Environmental Engineering Reference
In-Depth Information
reduce the yield or claim virtually the entire productivity of tree stands on scales
ranging from local to semicontinental: such long-standing pests as mountain pine
beetle (
Dendroctonus ponderosae
) and spruce budworm (
Choristoneura fumiferana
)
and Asian longhorned beetle (
Anoplophora glabripennis
), a relative newcomer to
North America, are common examples of invasive invertebrates that inl ict massive,
large-scale, and chronic damages. To these losses must be added those induced by
the periodically devastating locust (
Schistocerca gregaria
) swarms, which can destroy
crop harvests on regional and even national scales.
Vertebrate depredations range from elephants eating and trampling African crops
to deer and monkeys feeding on corn and birds picking off ripe grapes in vineyards
around the world. And highly variable, but in aggregate not insignii cant (often on
the order of 5%), shares of crops are not harvested because of lodging of stalks
(particularly common in grain and oil crops), shattering, and preharvest sprouting
of grain. These incessant probings and sustained or episodic attacks by heterotrophs
and physical damage by wind and rain can be only partially warded off by applying
antibacterial agents, fungicides, and insecticides, by breeding (at least somewhat)
resistant cultivars, or by frightening away the invaders, restricting their access by
nets, or killing them.
Undeniably, even in modern, highly managed agroecosystems, where a great deal
of energy and investment is spent on minimizing any heterotrophic depredations,
as well as in tree plantations, the terms NPP and NEP are far from identical: the
preharvest heterotrophic consumption remains substantial and will be never eradi-
cated. Obviously, the correct denominator should be the net ecosystem production
(NEP), not the NPP—but we would have to know its value at the time of actual
harvests in a particular year because highly variable weather and the presence of
pests will result in annual NEP averages that will easily l uctuate
±
10% even around
a short-term (say, i ve-year) mean.
Further, the harvested phytomass is subject to a second wave of heterotrophic
attacks during its storage: bacteria, fungi, insects, and rodents assert their claim
before the feed or food harvests can be consumed; improperly stored grain in low-
income countries is particularly vulnerable (more than 5% of it may be lost before
consumption), and tubers in the tropics sustain even higher preconsumption losses.
A case can be made that these storage losses should be classed under human appro-
priation, but their obvious benei ciaries are commensal or wild heterotrophs, and
this reality contradicts the claim of an “exclusive possession” of phytomass har-
vested by humans for their own use.
