Quantifying the variability and allocation patterns of aboveground carbon stocks across plantation forest types,structural attributes and age in sub-tropical coastal region of KwaZulu Natal,South Africa using remote sensing

Quantifying the variability and allocation patterns of aboveground carbon stocks across plantation forests is central in deriving accurate and reliable knowledge and understanding of the extent to which these species contribute to the global carbon cycle and towards minimizing climate change effects. The principal objective of this study was to quantify the variability and allocation patterns of aboveground carbon stocks across Pinus and Eucalyptus plantation forests, tree-structural attributes (i.e. stems, barks, branches and leaves) and age groups, using models developed based on remotely sensed data. The results of this study demonstrate that aboveground carbon stocks significantly (α = 0.05) vary across different plantation forest species types, structural attributes and age. Pinus taeda and Eucalyptus grandis species contained aboveground carbon stocks above 110 t C ha⁻¹, and Eucalyptus dunii had 20 t C ha⁻¹. Across plantation forest tree structural attributes, stems contained the highest aboveground carbon stocks, when compared to barks, branches and leaves. Aboveground carbon stock estimates also varied significantly (α = 0.05) with stand age. Mature plantation forest species (i.e. between 7 and 20 years) contained the highest aboveground carbon stock estimates of approximately 120 t C ha⁻¹, when compared to younger species (i.e. between 3 and 6 years), which had approximately 20 t C ha⁻¹. The map of aboveground carbon stocks showed distinct spatial patterns across the entire study area. The findings of this study are important for understanding the contribution of different plantation forest species, structural attributes and age in the global carbon cycle and possible climate change moderation measures. Also, this study demonstrates that data on vital tree structural attributes, previously difficult to obtain, can now be easily derived from cheap and readily-available satellite data for inventorying carbon stocks variability.     

Nest site characteristics and nesting success of the Western Burrowing Owl in the eastern Mojave Desert

We evaluated nest site selection at two spatial scales (microsite, territory) and reproductive success of Western Burrowing Owls (Athene cunicularia hypugaea) at three spatial scales (microsite, territory, landscape) in the eastern Mojave Desert. We used binary logistic regression within an information-theoretic approach to assess factors influencing nest site choice and nesting success. Microsite-scale variables favored by owls included burrows excavated by desert tortoise (Gopherus agassizii), burrows with a large mound of excavated soil at the entrance, and a greater number of satellite burrows within 5 m of the nest burrow. At the territory scale, owls preferred patches with greater cover of creosote bush (Larrea tridentata) within 50 m of the nest burrow. An interaction between the presence or absence of a calcic soil horizon layer over the top of the burrow (microsite) and the number of burrows within 50 m (territory) influenced nest site choice. Nesting success was influenced by a greater number of burrows within 5 m of the nest burrow. Total cool season precipitation was a predictor of nesting success at the landscape scale. Conservation strategies can rely on management of habitat for favored and productive nesting sites for this declining species.     

Floral ecology and insect visitation in riparian Tamarix sp. (saltcedar)

Climate change projections for semiarid and arid North America include reductions in stream discharge that could adversely affect riparian plant species dependent on stream-derived ground water. In order to better understand this potential impact, we used a space-for-time substitution to test the hypotheses that increasing depth-to-groundwater (DGW) is inversely related to Tamarix sp. (saltcedar) flower abundance (F) and nectar production per flower (N). We also assessed whether DGW affected the richness or abundance of insects visiting flowers. We examined Tamarix floral attributes and insect visitation patterns during 2010 and 2011 at three locations along a deep DWG gradient (3.2–4.1 m) on a floodplain terrace adjacent to Las Vegas Wash, an effluent-dominated Mojave Desert stream. Flower abundance and insect visitation patterns differed between years, but no effect from DGW on either F or N was detected. An eruption of a novel non-native herbivore, the splendid tamarisk weevil (Coniatus splendidulus), likely reduced flower production in 2011.     

Flower orientation in Pachycereus weberi (Cactaceae): Effects on ovule production, seed production and seed weight

Few studies have determined the importance of orientation on flower reproductive success. Flower orientation may affect reproduction of Cactaceae; the interception of photosynthetic active radiation (PAR) differs along the different sides of cacti stems, and translocation of resources between cacti ribs does not appear to occur. Therefore, PAR received by each cacti stem face may determine the resources available for reproduction. We examined the reproductive success of Pachycereus weberi flowers with contrasting orientations. Ovule production per ovary, number of seeds per fruit, seed set per fruit and seed weight were used as indicators of reproductive success for flowers facing southeast and northeast. PAR received on opposite stem sides was recorded as an estimator of resource availability for each side. Results showed that flowers facing southwards produced more ovules and seeds and produced heavier seeds. Seed set was not significantly different between flowers with contrasting orientations. The southern stem faces received more PAR than the northern faces. Reproductive success was different for flowers with contrasting orientations, suggesting that there is an association between PAR received on different P. weberi stem faces and floral reproductive success.     

