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.