The Effect of Seasons and Exposures on Microhabitat Modifications of Onobrychis cornuta Cushions

1- INTRODUCTION Mountainous habitats are characterized with low temperature, limited growing seasons, high mortality rate due to freezing and high radiance which limit occurrence of species. Such habitats also face early grazing and soil erosion. The most dominant shrubs in such habitats are cushions which have important roles in mountainous areas with high erosion potentials. However, their roles in soil conservations are not clear. Cushions can create microclimate in harsh conditions in the high altitudes by modifying soil moisture and temperature which could improve species establishments. In addition, exposure can also change soil moisture conditions and influence on temperature fluctuations. The aim of this study is to investigate the effect of exposures on improving microclimate of Onobrychis cornuta. 2- THEORETICAL FRAMEWORK In harsh conditions considering SGH (Stress gradient hypothesis), it is expected that shrubs facilitate establishments of species. Shrubs act as nurses in the disturbed conditions. However, the role of cushions has not been studied yet and it is needed to know how such woody species modify habitats and also how exposures influence on the microhabitat conditions. 3- METHODOLOGY The study area is located in Golestan national park and Alme-Gharatikan site with the altitude of 1800 m. The most dominant species are perennial grasses of Festuca valesiaca, shrubs of Onobrychis cornuta and perennial forbs of Cephalaria microcephala. Two exposures were selected where the North exposure has deep and developed soil compared to the South exposure with more stones. Minimum, maximum, mean and Diurnal Temperature Fluctuations (DTF) at the two exposures (North and South) were calculated for both under patches and open area using thermometers. Soil moisture was also measured by TDR instrument in the patches and open area during two time intervals. For the determination of the most important factors affecting soil moisture including exposure, time and their interactions, GLMM was applied and the compared means were tested by T-test.   4- RESULTS                                                          In the southern exposure, temperature fluctuation was 2-3.5 C (mean= 2.2 C) for under cushions and in the open plots was 2-11.5 C (mean= 7.1). Therefore, in the open plots, fluctuations are higher than under shrubs. In the North exposure, fluctuation is 0.5- 3.5 C (mean= 2.1) for under shrubs and ranged from 0.5 to 10.5 C (mean= 6.5). Maximum DFT belongs to the open plot of the South exposure (7.1 C) and the lowest DFT was observed below shrubs in the North exposure (3.9 C). The minimum and maximum temperatures were observed in the southern exposure. Thus, the Diurnal Temperature Fluctuations in the open area (7.1, 3.9 ºC) were greater than the patches (2.2, 1.9 ºC) in the South and North exposures, respectively. According to GLMM results, the time and exposures (F= 6.0; P < 0.05, F= 16.3; P < 0.01) had the highest significant impacts on soil moisture. At the second sampling time, the moisture increased in the northern slopes and reduced in the southern slopes. Under patches, time was the most important factor (F= 31.1; P < 0.01), which significantly reduced in both time intervals.  5- CONCLUSIONS & SUGGESTIONS This study indicates the importance of cushions in moisture maintains and temperature modifications influencing soil conservation and understory species survival. This could be used for the cushion roles in maintaining moisture in the mountain habitats. In general, cushions keep moisture for longer time in terms of the distances between them. High moisture availability reduces soil erosion which is critical in mountainous habitats. The moisture reduction in the South exposures and late spring is higher. Therefore, cushions play more ecological roles in such conditions. Cushions also modify temperature fluctuations which benefit species occurrence in these habitats. This modification is more important in the southern exposure which, due to earlier snow melting, species face longer freezing periods. In such conditions, cushions can play the nursing roles for species conservation. In addition, such microclimatic conditions facilitate the occurrence of species in such habitats and conserve them in the freezing and cold winters. Cushions’ role in Iran, due to overgrazing and high erosion, is more considerable, and in the conservational plans, these species should be considered. Considering the present results, this study suggests examining the role of different shrub functional types.