Role of genomics in the potential restoration of the American chestnut

The development of genomic tools will enhance traditional tree breeding technologies leading to more certain and timely recovery of the American chestnut, a keystone heritage tree of the eastern United States. Major efforts are being made in gene discovery, genetic marker development, construction of a BAC-based physical map, and DNA transformation technology. A strategy of map-based cloning, association genetics, and genetic engineering, combined with traditional and marker-assisted backcross breeding is proposed for the long-term genetic restoration of this iconic tree species.     

Selection,caching, and consumption of hardwood seeds by forest rodents: implications for restoration of American chestnut

Recent field trials on blight‐resistant hybrids (BC₃F₃) of American chestnut (Castanea dentata) and Chinese chestnut (C. mollissima) have intensified planning for widespread restoration of Castanea to eastern U.S. forests. Restoration will likely rely on natural seed dispersal from sites planted with chestnut; however, we do not know how dispersal agents such as granivorous rodents will respond to hybrid chestnuts. At one extreme, excessive seed consumption may impede restoration. Alternatively, scatter‐hoarding rodents might facilitate the spread of chestnut by dispersal of seeds from restoration plantings. We conducted trials with five rodent species to quantify foraging preferences and to evaluate the potential role of granivores in chestnut restoration. Specifically, we presented seeds from American and hybrid chestnuts (BC₃F₂) with other common mast species and recorded the proportion of seeds removed and the fates of tagged seeds. Mice, chipmunks, and flying squirrels harvested both chestnut types preferentially over larger, tougher black walnut, hickory, and red oak seeds, but fox squirrels and eastern gray squirrels preferred larger seeds to chestnuts. All rodents consumed a greater proportion of the chestnuts than other seed types. American and hybrid chestnut also differed in important ways: except for fox squirrels, rodents preferentially removed American chestnuts over hybrid chestnuts, but we estimated that fox squirrels carried a greater proportion of hybrid chestnuts beyond our tag search area, suggesting that hybrids may be dispersed farther and cached more often than American chestnut. These differences indicate that hybrid chestnut may not be functionally equivalent to American chestnut with regard to seed–granivore interactions.     

Ectomycorrhizal fungi: the symbiotic route to the root for phosphorus in forest soils

Many forest trees have evolved mutualistic symbioses with ectomycorrhizal (ECM) fungi that contribute to their phosphorus (P) nutrition. Forest productivity is frequently limited by P, a phenomenon that is likely to become more widespread under future conditions of elevated atmospheric CO₂ concentration [CO₂]. It is thus timely that this review considers current understanding of the key processes (absorption, translocation and transfer to the plant host) in ECM fungus-mediated P nutrition of forest trees. Solubilisation of inorganic P (P_i) and hydrolysis of organic P by ECM fungi in soil occurs largely at the growing mycelial front, where P_i absorption is facilitated by high affinity transporters. While large gaps remain in our understanding of the physiological and molecular mechanisms that underpin movement of P in ECM mycelia in soil and P transfer to the plant, host P demand seems likely to be a key driver of these processes. ECM fungi may make considerable contributions to meeting the likely increased P demand of trees under elevated [CO₂] via increased colonization levels, shifts in ECM fungal community structure and changed patterns of EMM production. Further research into the spatial scale of ECM-mediated P movements in soil, along with the interplay between ECM fungi and other soil microflora is advocated.     

Experimental assessment of ecological restoration options for compacted forest soils

It is ecologically undesirable to solve forest soil compaction due to mechanized harvesting at large spatial scales using agricultural mechanical soil loosening techniques. We therefore examined whether a stimulation of biological activity through litter manipulation, liming and/or inoculation of the anecic earthworm species Lumbricus terrestris could significantly contribute to the ecological restoration of compacted forest soils by comparing the impact of these treatments on the soil within and beside compacted wheel tracks. The replacement of native litter by litter with a better quality resulted in a faster litter decomposition. However, maximal decay rates were obtained only when litter manipulation, earthworm inoculation and liming were combined. Anecic earthworms were initially absent as soils were probably too acid. Liming as well as litter manipulation had a small positive influence on the numbers of retraced L. terrestris, inducing positive feedback mechanisms on soil pH and litter decomposition rates. None of the treatments, however, had a significant effect on the compaction degrees within or beside tracks within the small study period. L. terrestris realized only a small decrease of bulk density beside the tracks. Within the tracks a similar number of L. terrestris was retrieved, but effects on the compaction degree were negligible. Liming decreased penetration resistance, but only in the absence of anecic earthworms. Endogeic earthworms were overall more abundant than the anecics, especially within tracks where soil water contents and pH values were higher. However, endogeics only had a marginal effect on litter decomposition and although they positively influence soil structure, they could not realize a reduction of the compaction degree, quantified by bulk density and penetration resistance, due to different burrowing habits. Our results indicated that a positive impact of anecic earthworms on the structure of compacted forest soils can be obtained in the long-term, at least in case soil conditions (acidity, nutrient availability and moisture content) are favourable. This can be achieved by conversion of forests towards tree species with high quality litter.     

