Reza Jafari; Morteza Ansari; Mostafa Tarkesh
Abstract
Temperature is the most important parameter for studying spatiotemporal phenological changes in plants. Thus, the current study was aimed to investigate the potential of MODIS land surface temperature (LST) data for mapping growing degree days (GDD) and different phenological stages of Bromus tomentllus ...
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Temperature is the most important parameter for studying spatiotemporal phenological changes in plants. Thus, the current study was aimed to investigate the potential of MODIS land surface temperature (LST) data for mapping growing degree days (GDD) and different phenological stages of Bromus tomentllus and Astragalus effusus in Chaharmahal and Bakhtiari Province. MODIS extracted maps of maximum, minimum and mean temperature, GDD index and phenological stages from 2018 to 2019 during growing season were assessed against weather station data and also field-based phenilogical data using Pearson analysis in three regions with different altitudes. Results showed that MODIS LST and GDD maps had more than 91 and 99% correlations with field-based air temperature and GDD data, respectively (p<0.001). In early growing season, GDD values were less than 16 degree-days and they were more than 5200 degree-days in the late growing season which explained one and all the phenological stages of the studied species in the study area, respectively. The study findings indicated that MODIS data have high capability in spatiotemporal stratification of phenological stages of the Bromus tomentllus and Astragalus effuses plant species. The knowledge of different phenological stages is essential in species conservation and rangeland sustainable utilization, therefore, species phenology map can be used as an effective tool in rangeland management in the related organizations.
Fatemeh Hadian; Reza Jafari; Hossein Bashari; Mostafa Tarkesh
Abstract
Plants are one of the most important components of the ecosystem which are affected by natural and human factors. Therefore, the study of net primary production (NPP) is one of the main subjects in ecology. The main purpose of this research was to model spatial and temporal distributions of NPP ...
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Plants are one of the most important components of the ecosystem which are affected by natural and human factors. Therefore, the study of net primary production (NPP) is one of the main subjects in ecology. The main purpose of this research was to model spatial and temporal distributions of NPP and also to determine the degradation of vegetation types using Carnegie Ames Stanford Approach (CASA), Rain Use Efficiency (RUE) and Light Use Efficiency (LUE) models in semi-steppe rangelands of Isfahan Province. For this purpose, the 16- day MODIS NDVI images, metrological data, land cover maps and field study were applied in the study area. The results showed that the NPP rate increased from March (11.44gC/m2/mo) to May (41.07gC/m2/mo) while demonstrating a decreasing trend from the onset of June (2.2 g C/m2/mo) due to soil dryness. Climate , vegetation type and rangeland conditions had important roles in annual plant NPP and therefore the highest and lowest NPP were observed in Astragalus- Daphnae (38.85 gC/m2 y-1) and Artemisia sieberi - Scariola (4 g C/m2 y-1) vegetation types with maximum (0.13 g C (MJ)-1) and minimum (0.005 g C (MJ)-1) LUE, respectively. The amount of RUE decreased in degraded rangelands. Moreover, the correlation between field measurements and the CASA model decreased in semiarid warm climate and degraded rangelands. Therefore, rangeland conditions, vegetation type and climate condition must be taken into consideration in NPP monitoring and rangelands management.
