Abstract

The present study has been carried out in Al Baha region, southwest of Saudi Arabia. Five land use types were selected, namely abandoned terraces, communal areas, protected areas (enclosure areas), national parks and settlement areas. The quadrat of 25m * 25 m was laid over the different land uses to study the vegetation structure, plant composition, plant diversity and seedlings regenerating status. The results showed a total of 365 plant species belong to 72 families. The similarity in plant species composition among the land uses types was high in the abandoned terraces and protected areas with 92 %. The class distribution size of regenerated plant species was normal in abandoned terraces and protected areas but this normal trend was disturbed irregularly in communal areas, national parks and settlement areas due to a high level of human interference. However, a higher average of disturbance among the land uses was found to be significant with p- a value of 0.04 and 0.001 respectively. This amount of disturbance severely affecting the seedlings recruitment especially in the communal and settlement areas, indicating that there is an urgent need for planning the sustainable management for the appropriate measure to overcome the problem. IVI index revealed that there are somehow similarities in species composition between both communal areas and settlement areas. The outcomes of this study concluded that understanding the conflicts between human activities and land uses has to be taken into consideration for developing and sustainable management plans in futures. Therefore, the reduction of disturbances and creating participation management plans with local and indigenous people is essential to enhance the sustainability of the forests.

1. Introduction

The kingdom of Saudi Arabia has initiated significant changes in land use and vegetation cover since the government took a plan 30 years ago of exhaustive domestic development as a result of massive oil incomes ¹. In addition to the high complication to anthropogenic interference and climatic changes, the deterioration and degradation of the plant ecosystem are critical. This may be attributed to the extension of urbanization especially in the southwest of Saudi Arabia which is considered the most sensitive habitat for human disturbances due to the area geographical characteristic. The expected results to be occurred in such habitat are soil erosion, habitat loss and dieback of the conifer forest. These factors are leading to shrinkages in the plant populations and maybe extend or threat some sensitive species to the changes in the ecological aspect. Therefore, alteration in biological populations is expected to occur to immediate rates as human activities and global climate changes are increasing ². The government has initiated many of the protected areas (PAs) and National Parks (NPS) to enhance the restoration of the vegetation cover and increase biodiversity. Saudi Wildlife Authority (SWA) manages 15 protected areas around the kingdom, with an area of 86,582.4 km² (4.5%) of the total land ³. Further plan has been set to extend the protected areas to reach the total of 22 areas, covering approximately 10.42 % of the country (208,356 km²) and provides local communities with socio-economic benefits such as regulated and sustainable use of grazing, hunting, fishing, and other related recreational and tourism opportunities ^{4, 5}. However, the concept of land use management in Saudi Arabia is relatively not well-established ⁴. These could be attributed to the fact that people so far are not yet ready to lose their benefits of using the lands for grazing, woodcutting, and urbanization. Therefore, a lack of awareness may also be the obstacle and barrier for decision-makers to plan and set the package for land uses management, development, and restoration. Although, FAO ⁶ mentioned the rapid deterioration of forest cover from 2,728000 hectares to 977000 hectares from 1996 to 2008 respectively. Generally, such an approach to management plan often results in conflicts between local communities. This conflict may occur and increase forests' violation due to firewood smugglings and fire. Aref et al. ⁷ stated that forests of Southwestern Saudi Arabia are degraded and loss of environmental equilibrium as a result of changes has occurred to natural streams by road construction, conversion of natural forests to parks, random expanding in constructional, agricultural activities and fires. FAO ⁶ also confirmed the fact that the forests of Saudi Arabia are threatened by severe environment and human interaction factors including agricultural and urban expansion as well as firewood collection. The interaction of human activities and environmental factors is accelerated by a lack of qualified forestry personnel in comparison to the optimum required to implement the activities necessary to sustainably manage the resources. Darfaoui and Al Assiri ⁸ reported that both pasturelands and woodlands encounter critical challenges in Saudi Arabia, as a result of harsh environmental conditions (drought, unfertile soil) and anthropogenic pressures, (overutilization of firewood, over browsing and grazing, expansion of unmanaged civilization and serious recreation). However, the biological ecosystems are considered as being at risk with climatic changes in KSA including highlands forests and woodlands.

