Forest Health Fundamentals

"Forest Health" is a popular buzzword in forestry and natural resource circles nationwide (and worldwide). Everybody uses it, sometimes in different ways, and for different purposes. But what does it mean? Why is it popular? Are Florida's forests healthy? Are your forests healthy? Should we care?

Defining forest health has proven to be something akin to shooting at a moving target. Different groups and different folks often mean different things when they use the term. Attempts to formulate a standard "one size fits all" definition have occupied untold hours of bureaucratic, professional and academic meetings, and consensus remains elusive. Why? To begin with, when we talk about forest health, it is necessary to identify the scale of our focus. Are we talking about a pine plantation, a particular forest ownership, a county, a state, a region, etc.? Such scale is not always defined, and is often prioritized differently by different people for varying reasons. Another reason seems to be that one's concept of "healthy" is often inextricably linked to what he or she desires from the forest. What may be undesirable to forest managers emphasizing timber production may well be desirable to others interested primarily in wildlife habitat or biodiversity, and vice versa.

The Society of American Foresters has adopted what I believe to be a very good (if not short) working definition of forest health as "the perceived condition of a forest derived from concerns about such factors as its age, structure, composition, function, vigor, presence of unusual levels of insects or disease, and resilience to disturbance" and it properly recognizes that "perception and interpretation of forest health are influenced by individual and cultural viewpoints, land management objectives, spatial and temporal scales, the relative health of the stands that comprise the forest, and the appearance of the forest at a point in time" (ref., The Dictionary of Forestry edited by J. A. Helms, 1998). Well, without wearing ourselves out trying to define the term to everyone's satisfaction, let's consider a few realities that we all can comprehend.

To begin with, forest health is not the same thing as tree health. A sick and dying tree does not necessarily represent a health problem for the forest. In fact, dead and dying trees are perfectly normal parts of a healthy forest. Dr. Paul Manion of The State University of New York's College of Environmental Science and Forestry has documented that in healthy northeastern forests, for every increase in one-inch diameter class, there are generally 20% fewer trees on a given piece of ground. In other words, as trees in a healthy forest grow and age, "one in five's gotta die" as the trees progressively get larger, inch by inch. Percentages and actual numbers vary with tree species, geographic locations, etc., but the trend remains the same (Figure 1). This should not be particularly surprising. The land (any land) has an inherent and finite "carrying capacity", and as trees get larger and larger, the land supports fewer and fewer trees. This fundamental reality is an important factor as we attempt to understand and deal with forest health issues.

Why is the term "forest health" so popular? Clearly, for a variety of reasons. First of all, it just sounds good! It is also "politically correct," and often used by different groups to support differing political agendas. Who can argue against promoting healthy forests? Anybody interested in promoting unhealthy forests? More importantly, however, the term represents a very reasonable concept, and a goal with which all forest landowners and resource managers can identify, and to which they can (should) aspire.

Are Florida's forests healthy? Yes…. and no. Some are, some aren't. Is (are) your forest(s) healthy? You be the judge. Forests characterized by off-site species or genetically undesirable trees, overstocking (too many trees), a preponderance of old declining/dying trees, excessive mid-story vegetation and/or fire fuels (woody debris, flammable species, etc.) are, by most accounts, unhealthy. Off-site species grow poorly and lack vigor. Some genotypes or varieties of even the "right species" of trees are more susceptible to certain diseases than others. Overstocking results in intra-specific competition for light, nutrients, and water and reduces tree vigor. Some old declining/dying trees are prime habitat for certain pests (e.g., southern pine beetles) that build up populations therein and subsequently spread to neighboring (healthy) trees and forests. Excessive mid-story vegetation can negatively affect habitat for some desirable wildlife species (e.g., red cockaded woodpeckers). Further, mid-story vegetation competes for moisture and nutrients, often increasing the vulnerability of desired overstory trees to certain undesired pests (e.g., southern pine beetles). And, excessive mid-story vegetation and flammable fuels create high hazard fire scenarios. In forest stands with such fuel loads and fuel "ladders", wildfires and prescribed burns are frequently more damaging to trees, sometimes inviting additional damages or even death to trees by secondary pests such as bark beetles and certain root disease fungi.

Should we care? I think so. Not only do healthy forests assure us of sustainable wood production, they are vital for fresh air, wildlife habitat, clean water, enjoyable outdoor recreation and quality of life. Unhealthy forests have been major contributors in recent years to Florida's disastrous wildfires and her unprecedented outbreaks of southern pine beetles. In fact, more often than not, catastrophic wildfires and southern pine beetle outbreaks are simply fevers and sweats, symptoms of unhealthy forests, not the cause of same. To the extent that unhealthy forests and forest conditions remain, and to the extent that we focus on treating symptoms (e.g., killing beetles, putting out fires) while neglecting the underlying cause(s) of the problems (i.e., unhealthy forest conditions), we can expect more damaging wildfires and more pest outbreaks. And, contrary to the thinking of some, a "hands off" approach is not now a suitable option for developing and maintaining healthy forests in Florida. Historic land use and decades of fire exclusion have resulted in an abundance of now aging (Figure 2), overcrowded, early successional tree and plant associations which frequently constitute unhealthy forest situations. These realities, now exacerbated by threats posed by non-native invasive pest plants, increasing acreages of pest/disease-susceptible pines, and Florida's sprawling wildland-urban interface with its associated forest fragmentation and groundwater draw down demand intervention. Intelligent, and active forest resource management is essential. Take home lesson? . . . Florida needs healthy forests, and to get them Florida needs forestry and foresters. This is a message the public needs to hear. We can and we must make it our message.