Abstract

I’m going to give a two part presentation, firstly on my PhD research on snow-vegetation interactions in JULES (Joint UK Land Environment Simulator), the UK land surface model. Secondly, I’ll introduce my PDRA on representing plant growth processes in the HYBRID vegetation model, using data from a novel chilling experiment at Harvard Forest.

The radiative balance of sparse seasonally snow-covered forests are poorly represented within land surface models. High latitudes sparse canopies appear dense and impenetrable in early spring due to low solar elevation. Shortwave radiation penetration is highly spatial and temporally variable, and long shadows are cast over the snow surface. Yet incident shortwave radiation acts to increase longwave radiation to the snow surface. Field measurements are used to parameterise a new shaded gap tile, which improves the land-surface snow interactions in the JULES model.

Current global vegetation models drive plant growth with photosynthesis, which is controlled by light, temperature, water, and CO2 . In this way they are able to reproduce the historical land carbon sink as a consequence of CO2 fertilization. However, experimental work suggests that the vegetation response to rising CO2 is strongly limited by the sink (growth) capacity of the tree rather than the source (photosynthesis) under natural conditions. Studies have shown high concentrations of non-structural carbon (a product of photosynthesis) observed in wood, thus indicating photosynthesis is not limiting tree growth, at least in the short-term. Observations on mature pine, maple, and oak trees at Harvard Forest will be used to incorporate the processes controlling growth and wood development within a sink-limited vegetation model, which will examine the implications for the historical and future global carbon balance.