Measurements and estimations of biosphere-atmosphere exchange of greenhouse gases – Forests

Fluxes of carbon dioxide, methane, nitrous oxide, and carbon stocks were measured at selected Hungarian forests and at a Croatian stand 120 km far from the Hungarian border. Annual carbon balance for Hungarian forests was also determined. Carbon stock of dendromass in selected Hungarian beech, hornbeam-pedunculate oak, and Turkey oak forests was between 191 and 292 t C ha-1 in 2003-2005. The total carbon stock (dendromass and soil) of Hungarian forests is estimated to be 377 MtC (1991-2000), and the annual carbon uptake of dendromass is 6.9 MtC. According to the measurements and estimations, the gross primary production (GPP) in 2008-2009 at Jastrebarsko pendunculate oak forest was 1,428 and 1,633 g C m-2 year-1, while ecosystem respiration of CO2 was 1,044 and 1,049 gC m-2 year-1, yielding a net ecosystem exchange (NEE) of-384 and-584 g C m-2 year-1, respectively. Net primary production (NPP) of Hungarian forests (1991-2000) was 377 g C m-2 year-1 (246 g C m-2 year-1 excluding leaves) part of which is released back to the atmosphere by heterotrophic respiration and harvest. Comparison of CO2 sinks using forest inventory approach (and not considering carbon storage in durable wood products) of Hungary's forest (2.26 t CO2 ha-1 year-1) and pedunculate oak forests in Croatia (4.57 t CO2 ha-1 year-1) gives a good agreement considering differences between forests and management practice. However, flux measurements from Jastrebarsko indicate that forests are probably much stronger sink. The share of the other greenhouse gases (CH4 and N 2O) to the greenhouse balance between atmosphere and forest ecosystem (expressed in CO2 equivalent) is negligible in lowland forests of Bodrogköz region (average uptake of CH4 of 0.03 t CO 2-eq ha-1 year-1 and emission of N2O of 0.05 t CO2-eq ha-1 year-1). However, for the forests in Mátra mountain region, emissions of N2O are not negligible with 0.61 and 0.83 t CO2-eq ha-1 year -1 for spruce plantation and sessile oak-hornbeam forest, respectively. Due to the lack of long-term observations, these results have to be regarded as first approximations. © 2011 Springer Science+Business Media B.V.