According to a 20-year study led by researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences, planting small patches of native trees can help restore degraded tropical forests over the long term. However, the findings also indicate that, without active intervention, recovering areas may remain in an early successional stage dominated by sun-loving pioneer trees.

The study, published in Restoration Ecology on June 1, shows that the "applied nucleation" method, i.e., planting small tree patches to start recovery, has significantly restored a degraded tropical riparian corridor in southwest China.

Tropical forests cover more than half of the world's tropical land area, but they have suffered severe degradation due to human activities. Meanwhile, traditional large-scale reforestation is costly and can lead to ecological homogenization.

In 2003, the researchers planted small clusters (or "nuclei") of native trees along a 12-kilometer degraded riparian corridor. Each nucleus included three fig species (Ficus racemosa, Ficus benjamina, and Ficus hispida) and nine other native trees. After only two years of weeding and watering, the sites were left to regenerate naturally.

Over a 20-year monitoring and evaluation period (2003–2023), the researchers quantitatively assessed the effectiveness of the applied nucleation method at both community and landscape scales, while analyzing the impact of planting strategies that centered on fig species as core species for ecological restoration.

They compared three types of sites: planted nucleation areas (NAs), natural expansion areas (EAs) that developed from those nuclei, and reference plots in a nearby seasonal rainforest.

Twenty years later, the restored forest (NAs and EAs) had only 19–30% of the tree diversity and biomass levels of the reference forest. The functional composition revealed a "pioneer bottleneck": light-demanding pioneer species accounted for over 75% of the community, while shade-tolerant species dominated 80% of the reference forest. This indicates that the restored forest remains in an early successional stage.

Fig trees notably contributed 76.8% of the tree biomass in the NAs and acted as crucial foundation species that rapidly built the structural skeleton of the recovering forest.

"Applied nucleation, which requires less intensive land management and lower input costs than traditional large-scale plantings, offers a feasible path forward. However, recovery is a multi-decade process, and restoring biodiversity will require sustained effort and possibly additional active management," said SONG Liang of XTBG.

Based on their findings, the researchers recommended using high-biomass foundation species as nucleation cores while implementing proactive management of successional stage differences to optimize restoration outcomes.