Tuesday, May 12, 2009

Fun With Numbers

Environmentalists have harangued us all over the past 30+ years with fears of timber harvest run amok, which fact is attended by various natural calamities from the collapse of “native ecosystems, to the barren landscapes left by clearcutting; from the total elimination of “ancient forests” to the elimination of the last remnants of the original forests on the continent. As Rosie McDonald says: “you could Google it.”, so it might be useful to take her advice and use some information easily found on the internet to get a bit of a handle on the devastation.

All good stories should start at the beginning and so shall we. The total land area of the United States is 2.3 billion acres[1]. Of that total, forest land (land that is at least 10% stocked with trees) comprises 749 million acres. So, one third of the United States is forested. Within this forested portion of US land we find that 504 million acres is considered timberland. Timberland is defined as forestland that is capable of producing 20 ft3/acre/yr of wood under natural conditions (that is, each acre can grow the equivalent of 30 2x4’s a year). Therefore, two-thirds of the forested land and 22% of the total national land base is forested to the extent that the average person would consider it to be a forest.

So where does the idea come from that only (fill in the blank, but keep it low) of the original forests in the United States are left?[2] One of my unattributed sources states, “Since 1600, 90% of the virgin forests that once covered much of the lower 48 states have been cleared away.” Another[3] says that only 16% of the original 800 to 850 original acres of “well-formed, commercial forests” were left by 1920. My goodness, surely we must all be looking out our windows at huge expanses of desert and devastation. No, of course we aren’t.

Where do these horrendous numbers come from? Well, it’s important to keep in mind that the first statistically valid measurements of forests of any kind were done in the mid-20th century. Everything prior to that is an estimate of greater or lesser reliability. In fact prior to 1800 the area west of the Mississippi was not part of the U.S. and few people had ever seen it. Even up to the Civil War, very little was known of the area in a statistical sense. Many, if not most, of the current estimates of the extent of the original forests come from this antebellum period. Given that, it is probably reasonable to say that 40% to 50% of the country was covered by forests of some structure that was sufficiently stocked to engender the basic idea of forest in the minds of people who observed them.

Definitions. As a forester, I can accept the specific, concrete descriptions of forestland and timberland, indicated above, and understand that for the purposes of my work, other more finite descriptions may be necessary depending on management objectives and communication needs with my clients (ie, I might describe a particular forest as a 2-cohort stand in a Western White Pine Forest type). Alternatively, the U.N. and many of the environmentalist organizations have the following descriptions:

  • Primary forest: is a forest that has never been logged and has developed following natural disturbances and under natural processes, regardless of its age.
  • Secondary forests: are forests regenerating largely through natural processes after significant human or natural disturbance, and which differ from primary forests in forest composition and/or canopy structure
  • Disturbed forests: Any forest type that has in its interior significant areas of disturbance by people, including clearing, felling for wood extraction, anthropogenic fires, road construction, etc.

Frontier forests: large, ecologically intact, and relatively undisturbed forests that support the natural range of species and forest functions (WRI definition).

These definitions have no useful meaning to me in that they don’t convey useful information in a general discussion about how much timberland there may be on a national basis. They may be useful, as in my own example above, for a discussion in a client-based situation. In a larger context, they are political.

So, with those two caveats in mind, we can say that “it is estimated” that in 1630 there were about 1 billion acres of forestland in the United States and since then about 300 million acres were converted to (mostly) agriculture and (mostly) in the East. By 1920, the clearing of forests for agriculture had largely subsided[4]. What of the 700 million acres that were left after that? Are they “virgin” forests from the 1600’s? Well, no. Forests are born, grow, senesce and die just as people do, and any forest that was mature in 1630 would necessarily be 500+ years old now and, regardless of the hype, most temperate forests just don’t live that long.

The environmentalist community has apparently picked up on the silliness of all of this and have largely dropped that general construction in favor of more specific descriptions. They are now pitching ideas such as “Ninety five to ninety eight percent of forests in the continental United States have been logged at least once since settlement by Europeans”, implying that the very fact of logging destroys a forest forever (See “Primary Forests”, above). O.K. in this case we can say that any forest logged in the 1600’s would be about 300 years old now; in the 1700’s, 200 years old; “between 1850 and 1900”[5] (when the ostensible forest devastation which led to the formation of the National Forests occurred), would be 100 to 150 years old now. In a White Pine dominated 100 year old second-growth forest, whether it originated from logging or natural disturbance, you would typically see trees averaging 20”+ in diameter and over 100 feet tall spaced 16’ to 25’ apart. To those without the ultra-discerning eye of the environmentalist, I would contend that that’s a forest.

