Ecological Effects and Mechanisms of Soil Remediation by Restoring Native Herbage in a Xerothermic Valley Region in Yunnan Province, China

Main conclusions of Dr. Zhang Yingcui’s thesis at the South-West Agricultural University (SWAU), Bei Bei, Chongqing, China. Main local supervisor: Prof. Duan Changqun (Yunnan University)

Study on Ecological Effects and Mechanisms of Soil Remediation by Restoring Native Herbage in a Xerothermic Valley Region

Vegetation on misused Xerothermic soils and Vertisols in Yuanmou Longchuang River valley (Yunnan Province, China)  shows a notable regressive succession. Species richness as well as bushy species decrease dramatically with increasing degradation causes, such as erosion, grazing intensity etc., resulting in a physiognomy of open herbage with dominant dwarfed grasses, patched grasses and even bare land.

Heteropogon contortus, Bothriocola pertusa and/or Dichanthium annulatum are potentially the most promising species for revegetation on degraded Xerothermic soils and Vertisols, because of their high population growth through unique mechanisms.

Accumulation of soil organic matter is attributed to declined loss of biomass and ground organic mater, to lags in the formation of ground-litter as well as to reduced microbes’ activity in the dry season. The low decomposition rates of Heteropogon contortus on Xerothermic soils and Bothriocola pertusa and Dichanthium annulatum contribute to low soil organic matter as well.

Restoring herbaceous plants initiated the self-repair of hydraulic processes in degraded soil systems by strengthening infiltration, buffering runoff, minimizing evaporation and intercepting rainfall. The maximum water holding rate of native herbaceous litter was around 300 % while the storage capacity was 1.2 to 3 kg/m2, equaling to 0.12 to 0.3mm rainfall.

Soil structure is restored after 10 years of restoration processes. Water stable aggregates at >1mm and particle fractions at >0.25mm increased in Xerothemric soils; in the Vertisols, 0.25 to 0.05mm and 0.05 to 0.01 mm particle fractions increased.  Water stable aggregates at 1 to 2mm, <5mm and the particle fractions at <0.25mm, soil aggregation state as well as aggregation ratio both in Xerothemric soils and Vertisols correlated significantly with herbage root biomass, the length of roots and soil organic matter. Consequently, soil moisture and soil water storage capacity increased. Most notably, the duration of extreme lowest values in the dry seasons was shortened. However, water shortage remains in the dry seasons, inherently due to the local climate pattern..

During the 10 years of restoring, the vegetation showed a succession trend to grass-bush

and/or savanna on Xerothermic soil and Dichanthium annulatum dominant Vertisol with species richening, population growth of bushes and restoring of sparse trees. Species richening and the invasion of Heteropogon contortus and Dichanthium annulatum into the Bothriocola pertusa community occurred. Positive plant successions indicate that self-restoration of degraded soils had started.

[Edited by Kees Stigter, who was an adviser to this Ph.D.-research at the South West Agricultural University (SWAU) and the Yunnan Academy of Agricultural Sciences (YAAS) from 2000 – 2005, on behalf of Wageningen University’s Department of Meteorology’s Asian Picnic Model Project (APMP). For this work he visited twice SWAU (Bei Bei), YAAS (Yuanmou) and related institutes in Chongqing  (as a city-province embedded in Szechuan Province) and Kunming (Yunnan Province). See also under INSAM’s “Accounts of Operational Agrometeorology” of 6/8/’03 the paper “Restoring grasses to rehabilitate land in Yunnan hot-arid valley regions”, by Zhang Yingcui, Kees Stigter and Zhou Hongye. The research is an example of focusing on a local priority problem of fighting degradation of grazing land in mountainous regions due to over-grazing and related climate induced water erosion of unprotected soils that are suitable for controlled low-density grazing activities. A concurrently done M.Sc.-thesis of Zhou Hongye, husband of Dr. Zhang Yingcui, concluded that the restored plant community provides good prospects for the livestock industry. I was an adviser to that M.Sc.-thesis as well. KS.]