Understanding the Ecological Roles of Natural Disturbance

 

The key to sustaining forests is successfully renewing all their elements after disturbance, across landscapes and through time. NRS scientists are working to strengthen our understanding of the relationships of certain elements of forest communities in stands and forests of different ages, species compositions, and disturbance history and patterns. Many forest types result from natural disturbances such as fire, storm blowdown, and native tree pests. Generally these are not devastating disturbances; those usually result from non-native pests.

Research Studies

Designing Pest-Resistant Forest Landscapes: The Importance of Spatial Pattern
Defoliating insects damage millions of acres of forested land annually in the United States.  The balance of evidence suggests forest insect outbreaks today are more damaging than ever because of changes in forest composition and structure induced by fire suppression and post-harvest proliferation of tree species intolerant to herbivory.  Our central hypothesis is that landscape connectivity of acceptable host types increases defoliator population connectivity, altering the dynamics and spatial structure of defoliator populations, and thus increasing forest susceptibility to insect pest damage.   

Predicting global change effects on forest biomass and composition in south-central Siberia
Multiple global changes such as timber harvest of previously unexploited areas and climate change will undoubtedly affect the composition and spatial distribution of boreal forests, which will in turn affect the ability of these forests to sequester carbon.  To reliably predict future states of the boreal forest it is necessary to understand the complex interactions among forest regenerative processes (succession), natural disturbances (e.g., fire, wind and insects) and anthropogenic disturbances (e.g., timber harvest). 

Effects of Global Atmospheric Change on Forest Insects
We are studying seasonal and annual changes in forest insect populations at the Aspen FACE experiment site in northern Wisconsin where trees are growing under both elevated CO₂ (+200 ppm above ambient) and ozone (+50% above ambient).

Studying fire mitigation strategies in multi-ownership landscapes: Balancing management of fire-dependent ecosystems and fire risk.
Fire risk mitigation within multi-owner landscapes containing flammable but fire-dependent ecosystems epitomizes the complexities of managing public lands.  The cumulative effects of fire and forest management over the last century have exacerbated fire risk in some regions and threatened fire-dependent systems in many others.  The issue is further complicated by the recent encroachment of human homes into fire prone ecosystems that simultaneously increase fire ignitions and increase demands on fire suppression agencies to protect lives and property.  Consequently, the balance between forest restoration, human rural development, and fire risk remains an issue of major concern to natural resource agencies.

Effects of Insect Defoliation on Regional Carbon Dynamics of Forests
On an annual basis, insects severely defoliate more than 20 million acres of forested land in the conterminous United States, affecting a larger area and incurring higher economic costs than any other disturbance.  However, the long-term costs and ecosystem consequences of insect outbreaks on forest health and productivity are difficult to quantify at the regional scale because of the variety of pests involved, differences in forest types affected, and varying spatial scale and intensity of the impacts.  In particular, the effect of insect activity on carbon cycling and sequestration at the annual and decadal scale is poorly characterized.  

The Working Forest Initiative: Simulating the cumulative effects of the forest management strategies of multiple landowners on landscape pattern and biodiversity
Sustainable forestry involves the extraction of forest products while maintaining ecosystem integrity to conserve biodiversity and to provide other non-commodity benefits to society.  Population viability is a function of the combined actions of multiple landowners, which create a dynamic mosaic of forest types, stand structures and age distributions.  Consequently, it is necessary to understand how the actions of individual land owners interact with the actions of others to determine the spatial pattern of the landscape mosaic, and therefore its ability to maintain biodiversity. 

Modeling silvicultural treatments after natural disturbance
Modeling silviculture after natural disturbance to maintain biodiversity is a popular concept., yet its application remains elusive. We discuss difficulties inherent to this idea, and suggest approaches to facilitate implementation, using longleaf pine (Pinus palustris). In this species, natural disturbances such as lightning, hurricanes, surface fires, and windthrow all lead to similar structures, but at different rates. The outcomes of natural disturbances are inherently different from those of silviculture (for example, harvesting always removes boles) and it is instructive to think of silvicultural disturbances along a gradient in structural outcomes, reflecting degree of disparity with natural disturbance. Interactions of frequency, severity, intensity, seasonality, and spatial pattern define a disturbance regime and these components may not have equal weight in affecting biodiversity and some are easier to emulate with silviculture than are others.

Ice storms
Northern New England forests were heavily damaged by a severe ice storm in January 1988. Many branches were broken off and trees were toppled due to the weight of thick layers of ice. Trees’ response to injury, infection, and environmental change is based on dynamic changes in tree form and function. These changes in trees provide the resilience to disturbance that is the foundation of healthy forests. NRS scientists who study the effects of various disturbances— whether natural, mechanical, or stress induced (from pollutants and drought)—used this opportunity to follow the healing process in these damaged trees.