Juniperus procera is a tree species that dominates the natural forests of southwestern Saudi Arab... more Juniperus procera is a tree species that dominates the natural forests of southwestern Saudi Arabia. It is a very important species for its multiple uses and benefits for the locals for a long time. This species is suffering from the low capacity of natural regeneration so it is necessary to replant the deforested areas with seedlings grown from local seeds. Due to the sacristy of water, growing seedlings in the nurseries may face a shortage of water. Therefore, a pot experiment was carried out to examine the response of J. procera seedlings to water deficit. RCD was used including two watering treatments; every 3 days (well-water) and every 9 days (water deficit). After 180 days, water deficit caused decreases in stem height, total leaf area, branch number. Dry matter production reduced and by 68, 10, 40 and 56% for leaves, stem roots and whole plant, respectively. The relative growth rate, net assimilation rate, specific leaf area, leaf area ratio all reduced in water deficit. Relative water content and structural and non-structural carbon compounds in the leaves all reduced in water deficit and by 46, 12 and 24%. These results suggest that J. procera seedlings tolerated water deficit without marked injury, as they survived without losing much growth and looked shiny up to the end of the experiment.
The adverse effects of salinity on the growth of plants are well documented. These range between ... more The adverse effects of salinity on the growth of plants are well documented. These range between apparent symptoms and reduction of plant growth to death of the plant. Juniperus procera is the most widespread tree species that dominates the natural forests in southwestern Saudi Arabia and suffers from low capacity of the natural regeneration. Thus, there is a crucial need to grow the seedlings of this species in the nursery from local seeds and then planting them in these forests. Groundwater represents the main source of water used in agricultural irrigation and it classified as very saline water. A pot experiment was carried out using a randomized complete design with five replications and two treatments, mainly irrigation with high saline water (3500 ppm NaCl) and low saline water (500 ppm NaCl) to examine the growth of the J. procera seedlings under saline irrigation. The results revealed decreasing stem height, number of branches, total leaf area and consequently leaf, stem, root and total dry weight. Net assimilation rate (NAR) decreased due to high saline irrigation. There were also decreases in specific leaf area (SLA), leaf area ratio (LAR) and relative growth rate (RGR) but not significant. Irrigation with high saline water decreased the amount of both structural (SCC) and no-structural carbon compounds (NSCC). On the other hand, the percentage of non-structural carbon compounds (NSCC%) in the leaves, stem and roots of J. procera seedlings decreased in the high saline irrigation treatment at the expense of structural carbon compounds (SCC%). The ratios of non-structural/ structural carbon compounds (NSCC/SCC%) in the leaves, stem and the whole-plant of J. procera seedlings decreased significantly due to increasing the concentration of NaCl in the irrigation water from 500 ppm to 3500 ppm. The results suggest that J. procera seedlings tolerated the conditions of irrigation with saline water (i.e. 3500 ppm) and survived without showing any apparent injury.
Ensuring Sustainability in Forests Through the Participation of Locals: Implications for Extension Education, 2019
With very thin stands, the forests and other woody vegetation lands spread over a
limited area of... more With very thin stands, the forests and other woody vegetation lands spread over a limited area of 9770 km2, covering more or less 1.0% of the landmass of the Kingdom of Saudi Arabia (KSA), making it really a forest deficient country (World Bank 2014). The kingdom is blessed with a variety of landscapes like deserts, mountains and wadis representing a rich diversity of vegetation. Some stands of forests of varying degrees of density, volume, and age and species composition also thrive in the valleys of the desert areas, and some scattered scrubs can be noticed on the rangelands. According to the report submitted to UNCCD (2006), the Kingdom sustains a huge diversity of 2300 plant species on an area of about 2.7 million hectares representing roughly 1.35% of the total area of the Kingdom.
Desertification, its definition, features, causes, results and methods of combating it were addre... more Desertification, its definition, features, causes, results and methods of combating it were addressed.
The growth and biomass production of six acacia species were studied in the field for 4 years. Th... more The growth and biomass production of six acacia species were studied in the field for 4 years. The species used were Acacia asak, A. negrii, A. seyal, A. karroo, A. ampliceps, and A. stenophylla. The first three species are indigenous while the others are exotic. The results showed both A. ampliceps and A. asak with 100% survival while all A. negrii died. Acacia ampliceps attained the greatest height, diameter, relative growth rate and above-ground biomass while A. asak had the least. Height and diameter growth of acacia species decreased between warm and cold periods of the year.
19 and 10 acacia and eucalyptus exotic species were evaluated throughout 20 years to find out the... more 19 and 10 acacia and eucalyptus exotic species were evaluated throughout 20 years to find out their adaptability to the site which is afflicted by severe drought and salinity. After twenty years, some of the investigated species showed stability in the same degree of adaptability that was found in the previous assessment (i. e. after 5 and 10 years), while a group of the other species revealed a progress in the degree of adaptability to environmental conditions of the site and other species showed a decline in the degree adaptability. The evaluation showed that after twenty years, about half of the acacia species that were grown at the site had 100 percent survival rate while about half of the Eucalyptus species attained very good survival percentages. These results led to recommending planting most of those tree species at public and private garden in the similar sites.
