The effect of hurricanes on tropical moist forest soil

A new study published on the Global change biology, proposed an interesting retrospective on the issue

by Lorenzo Ciotti
The effect of hurricanes on tropical moist forest soil
© Ian Waldie / Staff Getty Images

Tropical rainforests occur in Asia, Australia, Africa, South America, Central America, southern Mexico and numerous Pacific islands. They represent the terrestrial biome with the greatest biodiversity, given that they alone host approximately half of the living terrestrial animal and plant species.

According to the authors of the WWF Global 200 list, which also proposes a classification of terrestrial biomes, the tropical rainforest is included in the biome of tropical and subtropical broad-leaved rainforests, which also includes equatorial rainforests and temperate rainforests by other authors.

Tropical rainforests have little undergrowth, as sunlight rarely reaches ground level. This makes movement in the forest easier for humans and animals. When the forest fabric is interrupted due to felling or natural events, the soil is rapidly colonized by pioneer plants and a dense network of lianas and young trees; this secondary vegetation is called jungle, due to its strong resemblance to this biome.

Tropical forest
Tropical forest© Mario Tama / Staff Getty Images

The study: The effect of repeated hurricanes on the age of organic carbon in humid tropical forest soil, published on the Global change biology, proposed an interesting retrospective on the issue.

The researchers explain: "Increasing hurricane frequency and intensity with climate change is likely to affect soil organic carbon (C) stocks in tropical forests. We examined the cycling of C between soil pools and with depth at the Luquillo Experimental Forest in Puerto Rico in soils over a 30-year period that spanned repeated hurricanes.

We used a nonlinear matrix model of soil C pools and fluxes ("soilR") and constrained the parameters with soil and litter survey data. Soil chemistry and stable and radiocarbon isotopes were measured from three soil depths across a topographic gradient in 1988 and 2018.

Our results suggest that pulses and subsequent reduction of inputs caused by severe hurricanes in 1989, 1998, and two in 2017 led to faster mean transit times of soil C in 0-10 cm and 35 -60 cm depths relative to a modeled control soil with constant inputs over the 30-year period. Between 1988 and 2018, the occluded C stock increased and δ13C in all pools decreased, while changes in particulate and mineral-associated C were undetectable.

The differences between 1988 and 2018 suggest that hurricane disturbance results in a dilution of the occluded light C pool with an influx of young, debris-deposited C, and possible microbial scavenging of old and young C in the particulate and mineral-associated pools.

These effects led to a younger total soil C pool with faster mean transit times. Our results suggest that the increasing frequency of intense hurricanes will speed up rates of C cycling in tropical forests, making soil C more sensitive to future tropical forest stressors."