A methodology for risk analysis of plurivorous fungi in biological weed control: Sclerotinia sclerotiorum as a model

In New Zealand, research is being performed on the use of the ubiquitous plurivorous ascomycete Sclerotinia sclerotiorum, as a biocontrol agent for Cirsium arvense in pasture. As a consequence of the wide host range of this fungus, the proposed biocontrol may pose a risk to non-target arable plants. Crop disease risk is primarily due to the formation of sclerotia. These perennating bodies may directly infect susceptible crops sown at the biocontrol site in years after the biocontrol event. Additionally they may cause infection in neighbouring crops through the formation of apothecia from which airborne ascospores are dispersed. A methodology for a risk analysis is proposed, embodying both temporal and spatial processes, where the relative disease risk from biocontrol is defined as the ratio of added to naturally occurring inoculum.Exponential decay is proposed as a suitable model for the survival of sclerotia in soils beneath pastures, and data from an ongoing study are used in a preliminary parameterisation. The model is applied to published data on initial sclerotium population size and unpublished data on natural levels of soilborne sclerotia, to reveal how a withholding period, defined as the interval of time that must elapse for the ratio of added to natural inoculum to equal unity, may be calculated.For quantifying escape and aerial dispersal of ascospores from a treated pasture, three mechanistic models are proposed. Firstly, a simple one-layer model of escape, giving a provisional estimation of 81% of released ascospores escaping the pasture canopy, is discussed. Secondly, ascospore dispersal within and close to the biocontrol site (<30 m) is described by a model revealing abrupt decline in the atmospheric concentration of ascospores within short distances from the biocontrol site. Thirdly, for predicting ascospore concentrations at greater distances (>100 m), a Gaussian plume model is proposed. In a first approximation, these models are used in an example calculation to show how a hypothetical safety zone might be determined. A map of the province of Canterbury showing the locations of different agricultural activities and infestations of dense populations of C. arvense, revealed that potential biocontrol sites mostly do not border arable land and that a safety zone would therefore be feasible.The study presented here provides conceptual and mathematical frameworks for risk analysis of the use of plurivorous fungi in biological weed control, using S. sclerotiorum as an example. However, before a judgement may be made about the phytosanitory risks associated with the use of S. sclerotiorum to control C. arvense in pastures in Canterbury, the models developed in this paper must be parameterized using data collected under a wide range of conditions in the field.     

Risk Analysis of Sclerotinia sclerotiorum for Biological Control of Cirsium arvense in Pasture: Ascospore Dispersal

Natural levels of Sclerotinia sclerotiorum ascsospores in the Canterbury region were determined over 3 years by trapping depositing ascospores in dishes containing a selective agar. Mean levels in 'horticulture', 'biocontrol-pasture', 'mixed cropping' and 'pasture' strata were 115, 56, 10 and 3 ascospores m -2 day -1 , respectively. Ascospore deposition downwind of small experimental biocontrol sites was measured on 2 days in 1994 and 9 days in 1997 in late spring. Exponential depletion models scaled up to represent a 1 ha biocontrol site, revealed that dispersing ascospores declined to natural levels at downwind distances of 2.5-7.9 m. These results imply that biological weed control in pasture using S. sclerotiorum creates no greater risk of crop disease than does horticulture, and that under the conditions of our experiments, an isolation distance of 8 m would have sufficed. However, such a safety zone may be inadequate under certain meteorological conditions not encountered in the experiments when ascospores may disperse in larger numbers over longer distances. To complete the information required to build a mechanistic model of spore dispersal (beyond the scope of this paper) which would cope with a variety of meteorological conditions, two studies were conducted on the dynamics of apothecium formation and ascospore release. In a two-year study, apothecium formation was confined to the spring (September-November), and population size peaked in mid October. In a 5-day study, ascospore release occurred during the daytime, reaching a maximum late morning on frost-free days and a lower maximum mid afternoon on days with morning frost.     

Specific inhibition of sclerotium formation by 2-mercaptoethanol and related sulfhydryl compounds in Sclerotium rolfsii.

