Heavy Shade Research Articles

Exogenous nitric oxide alleviates shade-induced oxidative stress in tall fescue (Festuca arundinacea Schreb.)

SummaryNitric oxide (NO) is an important signalling molecule involved in a diverse range of physiological processes. In this study, the effects of sodium nitroprusside (SNP), a donor of NO, on the growth and anti-oxidant capacity of leaves of tall fescue [Festuca arundinacea (Schreb.) cv. Arid3] were investigated under low shade (LS), moderate shade (MS), and heavy shade (HS) applied for 7 d and 14 d in all cases. LS plants exhibited slight injury, while MS and HS caused a significant increase in cell membrane damage throughout the stress period, which was measured by enhanced electrolyte leakage (EL) and increased malondialdehyde (MDA) concentrations. Exogenous application of 0.1 mM SNP alleviated this oxidative stress, increased leaf widths and chlorophyll (Chl) concentrations, and decreased leaf lengths in plants grown under shade stress. Spray applications of of 0.1 mM SNP also increased the activities of the anti-oxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX), and the accumulation of proline in stressed leaves. Significant increases in endogenous NO concentration were found in tall fescue leaves after 7 d and 14 d of shade. SNP-treated plants grown under shade stress produced higher concentrations of NO than untreated, shaded plants. The application of SNP was more effective at reducing the detrimental effects of shade stress on tall fescue leaves under MS than under LS or HS stress. These results suggest that one or more of the breakdown product(s) of SNP might be signalling molecule(s) which enhance the activities of anti-oxidant enzymes and increase proline concentrations to alleviate oxidative damage in the leaves of tall fescue plants grown under shade stress.

Measure post-bloodmeal dispersal of mosquitoes and duration of radioactivity by using the isotope ³²P.

The radioactive isotope 32 P-labeled disodium phosphate (Na 2 H 32 PO 4 ) was injected via the jugular vein into a cow kept in a shed in Maozhuang Village, Cao Township of Shanxian County, China. Over the following 5 d, mosquitoes feeding on the cow were captured at distances up to 400 m to determine dispersal distance. The duration of radioactivity in the cow and marked mosquitoes was 10 d. The results showed that after blood feeding, Anopheles sinensis and Culex tritaeniorhynchus temporarily rested in the cattle shed and then flew outdoors. In contrast, Culex pipiens pallens remained in the cattle shed after feeding. These findings confirmed that local An. sinensis and Cx. tritaeniorhynchus were partially endophilic and tended to rest out of doors, whereas Cx. pipiens pallens was endophilic. For marked An. sinensis and Cx. tritaeniorhynchus , there was a significant tendency for dispersal to be in a northeast and east direction, probably because of the presence of heavy shading by an agricultural field, a small river for mosquito oviposition sites, and locations downwind from the blood source. The furthest flight distances for An. sinensis and Cx. tritaeniorhynchus were 210 and 240 m; therefore, control of these mosquitoes should include resting places indoors and outdoors within a radius of 250 m from confirmed cases.

Relationship Between Woody Plant Colonization and Typha L. Encroachment in Stormwater Detention Basins

We studied stormwater detention basins where woody vegetation removal was suspended for 2 years in Virginia, USA to determine if woody vegetation can control Typha populations and how early woody plant succession interacts with Typha, other herbaceous vegetation, and site factors. Distribution and composition of woody vegetation, Typha and non-Typha herbaceous vegetation biomass, and site factors were assessed at 100 plots in four basins ranging in age from 7 to 17 years. A greenhouse study examined the interaction of shade and soil moisture on Typha biomass and persistence. Principal component analysis identified an environmental gradient associated with greater water table depths and decreased elevation that favored Typha but negatively influenced woody vegetation. Elevation was correlated with litter layer distribution, suggesting that initial topography influences subsequent environmental characteristics and thus plant communities. Soil organic matter at 0-10 cm ranged from 5.4 to 12.7%. Woody plants present were native species with the exception of Ailanthus altissima and Pyrus calleryana. In the greenhouse, shade and reduced soil moisture decreased Typha biomass and rhizome length. The shade effect was strongest in flooded plants and the soil moisture effect was strongest for plants in full sun. Typha in dry soil and heavy shade had 95% less total biomass and 83% smaller rhizomes than Typha in flooded soil and full sun, but even moderate soil moisture reductions decreased above- and below-ground biomass by 63 and 56%, respectively. Suspending maintenance allows restoration of woody vegetation dominated by native species and may suppress Typha invasion.

