Fertilization responses of soil litter fauna and litter quantity, quality, and turnover in low and high elevation forests of Puerto Rico

Abstract

This study evaluates the effects of chemical fertilization on litter production, litter arthropods, and earthworms in tropical wet and cloud forests in the Luquillo Mountains in northeastern Puerto Rico. Litter production, chemistry and turnover, forest floor mass, litter arthropod density (individuals g −1 dry litter), abundance (individuals m −2) and diversity, and earthworm abundance and fresh mass (g m −2) were measured in 20 m × 20 m control and fertilized plots. We hypothesized that fertilization would increase litter arthropod density, abundance and diversity in both forests through elevating litter production and improving litter quality, and the increased litter quality in fertilized plots was also expected to result in faster litter turnover rates. Fertilization significantly increased monthly litterfall production and litter quality as measured by leaf litter C/N and C/P ratios in both forests, and higher litter production led to significant litter accumulation on the forest floor. Litter arthropod abundance increased in the wet forest fertilized plots due to the accumulated litter. Higher litter quality did not affect litter arthropod density in either forest, and densities were slightly higher in the cloud forest. High litter quality increased litter turnover rate in the cloud forest only. A significant reduction in earthworm populations in fertilized plots may have offset the positive effect of litter quality on litter turnover in the wet forest. Shannon biodiversity index for litter arthropod taxa was similar between treatments in the wet forest, and was higher in the wet forest than cloud forest. We conclude that climate influences litter arthropod diversity, but differences in litter quantity and quality do not affect their densities in island tropical wet and cloud forests.