As the built environment seeks to decarbonize, many projects are establishing ambitious embodied carbon goals.

Wood has become an attractive material for its biobased/biophilic and perceived carbon attributes. However, current practice makes it difficult to know the true climate profile of wood products in most cases.

The current conventions of wood product Life Cycle Analyses (LCAs) and Environmental Product Declarations (EPDs) ignore landscape-level carbon flows and fail to shed light on the impacts and benefits associated with climate-smart forestry.

The Climate Smart Wood Group is working to develop trustworthy, replicable data solutions that differentiate the climate impacts of different forest management techniques and resulting wood products.

Until that time, accounting for forest carbon stock changes is not a replicable, consistently applicable procurement approach. The most reliable approach is to incorporate carbon stock change factors within other procurement options where the timber supply area(s) for a project can be defined (i.e., source forest disclosure ranging from Level 1 through Level 3). Projects can then take account of their options and objectives for overall climate-smartness, and incorporate some basic pro/con information about alternative approaches to their decision-making.

Carbon stock change factors offer a way of representing the carbon intensity (or “net ecosystem carbon balance”) associated with timber production over time. These factors incorporate forest inventory and monitoring data and reporting systems to depict the change in forest biomass and the volume of timber product outputs for a timber supply area over time.[1] The division of forest carbon stock change by timber output from a given area over time yields a stock change factor that can be interpreted as an “upstream” embodied carbon impact indicating a carbon benefit or burden for each unit of industrial roundwood (i.e., logs) coming from that area. This stock change factor can be used to replace the common assumption of biogenic carbon neutrality which generally treats all sustainably managed forests as exactly carbon neutral.

Carbon stock change factors can be incorporated into attributional and whole-building LCAs as an addition to the “downstream” life cycle impacts of forest product harvesting and processing that are generally incorporated into forest product LCAs and EPDs. Carbon stock change factors will generally be reported using functional units of industrial roundwood. To utilize these factors for specific forest products, the volume of roundwood required to produce a unit of a derived product (e.g., a kg of glulam) will need to be determined, with the most common source being a regional or facility-specific LCA or EPD.

Traceability & Transparency

Carbon stock change data can be found reported by landowner types at county-, multi-county, or regional scales. Thus, the application of stock change factors to projects should incorporate traceability and transparency  down to the level of the primary manufacturer supply area at minimum (Level 2) and to the level of the source FMU if possible (Level 3). More precise estimates may be employed where timber supply can be traced to specific owner types (e.g., industrial, federal, tribal, state) or to specific ownerships.

Carbon Stock Change Options

Carbon stock change factors can be developed or used in one of two primary ways, both of which require nuanced interpretation to justify claims of climate-smartness. As a novel and innovative approach, the specific methods, data sources, and the understanding of precision and uncertainty in their use are evolving and expected to improve over time. The use and scrutiny afforded by increasing adoption of this approach by more project teams will help improve them.

  • Option A: Linked to a specific climate smart forests: Carbon stock change factors can be calculated for specific timberland ownerships from which timber supply can be directly traced to a project, provided a sufficiently long and consistent history of ownership and timber output are known (at least 10 years). This suitability of this approach is expected to be limited to ownerships of sufficient size (e.g., hundreds to thousands of acres) and with relatively consistent management over time (e.g., comparable levels of timber harvest occur almost every year). The calculation of stock change factors for smaller properties and properties with irregular harvest practices may be too “noisy” to draw confident conclusions for these individual timberland owners. These cases would be better handled using regional factors based on landowner type (see Option B).
  • Option B: Regional stock change factors for distinct landowner types. In instances where the timber used to supply a project’s forest products cannot be traced to specific properties or where the calculation of carbon stock change factors under Option A would be too uncertain, regional averages may be used. Regional averages will generally be defined at county or multi-county scale for different types of forest owners, including private industry, private non-industry (e.g., family forests, conservation organizations), tribes, states, and federal owners. If the mills or manufacturing facilities supplying a project are able to provide estimates of the landscape from which they source wood and the proportion of wood sourced from different types of owners, a custom stock-change factor for products from that mill can be calculated as weighted average (sum of stock change factors for each landowner type in the supply area after being weighted/multiplied by the proportion of a facility’s wood sourced from that landowner type). If a project is unable to confirm the mix of sourcing used by a wood processing facility supplying the project, an overall regional average for that woodshed can be used.

Carbon & Climate Smartness

Forests whose carbon stocks are growing over time represent a sink for atmospheric carbon. This situation can only occur if forest growth exceeds timber harvest and natural mortality and disturbance. Following LCA conventions, carbon burdens are reported with a positive sign, and carbon benefits using a negative sign. Negative carbon stock change factors indicate a net gain of forest carbon stocks in the timber supply area and may be considered an upstream embodied carbon benefit, while positive carbon stock change factors indicate a net loss of forest carbon stocks in the timber supply area that may be considered an upstream embodied carbon burden.