Carbon pools in an arid shrubland in Chile under natural and afforested conditions

The pattern of carbon (C) allocation among the different pools is an important ecosystem structural feature, which can be modified as a result of changes in environmental conditions that can occur gradually (e.g., climatic change) or abruptly (e.g., management practices). This study quantified the C pools of plant biomass, litter and soil in an arid shrubland in Chile, comparing the natural condition (moderately disturbed by grazing) vs. the afforested condition (two-year-old plantation with Acacia saligna (Labill.) H.L. Wendl.), each represented by a 60 ha plot. To estimate plant biomass, allometric functions were constructed for the four dominant woody species, based on the volume according to their shape, which showed high correlation (R² > 0.73). The soil was the largest C pool in both natural and afforested conditions (89% and 94%, respectively) and was significantly lower in the afforested than natural condition at all five soil depths. The natural condition had in total 36.5 ton (t) C ha⁻¹ compared to 21.1 t C ha⁻¹ in the afforested condition, mainly due to C loss during soil preparation, prior to plantation of A. saligna. These measurements serve as an important baseline to assess long-term effects of afforestation on ecosystem C pools.     

Genetic diversity,conservation and sustainable use of wild Agave cupreata and Agave potatorum extracted for mezcal production in Mexico

Agave cupreata and Agave potatorum are semelparous species distributed on dry tropical forests in south Mexico. Extraction of reproductive individuals for spirits production has caused a decline of wild populations and has raised concerns about their long-term conservation. We assess the degree of genetic erosion of exploited populations and provide population genetics baseline data for developing sustainable use strategies of these species. ISSRs (Inter Simple Sequence Repeats, dominant nuclear markers associated to microsatellites) were used to analyze five populations of each species throughout their distribution range. We found high levels of variation (P > 80%; H > 0.30) and moderate to high differentiation (A. potatorum θ = 0.120; A. cupreata θ = 0.172). Isolation by distance was significant in A. cupreata. Our data indicate that these species are not genetically eroded in general, and that they retain their historical patterns of diversity inside populations. Three genetically distinct populations are identified where conservation efforts should be a priority. Our results are discussed in relation to the in situ reinforcement of populations based on seeds propagation, in contrast to micropropagation practices that may threaten the genetic diversity of the species studied considering previous reports on genetic bottlenecks and inbreeding depression in Agave.     

Reproductive phenology of Isolatocereus dumortieri (Cactaceae) in semiarid scrub in central Mexico: Effect of rain during the dry season

The giant cactus Isolatocereus dumortieri is a dominant species of the semiarid scrub of central Mexico. Its reproductive period is during the dry season, and it produces essential resources (pollen, nectar and fruits) for a great variety of animal species. We related the production of reproductive structures with water variables in the soil–plant system. The main goal of the present study was to evaluate the consequences of a change in rainfall pattern on the phenology of I. dumortieri. We watered some plants in the dry season to simulate heavy rain events, and to test the hypothesis that water availability during the reproductive season has a negative effect on fruiting and a positive effect on vegetative growth. The seasonality of rain events caused variations in soil water potential and plant osmotic potential, and we found that both variables influenced fruit production. The regression models relating the number of fruits with soil water potential, rainfall and osmotic potential were significant for all three study periods. The highest production of reproductive structures occurred in the driest year (2009), during which there was an ENSO event. Watering did not have a significant effect on osmotic potential or growth in the cacti. However, the watering × time interaction had a negative effect on the number of immature fruits. That is, at the end of the experiment, the plants that received the most water showed a decrease in the number of fruits. Plant growth during the rainy period was significantly greater than during the dry period. The results support the hypothesis that a change in rainfall pattern during the dry season has an effect on fruit production. Vegetative growth, however, occurred only during the wet season.     

Seed predation and moisture limit germination of recalcitrant Dobera glabra (Salvadoraceae) seeds in the Afar rangelands, Ethiopia

We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments.     