Thomas Pynchon, in Gravity’s Rainbow, has a list of “Proverbs for Paranoids” one of which states, “If they can get you asking the wrong questions, they don't have to worry about answers.” The idea that the virgin forests of the 1600’s are mostly gone seems to me to fit that idea. My response has always been, and I contend that yours should be as well, “…of course they are. What’s your point?” There’s no need to argue the point that they’re gone because the real revelation would be that they still existed.

Forests which are large expanses of land stocked with trees, are made up of stands which are management units within these forests which are differentiated by age, composition (types and ages of trees), structure (age, density, condition, etc.), site quality and geography[6]. Stand development is characterized by, among other criteria, by a successional pathway which begins with establishment and progresses through various stages to death, typically by some sort of disturbance (and logging qualifies as a disturbance). In general, we can describe these developmental stages as:[7]

  • Stand Initiation – the initial establishment of a new stand after a disturbance
  • Stem Exclusion – a period of competition of the trees in the stand for available growing space
  • Understory Re-initiation – as the stand ages competition and microsite disturbances open up gaps within which new seedlings become establishe
  • Old Growth – Trees are typically large (compared to other trees within the stand) and vigor has decreased. Insects and disease take their toll and overstory trees die at an increasing rate from these and other disturbance agents

Each of these stages lasts for a variable time period based on myriad of influences and the total sequence in temperate forests is typically from about 120 years to over 600 years, Complicating this is the fact that disturbances such as fire, wind and epidemic insect and disease attack can set the process back to zero or to any of the stages at any time. Also individual trees or groups of trees may escape the general consequences of these processes for an extended time or may be growing on an especially favorable site so that they may grow larger than their contemporaries.

Generally, in the U.S., the stand initiation stage is relatively short (15 to 30 years), stem exclusion is relatively long (50 to 100 years), stand re-initiation variable (30 to 100 years) and old growth moderately to very long (30 to 80 years and, in some cases longer). Therefore, it can be seen that each of these stages will occupy a different percentage of a given forest, that these percentages will change dynamically over time, and the percentages are not necessarily comparable between or even within larger geographical units (in fact, the larger the unit, the less comparable). The large, very old forest stands in the Pacific Coast interior forests cannot be compared to those in the inland Rocky Mountain forests, and White Pine forests in the northern Rocky Mountains are not the same the high subalpine forests of the Central Rockies. Likewise, it should be clear by now that western softwood forests are not comparable to eastern hardwood forests. In the end, forests are immensely complex, dynamic organisms that are not particularly susceptible to much human change on a macro level and only for a relatively short period on a micro level.

To say, then, that “…only 1-4% of the original forests in the United States are left…” or that the idea that “…“Ninety five to ninety eight percent of forests in the continental United States have been logged at least once since settlement by Europeans…” should be identifiable as misleading at best or flat out ridiculous at worst. Absent European influence the forests of the 1600’s would still not be the forests of today and in the pantheon of disturbances that influence forest development over the course of 150+ years, logging has no more effect than any other and would be unrecognizable over that time period.

[1] Smith, Brad W., Patrick D. Miles, John S Vissage, and Scott Pugh, Forest Resources of the United States, 2002, North Central Research Station, USDA-FS, www.ncrs.fs.fed.us
[2] Lester Brown, Michael Renner, Christopher Flavin, Vital Signs 1998, Worldwatch Institute, Washington, D.C.
[3] Williams, Michael, Americans and their Forests, Cambridge University Press, 1989
[4] Smith, Brad W., Patrick D. Miles, John S Vissage, and Scott Pugh, Forest Resources of the United States, 2002, North Central Research Station, USDA-FS, www.ncrs.fs.fed.us
[5] Ibid.
[6] Daniel, Theodore W., John A. Helms, Frederick S. Baker, Principles of Silviculture, McGraw-Hill, 1979
[7] Oliver, Chadwick Dearing, Bruce C. Larson, Forest Stand Dynamics, McGraw-Hill, 1990

No comments:

Post a Comment