Spatiotemporal variation in the strength of density dependence: implications for biocontrol of <Emphasis Type="Italic">Centaurea solstitialis</Emphasis>

Invasive plants often occupy large ranges in the introduced region and consequently, local population dynamics vary in ways that affect the potential for biological control. We used matrix models to describe how density and population growth rate of Centaurea solstitialis varies in time and space. Matrix models were parameterized with data collected over 4 years from invasions at the coast, interior valleys and Sierra Nevada Mountains in California (USA). Asymptotic population growth rates (λ) varied dramatically across all populations and years (0.24–6.45), density varied by an order of magnitude and had a measurable effect on survival and λ in all populations. We used simulations to estimate the degree to which a biocontrol agent would need to reduce plant survival to control the weed. Because seedling survival was dependent on density, an agent that reduced seedling density had the effect of increasing the probability that the remaining plants survived to flowering. Interestingly, this meant that in the highest density populations the plant had the largest compensatory response to agent attack and experienced decline (λ ≤ 1.0) only after heavy losses (≥90%) to the agent. Conversely, in populations where density was so low that it had only a weak effect on survival, the agent was able to control the plant (λ ≤ 1.0) at much lower levels of attack (≤50%). In other words, the impact of a biocontrol agent is predicted to be lower where the plant reaches its highest densities because the surviving plants, now experiencing less intraspecific competition, are more likely to survive to flowering and produce more seeds. This may also be true for other invasive species in which strong density dependent processes are operating. For this reason, prospective agents ought to target density-independence vital rates.     

Anti-cyanobacterial activity of <Emphasis Type="Italic">Moringa oleifera</Emphasis> seeds

Filtrates from crushed Moringa oleifera seeds were tested for their effects on growth and Photosystem II efficiency of the common bloom-forming cyanobacterium Microcystis aeruginosa. M. aeruginosa populations exhibited good growth in controls and treatments with 4- and 8-mg crushed Moringa seeds per liter, having similar growth rates of 0.50 (±0.01) per day. In exposures of 20- to 160-mg crushed Moringa seeds L⁻¹, growth rates were negative and on average −0.23 (±0.05) .day⁻¹. Presumably, in the higher doses of 20- to 160-mg crushed seeds per liter, the cyanobacteria died, which was supported by a rapid drop in the Photosystem II efficiency (Φ_PSII), while the Φ_PSII was high and unaffected in 0, 4, and 8 mg L⁻¹. High-density populations of M. aeruginosa (chlorophyll-a concentrations of ∼270 μg L⁻¹) were reduced to very low levels within 2 weeks of exposure to ≥80-mg crushed seeds per liter. At the highest dosage of 160 mg L⁻¹, the Φ_PSII dropped to zero rapidly and remained nil during the course of the experiment (14 days). Hence, under laboratory conditions, a complete wipeout of the bloom could be achieved. This is the first study that yielded evidence for cyanobactericidal activity of filtrate from crushed Moringa seeds, suggesting that Moringa seed extracts might have a potential as an effect-oriented measure lessening cyanobacterial nuisance.     

Postharvest growth dynamic of <Emphasis Type="Italic">Schoenoplectus californicus</Emphasis> along fluvio-estuarine and flooding gradients

The emergent wetland plant Schoenoplectus californicus is used as fiber in several American countries, but the effects of harvesting on this species have not previously been studied. We analyzed the biomass production, stem density and morphometry of this species along fluvio-estuarine and flooding gradients and evaluated the effects of harvesting on growth and recovery capacity in the Santa Lucía River (Uruguay), comparing river sections and surface elevations. Differences in biomass, length and stem density were associated with the dynamics of the hydrological regime. The mean biomass and length growth rates were 3.0 ± 2.8 g day^?1 and 0.8 ± 0.5 cm day^?1, respectively. The analysis of the postharvest growth dynamic showed variation among the stems, suggesting the existence of mechanisms of plant compensation for the harvest effect. Six months after the harvest, S. californicus had recovered, e.g., in stem length and density, while the biomass showed a slower recovery. Our results suggest that the recovery capacity of this species depends on the population structure before the harvest and on favorable conditions during the recovery period. Based on our results, we recommend strategies for sustainable harvest management.     

