Determinants of carbon sequestration in thinned forests

Area of Science:

• Forest Ecology
• Climate Change Mitigation
• Forest Management

Background:

• Global climate change necessitates enhancing forest carbon storage capacity.
• Understanding drivers of forest carbon density, especially after disturbances, is crucial for effective carbon sequestration.
• Forest ecosystems face disruptions that alter their carbon balance.

Purpose of the Study:

• To investigate the impact of stem-only harvest at various thinning intensities on forest structure and carbon density (aboveground carbon density - ACD, soil organic carbon stocks - SOCD, total carbon density - TCD).
• To identify key variables influencing carbon density changes using random forest analysis.
• To determine the drivers of forest carbon density changes through structural equation modeling (SEM).

Main Methods:

• Stem-only harvest at different thinning intensities (light: 0-19.9%, moderate: 20-35%, heavy: 35.1-59.9% trees removed).
• Measurement of aboveground carbon density (ACD), soil organic carbon stocks (SOCD), and total carbon density (TCD).
• Application of random forest analysis and structural equation modeling (SEM) to analyze influencing variables and drivers.

Main Results:

• Moderate thinning (20-35% trees removed) effectively increased total carbon density (TCD).
• Heavy thinning (35.1-59.9% trees removed) accelerated individual tree growth but did not compensate for carbon loss from harvesting.
• Light thinning (0-19.9% trees removed) reduced species richness and increased tree mortality, negatively impacting carbon density.
• Large live trees directly influenced ACD, while thinning indirectly affected ACD by altering canopy and deformed tree density.
• Increased dead tree density negatively impacted SOCD over time, whereas greater thinning intensity enhanced SOCD.
• TCD was directly influenced by tree height, large live trees, and stand density; thinning also indirectly controlled TCD by altering the conifer ratio.

Conclusions:

• Moderate thinning is a beneficial forest management practice for enhancing total carbon density in temperate forests.
• Thinning strategies must be carefully considered to balance carbon sequestration goals with impacts on forest structure and biodiversity.
• Understanding the direct and indirect effects of thinning on various carbon pools is essential for optimizing forest carbon storage.