Effects of Soil and Topography Variables on Canopy Cover of Dorema ammoniacum D.Don. in Soltan Mohammad Rangeland, Sabzevar, Iran
Alireza Arian
1
(
Assistant Prof. of Khorasan Razavi Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Mashhad, Iran
)
Majid Dashti
2
(
Associate Prof. of Khorasan Razavi Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Mashhad, Iran
)
Keywords:
Abstract :
Effects of Soil and Topography Variables on Canopy Cover of Dorema ammoniacum D.Don. in Soltan Mohammad Rangeland, Sabzevar, Iran
Alireza Ghasemi Arian A* and Majid Dashti B
Abstract.
Environmental factors have a huge impact on yield and distribution of plant species. For this purpose, the response of Dorema ammoniacum (Apiaceae( canopy cover to some environmental factors was investigated in its habitat in south of Sabzevar, Iran in 2020. Generalized Additive Models (GAM) was used to investigate the response of this species to soil and topography factors. The results showed that the edaphic and physiographic factors of the habitat had significant effect on the canopy size of D.ammoniacum. The response of canopy size to some environmental factors as (sand, litter, organic matter, lime, pH, N, P, K and altitude followed a monotonic increase model. By increasing these factors the canopy size of D. ammoniacum increased. However, the reaction of D. ammoniacum canopy cover in confronting with the gradient of clay, slope, EC, and SAR ensued the monotonic decrease model and with increasing these factors, the canopy percentage of D. ammoniacum decreased. Results of the soil study showed that the plant is principally distributed on sandy loam and loamy sand soils. The reaction pattern of D. ammoniacum canopy cover in confronting with the gradient of silt, bare soil, and stone and gravel followed unimodal model and the optimal levels for them were 1%, 30%, and 1%, respectively. Generally, investigation of D. ammoniacum canopy reaction to gradient of some environmental factors gave us profitable data for characterizing the ecological demands of this plant. In the other words, awareness of the impact of environmental factors on Vasha canopy cover helps us in preparing proper arable lands for planting this important species and recovering its destroyed habitats.
Keywords: Dorema ammoniacum, Environmental factors, GAM, Sabzevar, Rangeland
Introduction
Plant communities have undergone changed over time due to the profit-seeking human intervention in nature, such as environmental destruction, overexploitation of natural resources, increase in greenhouse gases, etc. (Siahmansour et al., 2022; Pickett and White, 1985). Recent studies show that the biomass of Iran's forests and pastures has decreased (Dashti et al., 2018; Heidari Sharifabad and Torknejad, 2000). Some factors such as overgrazing and off-season grazing as well as increasing the number of livestock in the rangeland, over time, lead to changes in plant composition, reduced rangelands production and regression in the (Dashti et al., 2020; Heidari Sharifabad and Torknejad, 2000).
Vasha plant (Dorema ammoniacum D. Don) from Apiaceae, also known as Oshke and Kandal, is an endangered plant (Ghasemi Arian, 2016). Vasha is a hemicryptophyte, perennial plant and monocarpic plant with leaves consisting of a number of leaflets and yellow flowers; Schizocarp fruit, bulky roots, and 1 to 2 m tall stem with gum-containing tubes running throughout the stem and root. Vasha gum, which seeps naturally from the stem, is used in the pharmaceutical and industry (Zargari, 1992; Mozaffarian, 2016; Amiri and Joharchi, 2016). The area of Vasha habitat in Iran is about 140,000 ha, which is located in arid and semi-arid zones of South Khorasan, Razavi Khorasan, Yazd, Kerman, Isfahan and Sistan and Baluchistan provinces, Iran (Ghasemi Arian, 2016). Vasha is a rare species that grows only in Iran, Afghanistan, Pakistan and parts of northern India (Irvani et al., 2010; Delnavazi et al., 2014).
Understanding the ecological characteristics of plants and their response to environmental factors can give us good information about the conservation and their reproduction in similar areas (Gholami et al., 2002). The study of interactions between vegetation, climate, soil, and landforms agents have an important topic in ecological studies (Guisan and Zimmermann, 2000). Studies show that although limited studies have been conducted on the ecological characteristics of Vasha, most of these studies are qualitative and so far, no research has been done on the expression of the response of this important plant to environmental agents.
There are a number of ecological studies on the relationship between plant distribution and edaphic agents. Some statistical methods are used to analyze the abundance of species and others are used to study the agents affecting the dispersal of plant species and predict their suitable (Tomy et al., 2021; Bakkenes et al., 2002; Peterson, 2001; Berg et al., 2004; Robertson, 2003; Engler et al., 2004). Various mathematical models are used in studies related to the reaction of plants to environmental factors. The Canonical correspondance analysis (CCA) method can quantitatively investigate the reaction of plants to edaphic factors by relying on agents affecting the dispersal of species using the generalized incremental model (GAM) (Traoré et al., 2012). The GAM model, due to its exponential functions, enables it to fine-tune nonlinear relationships between different variables (Guisan et al., 2002). The GAM model optimizes the prediction accuracy of the dependent variable and reduces the standard error by improving the robust analysis between the independent variables and the plant response to edaphic factors (Vaziri Nasab et al., 2013; Salehi et al., 2012; Mirdavoodi, 2013).