Sclerotium formation in Sclerotium rolfsii was completely inhibited by 2-mercaptoethanol at a concentration of 2-4 mM without any adverse effect on mycelial growth. Concentrations lower than 2 mM had no effect on mycelial growth and sclerotium formation, whereas both were inhibited at concentrations higher than 4 mM. Complete inhibition of sclerotium formation with no effect on mycelial growth was also obtained by propyl mercaptan, 1-butyl mercaptan and 2-butyl mercaptan at a concentration of 0.10 mM. Sclerotium formation was also inhibited by benzyl mercaptan and thioglycolic acid at 0.15 mM and 2-4 mM concentration respectively, whereas it was only partially inhibited by L-cysteine and glutathione at 20 mM. Mycelium grown for 21 days in nutrient medium supplemented with mercaptoethanol at a concentration of 3 mM, when transferred into fresh medium without the chemical, grew normally and produced abundant mature sclerotia. Mercaptoethanol inhibited the initiation as well as the further development of young, unpigmented sclerotia. The mechanism of sclerotium formation was arrested completely when mercaptoethanol was added to the growth medium at any time between inoculation and the appearance of sclerotia of the "development" stage. It is suggested that the specific inhibitory action of mercaptoethanol could be used to study the mechanism of sclerotium formation     

恒温和变温培养对羊肚菌菌丝生长及菌核形成影响的比较研究

为了探究恒温和变温培养对羊肚菌菌丝生长和菌核形成的影响,设置-9℃-30℃的7个恒温处理,3个变温处理,通过观察和记录在两种不同培养方式下菌丝的长势、生长速度、菌落干重、产核时间、菌核数量等内容,从而比较出恒温和变温培养对羊肚菌菌丝生长和菌核形成的影响效果。结果表明,在恒温条件下羊肚菌菌丝生长和菌核发育比变温好,20℃最适宜菌丝生长,菌丝生长速度较快,菌落干重最大;25℃最适宜菌核生长发育,产核最早。菌核数量最多。     

Regeneration of Seasonal Deciduous Forest Tree Species in Long-Used Pastures in Central Brazil

We tested the relationship between the length of pasture use and the density, richness, and composition of naturally regenerating tropical seasonal deciduous forest in pastures. We sampled regenerating trees in 25 pastures distributed in four age classes ranging from < 6 to 40 yr of use. Density and composition of regenerating trees did not change with pasture age, but richness was lower in 25- and 40-yr-old pastures. Nonetheless, a number of species seem to be able to resprout even after 40 yr of ranching.     

The structure and histochemistry of sclerotia of Ophiocordyceps sinensis

The structure and histochemistry of sclerotia of Ophiocordyceps sinensis (synonym: Cordyceps sinensis) are described. The remains of the caterpillar epidermis and sometimes setae of the caterpillar were attached to the pigmented layer that is external to the rind of the sclerotium. The outer aerial hyphae and hyphae of the inner medulla were densely interwoven around the epidermis of the caterpillar; these eventually differentiated into the rind of the sclerotium. The medulla of the sclerotium consisted of three intergrading regions of hyphal density: high, low and a region of intermediate hyphal density. All hyphae of the medulla contained large quantities of protein, polysaccharide and polyphosphate; only the region of high hyphal density was rich in beta-1,3 glucans; the center of the sclerotium was almost devoid of hyphae and contained what are most likely the remains of caterpillar tissue. These features are compared with those of sclerotia of other fungi, and their possible significance is discussed.     

Risk analysis for biological weed control – simulating dispersal of Sclerotinia sclerotiorum (Lib.) de Bary ascospores from a pasture after biological control of Cirsium arvense (L.) Scop.

