Oak Reproduction Research Articles

Effects of silvicultural release on artificial oak regeneration in bottomland hardwood forests in northern Missouri

In bottomland forests, managing oak regeneration is challenging due to competition with other species. Low understory light levels in mature stands favor more shade-tolerant tree species, whereas harvest often results in release of fast-growing competitors. In the late 1990s, a study was initiated in northeastern Missouri to evaluate the effects of overstory harvests on stand development of bottomland forests, with particular interest in oak regeneration. Canopy removal resulted in rapid growth of undesired soft-mast species without increasing the abundance of oak reproduction. In 2017, bare-rooted pin oak (Quercus palustris Muenchh.) and swamp white oak (Quercus bicolor Willd.) seedlings were planted, to increase the oak component through enrichment planting in the stands that had previously been harvested and underplanting in the stands that had received no regeneration harvest. For all planted seedlings, three levels of midstory release treatments were applied after planting in 2017, including a control (no release), and light release, and a heavy release. This study tested the effects of the original overstory harvests and the subsequent midstory release on survival and development of planted oak advance reproduction over 5 years. Our results suggest that establishing oak advance reproduction prior to overstory harvest is more efficient than enrichment planting after overstory harvest. A prior midstory release is important to develop competitive oak advance reproduction before a later overstory harvest to ensure successful oak regeneration.

Periodical Cicada Emergences Affect Masting Behavior of Oaks.

AbstractOaks (Quercus spp.) are masting species exhibiting highly variable and synchronized acorn production. We investigated the hypothesis that periodical cicadas (Magicada spp.), well known to have strong effects on the ecosystems in which they occur, affect acorn production of oaks through their xylem feeding habits as nymphs, the oviposition damage they inflict as adults during emergences, or the nutrient pulse resulting from the decomposition of their bodies following breeding. We found negative effects on acorn production during emergence years and the year following emergences and enhanced acorn production 2 years after emergence. We also found evidence indicating a significant effect of cicada emergences on spatial synchrony of acorn production by trees growing within the range of the same cicada brood compared with different broods. These results demonstrate that periodical cicadas act as a trophic environmental "veto" depressing acorn production during and immediately following emergences, after which the nutrient pulse associated with the cicada's demise enhances oak reproduction.

Evaluating the impact of prescribed surface fire on seedlings in the Central Hardwood Region, USA

Abstract Oak (Quercus) is being successionally replaced by maple (Acer) across much of the eastern deciduous forest. Past research on the close relationship between oak and fire has led forest managers to use prescribed surface fires to deter this replacement. However, there has not been a comprehensive evaluation of the effectiveness of prescribed fire by managers, particularly in the Central Hardwood Region. For example, it is not known how many repeat applications of prescribed fire are needed to accumulate enough oak reproduction to successfully re-establish oak-dominated stands. Tree reproduction and midstory composition were systematically surveyed across 63 mature, oak-dominated stands ranging in prescribed fire histories and aspects on the Hoosier and Wayne National Forests in southern Indiana and Ohio, respectively. These stands represent the vast majority of stands burned to promote oak regeneration since 1990 in these two National Forests. Across all sites, seedlings in the white oak group (section Quercus) and red oak group (section Lobatae) comprised 47.8 ± 3.3 per cent and 8.2 ± 1.6 per cent (mean ± SE), respectively, of all seedlings. In comparison, common competing species (maples and American beech) comprised 5.4 ± 1.4 per cent of all seedlings. Mid- and overstory basal area, percent slope, years since last burn, and total number of burns significantly affected oak seedling density. Greater increases in taller, competitive oak seedling density occurred after sites had been burned three times and with high frequency (≤4 years between burns). However, results also suggest that if an established midstory already exists or fire has not been used on the landscape for almost a decade, repeat applications of prescribed fire will not likely increase oak regeneration in the short term without concurrent treatment of midstory stems.

