Fig. 3

Conceptual illustration of the relationship between net annual increment (NAI), fellings, forest growing stock, sink and source in living trees over time. Other tree mortality is not considered in this figure. Note that, in the right column, net sink is shown below the x axis because it is conventionally denoted with a negative number in GHGI, while net source is denoted as a positive number. a NAI and harvest are stable (or increase at the same rate)—if NAI is higher than harvest, stock increases linearly and the sink is stable; b NAI increases more than harvest (or NAI remains constant and harvest decreases)—the stock increases exponentially and the sink increases linearly; c difference between NAI and harvest gets smaller—the stock increases at a slowing rate and the sink decreases. Sink turns into a source when harvest exceeds NAI; this is also when the stock starts to decrease