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Oak regeneration can tolerate open understory conditions (foreground) better than dense understories (background). A mixed red and white oak forest in Minnesota is shown with an invading front of understory buckthorn, which has remained green into November.
Source publication
We reviewed the literature to synthesize what is known about the use of fire to maintain and restore oak forests, woodlands, and savannas of the upper Midwestern United States, with emphasis on Minnesota, Wisconsin, and Michigan. Included are (1) known physical and ecological effects of fire on oaks from acorn through seedling, established sapling,...
Context in source publication
Context 1
... studies provide evidence of growth prior to releases from suppression that are slow, approximately equal to suppressed sugar maple and hemlock on mesic sites-and such periods of suppression prior to release can last 40-90 years-even for species such as red oak, black oak, and white oak ( Rentch et al. 2003). How- ever, this occurs in forests with oak-dominated canopies and open understories (Povak et al. 2008), which have light levels much higher than either mesic maple and hemlock forests or oak forests invaded by buckthorn ( fig. 7). Unfortunately, red maple, ash, and other moderately shade-tolerant tree species can also grow in open oak ...
Similar publications
Herbivores can be major drivers of environmental change, altering plant community structure and changing biodiversity through the amount and species of plants consumed. If natural predators can reduce herbivore numbers and/or alter herbivore foraging behavior, then predators may reduce herbivory on sensitive plants, and a trophic cascade will emerg...
Citations
... Lastly, fire recurrence showed a small negative effect on NDVI recovery rate, up to a maximum frequency of six fires. Higher fire frequency may lead to a diminishing capacity of oaks to resprout (Frelich et al. 2015), and its effect seems to be increasingly negative on sapling density, with Pedunculate oak and Pyrenean oak saplings being especially sensitive (Monteiro-Henriques and Fernandes 2018). Hence, recurrent fires may alter the stand structure and lead to a decrease in oak dominance in favour of other tree species (Burton et al. 2010;Frelich et al. 2015). ...
... Higher fire frequency may lead to a diminishing capacity of oaks to resprout (Frelich et al. 2015), and its effect seems to be increasingly negative on sapling density, with Pedunculate oak and Pyrenean oak saplings being especially sensitive (Monteiro-Henriques and Fernandes 2018). Hence, recurrent fires may alter the stand structure and lead to a decrease in oak dominance in favour of other tree species (Burton et al. 2010;Frelich et al. 2015). For example, repeated burning can transform an uneven-aged oak stand into an even-aged stand (Knapp et al. 2017). ...
Mediterranean Europe is experiencing a rise in severe wildfires, resulting in growing socioeconomic and ecological impacts. Postfire restoration has become a crucial approach to mitigate these impacts and promote ecosystem recovery. However, the ecological effects of such interventions are still not well understood. We employed remote sensing techniques to evaluate the impact of postfire emergency stabilization on the recovery of deciduous oak forests in Portugal. Our study encompassed 3013 sampling points located in areas with and without postfire interventions. We chose the Normalized Difference Vegetation Index (NDVI) as an indicator of oak forest recovery over a four-year period following wildfires that took place in 2016 and 2017. We used a Generalized Additive Mixed Model (GAMM) to assess how NDVI changed over time as a function of postfire restoration, fire characteristics, topography, and postfire drought events. We found that postfire restoration had a significant positive effect on NDVI recovery over time, although this effect was small. Severe drought and fire recurrence up to six fires had a negative effect on the recovery of NDVI. Conversely, severe wetness and either low or high burn severities had a positive effect on recovery. Our study emphasizes the importance of monitoring postfire restoration effects on forest recovery to guide restoration planning and improve forest management in burned areas. This becomes even more relevant under increased wildfire severity predicted for the Mediterranean region interacting with other climate-driven disturbances, which will further negatively affect forest recovery.
... maple) are rare, which may limit their ability to replenish rapidly when fire is excluded [16]. As forest succession continues, coniferous forests are replaced by red oak and maple [17]. ...