Responses of natural and artificial pin oak (Quercus palustris) reproduction to a sequence of silvicultural release treatments in bottomland hardwood forests in southern Missouri

Developing competitive oak advance reproduction prior to canopy disturbance is understood to be important for oak regeneration success. In the early 2000s, a study was installed in southeastern Missouri to examine the effects of midstory and understory release on natural and artificial sources of pin oak (Quercus palustris Muenchh.) advance reproduction. The findings obtained three years after midstory and understory release indicated photosynthetically active radiation increased from 3 to 15 % and a corresponding increase in density of pin oak reproduction as well as the survival and growth of both natural and artificial pin oak reproduction compared to control. In 2010, eight years after the midstory and understory was removed, three different overstory harvests were applied to release the established pin oak advance reproduction. Here, we investigated the effects of the midstory and understory removal and the subsequent overstory harvests on underplanted and naturally regenerated oak advance reproduction. We also tested effects of a later midstory release on the density of natural pin oak advance reproduction. Results indicate that the survival of bareroot pin oak seedlings increased with increasing initial basal diameter. The survival of Root Production Method (RPM®) container pin oak seedlings, however, was not dependent on the size at the time of planting. The early understory removal with triclopyr herbicide was ineffective in ensuring survival of planted pin oak seedlings. Shelterwood increased the growth of oak advance reproduction but did not eliminate competition from other species. A late release also failed to increase the growth of oak advance reproduction. Given shelterwood also favored oak competitors in our study, multiple applications of midstory and understory competition control treatments following the shelterwood treatment will be imperative for successful oak regeneration.

Modeling Advance Oak Reproduction at Landscape Scale: The Relative Importance of Abiotic and Biotic Factors

Abstract Establishing advance oak reproduction in the understory of mature oak forests before an overstory removal is critical to regenerate mixed-oak forests (Quercus spp.). Many studies have been conducted at the stand scale; however, studies at landscape scale can be particularly useful to guide silvicultural management investments. We developed a model of advance reproduction abundance at landscape scale using inventory, climate, topography, and soils data from ninety-seven mixed-oak forests located in Pennsylvania, USA. A negative binomial model was used to predict the abundance of oak seedlings between 15.2 and 91.4 cm in height and with a root collar diameter of 0.64 to 1.9 cm (established oak seedlings). This model had a Nagelkerke’s pseudo R2 of 58%. Deviance partitioning methods indicate that climate and overstory influence explain similar proportions of total deviance, but climate contributes a higher proportion of nonoverlapping information (22% versus 18%). Overstory basal area of two common oak species were positively associated with seedling abundance, whereas biotic stressors were negatively correlated. Biotic stressors showed considerable overlap with information provided by climate and overstory influences. The results of this study provide a reference to guide silvicultural management at a landscape scale.

Light and regeneration patterns following silvicultural gap establishment in Quercus dominated stands of the northern Cumberland Plateau, USA

We assessed short-term light and regeneration dynamics following silvicultural gap creation in intermediately productive oak (Quercus)-dominated stands of the Northern Cumberland Plateau, USA. We established 12 experimental units comprising a harvest gap (30-m radius) and a matrix zone extending 30 m beyond the circumference of the gap. Midstory removal was performed using manual felling and chemical deadening within the matrix zone of six experimental units, while those of the other six units remained undisturbed as controls. Belt transects extending 60 m from the gap center to the end of the matrix zone were delineated within each unit to quantify spatial light patterns and regeneration dynamics of oaks and woody competitors. Mean light transmittance ranged from 86% full sun at the gap center to<10% at the outer margin of the matrix zone. Light transmittance decreased from approximately 70% full sun within the gap at 10 m from the gap edge to 20% full sun at 10 m within the forest matrix. Two-year height growth and total heights of oaks were greatest within the gap interior and decreased toward the gap edge and subsequently into the adjacent forest matrix. We observed no statistical differences in light or regeneration patterns between control and midstory removal forest matrix zones. After two years, woody competition from non-oak stems, particularly yellow-poplar (Liriodendron tulipifera L.), was high within the gap interior, and >50% of non-oak stems were taller than the average oak seedling (50 cm). At the gap edge and within the adjacent forest matrix, <20% of non-oak stems were taller than 50 cm. Light conditions fostering taller oak reproduction and reduced rates of overtopping competition identify the gap edge environment as a zone of competitive oak reproduction within which future regeneration efforts may prove effective.

Both weather and resources influence masting in chestnut oak (Quercus montana Willd.) and black oak (Q. velutina Lam.)