Biological control of Cirsium arvense(L.) Scop. in pasture by the plurivorous plantpathogenic fungus Sclerotiniasclerotiorum (Lib.) de Bary mayresult in the formation, escape and aerialdispersal of ascospores, creating an additionaldisease risk in down-wind market garden crops. To determine the width of a safety zone for apasture subjected to this form of weed control,we simulated the spatial pattern in the ratioof added (due to biocontrol) to naturallyoccurring airborne ascospores (due to marketgarden crops) around a 1ha virtual biocontrolpasture under either sheep or dairy cattlegazing over a 91-day emission period in 1996 inCanterbury, New Zealand. This was achievedusing a unique combination of two computermodels; SPORESIM-1D (for spore escape from avegetation source) and PC-STACKS (a modernGaussian plume model for dispersal beyond asource). Plumes of dispersing ascospores weremodelled for each hour of the emission periodfor both the virtual market garden andbiocontrol sites, and the aerial density of theascospores was averaged over the period. Assuming that a 1:1 ratio of added to naturallypresent spores is acceptable, no safety zonewas necessary for either of the modeledpastures. A ten-fold ratio (1:10 added tonatural) necessitated safety zones of 300 and150 m for the sheep and dairy pasturerespectively. Uncertainties associated withextrapolation of this conclusion to individualpasture management scenarios, and to otheryears and climatically different regions arediscussed.     

Compatible solutes of sclerotia of Mycoleptodiscus terrestris under different culture and drying conditions

Mycoleptodiscus terrestris is a plant pathogen which has been shown to be effective in controlling invasive aquatic weeds in inundative biocontrol applications. The preferred propagule for production and application is the sclerotium. In the current study, we evaluated the accumulation of carbohydrates and polyols in the sclerotia of M. terrestris under different culture and drying regimes. The carbohydrates and polyols screened for represent a class of compatible solutes found in fungi. The results show mannitol and trehalose are the major analytes identified in the sclerotia of M. terrestris. We identified higher levels of mannitol and trehalose in liquid-culture produced samples relative to solid-state produced samples. The impact of fermentation time was examined and shown to impact solute levels. In addition, the drying regime was varied to produce samples dried to different moisture contents. The experiments show greater drying led to higher mannitol levels, while trehalose levels remained constant. Rapid drying of the sclerotia in a fluidized-bed dryer also show rapid accumulation of mannitol and trehalose, which suggest the enzyme activities needed for production are readily available. The findings confirm mannitol and trehalose are important metabolites in M. terrestris and their concentrations are responsive to osmotic stress conditions.     

Nose-Rings and Transmission of Helminth Parasites in Outdoor Pigs

Five growing pigs experimentally infected with low doses of Oesophagostomum dentation, Ascaris suum, and Trichuris suis were turned out with 5 helminth-naïve pigs on each of 3 pastures in June 1996 (Group 1). On one pasture all pigs received nose-rings. After slaughter of Group 1 in October, pasture infectivity was monitored using helminth-naïve, unringed tracer pigs. In 1997, helminth-naïve young pigs were turned out on the contaminated pastures in May (Group 2) and again in August (Group 3). Again all pigs on one pasture received nose-rings. All pigs and pastures were followed parasitologically and reduction in grass cover was monitored. Based on the acquisition of infection by the naïve pigs in Group 1, the estimated minimal embryonation times for eggs deposited on pasture were 23–25 days for O. dentatum, 5–6 weeks for A. suum and 9–10 weeks for T. suis. Results from tracer pigs and grass/soil samples indicated that pasture infectivity was light both years. Free-living stages of O. dentatum did not survive the winter. The nose-rings reduced rooting considerably, resulting in three-fold more grass cover on the nose-ring pasture compared to the control pastures by the end of the experiment. Nevertheless, the nose-rings did not significantly influence parasite transmission.     

Comparison of temperature and moisture requirements for sporulation of Aspergillus flavus sclerotia on natural and artificial substrates

A key step in the infection cycle by Aspergillus flavus in maize is sporulation of sclerotia present in soil or in crop debris. However, little information is available on this critical and important phase. This study included experiments on artificial (Czapek Dox Agar (CZ)) and natural (maize stalks) substrates under different conditions of temperature (T; from 5 to 45 °C) and water activity (a(w); from 0.50 to 0.99) levels to quantify sporulation from sclerotia. The mean numbers of spores were higher on defined nutritional medium in vitro on CZ agar than on maize stalks (4.5×10(6) spores/sclerotium versus 4.2×10(4) spores/sclerotium) with production initiated after 6 and 24h, respectively. Surprisingly, the optimal temperature was found at 30-35 °C for CZ agar (9.23×10(6) spores/sclerotium) and to be 20-25 °C for maize stalks (6.26×10(4) spores/sclerotium). Water stress imposition only reduced sporulation at ≤0.90 a(w.) With more available water no significant differences were found between 0.90 and 0.99 a(w). This type of data is critical in the development of a mechanistic model to predict the infection cycle of A. flavus in maize in relation to meteorological conditions.     