The government of Saudi Arabia has started several officials and/or legislative procedures and established many projects, to reduce the deterioration of forest lands, enhance the conservation plan, expand and develop existing forests. For instance, it signed a Memorandum of understanding with the Food and Agriculture Organization of the United Nations for partnership and cooperation in forest rehabilitation and conservation.

To enhance the government and other organizing efforts in developing and sustainable management of rangeland and forestry in Saudi Arabia, this study was conducted, to demonstrate the impact of land uses and sustainable management on vegetation cover and species richness, and to elevate the awareness among the local community to maintain and sustainable uses of lands.

2. Materials and Methods

Al Baha region is located in the southwest of the KSA, between the latitude of 19/20 and longitude of 41/42. The region is characterized by high mountains within the continental dry climate but alleviated by Al-Sarawat Mountains above the sea level and their exposure to humid winds blowing from the narrow strap of Tihama in western Saudi Arabia which forms a moderate climate in summer and cool in winter. It contains diverse physiographic features such as mountain peaks, highland plateaus, moderate to steep slope mountains and valleys, with an altitude ranges from 200 to 2485 m above the sea level.

The region is well known by having high plant diversity dominated by Juniperus procera, Acacia ehrenbergiana, A. asak, A. origena, Olea europaea, and Dodonaea viscose communities covering different ecological zones. Agricultural terraces spread over the high mountainous areas and produce field crops such as lentils millet wheat, sorghum, sesame, barley and vegetable crops like peppers, potatoes, a local pumpkin, tomatoes, carrots and others ⁹.

The study area is confined to the high mountains and plateau of the Al-Baha region stretching along the mountain chain from Baljurashi province in the south to Al Mandaq province, in the north between altitudes of 1900 m. a.s.l to 2385 m. a.s.l. The land use types in the region were classified to 5 land use types, they are found scattered on different ecological zones, few of them are overlapping or close to each other, the selected study sites were laid on these different land use types as shown in Figure 1 namely abandoned terraces, communal areas, protected areas (enclosure areas), national parks and settlement areas (Figure 1).

To demonstrate the impact of land uses on plant richness and diversity, five different overlapping land uses namely abandoned terraces, national parks, fenced areas (protected areas), communal areas and settlement areas were selected to be surveyed and evaluated. A single scale sampling method was used for sampling procedures described by Synnott ¹⁰; larpkern et al. ¹¹; Devi Prasad and Al-Sagheer ¹². In each land use, sixteen quadrats of 25*25m were constructed from a randomly chosen point in the area. To enumerate plant species richness and diversity in the quadrats system, all plant species were counted and morphologically identified to the species level using our experiences, a Handbook of Yemen Flora by Wood ¹³. Wildflowers of Saudi Arabia by Collenette ¹⁴: Flora of the Arabian Peninsula and Socotra by Miller et al. ¹⁵. Within each quadrat, four smaller plots of 1 m2 were laid out in the four corners of quadrat to evaluate the regeneration state to reach a total of sixty-four plots in each land uses. All tree species < 30 cm GBH (girth at breast height) were considered regenerated seedlings and enumerated separately into regeneration classes based on their height and girth, i.e., Class IV (Young trees) >100 cm height and >10 cm GBH, Class III (Poles) >100 cm height and<10 cm GBH, class II (saplings) between 40-100 cm height and class I (seedlings) <40 cm height ^{12, 16, 17}. To make comparative assessments of plant diversity and species richness in different land use, a human disturbance was taken into consideration as a mean driver of altering the vegetation structure and composition ^{16, 18, 19, 20}. Disturbances were taken into consideration based on the assumption that each land uses received different amounts of disturbances according to the land management plan and closer or distance to human activities. Therefore, a sign of disturbances like the formation of a footpath, presence of cut stumps or broken stems, domestic animal dungs (DAN) and animal grazing was measured. These factors were recorded in all quadrats and scores were given based on the author's observation on the amount of disturbance. Four levels of disturbance were set to each parameter namely high, medium, low and absent, with values of 1 to 4 for each parameter. The value of 1 was considered as the absence of disturbance whereas the value of 4 was considered as a severe disturbance ²¹.