Keywords: Acacia, adaptation, drought, Eucalyptus, salinity, Saudi Arabia
Three species of Casuarina namely C. Cunninghamiana, C. glauca and the natural hybrid C. Cunningh... more Three species of Casuarina namely C. Cunninghamiana, C. glauca and the natural hybrid C. Cunninghamiana X C. glauca were evaluated for their biomass production and volume. Seedlings of these species were planted in the year 1982 at initial spacing of 1.5 X 2.5 m in an experimental species trial under irrigation with treated municipal effluent. The experiment took place at the Agricultural Research station of the college of Agriculture at Dirab near Riyadh, Saudi Arabia. During the following years, repetitive selective thinning was applied to the whole experiment. At the age of 16 years, three trees from each species were randomly chosen and felled down. The dimensional parameters and biomass components of each tree were determined. The highest total above ground biomass “TAGB” (400 kg tree-1), as well as the highest merchantable stem volume “MV” (0.37 m3 tree-1) was recorded for C. Cunninghamiana followed by C. glauca (200 kg tree-1 and 0.21 m3 tree-1) then the hybrid (175 kg tree-1 and 0.19 m3 tree-1). Mathematical relationships were established for the prediction of both TAGB and MV using some dimensional parameters (e.g. diameter at breast height, DBH; total height, TH and merchantable height, MH). The correlation coefficients of these relationships were highly significant but differed according to species.
A survey of lignocellulosic agricultural residues was done in three major cities
of Saudi Arabia ... more A survey of lignocellulosic agricultural residues was done in three major cities of Saudi Arabia that were Dammam, Riyadh and Jeddah as a part of a research project conducted during 1999. Four of those materials namely pruning residues of street trees, planner sawdust of oak wood, mid rips date palm fronds and straw of wheat and barley were collected, prepared and mixed with cement to produce wood-cement boards. Both physical and mechanical properties of the manufactured boards were evaluated according to the American Society for Testing and Materials (ASTM). The results showed that the least significant increase in the weight of cement board after soaking in water for two hours was in those manufactured with date palm material compared with those contained either oak sawdust or pruning products. Similar trend was obtained longitudinal expansion after soaking in water for two or 24 hours where the least values were recorded for the boards manufactured with date palm material. The wood-cement boards contained oak sawdust surpassed all other boards in most of the mechanical properties measured. The woodcement boards manufactured with date palm material had significantly lower screw withdrawal power compared with those contained oak sawdust but did not vary from those contained pruning products. Manufacture wood-cement boards with straw particles of both wheat and barley had not succeeded that may indicate a presence of materials could not be removed through the method adopted in the present study and made the cement boards breakable.
Summary:
Effects of N supply, water stress and the water and nitrogen interaction on assimilat... more Summary:
Effects of N supply, water stress and the water and nitrogen interaction on assimilate partitioning in Populus ‘Balsam Spire’ hybrid (Populus balsamefera var. Muchuxii (Henery) × Populus trichocarpa var. Hastata (Dode) Farwell.) were studied through three greenhouse experiments.
The seedlings in the first experiment received either 1 or 3 or 9 mol N m-3 over almost a whole growing season. The growth of different parts of the trees increased markedly due to nitrogen supply. N supply increased whole tree photosynthesis through increasing total leaf area and decreased photosynthetic nitrogen use efficiency. Total respiration also increased with increasing N supply as a result of increasing leaf respiration and below-ground respiration. Below-ground respiration as a proportion of total respiration, however, decreased with increasing N supply. Nitrogen and carbon content and concentrations in different tree components and in the whole tree increased with increasing N supply. Partitioning of nitrogen into different parts of tree, however, showed no response to N supply. The proportion of carbon allocated to the leaves increased while that allocated to the roots decreased as a result of increasing N supply through increasing the concentrations of structural carbon compounds at the expense of those of non-structural carbon compounds. The ratio of total non-structural to total structural carbon compounds, therefore, increased with increasing N supply.
In the second experiment, three treatments were applied to trees in the second half of their growing season by withholding irrigation either suddenly or gradually. Water stress reduced growth of poplar with an earlier effect as a result of the sudden water-stressed treatment in comparison with the gradual water-stressed treatment. Although the sudden water-stressed trees adapted with time and performed similarly in growth to that of the gradual water-stressed trees in most variables measured, the means of the latter across harvests exceeded those of the sudden water-stressed treatment in many cases.
Water stress increased partitioning of dry matter to below-ground components through increasing the allocation of carbon into the roots as structural carbon compounds at the expense of non-structural carbon compounds. This increased carbon costs in below-ground respiration indicated by an increase in the proportion of fixed carbon respired through below-ground components and also increased below-ground respiratory intensity.
The study of the interaction between water and nitrogen was designed according to the results obtained from the first two studies. Four treatment combinations namely well-watered with high N, well-watered with low N, water-stress with high N, and water-stressed with low N were applied to 40-days-old seedlings. The stressed treatment combinations (well-watered with low N, water-stressed with high N, and water-stressed with low N) distinctly decreased growth of the trees compared with the control (well-watered with high N treatment). The frequent watering increased growth of trees at low N more than increasing N at water stress suggesting that fertilisation treatment to poplar when grown under water stress does not improve growth. The stressed treatments increased partitioning of dry matter to the roots at the expense of above-ground components. This implied an increase in the proportion of both N and C allocated to the roots. Increasing C partitioning into the roots was associated with an increasing concentration and partitioning of structural carbon compounds in the roots with a greater concentration and partitioning to the water-stressed trees at low N. Increasing partitioning of structural carbon compounds into the roots of the stressed trees increased the carbon costs in below-ground respiration where these trees partitioned greater proportions of their total respiration to below-ground components and in turn increased below-ground respiratory intensity, and also increased the proportion of fixed carbon respired through these components compared with above-ground components.