Distribution and habitats of <Emphasis Type="Italic">Phengaris</Emphasis> (<Emphasis Type="Italic">Maculinea</Emphasis>) butterflies and population ecology of <Emphasis Type="Italic">Phengaris</Emphasis><Emphasis Type="Italic">teleius</Emphasis> in China

Many species of the butterfly genus Phengaris are regarded as endangered in many parts of their distribution. Several species are also widely distributed across northern China. Due to land use change and overgrazing, their habitats are declining and many patches have been lost. This paper investigates the distribution and habitats of the Chinese Phengaris species (of the subgenus Maculinea). Shrub-grassland near forests seem the most frequent habitat for Phengaris, while flat open grasslands are mostly over-grazed and thus survival for Phengaris butterflies there seems difficult. Throughout Europe, P. teleius is an endangered species, while there is still no information on its status in China. To improve the knowledge on the population ecology of P. teleius, its population structure, adult behaviour and movement were studied through mark–release–recapture methods in the Qinling Mountains of Taibai County. Eight grassland patches which were potentially suitable were found in the area in 2013. In total, 480 individuals (274 females) were marked, resulting in an overall recapture rate of 16 %. The average daily population size was 44 butterflies (±23 SD) during the adult flight period. Sixty-seven percent of the females and 38 % of the males moved less than 50 m, and 17 % of recaptured females and 38 % of males moved more than 200 m. The mean movement distance was 107 ± 177 m for males and 182 ± 122 m for females. The majority of the recaptures (86 %) were made within the patches, only a few individuals (14 %) moved between patches. Due to human disturbance and destruction, all of the eight potentially suitable patches are becoming smaller and increasingly isolated, thus these populations of P. teleius may face an increasing risk of extinction, which may well be a tip of the iceberg of habitat loss and fragmentation of P. teleius in Taibai County and possibly beyond. Hence we hope our initial study of P. teleius could have positive impacts on the conservation of Phengaris butterflies in China.     

Different plant provenance same seed tolerance to abiotic stress: implications for <Emphasis Type="Italic">ex situ</Emphasis> germplasm conservation of a widely distributed coastal dune grass (<Emphasis Type="Italic">Uniola paniculata</Emphasis> L.)

Preservation of genetic diversity within germplasm repositories represents an important tool for plant conservation. However, seeds must tolerate extreme levels of post-harvest desiccation and cold to realize benefits of ex situ storage. Factors including local climate and habitat impact expression of desiccation and freezing tolerance especially for widely distributed species. Our aim here was to understand the influence of a latitudinal gradient on seed desiccation and cryo-freezing tolerance. We sampled mature U. paniculata seeds from two geographically and genetically distinct populations then examined seed-water relations and germination following desiccation via equilibrium drying assays (0.5 to 91% RH; ?797 to ?12.9 MPa). Germination ability after drying and subsequent cryo-freezing treatments (?196?°C, 1 to 1440 min) was also evaluated. Seeds of both populations displayed similar reverse sigmoid moisture sorption isotherms characteristic of desiccation tolerant tissues. Furthermore, initial seed water potential (?63 and ?90 MPa) was considerably lower than the lethal limit (?20 MPa) identified for desiccation sensitive tissues. Final germination (range 58–93%) and temporal patterns differed significantly between populations following desiccation and cryo-freezing stress, but these germination responses were similar to initial germination. A higher proportion of non-germinated, yet viable seeds remained for the northern compared to southern population. Location does influence germination response, but differential germination is related to seed dormancy rather than desiccation or cryo-freezing sensitivity. Ex situ conservation of U. paniculata is therefore feasible across the latitudinal gradient studied here.     

Reproductive biology of the endangered Bulgarian endemic <Emphasis Type="Italic">Centaurea achtarovii</Emphasis> (<Emphasis Type="Italic">Asteraceae</Emphasis>)