Masting is the synchronous and highly variable production of fruit within a population. Although several hypotheses have been proposed to explain why and how masting evolved in plants as a reproductive strategy, the factors that trigger a large reproductive effort in a particular year are still not well understood. While both weather and resources have been proposed to play an important role, testing these hypotheses has been challenging due to a lack of long-term data and appropriate experimental designs. In this manuscript, we used 18 years of acorn production data to analyze the relationship between resources, weather, and masting in black oak (Quercus velutina) and chestnut oak (Q. montana). The data were collected in southeast Ohio as part of the Fire and Fire Surrogate (FFS) study, which applied silvicultural treatments (i.e., thinning and prescribed fires) to reduce competition and manipulate resources. We found species-specific responses to the thinning and fire treatments, with an overall increase in acorn production for chestnut oak in the thin + burn treatment and an increase for black oak in the thin-only treatment compared to the control. Chestnut oak reproduction also had strong positive relationships with warm spring temperatures, and a positive change in summer temperatures compared to the previous year (i.e., summer temperatures that went from cool to warm). For black oak, warm spring temperatures increased acorn production while later starts to spring warming the year before decreased acorn production. These results support the hypotheses that both resources and weather (as a cue and as a limiting factor) are important for masting in oaks. Thus, both factors should be included in predictive models for acorn production under current and future climate conditions.

What drives phenological synchrony? Warm springs advance and desynchronize flowering in oaks

Annually variable and synchronous seed production, or masting, is often correlated with environmental factors and in oaks involves differential pollination success that depends on phenological synchrony in flowering. The synchronization of phenology of flowering was thought to be driven by temperature during flowering (microclimatic hypothesis). We tested an alternative, whereby phenological synchronization is driven by the timing of the onset of flowering (photoperiod-sensitivity hypothesis). This hypothesis assumes that flowering synchrony is driven by interaction between daylength and temperature, and individual variation in sensitivity to daylength as a phenological cue. We used long-term (23–26 years) records of airborne pollen in Quercus robur, Q. petraea, Q. ilex, and Q. humilis. Late pollen seasons were short, as predicted by photoperiod-sensitivity hypothesis. The onset of pollen seasons was delayed as preseason temperatures cooled over the last three decades at our Mediterranean sites, which was paralleled by shortening in pollen seasons, providing additional support for the photoperiod-sensitivity hypothesis. Global warming under the microclimatic hypothesis is predicted to lead to less frequent reproductive failures and thus decreased variability and synchrony of mast seeding. In contrast, warming under the photoperiod-sensitivity hypothesis should advance the onset of and desynchronize flowering, a pattern supported by our data. This pattern suggests that global warming will lead to more frequent vetoes and more stochastic and variable patterns of oak reproduction.

How does oak mast seeding affect the feeding behavior of sympatric red and roe deer?

Oak reproduction is characterized by mast seeding with high inter-annual fluctuations in fruit production. Such resource pulses can greatly affect ecosystem functioning and may cause seed consumers to alter their mobility, demography, or diet. Consequences of mast seeding for seed consumers remain poorly understood as their long timescale makes them difficult to study. We investigated impacts of oak mast seeding on the feeding behavior of two sympatric European deer species: red deer (Cervus elaphus) and roe deer (Capreolus capreolus). We analyzed their rumen content over a 31-year period in tandem with 10 years of data on oak fructification (i.e. 8 years of field monitoring and two modelled years). Acorn production is strongly correlated with consumption by both deer species. In years of high fructification, acorns represent more than 50% and 35% of red and roe deer diet, respectively, confirming assumptions that deer favor acorns when these are available. Red deer eat more acorns than roe deer both between and within years. High acorn production in mast years appears to saturate the capacity of deer to consume acorns. As the proportion of acorns increase in their diet, red deer eat more grasses and less conifer browse. No dietary shift was found for roe deer. By inducing dietary shifts in consumers, oak mast seeding can have cascading effects on ecosystem processes, notably on the damages on conifers caused by red deer and the consequences for forest dynamics.

