Natural Recovery of Steppe Vegetation on Vehicle Tracks in Central Mongolia
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Natural recovery of steppe vegetation on vehicle tracks in central Mongolia SHENG-GONG LI*, MAKI TSUJIMURA†, ATSUKO SUGIMOTO‡, GOMBO DAVAA§ and MICHIAKI SUGITA† Japan Science and Technology Agency, Kawaguchi, Saitama 332–0012, Japan †Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan ‡Graduate School of Environmental Earth Science, Hokkaido University, Sapporo Hokkaido 060–0810, Japan §Institute of Meteorology and Hydrology, Khudaldaany Gudamj–5, Ulaanbaatar 210646, Mongolia *Corresponding author (Fax, 81-29-8536878; Email, [email protected]) Steppe desertification due to vehicle travel is a severe environmental issue in Mongolia. We studied natural vegeta- tion recovery on abandoned vehicle tracks in the central Mongolia steppe through vegetation surveys and stable iso- topic techniques. The following issues were addressed: (i) invasion of pioneering plant species, (ii) alteration of soil surface features, and (iii) contribution of revegetated plants to soil organic matter (SOM). The pioneering plant species that firstly invaded the abandoned tracks are those that could germinate, root and survive in the compacted track surface. Salsola collina is one of these candidate plants. Due to revegetation, soil surface hardness was reduced. With the improvement of surface microenvironmental conditions, other plants began to colonize and establish; con- comitantly species richness and species diversity increased. Carbon isotope ratios of SOM at the top surface layer indicated that C4-derived carbon contributed more to SOM in the early phase of recovery and decreased with further recovery. [Li S-G, Tsujimura M, Sugimoto A, Davaa G and Sugita M 2006 Natural recovery of steppe vegetation on vehicle tracks in central Mongolia; J. Biosci. 31 85–93] 1. Introduction other human-related factors such as deforestation, improper agronomic management, fuel wood gathering, excessive Desertification is usually defined as land degradation in arid, water use, mining, and vehicle tracks are also important semiarid and dry subhumid areas caused by combined effects contributors (Batjargal 1997). of various natural and anthropogenic factors (UNEP 1992; Le With rapid economic and social transformation in Houérou 1996). Over 90% of territory in Mongolia belongs Mangolia starting from the early 1990s, the number of vehi- to arid, semiarid and dry subhumid regions, and is ecologi- cles increased tremendously from 43792 in 1990 to 81693 cally fragile and susceptible to economic overexploitation in 2000 with an annual increase of about 9% (NSOM 2000). (Batjargal 1997; MNEM 1997a). Over three fourth of the ter- This rapid growth in the number of vehicles far exceeded restrial ecosystems in the country (ca. 1.2 × 106 sq. km) is the growth of the capacity for road construction. As of 2001, subjected to various degrees of desertification, which is the total road length in Mongolia was 11100 km, out of critically affecting sustainable development of the Mongolian which only 11.9% was asphalt-paved, 12.5% gravel-paved, economy (Batjargal 1997; MNEM 1999). Although the and the remaining 75.6% earthy (UNESCAP 2001). The primary cause for desertification is overgrazing, however, unpaved earthy tracks are created on-site by compaction Keywords. Degradation; Mongolian steppe; recovery; soil organic matter; stable carbon isotope ratio; vehicle track http://www.ias.ac.in/jbiosci J. Biosci. 31(1), March 2006, 85–93, Indian Academy of Sciences 85 86 Sheng-Gong Li et al caused by many vehicles driving on the same spoor. As of 2. Materials and methods 1997, vehicle tracks have led to ca. 8000–10000 km2 of desertified land across the country, and were the primary The research site was located in Kherlenbayan-Ulaan (KBU), cause for steppe degradation in some places (MNEM Hentiy province, Mongolia (47°12.838’N, 108°44.240’E, 1997b). Vehicle tracks are, therefore, one of the serious 1235 m asl) (figure 1). People in this area have maintained environmental issues in Mongolia. When a vehicle track is the traditional nomadic life style for centuries. The climate abandoned, revegetation (recovery) may occur via self- is continental in the temperate zone. The season from rehabilitation mechanisms (Whisenant 1999). In this paper, November to late April is long, cold and dry. The spring by investigating vegetation and soil surface changes on from May to June is windy and dry. The summer from June abandoned vehicle tracks in a central Mongolian steppe, to September is warm and relatively wet. The growing we attempt to address: (i) which plants are the first to invade season is about six months from late April to late the abandoned tracks, (ii) how soil surface conditions October (Li et al 2005). According to the report of the KBU change with the recovery, and (iii) to what extent native Weather Station (averages from 1993–2002), the mean plants contribute to soil organic matter during the recovery annual air temperature of the region is 1.2°C. Mean daily process. temperatures for January and July are –22.9 and 21.4° C, UB KBU Figure 1. Location of the study site: Kherlenbayan-Ulaan (KBU), about 250 km away from Ulaanbaatar (UB), the capital of Mongolia. A, B, C, and D represent the current vehicle track (track A), the track abandoned for three to five years (track B), the track abandoned for ten to fifteen years (track C), and the native steppe (D) respectively. J. Biosci. 