Jamal Imani; Ataollah Ebrahimi; Bahram Gholinejad; Pejman Tahmasebi
Volume 28, Issue 3 , October 2021, , Pages 450-471
Abstract
The present study was conducted to investigate the differences between several remote sensing indices, four different plot sizes and two different sampling methods to estimate the percentage of plant cover and production in three plant communities in 2013. Ground sampling was performed in three communities ...
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The present study was conducted to investigate the differences between several remote sensing indices, four different plot sizes and two different sampling methods to estimate the percentage of plant cover and production in three plant communities in 2013. Ground sampling was performed in three communities with different dominant vegetation in two forms of six and three quadrats. Four different dimensions of the quadrats were used nested to estimate production and coverage percentage. Sampling was performed in each community within 30 pixels along three transects with different heights (sampling method and testing were performed according to the researcher opinion). Dominant plant density was measured by counting the bases per plot, plant cover percentage as an estimate and production in the form of double sampling in relation to cover percentage. The results showed that with increasing plot area, the degree of correlation of plant indexes of Landsat image and their significance in relation to production and percentage of plant cover will increase. But this increase in community 2 is more dramatic in most respects with predominantly shrubs. As in this community, most of the studied indicators in 3 × 3 plot have a correlation and a reliable model, and in the three sizes of 1×1, 2×1 and 2×2 plots, the resulting models are not valid enough and have high RMSE. In community one with dominant broadleaf plants, only the model obtained in 1×1 plot and in community two with dominant plants, the model obtained in 1×1 and 1×2 plots are not statistically valid, although sometimes they have a significant correlation. The results of two different models are statistically different in communites 1 and 3 and there was no significant difference between them in community 2. According to the results of the study of indicators in terms of correlation and model validity, the two indicators NDVI and CTVI can be used in community 1, NDVI and TSAVI1 in community 2 and NDVI, NRVI and TSAVI1 in community 3 recommended for estimating production and percentage of plant cover using satellite images.
Ali Mohammadian; Esmaiel Asadi borujeni; Ataollah Ebrahimi; Pezhman Tahmasebi; Ali Asghar Naghipour
Volume 27, Issue 1 , April 2020, , Pages 84-97
Abstract
This study was was don to investigate the interaction of fire and grazing effects on index of vegetation diversity in Semi-steppe rangelands in Chaharmahal - Bakhtiari Province.Therefore, 16 sites was selected with different periods of fire and grazing intensity and 18 quadrates along transects ...
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This study was was don to investigate the interaction of fire and grazing effects on index of vegetation diversity in Semi-steppe rangelands in Chaharmahal - Bakhtiari Province.Therefore, 16 sites was selected with different periods of fire and grazing intensity and 18 quadrates along transects at each site were determined and then a systematic -random sampling method was don. Then, species diversity and Beta diversity indices were calculated. To determine the effects of fire, grazing, number of year and their interactions on the diversity indices, the method of General Linear Model (GML) and for determining the significant effect between fire site and unfired site the method of T- Test was used. The results showed that in areas with moderate grazing intensity and with different periods time of fire, Diversity, Simpson, Shannon and species richness indices, compared to control areas significantly increased. But beta diversity has decreased. Simpson's and Shannon Index compared to control areas significantly increased, in areas with high grazing and different time periods of fire, and in areas with 1-3 and 3-5 years fire, Species Richness was increased and decreased respectively. Also with different time periods of fire, beta diversity was decreased. Despite the restoration of some shrub species with the passage of time at burned areas, Compared to control, the grazing intensities was significantly decreased and the highest percentage of perennial grasses coverage was observed in fire areas in places with moderate grazing intensity. After the fire, appropriate management methods in Semi-Steppe Rangelands, can increase the Forage quality and also cause an increase in species richness.
