Dwarf mistletoes are parasitic flowering plants that infect conifers, resulting in substantial loss of growth and mortality. Recently, forest managers in Iran are contemplating whether infection of Juniperus polycarpo...Dwarf mistletoes are parasitic flowering plants that infect conifers, resulting in substantial loss of growth and mortality. Recently, forest managers in Iran are contemplating whether infection of Juniperus polycarpos C. Koch forests by dwarf mistletoe, Arceuthobium oxycedri （DC.） M. Bieb, influences tree vigor and contributes to insuffieient natural regeneration. The present study aimed at assessing the severity of infection and its impact on growth and reproductive output of./., polycar- pos. Infected and uninfected trees （n =20 each） were selected for assess- ment of diameter, height, crown area, and crown volume as well as quantity and quality of cones and seeds. The severity of infection of trees was determined by Hawksworth＇s 6-class dwarf mistletoe rating （DMR） system. The DMR system revealed that 40% of the infected sample trees were lightly infected （DMR =1-2） and 60% were moderately infected （DMR =3--4）. Growth characteristics did not differ significantly （p 〉 0.05） between infected and uninfected trees. However, moderate infec- tion affected the reproductive output of./. polycarpos by significantly （p 〈0.05） reducing the mean number of cones per unit area of the crown, increasing the number of damaged seeds, and reducing seed size and seedgermination capacity. We conclude that reproductive output of J.. poly- carpos is more sensitive than growth characters to moderate infection by juniper dwarf mistletoe, and this might partly account for poor natural regeneration.展开更多
Soil characterization is a vital activity to develop appropriate and effective restoration protocols for mine wastelands while insights into the total content of heavy metals in the soil is an important step in estima...Soil characterization is a vital activity to develop appropriate and effective restoration protocols for mine wastelands while insights into the total content of heavy metals in the soil is an important step in estimating the hazards that the metals may pose to the vital roles of soil in the ecosystem.This study addressed the following research questions:(1)To what extent do the physico-chemical characteristics vary between mine waste sediments and the nearby forest soil?(2)Are the concentrations of heavy metals high enough to be considered as toxic?and(3)Are heavy metals present in mine waste sediments potential sources of pollution?We hypothesized that the physicochemical characteristics of mine waste sediments are less favorably for plant establishment and growth while the concentrations of heavy metals are very high,thus restricting the success of revegetation of mine waste lands.Mine waste sediments were sampled following a diagonal transect across tailings dams,overburden dump sites and the local forest soil from the top layer(0-20 cm)using a closed auger.Samples were analyzed for arsenic,barium,lead,cadmium,cobalt,copper,chromium,nickel,vanadium,and zinc as well as for soil physico-chemical properties.The mine waste sediments were dominated by silt whilst the forest soil by sand particles,with significantly high bulk density in the former.Both the forest soil and overburden sediments were acidic than the alkaline tailings dam sediment.Total organic carbon and nitrogen contents were significantly low in mine wasteland substrates but the concentration of Ca and Mg were significantly higher in tailings dam substrate than the forest soil.The concentrations of available P,K and Na were similar across sites.The mean concentrations of heavy metals were significantly(p<0.01)higher in mine waste sediments than the forest soil;except for cadmium(p=0.213).The order of contamination by heavy metals on the tailings was Cu>Co>Ba>Ni>As>Zn>Pb>Cr>V>Cd,and that on the overburdens was Cu>Co>Ba>Ni>Zn>Cr>Pb>V>As>Cd.The pollution load index(PLI)was nearly twice higher for the tailings dam(8.97)than the overburden(5.84).The findings show that the copper mine wastes(the tailings dams and overburden waste rock sites)are highly contaminated by heavy metals;which,in turn,might pose serious hazards to human health and agricultural productivity.In addition,poor macro-nutrient availability,substrate compaction and soil acidity(particularly on overburden sites)coupled with toxic level of heavy metals would be the main challenges for successful phytostabilization of copper mine wastelands.展开更多
