When the carbon balance changes

Forests

Disturbances can quickly shift the carbon balance. In forest ecosystems, storms, droughts, fires, or pest outbreaks such as bark beetles can suddenly reduce vegetation cover and change organic inputs. Human activities can have similar effects. Timber harvesting, for example, removes biomass and may disturb the forest floor. When trees are removed, soils become more exposed to sunlight, rainfall, and temperature fluctuations — often creating warmer and wetter conditions that stimulate microbial activity and accelerate the breakdown of organic matter.

One example is windthrow, where strong storms uproot trees or break parts of the forest canopy. The canopy opens and the organic layer on the forest floor may be disturbed or eroded. In forests where organic material has accumulated slowly over time, such disturbances may temporarily increase decomposition and lead to losses of soil organic matter. SOC stocks in forests are often higher than in pasture or arable soils, so disturbances can have a relatively large impact. However, these effects are not uniform — they vary with the type and severity of the disturbance and how the site is managed and recovers afterwards.

Optional: Explore how disturbances shape SOM dynamics in forests, and how the effects can be alleviated, in Mayer et al. (2023) and Pietrzykowski et al. (2025).