Developmental Response of St. Augustinegrass Cultivars and Experimental Lines in Moderate and Heavy Shade

St. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is considered to be one of the most shade-tolerant warm-season turfgrasses, yet information is lacking on intraspecies developmental responses and performance in shade. This greenhouse study was conducted to 1) compare quality, development, and physiological responses of 10 commercial and experimental lines of st. augustinegrass in moderate and heavy [32% and 15% photosynthetic photon flux (PPF), respectively] shade environments’ and 2) evaluate physiological and morphological indicators that could be used in rapid screening for shade tolerance among st. augustinegrass progeny from a segregating population. A range of shade tolerance was observed between the entries, as noted by quality and percent green cover after 10 weeks of imposed shade conditions. In moderate shade, most entries maintained acceptable (6 or greater) quality and greater than 50% green cover. However, in heavy shade, only ‘Captiva’, ‘Amerishade’, and ‘PI 600734’ maintained acceptable quality, with only PI 600734 and Captiva maintaining greater than 50% cover. ‘TAES 5732-6’, an embryo rescue-derived hybrid from ‘Floratam’, exhibited the least shade tolerance of the group in both shade environments. Neither chlorophyll content nor total nonstructural carbohydrates related well to observed shade quality differences between the entries. A strong correlation existed between shoot elongation rate of a cultivar and its corresponding final percent green cover in moderate shade (R2 = 0.66) but not in heavy shade (R2 = 0.19), suggesting that moderate shade may be the better environment for discriminating genetic differences among st. augustinegrass germplasm for shade tolerance.

Orchard Design Influences Fruit Quality, Canopy Temperature, and Yield of Satsuma Mandarin (Citrus unshiu ‘Owari’)

Satsuma growers in Alabama have used various orchard designs to minimize freeze damage. These designs include interplanting between pecan and pine trees, and planting behind windbreaks. Interplanting satsuma trees with pine trees resulted in warmer temperatures within the orchard, while the other orchard designs did not moderate orchard temperature during severe freeze events. Satsuma fruit harvested from plots shaded by pine tree canopies had higher soluble solids content and reduced fruit weight. Dense pine tree canopies can provide an insulating effect that reduces freeze damage and yield losses when severe freezes occur, but heavy shading can result in lower yields when damaging freezes do not occur.

Characterization of Power Optimizer Potential to Increase Energy Capture in Photovoltaic Systems Operating Under Nonuniform Conditions

Power optimizers, which perform power conversion and distributed maximum power point tracking (DMPPT) at the subarray level, are available to mitigate losses associated with nonuniform operating conditions in grid-tied photovoltaic (PV) arrays, yet there is not a good understanding of their potential to increase energy capture. This paper develops and demonstrates a methodology for the use of a detailed software tool that can accurately model both partial shading and electrical mismatch at the subpanel level in a PV array. Annual simulations are run to examine the device-independent opportunity for power recovery in arrays with light, moderate, and heavy shading, and subpanel electrical mismatch variations based on measurements from a monocrystalline silicon array. It is found that in unshaded arrays, the potential energy gain is <; 1% using power optimizers, but in shaded arrays it increases to 3-16% for panel-level DMPPT and 7-30% for cell-level DMPPT. In the set of simulated cases, panel-level power optimization recovers 34-42% of the energy that is lost to partial shading.

Effect of shading and plant density on growth, yield and oil composition of clary sage (Salvia sclarea L.) in north western Himalaya

The experiments were commenced in January 2009 and repeated in 2010 at the CSIR-Institute of Himalayan Bioresource Technology (Council of Scientific and Industrial Research), Palampur, India to investigate the effect of shading and plant density on plant growth, yield, volatile oil content and composition in clary sage. Four levels of shade (0, 25%, 50%, 75% shade) and three planting geometry levels (30 × 30 cm, 45 × 30 cm, 45 × 45 cm) were tested as per split plot design. Plants grown in full sunlight (control) produced significantly higher number of leaves than heavy shading (75% shade). Plant spread, root length, number of roots/plant, flower weight/plant, total biomass/plant, oil content and oil yield significantly reduced with increase in shade levels. Flower yield (q/ha) was significantly higher when the crop was planted under narrow spacing 30 × 30 cm compared with 45 × 30 cm and 45 × 45 cm spacing levels. Oil content and oil yield were not affected by different spacing levels. Linalyl acetate and sclareol were higher under 25% shade, germacrene D required 50% shade, but linalool was better in open environment.