Species richness was analyzed using the following methods:

Direct count of species

Species richness was computed by using the direct count of species number in equal size samples. ¹¹.

Shannon's diversity index, ²²

(1)

Where pi is the proportion of individuals of species in I the species.

Jaccard Similarity index ²³

(2)

Where c is the number of species present only in quadrat 2, b is the number of species present in the quadrat 1 and a is the total number of species present in both quadrats or samples being compared.

Rarity index

Relative species richness and species abundance are described as core elements of biodiversity ²⁴. Relative abundance refers to how rare or common species is relative to other species in a certain area or community ²⁵. Therefore, the rarity index was assessed from the calculation of the relative frequency of each plant species ²⁶.

Important value index for plant species (IVI)

Species importance value (IVI) was adapted for the assessment of the distribution of species abundance which is calculated by the following formula ^{27, 28}.

(3)

(4)

(5)

(6)

Published date of soil physical and chemical characteristics of Ragadan forest R3SI was copied from Forest inventory project in the southwestern region of Saudi Arabia, Volume III, and Inventory of natural forests in the second zone ²⁹.

Pearson correlation coefficients were computed between species diversity and disturbance parameters and soil characters based on Mukaka ³⁰.

3. Results and Discussion

The outcome of comparative studies on species structure and composition among different land uses came on a par with the fact that species structure and diversity status are deeply impacted by land uses. And it also came on a par with the Authors’ expectations and many researchers’ work. Mutalemwa ³¹ studied the influence of different land uses types on birds and tree species diversity around lake Victoria Basin and the results showed that fishing zone had high bird diversity while the highest diversity in tree species was recorded in forest reserve land use. This could mainly be attributed to the poor land management resulted in degraded large amounts of land, reducing the ability to produce enough food, and consist a major threat to rural livelihoods in many developing countries ³². Similarly, in the present study, many changes had been occurred due to the different land uses as shown in Table 1. The total plant species and families found in the study areas were counted to be 365 species and 72 families. This is considered high compared to a similar study conducted by Howladar et al ³³ in the same geographical areas. The highest number of species richness was recorded in abandoned terraces followed by protected areas, settlement areas, communal areas and national parks with the numbers 201, 168, 128, 110 and 72 respectively. Although, plant density per hectare showed the same trend of species richness with high value in the abandoned terraces (450 plants/ha) and protected areas (499 plants/ha) compared with communal areas, national parks and settlement areas with value of 297.3 plant/ha, 248 plant/ha and 256 plant/ha respectively, also they reported that a total of 224 species representing 56 families of vascular plants are found in Al Baha catchment areas. The floristic composition of the different geomorphologic landscape units showed differences in species richness. Abandoned terraces seem to be a good habitat for plant species and showed the highest species richness and diversity (Shannon and Weaver diversity index) with 202 and 2.19 respectively. National parks showed less richness and diversity 72 and 1.701 respectively.

This variation in species richness and diversity can be related to the characters and the history of disturbance received of each land use for decades. High level of diversity and rich land in abandoned terraces and protected areas are mainly due to protection status, less value of cumulative disturbance index and may also be related to the fertile soil conditions, especially the moisture content and nutrient availability. Arevalo et al. ³⁴ found that diversity and species richness were significantly found higher in the terraced plots when compared with the control plots. This also indicates differences in environmental and edaphic conditions. For a long time, the terrace soils have been prepared for the purpose of increasing yields and, once neglected, the level of the disturbance is not as high as with other disturbances (although the remaining soils generally offer characteristics for natural regeneration). These suitable conditions increase productivity and in some cases could be associated with higher diversity ^{35, 36, 37}. The outcome of this study revealed that disturbance was the main driver for alteration the species composition and diversity structures as shown in Table 2. However, species richness and diversity were found to be more in the abandoned terraces, protected areas when compared with the national parks, settlement areas indicating differences in cumulative average of disturbance parameters. The high average of disturbance was recorded in settlement areas, national parks and, communal areas with an average of 2.69, 2.40 and 2.13 respectively whereas the lowest were observed in abandoned terraces and protected areas with a cumulative value of 1.87 and 1.42 respectively. The average value of disturbance parameters such as lopping, cut stumps, road construction, fire, weeds, grazing, and footpath showed significant differences among parameters in different land uses P-value =0.04 and was highly significant among the land uses P-value 0.001.