Centaurea achtarovii Urum. is a Bulgarian endemic, distributed only in Pirin Mountain. It is protected by the Biodiversity Act and included in the Red Data Book of Bulgaria as “endangered”. Assessment of size and density was carried out of both known populations of the species, around Orelyak summit and Kazanite locality. It was conducted in 2 sampling plots of 1000 square meters in each population and revealed their good condition. Population of Orelyak was larger and with higher density than that of Kazanite: 75 ha, 0.58 individuals per m² (an average of 0.56 rosettes and 0.02 in flowering stage), and 35 ha, 0.23 individuals per m² (an average of 0.16 rosettes and 0.07 in flowering stage), respectively. Elucidation of the reproductive biology of C. achtarovii was important in order to find the most appropriate conservation strategy for the species. Flower buds and open flowers in different stages of development were treated by the classical paraffin methods. The structures in male and female generative spheres were stable, the processes leading to formation of embryos and seeds were balanced, and no apomixes was noticed. Pollen viability assessed by acetocarmine test was over 50%, and seed viability estimated by tetrazolium test was 17.5%. In vitro seed germination was poor and culture growth was slow. The low viability of seeds, and the small amount of pollen, although with relatively high fertility, determined a low reproductive capacity of the species. In situ strategies reducing competitive species like Juniperis sibirica were recommended.     

Linkages of <Emphasis Type="Italic">Firmicutes</Emphasis> and <Emphasis Type="Italic">Bacteroidetes</Emphasis> populations to methanogenic process performance

To identify potential linkages between specific bacterial populations and process performance in anaerobic digestion, the dynamics of bacterial community structure was monitored with high-throughput sequencing in triplicate anaerobic digesters treating animal waste. Firmicutes and Bacteroidetes were found as the two most abundant populations, however, with contrasting population dynamics in response to organic overloading. Firmicutes dominated the bacterial community during stable process performance at low organic loading rate, representing over 50 % of the bacterial abundance. In contrast, the onset of organic overloading raised the relative abundance of Bacteroidetes from 20 ± 2.6 to 44 ± 3.1 %. In addition to the significant negative correlation between the relative abundance of Firmicutes and Bacteroidetes, populations of Firmicutes and Bacteroidetes were found to be linked to process parameters including organic loading rate, volatile fatty acids concentration, and methane production. Therefore, the population abundance ratio of Firmicutes to Bacteroidetes (F/B ratio) was suggested as a potential indicator for process performance. The interactions between Firmicutes and Bacteroidetes populations could be exploited to develop strategies for the prevention of performance perturbation in anaerobic digestion processes.     

Analysis of wood thrush (<Emphasis Type="Italic">Hylocichla mustelina</Emphasis>) movement patterns to explain the spatial structure of American ginseng (<Emphasis Type="Italic">Panax quinquefolius</Emphasis>) populations

American ginseng (Panax quinquefolius) is America’s premier wild-harvested, medicinal plant that inhabits the forest understory of eastern deciduous forests. Recent research revealed that birds, particularly wood thrushes (Hylocichla mustelina), disperse ginseng seeds by regurgitating viable seeds 15–37 min after consuming the berries. We carried out two studies to examine the potential effect of thrushes on spatial dispersion patterns of ginseng. First, to analyze how far wood thrushes could disperse seeds, two wood thrushes were outfitted with radio transmitters and tracked for multiple days. Second, for 28 natural populations of ginseng, we created a clustering index to quantify to what degree populations were structured into spatially separated units. To further detect spatial impacts of thrushes, we analyzed inter-cluster distances and the overall spread of ginseng populations. Over the time period in which wood thrushes retain ginseng in their guts, the seeds would be dispersed a mean distance of 15.2–21.7 m. The observed distances ranged from 0–96.6 m. These distances were comparable to the overall spread metric for ginseng populations with wood thrushes, which had increased spacing in comparison to those without wood thrushes. The mean dispersion index differed for populations with and without wood thrushes. It is imperative to understand the interaction between wood thrushes and ginseng to facilitate conservation, as both species are experiencing population declines. Dispersal of seeds by wood thrushes could play an important role in allowing species such as ginseng to respond to climate change, deer browse, overharvesting, and other environmental stresses.     

Population Dynamics of <Emphasis Type="Italic">Agave marmorata</Emphasis> Roezl. under Two Contrasting Management Systems in Central Mexico

Population Dynamics of Agave marmorata Roezl. under Two Contrasting Management Systems in Central Mexico. This paper evaluates the impacts of traditional management on the population dynamics of Agave marmorata, a multipurpose, useful species that is dominant in the Zapotitlán Salinas Valley, Puebla, Mexico. During 2002–2003 and 2003–2004, we constructed matrix models for two populations—one unmanaged, the other subject to plant extraction and cutting of flowering stalks. We also conducted prospective (elasticity) and retrospective (life table response experiments) analyses. Overall, the unmanaged population had higher finite rates of increase (λ) than the managed one. This variation in λ was the result of a decrease in the individual growth and fecundity in the managed population. Survival and growth were the demographic processes with the highest contribution to λ in the unmanaged population, while survival was the most important in the managed one. Our results suggest that management and plant extraction practices could be having negative effects on the population dynamics of this plant species. Recommendations are provided in order to promote positive effects on its vital rates and regeneration capacity.     