Future advantages in energetics, activity time, and habitats predicted in a high‐altitude pit viper with climate warming

Summary A future warmer climate is generally predicted to threaten reptiles. But many high‐altitude reptiles that rely on external heat to survive current cold climate may benefit from future warmth. This prediction can be tested by simulating activity time and energetics of reptiles with a biophysical model. We modelled the potential response of a high‐altitude snake, Trimeresurus gracilis, to a 3 °C increase in air temperature, using the biophysical/behavioural NicheMapper™ model. Using animal and environmental properties, we first analysed the effects of shade level (i.e. the reduction of solar radiation) on activity time and energetics of T. gracilis. We then computed activity time, energetics and potential habitats in its current range of Taroko National Park, Taiwan (&gt;1800 m in altitude), with a spatial climate, vegetation and topography data set. In the current climate, increased shade levels were predicted to decrease activity time, maintenance energy requirements and discretionary energy (i.e. energy left after maintenance costs are met). In heavy shade (i.e. 81–100% reduction of solar radiation) at 3000 and 3500 m, T. gracilis was predicted to have impaired digestive capacity and hence to be unable to meet basic maintenance costs for survival. In a warmer climate, the predicted digestive capacity, energetics and activity time of T. gracilis increase. But in heavy shade at 3500 m, the digestive capacity was predicted to remain impaired for supporting basic energy requirements for survival. In the current climate, the predicted suitable habitat area (i.e. where T. gracilis obtains positive discretionary energy) in coniferous and coniferous–broadleaf forests decreased with increasing elevation. At elevations higher than 3000 m, most suitable habitats were in open areas like grasslands where T. gracilis was also predicted to have more discretionary energy than in heavily forested habitats. Our field sightings agreed with model predictions. A warmer climate was generally predicted to increase the activity time, energetics and habitat area, given the current vegetation pattern. Overall, we demonstrate that metabolism, digestive function and vegetative shade levels are critical elements affecting T. gracilis' energetics and habitats with climate change. Trimeresurus gracilis is likely to benefit energetically from future warmth.

PHOTOSYNTHETIC ACTIVITY AND EARLY GROWTH OF FOUR CACAO GENOTYPES AS INFLUENCED BY DIFFERENT SHADE REGIMES UNDER WEST AFRICAN DRY AND WET SEASON CONDITIONS

SUMMARYThe physiological performance of four cacao clones was examined under three artificial shade regimes over the course of a year in Ghana. Plants under light shade had significantly higher photosynthetic rates in the rainy seasons whereas in the dry season there was a trend of higher photosynthetic rates under heavy shade. The results imply that during the wet seasons light was the main limiting factor to photosynthesis whereas in the dry season vapour pressure deficit was the major factor limiting photosynthesis through stomatal regulation. Leaf area was generally lower under heavier shade but the difference between shade treatments varied between clones. Such differences in leaf area allocation appeared to underlie genotypic differences in final biomass production in response to shade. The results suggest that shade for young cacao should be provided based on the current ambient environment and genotype.

Post-planting treatments and shading effects in a Fraxinus angustifolia Vahl. silvopastoral system.

Silvopastoral systems present difficulties in their management due to their complexity. When trees are planted into grasslands, they need protection from livestock to prevent damage from trampling or browsing, especially during early years of establishment. One of the common post-planting protective treatments is the protection of individual trees with shelters. Trees also need protection from competition from herbaceous vegetation. The aim of present study was to evaluate the effects of using different types of tree shelters and of controlling competing herbaceous vegetation on the growth of planted young trees and, to assess the effects of heavy shading on the herbage production and composition. The study was conducted in a Fraxinus angustifolia silvopastoral system of a 2 x 2.5 m spacing plantation in northern Greece. The effects of solid-walled (tubex and handmade by greenhouse nylon) and wire mesh tree shelters as well as of herbicide application and mechanical removal of the competing herbaceous vegetation on tree height, height increment and the crown surface area of the trees were tested. The effects of artificial shading (80%) on the production of the natural herbaceous vegetation were also investigated. All measurements were recorded three years after plantation. The use of solid wall tubex shelters resulted in higher tree height and higher crown surface area in comparison to the other tested shelters. The solid wall Nylon shelters were more beneficial to the above growth parameters than the wire mesh ones. Both vegetation control treatments proved beneficial to all the growth parameters of Fraxinus angustifolia . The artificially applied heavy shading reduced herbage production by 54% compared to the control. The results indicated that post planting treatments in the Mediterranean droughty conditions are essential for the success of this tree species establishment. Furthermore, the later thinning of the dense spacing is important to maintain high herbage production.

