Fine-root biomass in three successional stages of an Andean cloud forest in Colombia

Stem density, basal area, the vertical distribution (0-25 cm) of roots (<2 mm and <5 mm) and its biomass were studied in a 10-year-old, a 20-year-old and a mature forest at La Planada cloud forest. There was an increase in canopy height (5-6 m to 20-22 m) and basal area (8.3 to 21.1 m(2) ha(-1)) with increasing forest age, and a decrease in stem density (17,466 to 651 stems >2.5 cm ha(-1)). In all three forests, there was an exponential reduction in root biomass with increasing depth. Root biomass (<5 mm) in the first 10 cm of the soil, measured with soil cores on flat terrain, was not significantly different among the three successional stages (3.46, 3.71, 4.00 Mg ha(-1), respectively). In contrast, the microtopography of the forest floor becomes more variable with increasing forest age. This increase in the surface roughness seems co be the result of increasing accumulation of dead logs and large branches that provide space for the expansion of root systems. Indeed, the aboveground root biomass (<5 mm) was higher in the mature forest (6.03 Mg ha(-1)) than in the 10-year-old successional forest (2.85 Mg ha(-1)). If changes in microtopography represent such an important resource for root growth, dead logs may be a key controlling factor in the succession of the aboveground biomass and structure of montane rain forests.