Rock outcrops (ROCs), the exposed bare rocks above the soil, i.e. pinnacles, are common features in limestone areas. However, the influence of presence of ROCs and their chemical characteristics on the relationship between the soil and forest recovery has not been thoroughly explored. 

In a study published in CATENA, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their collaborators attempted to quantify the impact of forest restoration under the ROC context on soil properties. They also wanted to analyze the relationship between soil property variations and vegetation characteristics, including plant diversity and plant biomass.  

The researchers compared the concentration of total potassium (TK) and available potassium (AK), soil organic matter (OM), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), volumetric proportions of soil (VPS), pH, and bulk density in soil with ROC emergence under a sequence of grass, shrubs, young regenerated forest, and closed forest on karst landforms at Shilin, S.W. China. 

They found that concentration of total and available soil K decreased, but OM, N, and P concentration increased during karst forest restoration. Slow improvement of pH and bulk density were the characteristic features as biomass accumulated and plant species became enriched under the context of ROCs. Potassium stock (merged rock proportion and concentrations) was more sensitive to biomass accumulation. 

Canonical correspondence analysis also detected that only certain groups of plant species were sensitive to the increase of soil K stock and other properties during forest recovery.  

The researchers thus suggest that K may play a much more important role in forest restoration than expected, especially in karst landscapes with a high ratio of ROC emergence. 

"Our finding of the sensitivity and correlation of potassium to forest restoration could provide valuable information for forest restoration and forest management. It implies that any measure to increase soil K could ameliorate this limitation and ensure against rocky desertification", said Prof. SHEN Youxin, first author of the study. 

A study site with rock outcrops at Shilin (Image by SHEN Youxin)