Soil Carbon Accumulation and CO 2

Experimental plots were established on severely eroded land surfaces in Iceland in 1999 to study the rates and limits of soil carbon sequestration during restoration and succession. The carbon content in the upper 10 cm of soils increased substantially during the initial eight years in all plots for which the treatments included both fertilizer and seeding with grasses, concomitant with the increase in vegetative cover. In the following five years, however, the soil carbon accumulation rates declined to negligible for most treatments and the carbon content in soils mainly remained relatively constant. We suggest that burial of vegetated surfaces by aeolian drift and nutrient limitation inhibited productivity and carbon sequestration in most plots. Only plots seeded with lupine demonstrated continued long-term soil carbon accumulation and soil CO2 flux rates significantly higher than background levels. This demonstrates that lupine was the sole treatment that resulted in vegetation capable of sustained growth independent of nutrient availability and resistant to disruption by aeolian processes

Biomass and Soil Carbon Stocks in Wet Montane Forest, Monteverde Region, Costa Rica: Assessments and Challenges for Quantifying Accumulation Rates

We measured carbon stocks at two forest reserves in the cloud forest region of Monteverde, comparing cleared land, experimental secondary forest plots, and mature forest at each location to assess the effectiveness of reforestation in sequestering biomass and soil carbon. The biomass carbon stock measured in the mature forest at the Monteverde Institute is similar to other measurements of mature tropical montane forest biomass carbon in Costa Rica. Local historical records and the distribution of large trees suggest a mature forest age of greater than 80 years. The forest at La Calandria lacks historical documentation, and dendrochronological dating is not applicable. However, based on the differences in tree size, above-ground biomass carbon, and soil carbon between the Monteverde Institute and La Calandria sites, we estimate an age difference of at least 30 years of the mature forests. Experimental secondary forest plots at both sites have accumulated biomass at lower than expected rates, suggesting local limiting factors, such as nutrient limitation. We find that soil carbon content is primarily a function of time and that altitudinal differences between the study sites do not play a role