As a consequence of disturbance, similarities (Jaccard index) in species composition and structures among different land uses have been found to be interesting (Table 3). They have been found to be high between abandoned terraces and protected areas (92%). The similarity between communal areas and settlement areas was found to be very high (95%) indicating that species composition did not differ and could be considered similar. This may be related to the amount of disturbance occurring in both land uses as shown in Table 2. Similarly, the higher vegetation abundance in the terraces may be related to better soil conditions, particularly the higher water and nutrient availability ³⁴. The communal areas, settlement areas, and national parks are open access areas and are exposed to an increasing amount of disturbance, resulting in an alteration of the species composition and forest structure ³⁸.

Although, disturbance changed the plant frequency in sampling plots, resulting in altering the species composition and structure. However, rare species were to be high in the communal areas, settlement areas and parks with a value of 85, 70, and 65%. Similarly, the common species were less in the same land uses with 15, 30, and 35% respectively as shown in Figure 2. The biological diversity of the open access areas (communal areas, settlement areas, and parks) are rapidly depleted due to the direct and indirect consequences of human activities. Rare species are generally thought to be more extinction prone than generalist or common species ³⁹, as a consequence of human activities, which is reportedly making forest ecosystems more prone to damage by altering the frequency, intensity, and timing of fire events ⁶

The arrangement of species in different land uses was thought to be affected by disturbance parameters as shown in Table 4. However, the alteration species arrangement was expected to change in different land uses. For instance, the dominant plant species in abandoned terraces were Cynodon dactylon, Cenchrus ciliaris, Urtica urens, Acacia origena and Onopordum heteracanthum and ranked from one to five, with an IVI value of 137.51, 125.38, 113.10, 102.30 and 94.30 respectively. On the other hand, the set of species, namely Erodium neuradifolium, Typha elephantine, Ipomoea sinensis subsp. blepharosepala, Centaurea pseudosinaica and Hyparrhenia hirta were ranked the top five dominated species with an IVI value 100.02, 94.17, 77.78, 75.00 and 75.00 in the communal areas, respectively whereas Typha elephantine, Centaurea pseudosinaica and Hyparrhenia hirta ranked seven, five and two in the settlement areas with an IVI value of 84.6, 95.00 and 115, respectively.

Interestingly, some similarities in species ranking were found with top five dominant plant species in abandoned terraces, national parks and protected areas. Hence, Cynodon dactylon and Cenchrus ciliaris were ranked first and third with an IVI value of 114.53 and 95.67 in the national parks, and third and second with an IVI value of 106.25 and 106.26 in the protected areas. Therefore, the partial similarities in the dominance of plant species among abandoned terraces, protected areas, and national parks from on the one hand and communal areas and settlement areas on the other were believed to be attributed to disturbance parameters, management plan, and ecological adaptation and site factors. Thus, the interactions among the environmental, edaphic and geographic factors finally resulted in controlling formation of vegetation types for each land use. Moro et al. ⁴⁰ investigated phylogenetic patterns along environmental gradients related to edaphic environment and climate in the Caatinga, in Brazil. The results showed that dissimilarities in plant clustering were likely to reflect a variety of environmental factors at different sites or times. Pelissier ⁴¹ stated that the varied distribution and dominance of species across the sites could be attributed to the topography of the region and micro environmental condition. Moreover, species rank and their values in different land uses seemed to be affected by disturbances as shown in Table 2.

