Large‐Scale Zostera marina (eelgrass) Restoration in Chesapeake Bay,Maryland, USA. Part I: A Comparison of Techniques and Associated Costs

The Chesapeake Bay, like many other temperate estuaries, has exhibited dramatic declines in the abundance of submerged aquatic vegetation (SAV) during the later half of the twentieth century. Because of the functions SAV serve in maintaining a healthy estuarine ecosystem, SAV restoration has become an important component of Chesapeake Bay restoration. Specifically, recent water quality improvements in areas from which populations of Zostera marina (eelgrass) have been extirpated have suggested that Z. marina restoration could succeed. Early restoration efforts involved transplanting Z. marina plants from healthy source beds to restoration locations, but this was labor intensive, time consuming, expensive, and potentially detrimental to donor beds. This multi‐year project investigated new techniques for large‐scale Z. marina seed collection and processing and compared two seed dispersal methods to evaluate cost effectiveness. Tens of millions of mature Z. marina seeds were collected through snorkeling, SCUBA, or with a mechanical harvester. Seed storage conditions and processing techniques were manipulated in order to maximize seed yield. Seeds were dispersed using two methods: spring seed buoys and fall seed broadcasts. Our costs for planting 1 ha of bottom with Z. marina seeds ranged from $6,674 to $165,699 depending on seeding density and dispersal method used. The average cost per Z. marina seed was $0.17. Interannual variations in seed collection yield and seed viability after summer storage had great impact on final costs. Our results suggest that the use of seeds for large‐scale Z. marina restoration offers a competitive advantage to more traditional transplanting methods.     

An Introduction to a Special Issue on Large‐Scale Submerged Aquatic Vegetation Restoration Research in the Chesapeake Bay: 2003–2008

The Chesapeake Bay is one of the world's largest estuaries. Dramatic declines in the abundance and distribution of submerged aquatic vegetation (SAV) in the Chesapeake Bay over the last few decades led to a series of management decisions aimed at protecting and restoring SAV populations throughout the bay. In 2003, the Chesapeake Bay Program established a goal of planting 405 ha of SAV by 2008. Realizing that such an ambitious goal would require the development of large‐scale approaches to SAV restoration, a comprehensive research effort was organized, involving federal and state agencies, academia, and the private sector. This effort differs from most other SAV restoration programs due to a strong emphasis on the use of seeds rather than plants as planting stock, a decision based on the relatively low labor requirements of seeding. Much of the research has focused on the development of tools and techniques for using seeds in large‐scale SAV restoration. Since this research initiative began, an average of 13.4 ha/year of SAV has been planted in the Chesapeake Bay, compared to an average rate of 3.6 ha/year during the previous 21 years (1983–2003). The costs of conducting these plantings are on a downward trend as the understanding of the limiting factors increases and as new advances are made in applied research and technology development. Although this effort was focused in the Chesapeake Bay region, the tools and techniques developed as part of this research should be widely applicable to SAV restoration efforts in other areas.     

The Use of Asian Ficus Species for Restoring Tropical Forest Ecosystems

Fig (Ficus spp.) trees have been promoted as framework species for tropical forest restoration throughout Asia, because they are considered to be keystone species. This article presents optimal propagation and planting techniques for six Asian dioecious Ficus species, which will enable their inclusion in forest restoration plantings across the Asia‐Pacific region: Ficus auriculata, F. fulva, F. hispida, F. oligodon, F. semicordata, and F. variegata. Nursery experiments compared the growth performance of propagating planting stock from seed and from leafy cuttings, whereas field experiments assessed the cost‐effectiveness and the relative performance of (1) direct seeding, (2) planting stock from seed, and (3) planting stock from cuttings. The most efficient method of producing Ficus spp. was from seed. Propagation from cuttings was much less successful. Seedlings produced from seed had the highest rates of growth and survival both in the nursery and in field trials. In field trials, use of planting stock from seed was also more cost‐effective than direct seeding and vegetative propagation. Establishment costs calculated on the basis of “per plant established” were $1.14 for seed, $6.95 for cutting, and $25.88 for direct seeding.     