Midstory Removal Facilitates Growth but Reduces Competitiveness of Oak Reproduction Prior to and after Shelterwood Establishment Cutting

Abstract This study examined the influence of midstory removal applied 9 years prior to a shelterwood establishment cut on survival, growth, and competitive status of black oak (Quercus velutina Lam.), white oak (Quercus alba L.), and an oak competitor, red maple (Acer rubrum L.), immediately before and at 6 years following shelterwood cutting on intermediate productivity sites in the Central Hardwood Forest Region. We also examined height and density distributions of the regenerating cohort to quantify seedling establishment and to elucidate relative oak competitiveness at each time period. Although oak seedlings were taller 9 years after midstory removal than in undisturbed controls, the midstory removal treatment reduced the frequency of free-to-grow oaks (relative to understory competitors) and increased the size of red maple and relative density of large competitors. Height growth of all three species following establishment cutting was increased by prior midstory removal and dependent on seedling competitive position immediately before shelterwood establishment. Additionally, we observed increased seedling densities 6 years following shelterwood establishment cutting and greater white oak seedling establishment when midstory removal preceded the shelterwood treatment.

Management Techniques to Stimulate Oak Reproduction in Midwestern Oak Savanna Landscapes

Oak reproduction is often scarce or lacking in oak savannas under ecological restoration management, despite the fact that large canopy gaps created by the removal of invasive brush allow abundant sunlight to reach the ground surface. I conducted two experiments to investigate the effect of manipulating surface vegetation on the acorn-caching behavior of squirrels (gray squirrel Sciurus carolinensis; fox squirrel S. niger; or southern flying squirrel Glaucomys volans) and blue jays (Cyanocitta cristata). In Experiment 1, I created 10 × 10 m bare-ground patches prior to the time of acorn dispersal in restored white oak (Quercus alba) savanna and in adjacent unrestored brushy oak woods. I then compared oak seedling establishment in these bare patches the following summer to seedling establishment in unaltered tall vegetation. In Experiment 2, I used a combination of late-summer burning, tilling with an agricultural disc, and applying herbicide to create bare-ground patches adjacent to established oak woods, and then compared oak seedling establishment in these areas the following summer to that in burn-only, mow-only, and unaltered vegetation. In both experiments, oak seedling establishment was greater in areas denuded of ground vegetation. This agrees with previous research, which concluded that blue jays have a preference for storing acorns in areas of low to bare surface vegetation.

White Oak (Quercus alba) Response to Thinning and Prescribed Fire in Northcentral Alabama Mixed Pine–Hardwood Forests

AbstractStrong white oak sawtimber markets, partially attributed to the stave and cooperage industries, are encouraging forest managers to re-examine silvicultural practices for white oak (Quercus alba). We examined recruitment and retention of white oak in mixed oak–pine stands on the William B. Bankhead National Forest in northcentral Alabama. Stands were subjected to three thinning levels (residual basal areas of 75 ft2/ac, 50 ft2/ac, and no thinning) and three fire frequencies (dormant season burns of none, one, three fires) in a factorial design. Both thinning treatments reduced overstory white oak tree densities, and fire had no effect on densities. For all reproduction height classes, regardless of thinning treatment, three prescribed burns increased white oak densities; thinned and burned stands had larger white oak seedling sprouts than those thinned with no burn. However, white oak reproduction height was primarily less than 2 ft tall, and seedlings larger than 4 ft tall were reduced. Thinning with one fire resulted in the highest densities of large white oak reproduction (4 ft tall up to 1.5 in. dbh). Red maple reproduction was the dominant competitor in all treatments and is positioned to dominate the reproduction cohort without additional tending treatments.

Oak Forest Canopy Resulting from the Methods of Forest Plantation in the Tellerman Experimental Forestry

Experimental studies in forest steppes show that the oak yields its position to associate species: the ash, Norway maple, field maple, lime, and elm. We conclude that the long-term exploitation of the same areas of oak forests hoping for coppice reforestation of clearcuts decreases its share in a stand canopy and productivity class. In the meanwhile, oak could go extinct from leaf stands of the forest steppe. We provide the taxation features of the stands, including the mass-based formula of stand composition in 2012 and the number-based formula of stand composition across stories, based on sample plots assessments made during 2012–2015. The number- based formula more vividly describes relations between species in a stand. This was significant in understanding the process of forest-canopy formation. We suggest that the only way to preserve the oak gene resources as edificatory species with regional protective functions and which are important for economic activity is the afforestation of oak at clearcuts. We suggest an improved way of oak reproduction, focusing on intensive monitoring of the stand until the canopy closes at around 15 years. This is the age when oak occupies the root and light space and makes associate species unable to compete. Two kinds of thinnings, cutting-backs and accretion cuttings, are excluded to significantly decrease the expenses for growth of an oak stand.

