The Gigante Litter Manipulation Experiment

The Gigante Litter Manipulation exPeriment (GLiMP) was established in 2000 to investigate the contribution to productivity made by nutrients in litterfall. Soil nitrate and nitrogen (N) concentrations in roots and leaves decreased quickly and significantly with litter removal (LR) and increased quickly and significantly with litter addition (LA). In contrast, phosphorus (P) concentrations in soil and plant tissues did not differ significantly between treatments and controls, but they were mostly higher in LA than LR treatments. Productivity responses developed more slowly. The LR treatment reduced trunk growth by 26%, litterfall production by 20%, and fine root mass by 20% and production by 7%, with effects becoming evident after 10 years of litter manipulation. The LA treatment increased litterfall by 11% in years 6–17 but did not significantly affect trunk growth or roots. The LR treatment reduced above- and belowground productivity, and the LA treatment increased one component of aboveground productivity. We hypothesize that N limitation is responsible for reduced productivity after litter removal.