Secondary succession on landslides in submontane forests of central Taiwan: Environmental drivers and restoration strategies

Posted on by

By Chien-Fan Chen, Ching-Feng Li, Chu-Mei Huang, Huan-Yu Lin & David Zelený

Sampling of spontaneously recovered vegetation after landslide disturbance in Central Taiwan, East Asia. A 20 m × 20 m plot was set up within the landslide area to investigate the species composition and environmental variables. (Photo credit: Chien-Fan Chen)

Landslides are a conspicuous type of disturbance caused by small-or larger-scale ground movements. About half of the land area worldwide is susceptible to this serious type of disaster, especially in tropical and subtropical regions. Moreover, as the ongoing climate change increases the intensity of extreme precipitation events followed by landslides, restoration of landslide-affected habitats becomes ever more important. Landslide risk management is becoming a significant issue for disaster prevention and mitigation and is essential for protecting the life and property of the people below the collapsed land.

Spontaneous vegetation can guide restoration practitioners in deciding on methods and plant species for restoring particular landslides. In our study, we aim to describe the species composition of vegetation that has recolonised landslides and describe its relationship to environmental variables. We also propose plant species and restoration strategies applicable for speeding up the restoration process.

We conducted the survey at an elevation between 240 and 1350 m a.s.l. in central Taiwan, East Asia. The boundaries of landslides were delimited using aerial photographs taken between 1975 and 2015. Then, a 20 m × 20 m plot was set up within each landslide area to investigate the species composition and environmental variables.

Our results show that the vegetation and species composition were mainly related to successional age, landslide position and soil conditions. For example, the slip zone of the landslide is often represented by a steep slope will fewer soil nutrients, while the deposition zone is usually flat and stable, with nutrient-rich soil. We identified two early successional types (aged 5–10 years) that mainly occur in habitats in steep slip zones, are dominated by pioneer woody species and have high coverage of grasses, forbs, or ferns thickets. In contrast, the middle successional vegetation type (aged 16–40 years), growing on flat habitats, can reach the middle successional stage and consists of pioneer woody species in the canopy layer, and seedlings or saplings of shade-tolerant species in the understory. Based on our results, we proposed a list of pioneer species and shade-tolerant woody species that can be applied to landslide scars.  We also constructed a conceptual diagram representing the plant species and physiognomic changes along the landslide successional sere in submontane forests of central Taiwan (see below).

Conceptual diagram representing the plant species and physiognomic changes along the landslide successional sere in submontane forests of central Taiwan. In the first five years (panel A), the Miscanthus, Dicranopteris, and saplings of pioneer tree species colonize bare ground generated by the landslide. As the succession advances (panel B), the bare ground is fully covered by the dense Dicranopteris thickets and Miscanthus tussocks, with fast-growing species of pioneer trees present above them. Then (panel C), the canopy of the forest is dominated by the pioneer species, and shade-tolerant species occur as seedlings or saplings in the understory. At the same time, the dominance of Miscanthus and Dicranopteris is gradually declining. (Schema from the paper, drawn by Yi-Mei Wu)

In conclusion, we suggest that the designation of restoration strategies and selection of plant species used for restoration should consider the landslide zones (slip vs deposition zone) and the successional age. Framework species, defined as plants with high tolerance to drought and irradiation, rapid growth in open habitats and production of attractive seeds, can be applied on the habitats suffering from a poor local species pool and dispersal limitation in early successional age. However, planting shade-tolerant woody species could be considered to speed up the restoration process when those desired species are absent in the local species pool in the middle successional stage. We believe that the results of our study will be useful when creating practical guidelines for restoring landslides and designing the landslide restoration policy.

This is a plain language summary for the paper of Chien-Fan Chen et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12635). The post was prepared by C.-F. Chen & D. Zelený.