Abstract
The negative landform of sinkholes provides belowground level refugia for a high diversity of forest species compared to the forests on the surface of surrounding karst plateaus in southeastern China. Bryophyte diversity in sinkhole forests is also likely to be high. In this study, bryophytes of an underground forest sinkhole (UFS), and two forests (Forest Karst Mountain 1; FKM1) and (Forest Karst Mountain 2; FKM2) on the surface of the karst plateau were compared to understand the role of the sinkhole forest in the conservation of bryophyte diversity and the relationships between bryophyte diversity, environmental factors, and soil nutrients. Significantly more bryophyte taxa were recorded from the sinkhole forest (71 taxa, 36 genera, 23 families) than those in the forest on the plateau surface, which was the closest to the sinkhole (FKM1; 29 bryophyte taxa, 16 genera, 12 families), and even fewer bryophytes were found in the forest more distant to the sinkhole (FKM2; 22 taxa, 17 genera, eight families). Twenty-four liverwort taxa were collected from the sinkhole forest, two from the closest surface forest (FKM1) and none from the furthest surface forest (FKM2). Ninety-three percent of the bryophytes in karst mountain sinkhole were not found on surface forest. The diversity index trend was as follows: UFS > FKM1 > FKM2, and the evenness index trend was in the opposite direction as follows: UFS < FKM1 < FKM2. The beta diversity showed that the Jaccard index among the three forests was 0–0.25, reflecting a huge difference between the sinkhole forest and the two surface forests. Canonical correspondence analysis showed that light was the most important factor affecting the distribution of bryophytes in the sinkhole forest, while temperature and humidity were key factors for the distribution of bryophytes in the two surface forests. Further, soil parameters, namely, soil organic carbon, total nitrogen, total phosphorus, total potassium, alkali-hydrolyzed nitrogen, and available phosphorus changed gradually from UFS to FKM1 and to FKM2. The sinkhole forest, located in a landform with the unique negative topography enclosed by cliffs, and with a complex microenvironment, provides a natural refuge for bryophyte species in areas where forests have been negatively impacted by karst rocky desertification.
Highlights
Karst sinkholes have a unique scientific value and are of significant economic benefit to the tourism industry (Shui et al, 2015)
Sinkholes can be divided into the following two types according to the manner of their formation (Zhu et al, 2003): (i) they can be formed as a result of underground water flow leading to rock dissolution, to the development of caves, followed by the collapse of surface rocks; or (ii) they can develop due to rock dissolution and erosion by surface water flow
The significantly higher bryophyte diversity in the sinkhole forest compared to that of the two forests on the plateau surface showed that the sinkhole forest provided a better condition for bryophyte maintenance and it could be a refuge for vulnerable bryophyte species
Summary
Karst sinkholes have a unique scientific value and are of significant economic benefit to the tourism industry (Shui et al, 2015). Most sinkholes are distributed in areas of mature karst and in tropical humid regions (Waltham & Zhang, 2006). Li et al / Sinkhole Forest Provides Refugium for Preservation of Bryophytes more than 100 m deep and 100 m wide, generating a closed environment with higher humidity and lower temperatures compared to those in the surrounding aboveground forested areas and providing a more habitable environment for living organisms Belowground level forests in sinkholes (UFS – underground forest sinkhole) develop on gravel slopes at the base of sinkholes. This is a long-term successional process that generates forests in unique hydrothermal environments with relatively independent structures connected with underground rivers (Robinson & Wells, 1956)
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