Landscape Dynamics in Northwestern Amazonia: An Assessment of Pastures,Fire and Illicit Crops as Drivers of Tropical Deforestation

Many studies have identified drivers of deforestation throughout the tropics and, in most cases, have recognised differences in the level of threat. However, only a few have also looked at the temporal and spatial dynamics by which those drivers act, which is critical for assessing the conservation of biodiversity as well as for landscape planning. In this study, we analyse land cover change between 2000 and 2009 in north-western Colombian Amazonia to identify the interactions between the use of fire, cultivation of illicit crops and establishment of pastures, and their impacts on the loss of forest in the region. Yearly analyses were undertaken at randomly selected sample areas to quantify the average areas of transition of land cover types under different landscape compositions: forest-dominated mosaics, pasture mosaics, fire mosaics, and illicit crop mosaics. Our results indicate that despite the fact that forest areas were well-preserved, deforestation occurred at a low annual rate (0.06%). Conversion to pasture was the main factor responsible for forest loss (the area of pastures tripled within forest mosaics over 8 years), and this process was independent of the landscape matrix in which the forests were located. In fire mosaics, burning is a common tool for forest clearing and conversion to pasture. Thus, forests in fire mosaics were highly disturbed and frequently transformed from primary to secondary forests. The use of fire for illicit cropping was not detected, partly due to the small size of common illicit crops. Forest regeneration from pastures and secondary vegetation was observed in areas with large amounts of natural forest. Overall, assuming the continuation of the observed pasture conversion trend and the use of forest fire, we suggest that our results should be incorporated into a spatially explicit and integrated decision support tool to target and focus land-planning activities and policies.     

Rainforest seed rain into abandoned tropical Australian pasture is dependent on adjacent rainforest structure and extent

It is well known that the recovery of abandoned tropical pastures to secondary rainforest benefits from the arrival of seeds from adjacent rainforest patches. Less is known, however, about how the structural attributes of adjacent rainforest (e.g. tree density, canopy cover and tree height) impact seed rain patterns into abandoned pastures. Between 2011 and 2013, we used seed traps and ground seed surveys to track the richness and abundance of rainforest seeds entering abandoned pastures in Australia's wet tropics. We also tested how seed rain diversity is related to the distance from forest, the proportion of forest cover in the landscape and several structural attributes of adjacent forest patches, specifically average tree height, canopy cover, tree species richness and density. Almost no seeds were captured in elevated pasture seed traps, even near forest remnants. Abundant forest seeds were found in ground surveys but only within 10 m of forest edges. In ground surveys, seeds from wind‐dispersed species were more abundant, but less species rich, than animal‐dispersed species. A survey of pasture seedling recruits suggested that some forest seeds must be dispersing more than 10 m into pasture at very low frequencies, but only a few species are establishing there. Recruits were predominantly animal‐dispersed not wind‐dispersed species. In addition to distance from forest and the proportion of forest within a 100‐ to 200‐m radius of sampling sites, the richness and density of adjacent forest trees were the most important factors for explaining the probability of seed occurrence in abandoned pastures. Results suggest that without some restoration assistance, the recovery of abandoned pastures into secondary rainforest in Australia's tropical rainforests will likely be limited, at least in part, by a very low rate of seed dispersal away from forest edges and by the diversity and density of trees in adjacent remnant forests.     

