocarp forest of the Philippines, Southeast Asia, utilising modern soil and plant sampling, coupled with the development of paleoenvironmental records from Bulusan Lake spanning the last 1,500 years. A range of standard geochemical techniques including iTrax trace element mapping, tephra identification and radiocarbon chronology will be applied alongside more novel, phosphate oxygen stable isotopes and ancient DNA analysis. This combined proxy approach aims to 1. robustly characterise the timing and intensity of volcanic ash deposition events, 2. identify the role these events have played in changing availability of P to plants, and 3. identify the resultant impact on forest vegetation, including its composition, structure and mass flowering dynamics. Only by gaining a thorough understanding of these natural cycles of P addition can we begin to reveal the true vulnerability of these critical biomes in areas of intense volcanic activity and predict how they may develop and survive under ever changing climatic and anthropogenic pressures.