Development and characterization of <Emphasis Type="Italic">japonica</Emphasis> rice lines carrying the brown planthopper-resistance genes <Emphasis Type="Italic">BPH12</Emphasis> and <Emphasis Type="Italic">BPH6</Emphasis>

The brown planthopper (Nilaparvata lugens Stål; BPH) has become a severe constraint on rice production. Identification and pyramiding BPH-resistance genes is an economical and effective solution to increase the resistance level of rice varieties. All the BPH-resistance genes identified to date have been from indica rice or wild species. The BPH12 gene in the indica rice accession B14 is derived from the wild species Oryza latifolia. Using an F₂ population from a cross between the indica cultivar 93-11 and B14, we mapped the BPH12 gene to a 1.9-cM region on chromosome 4, flanked by the markers RM16459 and RM1305. In this population, BPH12 appeared to be partially dominant and explained 73.8% of the phenotypic variance in BPH resistance. A near-isogenic line (NIL) containing the BPH12 locus in the background of the susceptible japonica variety Nipponbare was developed and crossed with a NIL carrying BPH6 to generate a pyramid line (PYL) with both genes. BPH insects showed significant differences in non-preference in comparisons between the lines harboring resistance genes (NILs and PYL) and Nipponbare. BPH growth and development were inhibited and survival rates were lower on the NIL-BPH12 and NIL-BPH6 plants compared to the recurrent parent Nipponbare. PYL-BPH6 + BPH12 exhibited 46.4, 26.8 and 72.1% reductions in population growth rates (PGR) compared to NIL-BPH12, NIL-BPH6 and Nipponbare, respectively. Furthermore, insect survival rates were the lowest on the PYL-BPH6 + BPH12 plants. These results demonstrated that pyramiding different BPH-resistance genes resulted in stronger antixenotic and antibiotic effects on the BPH insects. This gene pyramiding strategy should be of great benefit for the breeding of BPH-resistant japonica rice varieties.     

Landscape genetic structure of <Emphasis Type="Italic">Olea europaea</Emphasis> subsp. <Emphasis Type="Italic">cuspidata</Emphasis> in Ethiopian highland forest fragments

Understanding patterns of genetic diversity at the landscape scale will enhance conservation and management of natural populations. Here we analyzed the genetic diversity, population connectivity, and spatial genetic structure among subpopulations and age groups of Olea europaea subsp. cuspidata, a cornerstone species of the Afromontane highlands. The study was conducted at the landscape level within a radius of approximately 4 km, as well as on a fine scale (intensive study plot) of less than 300 m radius. In total 542 samples from four natural subpopulations in northwestern Ethiopia were analyzed using ten nuclear microsatellite markers. Inbreeding was higher in smaller populations. No genetic difference was detected among cohorts of different tree sizes in the intensive studied plot. Average population differentiation was low but significant (F _ST ?=?0.016). Landscape genetic analysis inferred two groups: the most distant subpopulation WE located less than 4 kms from the other three subpopulations formed a separate group. Sixty-four percent of the total migrants were shared among the three latter subpopulations, which are spatially clustered. Immigrants were non-randomly distributed inside of the intensive study plot. Significant spatial genetic structure (SGS) was found both at the landscape scale and in the intensive study plot, and adults showed stronger SGS than young trees. An indirect estimate of 220 m as mean gene dispersal distance was obtained. We conclude that even under fragmentation migration is not disrupted in wild olive trees and that large protected populations at church forests are very important to conserve genetic resources. However, the higher level of inbreeding and evidence for population bottlenecks in the small populations, as well as the persisting heavy pressure on most remaining populations, warrants quick action to maintain genetic diversity of wild olive in the Ethiopian highlands.     