Forage yield and nitrogen nutrition dynamics of warm-season native forage genotypes under two shading levels and in full sunlight

The successful achievement of a highly productive understorey pasture in silvopastoral systems depends on the use of well-adapted forage genotypes, showing good agronomic performance and persistence under shading and grazing. In this study, the herbage dry matter yield (DMY) and nitrogen nutrition dynamics were determined in three native warm-season grasses (Paspalum regnellii, Paspalum dilatatum and Paspalum notatum) and a forage legume (Arachis pintoi) under two shading levels compared with full sun. The experiment was conducted in the Campanha region, Bagé, state of Rio Grande do Sul, Brazil, during two evaluation cycles (2008/2009 and 2009/2010). Three shade cloth levels (0%, 50% and 80% of light restriction) were applied to the forage genotypes in a split plot design, in which shading levels were the main plot and forage genotypes were the subplots, with three replications. P. regnellii showed the highest accumulated DMY (1500 and 1700 g m-2, respectively, for the first and second evaluation cycles) at all shading levels and showed no DMY decreased under the heavy shade (80%). Average DMY over the four genotypes under the 50% shade level was higher or equal compared with full sun. Influence of rainfall was observed on the DMY performance of all genotypes: the positive effect of moderate shading (50%) on P. dilatatum and P. notatum DMY was associated to a low soil water availability status. Increased shading level resulted in high nitrogen nutrition index values on grasses, in comparison with full sun. All genotypes performed well under the moderate shading level, but the DMY of both P. regnellii and P. dilatatum and the herbage N content in P. notatum and A. pintoi of all genotypes stood out, showing that those main genotypes are promising to grow in silvopastoral systems at the Campanha region in southern Brazil.

Using combined measurements for comparison of light induction of stomatal conductance, electron transport rate and CO2 fixation in woody and fern species adapted to different light regimes

We aimed to understand the relation of photosynthetic rate (A) with g(s) and electron transport rate (ETR) in species of great taxonomic range and light adaptation capability during photosynthetic light induction. We studied three woody species (Alnus formosana, Ardisia crenata and Ardisia cornudentata) and four fern species (Pyrrosia lingus, Asplenium antiquum, Diplazium donianum and Archangiopteris somai) with different light adaptation capabilities. Pot-grown materials received 100 and/or 10% sunlight according to their light adaptation capabilities. At least 4 months after light acclimation, CO(2) and H(2)O exchange and chlorophyll fluorescence were measured simultaneously by equipment in the laboratory. In plants adapted or acclimated to low light, dark-adapted leaves exposed to 500 or 2000 µmol m(-2) s(-1) photosynthetic photon flux (PPF) for 30 min showed low gross photosynthetic rate (P(g)) and short time required to reach 90% of maximum P(g) (). At the initiation of illumination, two broad-leaved understory shrubs and the four ferns, especially ferns adapted to heavy shade, showed higher stomatal conductance (g(s)) than pioneer tree species; materials with higher g(s) had short at both 500 and 2000 µmol m(-2) s(-1) PPF. With 500 or 2000 µmol m(-2) s(-1) PPF, the g(s) for the three woody species increased from 2 to 30 min after the start of illumination, but little change in the g(s) of the four ferns. Thus, P(g) and g(s) were not correlated for all material measured at the same PPF and induction time. However, P(g) was positively correlated with ETR, even though CO(2) assimilation may be influenced by stomatal, biochemical and photoinhibitory limitations. In addition, was closely related to time required to reach 90% maximal ETR for all materials and with two levels of PPF combined. Thus, ETR is a good indicator for estimating the light induction of photosynthetic rate of species, across a wide taxonomic range and light adaptation and acclimation capability.