Silicate weathering in temperate forest soils: insights from a field experiment

Few studies of silicate mineral weathering have been conducted in carbonate-bearing temperate forest soils. With climate and vegetation held constant, we compared soil mineralogy and major element chemistry of soil waters from a carbonate-free temperate aspen forest site in the Cheboygan watershed, northern Michigan, with that from carbonate-containing soils from experimental tree-growth chambers (low- vs. high- fertility). All soils were well-drained sands (quartz, Na-rich plagioclase, and K-feldspar) with minor amounts of carbonate present only in the experimentally manipulated soils. The Na⁺ concentrations in soil waters corrected for atmospheric deposition (Na*) were used to compare relative rates of plagioclase feldspar weathering across sites. In natural soil water profiles, maximum concentrations of Na*, Si, and dissolved organic carbon (DOC) were observed by a depth of 15 cm, a soil zone free of carbonate minerals. Mean Na* and DOC concentrations were different in the three soils, and increased in the order natural soil < low-fertility chambers < high-fertility chambers. While low pH environments are generally viewed as enhancing weathering rates, here higher Na* appears to be related to high DOC, which is consistent with observed increases in active organic functional groups as pH increases. Our results suggest that under a specific vegetative cover, the soil carbon environment affects the weathering flux observed. Our study also suggests that disturbed soils provide an enhanced physical and chemical environment for weathering. Generalized silicate weathering models may benefit from including the enhancing effects of organic anions at moderate pH in addition to precipitation and temperature.     

The potential of paleoecology for functional forest restoration planning: lessons from Late Holocene Italian pollen records

We describe forest landscape transformations during the last two millennia in the Italian peninsula by analyzing local (Rieti basin – Lago Lungo) and regional (RF93-30 Adriatic Sea) sediment cores. We identify a dynamic forest ecosystem through paleoecologic reconstruction and consider potential interventions for effective restoration of the most ancient, least disturbed forest ecosystem. The most degraded ecosystems in consequence of human activities were hygrophilous (wet) and mesic forests. In the Rieti Basin, degraded forest ecosystems on mountain slopes are undergoing some degree of forest succession and have less need of restoration. However, management plans for biodiversity, ecosystem services and resources conservation are needed to achieve more sustainable development. In Rieti, the paleoecological investigation revealed a dramatic decrease of deciduous wet and mesic tree taxa through time due to human landscape transformation. The starting point for restoration of a Mediterranean forest ecosystem that preserves natural biodiversity and associated ecosystem services requires recreating some portion of the floodplain wetland ecological niche. Once floodplain forest ecological niche has been recreated, the original ecosystem composed of Alnus, Fraxinus excelsior, Tilia spp., Carpinus betulus and Acer spp., all species which today are rare, should be planted on the basis of microsite characteristics and tree autoecology.     

Assessing accuracy and precision for field and laboratory data: a perspective in ecosystem restoration

Unlike most laboratory studies, rigorous quality assurance/quality control (QA/QC) procedures may be lacking in ecosystem restoration (“ecorestoration”) projects, despite legislative mandates in the United States. This is due, in part, to ecorestoration specialists making the false assumption that some types of data (e.g. discrete variables such as species identification and abundance classes) are not subject to evaluations of data quality. Moreover, emergent behavior manifested by complex, adapting, and nonlinear organizations responsible for monitoring the success of ecorestoration projects tend to unconsciously minimize disorder, QA/QC being an activity perceived as creating disorder. We discuss similarities and differences in assessing precision and accuracy for field and laboratory data. Although the concepts for assessing precision and accuracy of ecorestoration field data are conceptually the same as laboratory data, the manner in which these data quality attributes are assessed is different. From a sample analysis perspective, a field crew is comparable to a laboratory instrument that requires regular “recalibration,” with results obtained by experts at the same plot treated as laboratory calibration standards. Unlike laboratory standards and reference materials, the “true” value for many field variables is commonly unknown. In the laboratory, specific QA/QC samples assess error for each aspect of the measurement process, whereas field revisits assess precision and accuracy of the entire data collection process following initial calibration. Rigorous QA/QC data in an ecorestoration project are essential for evaluating the success of a project, and they provide the only objective “legacy” of the dataset for potential legal challenges and future uses.     