Three models for the propagation of forest disease are revisited to include the effect of forest fires and disease spread. We study the global stability of the forest-disease model in the absence of forest fires and the spread of disease. When forest fires caused by grass cover are considered, we show that the equilibrium points are locally asymptotically stable. If both forest fires and the spread of disease exist in the second model, then Turing instability can occur. In this case, the system exhibits complex dynamic behavior. To determine the effect of fire on the forest disease model, we obtain the optimal control expression of the key parameter fire factor, and carry out sensitivity analysis. Finally, we use forest biomass data of some provinces in China from 2002 to 2018 for numerical simulation, and the results are in agreement with the theoretical analysis.
... Sites with broader scale co-occurrence had greater climatic water availability and sandy soils, which were associated with northern xeric species, especially pines. In Wisconsin, relatively frequent fires were features of both pine and oak systems, though fire regimes varied depending on species and system type (i.e., barrens, savanna, woodland;Curtis 1959;Nowacki and Abrams 2008;Frelich et al. 2015;Meunier et al. 2019). At the landscape scale, vegetation-fire feedbacks can maintain fire regimes that support the dominant vegetation and exclude competitors (Beckage et al. 2009;Pausas and Dantas 2017). ...
... This suggests that the processes creating patchy structures in mesic forests differed in the northern and southern edges of the Tension Zone. In southern Wisconsin, fire was the dominant driver (Curtis 1959;Frelich et al. 2015), causing soil properties to be a less-important determinant of vegetation cover type (Liu and Mladenoff 2013). In the southern part of the Tension Zone, where southern oaks were prevalent, it is likely that fire was a driver that overrode other environmental factors, leading to co-occurrence at broader scales regardless of whether oaks were meeting pine forest or mesic forest. ...
Context
Ecological structure in ecotones, defined by how species from adjacent systems co-occur, affects ecosystem functions and climate change responses. Ecotone structure can vary spatially, yet variability in broader-scale ecotones is poorly understood. In Wisconsin (USA) the Tension Zone is an ecoregional ecotone, separating northern and southern ecosystems.
Objectives
Characterize ecotone structure in the Tension Zone, examine how structure varied spatially, and identify how environmental drivers affected structure.
Methods
Using historical (1800s) tree occurrence data, we examined co-occurrence of northern and southern species at multiple scales (1.0 km to 7.5 km) at different locations in the Tension Zone, identifying the finest scale at which co-occurrence was detected. We assessed relationships between co-occurrence and environmental variables.
Results
Co-occurrence emerged at different scales, related to interacting climate and soil variables and location within the ecotone. Northern and southern trees co-occurred at broader scales near ecotone center and at locations with higher climatic water availability and sandier soils; they co-occurred at finer scales in locations with higher climatic water availability and richer soils. Sites with xeric tree species were associated with broader-scale co-occurrence.
Conclusions
We detected spatially variable structure within the Tension Zone, resulting from multi-scale processes among underlying environmental drivers. Finer-scale co-occurrence may have resulted from competition in high-resource environments, while broader scale co-occurrence may have been driven by fire and associated feedbacks. Characterizing structure in an ecoregional ecotone adds to a growing body of evidence that finer-scale factors play a role in defining the characteristics, functions, and responses of broader-scale ecotones.
... We think the difference in fire susceptibility between the two oak species may account for this difference. Q. macrocarpa is considered among the most fire-resistant oaks, particularly as compared to Q. ellipsoidallis (Frelich et al., 2015;Lorimer, 1985), and is illustrated by the much higher survival rate of Q. macrocarpa during this study. This means that Q. ellipsoidalis is more likely to serve as fuel, threatening the survival of its neighbours. ...
Successful management of fire‐prone woody ecosystems is challenging and requires knowledge of the spatial arrangement of the trees and how the tree distribution patterns influence the nature and consequences of subsequent fires.
