4.5. Geodiversity and Conservation implications
Geodiversity includes soil fertility, nutrient availability and topographic heterogeneity (Tukiainen et al. 2017), is the main strongest diver shaping the conifer richness pattern at vulnerability and endemism levels as indicated in the current study. Conservationists should give more attention to those areas in which geodiversity positively correlate with the conifer richness, particularly endemic-threatened (Bailey et al. 2017; Knudson et al.2018). Soil-nutrient fertility variables, e.g. carbon and nitrogen showed a strong positive effect on the richness pattern and this support the finding that rarity may be more related to reduced soil fertility than climatic factors (Ulrich et al. 2014; Quesada & Lloyd 2016). Thus those areas with high richness and characteristic geodiversity features are the key areas for conservation priority and provide greater insights to the distinctive soil conditions supporting the conifer diversity and ecosystem functioning, and thereby afforestation planning (Hjort et al. 2015; Knudson et al.2018); where, multi-species plantations result in increasing in forest productivity, carbon stock, and ecosystem resilience (Oliver et al. 2015; Liang et al. 2016; Chen et al. 2018; Liuet al. 2018a).
Moreover, soil ecosystem services of soil fertility and carbon sequestration have strong positive relationship with the conifer richness in the southwestern and central parts of Sichuan which are climatically stable and could be assumed as refugia (Dakhil et al. 2019), so protection of these areas will strengthen the conservation of ecosystem services of biodiversity and geodiversity (Comer et al. 2015; Tukiainen et al. 2017). Furthermore, this will strengthen the targets of GSPC concerning with the protection of IPAs and ecoregions (CBD 2012; Sharrock et al. 2014; Renet al. 2019). China’s national nature reserves focused primarily on the protection of mammals, so the entire habitats of plants were not well captured (Xu et al. 2017). Furthermore, the three hotspot ecoregions harbour only 7-25% nature reserves of their total areas (Yeet al. 2015). Accordingly, IPAs of the current study, around giant panda and alpine forests nature reserves (see Fig. 1E) with high richness of endemic and threatened conifers needs more protection; and this finding supports our hypothesis and agrees with the findings of Xuet al. (2017) and Dakhil et al. (2019) who suggested similar priority of conservation and establishing new proposed nature reserves in the same locations which are climatically stable, so we can conserve both biodiversity and ecosystem services (Threatened Conifers of the World 2019; Farjon et al. 2019 ; Tripathi et al.2019).
5. Conclusions
Geodiversity, including soil fertility, nutrient availability, and topographic heterogeneity, was the main driver of the conifer richness pattern at the vulnerability and endemism levels. Qionglai-Minshan, Hengduan Mountains, and Nujiang Langcang Gorge ecoregions were the major centres of threatened and endemic conifers in south-western China. Compared to all conifers, endemic-threatened conifers were more strongly affected by soil nutrients, MAT, and topographic heterogeneity, and this indicates that endemic-threatened conifers may face a high risk of extinction in the future due to habitat destruction and climate change. Sandy soil, carbon, nitrogen, and topographic heterogeneity showed the highest contribution and strongest positive relationships with all groups of conifer richness. Thus, global researchers should give more attention to soil nutrient-fertility hypothesis in the spatial ecological modelling of various taxa at the community, vulnerability and endemism levels, and this will provide greater insights into conservation and management of the biodiversity and ecosystem services of soil fertility and carbon sequestration. Furthermore, conservationists and policymakers should give more attention to the quantitative soil variables of sand fraction, carbon, nitrogen, and phosphorus along with elevational range during afforestation planning. The four proposed nature reserves should be protected to rescue the endemic and threatened conifers located in the buffer zones and surrounding areas of the nature reserves to protect biodiversity, IPAs, and ecoregions and thereby achieve the GSPC targets. Further logical research is required for understanding the effect of environmental factors of climate, energy, and water on soil fertility, nutrient availability, and carbon sequestration along the elevational gradient at a regional scale. Also, spatial conservation assessment of the endemic-threatened conifers under climate change scenarios at both species and community levels are needed, taking the findings of the current study as a helping tool for future conservation and ecosystem management.