Evidence for mutualist limitation: the impacts of conspecific density on the mycorrhizal inoculum potential of woodland soils

The ability of seedlings to establish can depend on the availability of appropriate mycorrhizal fungal inoculum. The possibility that mycorrhizal mutualists limit the distribution of seedlings may depend on the prevalence of the plant hosts that form the same type of mycorrhizal association as the target seedling species and thus provide inoculum. We tested this hypothesis by measuring ectomycorrhizal (EM) fine root distribution and conducting an EM inoculum potential bioassay along a gradient of EM host density in a pinyon–juniper woodland where pinyon is the only EM fungal host while juniper and other plant species are hosts for arbuscular mycorrhizal (AM) fungi. We found that pinyon fine roots were significantly less abundant than juniper roots both in areas dominated aboveground by juniper and in areas where pinyon and juniper were co-dominant. Pinyon seedlings establishing in pinyon–juniper zones are thus more likely to encounter AM than EM fungi. Our bioassay confirmed this result. Pinyon seedlings were six times less likely to be colonized by EM fungi when grown in soil from juniper-dominated zones than in soil from either pinyon–juniper or pinyon zones. Levels of EM colonization were also reduced in seedlings grown in juniper-zone soil. Preliminary analyses indicate that EM community composition varied among sites. These results are important because recent droughts have caused massive mortality of mature pinyons resulting in a shift towards juniper-dominated stands. Lack of EM inoculum in these stands could reduce the ability of pinyon seedlings to re-colonize sites of high pinyon mortality, leading to long-term vegetation shifts.     

Microbial inoculum production for biocrust restoration: testing the effects of a common substrate versus native soils on yield and community composition

Human activities are causing unprecedented disturbances in terrestrial ecosystems across the globe. To reverse soil deterioration in drylands, a promising tool is the ex situ cultivation of biological soil crusts, topsoil geobiological assemblages that provide key ecosystem services. One approach is to transplant biocrusts cultivated in greenhouse nursery facilities into degraded sites to accelerate recovery. Lichen‐ and moss‐dominated biocrusts have been successfully grown using a common, sandy soil. We compared the use of a common, sandy soil versus native soils as a substrate for the cultivation of cyanobacteria‐dominated biocrusts. In greenhouse experiments, we inoculated natural biocrusts collected from three Southwestern USA dryland sites on to either a common, sandy soil or on their respective native soils. The common substrate resulted in a moderate enhancement of growth yield relative to native soils. While changes in bacterial phyla composition remained low in all cases, the use of a common substrate introduced larger shifts in cyanobacterial community composition than did using native soils. The shift increase attributable to the common, sandy soil was not catastrophic—and typical cyanobacteria of field biocrusts remained dominant—unless textural differences between the common substrate and native soils were marked. Because collecting native soils adds a significant effort to growing cyanobacterial biocrusts in greenhouses for restoration purposes, the use of a common, sandy substrate may be considered by land managers as a standard practice. But we recommend to regularly monitor the composition of the grown biomass.     

Comparison of laboratory and field bioassays of laboratory‐reared Cydia pomonella (Lepidoptera: Tortricidae) quality and field performance

Maximum production and fitness of insect species that are mass‐reared for biological control programmes such as the sterile insect technique (SIT) have benefitted from the employment of quality control and quality management. With a growing interest in the use of SIT as a tactic for the suppression/eradication of key lepidopteran pests, such as the codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae), there is a parallel interest in inexpensive bioassays that can accurately detect differences in insect quality and monitor insect field performance. In this study, we examined laboratory (mating and flight ability) bioassays and field (field cage and open field release) bioassays simultaneously to discern the ability of the different bioassays to predict quality and field performance of codling moths produced in a commercial mass‐rearing facility. Moth quality was degraded by different levels of radiation during the sterilization procedure. Both the laboratory flight bioassay and the field cage bioassay successfully detected quality and performance differences that were relevant to moth performance in the field. However, the study data suggest that the field cage bioassay was a better predictor of the daily performance of males that had been released in the orchard than the laboratory flight bioassay. Conversely, data suggest that the controlled climatic conditions of the laboratory allowed the flight cylinder bioassay to be more sensitive in detecting daily fluctuations in the quality of moths caused by factors within the mass‐rearing facility. Therefore, both laboratory and field bioassays may be required to provide feedback on quality and performance of mass‐reared moths in a SIT programme.     

