1、  climatic classification system

The climatic classification system employed in this course was modified from a system proposed by G. T. Trewartha in his1968 edition of: An Introduction to Climate (McGraw-Hill Book Company, New York) and modified, based on 1961-1990 climatological data. This classification system includes six climatic groups. Five of the groups are humid in that total precipitation exceeds total evaporation (P>E); these groups are distinguished by temperature: tropical (A), subtropical (C), temperate (D), subartic (E) and polar (F). The sixth group is dry (B) in that total precipitation is less than total evaporation (P>E). Viewed as a matrix, the highest temperatures occur close to the equator in the tropical zone, where the moisture spectrum ranges from very wet in the rainy tropics (Ar) to very dry in the hot deserts (BWh). The coldest temperatures are associated with the polar climates located at or near the north and south poles. A tropical (A) climate occurs within a frost-free belt extending from the equator to approximately 20 deg. north and south latitudes. In marine areas, the average temperature for the coolest month is 65 deg. F. The main climatic types within this group are tropical wet (Ar) or "rainy tropics" with a wet season of 10 months or longer, and tropical wet and dry or "monsoon tropics" with two subtypes: one with a winter dry seaon or more than two months (Aw) and one with a summer dry season of more than two months (As). The monsoon tropics occur in the transition zones between the perennially wet rainy tropics and the perennially dry tropical deserts. Subtropical (C) climates extend poleward from the tropics to about 40 deg. F north and south latitudes. They have occasionally freezing temperatures in continental areas, but 8 months or more with average temperatures of 50 deg. F or higher. The main climatic types within this group are subtropical dry summer, subtropical dry winter, and subtropical humid. The subtropical dry summer (Cs) climatic type, also called the summer-dry subtropics or "Mediterranean" climate because of its dominence in coastal areas surrounding the Mediterranean Sea, occurs along the west side of continents. It has mild weather throughout the year, but a rainy winter season. The less common subtropical dry winter (Cw) climatic type is similar, but it has a rainy summer season. Finally, the subtropical humid (Cf) climatic type, of humid subtropics, occurs on the east side of continents; it has no dry season and occasional freezing temperatures. These climatic types include subtypes with hot (a) or cool (b) summers; the 81deg. isotherm for the warmest month was selected by the author to distinguish between subtropical a and b subtypes. Temperate (D) climates extend poleward from subtropical climates. They have average temperatures of 50 deg.F or more for four to seven months of the year. The main climatic types within this group are temperate oceanic (Do) and temperate continental (Dc). These may be further characterized as having a summer dry season (s), a winter dry season (w) or no dry season (f). Additionally, hot (a) and cool (b) subtypes can occur. The72 deg. F isotherm for the warmest month was selected by the author to distinguish between temperate a and b subtypes. Where Do and Dc climates are contiguous, the boundary separating them is the 32 deg.F isotherm for the coolest month; thus, mild winters are characteristic of the oceanic type, and relatively severe winters occur within the continental type. The oceanic type typically occurs on the western side of continents or on islands, while the continental type occurs on the leeward eastern side of continents or inland. Subarctic (E) or boreal climates occur in the northern hemisphere where they form a broad belt between northernmost temperate zones and the Arctic with its polar climate. Subarctic climates have from one to three months with average temperatures above 50 deg.F. It is characterized by short, cool summers and long cold winters. Rainfall throughout the year is relatively low compared to that of the warmer A, C and D climates. Summerless polar (F) climates occur at the highest latitudes where average temperatures for all months are below 50 deg.F. The two types within this group are polar tundra (Ft), in which the warmest month is above 32 deg.F, and polar icecap (Fi), which has temperatures below 32 deg.F for all months. To review the temperature-based climates, in tropical climates, all months have average temperatures above 50 deg.F; they include two types: tropical wet (Ar) with a wet season of 10 months or longer; and tropical wet and dry with two subtypes: one with a winter dry season or more than two months (Aw) and one with a summer dry season of more than two months (As). In subtropical climates, there are at least 8 months in which the average temperature is 50 deg.F or higher; they include