The natural forests of Saudi Arabia occupied a large area in the mountainous southwestern region.... more The natural forests of Saudi Arabia occupied a large area in the mountainous southwestern region. This forest area is considered a unique ecosystem in Saudi Arabia representing a semiarid zone while the rest of the country lies within arid zone. The forests in Saudi Arabia have been important for human life in this region for a long time, where it was the main source of woods used for house constructions, cooking and warming. In addition, they are important habitats for wildlife and flora. Now, they are open as recreation centers and for tourism. These forests have been suffering from varying degrees and types of degradation due to both human-induced and natural factors. Juniperus procera trees in these forests have exhibited a widespread decline with extensive tree dieback and die-off. Dieback is a phenomenon affects different tree species overall the world. It occurred in the natural forests of Saudi Arabia since about 35 years. Now, vast tracts in these forests are seen full of trees affected by dieback and die-off. The causes of dieback have not been clarified yet. Many researchers have expected natural disturbances, such as drought, sand storms, fire, and floods, insects and diseases, climate change that may lead to die-back and die-off. The magnitude of dieback of juniper trees vary from place to place and it existed in both lower and high areas. Indeed, it spreads overall the forest area in the southwestern Saudi Arabia. The percentage of juniper trees which are affected by dieback in Taif, Baha and Asir sub-region accounted for 5.1, 14.5 and 11.4, respectively. Solving this problem must base on information about its magnitude, effects, causes and then the way by which it can be eliminated.
Saudi Arabia is generally an arid country with a few exceptional subhumid regions on the southwes... more Saudi Arabia is generally an arid country with a few exceptional subhumid regions on the southwestern highlands. The southwestern highlands constitute one of the most fascinating and unusual ecoregions in the country with its natural forests. The main tree species prevailing in these forests is Juniperus procera Hochst. ex Endl. This species as well as other tree species are suffering an evident degradation due to different factors. Silvicultural practices are badly needed in order to rehabilitate the natural forests in Saudi Arabia. In this regard examining cross section characteristics and estimating the age of trees will offer the opportunity to obtain information about age, growth rates, and yield of these trees and to study the relation between tree growth and environmental factors. The results of the present investigation revealed that investigation of the disks from all sample trees showed that they had irregular shape and eccentric growth rings due to a lean form of the stem. Heartwood of Juniperus procera is purple red while sapwood is creamy white and they are clearly differentiated from each other with growth rings of both are distinct. Heartwood occupies the majority of the cross section surface at tree breast base (77.6%) while sapwood represented by only a narrow area (22%). So that the ratio of sapwood to heartwood accounted by about 28. Heart rot was seen in some of sampled trees. The estimate age of juniper trees in Taif ranged between 56 and 132 years with an average of 83 years while it was between 54 and 137 years with an average of 99 years in Baha region. Finally, the age of juniper trees in Asir region ranged between 52 and 142 years old with an average of 99.3 years. Key words: Juniperus procera, Cross section, Heartwood, Sapwood, Heart rot, age.
Hibiscus tiliaceus L. is the last tree species that has been spread in Riyadh City lately because... more Hibiscus tiliaceus L. is the last tree species that has been spread in Riyadh City lately because of its ability of tolerate the harsh environmental conditions and due to the beauty of its large yellow flowers. In the present study, four months old seedlings of Hibiscus tiliaceus were subjected to water stress (through withholding irrigation) and salinity (by increasing salt concentration in the irrigation water). Four treatments were applied to the plants growing in the pots included two levels of watering; every other day (well-watered treatment) and every 5 days (water stress treatment), and two levels of salinity (sodium chloride dissolved in the irrigation water); mainly tap water (0.97 dsm-1)(low salt concentration treatment) and 16 dsm-1 (high salt concentration treatment). The results showed that water stress decreased stem height and diameter, number of branches, total leaf area and specific leaf area. While increasing salt concentration caused decreases in stem height and diameter, number of leaves, total leaf area, leaf dry weight and specific leaf area. Both water stress and high salt concentration treatment resulted in a marked decrease in relative leaf water content and a significant increase in proline content in the leaves of Hibiscus tiliaceus seedlings. These results indicate that this species is tolerant to water and salinity stresses and suits the environmental conditions of Saudi Arabia.
Juniperus procera is a tree species that dominates the natural forests of southwestern Saudi Arab... more Juniperus procera is a tree species that dominates the natural forests of southwestern Saudi Arabia. It is a very important species for its multiple uses and benefits for the locals for a long time. This species is suffering from the low capacity of natural regeneration so it is necessary to replant the deforested areas with seedlings grown from local seeds. Due to the sacristy of water, growing seedlings in the nurseries may face a shortage of water. Therefore, a pot experiment was carried out to examine the response of J. procera seedlings to water deficit. RCD was used including two watering treatments; every 3 days (well-water) and every 9 days (water deficit). After 180 days, water deficit caused decreases in stem height, total leaf area, branch number. Dry matter production reduced and by 68, 10, 40 and 56% for leaves, stem roots and whole plant, respectively. The relative growth rate, net assimilation rate, specific leaf area, leaf area ratio all reduced in water deficit. Relative water content and structural and non-structural carbon compounds in the leaves all reduced in water deficit and by 46, 12 and 24%. These results suggest that J. procera seedlings tolerated water deficit without marked injury, as they survived without losing much growth and looked shiny up to the end of the experiment.
