Title: Introduction to Biomes
Author: Susan L. Woodward
Scope: 4 stars
Readability: 4 stars
My personal rating: 5 stars
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Topic of Book
Woodward overviews each of the biomes on our planet. She covers topography climate, vegetation and resident animals.
I believe that biomes are a neglected factor in accounting for differing levels of economic development. This book has nothing to do with human history or progress, but it is the best overview of biomes that I have ever read. This book is the lead book for an excellent series of books on the topic.
Important Points from Book
Biomes are classified by their dominant vegetation.
Biomes are created by the interaction among:
- Prevailing wind
The simplest biome; largely confined to Northern Hemisphere; treeless; dominated by ground-hugging vascular plants; mosses and lichen; caribou/reindeer and muskox are only large grazing mammals; temperatures are above freezing only 6-10 weeks per year; underlain by permafrost which make tree growth very difficult; permafrost thaws only a few inches below the surface each summer giving little anchorage for trees; unimpeded by tall vegetation, strong winds dry out any large plants
Boreal Forest Biome:
Dominated by conifers; restricted to Northern Hemisphere; usually only two or three species dominate vast areas (one of the spruce, fir, pines and deciduous larches); the characteristic mammals are fur-bearers (weasel, lynx and beaver); evergreen trees are well-adapted to short growing seasons, because they do not have to use precious time producing a set of new leaves each year; dark green pigments of needles absorb most wavelengths of sunlight and reradiate heat; winter’s frozen soils mean a long period of drought, so needles have waxy cuticles and sunken stomata; needles decay slowly and produce acidic soil which leach nutrients from soil, taking away its fertility.
Temperate Deciduous Forest Biome:
Six-eight month growing season, on eastern parts of continents; long enough to support regrowing leaves each season; bare branches of early spring let sunlight reach forest floor and allow growth of understory and herb layer; five layers total; Nut- and fruit-bearing plants are common and support a fairly rich mammal fauna; until steel plow, soil was most fertile soil for agriculture.
On west side of continents between latitudes 30 to 40; summer dry season and winter rainy season; short growing season when temperatures are mild and soil is moist; shrubs are dominant vegetation; most plants are evergreen; many plants have aromatic oils to repel herbivores;
Temperate Grassland Biome:
Dominated by perennial grasses and forbs; high seasonal variation of temperature; 10-20 inches rain each year; grasses and forbs grow from at or beneath the surface to protect from cold, fire and grazing; they have deep root systems to trap moisture and nutrient; very low diversity of animals; annual diedown of grasses promote high organic content in soil; with introduction of steel plow, it because most fertile soil for agriculture.
Tropical Rainforest Biome:
Between latitudes 10 North and 10 South; Year-round temperatures are warm and moisture is abundant; the real limiting factor is sunlight; dense foliage casts dark shadow on forest floor; have 3 layers; ground layer has little light or rainfall; to cope, small plants tend to grow not on the floor but high in trees; or they are parasitic on other trees; tree leaves of different species look very similar to each other; animal life is highly diverse; most animals live in trees; with growing season and plants not following a seasonal schedule, fruits are available all year; the heavy rainfall leaches nutrients from the soil; nutrients are held in plants, not in soil; warm temperatures allow rapid decomposition of leaf litter and those nutrients are absorbed by surface roots.
Tropical Seasonal Forest Biome:
Between 10-25 of latitude; have distinct dry season; Usually only have 1 or 2 layers; the longer the dry season, the greater the proportion of deciduous trees and the shorter the height of trees, the smaller the leaves and the greater the likelihood of thorns.
Tropical Savanna Biome:
At least 5 months per year see less than 5 inches rain; Continuous groundcover of grasses with open canopy of shrubs or tree above it; number of trees varies based upon rainfall; grasses are better able to withstand drought than trees; huge variety of ungulates, each with its own food preference, grazing or browsing height, time of day or year to use given area and different dry season refuges; supports many carnivores; termites
Less than 10 inches rain per year; shrubs dominate; have smaller leaves and often spines, thorns or aromatic oils; shallow but extensive root systems capture rainwater; long tap roots enable some plants to tap into groundwater; Perennial forbs are abundant; they store moisture and nutrients in bulbs and rhizomes; Ephemerals lie hidden in seeds within soil until rainfall is high; reptiles are dominant animal; sparse plant cover and tiny leaves produce little humus, so soil is not fertile
Bergman’s Rule: the colder the climate, the larger the body mass of a species.
An easier way to estimate fertility is to examine the color of the soil; If it is dark brown or black, it has lots of humus.
Nitrates are easily leached from soils, so nitrates are often a limiting factor in plant growth.
If you would like to learn more about the role of biomes and geography in human history, read my book From Poverty to Progress.