three types: subtropical dry summer (Cs) with mild weather throughout the year, but a rainy winter season; subtropical dry winter (Cw) with a rainy summer season.; and subtropical humid (Cf) with no dry season and occasional freezing temperatures. These climatic types include subtypes with hot (a) or cool (b) summers; the 81 deg. isotherm for the warmest month was selected by the author to distinguish between subtropical a and b subtypes. In temperate climates, there are 4 to 7 months in which the average temperature is 50 deg.F or higher; they include two types: temperate oceanic (Do) and temperate continental (Dc). These may be further characterized as having a summer dry season (s), a winter dry season (w) or no dry season (f). Additionally, hot (a) and cool (b) subtypes can occur. Where Do and Dc climates are contiguous, the boundary separating them is the 32 deg.F isotherm for the coolest month; thus, mild winters are characteristic of the oceanic type, and relatively severe winters occur within the continental type. In subarctic climates, there are 1 to 3 months with average temperatures above 50 deg.F. They have short, cool summers and long cold winters. And, finally, in polar climates, average temperatures for all months are below 50 deg.F. The two types are polar tundra (Ft), in which the warmest month is above 32 deg.F, and polar icecap (Fi), which has temperatures below 32 deg.F for all months. Dry (B) climates are those in which evaporation exceeds precipitation. The boundary between humid and dry climates occurs where annual evaporation and annual precipitation are exactly equal. This group includes the arid or desert climatic type (BW, from the German Wuste), and the semiarid or steppe climatic type (BS). The boundary between arid and semiarid climatic types occurs where annual precipitation is half the amount occurring at the humid/semiarid boundary, usually less than 10 inches. The dry climates are further divided into two subtypes: cold (k), which occurs in temperate and subarctic zones, and hot (h), occurring in subtropical and tropical zones. These may be further characterized as having a winter-dry season (w), or a summer-dry season (s). The North American continent encompasses nearly all climatics occurring on the globe. Within the United States, much of the eastern portion is temperate continental in the north and subtropical humid in the south with the southernmost portion of Florida being tropical. Heading west, dry climates begin to occur just east of the Rocky Mountains and through a vast region in the southwest. Along the west coast, climates range from subtropical dry summer in California to temperate oceanic in Oregon and Washington. To the north, much of Canada is subarctic; to the south, Mexico are Central America are predominently dry or tropical. Because at least half of South America is within 20 deg. of the equator, much of it is tropical. Vast stretches of tropical rain forest exist in Brazil. To the south, the occurrence of dry and subtropical climates is similar to those in the United States; however, temperate climates are largely restricted to the Chilean coast. The African and Australian continents in the eastern herisphere do not extend as far south as does South America in the western hemisphere; however, the northernmost reaches of Europe and Asia extend well into the polar zone. The continent of Africa has vast stretches of dry climates occurring north and south of the equator, with tropical climates occurring in the lowlands astride the equator. A subtropical dry summer climate (Cs) occurs within a narrow band in Northern Africa and Southern Europe surrounding the Mediterranean Sea; thus, this is commonly called the Mediterranean climate. This abruptly changes, however, as one moves inland. Because of the absence of major mountain ranges in Northwestern Europe, a temperate-oceanic exists across a much larger area than in Northwestern North America. As one moves further east, however, European climates are similar to those occurring in North America at similar latitudes and altitudes. Southern Asia has climates similar to those occurring in the southeastern portion of North America at similar latitudes. Because of extensive mountain ranges and the vastness of the Eurasian Continent, however, much of the interior of Central and Northern Asia is dry and, at high elevations, cold. Australia is a small continent about the size of the United States. Much of the interior is dry; however, subtropical climates occur along southern coastal areas while tropical climates cover a substantial portion of the northern coastal area. About 1000 miles to the east is New Zealand, a long island with subtropical-humid climate to the north and a temperate-oceanic climate to the south. North of Australia are a series of Pacific islands with tropical climates, including Indonesia, Phillipines, Malaysia and Singapore.