Elham Banihashemi; Pezhman Tahmasebi; Esmael Asadi
Volume 25, Issue 3 , November 2018, , Pages 547-561
Abstract
Livestock grazing is one of the most important factors influencing on the structure and dynamics of the rangeland vegetation. The aim of this study was to identify the plant functional traits as the indicators for the effects of grazing management on Karsanak semi-steppe rangelands ...
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Livestock grazing is one of the most important factors influencing on the structure and dynamics of the rangeland vegetation. The aim of this study was to identify the plant functional traits as the indicators for the effects of grazing management on Karsanak semi-steppe rangelands of Chahar Mahal Va Bakhtiari province. A randomized-systematic sampling method was used to survey vegetation in seven grazed and enclosure sites by estimating plant cover in five plots of 4 m2 along a 100-m transect in each site. Then, the plant traits were measured and compared among grazed and enclosure sites. The results showed that there were significant differences between grazed and enclosure sites in several functional groups including plant height, leaf area, total plant weight , palatability class I and II, annuals and perennials, therophytes , and geophytes (P<0.05). The results also showed that the mean value of leaf length, the plant cover of species with palatability class II, forbs, and therophytes were significantly increased in non-grazed area compared to grazing area. The results of PCA showed that the most affecting factors responsible for overall changes in vegetation were plant weight, perennial and annual plant species, shrub growth form, chaemophytes, phanerophytes and phanerophytes forms, leaf length, leaf width, leaf area, and palatability class II and class III, justifying 60% of total variation in plant community composition. Combining the results of t-test and PCA, the results indicate that plant traits including total plant weight, leaf length and width, leaf area, palatability class, and life form are among the most important indicators to evaluate the effect of grazing managements on the structure and dynamics of vegetation in semi- steppe rangelands.
Jamal Imani; Ataollah Ebrahimi; Bahram Gholonejad; Pezhman Tahmasebi
Volume 25, Issue 1 , April 2018, , Pages 152-169
Abstract
Identifying and evaluating rangeland ecosystems is the first step in managing these resources. Without knowledge of rangeland condition, no management plan can be developed for it. For this purpose, three sites with different dominant species were selected for sampling. In each site, ...
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Identifying and evaluating rangeland ecosystems is the first step in managing these resources. Without knowledge of rangeland condition, no management plan can be developed for it. For this purpose, three sites with different dominant species were selected for sampling. In each site, 30 sampling units of 900 m2 were determined along three transects and sampling quadrates were established in these units. After correction and processing, the NDVI and SAVI indices were extracted from Landsat 8 images, and their correlation with vegetation cover percentage and production was calculated. The results showed that the correlation of indices with the vegetation cover percentage and production was significant in each of the three sites. In each site, the NDVI had the most correlation with dominant vegetation form, while SAVI reduced the effect of soil and was more related with low vegetation cover species. This is related to the SAVI equation and this index could reduce the effect of soil. The broadleaf species had the highest correlation with the NDVI index due to the plant structure and more reflection.
Jamal Imani; Ataollah Ebrahimi; Pejman tahmasebi; Bahram Gholinejad
Volume 24, Issue 2 , July 2017, , Pages 429-440
Abstract
The use of satellite data is one of the proper methods, which makes studying ecosystems less costly. This research was carried out to determine the correlation among the vegetation cover of dominant species in three sites with the NDVI index. For this purpose, a study was conducted on three different ...