The adverse effects of salinity on the growth of plants are well documented. These range between ... more The adverse effects of salinity on the growth of plants are well documented. These range between apparent symptoms and reduction of plant growth to death of the plant. Juniperus procera is the most widespread tree species that dominates the natural forests in southwestern Saudi Arabia and suffers from low capacity of the natural regeneration. Thus, there is a crucial need to grow the seedlings of this species in the nursery from local seeds and then planting them in these forests. Groundwater represents the main source of water used in agricultural irrigation and it classified as very saline water. A pot experiment was carried out using a randomized complete design with five replications and two treatments, mainly irrigation with high saline water (3500 ppm NaCl) and low saline water (500 ppm NaCl) to examine the growth of the J. procera seedlings under saline irrigation. The results revealed decreasing stem height, number of branches, total leaf area and consequently leaf, stem, root and total dry weight. Net assimilation rate (NAR) decreased due to high saline irrigation. There were also decreases in specific leaf area (SLA), leaf area ratio (LAR) and relative growth rate (RGR) but not significant. Irrigation with high saline water decreased the amount of both structural (SCC) and no-structural carbon compounds (NSCC). On the other hand, the percentage of non-structural carbon compounds (NSCC%) in the leaves, stem and roots of J. procera seedlings decreased in the high saline irrigation treatment at the expense of structural carbon compounds (SCC%). The ratios of non-structural/ structural carbon compounds (NSCC/SCC%) in the leaves, stem and the whole-plant of J. procera seedlings decreased significantly due to increasing the concentration of NaCl in the irrigation water from 500 ppm to 3500 ppm. The results suggest that J. procera seedlings tolerated the conditions of irrigation with saline water (i.e. 3500 ppm) and survived without showing any apparent injury.
Ensuring Sustainability in Forests Through the Participation of Locals: Implications for Extension Education, 2019
With very thin stands, the forests and other woody vegetation lands spread over a
limited area of... more With very thin stands, the forests and other woody vegetation lands spread over a limited area of 9770 km2, covering more or less 1.0% of the landmass of the Kingdom of Saudi Arabia (KSA), making it really a forest deficient country (World Bank 2014). The kingdom is blessed with a variety of landscapes like deserts, mountains and wadis representing a rich diversity of vegetation. Some stands of forests of varying degrees of density, volume, and age and species composition also thrive in the valleys of the desert areas, and some scattered scrubs can be noticed on the rangelands. According to the report submitted to UNCCD (2006), the Kingdom sustains a huge diversity of 2300 plant species on an area of about 2.7 million hectares representing roughly 1.35% of the total area of the Kingdom.
Desertification, its definition, features, causes, results and methods of combating it were addre... more Desertification, its definition, features, causes, results and methods of combating it were addressed.
The growth and biomass production of six acacia species were studied in the field for 4 years. Th... more The growth and biomass production of six acacia species were studied in the field for 4 years. The species used were Acacia asak, A. negrii, A. seyal, A. karroo, A. ampliceps, and A. stenophylla. The first three species are indigenous while the others are exotic. The results showed both A. ampliceps and A. asak with 100% survival while all A. negrii died. Acacia ampliceps attained the greatest height, diameter, relative growth rate and above-ground biomass while A. asak had the least. Height and diameter growth of acacia species decreased between warm and cold periods of the year.
19 and 10 acacia and eucalyptus exotic species were evaluated throughout 20 years to find out the... more 19 and 10 acacia and eucalyptus exotic species were evaluated throughout 20 years to find out their adaptability to the site which is afflicted by severe drought and salinity. After twenty years, some of the investigated species showed stability in the same degree of adaptability that was found in the previous assessment (i. e. after 5 and 10 years), while a group of the other species revealed a progress in the degree of adaptability to environmental conditions of the site and other species showed a decline in the degree adaptability. The evaluation showed that after twenty years, about half of the acacia species that were grown at the site had 100 percent survival rate while about half of the Eucalyptus species attained very good survival percentages. These results led to recommending planting most of those tree species at public and private garden in the similar sites.
Keywords: Acacia, adaptation, drought, Eucalyptus, salinity, Saudi Arabia
Three species of Casuarina namely C. Cunninghamiana, C. glauca and the natural hybrid C. Cunningh... more Three species of Casuarina namely C. Cunninghamiana, C. glauca and the natural hybrid C. Cunninghamiana X C. glauca were evaluated for their biomass production and volume. Seedlings of these species were planted in the year 1982 at initial spacing of 1.5 X 2.5 m in an experimental species trial under irrigation with treated municipal effluent. The experiment took place at the Agricultural Research station of the college of Agriculture at Dirab near Riyadh, Saudi Arabia. During the following years, repetitive selective thinning was applied to the whole experiment. At the age of 16 years, three trees from each species were randomly chosen and felled down. The dimensional parameters and biomass components of each tree were determined. The highest total above ground biomass “TAGB” (400 kg tree-1), as well as the highest merchantable stem volume “MV” (0.37 m3 tree-1) was recorded for C. Cunninghamiana followed by C. glauca (200 kg tree-1 and 0.21 m3 tree-1) then the hybrid (175 kg tree-1 and 0.19 m3 tree-1). Mathematical relationships were established for the prediction of both TAGB and MV using some dimensional parameters (e.g. diameter at breast height, DBH; total height, TH and merchantable height, MH). The correlation coefficients of these relationships were highly significant but differed according to species.
A survey of lignocellulosic agricultural residues was done in three major cities
of Saudi Arabia ... more A survey of lignocellulosic agricultural residues was done in three major cities of Saudi Arabia that were Dammam, Riyadh and Jeddah as a part of a research project conducted during 1999. Four of those materials namely pruning residues of street trees, planner sawdust of oak wood, mid rips date palm fronds and straw of wheat and barley were collected, prepared and mixed with cement to produce wood-cement boards. Both physical and mechanical properties of the manufactured boards were evaluated according to the American Society for Testing and Materials (ASTM). The results showed that the least significant increase in the weight of cement board after soaking in water for two hours was in those manufactured with date palm material compared with those contained either oak sawdust or pruning products. Similar trend was obtained longitudinal expansion after soaking in water for two or 24 hours where the least values were recorded for the boards manufactured with date palm material. The wood-cement boards contained oak sawdust surpassed all other boards in most of the mechanical properties measured. The woodcement boards manufactured with date palm material had significantly lower screw withdrawal power compared with those contained oak sawdust but did not vary from those contained pruning products. Manufacture wood-cement boards with straw particles of both wheat and barley had not succeeded that may indicate a presence of materials could not be removed through the method adopted in the present study and made the cement boards breakable.
