What was done
Closed-top chambers were constructed around 30-year old mature Scots pine (Pinus sylvestris L.) trees growing in Finland.  The chambers were fumigated with air containing 350 and 700 ppm CO2 at ambient and elevated (ambient plus 4°C) air temperatures for one year to determine the effects of these variables on water-use in this economically important coniferous species.  Water-use was assessed indirectly by measuring cumulative sap flow for 32 days, following the one-year of differential CO2 treatment.

What was learned
Elevated CO2 reduced cumulative sap flow by 14% in mature Scots pine trees growing at ambient air temperatures.  In the trees growing at the elevated air temperatures, however, cumulative sap flow measurements were unaffected by atmospheric CO2 concentration.

What it means
As the CO2 content of the air increases, cumulative sap flow and, by implication, cumulative water-use will likely decrease in mature Scots pine trees.  This phenomenon will likely enable this economically important tree species to better cope with water stress in the future, unless the ambient air temperature rises by 4°C or more, which is highly unlikely.  Thus, we can anticipate greater wood production and greater water savings in this woody species as the CO2 content of the air continues to rise.