the total amount of living organic plant matter, of both higher and lower plants, accumulated at a given moment in the aboveground and underground spheres of a terrestrial phytocoenosis, for example, a section of forest or a meadow, or in an aquatic phytocoenosis. The aboveground sphere includes annual organs, such as leaves, needles, offshoots, flowers, and fruits, as well as perennial organs, such as tree trunks and branches, lignified shoots of subshrubs and lianas, and perennial leaves and needles. The underground sphere includes roots, rhizomes, tubers, and bulbs, which may be annual or perennial. A phytomass also includes thalli and rhizoids of lower plants.
The structure of a phytomass depends on certain characteristics of the phytocoenosis, for example, its geographical location, primarily its latitude and biogeographical region. For example, roots constitute 20–25 percent by weight of the phytomass in the taiga zone and 70–80 percent or more in the desert zone. A phytomass can be measured by the weight of its absolute dry organic matter or of its carbon content. It can also be measured by length (especially for roots) or surface area (especially for leaves and needles). In forestry, phytomasses are expressed most frequently in units of volume, for example, m3, while energy units such as the erg are used in specialized research.
In the USSR, Japan, and other countries, the diameter at chest height (DVN) of many trees is correlated with the structural elements of the phytomass; it is possible to elaborate formulas to measure, with a fair amount of accuracy, the quantity of leaves or needles, trunk wood, branches, and roots by means of one of the parameters, for example, the DVN. Aerial methods also show promise in measuring the aboveground phytomass (for example, the quantity of forage harvested from pastures) with enough accuracy for practical use. The size of a phytomass may be used to determine the biological physiognomy of a phytocoenosis, its cycle of matter and energy, and its economic value.
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Pozdniakov, L. K., V. V. Protopopov, and V. M. Gorbatenko. Biologicheskaia produktivnost’ lesov Srednei Sibiri i lakutii. Krasnoiarsk, 1969.
Gringof, I. G., K. G. Antonova, and B. M. Alekseev. “Operativnyi metod ucheta urozhaia rastitel’noi massy ilaka na pastbishchakh Karakumov.” Problemy osvoeniia pustyn’, 1969, no. 5, pp. 43–47.
Bazilevich, N. I., L. E. Rodin, and N. N. Rozov. “Skol’ko vesit zhivoe veshchestvo planety?” Priroda, 1971, no. 1.
Utkin, A. I. “Biologicheskaia produktivnost’ lesov (metody izucheniia i rezul’taty).” In Lesovedenie i lesovodstvo, vol. 1. Moscow, 1975.
L. E. RODIN