Disease and fire interact to influence transitions between savanna–forest ecosystems over a multi‐decadal experiment

Pellegrini, Adam F. A.; Hein, Andrew M.; Cavender‐Bares, Jeannine; Montgomery, Rebecca; Staver, A. Carla; Silla, Fernando; Hobbie, Sarah E.

doi:10.1111/ele.13719

Cited by 15 publications

(13 citation statements)

References 47 publications

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“…Rebertus and Burns (1997) found that tree survival in Quercus savannas was inversely related to grass cover. At CCESR, grass abundance is strongly negatively associated with tree canopy cover in the oak‐dominated habitats (Pellegrini et al, 2021; Peterson et al, 2007). In a separate CCESR study, Wragg et al (2018) showed that, compared to forbs, grass‐dominated areas generate higher temperatures, release heat to greater heights and burn more completely.…”

Section: Discussionmentioning

confidence: 99%

“…The site is a mosaic of wetlands, old fields, and patches of oak savannas, woodlands and forests. CCESR experiences a temperate mesic climate (780‐mm mean annual precipitation and 6.72°C mean annual temperature; Pellegrini et al, 2021). Except for that in a few small wetland patches, the soil in the area of CCESR where this study was conducted is of the Sartell series, excessively drained and low in organic matter and total nitrogen (Grigal et al, 1974).…”

Section: Methodsmentioning

confidence: 99%

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Neighbours consistently influence tree growth and survival in a frequently burned open oak landscape

Davis

Condit

2022

Journal of Ecology

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1. 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.2. 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 treeaggregated 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.3. 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. 4. 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.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Neighbours consistently influence tree growth and survival in a frequently burned open oak landscape

Davis

Condit

2022

Journal of Ecology

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“…It is possible, then, that oak wilt might have reduced the neighbor benefits over time. However, in a separate study at CCESR, Pellegrini et al (2021) found that while oak wilt dramatically increased tree mortality in unburned areas, where trees are densely packed and which are dominated by Q. ellipsoidalis , it had little effect in frequently burned sites. Also, since species in the red oak group lack tyloses, they are not as able to effectively compartmentalize scarring injuries as are white oaks, thereby making them considerably more susceptible than white oaks to subsequent fungal infection (Gibbs and French 1980, Juzwik et al 2011, Dey and Schweitzer 2018.…”

Section: Survivalmentioning

confidence: 93%

“…A second possible explanation for the decline in the strength of neighbor facilitation involves the arrival of oak wilt (Bretziella fagacearum ) in east-central Minnesota several decades ago (Gibbs and French 1980), and which is thought to have spread rapidly at CCESR since 2010 (Sapes et al 2021, Pellegrini et al 2021). The fungus is spread primarily through root grafting among neighboring trees and by sap beetles (Nitidulidae) (Kuntz andRiker 1956, Jagemann et al 2018).…”

Section: Survivalmentioning

confidence: 99%

Neighbors consistently influence growth and survival in a frequently burned savanna

Davis

Condit

2021

Preprint

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Successful management of savannas is challenging and requires knowledge of the causes and consequences of the spatial arrangement of the trees. In savannas, trees are often aggregated, and the ability of trees within the clumps to survive fires plays a significant role in determining the savannas landscape dynamics. Whether or not a tree survives a fire is often dependent on the nature of their interactions with neighboring trees, positive or negative. In cases where disturbances are episodic, detecting these interactions is only going to be possible through long-term studies. Data reported here, from twenty-five years of annual tree censusing of a large grid-plot in a frequently burned savanna, showed consistent neighbor facilitated survival, irrespective as to whether the neighbors were conspecifics or heterospecifics. The positive interactions likely involve the reduction of both herbaceous and woody fuel in denser sites, and possibly mycorrhizal sharing among nearby trees.

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“…The presence of oak wilt fungus has been documented in central Minnesota since the 1940’s where it has led to widespread mortality in forests not treated for the disease. At CCESR, the fungal pathogen oak wilt has spread rapidly in the last decade, leading to exponential increases in the number of standing dead trees as a result of recent mortality (Pellegrini et al, 2021). The diversity of tree species and the widespread presence of active oak wilt make CCESR well suited to assess the capacity of airborne spectroscopy to detect oak wilt in red oaks.…”

Section: Methodsmentioning

confidence: 99%

Canopy spectral reflectance detects oak wilt at the landscape scale using phylogenetic discrimination

Sapes

Lapadat

Schweiger

et al. 2021

Preprint

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The oak wilt disease caused by the invasive fungal pathogen Bretziella fagacearum is one of the greatest threats to oak-dominated forests across the Eastern United States. Accurate detection and monitoring over large areas are necessary for management activities to effectively mitigate and prevent the spread of oak wilt. Canopy spectral reflectance contains both phylogenetic and physiological information across the visible near-infrared (VNIR) and short-wave infrared (SWIR) ranges that can be used to identify diseased red oaks. We develop partial least square discriminant analysis (PLS-DA) models using airborne hyperspectral reflectance to detect canopies at early stages of disease development and assess the importance of VNIR, SWIR, phylogeny, and physiology for oak wilt detection. We achieve high accuracy through a three-step phylogenetic process in which we first distinguish oaks from other species (90% accuracy), then red oaks from white oaks (Quercus macrocarpa) (93% accuracy), and, lastly, infected from non-infected trees (80% accuracy). Including SWIR wavelengths increased model accuracy by ca. 20% relative to models based on VIS-NIR wavelengths alone; using a phylogenetic approach also increased model accuracy by ca. 20% over a single-step classification. SWIR wavelengths include spectral information important in differentiating red oaks from other species and in distinguishing diseased red oaks from healthy red oaks. We determined the most important wavelengths to identify oak species, red oaks, and diseased red oaks. We also demonstrated that several multispectral indices associated with physiological decline can detect differences between healthy and diseased trees. The wavelengths in these indices also tended to be among the most important wavelengths for disease detection within PLS-DA models, indicating a convergence of the methods. Indices were most significant for detecting oak wilt during late August, especially those associated with canopy photosynthetic activity and water status. Our study suggests that coupling phylogenetics, physiology, and canopy spectral reflectance provides an interdisciplinary and comprehensive approach that enables detection of forest diseases at large scales even at early disease stages. These results have potential for direct application by forest managers for early detection to initiate actions to mitigate the disease and prevent pathogen spread.

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Disease and fire interact to influence transitions between savanna–forest ecosystems over a multi‐decadal experiment

Cited by 15 publications

References 47 publications

Neighbours consistently influence tree growth and survival in a frequently burned open oak landscape

Neighbours consistently influence tree growth and survival in a frequently burned open oak landscape

Neighbors consistently influence growth and survival in a frequently burned savanna

Canopy spectral reflectance detects oak wilt at the landscape scale using phylogenetic discrimination

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