Red Oak Acorns Research Articles

Patterns of acorn selection in Peromyscus mice and possible implications in a changing climate

Abstract Rodents play a key role in forest regeneration by dispersing seeds and interspecific differences in seed preferences could have important consequences for forest growth. The White-footed Mouse (Peromyscus leucopus) and Deer Mouse (Peromyscus maniculatus gracilis) are 2 closely related species that can exploit Red Oak (Quercus rubra) acorns but may display different preference levels due to the high tannin concentration present in these acorns. Here we investigated how White-footed Mice and Deer Mice differ in their ability to exploit Red Oak acorns. We conducted a cafeteria-style experiment where we offered mice (n = 61) acorns of Red Oak and Bur Oak (Q. macrocarpa; control seed with lower tannin levels) and video-recorded their preference and the acorn fate (consumed or cached). Using mixed-effects models, we found that both mouse species selected and consumed Bur Oak acorns at a high rate; however, White-footed Mice were 6.67 times more likely to select and consume Red Oak acorns than Deer Mice. Furthermore, White-footed Mice tended to cache Red Oak acorns near the surface where there is a higher chance of germination, while they usually consumed Bur Oak acorns. Our results suggest that Red Oaks have a better strategy for avoiding predation than Bur Oaks (i.e., high tannin levels leading to caching), and the strong interaction between the White-footed Mouse and Red Oak might be an important mechanism behind the current range expansion of both species in response to climate change.

A novel low-cost plant-based adsorbent from Red Oak (Quercus rubra) Acorns for wastewater treatment: Kinetic study on removal of dye from aqueous solution

Oak species are a successful plant group that have colonized the world's largest areas of forest. Oak trees are also prevalent in urban green spaces in the United States and Canada. As a result, these trees produced an abundance of acorns each year. In urban areas, these acorns are frequently discarded as solid waste. Alternative uses for this forest/plant waste are highly desirable because they will not only be valorized but will also contribute to the reduction of solid waste. The purpose of this work was to manufacture low-cost activated carbon using Red Oak (Quercus rubra) acorns and utilize it to remove methyl blue colors in aqueous solutions. The results of experiments indicated that prepared carbons were effective at removing pollutants from water. The pH, starting dye concentration, temperature, duration of the adsorption process, and shaking rate all had an effect on the adsorption process. The basic pH system was found to have the most favourable conditions for dye removal after a 3-hour contact time. The starting concentration of adsorbate has a detrimental influence on the removal rate, while the other factors also may have effect. A kinetic analysis revealed for the first 2 hours, the dye adsorption was better characterized by a pseudo-second order kinetic model with an equilibrium concentration (qe) of 0.9756 mg/g and an equilibrium rate constant (k2) of 16.81 g/mg min. Given that Red Oak acorns are largely regarded as solid waste due to their low monitory value and their widespread availability, the resulting carbons are anticipated to be economically feasible for the treatment of wastewater. The study's various findings indicate that this novel material is an excellent biosorbent for dye removal from contaminated waters.

Avian dispersal of an invasive oak is modulated by acorn traits and the presence of a native oak

Successful invasions of non-native plants often depend on establishing mutualistic interactions with native organisms. Animal seed dispersers can greatly enhance the spread of invasive plants. Emerging seed dispersal mutualisms might also result in indirect interactions between non-native and native plants, mediated by shared dispersal agents. We investigated tripartite interactions between Eurasian jays (Garrulus glandarius), non-native northern red oaks (Quercus rubra), and native pedunculate oaks (Q. robur) in a lowland forest of Central Europe. We estimated the probability of acorn removal for both oak species in single vs. mixed treatment, and the effects of acorn length, width, and weight. We also radio-tracked removed acorns to determine their fate. While jays preferred to harvest the native acorns, they also removed almost all offered acorns of the invader. The removal rate of non-native acorns increased when the two oak species co-occurred, and was modulated by acorn traits: jays selected red oak acorns that were long and narrow. In comparison to pedunculate oak acorns, those of red oak were transported shorter distances and were more likely to be consumed rather than cached. Altogether, dispersal of red oaks by jays was less intense and brought smaller benefits relatively to the dispersal of pedunculate oak. Yet, these differences were moderate, and jays provided effective dispersal of both oaks. Our results highlight the role of keystone native seed dispersers in the expansion of non-native plants. Furthermore, they illustrate how dispersal quantity of non-native plants can be facilitated by the presence of native plants that attract shared seed dispersers.

