Feedbacks between forests and climate in tropical and boreal ecosystems

Abstract:

Both, tropical and boreal forests are critical components in the climate system and are an active driver for climate. In many aspects, such as biogeochemistry, biodiversity, meteorology and others, tropical and boreal forests are very different. Emissions and deposition of trace gases and aerosols by forests are key in regulating their atmospheric concentrations. VOC emissions regulates the atmospheric oxidation capacity in tropical forests. The biomass burning emissions has strong impact on the aerosol radiative forcing changes over these forest ecosystems. Organic aerosols have a very strong presence in terms of aerosol composition with 70 to 85% of PM1 mass for both boreal and tropical forests. In Amazonia, sulfates, nitrates and BC shows very low concentrations, and boreal sites shows 2-3 times higher concentrations. The anthropogenic pollution influences boreal forest atmospheric composition during wintertime. The secondary organic aerosol (SOA) in the tropics are mainly isoprene driven giving a slightly more hygroscopic SOA than the boreal monoterpene driven SOA, which have a significant effect on the cloud formation and radiation balance. The changes in diffuse to direct radiation driven by aerosols has important effects in tropical forests but minor in boreal, causing enhancements in the net ecosystem exchange of 30% in tropical forests and only 10% over boreal sites. For both tropical and boreal forests, the complex relationship between GPP, BVOC, SOA, CCN, clouds, radiation, temperature and CO₂ show multiple pathways, and some of them can be quantified. For tropical forests, the high biodiversity makes it difficult to study changes in emissions due to changes in precipitation and temperature. Feedbacks loops are quite different for tropical and boreal forests and will be discussed.