The Forest Identity Redux: Systematic Changes to National Forest Carbon Stocks Globally, 1990-2020

Some 20 years ago, The Forest Identity framework was introduced to describe systematic changes to national forest stock (i.e., carbon) as a function of rates of change to forest area, density, and biomass over 1990-2005.  Observations noted that most wealthier countries were increasing forest density, as well as forest area to a lesser degree, while most poorer countries were losing forest area without change to forest density.  In the context of global forest change, this framework rightfully raised the profile of forest management, complementing the Forest Transition model focused instead on agriculture, human settlement, and forest expansion into non-forest lands.  Since the 1990s and early 2000s, forest management and stocks have likely shifted in many poorer, typically tropical regions, altering trends to forest density relative to forest area: tree plantations have matured but also expanded, including as a proportion of total forest gains; net natural afforestation has occurred in certain regions, typically alongside forest conversion; atmospheric carbon fertilization has possibly enhanced forest density generally; and primary forest loss has often trended upward, including due to forestry in some countries (e.g., India).  At the same time, forest-change scholars have recognized, if begrudgingly, that conjoint trends to forest density, biomass, and area define more a varied, and more meaningful, array of nominal ‘forest transitions’ compared to the classical forest-transition model.  In this context, we revisit the Forest Identity framework and update its summarization of global forest change.  We reveal systematic shifts to the rates of change to forest density, biomass, and area between 1990-2005 and 2005-2020 for all countries globally.  Distinct couplings of density-area trends are identified, defining groups of countries with common trajectories of forest-stock change.  The primary driver(s) of shifts to these trajectories are explored to summarize general underpinnings of current forest (stock) change globally.