Adsorption of Methyl Blue onto Activated Carbon Derived from Red Oak (Quercus rubra) Acorns: a 26 Factorial Design and Analysis

In this study, red oak (Quercus rubra) acorns were used as precursor for preparing activated carbon by thermal activation. Red oak activated carbon (RAC) was evaluated for the removal of methyl blue (MB), using batch adsorption experiments. SEM images taken before and after adsorption experiments showed difference of surface morphology. A 26 full factorial design approach was used to determine the main and interaction effect of independent factors on dye removal rate. The six independent factors used for this study were sorbent dosage, initial dye concentration, pH, temperature, mixing rate (rpm), and mixing time. The response of this factorial design was percentage of dye removal (R%) from an aqueous solution. All independent factors showed significant influence. Initial dye concentration and adsorbent dose exhibited largest negative and positive influence on removal rate, respectively. The factorial experiments also demonstrated significant synergistic/ antagonistic interaction between all these factors. Optimum conditions for adsorption were adsorbent dosage = 0.25 g/50 ml, initial dye concentration = 10.0 mg L 1, pH = 10, temperature = 45 °C, mixing rate = 175 rpm, and mixing time = 2.0 h. Under these conditions, response, dye removal rate R, was maximized, with a value of 97.18%. The findings of this study could be useful for industrial wastewater treatment systems.

Prescribed fire promotes acorn survival and seedling emergence from simulated caches

Prescribed fire increasingly is used to promote oak (Quercus) establishment in many hardwood forests across North America. However, how prescribed fire affects several key components of the oak regeneration process, including acorn survival and germination, is relatively unknown. Acorn mortality during a prescribed fire is likely affected by acorn dormancy, burn season, and previous burial (caching) by scatterhoarding rodents. We assessed the effect of fall and spring prescribed fires on seedling emergence for artificially cached and un-cached northern red oak (Q. rubra) and white oak (Q. alba) acorns in situ in granivore-proof exclosures through eight prescribed fires over two years at two sites in central Indiana. The odds of cached acorn emergence were 3.4–12.1 times higher following fall and spring prescribed fires than the unburned control. Red oak emergence was 1.7 times higher following fall burns than spring burns, whereas white oak emergence was unaffected by burn season. Lower winter temperatures following fall burns may have driven observed differences between burn seasons for northern red oak acorns. Our study links the oak-rodent conditional mutualism hypothesis with the oak-fire hypothesis, by suggesting that prescribed fire may produce environmental conditions that shift interactions between oaks and scatterhoarding rodents toward a more mutualistic relationship.

Red oak acorn yields in green‐tree reservoirs and nonimpounded forests in Mississippi

ABSTRACTAlthough bottomland hardwood forests in southeastern United States are among the most productive ecosystems in North America, indigenous flora, wildlife, and system dynamics have been altered and affected by natural and anthropogenic effects. Historic spatio‐temporal dynamic flooding in hardwood bottomlands caused managers to create green‐tree reservoirs (GTR; i.e., impounded forested tracts) to enhance predictability of seasonal inundation chiefly for waterfowl habitat and hunting. Bottomland red oaks (Quercus spp.) are valuable trees for wildlife that consume acorns they produce. There was inconsistent evidence in the scientific literature, so we tested the null hypotheses of no differences in annual yield, percentage of sound acorns, and proportion of ‘high‐yielding’ red oaks in GTRs and nonimpounded naturally flooded forests (NFF) in western and east‐central Mississippi, USA, during autumn–winter, 2008–2012. Mean annual yields of sound acorns from GTRs and NFFs at Noxubee National Wildlife Refuge and Delta National Forest had overlapping confidence intervals in all years of our study; however, percentages of sound acorns were greater in GTRs in 3 of 8 site‐year comparisons. We also found conflicting results between study sites regarding which flood regime had the greatest proportion of high‐yielding oaks. Our results demonstrate differences in total acorn yield by red oaks may be neither statistically nor biologically different between GTRs and NFFs in Mississippi; however, the proportion of sound acorns may be greater in GTRs relative to NFFs in some years. Future research may determine whether these phenomena are related to surviving trees producing increased seed propagules in response to long‐term flooding stress in GTRs or residual trees possessing traits for increased acorn production in some years. Nonetheless, deleterious effects from persistent or prolonged within‐ and among‐year flooding of GTRs are well‐documented, suggesting managers should consider these possible consequences in sustaining and regenerating lowland red oak populations. © 2019 The Wildlife Society.