Reproductive and recruitment traits as indicators of the invasive potential of Kalanchoe daigremontiana (Crassulaceae) and Stapelia gigantea (Apocynaceae) in a Neotropical arid zone

Populations of two ornamental exotic species, Kalanchoe daigremontiana and Stapelia gigantea, have been recently detected inside a protected area containing arid ecosystems in Venezuela. We indirectly tested their invasive potential by characterizing their reproductive biology and recruitment patterns and comparing our estimates against Baker's Law and reproductive profiles reported for invasive plants. K. daigremontiana is autogamous, produces >16,000 seeds per plant and also reproduces clonally. Despite low seed viability (17.9%) and germination rates (11.9%), seeds were present in the seed bank. Plantlets of asexual origin showed high survival (75–100%) compared to seedlings of sexual origin (10%). S. gigantea is self-incompatible, xenogamous and produces close to 1500 seeds per m² of plant tissue. Seed viability (77%) and germination rates (62%) were high, but this species is not represented in the seed bank. It has a vegetative growth. A combination of reproductive and recruitment attributes, which match those considered in Baker's Law and others reported for invasive plants, confer K. daigremontiana and S. gigantea the potential to invade Neotropical arid zones; the former mainly through selfing and production of numerous asexual plantlets, and the latter through an association with a locally abundant pollinator and production of wind dispersed seeds.     

Parthenocarpy, attractiveness and seed predation by birds in Bursera morelensis

Parthenocarpy (production of seedless fruits) is a characteristic associated with a strategy to reduce seed predation by birds and to increase the attractiveness to frugivorous birds. Red cuajiote (Bursera morelensis) is an endemic tree species of Mexico that produces seeded and parthenocarpic fruits. The purpose of this work was to examine whether parthenocarpy is a factor that increases the number of bird visits to trees and if it is a strategy to diminish seeds predation by granivorous birds. We made field observations to determine the relation between the number of bird visits and fruit removal rate, to the total number of parthenocarpic fruits produced, and the number of birdpredated fruits to the number and proportion of parthenocarpic fruits in the trees. We found that in trees with a bigger amount of parthenocarpic fruits, both frugivoruos and granivorous birds made more visits; we then suggested that parthenocarpic fruits can act like a signal of attraction by means of a density and coloration effect. Also, we found that in trees with bigger proportions of parthenocarpic fruit, predation by granivorous birds is smaller. Parthenocarpy has an adaptative value for B.morelensis increasing bird visitation and reducing seed predation in the Tehuacan Valley.     

Benefits of mycorrhizal inoculation in reintroduction of endangered plant species under drought conditions

Numerous human activities constitute threats to biodiversity. The effects of climate change, including increasing drought in already arid lands, pose an additional layer of uncertainty in the fate of rare species. In the case of plants, reintroduction is becoming an important active management practice in species conservation. We hypothesized that even under extreme drought inoculation with mycorrhizal fungi would increase growth rates of an endangered plant in experimental reintroduction. We selected a plant species, Abronia macrocarpa, and conducted the experiment in Texas while the area was experiencing mild and extreme drought intensities. Treatment plots were planted with seed inoculated with arbuscular mycorrhizal fungi and control plots were planted with seed coated with autoclaved inoculant. We analyzed measurements of growth and development of germinated plants. Mean number of leaves was greater in treatment plants (P = 0.005) and mean aerial diameter was larger in treatment plants (P = 0.02) than in control plants. Significantly improved growth suggests that inoculation is a viable technique to increase reintroduction success in plant species especially during periods of drought.     

Parasitism and haustorium anatomy of Krameria lappacea (Dombey) Burdet & B.B. Simpson (Krameriaceae), an endangered medicinal plant from the Andean deserts

Krameria lappacea (Rhatany or Ratanhia, Krameriaceae) is an endangered, overexploited medicinal plant from the semi-deserts of Andean South America, and is destructively harvested from nature. There are published data on parasitism of Krameria from three North American species, but not on K. lappacea, the only economically important species. The present study investigates the presence or absence of hemiparasitism, host plant range and haustorium morphology/anatomy. The study was carried out at two sites in Peru, Department Arequipa, Prov. Arequipa. Hemiparasitism was confirmed, with 106 haustorical connections to 18 host plant species from 17 genera and 12 plant families observed, nearly doubling the number of host plant species known for Krameria (incl. four additional angiosperm families). Root and haustorium architecture and anatomy were found to be similar to the North American species. K. lappacea is a highly generalistic hemiparasite and host distribution and abundance are likely not limiting factors for Krameria recruitment and establishment. Due to its wide range of host plants K. lappacea likely influences the performance of the bulk of perennial species in its habitat and overcollection affects the overall vegetation. Conservation strategies and adequate management should have high priority because of the likely ecological and known economical importance of this species.     

