The tropical rainforest comprised more biomass than temperate as discussed here could be because of the high rainfall events in this zone. The litterfall from the trees contribute to the maintenance of the soil fertility in those areas. The sun remains for most of the times in this belt providing the favorable conditions for better photosynthesis and again contribute to the higher biomass.

High rainfall that cause fast degeneration of dead plants that ultimately increase the soil fertility.

Water (rainfall) and temperature are two great important factor in decomposition (thus greater biomass). However, the fertility is somewhat "short-lived" which leads to low fertility because plants as well as microorganisms assimilate nutrients in the soil.

This article may help:

https://www.nature.com/articles/srep45017

The two maim growth factors (moisture and temperatures) are more favorable and suitable compared with temperate areas.

frequent rain fall with sun rays suitable for photosynthesis. so energy source high to maintain entire food web

Higher optimum temperature increases the rate of photosynthesis and stomatal conductance, resulting into higher carbon dioxide fixation rate in tropical area.

More biomass will be in tropical rain forest than temperate because of the high rainfall occurring in this zone.

Basuki Wasis , here are some recent articles on this topics for you to read:

• Article Explaining biomass growth of tropical canopy trees: the impo...

• Article Lianas have a greater competitive effect than trees of simil...

• https://www.ncbi.nlm.nih.gov/pmc/?term=High+Biomass+tropical+rain-forest

Thank you Mr. Sam Pal Singh, Mr. Lalit Bc, Mrs. Marilou Sarong, Mr. Yahya Shakhatreh, Mrs. Nagalakshmi, Mr. Madhav Napal and Mrs. Deeksha Krishna . Maybe someone knows the natural threat that will damage the tropical rain forests