writes: "The results of a study discussed in an article in the May 24
research journal Nature indicate that elevated levels of atmospheric carbon dioxide may have more limited effect on forest growth than previously expected. While many short-term studies have shown atmospheric carbon dioxide (a "greenhouse" gas) increases tree growth, the experiments reported in Nature showed that without additional nutrients, initial growth increases of mature loblolly pine trees leveled off after the first three years of exposure. The presence of elevated levels of carbon dioxide alone, which is occurring due to global industrialization and land use changes, may not result in a long-term increase in the rate of tree growth. However, the results also suggest that forest fertilization, already a practice in Southern pine plantations, might become even more beneficial in a high carbon dioxide world."
In a nutshell (or a pinecone): it doesn't seem that increasedw forest growth will "cancel" out increased carbon dioxide in the atmosphere.