Effects of shading and herb/liana eradication on the assembly and growth of woody species during soil translocation in Southwest China
Introduction
As a consequence of the intensification of human activities and global climate change, large areas of forest have been degraded and converted to other land uses, reducing available habitats and resources for forest-dependent species and people, and compromising the ecosystem services that support all life on earth (Bierregaard et al., 1992; Lewis et al., 2015). Conservation and sound management of remaining forest are essential to stem further losses of biodiversity (Gibson et al., 2011) and supply the perquisite seed sources for use in the restoration of neighboring degraded sites (Asner et al., 2009). But these steps only slow the loss of natural forests; they are insufficient for conserving species diversity, mitigating climate change, and providing the levels of ecosystem services required by growing human populations (Chazdon et al., 2009; Harvey et al., 2008; Houghton et al., 2015; Martinez-Ramos et al., 2016). In short, we urgently need new methods and strategies to reproduce forests that are higher similarity to the donor forests.
Many scientists and practitioners aim to restore degraded forest to a state with high similarity to natural forest. Forest degradation destroys propagule banks, including soil seed bank and reproductive tissues (Sanou et al., 2018), potentially impacting the restoration of preferred woody species (Dilrukshi and Ranwala, 2016; Morici et al., 2009). Hence, replacing the topsoil layer of a degraded site with natural forest topsoil offers a promising method for restoring vegetation (Hong et al., 2012; Wang et al., 2016), primarily because it carries many seeds and vegetative propagates that possess regionally specific species composition and hereditary characters, which should effectively sustain the diversity and stability of native species (Jalili et al., 2003). Soil translocation had been applied successfully in the recovery of mining wasteland in Australia (Tacey and Glossop, 1980), bauxite ore desert in Brazil (Parrotta and Knowles, 1999), marshy meadow (Madsen and Mindess, 1986), and prairie meadows in Canada (Vecrin and Muller, 2003). But for forest restoration in most subtropical and temperate areas, many researches confirmed that soil translocation led to either much of the existing vegetation in the donor forest, especially dominant species, undiscovered in the receiving site (Pywell et al., 2002b), or that similarity was low between the established vegetation and the donor forest (Ehrenfeld, 2000; Hodder and Bullock, 1997; Thompson and Grime, 1979), which restricted its application for the ecological restoration and biodiversity compensation (Shen et al., 2013; Valkó et al., 2011).
Forest gaps provide a favorable environment for preserving the soil seed bank and maintaining gap-phase regeneration dynamics of forest ecosystems (Lu et al., 2018). Even small canopy openings can alter environmental conditions mainly due to the increased light heterogeneity they provide (Galhidy et al., 2006; Rozenbergar et al., 2007) and afford diverse microsite patches for forest seedlings' regeneration (Nakashizuka, 1989; Orman et al., 2018; Orman and Szewczyk, 2015; Zielonka et al., 2006). Moreover, recent work showed that the formation of diverse forest gaps was also a strategy to inhibit the germination and growth of dormant seed and herbaceous seeds in the shaded understory (Tamura and Nakajima, 2017). Soil translocation involves the removal of an assemblage of plant species from a donor forest, with the aim to establish it as a functional community at a receiving site (Bullock, 1998). Nevertheless, this can lead to a changed habitat harsh for soil seed bank germination, mainly from exposure of donor topsoil to strong sunlight, which also breaks the dormancy of the persistent soil seed bank, especially herbaceous species (Metcalfe and Grubb, 1995a, Metcalfe and Grubb, 1995b; Pywell et al., 2002a, Pywell et al., 2002b; Warr et al., 1993); both factors may limit the germination and establishment of most woody species.
This field study aimed at confirming the hypothesis that shading treatment and herb/liana eradication would improve the germination of woody species' seeds and their subsequent seedling growth and similarity following soil translocation. Specifically, our study addressed three questions: (1) How similar is the established community to the donor forest or soil seed bank of donor forest? (2) Is soil translocation with shade an effective technique to promote species diversity and growth? (3) Does weeding further increase the similarity between germinated seedlings and donor forest?
Section snippets
Study site
This study was conducted in Jianshui County (E 102。56′ 50.33″, N 23。41′ 42.98″), located in south of Yunnan Province, China, which belongs to the representative Honghe dry-hot-valley rocky desertification region (Bulletin on the Status of Rocky Desertification in China, 2012). The annual average temperature is 19.6 °C, and the highest monthly average temperature is 24.3 °C (June) and the lowest monthly average temperature is 12.8 °C (January). Mean annual precipitation is 785.1 mm, most of it
Aboveground vegetation characteristics of donor forest and receiving site
The vegetation survey showed that vegetation structure and species density varied greatly across the two sites. A total of 50 plant species, belonging to 29 families and 46 genera, were recorded in donor forest, in which the richness of trees, shrubs, herbs, and lianas species were 16, 9, 19, and 6 species respectively. By contrast, 33 species, belonging to 16 families and 31 genera, were found in receiving site, of which 5 were shrubs (i.e., plants with heights <1 m) and 28 were herb species,
Can the community reassembled by soil translocation with blank control resemble the aboveground vegetation and soil seed bank of donor forest?
The soil seed bank is defined as the viable seeds that exist on the soil surface or are buried in soil (Walck et al., 2005). As such, it represents the pooled progeny of the current plant community as well as the potential species pool available for future communities to develop at a given place and time (Fisher et al., 2009). Understanding the characteristics of soil seed bank and its aboveground vegetation is essential not only for assessing the vulnerability of degraded sites, but especially
Author contribution section
Gaojuan Zhao: The first author, participate in experiment design, experiment conduct, experiment management, data recording, data analysis and manuscript writing.
Youxin Shen: corresponding author, participate in test design and manuscript revision.
Wenyao Liu: corresponding author, participate in test design and manuscript revision.
Zhenjiang Li: participate in experiment operation and data recording.
Beilin Tan: participate in data recording.
Zhimeng Zhao: participate in data recording.
Juan Liu:
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was supported by the National Key Research and Development Program of China (2016YFC0502504), the CAS 135 Program (No.2017XTBG-F01), and the National Natural Science Foundation of China (41671031). We are also very grateful to Jianshui Research Station, School of Soil and Water Conservation, Beijing Forestry University.
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Response strategies of woody seedlings to shading and watering over time after topsoil translocation in dry-hot karst region of China
2022, Forest Ecology and ManagementCitation Excerpt :Restoration of lost forests has become a critical step for conserving species diversity and improving ecological function (Harris et al., 2006; Benayas et al., 2009). Topsoil translocation has been demonstrated as a promising method for vegetation restoration in mined areas and other severely degraded areas (Parrotta and Knowles, 1999, 2001; Koch, 2007; Zhao et al., 2020a) because forest topsoil contains a variety of seeds and vegetative propagules (Vecrin and Muller, 2003; Jalili et al., 2003; Shen et al., 2013; Zhao et al., 2020b). However, plant stress in degraded site, such as intense solar radiation and intermittent and long-term drought (Allen et al., 1995; Chirino et al., 2009; Padilla et al., 2009), may negatively affect the survival, growth performance and establishment of woody species in the seedling stage, leading to poor recovery effect and low similarity between new communities and donor forest (Hopfensperger, 2007; Bossuyt and Honnay, 2008; Chenot et al., 2017; Tong et al., 2017; Valliere et al., 2019).
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