Carbon stocks in above‐ground biomass of monoculture plantations,mixed species plantations and environmental restoration plantings in north‐east Australia

Summary The emergence of carbon markets has provided a potential source of funding for reforestation projects. However, there is concern amongst ecologists that these markets will promote the establishment of monoculture plantations rather than more diverse restoration plantings, on the assumption that fast‐growing monocultures are likely to store more carbon than restoration plantings. We examined the validity of this assumption for three predominantly rainforest plantation types established in the moist tropical uplands of north‐east Australia: monoculture plantations of native rainforest conifers (n = 5, mean age 13 years); mixed species plantations of rainforest cabinet timber species, rainforest conifers and eucalypts (n = 5, mean age 13 years); and, environmental restoration plantings comprised mostly of a diverse range of rainforest trees (n = 10, mean age 14 years). We found that restoration plantings stored significantly more carbon in above‐ground biomass than monoculture plantations of native conifers (on average, 106 t vs 62 t carbon per ha); and tended to store more carbon than mixed species timber plantations which were intermediate in value (86 t carbon per ha). Carbon stocks were higher in restoration plantings than in monoculture and mixed species plantations for three reasons. First, and most importantly, restoration plantings were more densely stocked than monoculture and mixed species plantations. Second, there were more large diameter trees in restoration plantings than monoculture plantations. Third, the trees used in restoration plantings had a higher average wood density than the conifers used in monoculture plantations. While, on average, wood density was higher in mixed species plantations than restoration plantings, the much higher stocking rate of restoration plantings meant they stored more carbon than mixed species plantations. We conclude that restoration plantings in the moist tropics of north‐east Australia can accumulate relatively high amounts of carbon within two decades of establishment. Comparison with reference rainforest sites suggests that restoration plantings could maintain their high stocking rates (and therefore high biomass) as they develop in future decades. However, because restoration plantings are currently much more expensive to establish than monoculture plantations, restoration plantings are unlikely to be favoured by carbon markets. Novel reforestation techniques and designs are required if restoration plantings are to both provide habitat for rainforest biota and store carbon in biomass at a cost comparable to monoculture plantations.     

Softening the agricultural matrix: a novel agri‐environment scheme that balances habitat restoration and livestock grazing

The loss and degradation of woody vegetation in the agricultural matrix represents a key threat to biodiversity. Strategies for habitat restoration in these landscapes should maximize the biodiversity benefit for each dollar spent in order to achieve the greatest conservation outcomes with scarce funding. To be effective at scale, such strategies also need to account for the opportunity cost of restoration to the farmer. Here, we critique the Whole‐of‐Paddock Rehabilitation program, a novel agri‐environment scheme which seeks to provide a cost‐effective strategy for balancing habitat restoration and livestock grazing. The scheme involves the revegetation of large (minimum 10 ha) fields, designed to maximize biodiversity benefits and minimize costs while allowing for continued agricultural production. The objectives and design of the scheme are outlined, biodiversity and production benefits are discussed, and we contrast its cost‐effectiveness with alternative habitat restoration strategies. Our analysis indicates that this scheme achieves greater restoration outcomes at approximately half the cost of windbreak‐style plantings, the prevailing planting configuration in southeastern Australia, largely due to a focus on larger fields, and the avoidance of fencing costs through the use of existing farm configuration and infrastructure. This emphasis on cost‐effectiveness, the offsetting of opportunity costs through incentive payments, and the use of a planting design that seeks to maximize biodiversity benefits while achieving production benefits to the farmer, has the potential to achieve conservation in productive parts of the agricultural landscape that have traditionally been “off limits” to conservation.     

Determining factors of cottonwood planting survival in a desert river restoration project