The germination of freshly collected Juniperus polycarpos（K. Koch） seeds is very low and attributed to the large proportion of nonviable seeds in the seed lots.Thus, the aim of this study was to improve seed lot qua...The germination of freshly collected Juniperus polycarpos（K. Koch） seeds is very low and attributed to the large proportion of nonviable seeds in the seed lots.Thus, the aim of this study was to improve seed lot quality by removing nonviable seeds using two flotation techniques： incubation-drying-separation（IDS） and modified specific gravity（MSG） separation. We examined different IDS conditions（the specific incubation time, subsequent drying time and sorting media） for effectively sorting out nonviable seeds; and tested the feasibility of modified SG separation, which involved soaking seeds in water for a certain period before sorting in different concentrations of sucrose solution. Viable seeds were expected to absorb and metabolically bind more water during soaking than dead seeds could, and hence be sorted effectively depending on the viscosity of the sucrose solution. The viability of the seeds that floated or sank was determined in a topographical tetrazolium chloride（TTC） test. For the IDS trial,7 days incubation followed by 9 h of drying and sedimentation in pure water or 200 g L-1sucrose solution identified, respectively, 75 and 82 % of the seeds as viable（sunken） seeds. For the MSG trail, 77 % viable seeds were recovered in the sunken fraction when seeds were soaked for 48 h then immediately sorted in 600 g L-1sucrose solution. In both cases, the loss of viable seeds in the discarded floating fraction was only 4 %. The results demonstrate that both IDS and MSG separation techniques substantially improved seed lot viability, but MSG separation is simple and needs no modern seed handling facility, and its efficacy relies on seed mass（due to the initial soaking） and the specific density and viscosity of the flotation medium.展开更多
A study was conducted to examine the germination requirements of Cedrela odorata, Guaiacum sanctum and Calycophyllum candidissimum seeds, and the effect of light intensity on survival and growth of C.odorata and G.san...A study was conducted to examine the germination requirements of Cedrela odorata, Guaiacum sanctum and Calycophyllum candidissimum seeds, and the effect of light intensity on survival and growth of C.odorata and G.sanctum seedlings planted on open, partially-open and beneath the canopy of a dry forest in Nicaragua.The results show that germination of C.candidissimum seeds was significantly higher in light than darkness at constant temperatures ranging from 20-35oC.Both C.odorata and G.sanctum seeds germinated in light and darkness to a varying extent, and the optimal germination temperature was around 20-25oC.Alternating temperature regimes did not improve germination.Survival of G.sanctum seedlings was 70% beneath the canopy and 80% in the open, and its relative growth rate in collar diameter was 1.88 mm/month in the open and 1.42 mm/month in the understory.Survival was generally poor for C.odorata, particularly in the understory.We concluded that light is an absolute requirement for the germination of C.candidissimum seeds while germination of C.odorata and G.sanctum seeds are more sensitive to temperature.Owing to its high survival rate on open site, G.sanctum could serve as a candidate species for reforestation of degraded sites.展开更多
Species composition, diversity and population structure of woody species recovered on three abandoned agricultural fields after 4, 9 and 14 years were characterized. Seedlings, saplings/poles and mature trees were ide...Species composition, diversity and population structure of woody species recovered on three abandoned agricultural fields after 4, 9 and 14 years were characterized. Seedlings, saplings/poles and mature trees were identified and counted in 70 plots of 100 m2 in each abandoned site. A total of 13, 29 and 22 families represented by 17, 48 and 44 species were registered in 4-, 9-and 14-year-old stands, respectively. There was a shift in dominant species across successional stages. Lonchocarpus acuminatus had the highest importance value in the 4-year old stand, whereas, Myrospermun frutescens, Guazuma ulmifolia and Cordia alliodora had the highest importance value in the 9-year-old-stand and Caesaeria corymbosa, Muntingia calabura, Gliricidia sepium and Tabebuia rosea in the 14-year-old stand. The total stem density increased from 5011 to 9631 individuals per hectare as the age of abandonment increased from 4 to 14 years. The total basal area of individuals ≥ 1cm d.b.h. also increased with the age of abandonment. Overall, small individuals (< 10 cm dbh) contributed to more than half of the total basal area. Species diversity was the highest in the 9-year old stand followed by 14-and 4-year-old stands. We concluded that floristic composition of secondary forests recovers rapidly to the mature forest level compared to structural attributes, which is consistent with the general successional trajectories of tropical dry forest.展开更多
