Chapter 11: Plant Production and Prey Biomass

Aboveground annual plant production (dry weight)

How much aboveground vegetation do the different zonal plant-covers of the northern part of the Northern Hemisphere now produce? How much of this vegetation are the animals able to eat? And how much hoofed mammal biomass do these different zonal plant-zones now support?

We shall find out more about this in, "Grazing in Tundra and Northern Boreal Environments" by R. J. Hudson and F. L. Bunnel in: Grazing Animals, F.H.W. Morley (Editor) (1980):

Climate. "The high albedo [reflection] of snow and water reduces absorption and keeps net radiation income small, about 15 kly (15 kcal/cm²) y on the tundra, 15-20 kly (15-20 kcal/cm²) y at the forest-tundra ecotone (transition zone) and 20-35 kly (20-35 kcal/cm²) y in the boreal forest. ... The tundra experiences only about 125 snow-free days annually, while the boreal forest experiences about 185." Hudson, R. J. and F. L. Bunnel (1980:205)

Pleistocene fauna. "Tundra and boreal biomes supported a much more diverse and abundant fauna in the Pleistocene, during times, when environments may have been less harsh and vegetation more productive. ... Reasons for the sudden impoverishment of this megafauna are disputed." Hudson, R. J. and F. L. Bunnel (1980:206). Emphasized by me.

 

Typical values for standing crop,

net annual primary productivity and sustained forage production

Zone

Standing crop (g/m²)

Net annual primary productivity (g/m² y)

Sustained forage production (g/m² y)

Polar desert

20.0

5.0

1.0

Tundra (proper)

700.0

300.0

20.0

Forest tundra

2000.0

300.0

40.0

Open boreal woodland

7000.0

400.0

50.0

Boreal forest (proper)

20,000.0

600.0

70.0

Boreal mixed wood

35,000.0

1000.0

85.0

After Hudson, R. J. and F. L. Bunnel (1980:209) Table 11.1.

"The standing crop of the forest-zone includes also the wood of the trees, which the animals are not able to eat. Sustained forage production includes non-woody vascular plants, lichens and current growth of browse. Assumes 50% of non-woody vascular plants, 10% of lichens and current annual growth of shrubs can be grazed each year. No correction is made for availability under snow cover." R. J. Hudson and F. L. Bunnel (1980:209)

Secondary productivity of northern grazing systems

Zone

Animal species

Biomass (kg/km² y)

Productivity (kg/km² y)

Polar desert

Muskoxen, Peary caribou

0.0-10

0.5

Tundra

Caribou, muskoxen

18-26

2

Forest tundra

Caribou

50-200

10

Open boreal woodland

Caribou, moose

200-500

100

Boreal forest

Moose, reed deer, reindeer, musk deer

3000

500

Boreal mixed wood (Europe)

Moose, red deer, roe deer, wild boar

4000

700

Boreal mixed wood (North America)

Bison, wapiti, moose

5700

1100

After Hudson, R. J. and F. L. Bunnel (1980:210) Figure 11.2. Changed from kg/ha to kg/km².

"In general, biomass and productivity of large herbivores parallel latitude and gradients of primary productivity. Polar deserts support ungulate biomasses of only 0.1 kg ha (0.0-10 kg/km²) (Kevan, 1974). Tundra ranges, on average, support about 0.18 kg ha (18 kg/km²) (Klein, 1970). Biomass increases in the boreal forest to a maximum of over 50 kg ha under optimal conditions at the boreal forest/prairie transition (Telfer and Scotter, 1975).

"These latter values compare favourably with maximal values of several hundred kg ha observed in the most rich African savannahs. However, the high densities, observed in Elk Island National Park, may be influenced by fences, which prevent animal dispersal and therefore normal regulation of populations. More typical values, represented in European forest, are 4-10 kg ha (Grodzinski, 1975, citing others)."

"In comparing biomass densities of individual species, it is important, to distinguish those, which attain high local densities, but which are not widely distributed, from those, which are more widely dispersed and exploit a wider range of habitats. Bison, muskoxen and wild sheep are examples of the former, while moose and reindeer are examples of the latter. (1980:211).

"In the high arctic, muskoxen often achieve higher local biomass densities, than do caribou, and in the boreal forest, bison usually attain a higher biomass, than the smaller species, with which they are associated. A similar pattern has been observed in grazing systems in southern latitudes.

"In polar deserts, muskoxen are most abundant in wet sedge meadows, whereas Peary caribou are common only in uplands, supporting plant communities, dominated by Dryas, sedges, grasses and lichens." Hudson, R. J. and F. L. Bunnel (1980:211)

 

Location

Number of species

Census Area (km²)

Biomass Density kg/km²

References

Siberia

1

 

81

Vassiljevskaja

Yukon, Canada

6

7160

80

Geist (1978)

N.W.T., Canada

1

5600

36

Parker (1975)

After: Redmann, R.E. in, Paleoecology of Beringia (1982:230) Table 230. Kg ha changed into kg/km². These ungulate biomass values are mostly from the forest tundra, not from the arctic tundra.

Group of saber-tooth cats Smilodon fatalis hunting a bison. Probably only a group of these cats would have been able to catch an adult bison. The species depicted, Bison antiquus is the most commonly found large plant-eater in the Rancho La Brea deposits, California, and was very likely a common prey of Smilodon. From: Maurico Antón and Alan Turner The Big Cats 1997 Plate 12.

The steppe bison has grazed during the time of the woolly mammoth up to the shores of the Arctic Sea, and still further north, on the now submerged continental shelf. Both species of bison, which live now in the northern part of North America, the Plains bison and the Wood bison, are only able to survive the long cold winter, where there are dense patches of forests. In winter, during cold weather and during blizzards, snow-storms, the bison herd moves into these dense forests. When it is very cold, and when the snowstorms blows for a long time, the bison do look within this forest for food. There they are protected from the cold wind and the wind-chill-effect (cold without wind).

The bison is only able to live now in the North, where there are such dense stands of trees. Where there are no patches of forest, the bison is not able to live: Because it is not adapted to life in the open country in winter, like the musk-ox, because its hair-coat is too short. It would lose there too much body heat. In open arctic tundra the bison is not able to live. It would freeze there to death in winter. The bison it not able to live in the arctic tundra, because of still another reason: In winter the most fertile spots are covered with hard drifted snow. The bison, and any other plant-eater, as large as the bison, would starve to death up there. Thus, also the still large mammoth could not have lived up there in an arctic climate, neither on arctic tundra, nor on an arctic “mammoth-steppe”.

From this I do conclude: When the large herds of steppe bison were living in the central and northern part of Alaska and the Yukon, the country was covered with open grassland. And within this grassland, at the moister spots, aspen, poplar, spruce, pine, and birch trees were growing. These trees and shrubs formed then islands of dense forest in a sea of grass. This painting gives us an idea, what Alaska and the Yukon must have looked like, when large herds of mammoth, bison and horses were grazing up there. There was then no permafrost in the ground in central and northern Yukon-Alaska, at least not several meters below the surface.