Planting native riparian trees can help recover wildlife and fish habitat on a local scale, when full recovery of natural processes that sustain riparian ecosystems is infeasible. To help improve planting success, we determined which environmental factors and management practices most influenced survival of planted Populus fremontii (Fremont cottonwood) in a field experiment on the San Rafael River, Utah, U.S.A. We planted 474 approximately 2‐m‐tall trees and tracked survival for 1.25 years. We used logistic regression to evaluate whether tree height, elevation above the river channel, distance to existing cottonwood or Salix exigua (coyote willow), soil conductivity, soil texture, planting depth, planting method (mechanical auger vs. hand‐digging), and provision of natural and commercial supplements affected survival probability. Survival probability decreased with elevation above the river channel bottom and was greater in auger‐dug than hand‐dug holes. Survival probability was lower in soils with the highest salinity levels and was lower in sandy soils than soils with silt and clay. Survival may be improved by planting well above the channel to avoid flooding impacts but within 2 m above the channel in auger‐dug holes to ensure access to soil moisture. Testing soil salinity and texture in areas with suitable elevation could also help improve survival. Approximately 35% of trees survived to the end of the study period, indicating that planting can help recover riparian habitat locally, especially if survival is improved in future planting efforts. However, full recovery of desired riparian habitat throughout the floodplain will require natural flows.     

Protocols for Argentine ant eradication in conservation areas

The Argentine ant (Linepithema humile) is a widespread, abundant and ecologically disruptive invader that is present throughout major portions of coastal California and on half of the California Channel Islands. On Santa Cruz Island, the Argentine ant had invaded about 2% of the island's area in four distinct locations as of 2012. Given the negative ecological effects resulting from Argentine ant invasions, we sought to develop a cost‐effective method of eradication. Here, we describe the results of large‐scale, field‐tested methods for Argentine ant eradication and post‐treatment detection. Our eradication protocol employs a novel toxicant‐delivery system: an aqueous solution of sucrose and 6 ppm of thiamethoxam mixed with hydrating polyacrylamide beads. Ants feed on the solution present on the bead's surface for about 24 h after which time bead dehydration prevents feeding. We distributed hydrated beads by helicopter over 74 ha of infested areas plus a 50‐m buffer on 14 occasions between June 2013 and September 2014. Treatments reduced Argentine ant activity to subdetectable levels within four months. In 2014, we conducted a high‐intensity detection protocol using lures (n = 55 363) in areas treated in 2013. This effort did not detect Argentine ants. In 2015, we conducted a medium‐intensity detection protocol using lures (n = 2250) in areas treated in 2013 and 2014 but not searched in 2014; this sampling effort did not detect Argentine ant activity except for a single remnant infestation (c. 0.3 ha in area), which was retreated in 2015. The cost of treatments was approximately $1400 per ha; this cost is comparable to other ant eradication efforts. The cost of our preferred detection method, which used lures spaced every 10 m, was $500 per ha. These results demonstrate sufficient protocol efficacy to justify expansion of treatments to other infested areas in ecologically sensitive areas.     

Non‐continuous reproductive phenology of animal‐dispersed species in young forest restoration plantings

Tree species that produce resources for fauna are recommended for forest restoration plantings to attract pollinators and seed dispersers; however, information regarding the flowering and fruiting of these species during early growth stages is scarce. We evaluated the reproductive phenology of animal‐dispersed tree species widely used in Atlantic Forest restoration. We marked 16 animal‐dispersed tree species in 3‐ to 8‐year‐old forest restoration plantings in Itu‐São Paulo, southeast Brazil. We noted the age of the first reproductive event, flowering and fruiting seasonality, percentage of trees that reached reproductive stages, and intensity of bud, flower, and fruit production for each species. Flowering and fruiting are seasonal for most species; only two, Cecropia pachystachya and Ficus guaranitica, exhibited continuous flowering and fruiting throughout the year; we also identified Schinus terebinthifolia and Dendropanax cuneatus fruiting in the dry season during resource scarcity. Therefore, we recommend all as framework species, that is, species that are animal‐dispersed with early flowering and fruiting potential, for forest restoration. Further, we recommend identifying and planting similar animal‐dispersed tree species that produce fruits constantly or in the dry season to maximize fauna resource availability throughout the year in tropical forest restoration plantings. Abstract in Portuguese is available with online material     

Linkages of Farmers' Operations with Rhizoctonia Root Rot Spread in Bean Crops on a Regional Basis