Literature review shows that the GAM model has been used in several rangeland and forest ecosystems in Iran. Mirdavoodi (2013) used the GAM model to investigate the response of some species to edaphic factors. He found that the reaction of some plants to excessive grazing causes an increase on soil bulk density. Another researcher reported that yarrow and Bromus tomentellus react differently to altitude. Also, the percentage of sand in the soil had a positive effect on the dispersal of B. tomentellus, but this factor does not have a favorable effect on the presence of yarrow (Achilla millefolium) (Heidari Sharifabad and Torknejad, 2000).
Considering that the Vasha plant is a rare and endangered species. Therefore, this study was conducted with the aim of investigating the response of D. ammoniacum canopy percentage to soil and topographical variables using GAM model to determine the reaction of Vasha canopy area to environmental factors. Also, the results of this research can be used to restore other damaged habitats of this species.
Materials and Methods
To investigate some environmental factors affecting D. ammoniacum canopy cover percentage, and some of its important companion plants such as (Artemisia sieberi, Convolvulus orientalis, Rosa persica, and Scariola orientaslis) a habitat named Sultan Mohammad (75 km south of Sabzevar, located in the Shekasteh region in Razavi Khorasan province, Iran) was selected in 2020 (Table 1 and Fig. 1).
Fig 1. D. ammoniacum habitat in Soltan Mohammad rangeland located in south of Sabzevar, Iran
Table 1. Physiographic, climatic, soil and vegetation type characteristics of D. ammoniacum habitat in Khorasan Razavi province, Sabsevar, Iran.
Characteristics | Soltan Mohammad rangeland |
Longitude | 57°30′25″ to 57°30′30″ E |
Latitude | 35°42′15″ to 35°42′21″ N |
Plant types | Artemisia sieberi - Convolvulus orientalis |
Condition of plant type | Poor |
Trend of Plant type | Downward |
Density of D. ammoniacum | 0.19/m2 |
Chorotype | Irano-Tourani region |
Ecological zone type | Steppe |
Mean annual precipitation (mm) | 166 |
Mean annual temperature (oC) | 14.5 |
Climate* | Cold arid |
Altitude (m. asl) | 1400-1500 |
Mean slope (%) | 1-12 |
Geographical aspects | Flat |
Landform | Plain & hill |
Soil texture | Sandy loam |
Lithology | Quaternary |
* Climate conditions according to Emberger classification
Sampling of vegetation and environmental factors was performed by systematic-random method (Dashti et al., 2021; Arzani and Abedi, 2015). For sampling of vegetation and soil, we divided the Vasha habitat into 4 classes (0-3%, 3-6%, 6-9%, and 9-12%) based on land slope. Then in each of the slope classes, four transects with a length of 1000 m were randomly selected (Mirdavoudi et al., 2021) and in each transect, five plots with an area of 4 m2 (minimal area by Releve method) were placed at an equal distance (200 m) from each other. Then all vegetation data were measured at the flowering stage of D. ammoniacum. The measured data in each plot were canopy cover percentage of D. ammoniacum, and other species and the amount (litter, gravel, rock) and bare soil percentage. To investigate the effect of some ecological factors on canopy cover of D. ammoniacum, a soil sample was collected from each plot to the depth of the plant root (0-50 cm). The soil analysis including percentage of sand, silt, and clay by Bouyoucos-hydrometer, N by Kjeldahl method, P by Olsen method, K by Flame photometer, EC by electrical conductivity method, SAR by sodium absorption ratio formula, pH by electrometric method, organic carbon content (OC%) by walkley black method, and lime by titration method were measured (Robertson et al., 1999). Among the factors related to physiological studies of Vasha habitat, aspect, slope and altitude were measured by GPS in each plot. To investigate the phenology of D. ammoniacum, we examined its vegetative and reproductive growth stages during 3 years (2018-2020). For this purpose, we selected 10 random Vasha plants inside each plot and took notes their phenological stages every 10 day (Dashti et al., 2021) (Fig. 7).
