Allometric relationships used in the CARAT and ACORN tools to assess evolution of tree biomass and tree carbon storage over time for 19 tree species in temperate agroforestry

Agroforestry is receiving increasing attention in temperate agricultural systems as a promising agroecological practice. It can contribute to climate change mitigation and adaptation, as well as greater diversity and resilience on the farm. Additionally, agroforestry provides opportunities to compensate for lower crop yields through the production of wood, fruit, or nuts. Several calculation tools (see also DigitAF tool catalogue) have been developed to quantitatively assess ecosystem services and/or productivity within agroforestry systems, among others the CARAT and ACORN tools, which are part of the “Agroforestry Planner Flanders”. ACORN supports the design of agroforestry systems by combining simulations of crop yields, crop quality, and wood production with an economic evaluation. The tool focuses on alley-cropping systems and simulates yields over a ten-year period following the establishment of the alley-cropping system. CARAT (CARbon Agroforestry Tool) was developed to quantify the carbon sequestration in agroforestry systems. It currently focuses on high stem trees in alley cropping or silvopastoral systems. Both tools require calculation of the (temporal evolution of) tree biomass, for which we use allometric relationships based on the diameter at breast height (DBH). This is done in two steps: (1) predicting the development of DBH as a function of time, and (2) calculating biomass based on the estimated DBH using allometric relations and species-specific wood density values. Next, also the (temporal evolution of) carbon storage in tree biomass can ultimately be determined by multiplying the total above-ground biomass by a factor of 47% (a typical value used for trees in temperate forests; IPCC 2006). In this brief overview, we share the allometric relationships which are currently (April 2026) used for 19 tree species in temperate regions. We also add the exemplary calculation for an individual Poplar and Walnut tree, for the first twenty years after planting. Note that we currently also continue to collect empirical data in real-farm agroforestry context, so as to further calibrate these relationships in the near future.