In open tree landscapes, trees are often aggregated, and the ability of trees within the clumps to survive fires plays a significant role in determining subsequent landscape dynamics. If positive interactions exist among neighbouring trees, this will help maintain the patterns of clumped trees. However, the tree‐aggregated landscape will continue to exist only if the positive neighbour interactions persist consistently over time. In cases where disturbances are episodic, detecting these interactions is only possible through long‐term studies.
Data reported here are from a 25‐year study involving the annual tree censusing of a large grid‐plot in a frequently burned open oak landscape dominated by Quercus macrocarpa and Quercus ellipsoidallis. The results showed that while having neighbours reduced tree growth, neighbours consistently facilitated survival, irrespective as to whether the neighbours were conspecifics or heterospecifics. Trees of all sizes in close proximity to neighbours were considerably more likely to survive fire throughout the study. This neighbour facilitation is likely the result of a reduction of both herbaceous and woody fuel within clumps.
Synthesis. This is the first study to document consistent neighbour facilitation among trees experiencing repeated stressors over an extended time period. Our findings support the literature documenting positive neighbour effects among plants in stressful and highly disturbed environments, in accordance with the stress‐gradient hypothesis. While aggregated tree regeneration is typically viewed as the primary cause for the development of tree clumps in fire‐prone ecosystems, our study showed that aggregated tree survival, by itself, can also be an important driver of post‐fire tree clumping. Our results support the growing literature emphasizing the importance of landscape heterogeneity as a driver of resilience in fire‐prone tree ecosystems, and the value of maintaining or creating this heterogeneity during forest management.
... maple) and are almost completely absent in the plots that have remained savanna, likely limiting their ability to rapidly recruit when fire was excluded (Peterson & Reich 2001). As forest succession continues, pin and bur oak forests are replaced by red oaks and maples (Frelich et al. 2015), but this has not yet occurred in CCSFE. While oak forests in eastern Minnesota can still burn (but fire is heavily suppressed), they would do so less frequently even under a natural fire regime than the savanna (fire return intervals of 15-50 vs. 3-6 years respectively). ...
Global change is shifting disturbance regimes that may rapidly change ecosystems, sometimes causing ecosystems to shift between states. Interactions between disturbances such as fire and disease could have especially severe effects, but experimental tests of multi-decadal changes in disturbance regimes are rare. Here, we surveyed vegetation for 35 years in a 54-year fire frequency experiment in a temperate oak savanna-forest ecotone that experienced a recent outbreak of oak wilt. Different fire regimes determined whether plots were savanna or forest by regulating tree abundance (r 2 = 0.70), but disease rapidly reversed the effect of fire exclusion, increasing mortality by 765% in unburned forests, but causing relatively minor changes in frequently burned savannas. Model simulations demonstrated that disease caused unburned forests to transition towards a unique woodland that was prone to transition to savanna if fire was reintroduced. Consequently, disease-fire interactions could shift ecosystem resilience and biome boundaries as pathogen distributions change.
... While prescribed fire is used to maintain open ecosystems, particularly prairie and to a lesser extent savanna and barrens (Vogl, 1971;Melvin, 2018), direct knowledge of historical fire regimes and subsequent changes are more https://doi.org/10.1016/j.foreco.2020.118246 Received 10 March 2020; Received in revised form 13 May 2020; Accepted 14 May 2020 limited in northern forests despite the historic prevalence of fire-dependent pines and oaks (Fahey, 2014;Frelich et al., 2015). ...
... Prior to European settlement, oak savannas were common across the upper Midwest (Curtis, 1959), but urban expansion and land conversion to agriculture substantially decreased coverage of savannas (Anderson et al., 1999;Pogue and Schnell, 2001;Brewer and Vankat, 2004;Rhemtulla et al., 2007) to < 1% of pre-settlement area (Bray, 1955(Bray, , 1960Nuzzo, 1986). Frequent disturbance (often by fire) is required to maintain savanna structure and composition (Peterson and Reich, 2001;Frelich et al., 2015) and the exclusion of fire from systems in recent decades has triggered canopy closure and mesophication (Nowacki and Abrams, 2008). Remnant savanna sites are often small, isolated, and lack frequent, low-intensity fire or grazing to maintain their open structure resulting in canopy closure and large changes to species composition (Ladwig et al., 2018a;Nowacki and Abrams, 2008). ...