Prescribed fire and partial overstory removal alter an acorn-rodent conditional mutualism.

In eastern North America, oak (Quercus) regeneration failure has spurred management using silvicultural approaches better aligned with the autecology of oaks. In particular, shelterwood harvests can create favorable intermediate light conditions for oak establishment and prescribed fire is predicted (by the oak-fire hypothesis) to favor oak regeneration. These approaches substantially modify forest structure and may affect crucial trophic interactions including the conditional mutualism between oaks and granivorous rodents that scatterhoard acorns, which shifts along a continuum from antagonistic to mutualistic depending on external factors. We investigated how overwinter survival and dispersal of northern red oak (Quercus rubra) acorns were influenced by location within or outside of group shelterwood harvests (small canopy gaps created throughout an intact forest stand) with and without prescribed fire. We conducted two concurrent experiments to test (1) dispersal and survival of acorns presented on the forest floor and (2) acorn pilferage rates from caches that mimic squirrel scatterhoards in shelterwood gap/group interiors, edges, and the uncut forest matrix in burned and unburned forest stands. In both experiments, acorn survival was generally higher in burned than unburned stands. Acorn survival from forest floor presentations was higher in the unharvested forest matrix than harvest gap interiors; however, there was no effect of proximity to harvest gaps on survival of cached acorns. Survival of cached acorns was associated with understory vegetative cover (-), coarse woody debris cover (-), and distance to nearest tree (+), but uncorrelated with canopy cover above the cache. Our results suggest that reduced understory cover following prescribed fire may increase perceived habitat riskiness for granivores resulting in higher acorn survival up to 2yr post-fire. These findings unify the oak-fire and oak-granivore conditional mutualism hypotheses, and suggest that the environmental conditions following prescribed fire and group shelterwood harvests may shift the oak-granivore conditional mutualism in a direction beneficial for oak regeneration.

Habitat-dependent seed dispersal of an introduced tree species by native rodents

Invasions of many plant species strongly depend on propagule pressure. Thus, habitat-related differences in seed dispersal could affect susceptibility of distinct habitat types to plant invasions. We examined the fate of northern red oak (Quercus rubra, invasive in Europe) and pedunculate oak (Quercus robur, native in Europe) acorns dispersed by yellow-necked mice (Apodemus flavicollis) in (i) hardwood stands invaded by northern red oak, (ii) uninvaded hardwood stands dominated by native oaks, and (iii) uninvaded coniferous stands dominated by Scots pine (Pinus sylvestris). Regardless of forest type, mice preferred to harvest and consume pedunculate rather than red oak acorns. Similarly, acorn harvest rates were unaffected by forest type. However, the fate of acorns, and thus effectiveness of seed dispersal, varied considerably among forest types. Acorns had the highest probability of being cached in uninvaded hardwood stands, while coniferous stands were characterized by the longest seed dispersal distances and a high proportion of missing seeds (probably indicating larderhoarding). Relative to the other forest types, stands with northern red oak were characterized by a combination of low acorn caching rates and short dispersal distances. These findings suggest that differences in rodent-mediated seed dispersal might increase recruitment rates of northern red oak at the edges of invaded range.