The associations of Rhizoctonia root rot (RRR) with a number of agronomic and yield variables were characterized at different growth stages in 122 commercial bean fields in Zanjan, Iran. A lower RRR incidence was detected in red beans compared with white beans. RRR incidence was greater in drought‐exposed fields compared with drought‐free fields. RRR incidence was higher following frequent irrigations at 2‐ to 3‐day intervals than at 4‐ to 9‐day intervals. The highest RRR incidence was associated with the densest category of plant populations and with the deepest plantings at 10–22 cm. Beans grown following alfalfa, bean and maize had a lower disease than rotations with potato. RRR incidence was greater in fields that received 50–500 kg/ha of urea compared with nonfertilized fields. RRR‐affected fields were recognized with a closer irrigation, earlier and deeper planting, denser weed population and lower yields than RRR‐free fields. According to loadings for second principal component, planting density and depth, urea usage and weed density corresponded with RRR incidence. Findings extend our understanding of RRR epidemics in diverse bean cropping systems.     

Tree guards and weed mats in a dry shrubland restoration in New Zealand

Associated with restoration of 150 ha of native plant communities within a highly exposed low rainfall landscape, we evaluated whether the benefits of tree guards and weed mats justified a doubling of planting costs. One‐year‐old nursery‐grown specimens of Kānuka (Kunzea serotina) and Pomaderris (Pomaderris amoena) were planted with and without polythene and rigid plastic tree guards, and weed mats, then monitored for 12 months. Herbivory was reduced with both types of tree guard by 10–35%, but mortality was largely caused by desiccation. Polythene tree guards provided the best protection, buffering extremes of ambient and soil temperature in summer but with no effect on soil temperature in winter. Weed mat addition reduced soil temperature fluctuation further in winter; a moss turf mat was best. Both mulch and moss weed mats reduced soil temperature in summer and raised soil moisture in winter. We showed that tree guards could save at least NZ$ 70 k/ha, but this is likely to vary with plant species traits and site conditions.     

Weather effects on birds of different size are mediated by long‐term climate and vegetation type in endangered temperate woodlands

Species occurrence is influenced by a range of factors including habitat attributes, climate, weather, and human landscape modification. These drivers are likely to interact, but their effects are frequently quantified independently. Here, we report the results of a 13‐year study of temperate woodland birds in south‐eastern Australia to quantify how different‐sized birds respond to the interacting effects of: (a) short‐term weather (rainfall and temperature in the 12 months preceding our surveys), (b) long‐term climate (average rainfall and maximum and minimum temperatures over the period 1970–2014), and (c) broad structural forms of vegetation (old‐growth woodland, regrowth woodland, and restoration plantings). We uncovered significant interactions between bird body size, vegetation type, climate, and weather. High short‐term rainfall was associated with decreased occurrence of large birds in old‐growth and regrowth woodland, but not in restoration plantings. Conversely, small bird occurrence peaked in wet years, but this effect was most pronounced in locations with a history of high rainfall, and was actually reversed (peak occurrence in dry years) in restoration plantings in dry climates. The occurrence of small birds was depressed—and large birds elevated—in hot years, except in restoration plantings which supported few large birds under these circumstances. Our investigation suggests that different mechanisms may underpin contrasting responses of small and large birds to the interacting effects of climate, weather, and vegetation type. A diversity of vegetation cover is needed across a landscape to promote the occurrence of different‐sized bird species in agriculture‐dominated landscapes, particularly under variable weather conditions. Climate change is predicted to lead to widespread drying of our study region, and restoration plantings—especially currently climatically wet areas—may become critically important for conserving bird species, particularly small‐bodied taxa.     

Flower and Fruit Availability along a Forest Restoration Gradient

Frugivores and pollinators are two functional groups of animals that help ensure gene flow of plants among sites in landscapes under restoration and to accelerate restoration processes. Resource availability is postulated to be a key factor to structure animal communities using restoration sites, but it remains poorly studied. We expected that diverse forests with many plant growth forms that have less‐seasonal phenological patterns will provide more resources for animals than forests with fewer plant growth forms and strongly seasonal phenological patterns. We studied forests where original plantings included high tree species diversity. We studied resource provision (richness and abundance of flowers and fruits) of all plant growth forms, in three restoration sites of different ages compared to a reference forest, investigating whether plant phenology changes with restoration process. We recorded phenological data for reproductive plant individuals (351 species) with monthly sampling over 2 years, and found that flower and fruit production have been recovered after one decade of restoration, indicating resource provision for fauna. Our data suggest that a wide range of plant growth forms provides resource complementarities to those of planted tree species. Different flower phenologies between trees and non‐trees seem to be more evident in a forest with high non‐tree species diversity. We recommend examples of ideal species for planting, both at the time of initial planting and post‐planting during enrichment. These management actions can minimize shortage and periods of resource scarcity for frugivorous and nectarivorous fauna, increasing probability of restoring ecological processes and sustainability in restoration sites.     