Summary:
Effects of N supply, water stress and the water and nitrogen interaction on assimilat... more Summary:
Effects of N supply, water stress and the water and nitrogen interaction on assimilate partitioning in Populus ‘Balsam Spire’ hybrid (Populus balsamefera var. Muchuxii (Henery) × Populus trichocarpa var. Hastata (Dode) Farwell.) were studied through three greenhouse experiments.
The seedlings in the first experiment received either 1 or 3 or 9 mol N m-3 over almost a whole growing season. The growth of different parts of the trees increased markedly due to nitrogen supply. N supply increased whole tree photosynthesis through increasing total leaf area and decreased photosynthetic nitrogen use efficiency. Total respiration also increased with increasing N supply as a result of increasing leaf respiration and below-ground respiration. Below-ground respiration as a proportion of total respiration, however, decreased with increasing N supply. Nitrogen and carbon content and concentrations in different tree components and in the whole tree increased with increasing N supply. Partitioning of nitrogen into different parts of tree, however, showed no response to N supply. The proportion of carbon allocated to the leaves increased while that allocated to the roots decreased as a result of increasing N supply through increasing the concentrations of structural carbon compounds at the expense of those of non-structural carbon compounds. The ratio of total non-structural to total structural carbon compounds, therefore, increased with increasing N supply.
In the second experiment, three treatments were applied to trees in the second half of their growing season by withholding irrigation either suddenly or gradually. Water stress reduced growth of poplar with an earlier effect as a result of the sudden water-stressed treatment in comparison with the gradual water-stressed treatment. Although the sudden water-stressed trees adapted with time and performed similarly in growth to that of the gradual water-stressed trees in most variables measured, the means of the latter across harvests exceeded those of the sudden water-stressed treatment in many cases.
Water stress increased partitioning of dry matter to below-ground components through increasing the allocation of carbon into the roots as structural carbon compounds at the expense of non-structural carbon compounds. This increased carbon costs in below-ground respiration indicated by an increase in the proportion of fixed carbon respired through below-ground components and also increased below-ground respiratory intensity.
The study of the interaction between water and nitrogen was designed according to the results obtained from the first two studies. Four treatment combinations namely well-watered with high N, well-watered with low N, water-stress with high N, and water-stressed with low N were applied to 40-days-old seedlings. The stressed treatment combinations (well-watered with low N, water-stressed with high N, and water-stressed with low N) distinctly decreased growth of the trees compared with the control (well-watered with high N treatment). The frequent watering increased growth of trees at low N more than increasing N at water stress suggesting that fertilisation treatment to poplar when grown under water stress does not improve growth. The stressed treatments increased partitioning of dry matter to the roots at the expense of above-ground components. This implied an increase in the proportion of both N and C allocated to the roots. Increasing C partitioning into the roots was associated with an increasing concentration and partitioning of structural carbon compounds in the roots with a greater concentration and partitioning to the water-stressed trees at low N. Increasing partitioning of structural carbon compounds into the roots of the stressed trees increased the carbon costs in below-ground respiration where these trees partitioned greater proportions of their total respiration to below-ground components and in turn increased below-ground respiratory intensity, and also increased the proportion of fixed carbon respired through these components compared with above-ground components.
The natural forests of Saudi Arabia occupied a large area in the mountainous southwestern region.... more The natural forests of Saudi Arabia occupied a large area in the mountainous southwestern region. This forest area is considered a unique ecosystem in Saudi Arabia representing a semiarid zone while the rest of the country lies within arid zone. The forests in Saudi Arabia have been important for human life in this region for a long time, where it was the main source of woods used for house constructions, cooking and warming. In addition, they are important habitats for wildlife and flora. Now, they are open as recreation centers and for tourism. These forests have been suffering from varying degrees and types of degradation due to both human-induced and natural factors. Juniperus procera trees in these forests have exhibited a widespread decline with extensive tree dieback and die-off. Dieback is a phenomenon affects different tree species overall the world. It occurred in the natural forests of Saudi Arabia since about 35 years. Now, vast tracts in these forests are seen full of trees affected by dieback and die-off. The causes of dieback have not been clarified yet. Many researchers have expected natural disturbances, such as drought, sand storms, fire, and floods, insects and diseases, climate change that may lead to die-back and die-off. The magnitude of dieback of juniper trees vary from place to place and it existed in both lower and high areas. Indeed, it spreads overall the forest area in the southwestern Saudi Arabia. The percentage of juniper trees which are affected by dieback in Taif, Baha and Asir sub-region accounted for 5.1, 14.5 and 11.4, respectively. Solving this problem must base on information about its magnitude, effects, causes and then the way by which it can be eliminated.