Data Analysis
To investigate the relationship between environmental factors and the canopy cover percent of D. ammoniacum, we used the Detrended Correspondence Analysis (DCA) method as a nonlinear model and obtained the gradient length. Due to the length of the first axis in DCA was less than 3, we used the RDA1 method. First, environmental factors were parted into 3 groups including soil (sand, silt, clay, pH, EC, lime, N, P, K, and organic matter), topography (altitude, and slope), rock outcrop (bare soil, rock, and gravel, and litter), then spatial correlation between sample plots was investigated (Borcard et al., 1992). In this study the data analysis was performed by Canoco software version 4.5 (Ter Braak and Smilauer, 2002). For plotting the reaction of D. ammoniacum to environmental agents, we used the GAM model (Bakkenes et al., 2002; Godefroid and Koedam, 2004; Traoré et al., 2012). We used the Akaike Information Criterion (AIC) to rank the environmental variables affecting the D. ammoniacum canopy cover (Akaike, 1974). Therefore, the smaller the AIC value, the greater the variable effect on the canopy coverage percentage, in other words, the proposed model is the most suitable model for fitting the response curve of the species. In this research, we used the percentage of D. ammoniacum D. ammoniacum canopy to peruse the relationship between species and environmental factors and Gaussian response was calculated (Ardekani, 2009).
Results
Vegetation Attributes
The results showed that Artemisia sieberi, Convolvulus orientalis, Rosa persica, Carex physodes, and D. ammoniacum D. ammoniacum had the highest canopy cover percentage with the amounts of 2.94, 2.86, 2.35, 2.22, 1.82, and 1.14 respectively. In addition to D.ammoniacum, there are 39 plant species belonging to 38 genera from 23 families in Vasha habitat. The average of soil factors along with some environmental features of D. ammoniacum D. ammoniacum habitat are given in Table 2. The average percentage of D. ammoniacum D. ammoniacum canopy and some important species of Vasha habitat is demonstrated in Fig. 2.
Table 2. Average features of physiography, soil, and canopy cover in D. ammoniacum habitat
Slope (%) | Altitude (m) | Aspect | Vasha canopy cover (%) | Total canopy cover (%) | Litter (%) | Gravel & rock (%) | Bare soil (%) |
6.6 | 1461 | Non aspect | 1.14 | 32.1 | 10.59 | 10.62 | 46.69 |
Fig 2. Mean canopy cover percentage for major species in Soltan Mohammad habitat
Habitat characteristics
The results of physiography and climate studies showed that D. ammoniacum species grows in low slope and no aspect lands. Altitude changes for this species were obtained from 1420 to 1503 m above sea level. Precipitation and temperature data indicated that Vasha plant can resist a drop or rise in temperatures (Ghasemi Arian, 2016). Other results related to soil analysis demonstrated that Vasha plant prefers sandy-loamy texture, alkaline pH, low organic matter, and low exchangeable sodium ratio (SAR) (Tables 3 and 4).
Table 3. Minimum, Maximum and mean values Physiographic and climatic characteristics of D. ammoniacum habitat
Physiography Climate |
Alt. (m) slope (%) precipitation (mm) Temperature (oC) |
Min. 1420 1 0.6 -5 Max. 1503 12.5 33.8 34 Mean 1462 6.6 166 15 |
Table 4. Minimum and maximum environmental factors in D. ammoniacum habitat
Factor | Sand(%) | Silt(%) | Clay(%) | pH | EC | SAR | Lime (%) | N(%) | P(%) | K ppm | OM(%) | Litter (%) | Rock & ravel(%) | Bare soil(%) |
Min. | 51 | 4 | 4 | 7.9 | 0.5 | 0.35 | 14 | 0.01 | 1.8 | 190 | 0.01 | 7 | 7 | 31.4 |
Max. | 83 | 34 | 18 | 8.3 | 0.88 | 0.6 | 34 | 0.07 | 8 | 450 | 0.27 | 15 | 25 | 56.9 |
Mean | 69 | 19 | 12 | 8 | 0.81 | 0.47 | 24 | 0.03 | 5 | 307 | 0.41 | 10.6 | 15.6 | 41.6 |
Table 4. Minimum and maximum and mean values of environmental factors in D. ammoniacum habitat
Environmental factors | Min. | Max. | Mean |
Sand (%) | 51.0 | 83.0 | 69.0 |
Silt (%) | 4.0 | 34.0 | 19.0 |
Clay (%) | 4.0 | 18.0 | 12.0 |
pH | 7.9 | 8.3 | 8.0 |
EC | 0.50 | 0.88 | 0.81 |
SAR | 0.35 | 0.60 | 0.47 |
Lime (%) | 14.0 | 34.0 | 24.0 |
N (%) | 0.01 | 0.07 | 0.03 |
P (%) | 1.8 | 8.0 | 5.0 |
K (ppm) | 190 | 450 | 307 |
OM (%) | 0.01 | 0.27 | 0.41 |
Litter (%) | 7.0 | 15.0 | 10.6 |
Rock & ravel (%) | 7.0 | 25.0 | 15.6 |
Bare soil (%) | 31.4 | 56.9 | 41.6 |
Altitude (m) | 1420 | 1503 | 1462 |
Slope (%) | 1.0 | 12.5 | 6.6 |
Precipitation (mm) | 0.6 | 33.8 | 166.0 |
Temperature (C°) | -5.0 | 34.0 | 15.0 |
Relationship between canopy cover and environmental factors
Using canonical classification model, 8 variables were selected from 16 primary variables. Selected variables among physiographic and soil factors are slope, clay, rock and gravel, litter, pH, lime, EC, and P respectively (Table 5).