Practical aspects of mycorrhizal technology in some tropical crops and pastures

Summary Greenhouse and field experiments were conducted on the effect of VA mycorrhiza (VAM) on the growth of cassava, various tropical grass and legume species, as well as beans, coffee and tea. A large number of VAM fungal species were evaluated for effectivity in increasing cassava growth and P uptake in acid low-P soils. The effectivity of VAM species and isolates was highly variable and dependent on soil pH and fertilizer applications, as well as on soil temperature and humidity. Two species,Glomus manihotis andEntrophospora colombiana were found to be most effective for a range of crops and pastures, at low pH and at a wide range of N, P, and K levels. At very low P levels nearly all crops and pasture species were highly mycorrhizal dependent, but at higher soil P levels cassava and several pasture legumes were more dependent than grass species. Mycorrhizal inoculation significantly increased cassava and bean yields in those soils with low or ineffective indigenous mycorrhizal populations. In these soils cassava root yields increased on the average 20–25% by VAM inoculation, both at the experiment station and in farmers’ fields. VAM inoculation of various pasture legumes and grasses, in combination with rock phosphate applications, increased their early growth and establishment. Agronomic practices such as fertilization, crop rotations, intercropping and pesticide applications were found to affect both the total VAM population as well as its species composition. While there is no doubt about the importance of VA mycorrhiza in enhancing P uptake and growth of many tropical crops and pastures grown on low-P soils, much more research is required to elucidate the complicated soil-plant-VAM interactions and to increase yields through improved mycorrhizal efficiency.     

Changes in fatty acid profile of Bovec sheep milk due to different pasture altitude

Sheep rearing on mountain pastures is an ancestral tradition in northwestern Slovenia. The indigenous Bovec sheep are widespread there and are well adapted to the rough Alpine rearing conditions. Every year, after weaning, the sheep start grazing in the lowlands (L) and then gradually move to mountain pastures, and finally, to the highland (H) pastures of the Alps. Grazing positively affects the fatty acid (FA) composition in sheep milk fat with increased availability of polyunsaturated FA (PUFA) in grass, and subsequently, in milk. Consequently, the objective of this work was to study the FA profile in sheep milk during grazing in four geographical areas in the Alps. A total of 15 ewes of the Bovec sheep breed were randomly selected and milk samples from these ewes were taken at four different pasture locations that differed with regard to altitude: the L pasture location at an altitude of 480 m, the mountain pastures (M1 and M2) at altitudes of 1100 to 1300 m and 1600 to 1900 m, respectively, and the H pastures at altitudes of 2100 to 2200 m. Milk samples from the ewes were taken during the grazing season from April to September. The chemical and FA composition of the milk samples from each pasture location were determined. There were significant differences in the concentrations of FA among the L, M1, M2 and H milk samples. We observed decreases of the concentrations of saturated FA (SFA) in milk from L to H pastures. The concentration of α-linolenic FA, monounsaturated FA (MUFA), PUFA and n-3 PUFA in milk were increased significantly with pasture altitude. The n-6/n-3 PUFA ratio was reduced by the change of pasture altitude with the lowest value at the M1 pasture (1.5). The concentrations of total SFA decreased significantly and was lowest at the L pasture. Our results underline the importance of the effect of grazing in the Alpine region associated with pasture altitude on the FA profile of sheep milk. The first variation in FA concentration in sheep milk occurred between L and M1, although it was more evident on H pastures in the Alpine mountains. Changes of the FA profile in sheep milk due to pasture altitude were related to variation in FA concentration in the pasture and the botanical composition of the pasture location.     