PHOTOSYNTHESIS AND BIOMASS PRODUCTION BY MILLET (PENNISETUM GLAUCUM) AND TARO (COLOCASIA ESCULENTA) GROWN UNDER BAOBAB (ADANSONIA DIGITATA)AND NÉRÉ (PARKIA BIGLOBOSA) IN AN AGROFORESTRY PARKLAND SYSTEM OF BURKINA FASO (WEST AFRICA)

SUMMARYPhotosynthesis and biomass production by millet (Pennisetum glaucum) and taro (Colocasia esculenta) grown under baobab (Adansonia digitata) and néré (Parkia biglobosa) was studied at Nobéré (Burkina Faso) with the aim of optimising parkland systems productivity. Millet yielded the highest biomass under Baobab and the lowest biomass was recorded in the zone close to the tree trunk of néré. In contrast, the biomass of taro was higher in heavy shaded zones under néré and the zone close to baobab's trunk. The two crops showed an increasing trend of photosynthesis rate (PN) from tree trunk to the open area. However, the increase in thePNof taro from tree trunk to the open field was lower compared to that of millet. By increasing its leaf area index (LAI) under shade, taro displayed higher biomass production under tree compared to the open area while an opposite trend was observed in millet. The high millet biomass production under baobab could be explained by light availability and the reduction of temperature under shade compared to the open field. The adaptation of taro to shade by increasing its LAI and thus avoiding drastic reduction inPNunder shade resulted in better biomass production under heavy shade. Therefore, it was concluded that by replacing millet with taro under dense tree crowns the productivity of agroforestry parkland systems could be increased.

Timing and magnitude of C partitioning through a young loblolly pine (Pinus taeda L.) stand using 13C labeling and shade treatments

The dynamics of rapid changes in carbon (C) partitioning within forest ecosystems are not well understood, which limits improvement of mechanistic models of C cycling. Our objective was to inform model processes by describing relationships between C partitioning and accessible environmental or physiological measurements, with a special emphasis on short-term C flux through a forest ecosystem. We exposed eight 7-year-old loblolly pine (Pinus taeda L.) trees to air enriched with (13)CO(2) and then implemented adjacent light shade (LS) and heavy shade (HS) treatments in order to manipulate C uptake and flux. The impacts of shading on photosynthesis, plant water potential, sap flow, basal area growth, root growth and soil CO(2) efflux rate (CER) were assessed for each tree over a 3-week period. The progression of the (13)C label was concurrently tracked from the atmosphere through foliage, phloem, roots and surface soil CO(2) efflux. The HS treatment significantly reduced C uptake, sap flow, stem growth and fine root standing crop, and resulted in greater residual soil water content to 1 m depth. Soil CER was strongly correlated with sap flow on the previous day, but not the current day, with no apparent treatment effect on the relationship. Although there were apparent reductions in new C flux belowground, the HS treatment did not noticeably reduce the magnitude of belowground autotrophic and heterotrophic respiration based on surface soil CER, which was overwhelmingly driven by soil temperature and moisture. The (13)C label was immediately detected in foliage on label day (half-life = 0.5 day), progressed through phloem by Day 2 (half-life = 4.7 days), roots by Days 2-4, and subsequently was evident as respiratory release from soil which peaked between Days 3 and 6. The δ(13)C of soil CO(2) efflux was strongly correlated with phloem δ(13)C on the previous day, or 2 days earlier. While the (13)C label was readily tracked through the ecosystem, the fate of root C through respiratory, mycorrhizal or exudative release pathways was not assessed. These data detail the timing and relative magnitude of C flux through various components of a young pine stand in relation to environmental conditions.