Table 5. The major eight environmental factors effective in D. ammoniacum growth
Environmental factors | Variance | F values |
Slope | 11.6 | 7.6** |
Clay | 4.9 | 3.3** |
pH | 3.8 | 2.7** |
EC | 2.9 | 2.1** |
CaCo3 | 3.2 | 2.3** |
Litter | 3.1 | 2.3** |
P | 2.3 | 1.7* |
Rock & gravel | 2.1 | 1.6* |
*, ** are significant level at 0.05 and 0.01, respectively
Data analysis showed that the total variance of vegetation in the RDA method is equal to 17799.4 which is equivalent to 33.8% of the total variance. In the RDA model, using spatial correlation and considering all selected variables as limiting variables, finally 8 variables including slope, clay, pH, EC, lime, litter, phosphorus and gravel are obtained among 16 main variables (Table 5). Vasha’s ecological gradient showed that the first axis with an eigenvalue of 0.12, 12.4% and the second axis with an eigenvalue of 0.07, 19.7% can justify the vegetation variations. Fig. 3 shows the results of plant species distribution related to ecological gradient in the first and second axes of the RDA model.
In Fig. 3, the interval of species from the coordinate axes demonstrates the power the relationship. In one hand, the greater the distance of the species from the center of the axes, the less environmental factors affect their distribution, but on the other hand the greater the correlation between environmental agents, the D.ammuniacum and other accompanying species have a stronger relationship with the characteristics of environmental factors. As well as, the larger the length of vectors and the smaller their angles with the axes, the greater the correlation between environmental factors with the growth of D. ammoniacum and other plants of habitat.
Fig. 3. Plant species distribution related to ecological gradients
The results of analysis of variables in the GAM model indicated that more of environmental factors had a significant effect on the canopy cover percentage of D. ammoniacum (Table 7).
Table 7. The level of Significant of environmental variables in the GAM model
Environmental factors | F | Akaike Information Criterion (AIC) |
Sand (%) | 8.2** | 72.32 |
Silt (%) | 3.0* | 85.35 |
Clay (%) | 10.7** | 14.79 |
pH | 10.8** | 67.06 |
EC (ds/m) | 9.5** | 69.80 |
SAR | 9.2** | 70.20 |
CaCO3 (%) | 9.6** | 69.23 |
N (%) | 22.8** | 49.40 |
P (%) | 9.4** | 69.72 |
K (ppm) | 10.0** | 68.44 |
OM (%) | 10.5** | 67.83 |
Slope (%) | 9.2** | 70.45 |
Altitude (m) | 10.7** | 67.87 |
Litter (%) | 7.5** | 73.76 |
Bare soil (%) | 31.1* | 41.49 |
Stone & gravel (%) | 2.2ns | 88.73 |
* and ** = significant at P< 0.05 and P< 0.01 probability level, ns: not significant
The response of D. ammoniacum canopy cover percentage in relation to the environmental variables (sand, litter, organic matter, lime, pH, N, P, K, and Altitude,) conformed the monotonic increase model and canopy cover percentage of Vasha increased with increasing these factors, (Fig. 4a-h & Fig. 5o), But it decreased with the increase of some gradients such as clay, slope, EC and SAR (Fig 5i-l).
The canopy cover percentage of Vasha in relation to the factors of silt, stone & gravel and bare soil, showed that the response of D. ammoniacum to these agents was unimodal. According to Figs 5j and 5p, first with increasing the amount of silt up to 12% and gravel up to 10%, the D. ammoniacum canopy increased, then with further increase of these factors, the D. ammoniacum canopy decreased. Contrarily, with the increase of bare soil up to 45%, the D. ammoniacum canopy decreased, and after that with increasing this factor the D. ammoniacum canopy increased (Fig. 5m).
Fig 4. D. ammoniacum responses to Sand (a), Litter (b), OM (c), clay (d), pH (e), N (f), P (g), and K (h)
Fig 5. D. ammoniacum responses to Sand (a), Litter (b), OM (c), clay (d), pH (e), N (f), P (g), and K (h), Clay (i), Silt (j), EC (k), SAR (l), Bare soil (m), Slope (n), Altitude (o), Stone & Gravel (p)
Phenology of D. ammoniacum