Abstract
Reforestation is an effective way to alleviate deforestation and its negative impacts on ecosystem services. In tropical rainforest ecosystem, however, frequent typhoons and heavy rainfall can result in landslides and uprooting of many seedlings, making reforestation efforts very difficult, especially within extremely degraded sites where soil conditions cannot support any plant life. Here, we described a reforestation protocol which is based on tropical rainforest successional processes to not only prevent landslides and tree uprooting due to frequent typhoon and heavy rain, but also accelerate tropical forest succession. This protocol first used the slope and soil layer of the undisturbed old-growth tropical rainforest as a reference to reconstruct slope and soil layers. Then multiple tropical tree species with high growth and survival rate were separately monocultured in the reconstructed soil layers. In the year of 2015 and 2016, we tested the effectiveness of this protocol to recover a 0.2 km2 extremely degraded tropical rainforest which consists of bare rock and thus does not support any plant life, in Sanya city, China. Our results showed that, both typhoons and heavy rains did not result in landslide or any tree damages in the area this reforestation protocol was used. Moreover, our separately monocultured eight fast-growing tree species have much higher fast-growing related functional traits than those for tree species in the adjacent undisturbed tropical seasonal forest, which in turn resulted in large soil water and nutrient loss within 3 years. This seemed to simulate a quick transition from primary succession (consist of bare rock and cannot support any plant life) to mid-stage of secondary tropical rainforest succession (many fast-growing pioneer tree species induced high soil water and nutrient loss). Thus, mixing the late-successional tropical tree species with each of the separately monocultured eight fast-growing tree species can accelerate recovery to the undisturbed tropical rainforest as soon as possible. Overall, based on tropical rainforest successional processes, our research provides an effective protocol for quickly and effectively restoring an extremely degraded tropical rainforest ecosystem. We expect that this work will be important for the future recovery of other extremely degraded tropical rainforest ecosystems.
Highlights
Tropical rain forests are highly important ecosystems due to their high biodiversity and ability to store large amount of carbon thereby to play a key role in regulating global climate change (Houghton et al, 2000; Mitchard 2018)
In this study we aim to quantify whether using our reforestation protocol to recover this 0.2 km2 extremely degraded tropical rainforest can prevent landslides resulting from frequent typhoon and heavy rain while simulating a quick transition from primary succession to mid-stage of the secondary succession and thereby accelerate tropical rainforest succession
We compared differences in soil water content, available nitrogen, and phosphorus content among the initial local high nutrient soil before reforestation sampled in July, 2015, soils in undisturbed old growth forest sampled in July, 2015, soils in reforestation area sampled in July, 2019 and soils in undisturbed old growth forest sampled in July, 2019. Both typhoons and heavy rains have not resulted in landslide or tree damages in this reforestation project (Figure 1)
Summary
Tropical rain forests are highly important ecosystems due to their high biodiversity and ability to store large amount of carbon thereby to play a key role in regulating global climate change (Houghton et al, 2000; Mitchard 2018). Human disturbances in tropical rain forests, including mining, and agricultural use have resulted in heavy deforestation and degradation of these systems and it has been predicted that tropics will have the most deforestation in the near future (Laurance et al, 2014) This degradation, in turn, has led to a global loss in tropical biodiversity, increased carbon emissions, and excessive water loss (Aleman et al, 2018; Symes et al, 2018; Taubert et al, 2018). In extremely degraded tropical rainforest (i.e., long ore mining induced extremely degraded tropical rainforest), only a bare rock environment can be found and any plant life can be supported This is another challenge for performing reforestation that must be overcome. It is highly needed to develop a quick and effective reforestation protocol to prevent the landslide resulting from the frequent typhoon and heavy rain, and facilitate quick forest restoration
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