Study finds that industrial rainforest logging cannot be sustained at any level

By Jeremy Hance / Mongabay

The very ecology of tropical rainforests—their rich biodiversity, unparalleled variety, and hugely complex interconnections between species—makes them particularly susceptible to disturbance. Targeting only a few key tree species in the forest, loggers quickly plunder these species while leaving the rest standing, rapidly changing the overall structure of the ecosystem. In this way, loggers undercut the very ecological system that allows their favored trees to replenish.

“Virtually all currently high-value timber species, are exceptionally long lived and slow growing, occur at low adult density, undergo high rates of seed and seedling mortality, sustain very sparse regeneration at the stand level, and rely on animal diversity for reproduction, all of which point to the conclusion that tropical trees probably need very large continuous areas of ecologically intact forest if they are to maintain viable population sizes,” Zimmerman and Kormos write in their paper.

The particular ecology of these trees has resulted in most logging companies simply entering a primary forest, cutting all high-value species, and then leaving it to colonizers or razing everything for cattle pasture or monoculture plantations (such as pulp and paper, rubber, or palm oil).

“Logging in the tropics follows the same economic model as is evident in most of the world’s ocean fisheries,” Zimmerman and Kormos write. “The most-valuable species are selectively harvested first, and when they are depleted, the next-most-valuable set is taken, until the forests are mined completely of their timber.”

While initial logging can be quite profitable, later harvests bring in less-and-less money: fewer target trees can be found and the regenerative process for such species is compromised overall. Eventually industrial logging kills itself, leaving an economic vacuum that in accessible areas is often filled by conversion to pasture land, oil palm estates, industrial agriculture or timber plantations.

Some scientists have argued that the solution to this problem is to inject sustainable forest management practices into logging companies in the tropics. According to these sustainability proponents, this would ensure harvests over the long-term while protecting overall forest health.But according to their paper, even so-called reduced-impact logging—which is currently the exception rather than the norm in the tropics—considerably changes a forest’s ecology. With many of the forest’s vital seed and crop trees cut, Kormos and Zimmerman point out that “low-impact” logging leaves 20-50 percent of the canopy open, when “even small openings in the canopy (5-10 percent) can have significant impacts on the moisture content in the forest and increase risk of fire.” Debris left on the forest floor quickly dries out, creating perfect fodder for fire. Unlike temperate forests, fires in primary rainforests are almost unheard of, but low-impact logging creates a new set of ecological conditions that leave the forest vulnerable to heat, wind, and, yes, fire.

“We now know that under the present sustainable forestry management guidelines, tropical forests left to regenerate naturally will be composed largely of light-wooded tree species of no to low commercial value, whereas dense-wood, high-value timber species will experience severe population declines,” Kormos and Zimmerman write, noting that current guidelines are far too lax to keep forests intact.

True sustainability is not impossible to achieve, write Zimmerman and Kormos, but guidelines would need to be considerably toughened. Forestry companies would need to cut only every 60 years or more, harvest less than five trees per hectare, leave smaller logging gaps in the canopy, avoid cutting young trees, and use siliviculture techniques to plant new seedlings, among other considerations.

“The key to a forest’s ability to recover most of its original attributes after selective logging is low harvest intensity,” they write.

But, there is a reason why there are no industrial loggers in the tropics putting such stringent rules in place.

“The problem with implementing this kind of protocol is that it would substantially diminish harvestable timber volume while further increasing management and training costs, which would make the timber operation economically unviable,” Zimmerman and Kormos told

It’s no wonder then that logging companies generally cut-and-run, a practice which has resulted in loggers moving from one untouched tropical forest to the next, always looking for the short-term gain. For example, after logging out most of the forests in Borneo, loggers moved into places like Sumatra. Now that Sumartra has been devastated—with many of its forests turned into monoculture plantations—industrial logging went to New Guinea and the Solomon Islands. Primary rainforest is vanishing worldwide.

Logging not a “middle way”

Zimmerman and Kormos’ paper is one among several that debates, sometimes heatedly, the role of logging in protecting or destroying tropical forests. For example, a paper in Conservation Letters recently came to a very different conclusion than Zimmerman and Kormos, describing well-managed logging as a middle way between conservation and outright destruction of tropical forests for agriculture or ranching.

“Selectively logged tropical forests, especially if they are logged gently and with care, retain most of their biodiversity and continue to provide ecosystem services such as carbon sequestration and hydrological functions,” lead author of that study, Francis Putz with the University of Florida told in May.

Putz’s paper did not argue that logging had no impact, but rather that any impact from logging was far preferable than clearing a forest entirely. While Kormos and Zimmerman agree with this point, they see a different remedy.  “There is no question that industrial logging is better than cattle pastures or oil palm or other plantations—but the fact that industrial logging is better than total forest conversion doesn’t mean we should subsidize it,” Zimmerman and Kormos told “Subsidies should be directed towards activities that maximize carbon, biodiversity and social benefits.”

They also say some of the paper’s findings are problematic. “The article includes introduced species in the biodiversity totals, and the biodiversity surveys cited were all done soon after logging and before a second harvest, so there would be an expectation that there would still be biodiversity left in the short term—the question is what happens to biodiversity in the medium term, in particular after a second harvest? In addition, the article states that a logged forest retains 76% of its carbon. But 24% of a forest’s carbon is a very substantial amount of carbon emissions—it could take several decades just to recapture that carbon, whereas we need to be maximizing forest carbon right now.”

Even more importantly, perhaps, is that economic problems remain, dooming many logged forests to total clearance.

“The ‘middle way’ does not make logging sustainable. The Putz et al article clearly acknowledges that the middle way does not achieve sustained timber yields. As a result, it does nothing to change the fundamental dynamic, which is that logging usually precedes conversion to higher value agriculture use. So the ‘middle way’ could actually make things worse—accelerating forest conversion,” Zimmerman and Kormos say.

Leave a Reply

Your email address will not be published. Required fields are marked *