Ecological restoration offers an effective way to promote recovery of natural communities and is particularly important for ecosystems that have experienced extensive habitat loss, such as oak savannas in the Midwestern USA. Seeds are commonly added to restoration sites to introduce desired species, but the identity and composition of which species are included in seed mixes varies greatly and may be influenced more by seed availability and cost rather than historic prevalence or ecological function. Therefore, a key question is how the composition and function of seeded species differs from what was historically present. Here, we compare the taxonomy, phylogeny, and functional traits of savanna seed mixes that are commercially available in the Midwest with historical vegetation surveys of savannas in southern Wisconsin. Species composition differs greatly between historical savannas and seed mixes; most species are unique to either seed mixes or historical savannas rather than shared between them. The functional overlap of species (measured via functional traits: seed mass, SLA, and plant height), however, is remarkably similar between seed mixes and historical savannas. The phylogenetic representation between the two groups is also similar, however seed mixes tend to not include certain plant families and species are more clustered across the phylogeny in seed mixes. Together, this suggests that restoration efforts using commercially available seed mixes may only partially recover the species composition of historical oak savannas, but that the functional capacity of restored sites is similar to the past. Determining how restoration seeding efforts compare to historical reference conditions is an important aspect of assessing whether restoration goals related to species composition and ecosystem function are being achieved and may identify gaps that can be filled when designing seed mixes.
... Continued removal of R. maximum would also allow for the potential regeneration of Quercus species because favorable mast years occur at multi-year intervals (Greenberg and Parresol, 2002;Greenberg et al., 2014). However, if repeated fire is prescribed, its timing should be coordinated with seed mast years and tree seed germination so that fire does not eliminated new recruits (Arthur et al., 2012(Arthur et al., , 2015Frelich et al., 2015). ...
Forest ecosystems dominated by Tsuga canadensis are undergoing fundamental changes in function and composition from infestations by hemlock woolly adelgid (Adelges tsugae). We proposed that the first step to restoring southern Appalachian riparian forests following T. canadensis mortality would be eliminating the evergreen shrub, Rhododendron maximum. We hypothesized that removing R. maximum would increase light transmittance, soil moisture and temperature; and subsequently, enhance herbaceous-layer diversity and promote tree seedling recruitment and survival. We tested these hypotheses at two locations, (CWT, Coweeta Hydrologic Laboratory; WOC, White Oak Creek) in the Nantahala Mountain Range of western North Carolina, both with heavy T. canadensis mortality and a dense R. maximum subcanopy. The treatments were designed to remove only soil O-horizon (FF), remove only R. maximum (CR), remove R. maximum and soil O-horizon (CFFR), and untreated, reference (REF). We installed permanent plots across treatments and locations and measured light transmittance (Qi/Qo), soil water content (θ), herbaceous-layer cover and diversity (Shannon's index (H′cover) and species richness), and tree seedling recruitment. As expected, cutting the R. maximum subcanopy (CR and CFFR) immediately increased Qi/Qo in the spring months across locations, and it was sustained through the first growing season. θ was generally high across plots, averaging 26% during the growing season, and didn't vary over time. By the second growing season (2017) after treatments, herbaceous-layer cover and diversity increased on CR and CFFR. Herbaceous-layer cover was significantly related to Qi/Qo (r² = 0.22, p < 0.001) and θ (r² = 0.13, p = 0.009), while diversity was only related to Qi/Qo (H′cover, r² = 0.14, p < 0.001; species richness, r² = 0.21, p < 0.001). Tree seedling density was related to Qi/Qo (r² = 0.10, p = 0.001) and θ (r² = 0.26, p < 0.001). Tree seedling density was low before treatment (1.4 ± 0.3 seedlings m⁻²) and increased by 10-fold in CR and CFFR two growing seasons after treatment. In CR, species with the highest density ranked Betula spp. > Acer rubrum > Quercus coccinea > Liriodendron tulipifera > Q. rubra. In CFFR, tree seedling recruitment ranked Betula spp. > A. rubrum > L. tulipifera. These vegetation responses have important implications for potential recovery of riparian forests following T. canadensis mortality.