青藏高原人工草地土壤可溶性氮组分与植被生产力动态变化过程

氮作为人工草地最为重要的限制性因子, 在时间、空间上分布不均匀, 且在形态上存在差异, 与种植方式及地上净初级生产力(ANPP)存在相关关系。该研究以青海省同德牧场的无芒雀麦(Bromus inermis)、老芒麦(Elymus sibiricus)、垂穗披碱草(E. nutans)、西北羊茅(Festuca ryloviana)、中华羊茅(F. sinensis)、青海扁茎早熟禾(Poa pratensis var. anceps ‘Qinghai’)、冷地早熟禾(P. crymophila)、星星草(Puccinellia tenuiflora) 8种牧草单播人工草地为研究对象, 分析人工草地土壤可溶性氮库季节和年际动态变化过程及与ANPP之间的相互关系。该人工草地种植于2013年, 在2014-2016年(二龄、三龄和四龄)生长季6-9月测定土壤铵态氮(NH₄⁺-N)、硝态氮(NO₃^--N)、可溶性有机氮(SON)和可溶性总氮(STN)含量, 每年9月初测定ANPP, 所有样地没有施肥, 每年9月中旬刈割, 留茬5 cm。研究发现: (1) 8种禾本科牧草的ANPP在329.67-794.67 g·m^-2之间, 其中垂穗披碱草为794.67 g·m^-2, 显著高于其他牧草。(2)在二至四龄人工草地中, 土壤NO₃^--N、SON和STN含量均显著下降, 但NH₄⁺-N含量却显著增加。(3)土壤可溶性氮以SON为主, 占STN的45.11%-88.76% (0-10 cm)和47.75%-88.18% (10-20 cm); 其次为NO₃^--N, 占STN的5.81%-34.85% (0-10 cm)和6.08%-40.42% (10-20 cm); NH₄⁺-N最少仅3.41%-22.18% (0-10 cm)和3.09%-19.56% (10-20 cm)。(4)非度量多维尺度分析(NMDS)结果显示, 随种植年限的增加, 不同禾本科牧草对0-10 cm土壤可溶性氮影响趋于离散, 而对10-20 cm土壤的影响则相反, 且牧草对土壤可溶性氮含量的影响程度与土壤深度有关。(5)相关性分析表明, 土壤SON、STN含量与人工草地ANPP呈正相关关系, 与无机氮(IN)含量呈负相关关系。综上所述, 三至四龄人工草地增施氮肥是维持草地生产力的关键因素。以上结果为更深入了解青藏高原人工草地土壤可溶性氮动态变化及维持人工草地生产力和稳定性提供了科学依据。     

Feeding Life Style of Redlegged Earth Mite, Halotydeus Destructor (Acari: Penthaleidae), in pastures and the role of broad-leafed weeds

Redlegged earth mite, Halotydeus destructor, is a major pest of pastures and crops in Australia, and also feeds on lower plants on the soil surface. Feeding behaviour is reviewed, and the role of Arctotheca calendula, capeweed, in determining occurrence and abundance in pastures is investigated. Mites fed more and produced more progeny on Trifolium subterraneum (subclover) than on capeweed in non-choice experiments. In pastures with mixed species three times more mites were feeding on subclover than on capeweed foliage. However, twice as many mites were found on the soil surface under pasture patches consisting mainly of capeweed than of subclover. Patches were selected on the basis of pasture height, irrespective of plant composition. Twice as many mites were found in populations under patches of tall than short pasture. The daytime relative humidity was higher in tall than short patches, and the temperature slightly lower, making tall patches a more favourable niche for these mites. Ninety per cent of H. destructor were on the soil surface, while 10% were feeding on the upper canopy of pasture. The proportion of each population that was feeding was greater on subclover than capeweed, and subclover was a more suitable food. In Australia H. destructor occurs in regions with mixed pasture species, grown in rotation with grain crops. The ability of H. destructor to utilize foliage of a range of plant species of differing suitability for food, while living mostly on the soil surface in niches favourable for survival, has enabled it to become very abundant.     

Winter Resistant Oocysts in the Pasture as a Source of Coccidial Infection in Lambs

Lambs born in pens with slatted floor were brought out at 2–5 weeks of age on pastures heavily grazed by sheep the previous years. About 16 days later the oocyst output of the lambs rapidly increased to high levels. Lambs on pastures which never had been grazed by sheep earlier, had moderate oocyst counts. Between 11 and 25 days after the beginning of grazing there were significantly more lambs with diarrhoea on permanent pastures compared with pastures never grazed by sheep earlier. It was found that lambs were heavily infected during the first 2 days on permanent pastures. Thirteen housed lambs were given 10–50 g of soil from a permanent pasture as a water suspension by a stomach tube. Fifteen days later there was a steep rise in the oocyst output in most of them, and 11 of the 13 lambs developed diarrhoea and 2 died. None of 10 lambs given uninfected soil and none of 12 untreated controls showed diarrhoea and the oocyst output remained on a moderate level. It is concluded that oocysts which have survived the winter in the pasture are the main source of infection with Eimeria spp. in lambs with this kind of management. Soil-eating is the most likely source of infection during the first days on pasture.     