Comparisons of carbon stock change factors between timber suppliers within and across regions can help steer procurement towards suppliers that are adding more carbon to the landscape than other suppliers while continuing to produce timber.

However, carbon stock change factors should not be used as the exclusive indicator of climate-smartness.

There are no absolute thresholds for deeming a timber source as climate smart based solely on carbon stock change factors. To be used to characterize climate-smartness, carbon stock change factors should be interpreted with relevant regional context considering forest ecology and management practices.

In many regions and forest types, climate-smart forestry may involve the reduction of carbon stocks over time to restore forest resilience and ecological functioning.

These same regions and forest types are also often where market access and increased demand for forest products are critical enabling conditions for improved forest management. The restoration of drier fire-prone forests across the US West are a clear example where carbon stock change should be accompanied with a more holistic consideration of forest and community impacts beyond carbon stock changes.

The carbon intensity of timber production is best viewed as an emergent property of a forest management system that accumulates through numerous interventions across a managed landscape over time. This approach is designed to characterize carbon impacts of a forest management or timber production system rather than to characterize impacts of a specific timber harvest. Calculations of carbon stock change factors should generally encompass all working forest areas controlled by a timberland owner or type of landowner in a particular timber supply area. This analysis should not be applied in isolation to individual harvest areas or cut blocks.

Thus, a timber supply area used for this type of analysis should include areas that are regrowing from previous harvests, areas that are expected to be harvested in the future, and areas where management may be limited or constrained as part of best management practices (e.g., riparian management zones, steep and erodible slopes, or areas of high conservation value within an actively managed landscape).

This type of analysis should not include areas that are permanently reserved from timber harvesting (e.g., wilderness areas or parks).

Pros / Cons of Utilizing Carbon Stock Change Factors

CSWG encourages the use of carbon stock change information to inform decision-making for projects with embodied carbon or climate-smart sourcing objectives. However, there are trade-offs to consider. Consulting with CSWG’s network  of scientists, climate-smart forestry practitioners and supply chain partners can provide projects and portfolio initiatives with more detailed assessment of options and their veracity.


  • Based on Objective Measures: This approach is based on observational data of how a timber supply area has actually changed over time rather than relying on industry-wide averages or simulations of hypothetical landowner behavior.
  • Identifying Source Forest Not Required: Does not require tracing to a specific source forest, but increased levels of disclosure would lead to less uncertainty in carbon stock change factors. Additional discounts or penalties applied to sourcing decisions could also be corresponding to increasing levels of uncertainty.
  • Increasing Availability: Data is becoming readily available for most forests across the continental United States, and national-scale reporting by smaller countries that may be suitable for estimating carbon stock change factors is often available for countries that report forest carbon stock changes under the UN Framework Convention on Climate Change and that report timber product output and forest conditions to the UN Food & Agriculture Organization.


  • Still in Development: Peer review and methodology refinement are needed to establish confidence that carbon stock changes are being attributed appropriately to timber production over time. For example, more research is needed to better separate the impacts of natural disturbance on carbon stock changes compared to impacts of management.
  • Boundary Size-Dependent: The calculation of stock change factors is very sensitive to the definition of the timber supply area in terms of geographic extent and lookback period. In terms of geography, the inclusion of areas that do not contribute to the timber supply (e.g., parks or protected areas reserved from timber harvesting) obscures and confounds the carbon stock change that can reasonably be attributed to timber production. The calculation of a stock change factor may also vary significantly based on the lookback window chosen and the consistency of timber harvesting. It may ultimately be infeasible to generate usable carbon stock change factors for smaller properties with more irregular harvesting activity over time, and further research is needed to define appropriate levels of confidence to justify reporting and using these factors when they vary substantially over time.
  • Narrow Focus: Although growth in carbon stocks can often be a useful indicator of “climate smartness”, growth in carbon stocks does not necessarily indicate improvements in ecological health and resilience, and information on climate, community, and biodiversity impacts beyond carbon stock change may be necessary to confidently characterize the climate-smartness of a particular timber supplier or timber supply area.
  • Lack of Data Availability: The development of these factors is limited by the availability of data on forest carbon stocking and timber output over time. Publicly available data for carbon stocking and timber outputs across the contiguous United States currently lag the present by several years, and new systems to provide at least annual updating are under development. Data needed for this approach is hard to find and may not ever be statistically rigorous enough to drill down to the individual FMU or landowner scale.