Evaluation of Reforestation in the Lower Mississippi River Alluvial Valley

Only about 2.8 million ha of an estimated original 10 million ha of bottomland hardwood forests still exist in the Lower Mississippi River Alluvial Valley (LMAV) of the United States. The U.S. Fish and Wildlife Service, the U.S. Forest Service, and state agencies initiated reforestation efforts in the late 1980s to improve wildlife habitat. We surveyed restorationists responsible for reforestation in the LMAV to determine the magnitude of past and future efforts and to identify major limiting factors. Over the past 10 years, 77,698 ha have been reforested by the agencies represented in our survey and an additional 89,009 ha are targeted in the next 5 years. Oaks are the most commonly planted species and bare-root seedlings are the most commonly used planting stock. Problems with seedling availability may increase the diversity of plantings in the future. Reforestation in the LMAV is based upon principles of landscape ecology; however, local problems such as herbivory, drought, and flooding often limit success. Broad-scale hydrologic restoration is needed to fully restore the structural and functional attributes of these systems, but because of drastic and widespread hydrologic alterations and socioeconomic constraints, this goal is generally not realistic. Local hydrologic restoration and creation of specific habitat features needed by some wildlife and fish species warrant attention. More extensive analyses of plantings are needed to evaluate functional success. The Wetland Reserve Program is a positive development, but policies that provide additional financial incentives to landowners for reforestation efforts should be seriously considered.     

If you build it,will they come? Use of restored dunes by beach mice

Restoration of coastal habitat fragmented, degraded, or destroyed by development and climate‐related processes such as sea level rise and storm surge usually involves planting native plants to restore habitat structure, but whether and how restored areas benefit taxa other than plants is rarely reported. Installing restoration plantings is one method used to build habitat such as beach dunes where dunes have been lost, potentially creating habitat for dune‐dependent species. We compared use of natural vegetated dunes, open sand gaps, and restoration plantings (habitat treatment) by Perdido Key beach mice (Peromyscus polionotus trissyllepsis) over 3 years using tracking tubes to assess the value of restoration plantings for beach mice. Tubes were monitored in two seasons (early and mid‐summer), and under new and full moon conditions. Mice used restoration plantings less than natural vegetated dunes but more than open sand gaps, which suggests restoration plantings may facilitate movement of mice across fragmented areas. Both season and moon phase influenced the effect of habitat treatment, interactions which may be attributable to perceived risk associated with movement under a combination of different conditions of ambient light, vegetation cover, and habitat novelty. Our results show restoration plantings provide habitat for movement and foraging, and may ameliorate some consequences of sea level rise and storms for beach mice and potentially other dune‐dependent species into the future.     

Feasibility of early outplanting of sexually propagated Acropora verweyi for coral reef restoration demonstrated in the Philippines

Over the last 20 years, coral sexual propagation techniques for reef restoration have been steadily developed and improved. However, these techniques involve considerable time and costs to grow coral propagules. There is a need to examine the optimal size of juvenile corals for outplantation. Here, we outplanted sexually propagated small (3–5 mm diameter) and large (10–15 mm diameter) Acropora verweyi corals at 4 months after fertilization at two sites in northwestern Philippines, and compared their survival and radial growth rate after a year. A. verweyi coral juveniles (n = 240) exhibited an overall mean survival of 29.5% and growth rate of 11.12 ± 6.2 mm/year (mean ± SD). Large colonies had a significantly higher growth rate than smaller colonies. Although survivorship of large juveniles was significantly better than that of the smaller ones at one site, it did not differ significantly at the other. Each 4‐month‐old coral cost US$1.52 to produce, while the cost of each of the outplanted juveniles (n = 240) was about US$2.67, whereas the cost of each survivor about a year after outplantation was US$11.47. Results suggest that A. verweyi reared in ex situ nurseries for only 4 months can survive reasonably well when outplanted onto coral reefs.     

