Work in the landscape ecology lab centers around understanding how natural disturbances and forest management shape forest structure and function at multiple scales. Currently, our work emphasizes four major areas including quantifying forest hurricane risk, improving restoration outcomes, ecological management of longleaf pine, and interactions among forest disturbances.
Soil saturation during tree winching experiment
Hurricanes are a common disturbance affecting southeastern forests, and together with frequent fire, they have shaped the characteristic open structure of longleaf pine systems. One of our newest projects involves understanding the factors that determine hurricane risk, and what management techniques can mitigate hurricane damage. Along with collaborators from the University of Georgia and Tall Timbers Research Station, we are developing several studies to test hypotheses about how factors at the scale of individual trees, forest stands, and entire regions can be used to improve understanding and prediction of hurricane impacts.
We are currently conducting tree winching studies, where individual trees are pulled over using a winch, which can provide information on some of the characteristics of stems and soils to predict the forces needed to topple individual trees. We are investigating how differences in tree stability vary with tree size for several southeastern species and are using irrigation studies to measure how much precipitation prior to windstorms affects tree vulnerability. Using data from light detection and ranging studies, we are examining what role tree crown architecture plays in determining wind risk. Future studies will combine wind damage models with our field winching data to help develop silvicultural strategies to protect both natural and planted forests.
Experimental tree winching to study tree wind firmness.
Peterson, C. J., Cannon, J. B. & Godfrey, C. M. First Steps Toward Defining the Wind Disturbance Regime in Central Hardwoods Forests. in Natural Disturbances and Historic Range of Variation: Type, Frequency, Severity, and Post-disturbance Structure in Central Hardwood Forests, USA (eds. Greenberg, C. H. & Collins, B. S.) 89–122. [Link]
Bigelow, S. W., Cannon. J. B., Looney, C. Hurricane effects on climate-adaptive silviculture treatments to longleaf pine woodland in southwestern Georgia, USA. Forestry: An International Journal of Forest Research. cpaa042 (2020). [Link]
Improving Restoration Outcomes
From the fire-starved pine forests of the eastern. U.S. to the wildfire-prone forests of the west, pine forests across the U.S. have a growing need for conservation and restoration. Longleaf pine restoration typically means replanting or re-introducing prescribed fire into otherwise degraded forest systems. In ponderosa pine forests, restoration means reducing tree density and restoring the structural variability that once characterized these stands. Although restoration treatments to pine forests typically occur on the scale of a few hundred acres, restoration affects processes that occur at the scale of a few thousands of acres. Longleaf pine restoration treatments can improve water yields in surrounding watersheds in varying degrees depending on planting density, surrounding landscape use, and topography. Likewise, a ponderosa pine restoration treatment may be more or less effective at preventing soil loss after a fire depending on the fire hazard and soils, but also on the fire hazard and topography of the surrounding landscape. Thus, a puzzle arises: Given limited opportunities for restoration, how can projects be placed so that maximum ecological benefits can be gained?
Our lab is currently working with the Natural Resources Conservation Service Conservation Effectiveness Assessment Project and other partners to develop methods to evaluate the ecological impact of restoration activities on a variety of landscape-scale ecological processes to address this question. We use landscape-scale simulations of restoration coupled with existing ecological models to explore the impacts of restoration placement and prioritization on realizing ecological benefits. Early work in ponderosa pine forests of the Colorado Front Range (in review), is showing that incorporating historic reference conditions into restoration treatments provides benefits including reduction of wildfire hazard and post-fire erosion risk, as well as improving a number of landscape-scale structural metrics related to forest biodiversity. Beginning in 2021, we will begin to evaluate how to improve ecological outcomes in longleaf pine restoration. Ideally, restoration of longleaf pine forests results in stands with lower density, lower leaf area, and an understory dominated by C4 grasses—all properties that reduce losses through evapotranspiration and may result in greater water yield to nearby streams. Our upcoming work will examine how the type and placement of restoration activities affect water yields.