Saudi Arabia is generally an arid country with a few exceptional subhumid regions on the southwes... more Saudi Arabia is generally an arid country with a few exceptional subhumid regions on the southwestern highlands. The southwestern highlands constitute one of the most fascinating and unusual ecoregions in the country with its natural forests. The main tree species prevailing in these forests is Juniperus procera Hochst. ex Endl. This species as well as other tree species are suffering an evident degradation due to different factors. Silvicultural practices are badly needed in order to rehabilitate the natural forests in Saudi Arabia. In this regard examining cross section characteristics and estimating the age of trees will offer the opportunity to obtain information about age, growth rates, and yield of these trees and to study the relation between tree growth and environmental factors. The results of the present investigation revealed that investigation of the disks from all sample trees showed that they had irregular shape and eccentric growth rings due to a lean form of the stem. Heartwood of Juniperus procera is purple red while sapwood is creamy white and they are clearly differentiated from each other with growth rings of both are distinct. Heartwood occupies the majority of the cross section surface at tree breast base (77.6%) while sapwood represented by only a narrow area (22%). So that the ratio of sapwood to heartwood accounted by about 28. Heart rot was seen in some of sampled trees. The estimate age of juniper trees in Taif ranged between 56 and 132 years with an average of 83 years while it was between 54 and 137 years with an average of 99 years in Baha region. Finally, the age of juniper trees in Asir region ranged between 52 and 142 years old with an average of 99.3 years. Key words: Juniperus procera, Cross section, Heartwood, Sapwood, Heart rot, age.
Hibiscus tiliaceus L. is the last tree species that has been spread in Riyadh City lately because... more Hibiscus tiliaceus L. is the last tree species that has been spread in Riyadh City lately because of its ability of tolerate the harsh environmental conditions and due to the beauty of its large yellow flowers. In the present study, four months old seedlings of Hibiscus tiliaceus were subjected to water stress (through withholding irrigation) and salinity (by increasing salt concentration in the irrigation water). Four treatments were applied to the plants growing in the pots included two levels of watering; every other day (well-watered treatment) and every 5 days (water stress treatment), and two levels of salinity (sodium chloride dissolved in the irrigation water); mainly tap water (0.97 dsm-1)(low salt concentration treatment) and 16 dsm-1 (high salt concentration treatment). The results showed that water stress decreased stem height and diameter, number of branches, total leaf area and specific leaf area. While increasing salt concentration caused decreases in stem height and diameter, number of leaves, total leaf area, leaf dry weight and specific leaf area. Both water stress and high salt concentration treatment resulted in a marked decrease in relative leaf water content and a significant increase in proline content in the leaves of Hibiscus tiliaceus seedlings. These results indicate that this species is tolerant to water and salinity stresses and suits the environmental conditions of Saudi Arabia.
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limited area of 9770 km2, covering more or less 1.0% of the landmass of the
Kingdom of Saudi Arabia (KSA), making it really a forest deficient country (World
Bank 2014). The kingdom is blessed with a variety of landscapes like deserts,
mountains and wadis representing a rich diversity of vegetation. Some stands of
forests of varying degrees of density, volume, and age and species composition also
thrive in the valleys of the desert areas, and some scattered scrubs can be noticed on
the rangelands. According to the report submitted to UNCCD (2006), the Kingdom
sustains a huge diversity of 2300 plant species on an area of about 2.7 million hectares
representing roughly 1.35% of the total area of the Kingdom.
Keywords: Acacia, adaptation, drought, Eucalyptus, salinity, Saudi Arabia
Saudi Arabia. During the following years, repetitive selective
thinning was applied to the whole experiment. At the age of 16
years, three trees from each species were randomly chosen and felled down. The dimensional parameters and biomass components of each tree were determined. The highest total above ground biomass “TAGB” (400 kg tree-1), as well as the highest merchantable stem volume “MV” (0.37 m3 tree-1) was recorded for C. Cunninghamiana followed by C. glauca (200 kg tree-1 and 0.21 m3 tree-1) then the hybrid (175 kg tree-1 and 0.19 m3 tree-1). Mathematical relationships were established for the prediction of both TAGB and MV using some dimensional parameters (e.g. diameter at breast height, DBH; total height, TH and merchantable height, MH). The correlation coefficients of these relationships were highly significant but differed according to species.
of Saudi Arabia that were Dammam, Riyadh and Jeddah as a part of a research project
conducted during 1999. Four of those materials namely pruning residues of street trees,
planner sawdust of oak wood, mid rips date palm fronds and straw of wheat and barley
were collected, prepared and mixed with cement to produce wood-cement boards. Both
physical and mechanical properties of the manufactured boards were evaluated according to
the American Society for Testing and Materials (ASTM). The results showed that the least
significant increase in the weight of cement board after soaking in water for two hours was
in those manufactured with date palm material compared with those contained either oak
sawdust or pruning products. Similar trend was obtained longitudinal expansion after
soaking in water for two or 24 hours where the least values were recorded for the boards
manufactured with date palm material. The wood-cement boards contained oak sawdust
surpassed all other boards in most of the mechanical properties measured. The woodcement
boards manufactured with date palm material had significantly lower screw
withdrawal power compared with those contained oak sawdust but did not vary from those
contained pruning products. Manufacture wood-cement boards with straw particles of both
wheat and barley had not succeeded that may indicate a presence of materials could not be
removed through the method adopted in the present study and made the cement boards
breakable.
Effects of N supply, water stress and the water and nitrogen interaction on assimilate partitioning in Populus ‘Balsam Spire’ hybrid (Populus balsamefera var. Muchuxii (Henery) × Populus trichocarpa var. Hastata (Dode) Farwell.) were studied through three greenhouse experiments.
The seedlings in the first experiment received either 1 or 3 or 9 mol N m-3 over almost a whole growing season. The growth of different parts of the trees increased markedly due to nitrogen supply. N supply increased whole tree photosynthesis through increasing total leaf area and decreased photosynthetic nitrogen use efficiency. Total respiration also increased with increasing N supply as a result of increasing leaf respiration and below-ground respiration. Below-ground respiration as a proportion of total respiration, however, decreased with increasing N supply. Nitrogen and carbon content and concentrations in different tree components and in the whole tree increased with increasing N supply. Partitioning of nitrogen into different parts of tree, however, showed no response to N supply. The proportion of carbon allocated to the leaves increased while that allocated to the roots decreased as a result of increasing N supply through increasing the concentrations of structural carbon compounds at the expense of those of non-structural carbon compounds. The ratio of total non-structural to total structural carbon compounds, therefore, increased with increasing N supply.