... Under regulated anthropogenic application and in conjunction with edaphic and topo- graphic conditions, low severity surface fire was the primary stabilizing mechanism for most open forest systems (Bray 1906, Heyward 1939, Garren 1943, Beilmann and Brenner 1951, Forman 1979, Abrams 1992, Earley 2004, Frelich et al. 2015, Veldman et al. 2015). ...
We present a reconceptualization of forests in eastern North America by differentiating the ecological characteristics of open oak (Quercus) and pine (Pinus) forests from closed successional and old‐growth forests. Despite historical abundance of savannas and woodlands, the fundamental ecology of open forest ecosystems remains ill‐defined when compared to either closed forests or grasslands. Open forests were characterized by simple internal stand structure consisting of a single stratum of variably spaced, often very old overstory trees and limited midstory, maintained by understory disturbance that controlled tree regeneration and allowed instead a taxonomically rich herbaceous groundlayer. In contrast, closed forests have dense woody growth throughout the vertical profile, limiting herbaceous plants. To provide further clarity about these ecosystems, we developed a canopy closure spectrum model dependent on the interactions between prevailing disturbance regimes of the historical and current eras, which affect either the tree understory (regeneration) or overstory, and tree traits of fire and shade tolerance. Recognition of different stand structures, disturbance regimes, and their interrelationships should expand understanding of open forests and limit ecological misunderstandings and restoration misapplications, thereby improving management of these once historically extensive ecosystems.
... In the absence of structure and composition indicative of resilience (i.e., overstory species diversity or advance reproduction), passively waiting for what may be an inevitable spruce beetle outbreak represents an important lost opportunity. There are extensive examples of the cost and uncertainty of restoration in diverse systems including oak-savannas across the Great Plains [38], and floodplain forests along the Mississippi River [39]. Having to start "from scratch", post-outbreak, (i.e., reacting to the outbreak) presents a restoration challenge that squanders the considerable opportunity that extant forests represent for the management of desired future structure and composition. ...
Contemporary forest planning has tasked managers with developing goals associated with resistance and resilience. In practice, silviculturists use forest structure and tree species composition to characterize goals and desired future conditions, write prescriptions, and monitor outcomes associated with resistance and resilience. Although rarely discussed in the exploding literature relating to forest resistance and resilience, silvicultural regeneration methods are important and underutilized tools to meet these goals. We propose alternative silvicultural systems for building resistance and resilience to two common large-scale bark beetle disturbance agents in the Intermountain West, United States: mountain pine beetle (Dendroctonus ponderosae Hopkins) and spruce beetle (Dendroctonus rufipennis Kirby). Shelterwood, and shelterwood-with-reserves, silvicultural systems provide the desirable facilitative characteristics of a mature overstory on maintaining advance reproduction and the establishment of new cohorts of desirable tree species. These also allow the timely regeneration of large treatment areas necessary to rapidly promote desired future conditions in the face of inevitable disturbance. When implemented proactively, regeneration treatments allow silviculturists to take advantage of currently existing vegetation for the creation of age class and tree species diversity. In general, these examples illustrate the need for proactive planning for regeneration in response to any disturbance where desired future conditions include particular species. Furthermore, we argue that timely silvicultural interventions that focus on regenerating trees may be a key factor in achieving goals relating to resilience to specific disturbance types. Waiting until after the disturbance has occurred could result in the lost opportunity to establish desired species composition or stand structure—and may well result in a considerable restoration challenge.
