Division Of Ecological Site And Construction Of State-and-transition Model Based On High Resolution Remote Sensing Image In Family Ranch Scale

Ecological site is a classification unit which has potential ecological characteristics that synthesize of climate, topography, vegetation, soil and ecological processes. Different ecological sites have various grassland utilization ways and management modes. Each ecological site corresponds to a specific state-and-transition model. Usually, state-and-transition model and ecological site are used together to indicate whether plant communities are in degradation and to forecast the developmental trend of plant communities, providing theoretical support for grassland management. This study was conducted on family ranch scale in four pastoral areas (Inner Mongolia, Northeast, Xinjiang and Tibetan Plateau) in five grassland types (meadow steppe, typical steppe, Leymus chinensis meadow steppe, mountain grassland and alpine meadow). Using high resolution remote sensing images such as ALOS and SPOT5, combining with GIS technology and field survey on family ranch scale, the grassland was divided into various ecological sites. In addition, according to a number of materials, the state-and-transition models of every zonal ecological site were established. The main results were as follows.1. There were two kinds of ecological sites in meadow steppe, including high plain-alluvium dark chestnut soil-Leymus chinensis+Stipa baicalensis and lowland beach-meadow soil-Careex appendiculata+Potentilla chinensis. The area was3966hm2and70hm2respectively. There were two kinds of ecological sites in typical steppe, including high plain-sandy chestnut soil-Stipa Krylovii+Cleistogenes squarrosa and high plain-meadow soil-lowland saline meadow, with the area of749hm2and87hm2respectively. There were two kinds of ecological sites in Leymus chinensis meadow steppe, containing plain-light chernozem soil-Leymus chinensis and plain-light chernozem soil-Phragmites australis, with the area of30351hm2and10298hm2respectively. There were four kinds of ecological sites in mountain grassland, containing mountain-chernozem soil-Poa pretense+Achnatherum inebrians+Carex sp., mountain-brown calcic soil-Stipa caucasica+Seriphidium borotalalense mountain-chestnut soil-Festuca ovina+Seriphidium borotalalense and mountain-grey desert soil-Petrosimonia sibirica+Ceratocarpus arenarius+Seriphidium transillense, with the area of330hm2,320hm2,65hm2and118hm2respectively. There were two kinds of ecological sites in alpine meadow, including plateau-meadow soil-Kobresia humilis+Potentilla anserinal and plateau-meadow boggy soil-Kobresia humilis+Potentilla anserinal, with the area of1126hm2and148hm2respectively.2. Divisions of ecological sites in five kinds of grassland which were meddow steppe, typical steppe, Leymus chinensis meadow steppe, mountain grassland and alpine meadow were conducted in this study. Ecological sites in different grassland areas had significantly differences in topography, soil and vegetation. However, for same ecological site, there was high level of similarities in above mentioned characteristics.3. Sate-and-transition models of every zonal ecological site were established, which reflected the variation of different ecological sites in disturbance and it had reference value for grassland succession. There were two ecological states in high plain-alluvium dark chestnut soil-Leymus chinensis+Stipa baicalensis. One was Leymus chinensis dominated ecological state, the other was Leymus chinensis degraded ecological state. According to the succession theory, there were three association in Leymus chinensis dominated ecological state which included Leymus chinensis+Stipa baicalensis+Carex duriuscula, Leymus chinensis+Carex duriuscula and Leymus chinensis+Cleistogenes squarrosa+Carex duriuscula. There was one association, that was the Cleistogenes squarrosa+Carex duriuscula in Leymus chinensis degraded state. These states were77%and21%of the total area respectively. If the dominant species Leymus chinensis declined and Leymus chinensis dominated state would be sustained. If Leymus chinensis was gradually replaced by Cleistogenes squarrosa and Carex duriuscula, it would be transformed into degraded ecological state. Then it was the time to take some actions to prevent the degradation of grassland. High plain-sandy chestnut soil-Stipa krylovii+Cleistogenes squarrosa had two ecological states, there were Stipa krylovii dominated ecological state and Stipa krylovii degraded ecological state respectively. Association in Stipa krylovii dominated ecological state was Stipa krylovii+Cleistogenes squarrosa. Association in Stipa krylovii degraded state were Leymus chinensis+Artemisia frigida, Cleistogenes squarrosa+Leymus chinensis+Artemisia frigida and Cleistogenes squarrosa+Artemisia frigida. The proportions of two states were43%and57%respectively, and most of the areas had been degraded. Stipa krylovii was gradually replaced by Cleistogenes squarrosa and Artemisia frigida, which meand that grassland had already been in Stipa krylovii degraded state. Protective measures must be applied to restore grassland to Stipa krylovii dominated ecological state. There were two ecological states in plain-light chernozem soil-Leymus chinensis, including Leymus chinensis dominated and degraded ecological state. Association in Leymus chinensis dominated ecological state was Leymus chinensis. Association in Leymus chinensis degraded state were Chloris virgata+Puccinellia distans+Leymus chinensis, and Carex duriuscula+Scirpus planiculmis+Leymus chinensis. The proportions of two states were62%and34%respectively. Because of overgrazing and non rational utilization, Leymus chinensis was gradually replaced by Chloris virgata, Puccinellia distans, Carex duriuscul and Scirpus planiculmis, signing the deterioration of rangeland. If this phenomenon occurred, it should take some actions to prevent grassland degradation. Grassland in mountain-chernozem soil-Poa pratense+Achnatherum inebrians+Carex sp. in Xinjiang was in degraded state as well, Achnatherum inebriants and Carex s p. took over50-60%of plant communities. Grassland in mountain-grey desert soil-Petrosimonia sibirica+Ceratocarpus arenarius+Seriphidium transillense was of the same situation, but appropriate methods would be brought it back to reference state. Grazing prohibition should be applied to Tibetan Plateau, such as plateau-meadow soil-Kobresia humilis+Potentilla anserinal and plateau-meadow boggy soil-Kobresia humilis+Potentilla anserinal as the proportion of Kobresia humilis reduced dramatically.