In the second experiment, three treatments were applied to trees in the second half of their growing season by withholding irrigation either suddenly or gradually. Water stress reduced growth of poplar with an earlier effect as a result of the sudden water-stressed treatment in comparison with the gradual water-stressed treatment. Although the sudden water-stressed trees adapted with time and performed similarly in growth to that of the gradual water-stressed trees in most variables measured, the means of the latter across harvests exceeded those of the sudden water-stressed treatment in many cases.
Water stress increased partitioning of dry matter to below-ground components through increasing the allocation of carbon into the roots as structural carbon compounds at the expense of non-structural carbon compounds. This increased carbon costs in below-ground respiration indicated by an increase in the proportion of fixed carbon respired through below-ground components and also increased below-ground respiratory intensity.
The study of the interaction between water and nitrogen was designed according to the results obtained from the first two studies. Four treatment combinations namely well-watered with high N, well-watered with low N, water-stress with high N, and water-stressed with low N were applied to 40-days-old seedlings. The stressed treatment combinations (well-watered with low N, water-stressed with high N, and water-stressed with low N) distinctly decreased growth of the trees compared with the control (well-watered with high N treatment). The frequent watering increased growth of trees at low N more than increasing N at water stress suggesting that fertilisation treatment to poplar when grown under water stress does not improve growth. The stressed treatments increased partitioning of dry matter to the roots at the expense of above-ground components. This implied an increase in the proportion of both N and C allocated to the roots. Increasing C partitioning into the roots was associated with an increasing concentration and partitioning of structural carbon compounds in the roots with a greater concentration and partitioning to the water-stressed trees at low N. Increasing partitioning of structural carbon compounds into the roots of the stressed trees increased the carbon costs in below-ground respiration where these trees partitioned greater proportions of their total respiration to below-ground components and in turn increased below-ground respiratory intensity, and also increased the proportion of fixed carbon respired through these components compared with above-ground components.
of the disks from all sample trees showed that they had irregular shape and eccentric growth rings due to a lean form of the stem. Heartwood of Juniperus procera is purple
red while sapwood is creamy white and they are clearly differentiated from each other with growth rings of both are distinct. Heartwood occupies the majority of the cross
section surface at tree breast base (77.6%) while sapwood represented by only a narrow area (22%). So that the ratio of sapwood to heartwood accounted by about 28. Heart rot
was seen in some of sampled trees. The estimate age of juniper trees in Taif ranged between 56 and 132 years with an average of 83 years while it was between 54 and 137
years with an average of 99 years in Baha region. Finally, the age of juniper trees in Asir region ranged between 52 and 142 years old with an average of 99.3 years.
Key words: Juniperus procera, Cross section, Heartwood, Sapwood, Heart rot, age.
applied to the plants growing in the pots included two levels of watering; every other day (well-watered treatment) and every 5 days (water stress treatment), and two levels of salinity (sodium chloride dissolved in the irrigation water); mainly tap water (0.97 dsm-1)(low salt concentration treatment) and 16 dsm-1 (high salt concentration treatment). The results showed that water stress decreased stem height and diameter, number of branches, total leaf area and specific leaf area. While increasing salt concentration caused decreases in stem height and diameter, number of leaves, total leaf area, leaf dry weight and specific leaf area. Both water stress and high salt concentration treatment resulted in a marked decrease in relative leaf water content and a significant increase in proline content in the leaves of Hibiscus tiliaceus seedlings. These results indicate that this species is tolerant to water and salinity stresses and suits the environmental conditions of Saudi Arabia.
limited area of 9770 km2, covering more or less 1.0% of the landmass of the
Kingdom of Saudi Arabia (KSA), making it really a forest deficient country (World
Bank 2014). The kingdom is blessed with a variety of landscapes like deserts,
mountains and wadis representing a rich diversity of vegetation. Some stands of
forests of varying degrees of density, volume, and age and species composition also
thrive in the valleys of the desert areas, and some scattered scrubs can be noticed on
the rangelands. According to the report submitted to UNCCD (2006), the Kingdom
sustains a huge diversity of 2300 plant species on an area of about 2.7 million hectares
representing roughly 1.35% of the total area of the Kingdom.
Keywords: Acacia, adaptation, drought, Eucalyptus, salinity, Saudi Arabia
Saudi Arabia. During the following years, repetitive selective
thinning was applied to the whole experiment. At the age of 16
years, three trees from each species were randomly chosen and felled down. The dimensional parameters and biomass components of each tree were determined. The highest total above ground biomass “TAGB” (400 kg tree-1), as well as the highest merchantable stem volume “MV” (0.37 m3 tree-1) was recorded for C. Cunninghamiana followed by C. glauca (200 kg tree-1 and 0.21 m3 tree-1) then the hybrid (175 kg tree-1 and 0.19 m3 tree-1). Mathematical relationships were established for the prediction of both TAGB and MV using some dimensional parameters (e.g. diameter at breast height, DBH; total height, TH and merchantable height, MH). The correlation coefficients of these relationships were highly significant but differed according to species.