Ectomycorrhizal fungal communities of pedunculate and sessile oak seedlings from bare-root forest nurseries

In this study, we present the detailed molecular investigation of the ectomycorrhizal (ECM) community of Quercus petraea and Quercus robur seedlings grown in bare-root forest nurseries. In all tested oak samples, mycorrhizal colonization was nearly 100%. Morphological observation and molecular investigations (sequencing of fungal ITS rDNA) revealed a total of 23 mycorrhizal taxa. The most frequent and abundant fungal taxa were Hebeloma sacchariolens, Tuber sp., and Peziza sp.; from the detected fungal taxa, 20 were noted for Q. petraea and 23 for Q. robur. Depending on the nursery, the species richness of identified ECM fungal taxa for both oak species ranged from six to 11 taxa. The mean species richness for all nurseries was 5.36 and 5.82 taxa per Q. petraea and Q. robur sample, respectively. According to the analysis of similarity, ECM fungal communities were similar for Q. petraea and Q. robur (R = 0.019; p = 0.151). On the other hand, detected fungal communities were significantly different between nurseries (R = 0.927; p < 0.0001). Using the Spearman rank correlation, it was determined that the ectomycorrhizal diversity (in terms of richness, the Shannon diversity, evenness, and Simpson dominance indices) is significantly related to the soil parameters of each nursery. We conclude that individual nursery may be considered as separate ecological niches that strongly discriminate diversity of ECM fungi.     

The potential of some adjuvants in promoting infection with Verticillium lecanii: laboratory bioassays with Myzus persicae

The potential of 14 adjuvants, including mineral oils, vegetable oils, stickers, spreaders, surfactants and nutrients, in promoting the virulence of the entomopathogenic fungus Verticillium lecanii were compared relative to a commercial formulation of the pathogen. The rate of infection over time with each adjuvant relative to the commercial formulation was tested using the peach potato aphid Myzus persicae. The proportion of infected aphids was modelled binomially with a logistic rate function assumed for the proportion infected over the time period of the experiment. Four of the adjuvant treatments, Codacide, skimmed milk, glycerol and Cutinol together with the commercial control had similar logistic slope parameters and were modelled using parallel regressions. The parallel regressions model showed significant differences between the intercepts with both glycerol and Cutinol significantly better than V. lecanii alone. Glycerol had a more positive intercept than Cutinol but the difference was not statistically significant. Although highly variable, the numbers of progeny produced by the treated aphids were significantly reduced by all the treatments relative to untreated control aphids. Glycerol and Cutinol were the only treatments that significantly reduced the number of progeny relative to the V. lecanii control.     

The roles of top and intermediate predators in herbivore suppression: contrasting results from the field and laboratory

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Effects of erosion on ecto- and VA-mycorrhizal inoculum potential of soil following forest fire in southwest Oregon

The Longwood Complex wildfire in the Siskiyou Mountains of southern Oregon in August 1987 created an opportunity to study erosion and its effects on mycorrhizal fungus inoculum potential of a forest soil on steep slopes. As measured by the erosion-bridge method, most erosion occurred in a single, intense storm in December after the fire and amounted to an estimated 2 to 4 cm of surface soil. Captured eroded soil had a higher pH and P and Mg levels than residual soil. Seedlings ofLibocedrus decurrens andPseudotsuga menziesii were planted on eroded plots with additions of captured eroded soil (ET) or pasteurized eroded soil (PET) transferred to the planting holes. After one growing season,Libocedrus seedlings formed nearly 4 times the vesicular-arbuscular mycorrhizae in ET treatments and more than twice as much in PET treatments than in controls. Survival and basal area growth were significantly better in ET than in the other treatments, and both ET and PET produced more seedling shoot growth than did controls.Pseudotsuga seedlings did not differ in measured characteristics between treatments; ectomycorrhiza formation was slight, evidently the result of reduced inoculum potential resulting from the fire.     

Drivers of truffle biomass,community composition,and richness among forest types in the northeastern US

Truffle-producing fungi (hypogeous sporocarps) are important mycorrhizal symbionts and provide a key food source for many animals, including small mammals. To better understand truffle diversity and associations in the northeastern US, we surveyed for truffles and analyzed spores in eastern chipmunk (Tamias striatus) scat across hardwood (angiosperm-dominated), softwood (gymnosperm-dominated), and mixed forest at Bartlett Experimental Forest, New Hampshire. Truffle biomass ranged from 3.8 kg/ha in hardwood forest to 31.4 kg/ha in softwood forest and was up to 35 times greater than mushroom (epigeous sporocarp) production in softwood forest. Elaphomyces species were the most common truffle taxa in both field surveys and chipmunk scat. Scat analysis indicated that truffle richness increased over the summer and accurately reflected fruiting time, providing greater resolution of richness than field surveys alone. Basal area of eastern hemlock (Tsuga canadensis) was the primary driver of Elaphomyces biomass and was the best explanatory variable of truffle community composition. We discuss implications of hemlock loss, due to the introduced hemlock woolly adelgid (Adelges tsugae), on forest mycorrhizal communities and food webs.     

