Chapter 2 Life On Land 1 Chapter 2 Life On Land Introduction Daniel Janzen s goal was to restore tropical rain forest to Guanacaste National Park Costa Rica Janzen s restoration of tropical dry forest was guided by his knowledge of natural history the study of how organisms in a particular area are influenced by factors such as climate soils predators competitors and evolutionary history Janzen recognized the practical value of livestock as seed dispersers and included them in his plan for tropical dry forest restoration Janzen s approach called biocultural restoration seeks to preserve tropical dry forest for its own sake and as a place that provides a host of human benefits ranging from drinking water to intellectual stimulation Terrestrial Biomes Biomes are distinguished primarily by their predominant plants and are associated with particular climates Pay attention to the geographic distributions of the major biomes the climate associated with each their soils their salient biological relationships and the extent of human influences 2 1 Large Scale Patterns of Climatic Variation Uneven heating of the earth s spherical surface by the sun and the tilt of the earth on its axis combine to produce predictable latitudinal and seasonal variation in climate Geographic and seasonal variations in temperature and precipitation are fundamental aspects of terrestrial ecology and natural history Average temperatures are low and more seasonal at middle and high latitudes Temperature generally shows little seasonality near the equator while rainfall may be markedly seasonal Deserts which are concentrated in a narrow band of latitudes around the globe receive little precipitation which generally falls unpredictably in space and time Temperature Atmospheric Circulation and Precipitation Much of earth s climatic variation is caused by uneven heating of its surface by the sun This uneven heating results from the spherical shape of the earth and the angle at which the earth rotates on its axis 23 5 degrees as it orbits the sun This seasonal shift of the latitude at which the sun is directly overhead drives the march of the seasons At high latitudes in both the Northern and Southern Hemispheres seasonal shifts in input of solar energy produce winters with low average temperatures and shorter day lengths and summers with high average temperatures and longer day lengths Heating of the earth s surface and atmosphere drives circulation of the atmosphere and influences patterns of precipitation The sun heats air at the equator causing it to expand and rise This warm moist air cools at it rises Cool air holds less water vapor and condenses to form clouds which produce heavy rainfall associated with tropical environments There are three air circulating cells on either side of the equator Rising air at the equator is associated with a moist tropical climate Dry descending air absorbs moisture forming deserts Subtropical and polar air masses meet creating a moist temperate climate An observer at tropical latitudes observes winds that blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere These are northeast and southeast trades Studying winds within the temperate belt between 30 60 degrees latitude would observe that winds blow mainly from the west These are the westerlies of temperate latitudes At high latitudes our observer would find that the predominant wind direction is from the east These are polar easterlies Prevailing winds do not move in a straight north south direction because of the Coriolis effect In the Northern Hemisphere the Coriolis effect causes an apparent deflection of winds to the right clockwise of their direction of travel and to the left counterclockwise in the Southern Hemisphere Climate diagrams were developed by Heinrich Walter 1985 to explore the relationship between the distribution of terrestrial vegetation and climate Climate diagrams summarize a great deal of useful climatic information including seasonal variation in temperature and precipitation the length and intensity of wet and dry seasons and the portion of the year during which average minimum temperature is above and below 0 Climate Diagrams Chapter 2 Life On Land 2 The months are plotted on the horizontal axis beginning with Jan and ending with Dec in the Northern Hemisphere and beginning with Jul and ending with Jun in the Southern Hemisphere The temperature and precipitation scales are constructed so that 10 C equals 20 mm of precipitation therefore the relative positions of the temperature and precipitation lines reflect water availability Adequate moisture for plant growth exists when the precipitation line lies above the temperature line When the temperature line lies above the precipitation line potential evaporation rate exceeds precipitation Climate diagrams display the mean annual temperature in the upper left hand corner and the mean annual precipitation in the upper right hand corner 2 2 Soil The Foundation of Terrestrial Biomes Soil structure results from the long term interaction of climate organisms topography and parent mineral material O Organic horizon lies on top of the soil profile The most superficial layer of the O horizon is made up of freshly fallen organic matter including whole leaves twigs and other plant parts Fragmentation and decomposition of the organic matter in this horizon are mainly due to the activities of soil organisms including bacteria fungi and animals A horizon contains a mixture of mineral materials such as clay silt and sand and organic material derived from the O horizon The A horizon is generally rich in mineral nutrients Gradually leached of clays iron aluminum silicates and humus which is partially decomposed organic matter B horizon contains the clay humus and other materials that have been transported by water from the A horizon The decomposition of these materials gives the B horizon a distinctive color and banding pattern The roots of many plants usually occupy this horizon C horizon is the deepest layer in our soil pit consisting of weathered parent material which has been worked by the actions of frost water and the deeper penetrating roots of plants The C horizon contains many rock fragments from the weathering of the parent material producing sand silt and clay sized particles Soil structure is in a constant state of flux as a consequence of several influences climate organisms topography parent material and time