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The use of satellite data is one of the proper methods, which makes studying ecosystems less costly. This research was carried out to determine the correlation among the vegetation cover of dominant species in three sites with the NDVI index. For this purpose, a study was conducted on three different vegetation types. In each region, a range was determined for sampling. Then, within this range and in the horizontal direction, 30 sampling units of 30 x 30 m were selected along three 900-meter transects in a random-systematic manner. In each sampling unit, nested quadrates with dimensions of 1 × 1, 2 × 2 m were placed. In order to prevent geometric errors, the 900-meter ranges were 60 meters apart. Within each sampling unit, geographic coordinates were recorded with GPS. The number of individuals and canopy cover percentage of dominant species were recorded separately in the plots. Then, the correlation of canopy cover percentage with NDVI index was obtained by processing Landsat 8 images. The distribution pattern was also determined using species density data. The results showed that in all species, the correlation coefficient of NDVI index was higher in the plots with higher area. Also, the correlation coefficient with one quadrat increased towards five quadrats. Due to the lack of high correlation between the total canopy cover percentage of a quadrat and the NDVI index, the use of one quadrat inside the pixel is not recommended in any way. Selecting the type of sampling depends on distribution pattern and species size as well as access to facilities and correlation coefficient acceptability. For species with clumped distribution, more quadrats are needed with proper distribution inside the pixel on the ground, so that sampling could be a good representation of the total pixel. In uniform distribution, fewer samples are needed since the whole pixel is the same in terms of plant growth.
ali goharnejad; pejman tahmasebi; esmael asadi; javad motamedi
Volume 24, Issue 1 , May 2017, , Pages 1-15
Abstract
In contrast to the taxonomic biodiversity, based only on the relative abundance of species in the community, functional diversity summarizes various aspects of the biological composition and, hence, the role of populations in the community. Functional diversity may be linked directly to the ecosystem ...
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In contrast to the taxonomic biodiversity, based only on the relative abundance of species in the community, functional diversity summarizes various aspects of the biological composition and, hence, the role of populations in the community. Functional diversity may be linked directly to the ecosystem services; the plant biomass encompasses many ecosystem services such as food supply, conservation, tourism, and pollination. In this study, we tested several hypotheses (1) existence of a close relationship between species richness and plant biomass (2) existence of a close relationship between FAD2 (Functional Diversity index) and plant biomass (3) explaining the high percentage of plant biomass variations. The results showed that the species richness in order to predict the plant biomass with a correlation coefficient equal to three does not count as a proper indicator. However, the correlation coefficient of FAD2 Functional Diversity with plant biomass was about 0.4, which is relatively good indicator to estimate the plant biomass because of explaining a significant percentage of the biomass variations. Finally, our results clearly showed that the incorporation of abiotic factors, plant traits and functional diversity (FAD2), containing the parameters of rainfall, leaf length, plant height and FAD2 index, could explain 75% of plant biomass variations and was considered as the most appropriate model predicts plant biomass.
Ali Asghar Naghipour borj; Jamaladdin Khaeddin; Hosein Bashari; Majid iravani; Pejman Tahmasebi
Volume 23, Issue 3 , January 2017, , Pages 442-453
Abstract
The structure and composition of plant communities are mainly affected by fire and grazing, especially in arid and semiarid rangelands. This study aimed to investigate the role of fire and grazing on soil seed bank characteristics (density, diversity and species richness) in semi-steppe rangelands of ...
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The structure and composition of plant communities are mainly affected by fire and grazing, especially in arid and semiarid rangelands. This study aimed to investigate the role of fire and grazing on soil seed bank characteristics (density, diversity and species richness) in semi-steppe rangelands of Central Zagros. A stratified random sampling was used to collect the data from 12 sites with one and five years after the last fire, and with long term light and heavy grazing history. Soil samples were collected in the autumn by auger from 0-5 and 5-10 cm from the soil surface, and the samples were cultivated in the greenhouse. All the germinated seeds were identified and counted for a 6-month period. The results showed that the one year after fire treatment under both light and heavy grazing resulted to a significant decrease in density, richness, and diversity of the soil seed bank. The richness and diversity of soil seed bank in the five-year after fire treatment and under light grazing pressure increased significantly compared to its control site. According to the results, the soil seed bank in 5 to 10 cm from the soil surface did not vary statistically under fire and grazing pressure, indicating the role of soil depth in reducing the impact of fire and grazing. Overall, it can be concluded that the grazing management after a fire event has a key role in vegetation restoration through its effects on the soil seed bank.