Fruit production ofattalea colenda (arecaceae) in coastal ecuador—an alternative oil resource?

Attalea colenda is a monoecious palm found in pastures in coastal Ecuador. In dry regions, it is a valuable source of oil in self-sufficiency farming or in combination with cattle in pastures. The palm was studied over a gradient of dry to humid environments during two fruiting seasons. Palm growth, production of leaves, inflorescences, and infructescences, number of fruits per infructescence, and seed weight of five populations were evaluated. The individual of average size is 15 m tall, which corresponds to approximately 30–40 years of age. No difference in fruit production was recorded between wet and dry regions of coastal Ecuador. The average production of one hectare of pasture, with 50 palms, was 0.9 t of oil per year. One population that was part of an agroforestry system produced 50% more fruits than the average of all populations in pasture.     

Pollen dispersal and genetic structure of the tropical tree Dipteryx panamensis in a fragmented Costa Rican landscape

In the face of widespread deforestation, the conservation of rainforest trees relies increasingly on their ability to maintain reproductive processes in fragmented landscapes. Here, we analysed nine microsatellite loci for 218 adults and 325 progeny of the tree Dipteryx panamensis in Costa Rica. Pollen dispersal distances, genetic diversity, genetic structure and spatial autocorrelation were determined for populations in four habitats: continuous forest, forest fragments, pastures adjacent to fragments and isolated pastures. We predicted longer but less frequent pollen movements among increasingly isolated trees. This pattern would lead to lower outcrossing rates for pasture trees, as well as lower genetic diversity and increased structure and spatial autocorrelation among their progeny. Results generally followed these expectations, with the shortest pollen dispersal among continuous forest trees (240 m), moderate distances for fragment (343 m) and adjacent pasture (317 m) populations, and distances of up to 2.3 km in isolated pastures (mean: 557 m). Variance around pollen dispersal estimates also increased with fragmentation, suggesting altered pollination conditions. Outcrossing rates were lower for pasture trees and we found greater spatial autocorrelation and genetic structure among their progeny, as well as a trend towards lower heterozygosity. Paternal reproductive dominance, the pollen contributions from individual fathers, did not vary among habitats, but we did document asymmetric pollen flow between pasture and adjacent fragment populations. We conclude that long-distance pollen dispersal helps maintain gene flow for D. panamensis in this fragmented landscape, but pasture and isolated pasture populations are still at risk of long-term genetic erosion.     

Young restored forests increase seedling recruitment in abandoned pastures in the Southern Atlantic rainforest

Planting seedlings is a common technique for abandoned pastures restoration in the tropics, supposedly by increasing the seedling recruitment and accelerating succession. In this study we evaluated the role of a young restored forest (one year old) in enhancing seedling establishment from two sources (seed rain and seed bank), in the Atlantic Rainforest region in Southern Brazil. We compared abandoned pasture, young restored forest and old-growth forest with respect to the seedlings recruited from different sources, by monitoring 40 permanent plots (0.5 m x 0.5 m) over 20 months. From the three studied areas a total of 392 seedlings of 53 species were recruited. Species were mainly herbaceous (85%), pioneers (88%), zoochorous (51%) and small-seeded species (60%). Seedling recruitment from the seed bank (density and species richness) was higher and dominated by herbaceous species in the abandoned pasture and in the young restored forest; on the other hand, the recruitment of woody species from seed rain was more pronounced in the old-growth forest. The young restored forest increased the species richness of woody seedlings recruitment from the seed bank (two-fold) and from seed rain (three-fold) compared to the abandoned pasture. Also, the seedling density in young restored forest was still higher than abandoned pastures (seed bank: four times; seed rain: ten times). Our results show that even young restored areas enhance the establishment of woody species and should be considered an important step for pasture restoration.