基金supported by the Iran Government Science and Technology Scholarship Program
文摘Dwarf mistletoes are parasitic flowering plants that infect conifers, resulting in substantial loss of growth and mortality. Recently, forest managers in Iran are contemplating whether infection of Juniperus polycarpos C. Koch forests by dwarf mistletoe, Arceuthobium oxycedri （DC.） M. Bieb, influences tree vigor and contributes to insuffieient natural regeneration. The present study aimed at assessing the severity of infection and its impact on growth and reproductive output of./., polycar- pos. Infected and uninfected trees （n =20 each） were selected for assess- ment of diameter, height, crown area, and crown volume as well as quantity and quality of cones and seeds. The severity of infection of trees was determined by Hawksworth＇s 6-class dwarf mistletoe rating （DMR） system. The DMR system revealed that 40% of the infected sample trees were lightly infected （DMR =1-2） and 60% were moderately infected （DMR =3--4）. Growth characteristics did not differ significantly （p 〉 0.05） between infected and uninfected trees. However, moderate infec- tion affected the reproductive output of./. polycarpos by significantly （p 〈0.05） reducing the mean number of cones per unit area of the crown, increasing the number of damaged seeds, and reducing seed size and seedgermination capacity. We conclude that reproductive output of J.. poly- carpos is more sensitive than growth characters to moderate infection by juniper dwarf mistletoe, and this might partly account for poor natural regeneration.
基金This work was supported by the Swedish Science Council(Vetenskapsra det,C0626501 and D0650301).
文摘Soil characterization is a vital activity to develop appropriate and effective restoration protocols for mine wastelands while insights into the total content of heavy metals in the soil is an important step in estimating the hazards that the metals may pose to the vital roles of soil in the ecosystem.This study addressed the following research questions:(1)To what extent do the physico-chemical characteristics vary between mine waste sediments and the nearby forest soil?(2)Are the concentrations of heavy metals high enough to be considered as toxic?and(3)Are heavy metals present in mine waste sediments potential sources of pollution?We hypothesized that the physicochemical characteristics of mine waste sediments are less favorably for plant establishment and growth while the concentrations of heavy metals are very high,thus restricting the success of revegetation of mine waste lands.Mine waste sediments were sampled following a diagonal transect across tailings dams,overburden dump sites and the local forest soil from the top layer(0-20 cm)using a closed auger.Samples were analyzed for arsenic,barium,lead,cadmium,cobalt,copper,chromium,nickel,vanadium,and zinc as well as for soil physico-chemical properties.The mine waste sediments were dominated by silt whilst the forest soil by sand particles,with significantly high bulk density in the former.Both the forest soil and overburden sediments were acidic than the alkaline tailings dam sediment.Total organic carbon and nitrogen contents were significantly low in mine wasteland substrates but the concentration of Ca and Mg were significantly higher in tailings dam substrate than the forest soil.The concentrations of available P,K and Na were similar across sites.The mean concentrations of heavy metals were significantly(p<0.01)higher in mine waste sediments than the forest soil;except for cadmium(p=0.213).The order of contamination by heavy metals on the tailings was Cu>Co>Ba>Ni>As>Zn>Pb>Cr>V>Cd,and that on the overburdens was Cu>Co>Ba>Ni>Zn>Cr>Pb>V>As>Cd.The pollution load index(PLI)was nearly twice higher for the tailings dam(8.97)than the overburden(5.84).The findings show that the copper mine wastes(the tailings dams and overburden waste rock sites)are highly contaminated by heavy metals;which,in turn,might pose serious hazards to human health and agricultural productivity.In addition,poor macro-nutrient availability,substrate compaction and soil acidity(particularly on overburden sites)coupled with toxic level of heavy metals would be the main challenges for successful phytostabilization of copper mine wastelands.