Seedlings recruitment and regenerated plant species were deeply impacted by anthropogenic disturbances especially in communal areas, settlement areas, and parks. However, the open-access areas for human disturbances altered the natural process of plant regeneration and showed irregularly shaped curved classes as shown in Figure 3. The frequency of the seedlings in classes I, II, III, and IV have unregulated distribution in contrast with areas that have less disturbance. The reason could be related to open access areas and exposition to cattle grazing, trampling and other human activities; in addition to the fact that the life cycle of plant species is impacted and plants did not bear fruits (seeds) naturally. These findings are expected due to the high average of disturbance in such land uses as shown in Table 2. Vazquez-Yanes and Orozco-Segovia ⁴² reported that seed establishment may also be affected by the intensity of disturbance while less intense disturbances such as canopy opening may induce many seeds to recruit. In both abandoned terraces and protected areas, size class follows a reverse J-shaped curve (Figure 1), which indicates the normal trend of regeneration. The frequency of the seedling in the first regeneration class (I) was the highest compared with the second (II), third (III) and the fourth (IV) regeneration classes. The stable trend has been obtained due to fewer disturbances and the remaining soils in the terraces and protected areas that offer favorable habitats for natural regeneration. These results came on a par with the findings of Boring et al. ⁴³; Lange and Graham ⁴⁴; Khan et al. ⁴⁵. They reported that the regeneration of tree species is greatly influenced by the interaction of biotic factors and environmental factors. Such favored interactions and also relatively lower disturbance levels as evidenced by the cumulative disturbance index could be attributed to health regeneration.

Disturbances and soil characteristics played a significant role in species diversity and dominance. Therefore, the alteration in species composition and vegetation structure in land-use types was the consequence of interaction among edaphic, geographic, environmental and anthropogenic factors. However, the Pearson correlation coefficient matrix showed a relatively significant correlation between some parameters with species richness and diversity as shown in Table 5. For instance, cut stumps, road construction, grazing, fire, and footpath had a significant negative correlation with the plant richness with value r=.-0.815, r=-0.716, r=-0.391, r= -0.924 and r=-0.665 respectively. Similarly, road construction was negatively correlated with the Number of Shannon’s diversity index, density, and frequency with a value of r= -0.730, r= -0.421, r=-0.852 and r=-0.987 respectively. Grazing also negatively correlated with species richness, a number of individuals, Shannon’s diversity index, density, and frequency with a value of r=-0.391, r=-0.467,r=-0.605 and r=-0.810 and -0.722. Road construction, especially in the sensitive habitats, have mostly negative effects on the distribution and dominancy of native plants than positive effects ^{46, 47}. Soil traits are a key driver for plant biological processes and an important limiting factor for plant richness and diversity. This effect was even more pronounced in the positively correlated between clay and species richness, a number of individuals, Shannon’s diversity index, density and frequency with a value of r=0.859, r=0.628, r=0.465, r=0.684 and r=0.818, respectively. This finding came according to the finding of Dolarslan et al. ⁴⁸.

4. Conclusion

Species richness, Shannon Diversity Index, evenness and density were higher in the abandoned terraces and protected areas than national parks, communal areas, and settlement areas. These variations were driven by the cumulative disturbance index which is found to be significant among the different disturbance indexes and land uses types. However, the size class distribution of regenerated seedlings in abandoned terraces and protected areas showed a reverse J-shaped curve revealing the normal status of regeneration. This finding has been obtained due to fewer disturbances whereas the normal trend has been disturbed in the communal areas, settlement areas, and national parks, indicating the presence of disturbances in the land use types. Rarity index showed that the land uses with high disturbance have more rare plant species, indicating the impact of disturbance on alteration of species composition and forest structure. An important value index showed clearly the impact of disturbance in altering species dominance and distribution among land uses. Thus, the success of future management and conservation strategy depends on how it can reduce the amount of disturbance and enhance seedlings recruitment in settlements areas and communal areas. However, serious steps have to be taken either by researchers or decision-makers to enhance conservation plan strategies and elevating awareness among indigenous people.

Acknowledgements

The authors appreciate the constant help and work facility provided by the Ministry of Environment, Water and Agriculture branch in Al-Baha. Also, they would like to thank Dr. Mutee al-Sarory for his valuable time in reviewing the paper linguistically.

References