Resistance to herbivory of two populations of <Emphasis Type="Italic">Elodea</Emphasis><Emphasis Type="Italic">canadensis</Emphasis> Michaux and <Emphasis Type="Italic">Elodea nuttallii</Emphasis> Planchon St. John

In this article, we compared the resistance of two introduced populations of Elodea nuttallii and Elodea canadensis to two different herbivores. Samples were collected from the River Rhine and River Rhône in eastern France. The two populations of E. nuttallii differed in their introduction history, whereas E. canadensis was introduced at the same time in the two sites. The Daily Food Consumption (DFC) rates of the two macrophyte populations were evaluated in no-choice experiments using the scraper Lymnaea stagnalis and the shredder Gammarus roeseli. At the same time, we assessed four plant traits: dry matter content (DMC), total nitrogen content, carbon/nitrogen ratio and total phenolic content. The two populations of E. canadensis were consumed at low levels by both the herbivores. L. stagnalis showed a higher DFC on the Rhône population of E. nuttallii than on the Rhine population. No significant difference between the two populations was established with G. roeseli, but the level of DFC was high. This result demonstrates that the assessment of plant palatability should be carried out with several generalist herbivores belonging to various feeding groups (e.g. scrapers or shredders). Although the Rhône population of E. nuttallii had higher levels of phenols than the other populations, it was consistently consumed in greater quantities than E. canadensis. Neither the phenolic contents were not effective against these herbivores, nor the levels of phenolics too low to induce an efficient resistance. The higher DMC and the lower DFC of the two populations of E. canadensis suggest that this introduced plant has co-evolved with indigenous enemies in the introduced range.     

Simultaneous production of intracellular triacylglycerols and extracellular polyol esters of fatty acids by <Emphasis Type="Italic">Rhodotorula babjevae</Emphasis> and <Emphasis Type="Italic">Rhodotorula</Emphasis> aff. <Emphasis Type="Italic">paludigena</Emphasis>

Microbial oils have been analyzed as alternatives to petroleum. However, just a handful of microbes have been successfully adapted to produce chemicals that can compete with their petroleum counterparts. One of the reasons behind the low success rate is the overall economic inefficiency of valorizing a single product. This study presents a lab-scale analysis of two yeast species that simultaneously produce multiple high-value bioproducts: intracellular triacylglycerols (TG) and extracellular polyol esters of fatty acids (PEFA), two lipid classes with immediate applications in the biofuels and surfactant industries. At harvest, the yeast strain Rhodotorula aff. paludigena UCDFST 81-84 secreted 20.9 ± 0.2 g L^?1 PEFA and produced 8.8 ± 1.0 g L^?1 TG, while the yeast strain Rhodotorula babjevae UCDFST 04-877 secreted 11.2 ± 1.6 g L^?1 PEFA and 18.5 ± 1.7 g L^?1 TG. The overall glucose conversion was 0.24 and 0.22 g_{(total lipid)} g _(glucose) ^?1 , respectively. The results present a stable and scalable microbial growth platform yielding multiple co-products.     

<Emphasis Type="Italic">In vitro</Emphasis> germination and axillary shoot propagation of <Emphasis Type="Italic">Centaurea zeybekii</Emphasis>

In vitro culture is an important aid for ex situ conservation of rare, endemic or threatened plants. In this work, we establish an efficient method for the seed germination, seedling development, and axillary shoot propagation of Centaurea zeybekii Wagenitz. The seeds, collected from a wild population, were surface sterilised and cultured on various in vitro germination media. The effects of photoperiod and temperature on seed germination were also investigated. Germinations were obtained after 6 weeks in culture and the radicle emergence was evaluated as a main indicator. A high frequency of germination was obtained on distilled water supplemented with vitamines and 1 mg/L GA₃. Although the seed germination frequencies were not affected by photoperiod, the highest germination frequency was obtained at 24 ± 2°C. A high frequency of axillary shoot proliferation was produced on MS medium supplemented with 1 mg/L BA. Then, the axillary shoots were separated and transferred to MS medium with or without plant growth regulators for rooting. Rhizogenezis was promoted after 6 weeks only in MS and 1/2 MS media containing 0.5 mg/L IBA. The rooting process was very slow and the percentage of shoot rooting was also very low (15%). The present study not only enables reinforcement of wild plant populations using ex situ growth of individuals, but it also helps to large number of aseptic seedling to use it in clonaly micropropagation studies.     