of Saudi Arabia that were Dammam, Riyadh and Jeddah as a part of a research project
conducted during 1999. Four of those materials namely pruning residues of street trees,
planner sawdust of oak wood, mid rips date palm fronds and straw of wheat and barley
were collected, prepared and mixed with cement to produce wood-cement boards. Both
physical and mechanical properties of the manufactured boards were evaluated according to
the American Society for Testing and Materials (ASTM). The results showed that the least
significant increase in the weight of cement board after soaking in water for two hours was
in those manufactured with date palm material compared with those contained either oak
sawdust or pruning products. Similar trend was obtained longitudinal expansion after
soaking in water for two or 24 hours where the least values were recorded for the boards
manufactured with date palm material. The wood-cement boards contained oak sawdust
surpassed all other boards in most of the mechanical properties measured. The woodcement
boards manufactured with date palm material had significantly lower screw
withdrawal power compared with those contained oak sawdust but did not vary from those
contained pruning products. Manufacture wood-cement boards with straw particles of both
wheat and barley had not succeeded that may indicate a presence of materials could not be
removed through the method adopted in the present study and made the cement boards
breakable.
Effects of N supply, water stress and the water and nitrogen interaction on assimilate partitioning in Populus ‘Balsam Spire’ hybrid (Populus balsamefera var. Muchuxii (Henery) × Populus trichocarpa var. Hastata (Dode) Farwell.) were studied through three greenhouse experiments.
The seedlings in the first experiment received either 1 or 3 or 9 mol N m-3 over almost a whole growing season. The growth of different parts of the trees increased markedly due to nitrogen supply. N supply increased whole tree photosynthesis through increasing total leaf area and decreased photosynthetic nitrogen use efficiency. Total respiration also increased with increasing N supply as a result of increasing leaf respiration and below-ground respiration. Below-ground respiration as a proportion of total respiration, however, decreased with increasing N supply. Nitrogen and carbon content and concentrations in different tree components and in the whole tree increased with increasing N supply. Partitioning of nitrogen into different parts of tree, however, showed no response to N supply. The proportion of carbon allocated to the leaves increased while that allocated to the roots decreased as a result of increasing N supply through increasing the concentrations of structural carbon compounds at the expense of those of non-structural carbon compounds. The ratio of total non-structural to total structural carbon compounds, therefore, increased with increasing N supply.
In the second experiment, three treatments were applied to trees in the second half of their growing season by withholding irrigation either suddenly or gradually. Water stress reduced growth of poplar with an earlier effect as a result of the sudden water-stressed treatment in comparison with the gradual water-stressed treatment. Although the sudden water-stressed trees adapted with time and performed similarly in growth to that of the gradual water-stressed trees in most variables measured, the means of the latter across harvests exceeded those of the sudden water-stressed treatment in many cases.
Water stress increased partitioning of dry matter to below-ground components through increasing the allocation of carbon into the roots as structural carbon compounds at the expense of non-structural carbon compounds. This increased carbon costs in below-ground respiration indicated by an increase in the proportion of fixed carbon respired through below-ground components and also increased below-ground respiratory intensity.
The study of the interaction between water and nitrogen was designed according to the results obtained from the first two studies. Four treatment combinations namely well-watered with high N, well-watered with low N, water-stress with high N, and water-stressed with low N were applied to 40-days-old seedlings. The stressed treatment combinations (well-watered with low N, water-stressed with high N, and water-stressed with low N) distinctly decreased growth of the trees compared with the control (well-watered with high N treatment). The frequent watering increased growth of trees at low N more than increasing N at water stress suggesting that fertilisation treatment to poplar when grown under water stress does not improve growth. The stressed treatments increased partitioning of dry matter to the roots at the expense of above-ground components. This implied an increase in the proportion of both N and C allocated to the roots. Increasing C partitioning into the roots was associated with an increasing concentration and partitioning of structural carbon compounds in the roots with a greater concentration and partitioning to the water-stressed trees at low N. Increasing partitioning of structural carbon compounds into the roots of the stressed trees increased the carbon costs in below-ground respiration where these trees partitioned greater proportions of their total respiration to below-ground components and in turn increased below-ground respiratory intensity, and also increased the proportion of fixed carbon respired through these components compared with above-ground components.
of the disks from all sample trees showed that they had irregular shape and eccentric growth rings due to a lean form of the stem. Heartwood of Juniperus procera is purple
red while sapwood is creamy white and they are clearly differentiated from each other with growth rings of both are distinct. Heartwood occupies the majority of the cross
section surface at tree breast base (77.6%) while sapwood represented by only a narrow area (22%). So that the ratio of sapwood to heartwood accounted by about 28. Heart rot
was seen in some of sampled trees. The estimate age of juniper trees in Taif ranged between 56 and 132 years with an average of 83 years while it was between 54 and 137
years with an average of 99 years in Baha region. Finally, the age of juniper trees in Asir region ranged between 52 and 142 years old with an average of 99.3 years.
Key words: Juniperus procera, Cross section, Heartwood, Sapwood, Heart rot, age.
applied to the plants growing in the pots included two levels of watering; every other day (well-watered treatment) and every 5 days (water stress treatment), and two levels of salinity (sodium chloride dissolved in the irrigation water); mainly tap water (0.97 dsm-1)(low salt concentration treatment) and 16 dsm-1 (high salt concentration treatment). The results showed that water stress decreased stem height and diameter, number of branches, total leaf area and specific leaf area. While increasing salt concentration caused decreases in stem height and diameter, number of leaves, total leaf area, leaf dry weight and specific leaf area. Both water stress and high salt concentration treatment resulted in a marked decrease in relative leaf water content and a significant increase in proline content in the leaves of Hibiscus tiliaceus seedlings. These results indicate that this species is tolerant to water and salinity stresses and suits the environmental conditions of Saudi Arabia.