Re-caching of acorns by rodents: Cache management in eastern deciduous forests of North America

Scatter-hoarding rodents such as tree squirrels selectively cache seeds for subsequent use in widely-spaced caches placed below the ground surface. This behavior has important implications for seed dispersal, seedling establishment, and tree regeneration. Hoarders manage these caches by recovering and eating some seeds, and moving and re-caching others. This process of re-caching, however, is poorly understood. Here, we use radio-telemetry to evaluate re-caching behavior for the management of acorn caches by rodents in eastern deciduous forests. We also test the hypothesis that as seeds are re-cached, the distance from the source increases. Radio transmitters were implanted in Northern red oak (Quercus rubra) acorns and presented to rodents in a natural setting over 3 seasons. We used radio-telemetry to track and document evidence of recovery and re-caching. We tracked a total of 102 acorns. Of the 39 radio-tagged acorns initially cached, 19 (49%) were cached on two or more occasions; one acorn was cached four times. The hypothesis that rodents move seeds to progressively greater distances from the source is not well-supported, suggesting that acorns are being moved within an individual's home range. Given the species of rodents in the study area, gray squirrels (Sciurus carolinensis) are the most likely to be responsible for the caching and re-caching events. Gray squirrels appear to engage in extensive re-caching during periods of long-term food storage, which has important implications for understanding how caching behavior influences acorn dispersal and oak regeneration.

Invasive oaks escape pre-dispersal insect seed predation and trap enemies in their seeds.

Species introduced to habitats outside their native range often escape control by their natural enemies. Besides competing with native species, an alien species might also affect the native herbivores by introducing a new source of different quality food. Here, we describe the case of northern red oak (Quercus rubra) invasion in Europe. We collected data on insect (moth Cydia spp. and weevil Curculio spp.) seed predation of northern red oak in its native (USA, North America) and invasive (Poland, Europe) range, as well as for sessile oaks (Quercus petrea) in Europe. We also evaluated the quality of acorns as hosts for weevil larvae by collecting infested acorns and measuring weevil developmental success, and quantifying acorn traits such as seed mass, tannins, lipids and protein concentration. We used DNA barcoding to identify insects to the species level. The predation by moths was similar and very low in both species and in both ranges. However, red oaks escape pre-dispersal seed predation by weevils in Europe. Weevil infestation rates of northern red oak acorns in their invasive range were 10 times lower than that of sessile oaks, and also 10 times lower than that of red oaks in North America. Furthermore, even when weevils oviposited into northern red oaks, the larvae failed to develop, suggesting that the exotic host created a trap for the insect. This phenomenon might gradually decrease the local abundance of the seed predator, and further aid the invasion.

A test of the predator satiation hypothesis, acorn predator size, and acorn preference

Mast seeding is hypothesized to satiate seed predators with heavy production and reduce populations with crop failure, thereby increasing seed survival. Preference for red or white oak acorns could influence recruitment among oak species. We tested the predator satiation hypothesis, acorn preference, and predator size by concurrently measuring acorn production, mouse abundance, and white versus red oak acorn removal rates in exclosures allowing access by mice (HW), squirrels and smaller-sized vertebrates (WW), or all-sized vertebrates (C) for 12 years. Annual removal rate varied, but virtually all acorns were eventually removed from all exclosure types all years except one. Acorns were removed more slowly from HW than from WW or C exclosures, indicating that large vertebrates were not major acorn consumers, locally. Red and white oak acorn removal rates were similar except in two years, when red oak acorns were removed more rapidly. Removal slowed with increasing acorn crops, suggesting that heavy crops can “swamp” predators. Removal rate was negatively correlated with crop size the previous fall. A positive trend between mouse abundance and crop size the previous fall was evident; abundance decreased sharply the year following crop failures but not after moderate or heavy crops, suggesting that poor crops can dampen acorn predation the following year.

Deciphering the effects of disperser assemblages and seed mass on patterns of seed dispersal in a rodent community.