Ten-Year Responses of Underplanted Northern Red Oak to Silvicultural Treatments, Herbivore Exclusion, and Fertilization

Establishing adequate advanced oak reproduction prior to final overstory removal is crucial for regenerating oak forests in the eastern U.S. Many management approaches exist to this end, but benefits associated with any individual technique can depend on the suite of techniques employed and the geographic location. At four mixed-hardwood upland forest sites in central and southern Indiana, we tested factorial combinations of deer fencing, controlled-release fertilization, and various silvicultural techniques (midstory removal, crown thinning, and a shelterwood establishment cut) for promoting the growth and survival of underplanted red oak seedlings. Crown thinning resulted in slow growth and low survival. Midstory removal and the shelterwood establishment cut were nearly equally effective for promoting seedling growth. Seedling survival was strongly influenced by fencing, and differences in survival between silvicultural treatments were minimal when fencing was employed. Fertilization had minimal effects overall, only increasing the probability that unfenced seedlings were in competitive positions relative to surrounding vegetation. We suggest that underplanting oak seedlings can augment natural reproduction, but the practice should be accompanied by a combination of midstory removal and fencing, at a minimum, for adequate growth and survival.

A Comparison of the Survival and Development of the Seedlings of Four Upland Oak Species Grown in Four Different Understory Light Environments

Oak (Quercus spp.) research and management often focus on northern red oak (Quercus rubra) and assume that associated upland oaks have similar growth patterns. To test this premise, we measured the survival and development of four species of acorn-origin oak seedlings growing in four different levels of understory sunlight for 8 years. Northern red oak had better survival than black (Quercus velutina), chestnut (Quercus montana), and white oak (Quercus alba) in 5% sunlight, but none of the species exhibited much growth. In 15 and 40% sunlight, survival was equal among species, but for growth the seedlings formed two groups with chestnut/northern red oak growing more than black/white oak. In 75% sunlight, survival was equal among species, but northern red oak grew faster than the other three species. Assuming that other oaks have growth habits similar to those of northern red oak could lead to a reduction in or the inadvertent loss of an oak species. Management and Policy Implications This study points out key differences in the survival and growth of black, chestnut, northern red, and white oak seedlings at the light levels created by a three-cut shelterwood sequence. Important management recommendations based on those differences include the following: In advance of an acorn crop, decrease dense shade to diffuse or partial shade (15–40% sunlight) by removing the midstory and understory canopies. If premasting shade control is not possible, begin regeneration treatments no later than 1–2 years after black, chestnut, and white oaks mast or no later than 3–5 years after northern red oak produces acorns. Conduct species-specific inventories for oak seedlings rather than grouping them together as oak reproduction. To emphasize chestnut or northern red oak, use the two-cut or three-cut shelterwood sequence because seedlings of these two oak species can grow reasonably well in 15–40% sunlight. To emphasize black or white oak, use a two-cut shelterwood because seedlings of these species need approximately 40% sunlight or more to initiate and sustain vigorous height growth.

Silviculture to Restore Oak Savannas and Woodlands

Variability in historic fire regimes in eastern North America resulted in an array of oak natural communities that were dominant across the region. In the past century, savannas and woodlands have become scarce because of conversion to agriculture or development of forest structure in the absence of fire. Their restoration is a primary goal for public agencies and conservation organizations. Although they can be restored with a long-term regimen of prescribed burning, a combination of fire, timber harvesting, and forest thinning produces the desired structure and composition more efficiently. Prescribed fire is useful for sustaining oak savannas and woodlands, but it must be used judiciously to minimize timber damage and decreases in value. Integrating fire within a modified shelterwood approach promotes competitive oak reproduction and is flexible enough to produce savannas or woodlands. Sustaining these communities requires the replacement of the overstory during periods of no fire.