Sympatric reinforcement of reproductive barriers between <Emphasis Type="Italic">Neotinea tridentata</Emphasis> and <Emphasis Type="Italic">N. ustulata</Emphasis> (Orchidaceae)

Reinforcement is the process by which selection favors traits that decrease mating between two incipient species in response to costly mating or the production of maladapted hybrids, causing the evolution of greater reproductive isolation between emerging species. I have studied a pair of orchids, Neotinea tridentata and N. ustulata, to examine the level of postmating pre- and post-zygotic isolating mechanisms that maintain these species, and the degree to which the boundary may still be permeable to gene flow. In this study, I performed pollen tube growth rate experiments and I investigated pre- and post-zygotic barriers by performing hand pollination experiments in order to evaluate fruit set, embryonate seed set and seed germination rates by intra- and interspecific crosses. Fruit set, the percentage of embryonate seeds and germinability of interspecific crosses were reduced compared to intraspecific pollinations, showing significant differences between sympatric and allopatric populations. While in allopatric populations the post-pollination isolation index ranged between 0.40 and 0.11, in sympatric populations orchid pairs showed total isolation due to post-pollination prezygotic barriers, guaranteed at the level of pollen–stigma interactions. Indeed, in sympatric populations, pollen tubes reached the ovary after 24 h in only 8 out of 45 plants; in the remaining cases, the pollen tubes did not enter the ovary, and thus no fruit set occurred. This pair of orchids is characterized by postmating pre-zygotic reproductive isolation in sympatric populations that prevents the formation of hybrids. This mechanism of speciation, starting in allopatry and triggering the reinforcement mechanisms of reproductive isolation in secondary sympatry, is the most likely explanation for the pattern of evolutionary transitions found in this pair of orchids.     

High-efficient <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated <Emphasis Type="Italic">in planta</Emphasis> transformation in black gram (<Emphasis Type="Italic">Vigna mungo</Emphasis> (L.) Hepper)

In vitro culture and genetic transformation of black gram are difficult due to its recalcitrant nature. Establishment of gene transfer procedure is a prerequisite to develop transgenic plants of black gram in a shorter period. Therefore, genetic transformation was performed to optimize the factors influencing transformation efficiency through Agrobacterium tumefaciens-mediated in planta transformation using EHA 105 strain harbouring reporter gene, bar, and selectable marker, gfp-gus, in sprouted half-seed explants of black gram. Several parameters, such as co-cultivation, acetosyringone concentration, exposure time to sonication, and vacuum infiltration influencing in planta transformation, have been evaluated in this study. The half-seed explants when sonicated for 3 min and vacuum infiltered for 2 min at 100 mm of Hg in the presence of A. tumefaciens (pCAMBIA1304– bar) suspensions and incubated for 3 days co-cultivation in MS medium with 100 µM acetosyringone showed maximum transformation efficiency (46 %). The putative transformants were selected by inoculating co-cultivated seeds in BASTA^® (4 mg l^?1) containing MS medium followed by BASTA^® foliar spray on 15-day-old black gram plants (35 mg l^?1) in green house, and the transgene integration was confirmed by biochemical assay (GUS), Polymerase chain reaction, Dot-blot, and Southern hybridisation analyses.     

Regional chronologies of <Emphasis Type="Italic">Cedrela</Emphasis><Emphasis Type="Italic">fissilis</Emphasis> and <Emphasis Type="Italic">Cedrela angustifolia</Emphasis> in three forest types and their relation to climate

Key message

Although tree-ring chronologies of Cedrela fissilis and Cedrela angustifolia showed a common climatic signal, local conditions influence growth, suggesting that forest guidelines should be appropriate to the species and context.

