Agroforestry carbon stocks and greenhouse gas emission rates in central Alberta, Canada

Agroforestry systems (AFS) contribute to carbon (C) sequestration and
reduction in greenhouse gas emissions from agricultural lands. However,
previously understudied differences among AFS may underestimate their
climate change mitigation potential. In this 3-year field study, we
assessed various C stocks and greenhouse gas emissions across two common
AFS (hedgerows and shelterbelts) and their component land uses: perennial
vegetated areas with and without trees (woodland and grassland,
respectively), newly planted saplings in grassland, and adjacent annual
cropland in central Alberta, Canada. Between 2018 and 2020
(~April–October), nitrous oxide emissions were 89% lower under perennial
vegetation relative to the cropland (0.02 and 0.18 g N m−2 year−1,
respectively). In 2020, heterotrophic respiration in the woodland was 53%
lower in shelterbelts relative to hedgerows (279 and 600 g C m−2 year−1,
respectively). Within the woodland, deadwood C stock was particularly
important in hedgerows (35 Mg C ha−1 or 7% of ecosystem C) relative to
shelterbelts (2 Mg C ha−1 or < 1% of ecosystem C), and likely
affected C cycling differences between the woodland types by enhancing
soil labile C and microbial biomass in hedgerows. Deadwood C stock was
positively correlated with annual heterotrophic respiration and total (to
~100 cm depth) soil organic C, water-soluble organic C, and microbial
biomass C. Total ecosystem C was 1.90–2.55 times greater within the
woodland than all other land uses, with 176, 234, 237, and 449 Mg C ha−1
found in the cropland, grassland, planted saplings treatment, and
woodland, respectively. Shelterbelt and hedgerow woodlands contained 2.09
and 3.03 times more C, respectively, than adjacent cropland. Our findings
emphasize the importance of AFS for fostering C sequestration and reducing
greenhouse gas emissions and, in particular, retaining hedgerows (legacy
woodland) and their associated deadwood across temperate agroecosystems to
help mitigate climate change.