Cannon, J. B., Gannon, B. M., Feinstein, J. A., Padley, E. A. & Metz, L. J. Simulating spatial complexity in dry conifer forest restoration: Implications for conservation prioritization and scenario evaluation. (in review)
Ecological Forestry (Silviculture of Fuels)
Long before human influence, natural disturbances shaped forests in many ways, and many organisms depend on the legacies left from natural disturbances for persistence. For example, lightning-struck trees become a habitat for diverse insect communities. Hurricanes remove trees creating space for growing individuals beneath the canopy. Fire stimulates seed germination and removes competing plants. Ecological forestry (also called natural disturbance-based management) is a forest management approach that uses natural disturbances and ecological processes as a guide to developing silviculture prescriptions and the desired forest structure. Frequent fire is an important driver of many forests and woodlands, especially longleaf pine systems. In contrast to the evenly spaced rows of planted pine stands, forests shaped by natural disturbances and fire have a complex arrangement of individuals with a variety of ages, sizes, and spacings. How different are natural and planted pine stands from each other and how do these changes in structure affect the variety of ecological processes happening within them? And what can we learn about natural systems that may improve how we manage silvicultural stands?
In 2009, the Jones Center at Ichauway began a long-term experiment to answer these questions. Our lab is continuing this experiment by focusing on how changing forest structure can influence leaf litter and fuel beds, the behavior of fire, and ultimately, the effects on forest dynamics. To kick off this series of experiments, we will soon be using 10 years of data on leaf litter collection, stand stem maps, and neighborhood models to better understand how forest density and spatial structure can alter fuels. The lab has also developed a stand-scale forest simulation tool focused on maintaining spatial heterogeneity. This tool has previously been used to understand the effects of variable forest patterns on light environments, and future work from the lab will explore how changing spatial patterns impact the fuel environment.
Mitchell, R. J., Hiers, J. K., O’Brien, J. J., Jack, S. B. & Engstrom, R. T. Silviculture that sustains: The nexus between silviculture, frequent prescribed fire, and conservation of biodiversity in longleaf pine forests of the southeastern United States. In Canadian Journal of Forest Research vol. 36 2724–2736 (2006). [pdf]
All ecosystems are continuously subjected to disturbances, which cause mortality of individuals and free up resources. Forest ecologists have long studied the effects and recovery from single disturbances such as hurricane damage, tree harvesting, and fire. However, many ecosystems are impacted by multiple disturbances occurring in short succession, which may lead to difficulties in predicting any individual effects. For example, it is well known that low-intensity frequent fire is important in the structure and function of longleaf pine systems. As a coastal forest, it is also frequently impacted by the effects of hurricane winds and tropical storms. Together these disturbances may interactively shape the characteristic structure of longleaf pine forests. One obvious example is that wind damage provides fuel for intense fires. But what other ways may wind and fire interact? And how does the combination of wind and fire differ from their individual effects?
Our lab has been involved with a range of studies involving tree winching experiments to experimentally create wind damage and measure the impacts of a subsequent prescribed fire. Overall, we have found that although wind damage can fuel intense fires, that is not the whole story. Wind and fire can interact in other non-intuitive and indirect ways. For example, wind damage can allow for the establishment of fire-promoting invasive species like cogongrass. Interestingly, windthrow can actually reduce the intensity of the fire in some cases by toppling large trees and disrupting the main source of leaf litter critical for maintaining continuous fuel beds. Wind and fire can interactively affect the recovery trajectory of pine forests. Some species like winged sumac (Rhus coppalinum) have fire-stimulated germination and clonal growth and show a growth explosion after both disturbances. Resprouting species like red maple (Acer rubrum) which are severely set back by fire can recover more quickly if they are in wind-disturbed gaps. Some of the lab’s upcoming work involves further exploring the complex mechanisms that drive disturbance interactions.
Cannon, J. B., Henderson, S. K., Bailey, M. H. & Peterson, C. J. Interactions between wind and fire disturbance in forests: Competing amplifying and buffering effects. For. Ecol. Manage. 436, 117–128 (2019). [pdf]
Kim, Geonho, JB Cannon (2019). National analysis of interactions between compounded forest disturbances from tornado and fire over 30 years (1984-2014). 2019 Annual meeting of the US Chapter of the International Association for Landscape Ecology. Fort Collins, CO. [Poster presentation [pdf]
Cannon, J. B., O’Brien, J. J., Loudermilk, E. L. L., Dickinson, M. B. & Peterson, C. J. The influence of experimental wind disturbance on forest fuels and fire characteristics. For. Ecol. Manage. 330, 294–303 (2014). [pdf]