Forest Pests and Forest Sustainability

Forest pests and diseases are a major challenge for U.S. forest sustainability in the 21st century

Guy Robertson,

The National Report on Sustainable Forests—2010 identified forest disturbance processes, and insect infestations in particular, as the greatest single threat to the current sustainability of America’s forests and perhaps the greatest challenge for forest management in our generation. This is not news to many in the forestry profession nor to many other people who care about forests. The media is full of stories about the latest forest fire, the land it has destroyed and the lives it has disrupted. Less covered but still well understood by those paying attention are the deteriorating forest conditions that are driving major changes in our forests and, in fire prone areas, leading to bigger and more intense fires. Pathogens, drought, fire suppression, and a number of other factors all play their part, but it is the rapid increase in forest pests, diseases and invasive species in recent decades that is the clearest signal that forests as we have known them are under threat.

Forest pests and diseases are challenging traditional notions of sustainability

For much of the history of forestry the central question has been one of “harvest regulation”: when, where and how much timber can we harvest without depleting the forest resources upon which we rely? Those days are gone, at least in the United States. In fact, the total amount of U.S. land covered in forests has remained quite stable for close to a century, and the volume of wood growing in these forests is increasing. Now we face a much more complex problem involving the management of vast forest lands, some dedicated to timber production but most not, and all subject to both natural processes and human influences interacting over time and space. The forest pests and diseases that are the focus of this article are a perfect example of this management challenge. Whatever we do, these forces will substantially shape the forests of the future. Now, the key question for sustainability is not simply about how much wood we can take; it’s about how we can design our actions to limit damage to forest ecosystems and enhance the many different benefits we derive from them.

Data to inform discussions and decisions

A first step in responding to the problem is to develop the data needed to understand it. The Forest Service’s Forest Health Protection Unit [hot link] (FHP) has been working for over 60 years to inventory the various health threats confronting U.S. forests. The information they have developed was crucial to producing the forest health and disturbance indicators [hot link] in the National Report on Sustainable Forests. The key finding that pest-caused tree mortality had increased three-fold since the release of the previous Sustainability Report in 2003 emerged as the brightest red-flag in the 2010 Report. This finding masks considerable year-on-year variability, but the signal indicating substantial increases in insect activity is clear. We will be paying close attention to these statistics as we prepare for the publication of the next edition in 2015.

Figure 1 FHP surveyed acres of tree mortality due to insects and diseases 1998-2011.


Source: USDA Forest Service, Forest Health Protection. 2012. Major Forest Insect and Disease Conditions in the United States: 2011. United States Department of Agriculture Forest Service FS-1000. Washington D.C.

Dynamic and Complex Relationships

When interpreting aggregate national statistics it is important to remember that they represent a combination of many different insect and disease events, each with a unique set of characteristics and impacts, and each posing different levels of threat. The relationship of specific pests to other disturbance events and natural processes is also unique. Bark Beetles in the West, for example, attack drought weakened trees and alter fire behavior and risk. Gypsy Moth populations in the East are held in check by moist springs. While the Southern Pine Beetle is endemic and its numbers are declining, the Emerald Ash Borer was first discovered in America as recently as 2002 and is rapidly spreading through the upper Midwest. The future response of each of these pests (and those that are discovered in the coming years) to changing climate conditions can be predicted in theory, but the actual result on the ground is a substantial unknown.

Challenges for Management

Even without climate change, responding to the different pests, diseases and invasive species in our forests would present a major challenge for forest managers. Climate change increases the uncertainty, and the urgency with which we must develop appropriate responses. The U.S. Forest Service has identified the restoration of forest health and resiliency as a core element in its management of National Forest lands [hot link?], as have states, municipalities and other land managers across the nation. The problem of exactly how we do this, however, remains a central question. The answer to this question will emerge over time, but we can enumerate several “rules of thumb” to help guide us in the process:

Management has to adapt. In the face of change and uncertainty we cannot simply rely on business-as-usual approaches to forestry. Instead, we have to foster adaptive techniques for developing management actions that actually work in the specific settings where they are applied. This means a dedication to experimentation and a willingness to discard failed approaches.

Nature doesn’t always take care of itself. Through our impacts on climate, the introduction of invasive pathogens and species, fires suppression, and various other activities we have essentially altered every acre of forest in the United States. In many places, letting nature run its course is simply not an option. In others, we may rightly choose to let natural processes continue without management interventions, but we must anticipate the consequences and be willing to live with them.

Working with nature and people. Major ecosystem processes occurring over vast landscapes and long time-spans are not something we can tackle head on just with chainsaws and bulldozers, or with a single government initiative. But sustained collaborative efforts involving multiple levels of government, the private sector and individuals can yield positive results over the long run, especially if we work smart, channeling natural processes rather than simply trying to obstruct them.

Look beyond the usual boundaries (and suspects) of forestry. Pests and diseases affect trees everywhere, not just in our timberlands or national forests. Urban residents, farmers, and others benefit from the forests around them, they have a stake in the outcome, and they have energy, ideas and resources to bring to the table.

What’s natural? What’s sustainable?

As human influences and natural processes continue to shape and change the forests around us, the definition of what’s natural or sustainable will remain a moving target. In most cases, it will likely prove impossible to simply freeze forests in their current state, much less return them to how they were 100 or 200 years ago. As a result, questions about exactly which forest characteristics we want to sustain and which values we want our forests to produce will continue to engage forest professionals and interested publics for the foreseeable future. The options, however, will be limited and the outcomes, in many cases, largely beyond our immediate control. Forest pests and diseases will play a big part in determining the future evolution of forest ecosystems in our country and the options available to society to manage this evolution.