Spatiotemporal assessment of farm‐gate production costs and economic potential of Miscanthus × giganteus,Panicum virgatum L., and Jatropha grown on marginal land in China

Spatially explicit farm‐gate production costs and the economic potential of three types of energy crops grown on available marginal land in China for 2017 and 2040 were investigated using a spatial accounting method and construction of cost–supply curves. The average farm‐gate cost from all available marginal land was calculated as 32.9 CNY/GJ for Miscanthus Mode, 27.5 CNY/GJ for Switchgrass Mode, 32.4 CNY/GJ for Miscanthus & Switchgrass Mode, and 909 CNY/GJ for Jatropha Mode in 2017. The costs of Miscanthus and switchgrass were predicted to decrease by approximately 11%‐15%, whereas the cost of Jatropha was expected to increase by 5% in 2040. The cost of Jatropha varies significantly from 193 to 9,477 CNY/GJ across regions because of the huge differences in yield across regions. The economic potential of the marginal land was calculated as 28.7 EJ/year at a cost of less than 25 CNY/GJ for Miscanthus Mode, 4.0 EJ/year at a cost of less than 30 CNY/GJ for Switchgrass Mode, 29.6 EJ/year at a cost of less than 25 CNY/GJ for Miscanthus & Switchgrass Mode, and 0.1 EJ/year at a cost of less than 500 CNY/GJ for Jatropha Mode in 2017. It is not feasible to develop Jatropha production on marginal land based on existing technologies, given its high production costs. Therefore, the Miscanthus & Switchgrass Mode is the most economical way, because it achieves the highest economic potential compared with other modes. The sensitivity analysis showed that the farm‐gate costs of Miscanthus and switchgrass are most sensitive to uncertainties associated with yield reduction and harvesting costs, while, for Jatropha, the unpredictable yield has the greatest impact on its farm‐gate cost. This study can help policymakers and industrial stakeholders make strategic and tactical bioenergy development plans in China (exchange rate in 2017: 1€ = 7.63￥; all the joules in this paper are higher heat value).     

An Effective Method for Collecting and Storing Seeds from Zostera marina (Eelgrass) in the Yellow Sea,China

The coast of the Yellow Sea in China, like many other temperate coastal zones, has been experiencing a dramatic decline in the abundance of seagrass. Intensive efforts have been made to restore seagrass communities along the coast to restore the function of the coastal ecosystem. Transplanting adult Zostera marina shoots is labor‐intensive, time‐consuming, expensive, and detrimental to donor beds; thus, restoring seagrass communities through the use of seeds is highly valued in current, large‐scale restoration trials. In this study, an effective method for collecting, processing, and storing Z. marina seeds was developed. From 2009 to 2013, respectively, 122,000, 421,000, 364,000, 1,041,000, and 1,091,000 seeds were successfully collected. Two‐way analysis of variance (ANOVA) showed the interaction between salinity and temperature significantly affected the cumulative germination rate (CGR) (p < 0.01) during the storage period and the viability (p < 0.01) of seeds after storage. The germination rate after storage was significantly affected by salinity and temperature (p < 0.01). The highest viability (89.8 ± 1.0%) and germination rate (75.6 ± 4.5%) were found among seeds stored at 4°C and a salinity of 44.5 psu for 7 months. The cost for planting 1 ha of sea bottom with Z. marina seeds ranged from $2,613 to $80,900 depending on the seeding density and seed loss during storage. The average cost per Z. marina seed in this study was $0.00586.     

Putting it back: Woody debris in young restoration plantings to stimulate return of reptiles

Despite active investment in restoration, some habitat features can be slow to develop on formerly degraded land and can consequently pose persistent barriers to the re‐establishment of specialist species. Coarse woody debris (CWD) is a critical resource for a whole suite of animal taxa but remains an underappreciated component of some forest ecosystems and restoration activities. The extent to which recovery of animal communities can be accelerated through artificial supplementation of woody debris is poorly understood especially for highly diverse tropical forest systems. Here, we report early results from an experiment designed to manipulate CWD in young restoration plantings (0–7 year old) in tropical north‐east Australia for the purposes of facilitating re‐establishment of rainforest reptiles. After 1 year, we demonstrate that CWD addition within restoration plantings adjacent to remnant forest can increase the local abundance of reptiles and promote colonisation of the log‐specialist Prickly Skink (Gnypetoscincus queenslandiae). These preliminary results, however, are based on observations of just 44 individual reptiles encompassing seven species. Ongoing monitoring will elucidate longer‐term outcomes to enable a proper evaluation of when and where CWD addition might be most beneficial in realising restoration goals.     