31(1), March 2006 Natural recovery of steppe vegetation on vehicle tracks in central Mongolia 87 respectively. Mean annual precipitation is 196 mm, of with a soil corer (0.06 m in diameter). The soil at each depth which 88% falls between June and September. The soil is a was collected from three cores (holes, about 0.5 to 1.0 m typical chestnut soil (Kastanozem), characterized by low apart), mixed and passed through a 2 mm sieve on the spot. organic matter content, low levels of nitrogen, thin in depth, To avoid spatial heterogeneity, the soil profile samples at and sandy in texture (Asano 2004). There are scattered the sites excluding track A had three replicates from three stones on the surface and in the soil. Lime (sometimes gyp- locations (20 m apart). The soil profile sample at track A sum) often accumulates in the subsoil. The short-grass had no replication, but was collected from 5 soil cores (10 steppe is the major vegetation type in the region, and is m apart), and respectively mixed for each depth. In addition, dominated by cool-season C3 species, including mainly sunny healthy leaf samples from dominant plant species at Stipa krylovii (feather-grass), Carex duriuscula (needle-leaf the native steppe were collected for isotope analysis. Soil sedge), Artemisia frigida (fringed sagebrush), Allium mon- samples were oven-dried at 105°C for three days in the lab golicum (Mongolian onion), Leymus chinensis (Chinese while the leaf samples were air-dried in the field and then wild-ryegrass), and Caragana microphylla (littleleaf oven-dried in the lab at 65°C for three days. Coarse grind- peashrub), and a few C4 plants such as Cleistogenes squar- ing was done for the soil samples with a mortar and pestle. rosa (bridlegrass) and Salsola collina (Russian thistle, Leaf samples were frozen using liquid nitrogen and then tumbleweed). ground with mortar and pestle. Both the soil and plant sam- There were many unpaved earthy multi-lane vehicle ples were sifted with 40 mesh (425 µm) sieve, and then tracks at the KBU steppe. These tracks were created by sealed in glass vials. In order to remove inorganic carbonate changing lanes, passing, and driving randomly. When sur- carbon, soil samples were treated with 1 N HCl at 25°C for face conditions became unsuitable for driving, the tracks one to three days and then rinsed with distilled water was then abandoned. The abandoned tracks may be natural- (Midwood and Boutton 1998). Sub-samples (about two mg ly recovered through revegetation (secondary succession) for leaf samples, and 2 to 15 mg for soil samples depending (Whisenant 1999). At the KBU steppe, we selected two on depths) from these samples were placed in tin capsules abandoned tracks (track B and track C), which were in (Universal tin container, Thermoquest Italia SPA, Rodano, parallel and adjacent to the current track (track A) (figure 1), Milan, Italy) for determination of stable carbon isotopic to investigate vegetation recovery. Each investigated track composition (δ13C), carbon (C) content, and nitrogen (N) extended over 500 m and was 2–3 m in width. According to content using an isotope ratio mass spectrometer (Finnigan the drivers who often drove through these tracks over the MAT delta S, Bremen, Germany) coupled with an elemen- past 20 years and the herdsmen who live in KBU, track B tal analyser (Carlo Erba EA1108 elemental analyzer, Fisons was abandoned three to five years ago, and track C was Instruments, Danvers, MA, USA) at the Center for abandoned around ten to fifteen years ago. Both track B and Ecological Research, Kyoto University, Japan. Precision of track C were not used by vehicles recently. A section of the individual measurement on the spectrometer was ± 0.15‰ steppe close to track C (D in figure 1) was selected as a ref- for δ13C. Stable isotopic compositions of the samples are erence treatment (called native steppe here after). expressed as part per thousand (per mil, ‰) using the delta In July 2003, vegetation investigation, including species (δ ) notation: composition and frequency, was conducted on ten random quadrats of 50 × 50 cm at each site with the exception of R δ =−sample 1× 1000, sample (2) track A, where there was no surface vegetation. Total vege- Rstandard tation cover and cover for each species at each quadrat was visually estimated. Species diversity is a descriptive meas- where Rsample and Rstandard represent the heavy-to-light iso- ure of plant community structure.