The sizes of both seed dispersers and seeds are traits that are likely to interact to influence seed fate in many synzoochoric plant species. Here, we examined whether members of a granivorous rodent community consisting of species of different body size vary in their effectiveness as seed dispersers, and how this relationship may be altered by seed size. We marked northern red oak (Quercus rubra) acorns with plastic tags and placed them in size-selective rodent exclosures. The exclosures allowed differential access of rodent groups based on different body size: (i) small (e.g. Peromyscus spp.); (ii) small and medium (e.g. Tamias striatus); and (iii) small, medium and large (e.g. Sciurus carolinensis) species of rodents. Acorn removal did not differ among exclosure types, but more seeds were missing when removed by small rodents, probably because of larderhoarding. The treatments did not influence the relative frequency of acorn consumption. However, small rodents cached considerably fewer and partially ate more acorns than the other 2 groups. The mean dispersal distance was the longest for cages with medium openings, intermediate for cages with large openings and the shortest for cages with small openings. Acorn mass positively affected the probability of caching and this relationship was unaffected by exclosure type. In conclusion, granivorous rodents of different body sizes strongly differed in their interactions with acorns, with small rodents acting primarily as acorn predators and medium and large species contributing significantly more to dispersal of red oaks.

Acorns of introduced Quercus rubra are neglected by European Jay but spread by mice

Northern Red Oak (Quercus rubra L.; native in North America) is regarded as an invasive species in Central Europe, where it is the most common non-indigenous broad-leafed tree species in forestry. The species’ impact on native ecosystems and thus its future management are discussed controversially. Because dispersal is an important step in an invasion process, we studied whether European Jays (Garrulus glandarius L.) and mice, both main dispersers of native oaks in Europe, mediate the dispersal of Q. rubra seeds. Morphological characteristics of Q. rubra and native Q. robur L. acorns were quantified according to their implications for dispersal. We tested experimentally whether and to what extent mice and jays collect acorns of both oak species and if their behavior depends on choice options (dual choice vs. no-choice). Acorns were offered on feeding platforms, controlled by scouting cameras. Results showed that Q. rubra acorns have a thicker pericarp, a rounder shape and a higher dry weight compared to acorns of Q. robur. In the behavioral assays jays avoided acorns of Q. rubra if they were offered together with those of Q. robur (dual choice) as well as when Q. rubra acorns were offered alone (no-choice). This selection behavior could be caused by the differences in morphological traits observed between the acorns of the two species. In contrast to jays, mice took acorns of both oak species likewise indicating that seed morphology does not affect the attractiveness of Red Oak acorns for rodents. In conclusion, Quercus rubra is collected by animals in Central Europe to a considerable amount but dispersal should be restricted to moderate distances mediated by mice, leading mainly to stabilizing and increasing existing populations rather than founding of new ones.

Allegheny woodrat hard mast preference and response to food supplementation

ABSTRACTRange‐wide declines of the Allegheny woodrat (Neotoma magister) have been attributed, in part, to reductions in mast associated with extirpation of American chestnut (Castanea dentata) and transition to oak (Quercus)‐dominated forests prone to periodic mast failure. Chestnuts produce mast more consistently than oaks; hence, efforts to restore a blight‐resistant hybrid chestnut may facilitate woodrat recovery. Our goal was to describe the implications of chestnut restoration for imperiled Allegheny woodrat populations. Our objectives were to evaluate woodrat preferences for American chestnuts, blight‐resistant hybrid chestnuts, and other hard mast items and to describe the response of woodrats to artificial increases in mast availability. From 2011 to 2013, we conducted a series of cafeteria‐style experiments among woodrat populations in southern Indiana in which we used remote cameras to quantify woodrat preferences for various mast items. Additionally, we introduced an abundance of mast into occupied den sites and evaluated differences in apparent survival, apparent recruitment, population growth rate, and body mass between mast‐supplemented and control populations. Discrete choice modeling revealed that woodrats preferentially removed northern red oak (Q. rubra) and black oak (Q. velutina) acorns over chestnuts and other seed types (i.e., hickories [Genus spp.], walnuts [Genus spp.]). Further, woodrats preferred American over hybrid chestnuts, suggesting that these seeds were not perceived as equivalent food resources. Apparent survival, apparent recruitment, population growth rate, and body mass did not differ between supplemented and control populations. Although chestnuts, as annually consistent mast producers, may benefit woodrat populations by reducing the risk of complete mast failure, our results suggest that the restoration of chestnut mast is unlikely to benefit woodrat populations during years of abundant acorn production. Accordingly, managers should foster a diverse and abundant oak community to ensure sufficient acorn resources are available to sustain woodrat populations as chestnut restoration efforts progress. © 2015 The Wildlife Society.

