Although pest and pathogen problems will probably be more serious in tropical and subtropical forest plantations than in temperate and boreal forest plantations, there seem to be good inverse relationships of wood productivity in forest plantations with latitude and with elevation of the forest plantation sites. Thus, to supply civilization’s likely future needs for wood, lower-latitude and lower-elevation forest plantations should supply relatively more wood on a unit-area basis.
Although per-capita use of wood is now highest in temperate and boreal countries such as the United States and the Nordic countries, per-capita differences in wood use should become less as standards of living are improved in the developing countries. Furthermore, some of the largest current populations and most of the highest rates of population growth are in the developing countries. If wood is to be efficiently delivered, it should be grown near the people who will need it. Many of the largest and fastest-growing human populations are in tropical and subtropical developing countries.
Until recently, most planners and the general public assumed or accepted that the present climate is stable, and the future was planned for similar conditions. More recently, planners began to comprehend that increased levels of greenhouse gases will result in general global warming, with uncertain but probably serious consequences for near-sea-level communities, and for most or all ecosystems globally. However, the possibility has been raised that Earth is in a general cooling phase being masked by greenhouse-gas warming. Thus, when planning future strategies, it is now more appropriate to consider that meaningful climate change is likely, without being too certain about either the amount or even direction of average temperature change.
It is reasonably clear that, during the past 2.6 million years, Earth’s climate has been cycling from glacial to interglacial periods and back again. There have been about 10 such cycles during the past million years, with pretty consistent periodicity and large differences in temperature between the warm interglacial and cold glacial periods (Millar and Woolfenden 1999). The past 10 major cycles have generally been about 90,000-to-125,000 years for each glacial period, followed by about 10,000 years of each interglacial period. Each major period contains secondary and lower-order cycles of warmer-than-recent-average or colder-than-recent-average periods, or vice-versa, each lasting from a few years to many centuries.
Warming from the most recent glacial period to the present interglacial (the Holocene) apparently began about 13,000 or perhaps about 11,000 years ago. Thus, it appears that Earth is about due for the next glacial period, and may have already started into it. Furthermore, studies of the past interglacial (the Eemian) indicate that transitions from warm-to-cold or cold-to-warm sometimes occurred over periods of only a few decades, perhaps as short as 10-to-20 years. Such rapid transitions also occurred at both the onset and termination of the Younger Dryas, a 1,300-year glacial event between 13,000 and 11,000 years ago. In theory, such rapid transitions could be triggered by such things as higher atmospheric temperatures melting enough polar ice to flood the North Atlantic with heavy fresh water, resulting in a shift in the Gulf Stream and a consequent rapid decrease in temperature in western Europe and the greater Eurasian continent. The persisting snow on that continent could then reflect sufficient sunlight to drop temperatures throughout the Northern Hemisphere, with cascading rapid changes as snow persists elsewhere.
It is clear that the human species has survived at least two glacial periods. It is not clear that 10 billion people can be sustained on Earth for the 90,000 or more years of the next one. But it is likely that those peoples living at the higher latitudes and elevations will probably move to lower latitudes and elevations. That is another reason for concentrating the forest plantations that will sustain those chilly folks at the lower and probably much more wood-productive latitudes of the subtropics and tropics.