Effects of nitrogen deposition on reproduction in a masting tree: benefits of higher seed production are trumped by negative biotic interactions

Summary Relatively little is known about the effects of anthropogenic environmental changes on reproductive ecology of trees. Yet, recruitment is a primary determinant of the long‐term dynamics of plant populations in changing environments. We used the Long‐Term Ecological Research site at Harvard Forest to evaluate the effects of chronic (over 25 years) nitrogen fertilization on reproductive ecology of red oaks (Quercus rubra). Oaks growing in fertilized plots produced 4–9 times more acorns than control trees. However, nitrogen deposition simultaneously affected oaks’ biotic interactions. It increased pre‐dispersal seed predation by insects (primarily weevils, Curculio spp.) on fertilized plots, most likely as the result of the disruption of predator satiation. In addition, infestation by weevils was more likely to result in embryo destruction in fertilized than in control acorns. Furthermore, the proportion of acorns dispersed and cached by rodents decreased on fertilized plots. Finally, germination of fertilized acorns was lower than control acorns, even after controlling for the effects of weevils and rodents. Inclusion of the altered biotic interactions reversed the final picture of the effects of long‐term nitrogen fertilization on oak reproduction: the positive effects on acorn quantity were trumped by the nitrogen‐mediated changes in biotic interactions. Synthesis. Our results stress the importance of considering indirect effects and consumer interactions when evaluating the effects of environmental change on plant population dynamics. Long‐term nitrogen fertilization has a strong potential to decrease the recruitment of masting trees. Given the ubiquitous increase in the anthropogenic nitrogen deposition, processes similar to those found in our system might operate in others, resulting in a widespread alteration in trees’ recruitment dynamics.

Repeated Application of Fuel Reduction Treatments in the Southern Appalachian Mountains, USA: Implications for Achieving Management Goals

Fire and resource managers of the southern Appalachian Mountains, USA, have many questions about the use of prescribed fire and mechanical treatments to meet various land management objectives. Three common objectives include restoration to an open woodland, oak regeneration, and fuel reduction. This paper provides information about reaching each of these three management objectives by using prescribed burning (B), mechanical fuel reduction (M), and a combination of both fire and mechanical treatment (MB). The southern Appalachian site of the National Fire and Fire Surrogate study has been burned three times and a mechanical treatment has been conducted twice since 2002. Stand structure was changed by each active treatment but restoration to an open woodland was not achieved by any. The MB treatment units developed the desired overstory structure but heavy sprouting of woody species in the understory prevented the establishment of a diverse herbaceous forest floor. Oak reproduction was increased by all active treatments, largely by sprouting of top-killed stems. The degree of fuel reduction differed by treatment. All treatments reduced the shrub layer, thus reducing the vertical fuel component. The B and MB treatments reduced most fuels and likely reduced the severity of a subsequent wildfire. We conclude that additional burning is required to meet each management objective, and that fires should be conducted more frequently, in different seasons, or in combination with other treatments.

Efficacy and Associated Factors of Even- and Uneven-Aged Management to Promote Oak Regeneration in the Missouri Ozarks

Oak regeneration problems have been noted in the Missouri Ozarks and elsewhere in the eastern United States. Alteration of disturbance regimes, competition from nonoak species, and high overstory stocking are believed to be major barriers that impede oak regeneration. We studied regeneration in upland oak forests that were harvested by both even-aged (clearcutting) and uneven-aged (single-tree selection and group selection) regeneration methods, focusing on differences in oak regeneration among stands that received alternative harvest treatments. Ten years after treatments, the density of oak regeneration generally increased with increased removal of overstory trees, but only the clearcutting treatment resulted in a statistically significant increase in the density of oak seedlings and saplings over that in the no harvest treatment (the control). There were no differences among treatments in the relative proportions of oak seedlings and saplings as a whole or by size classes among the treatments. Successful oak regeneration after removal of overstory trees highly depends on the number and size of advance oak reproduction and is closely related to site conditions such as aspect and bedrock geology. Both site factors and advance oak reproduction must be considered when a regeneration method to promote oak is chosen. Compared with the uneven-aged methods (single-tree selection and group selection), clearcutting favored the red oak species over the white oak species.

Evaluating Initial Responses of Natural and Underplanted Oak Reproduction and a Shade-Tolerant Competitor to Midstory Removal

Evaluating Initial Responses of Natural and Underplanted Oak Reproduction and a Shade-Tolerant Competitor to Midstory Removal