Weather affects diet composition of rusty blackbirds wintering in suburban landscapes

ABSTRACTThe rusty blackbird (Euphagus carolinus) is a species of conservation concern throughout its range and the cause of the species' population decline is unknown. We studied diet composition of rusty blackbirds with stable isotope mixing models in suburban landscapes in the southeastern United States. We captured blackbirds in Georgia and South Carolina from 2009 to 2012, and estimated proportions of earthworm, other animals, pecan, and acorn incorporated into individual diets. On the Piedmont Plateau, terrestrial and aquatic earthworms constituted the largest proportion incorporated into the diet (39% ± 2.9; mean ± SD by site and year) and animals other than earthworms (mostly larval invertebrates Odonata and Diptera) constituted 27% ± 12.9. In contrast, on the Coastal Plain, which featured milder winters than the Piedmont, earthworms constituted a lower proportion (19% ± 1.2) of incorporated food items and animals other than earthworms comprised 62% ± 3.3% of the diet. Increased incorporation of earthworms in the diet was related to increased upcoming precipitation and daily maximum temperature. Rusty blackbirds incorporated more tree mast into their diet on the Piedmont Plateau than the Coastal Plain. Increased incorporation of tree mast was related to advancing cold temperature. Mast, including crushed pecans (Carya illinoenensis) and pre‐opened small‐seeded red oak (Quercus spp.) acorns, is a high‐lipid dietary component of blackbirds wintering in colder climates, and is incorporated prior to extreme cold weather. Therefore, planting mast trees, especially lipid‐rich pecan, could be used to augment resources in known rusty blackbird wintering hotspots. Maintaining shallowly flooded wetlands with a fluctuating water regime and residential lawns with abundant red oak (Quercus spp.) leaf litter would promote acorn and invertebrate resources including earthworms. © 2015 The Wildlife Society.

The overwintering biology of the acorn weevil, Curculio glandium in southwestern Ontario

The acorn weevil, Curculio glandium, is a widespread predator of acorns in eastern North America that overwinters in the soil as a larva. It is possible that low temperatures limit its northern geographic range, so we determined the cold tolerance strategy, seasonal variation in cold tolerance, and explored the physiological plasticity of overwintering larvae. Weevil larvae were collected from acorns of red and bur oak from Pelee Island, southwestern Ontario in fall 2010 and 2011. C. glandium larvae are freeze avoidant and larvae collected from bur oak acorns had lower supercooling points (SCPs: −7.6±0.36°C, LT50: −7.2°C) than those collected from red oak acorns (SCPs: −6.1±0.40°C, LT50: −6.1°C). In the winter of 2010–2011, SCPs and water content decreased, however these changes did not occur in 2011–2012, when winter soil temperatures fluctuated greatly in the absence of the buffering effect of snow. To examine whether larvae utilize cryoprotective dehydration, larvae from red oak acorns were exposed to −5°C in the presence of ice for seven days. These conditions decreased the SCP without affecting water content, suggesting that SCP and water content are not directly coupled. Finally, long-term acclimation at 0°C for six weeks slightly increased cold tolerance but also did not affect water content. Thus, although larval diet affects cold tolerance, there is limited plasticity after other treatments. The soil temperatures we observed were not close to lethal limits, although we speculate that soil temperatures in northerly habitats, or in years of reduced snow cover, has the potential to cause mortality in the field.

The effect of storage temperature and duration on northern red oak acorn viability and vigour

Three separate collections of Ontario sources of northern red oak (Quercus rubra L.) acorns were made to determine the effects of long-term cold storage at +2°C, −1°C, and −2°C on their viability and vigour. We measured acorn moisture content, percent germination during storage, speed of germination and total germination values, root regrowth of seeds that germinated in storage, incidence of fungal contamination, and condition of ungerminated acorns. Viability and vigour peaked six to 12 months after acorns were placed in storage, but decreased with continued storage. After 18 months in storage, ≥60% of the acorns germinated in four of the five seedlots tested and, after 30 months in storage, ≥53% of the acorns germinated in three of the five seedlots tested. Acorn viability was only minimally affected by storage temperature; however, since temperatures above −2°C allowed acorns to germinate during storage, the preferred long-term storage temperature was −2°C. Our results suggest that, assuming proper storage conditions, most red oak seedlots will maintain relatively high germination levels when stored at −2°C for 18 months. Seedlots with particularly high initial germination and vigour may be successfully stored for up to 30 months.