Temperature responses of carbon mineralization in conifer forest soils from different regional climates incubated under standard laboratory conditions

¹⁴C‐labelled straw was mixed with soils collected from seven coniferous forests located on a climatic gradient in Western Europe ranging from boreal to Mediterranean conditions. The soils were incubated in the laboratory at 4°, 10°, 16°, 23° and 30 °C with constant moisture over 550 days. The temperature coefficient (Q₁₀) for straw carbon mineralization decreased with increasing incubation temperatures. This was a characteristic of all the soils with a difference of two Q₁₀ units between the 4–10° and the 23? 30 °C temperature ranges. It was also found that the magnitude of the temperature response function was related to the period of soil incubation. Initial temperature responses of microbial communities were different to those shown after a long period of laboratory incubation and may have reflected shifts in microbial species composition in response to changes in the temperature regime. The rapid exhaustion of the labile fractions of the decomposing material at higher temperatures could also lead to underestimation of the temperature sensitivity of soils unless estimated for carbon pools of similar qualities. Finally, the thermal optima for the organic soil horizons (Of and Oh) were lower than 30 °C even after 550 days of incubation. It was concluded that these responses could not be attributed to microbial physiological adaptations, but rather to the rates at which recalcitrant microbial secondary products were formed at higher temperatures. The implication of these variable temperature responses of soil materials is discussed in relation to modelling potential effects of global warming.     

The forest Gribskov, Denmark: lessons from the past qualify contemporary conservation, restoration and forest management

Knowledge of forest history is crucial for understanding the processes, structures, functions and current status of forest ecosystems. An enhanced understanding of the long history of disturbance factors affecting forest development and thereby the present state of the forest is particularly valuable when working with forest management, conservation and restoration. Integrating the legacies of past disturbances—natural as well as anthropogenic—into conservation and management strategies is likely to favour natural values and ecosystem services. A case-study in Gribskov, Denmark, using palaeoecological data and historical source materials explores the lessons learned from the past and leads to the suggestion of a conceptual model of how information from the past can increase understanding of long-term ecological processes.     

Isolation and identification of threeCellulomonas spp. from forest soils

Three stains of cellulose-degrading, aerobic, mesophilic bacteria were isolated from forest soils and, from their cultural, biochemical, and physiological characteristics, they were identified as members of the genusCellulomonas. Unusual biochemical characteristics, e.g. urea hydrolysis, were observed in two isolates. These characteristics have not previously been reported for cellulomonads and may prove to be significant for characterization ofCellulomonas spp. The isolates were able to use urea as a N source in cellulose fermentation. All three strains were motile, with one to four peritrichous flagella observed. Amino acid and polysaccharide composition of the cell walls of the three isolates were identical.     

Effects of non-native Asian earthworm invasion on temperate forest and prairie soils in the Midwestern US

Effects of invasive European earthworms in North America have been well documented, but less is known about ecological consequences of exotic Asian earthworm invasion, in particular Asian jumping worms (Amynthas) that are increasingly reported. Most earthworm invasion research has focused on forests; some Amynthas spp. are native to Asian grasslands and may thrive in prairies with unknown effects. We conducted an earthworm-addition mesocosm experiment with before–after control-impact (BACI) design and a complementary field study in southern Wisconsin, USA, in 2014 to investigate effects of a newly discovered invasion of two Asian jumping worms (Amynthas agrestis and Amynthas tokioensis) on forest and prairie litter and soil nutrient pools. In both studies, A. agrestis and A. tokioensis substantially reduced surface litter (84–95 % decline in foliage litter mass) and increased total carbon, total nitrogen, and available phosphorus in the upper 0–5 cm of soils over the 4-month period from July through October. Soil inorganic nitrogen (ammonium– and nitrate–N) concentration increased across soil depths of 0–25 cm, with greater effects on nitrate–N. Dissolved organic carbon concentration also increased, e.g., 71–108 % increase in the mesocosm experiment. Effects were observed in both forest and prairie soils, with stronger effects in forests. Effects were most pronounced late in the growing season when earthworm biomass likely peaked. Depletion of the litter layer and rapid mineralization of nutrients by non-native Asian jumping worms may make ecosystems more susceptible to nutrient losses, and effects may cascade to understory herbs and other soil biota.