Abstract

Cedrela species are highly valued because of the quality of their timber. Understanding the behaviour of each different Cedrela species and their ecology is of importance to ensuring that forest harvesting and management do not endanger the survival of natural populations. These species grow in a wide range of environmental gradients and different types of forests in Bolivia. This study used dendrochronological methods to analyse growth–precipitation relationships of two Cedrela species coming from three locations with different environmental conditions: dry Chiquitano (Concepción), Chiquitano transitional Amazonian (Guarayos), and Bolivian-Tucuman montane forests (Postrervalle). The rainy season in all locations runs from October to April and the dry season runs from May to September. Twelve Cedrela fissilis specimens were sampled from dry Chiquitano, 11 Cedrela fissilis specimens from Chiquitano transitional Amazonian, and 30 Cedrela angustifolia specimens from Bolivian-Tucuman montane forests. The samples were crossdated and exhibited a common signal between trees from three sites, despite tree rings from the Chiquitano transitional Amazonian forest being narrower and displaying blurred bands of parenchyma in the boundaries. Significant inter-series correlation was found for the C. fissilis species series from dry Chiquitano with r = 0.261 (p < 0.01) and Chiquitano transitional Amazonian forests with r = 0.284 (p < 0.01), and for Cedrela angustifolia from Bolivian-Tucuman montane forests with r = 0.374 (p < 0.01). Mean annual growth was 2.07, 1.92, and 2.82 mm year^?1 at the three sites, respectively. Cedrela species from dry Chiquitano and Bolivian-Tucuman montane forests were sensitive to precipitation from October to April of the current growth year (wettest season) and to low temperatures from May to July of the current growth year (driest season). Samples from Chiquitano transitional Amazonian were more sensitive to precipitation during late rainy season (March, April, and May of the current growth year) and high temperatures during the rainy months (November–December). Growth differences between sites and species in response to climate variations and local conditions should be taken into account and handled with different forest management guidelines.

     

Comparative <Emphasis Type="Italic">in vitro</Emphasis> germination ecology of <Emphasis Type="Italic">Calopogon tuberosus</Emphasis> var. <Emphasis Type="Italic">tuberosus</Emphasis> (Orchidaceae) across its geographic range

Seed responses to temperature are often essential to the study of germination ecology, but the ecological role of temperature in orchid seed germination remains uncertain. The response of orchid seeds to cold stratification have been studied, but the exact physiological role remains unclear. No studies exist that compare the effects of either cold stratification or temperature on germination among distant populations of the same species. In two separate experiments, the role of temperature (25, 22/11, 27/15, 29/19, 33/24°C) and chilling at 10°C on in vitro seed germination were investigated using distant populations of Calopogon tuberosus var. tuberosus. Cooler temperatures promoted germination of Michigan seeds; warmer temperatures promoted germination of South Carolina and north central Florida seeds. South Florida seed germination was highest under both warm and cool temperatures. More advanced seedling development generally occurred at higher temperatures with the exception of south Florida seedlings, in which the warmest temperature suppressed development. Fluctuating diurnal temperatures were more beneficial for germination compared to constant temperatures. Cold stratification had a positive effect on germination among all populations, but South Carolina seeds required the longest chilling treatments to obtain maximum germination. Results from the cold stratification experiment indicate that a physiological dormancy is present, but the degree of dormancy varies across the species range. The variable responses among populations may indicate ecotypic differentiation.     

<Emphasis Type="Italic">Espeletia</Emphasis> giant rosette plants are reliable biological indicators of time since fire in Andean grasslands

Páramo grasslands in the tropical Andes are fire-prone ecosystems and an understanding of their fire ecology is fundamental to biodiversity conservation and ecosystem management. Fire registers are normally impractical in these remote, cloud-covered landscapes, but Espeletia giant rosette plants have been proposed as biological indicators of time since fire in páramos. Espeletia giant stem rosettes tolerate fire well, protecting apical buds in at the heart of their leaf rosettes, and for some species, germination is known to be enhanced by fire. As the plant grows, its dead leaves remain attached to the stem, but fire removes these and resets the “leaf clock”. This study uses a unique register of fires in one Ecuadorian páramo to assess the robustness of this biological indicator. Dead leaf cover on Espeletia pycnophylla giant rosette plants was measured in fifteen different sites with known fire dates from 2000 to 2014. The growth rates of plants at four different elevations were measured over a 2-year period and used to estimate time since fire based on dead leaf cover in the known sites. Estimates were accurate to ± 2 year. Thus, where fire records are missing, relatively easy measurements of growth rates and dead leaf cover of Espeletia giant rosette plants can provide reliable estimates across a wide range of times since fire. This approach has value for direct investigations into fire ecology but also for studies in which controlling for fire dynamics is necessary to reveal underlying patterns. Therefore, this approach also offers a means to obtain better information on other landscape-scale processes such as the impact of climate change on biodiversity or the provision of ecosystem services.