The altitudinal distribution center of a widespread cushion species is related to an optimum combination of temperature and precipitation in the central Tibetan Plateau

Climate warming may threaten the survival of alpine cushion plants, which may have great implications for the stability of alpine ecosystems. However, little research has investigated the climatic causes of the altitudinal distribution of cushion plants. We hypothesize that for a widespread cushion species in semi-arid regions, there is a unimodal pattern of plant cover associated with an optimum combination of temperature and precipitation. We conducted a livestock exclosure experiment across the upper (5300 m) and lower (4430 m) limits of a widespread cushion species (Androsace tapete) along the south-facing slope of the Nyaiqentanglha Mountains during the period 2006–2010. The plant cover and survival across the fenced and unfenced quadrats were observed near weather stations at eight altitudes. There was a unimodal pattern in the coverage of A. tapete along the experimental gradient, which was confirmed by additional data from other species and mountains in this region. The coverage showed quadratic relationships with mean temperatures and the ratio of growing-season precipitation to the ≥5 °C accumulated temperature sum. Five-year monitoring data under fenced conditions demonstrated that the annual survival of A. tapete decreased away from the optimum distribution center. The results supported the hypothesis, suggesting a shift in the limiting factors of plant distribution between low and high altitudes.     

Heliotropium europaeum only germinates following sufficient rainfall to allow reproduction

Regions with Mediterranean climates are seasonally arid and provide a niche for ephemeral species which germinate following discrete and variable rainfall during summer. These species must be able to detect when conditions are suitable for completion of their life cycle. Common heliotrope (Heliotropium europaeum) is one such species. It is considered a weed in its naturalised habitat in southern Australia as it uses resources that could be used by ensuing crops, and is toxic to livestock.We examined common heliotrope's germination responses to temperature and water potential, the effect of simulated rainfall on seedling emergence and plant growth in lysimeters.Fresh seeds of common heliotrope have relatively high optimum temperatures and water potentials for germination (around 35 °C and 0 MPa). Germination percentage of seeds extracted from the soil seed bank varies seasonally. In the soil types and climate of the study area, 24.2 mm is the minimum amount of rainfall resulting in emergence. Evapotranspiration required to reach minimal reproductive output was 19.4 mm.Common heliotrope's germination requirements have been selected to ensure that it will only germinate after sufficient rainfall to allow reproductive output. This is the mechanism through which common heliotrope detects its temporal niche.     

Recruiting mechanisms of Cylindropuntia leptocaulis (Cactaceae) in the Southern Chihuahuan Desert

Sexual reproduction and vegetative propagation require the establishment of morphologically diverse reproductive structures (seedlings and stem segments). This study assesses both types of Cylindropuntia leptocaulis recruitment in two microenvironments protected from herbivory (in open space and under the canopy of Larrea tridentata) and with two soil types (collected below L. tridentata canopy and from open space).An observational study revealed that sexual establishment was very limited (only 8 juveniles/ha were found), while clonal establishment was more frequent (59 juveniles/ha); both types of propagule were found only under shrub canopy.Field experiments showed that, as in other Cylindropuntia species but contrasting with findings for Opuntia species, seeds germinated and seedlings survived under nurse plants as well as in open space, but they grew faster in the former environment. Faster growth under canopy shade provides better chances of successful recruitment to later life-cycle stages. Stem segments never established in open space, requiring the shade of nurse plants. This may be due to physiological constraints imposed by their small volume. In synthesis, the results indicate that clonal propagation is the most important recruitment mechanism in C. leptocaulis populations, and that it takes places under shrub canopy.     

Predispersal reproductive ecology of an arid land crucifer,Moricandia moricandioides: effect of mammal herbivory on seed production

In this paper the effect of herbivory on the seed production ofMoricandia moricandioides(Cruciferae), an annual species living in arid habitats of south-eastern Spain, is analysed. Firstly, the flowering and fruiting phenology and the composition and structure of the pollinator guild is described, in order to compare the overall effect of mutualistic speciesvs. that of antagonistic species onM. moricandioidesseed production. The loss of female reproductive success due to each herbivore species attacking the plant is then quantified, in an attempt to differentiate the effects on plant seed production of each herbivorous species. The results indicate that only antagonistic organisms interacting withM. moricandioidesinfluenced the female fitness of this plant species. In fact, pollinator abundance or activity did not correlate with the number of seeds dispersed by the plants. In addition, of all the herbivore species, only sheep activity significantly influenced seed production ofM. moricandioidesindividuals, the effect of the remaining crucivorous herbivores being cancelled by the stronger herbivory of sheep. The results of this study suggest that herbivory by sheep, in addition to decreasing the seed production ofM. moricandioides, could be an important determinant of the current distribution pattern of this crucifer species on the ramblas of the Baza basin.     