Leaf litter chemistry, decomposition and assimilation by macroinvertebrates in two tropical streams

Riparian vegetation typically provides substantial allochthonous material to aquatic ecosystems where micro-organisms can play an important role in organic matter degradation which can support consumer biomass. We examined the effects of leaf litter quality (e.g., leaf nutrients, lignin and cellulose content), leaf species mixing, and microbial community diversity on in-stream breakdown rates of litter from dominant riparian trees (Melaleuca argentea, M. leucadendra, and Nauclea orientalis) in both a perennial and intermittent river in Australia’s wet-dry tropics. Leaf mass remaining after 82 days of in-stream incubation was negatively correlated (P < 0.05) with initial leaf N and P content while initial lignin and cellulose content had no statistically significant effect. Breakdown rates of incubated leaves of both Melaleuca and Nauclea were significantly higher in mixed litter bags compared with single species litter bags. Although it was expected that leaf N content would decrease from initial levels during decomposition, we found either similar or slightly higher N content following in-stream incubation suggesting microbial colonisation increased overall N content. Stable isotopes of δ13C and δ15N for the major sources and consumers in both rivers provide evidence that leaf litter was an important macroinvertebrate food source in the perennial river where heavy shading may limit algal production. However, in the intermittent river where riparian cover was low, benthic algae were the major organic carbon source for consumers. Our findings suggest that riparian tree species influence rates of in-stream organic matter processing, microbial community composition, and aquatic food web dynamics in tropical wet-dry streams.

Differences in spatial distribution, morphology, and communities of herbivorous insects among three cytotypes of Solidago altissima (Asteraceae)

Polyploidy in plants can result in genetic isolation, ecological differences among cytotypes, and, ultimately, speciation. Cytotypes should be sympatric only if they are segregated in an ecological niche or through prezygotic isolation. We tested whether sympatric diploid, tetraploid, and hexaploid ramets of Solidago altissima L. (Asteraceae) differ in their ecological niche. We measured how cytotypes were distributed within habitats, their morphology, and the composition of their communities of herbivorous insects at 10 natural field sites. We also conducted a common garden experiment to confirm whether observed differences in morphology or communities of herbivores were due to cytotype or environmental effects. Diploid ramets often grew in open areas, relatively far from woody plants, and were associated with a high species richness of herbaceous plants, especially grasses. Hexaploids often grew in heavy shading under woody plants where grasses were scarce. Finally, tetraploids usually grew in transition areas between diploids and hexaploids. Hexaploid ramets also were taller than ramets of the other cytotypes and had larger leaves. Two species of insects, the leaf-galling fly Asteromyia carbonifera and the phloem-tapping aphid Uroleucon nigrotuberculatum, were more abundant on hexaploid ramets than on ramets of other cytotypes in the field. When grown in a common garden, however, cytotypes were similar in morphology and communities of herbivores. We conclude that cytotypes of S. altissima differ in their spatial distribution within habitats and that spatial variation in environmental factors influence plant morphology and communities of herbivorous insects.

Screening Potential New Tropical Ornamentals for Alkalinity, Salinity, and Irradiance Tolerances

Abstract With the rapid introduction of new herbaceous or woody perennial tropical and subtropical taxa to the U.S. nursery trade for use as summer annuals, methods for quickly assessing their tolerances to various environmental stresses will be needed. Three screening methods, one each for substrate alkalinity, soil salinity, and varied irradiance levels, were tested on four tropical taxa, Rotheca myricoides (Hochst.) Steane &amp; Mabb. (blue butterfly bush), Graptophyllum pictum (L.) Griff, (caricature plant), Jatropha integerrima Jacq. (firecracker jatropha), and Chrysothemis pulchella (Don. ex J. Sims) Desc. (dozakie), with potential for use as summer annuals. Specialized portable structures for testing irradiance levels were developed which minimized confounding of restricted air movement often associated with imposing shade treatments. Irradiance and salinity screening procedures were deemed successful, while further refinement is needed with the alkalinity screening method tested. Decreased irradiance levels suppressed flowering of R. myricoides, while full sun exposure decreased foliar appearance and growth of C. pulchella. Only J. integerrima showed adverse responses to elevated substrate alkalinity. Jatropha integerrima and G. pictum exhibited adaptation to a wide range of light exposures and salinity levels while maintaining attractive foliage. Although flowering of J. integerrima was reduced with heavy shade (66%), some flowering continued.

The production of flowers, fruit and leafy shoots in pruned macadamia trees.

