Over the past two decades, the rapid expansion of rubber (Hevea brasiliensis) monocultures in tropical regions has led to loss of primary rainforest and severe ecological degradation. Numerous efforts have been made to restore abandoned rubber plantations to rainforest through strategies such as natural regeneration and restoration planting. However, the effectiveness of the restoration strategies and their influencing factors remain unclear.

In a study published in Biotropica, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences showed that restoring tropical forests on former rubber plantation lands effectively mitigates carbon and nutrient limitations for soil microorganisms. Both natural regeneration and restoration planting facilitate positive shifts in soil microbial activity, alleviate microbial nutrient constraints, and promote a more balanced nutrient-acquisition strategy.

The researchers compared soil properties across several land-use types, including active rubber monocultures, mature tropical rainforests, and restored forests through natural regeneration (where vegetation regrows spontaneously) and restoration planting (i.e. planting native species between rubber tree rows).  

By analyzing soil nutrient concentrations and key extracellular enzyme activities (EEAs), the researchers assessed microbial nutrient limitations and identified the drivers behind these changes.

The results showed that as forest restoration progresses, the balance of carbon (C), nitrogen (N), and phosphorus (P) acquiring enzymes in the soil becomes more stable. Both natural regeneration and restoration planting were similarly effective at reducing microbial carbon limitation. However, restoration planting led to a stronger and faster alleviation of microbial nitrogen limitation.

Furthermore, they found that soil pH was the primary factor influencing enzyme activity. Increases in soil phosphorus concentration, as well as in the ratios of carbon to phosphorus and nitrogen to phosphorus, were crucial in shifting microbial nutrient limitations.

“Our study demonstrates that managing soil nitrogen and phosphorus is essential for effective restoration. Planting nitrogen-fixing tree species could be particularly beneficial in converting monoculture rubber plantations back into tropical forests,” said SONG Liang of XTBG.

Experimental plots of natural and artificial restoration gradients (Image by Sujan Balami)

First published: 22 September 2025