The effects of human visits on the use of a waterhole by endangered ungulates

We report the impacts of human visits at a waterhole used by mountain gazelles, Gazella gazella, and Nubian ibex, Capra ibex nubiana, in the Ibex Reserve of Saudi Arabia. Our hypothesis was that the species that normally used the waterhole during the day, the typical period of human visits, would be negatively affected. The results did not support our hypothesis, as both the diurnal mountain gazelles and partly nocturnal Nubian ibex avoided the waterhole within 6 h after human visits. We found no significant difference of waterhole use by Nubian ibex and mountain gazelles within the period of 6–12 h or 12–24 h after human visits. Given the high conservation concern of these species and the rarity of waterholes, we suggest that human visits continue to be regulated by allowing visits on non-consecutive days to give the ungulates opportunities to drink, especially during the summer and droughts when heat stresses are higher, animals are less tolerant of water deprivation, and there are less alternative waterholes.     

迁地保护条件下4种沙拐枣(Calligonum)的花部特征和传粉特性

通过观测花器官、开花动态、花粉胚珠比、访花昆虫,对生长在吐鲁番沙漠植物园的4种沙拐枣(Calligonum)的花部特征和传粉特性进行研究。结果表明:4种沙拐枣均具两性花,但花部各器官的颜色、大小等在种间存在一定差异;单花开放动态相似,花粉序次呈现;花香气主要来自于花药和花托;花粉为“淀粉质”;花粉胚珠比值31 000～44 750,需要传粉者,虫媒和风媒并存;意大利蜂为主要有效的传粉昆虫,为典型的高移出低沉降;花粉序次呈现、意大利蜂较高的访花频率及重复拜访有利于提高传粉效率;花粉数量和品质不是造成果实无胚率高的原因,可能是由自身花粉阻塞和资源限制造成的,还有待于进一步研究。     

Pine plantation bands limit seedling recruitment of a perennial grass under semiarid conditions

Pine plantations coexist with Stipa tenacissima grasslands in many semiarid western Mediterranean areas. We compared three microsites created by a 30-year-old Pinus halepensis plantation: below pine plantation line (BP), below canopy of pines (BC) and interline bare band (BA). They were evaluated in terms of soil properties, pine litter and suitability as recruitment niches for S. tenacissima. Next, in a manipulative experiment in growth chambers we tested the hypothesis that pine litter interferes with the seedling emergence of S. tenacissima. Three treatments in pots were compared: (a) soil from BA; (b) intact soil + litter from BP; and (c) soil + litter from BP, which was mixed in the laboratory (BPMX). In the field the main microsite differences were pine cover and litter cover and thickness. Seedling emergence was significantly greater in BA than in BP. Emergence and litter depth fits a linear regression model. In the growth chamber litter did not interfere with the emergence of S. tenacissima. However, seedlings grown without litter were 28% longer and their mass was 27% greater than in the litter treatments. The detected pine litter interference may be relevant for plant dynamics and might be considered in forestry management programs.     

Differential seedling performance and environmental correlates in shrub canopy vs. interspace microsites

Shrubs in semi-arid ecosystems promote micro-environmental variation in a variety of soil properties and site characteristics. However, little is known regarding post-fire seedling performance and its association with environmental variation in former shrub canopy and interspace microsites. We compared post-fire seeding success and various soil properties important for seedling establishment between shrub canopy and interspace microsites in Wyoming big sagebrush (Artemisia tridentata) plant communities in southeast Oregon, U.S.A. We burned 5, 20 × 20 m sites and established paired canopy and interspace micro-transects seeded with bluebunch wheatgrass (Pseudoroegneria spicata, 193 seeds/m) or crested wheatgrass (Agropyron cristatum, 177 seeds/m). At one year post-fire, seedling density was 69% higher (p = 0.012) for crested wheatgrass (compared to bluebunch wheatgrass) and 75% higher (p = 0.019) for interspace microsites (compared to canopy). However, tiller and leaf area production were over twice as high (p < 0.05) in canopy microsites. Soil color and soil temperature, explained 19–32% of variation in seedling performance metrics. Shrub effects on seeding success are complex and interact with abiotic disturbances, but patterns of increased seedling performance in canopy microsites and their relationships to soil variables may suggest tactics for increasing success of restoration practices.