Long-term edaphic changes in a second-growth forest following abandonment from agriculture

Background/Question/Methods

To assess the role of physical site changes in limiting the long-term restoration of deciduous forest, ten soil and four structural variables were described at ninety-two second-growth forest sites in northern Delaware, USA, which formed a 100-year chronosequence. 

Results/Conclusions

In ordinations, two independent groups of soil variables separated sites.  In the first group, soil moisture, organic content, and sulfur content increased significantly through the chronosequence.  In the second group, soil calcium and pH declined.  All variables showed the greatest contrast between sites 10 and 50 years old.  Rocky sites and those with pit & mound microtopography tend to have soil features similar to old sites regardless of their age.  On a broad geographic scale, concentrations of potassium, calcium, magnesium, pH, and soil moisture increase as one moves northwest, away from the Delaware River.  These results suggest that second-growth forest sites have reached the physical condition of long-established forest after fifty years – substantially less than the 100+ years estimated elsewhere for re-assembly of this forest community – and that microtopography and geographical gradients underlay those associated with forest age.