LONG-TERM PHOSPHORUS FERTILIZATION EFFECTS ON THE LITTER DYNAMICS OF AN AGE SEQUENCE OF PINUS-ELLIOTTII PLANTATIONS IN THE SOUTHERN CAPE OFSOUTH-AFRICA

The effects of phosphorus fertilization and its duration of impact on litter dynamics were investigated in an 8-, 20- and 25-year-old Pinus elliottii (Engelm.) plantation age sequence. Each stand contained plot s fertilized with 30-60 kg ha(-1) super phosphate at establishment and an equal number of control (unfertilized) plots. At the oldest stand there were additional variables, namely timing of fertilizer applicati on and fertilization frequency. Annual litterfall rates and the mass o f pine litter accumulated on the forest floor were significantly highe r in the fertilized plots. Fertilization also increased the age of pea k litterfall rates. The significance of litterfall and estimated decom position constants in controlling litter accumulation was tested. At t he youngest stand (8 years old) only litterfall contributed to litter accumulation, whereas in the 25-year-old stand, both litterfall and de composition were significant factors. Contrary to predictions that pho sphorus fertilization increases decomposition rates, lower decay const ants were found in the fertilized plots in spite of the higher phospho rus content of the litter. These lower decay constants were ascribed t o the lower nitrogen concentration of the fertilized litter which in t urn was due to the greater extent of nitrogen retranslocation from nee dles of the fertilized trees. The extent of phosphorus retranslocation decreased with phosphorus fertilization which also meant reduced phos phorus use efficiency in the fertilized stands. The aspects of litter dynamics shown in this study to be affected by phosphorus fertilizatio n (especially where there are adverse effects) should be considered wh en recommending a fertilization regime aimed at maintaining long-term productivity in pine plantations.