Another perhaps more straightforward way to look at tree debt is to consider the following: what population of trees do I need to personally plant and sustain to equal my carbon emissions? Thinking of it this way tries to equalize two rates: the rate of emissions on one hand and the rate of absorption by trees on the other. So tree debt could be thought of as an obligation to personally plant and maintain a grove of trees (not necessarily all in one location) of a certain size.
To determine my own grove size, I used a reputable carbon calculator to determine our household emissions. The result was 20.5 metric tonnes of CO2 per year. Then I divided that in half for my share, and then again by 3.67 to convert into C from CO2. That’s 2792 kg of C per year. Using the value of 10 kg C / year / tree, this results in a grove size of 280 trees. If I plan to build up this grove over 10 years, this means I should be planting 28 trees a year. I’ll also need to ensure that all the trees I plant stay alive and healthy and plant additional trees if some don’t.
Of course this isn’t to say that I can’t or shouldn’t decrease emissions — and indeed I should. But I’ll take 28 trees per year as my personal target going forward.