Interannual Consistency of Gross Energy in Red Oak Acorns

Abstract Red oak Quercus spp., Subgenus Erythrobalanus acorns are forage for mallards Anas platyrhyncos, wood ducks Aix sponsa, and other wildlife that use bottomland hardwood forests in the southeastern United States. However, annual variation in true metabolizable energy from acorns would affect carrying-capacity estimates of bottomland hardwood forests for wintering ducks. Because gross energy and true metabolizable energy are strongly positively correlated and gross energy is easier to measure than true metabolizable energy, we used gross energy as a surrogate for true metabolizable energy. We measured gross energy of six species of red oak acorns in autumns 2008 and 2009. Within species, mean gross energy of these acorns varied less than 2% between years. The small interannual variation in gross energy of red oak acorns found in this study would have negligible effect on estimates of carrying capacity of bottomland hardwood forests for wintering ducks and other wildlife.

Effect of winter flooding on mass and gross energy of bottomland hardwood acorns

AbstractDecomposition of red oak acorns (Quercus spp.; Section Erythrobalanus) could decrease forage biomass and gross energy (GE) available to wintering ducks from acorns. We estimated changes in mass and GE for 3 species of red oak acorns in flooded and non‐flooded bottomland hardwood forests in Mississippi during winter 2009–2010. Mass loss of acorns was ≤8.1% and reduction in GE ≤0.03 kcal/g after exposure for 90 days. These small changes in mass and GE of red oak acorns would have minimal effect on carrying capacity of bottomland hardwood forests for ducks. © 2012 The Wildlife Society.

Acorn viability following prescribed fire in upland hardwood forests

Restoration of structure and function of mixed-oak (Quercus spp.) forests is a focal issue of forest land managers in the eastern United States due to widespread regeneration failure and poor overstory recruitment of oaks, particularly on productive sites. Prescribed fire is increasingly used as a tool in oak ecosystem restoration, with the goal of reducing competition, and creating light and seedbed conditions conducive to germination and growth of oak seedlings. Yet, oak seedling establishment is dependent on the presence of viable acorns, which may be vulnerable to prescribed fire. We assessed the effect of prescribed burning and fire temperature on the viability of white oak and northern red oak acorns placed on the leaf litter surface, in the duff, or in the mineral soil during five winter prescribed burns in southern Appalachian upland hardwood forests. Fire temperatures varied among acorn plots, ranging from <79 to <371°C. After the burns, acorns were planted in trays with water-saturated vermiculite, exposed to 14 continuous hours of light daily, and maintained at 27°C on germination beds in a greenhouse. After three weeks we recorded the proportion of acorns germinating and the proportion of germinants with shoots. Our study indicated that patchy, low-intensity dormant season prescribed fire in upland hardwood forests reduced viability of white oak and northern red oak acorns located on the leaf litter surface, but did not generally affect acorns in the duff or mineral soil. Germination rates of both northern red oak and white oak acorns on the leaf litter surface decreased with increasing fire temperature. Shoot production by northern red oak germinants from acorns on the leaf litter surface (and less so in the duff), also decreased with increasing fire temperature. Acorns of both species on the leaf litter surface burned at temperatures ⩾204°C showed high mortality levels, with mortality virtually 100% at temperatures ⩾260°C. Fall burns, especially after a heavy acorn crop, could result in high acorn mortality, potentially impacting oak regeneration from seedlings for many years given erratic acorn production patterns among years and species. Frequent burning that reduces litter and duff depth could compromise availability of ‘safe sites’ where acorns are insulated from high fire temperatures. When oak ecosystem restoration is a goal, land managers should consider the timing and size of acorn crops, as well as the forest floor condition when determining the timing and frequency of prescribed burning.