基金financially supported by the Iranian government scholarship program
文摘The germination of freshly collected Juniperus polycarpos（K. Koch） seeds is very low and attributed to the large proportion of nonviable seeds in the seed lots.Thus, the aim of this study was to improve seed lot quality by removing nonviable seeds using two flotation techniques： incubation-drying-separation（IDS） and modified specific gravity（MSG） separation. We examined different IDS conditions（the specific incubation time, subsequent drying time and sorting media） for effectively sorting out nonviable seeds; and tested the feasibility of modified SG separation, which involved soaking seeds in water for a certain period before sorting in different concentrations of sucrose solution. Viable seeds were expected to absorb and metabolically bind more water during soaking than dead seeds could, and hence be sorted effectively depending on the viscosity of the sucrose solution. The viability of the seeds that floated or sank was determined in a topographical tetrazolium chloride（TTC） test. For the IDS trial,7 days incubation followed by 9 h of drying and sedimentation in pure water or 200 g L-1sucrose solution identified, respectively, 75 and 82 % of the seeds as viable（sunken） seeds. For the MSG trail, 77 % viable seeds were recovered in the sunken fraction when seeds were soaked for 48 h then immediately sorted in 600 g L-1sucrose solution. In both cases, the loss of viable seeds in the discarded floating fraction was only 4 %. The results demonstrate that both IDS and MSG separation techniques substantially improved seed lot viability, but MSG separation is simple and needs no modern seed handling facility, and its efficacy relies on seed mass（due to the initial soaking） and the specific density and viscosity of the flotation medium.
基金supported by the Swedish International Development Agency (Sida)
文摘A study was conducted to examine the germination requirements of Cedrela odorata, Guaiacum sanctum and Calycophyllum candidissimum seeds, and the effect of light intensity on survival and growth of C.odorata and G.sanctum seedlings planted on open, partially-open and beneath the canopy of a dry forest in Nicaragua.The results show that germination of C.candidissimum seeds was significantly higher in light than darkness at constant temperatures ranging from 20-35oC.Both C.odorata and G.sanctum seeds germinated in light and darkness to a varying extent, and the optimal germination temperature was around 20-25oC.Alternating temperature regimes did not improve germination.Survival of G.sanctum seedlings was 70% beneath the canopy and 80% in the open, and its relative growth rate in collar diameter was 1.88 mm/month in the open and 1.42 mm/month in the understory.Survival was generally poor for C.odorata, particularly in the understory.We concluded that light is an absolute requirement for the germination of C.candidissimum seeds while germination of C.odorata and G.sanctum seeds are more sensitive to temperature.Owing to its high survival rate on open site, G.sanctum could serve as a candidate species for reforestation of degraded sites.
基金supported by the Swedish International Development Agency (Sida)
文摘Species composition, diversity and population structure of woody species recovered on three abandoned agricultural fields after 4, 9 and 14 years were characterized. Seedlings, saplings/poles and mature trees were identified and counted in 70 plots of 100 m2 in each abandoned site. A total of 13, 29 and 22 families represented by 17, 48 and 44 species were registered in 4-, 9-and 14-year-old stands, respectively. There was a shift in dominant species across successional stages. Lonchocarpus acuminatus had the highest importance value in the 4-year old stand, whereas, Myrospermun frutescens, Guazuma ulmifolia and Cordia alliodora had the highest importance value in the 9-year-old-stand and Caesaeria corymbosa, Muntingia calabura, Gliricidia sepium and Tabebuia rosea in the 14-year-old stand. The total stem density increased from 5011 to 9631 individuals per hectare as the age of abandonment increased from 4 to 14 years. The total basal area of individuals ≥ 1cm d.b.h. also increased with the age of abandonment. Overall, small individuals (< 10 cm dbh) contributed to more than half of the total basal area. Species diversity was the highest in the 9-year old stand followed by 14-and 4-year-old stands. We concluded that floristic composition of secondary forests recovers rapidly to the mature forest level compared to structural attributes, which is consistent with the general successional trajectories of tropical dry forest.
