Cycling Rates in the Tropics

Because energy moves through tropical ecosystems more rapidly than in ecosystems of higher latitude, it might be expected that nutrients also cycle faster in tropical ecosystems, since nutrients follow energy in such functions as leaf production and decomposition. Rates of nutrient cycling can be compared among tropical and temperate forests by taking a systems approach. We can assume that the forest consists of a series of compartments (wood, leaves, litter, soil) each with a stock of a particular nutrient, and then examine the movement of that nutrient in and out of each compartment. The sum of turnover times for all the major compartments in a forest equals the total cycle time for that nutrient. A comparison of turnover times of calcium in various ecosystems indicates that the total cycle time for calcium in tropical forests is shorter than for forests at higher latitudes (Table 2.3). In tropical rain forests, constant warm temperatures and plentiful rainfall throughout the year mean that the processes that govern nutrient cycling never cease. It is the distribution of temperatures throughout the year that differentiates energy flow in the tropics from these processes at higher latitudes (Walter 1971).

Nutrient cycling is higher in forests on fertile soils in the wet tropics than on forests on infertile soils. Studies of nutrient transfer by leaf litter fall in tropical forest ecosystems (Table 2.4) show a large difference in the rate of nutrient transfer through this flux in forests on soils of varying fertility. For

Table 2.3. Compartmental turnover and cycling times for calcium. (Reprinted from Jordan 1995)

Location of Type of ecosystem Soil Wood Canopy Litter Total cycle ecosystem time

(years)

Location of Type of ecosystem Soil Wood Canopy Litter Total cycle ecosystem time

(years)

Puerto Rico

Rain forest

0 0

Post a comment