Commercial experience with miscanthus crops: Establishment,yields and environmental observations

This study investigates the condition of commercial miscanthus fields, growers’ concerns and reasons for growing the crop and also the modelling of a realistic commercial yield. Juvenile and mature Miscanthus × giganteus crops of varying age are surveyed in growers’ fields across mid‐England. We record in‐field plant density counts and the morphology of crops of different ages. Mature crops thrive on both clay and sandy soils. Plants surveyed appear robust to drought, weeds and disease, the only vulnerability is rhizome condition when planting. Mature miscanthus planted pre‐2014 continues to develop, spreading into planting gaps and growing more tillers. In stands planted post‐2014, improved planting techniques reduce planting gaps and create a reasonably consistent planting density of 12,500 plants/ha. The main reason for growers' investment in miscanthus is not financial return, but relates to its low requirement for field operations, low maintenance cost and regeneration. This offers practical solutions for difficult field access and social acceptability near public places (related to spray operations and crop vandalism). Wildlife is abundant in these fields, largely undisturbed except for harvest. This contributes to the greening of agriculture; fields are also used for gamebird cover and educational tours. This crop is solving practical problems for growers while improving the environment. Observed yield data indicate gradual yield increase with crop age, a yield plateau but no yield decrease since 2006. In stands with low planting densities, yields plateau after 9 years. Surveyed yield data are used to parameterize the MiscanFor bioenergy model. This produces options to simulate either juvenile yields or a yield for a landscape containing different aged crops. For mature English crop yields of 12 t ha^?1 year^?1, second‐ and third‐year juvenile harvests average 7 t ha^?1 year^?1 and a surrounding 10 km by 10 km area of distributed crop age would average 9 t ha^?1 year^?1.     

Citrus dwarfing viroid: effects on tree size and scion performance specific to Poncirus trifoliata rootstock for high‐density planting

The term ‘transmissible small nuclear ribonucleic acids' (TsnRNAs) describes well‐characterised viroid RNA species that do not induce any pronounced disease syndromes in specific citrus hosts, but rather act as regulatory genetic elements modifying tree performance. The canopy volume (CV) of 13‐year‐old navel orange trees (Citrus sinensis) on Poncirus trifoliata rootstock treated with TsnRNA‐IIIb (syn. Citrus dwarfing viroid) was reduced by 45% and 53.5% in standard‐density (6 m × 6.7 m) or high‐density (3 m × 6.7 m) plantings, respectively. The total yield of eight consecutive harvests was not affected significantly by the TsnRNA‐IIIb treatments or the two planting densities. However, the yield per land surface unit (Y/LSU) was almost doubled (increased by 97.5%) for the high‐density plantings over the standard‐density plantings of the untreated controls. The Y/LSU of the TsnRNA‐IIIb treated navel orange trees in the standard‐density planting was reduced by 32.7%. The TsnRNA‐IIIb treatment in both planting densities concentrated significantly more fruit production (approximately 60%) in the economically advantageous middle canopy height zone (0.6–2.4 m) in comparison with the untreated controls (35%). Fruit grade, size, appearance, organoleptic characteristics or time of maturation of the TsnRNA‐IIIb dwarfed navel trees were not significantly different between the two planting densities and the controls. Fruit with higher commercial value was produced in the TsnRNA‐IIIb dwarfed navel trees in the high‐density planting by 3.9% and 4.6% over the TsnRNA‐IIIb or controls in standard‐density planting respectively. The increase in Y/LSU and fruit value for the TsnRNA‐IIIb treated navel trees in the high‐density plantings in combination with the reduced management cost of dwarfed trees could result in substantial higher profits for a commercial grove despite the higher establishment cost of high‐density plantings.