For Macadamia integrifolia Maiden and Betche var. 849, we compared four limb removal strategies of varying style and severity over 4 years, in terms of effects on yield, on the distribution of light, and new vegetative shoots, racemes and fruit within the canopy. Limb removal reduced yields. The reduction corresponded with the severity of pruning, not with the style of pruning. Limb removal had little impact in the medium term on light penetration to the orchard floor. Within the canopy, shoot production and raceme production were inversely related. Shoot production was favoured by high light conditions; raceme production occurred predominantly in areas of heavy shade, with 49% of racemes produced at canopy locations receiving less than 2% full daylight, and 94% produced at locations receiving less than 16% full daylight. Most flowering appeared to occur on wood more than 3 years old. The capacity of different parts of the canopy to support fruit set and retention increased with proximity to the more irradiated parts of the canopy, but fruit production was still high deep within the lower part of the canopy, with 50% of fruit produced at canopy locations receiving less than 2% full daylight, and 90% produced at locations receiving less than 16% full daylight.

Biological Flora of the British Isles:Spiranthes spiralis(L.) Chevall.

Summary1. This account presents information on all aspects of the biology ofSpiranthes spiralis(L.) Chevall. that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of theBiological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation.2. Spiranthes spiralisis a long‐lived orchid species that is widely distributed in the southern part of the British Isles, southern Europe and the Mediterranean. It is native to Britain. Its most characteristic habitats are unimproved, well‐grazed grasslands on dry calcareous soils, particularly chalk and limestone, cliff‐tops and grassy coastal dunes. It can also be found in garden lawns and, less frequently, in slightly acidic heathland habitat. It occurs on both dry and wet soils, but it does not tolerate heavy shading.3. Spiranthes spiralisis a non‐bulbous geophyte regenerating by sexual reproduction and by vegetative spread, although the latter is limited. Vegetative reproduction involves the growth of a lateral bud on the underground stem. The new plant forms its own tubers, and eventually the connection between the mother plant and the vegetatively produced daughter plant withers away.4. The main perennating organ is a tuberous root. In most years, the tuber generates a rosette of expanded leaves, and at the end of every year of the plant’s life, the tuber is completely replaced. In some cases, however, only part of the reserves is exhausted in flowering and, when this happens, a tuber may survive for several years. Vegetative adult dormancy – the failure of above‐ground parts to appear in a growing season, followed by reappearance of full‐sized photosynthetic plants in subsequent seasons – has been observed. It most commonly lasts for only 1 year, but sometimes plants can remain dormant for several years.5. The species is not autogamous and pollinators – mainly bumblebees and bees – are necessary for successful pollination and fruit set. Natural levels of fruit set are usually &lt;50%. Hand‐pollination increases fruit set toc. 75%, indicating that reproduction is to some extent pollen‐limited. Sexual reproduction comes at a cost, and few individuals flower for two or more consecutive years. Within fruits many very small seeds are produced, but most are dispersed to a distance of less than a few dm from maternal plants, leading to strongly aggregated distribution patterns and significant spatial genetic structuring within natural populations.6. Spiranthes spiralishas suffered significant declines in distribution in Britain and other European countries. In Britain, populations were lost from many sites before 1930, when many pastures were re‐sown or converted to arable land. Losses of populations due to agricultural intensification (ploughing of old fields and fertilization) still occur and are the major causes of the decline of the species. Conservation of remnant populations primarily requires the maintenance of a short turf by grazing, most often by sheep. Ideally, grazing should be suspended during flowering and seed set, allowing new recruits to become established and adult plants to flower profusely and to produce seeds.

Acer saccharum response to concurrent disturbances: the importance of stem layering as an adaptive trait

For shade-tolerant saplings persisting under heavy forest shade, the probability of release by disturbance is directly related to longevity. We examined the effects of two concurrent disturbances, overstory removal and herbivory, on the regeneration dynamics and release response of Acer saccharum Marsh. within 20 artificial canopy gaps ranging in size from 50 to 450 m2. To examine the influence of herbivory, we constructed arrays of deer exclosures within each canopy gap. Five years after gap creation, A. saccharum dominated the taller sapling classes across the entire range of gap sizes examined, and evidence of stem layering in this species was common across all treatments (52%), especially in taller saplings. The presence of stem layering was significantly associated with greater postdisturbance height growth (P &lt; 0.001), regardless of gap area or herbivory. The increase in height of layered A. saccharum on control plots was in spite of the fact that 70% of these saplings were browsed at least once following gap creation; compared with 46% of nonlayered individuals. Consequently, our results suggest that stem layering likely fosters resilience in the face of complex or interacting disturbances and may be an important trait for forecasting gap capture and succession.