New paper(s)!

August is a good month! Not only because it’s my birth month, but also because I and my coauthors have had 4 papers accepted. It has been SUCH a boost to my confidence. The first of these is now available online. It is one of the chapters of my dissertation, where I employed some very fun tools, like heavy liquids (at one point I made sand grains float!) and radioactive isotopes, to figure out what old-field forest succession does to soil carbon and nitrogen. What I learned is that shallow soils and deeper subsoils respond very differently. When the forest was planted in the old cotton fields, soil carbon and nitrogen began to decrease, because the trees were using the nitrogen and the carbon left over from the crops was decomposing faster than the forest was adding new dead leaves and roots. After about 20 years, after the forest started to accumulate a thick layer of leaf litter on the ground, the surface mineral soil started to increase in carbon. It wasn’t until the forest basically stopped growing after about 30 years (individual trees were still growing, but so many others were dying that the forest as a whole stopped accumulating biomass) that soil nitrogen stopped going down. Deeper in the soil, soil carbon decreased for about 40 years after the forest was planted. What we think happened there is that the forest’s deep roots lowered the water table, which allowed carbon that was previously too wet to decompose to now do so. At the same time, an abundance of little tree roots that die quickly and release their carbon provided energy to soil microbes to do the work decomposing that old carbon and releasing the associated nitrogen. So, 50 years after the loblolly pine forest was planted in an old cotton field, only the leaf litter layer has accumulated carbon. The mineral soil down to 60 cm below that has not changed, because the loss of carbon in subsoil canceled the gain in surface soil. The lesson is that it takes a long time (well over 50 years) for reforestation to result in an increase in mineral soil carbon.