2、  morphology

The most visible components of grass plants are the leaves that occur alternately on opposite sides of each shoot. The lower portion of the leaf, called the leaf sheath, is tightly rolled or folded around the main axis of the shoot, while the upper portion, called the leaf blade, is relatively flat and extends outward at a angle from the sheath. At the junction of the blade and the sheath on the inner side of the leaf is the ligule, a membranous or hairy structure varying in size and shape. Opposite the ligule, on the outer side of the leaf, is a light green or whitish band, called the collar, varying in size and shape. In some grasses, the base of the leaf blade extends into two clawlike appendages called auricles.

At the base of the leaves and hidden within a series of enclosing leaf sheaths is the crown. In the vegetative stage of growth, the crown is a highly compressed stem with a succession of nodes separated by very short internodes. Elongation of the internodes occurs during flowering when a flowering culm emerges and terminates in an inflorescence.

Roots of a grass plant are of two types: seminal and adventitious. The seminal (also called primary) roots develop during seed germination and survive for a short period. The adventitious (also called secondary or nodal) roots arise from nodes along a stem; in mature turfgrass community, these usually constitute the entire root system.

In addition to the crown and flowering culm, other stems of the grass plant include those associated with rhizomes and stolons. Rhizomes grow below the surface of the ground and give rise to new shoots at their terminals and nodes. Likewise stolons produce new shoots and adventitious roots; however, they differ from rhizomes in that they grow along the surface of the ground. In a new turfgrass plant from seed, a rhizomelike structure, called a mesocotyl, may be present. Where some seeds germinate from a position below the surface of the ground, the growing point rises to a position closer to the surface via the mesocotyl. Where elongation of the mesocotyl occurs, the seminal and adventitious root systems may be entirely separated from each other. The morphology of a turfgrass leaf blade varies with species. The upper, or adaxial, surface of the blade may be ridged or smooth; additionally, it may be flat across the blade or contain a prominent midrib. The lower, or abaxial, surface may be dull or glossy. If the adaxial surface has a midrib, the abaxial surface may be keeled (i.e., appearing as the keel of a boat). This is the adaxial leaf surface of tall fescue; it is flat and prominently ridged. Notice how the adaxial leaf surface of perennial ryegrass differs from tall fescue; while prominently ridged, it is not flat due to the presence of a midrib that pulls the leaf in at the center. And the abaxial leaf surface of perennial ryegrass is smooth, prominently keeled and glossy. Annual bluegrass has a smooth, prominently keeled abaxial leaf surface, and a flat adaxial leaf with a midrib. Rough bluegrass is similar to annual bluegrass in the appearance of its leaf blades; however, one important distinction is the glossy nature of the abaxial leaf.  Meyer zoysiagrass is smooth and relatively flat with long, slender hairs on its adaxial leaf surface. The morphology of turfgrass leaf tips also varies with species; some are pointed, others tapered and a few species have boat-shaped tips. This shows the tip of a Kentucky bluegrass leaf. Notice how the two sides of the leaf blade come together to form the boat-shaped tip. This feature is characteristic of all bluegrass species. This is a comparison of the leaf tips of four bluegrass species. From left to right are: Kentucky bluegrass, annual bluegrass, rough bluegrass and Canada bluegrass. While all of these species have boat-shaped tips, notice that this feature is more evident in Kentucky and annual bluegrass; this is due to tapered shape of rough and Canada bluegrass leaves compared with the relatively parallel-sided shape of Kentucky and annual bluegrass. Redtop has a sharply pointed leaf tip. Zoysiagrass is also pointed. This is a comparison of centipedegrass (left) and St. Augustinegrass (right). In addition to being coarser-textured, St. Augustinegrass has a tapered leaf tip while centipedegrass is pointed. An important morphological feature of turfgrasses is the vernation; this is the shape of the leaf as it emerges from its subtending leaf sheaths. Some turfgrasses have a folded vernation while others are rolled. This shows a comparison of Kentucky bluegrass (left) and seashore paspalum (right) leaf sheaths after the blades were severed. One has the folded vernation while the other is rolled. Which is which? This is a picture of Kentucky bluegrass showing the junction of the leaf sheath and blade of the older leaf, and the younger, emerging leaf. Notice that the vernation is folded. This is a picture of creeping bentgrass showing a rolled vernation. Another important morphological feature of turfgrasses is the shape, size and composition of the ligule situated at the junction of the leaf blade and sheath on the adaxial side. Ligules may be a membranous structure or a fringe of hairs. The size varies from minute to long, and the shape may be pointed, curved or truncate. Rough bluegrass has a long, membranous, pointed ligule, as shown in this photograph. Annual bluegrass also has a long, membranous, pointed ligule. Notice that, even if the associated leaf blade is not pulled away from the adjoining leaf, the shape, size and composition of this ligule is easily recognized. In contrast, tall fescue has a minute, membranous, truncate ligule. If, as in this photograph, the associated leaf blade is not pulled away from the adjoining leaf, tall fescue's minute ligule is not visible at all. The ligule associated with hybrid bermudagrass is a fringe of short hairs. The long hairs occurring at the ends of a hybrid bermudagrass ligule are especially evident in this photograph. Another distinguishing morphological feature of turfgrasses is the auricles. These are extensions of the bases of leaf blades and may be long and slender, short and blunt, or absent. This photograph shows the very long, pointed, clawlike auricles of annual ryegrass. In contrast, perennial ryegrass has very short, clawlike auricles. Tall fescue's auricles are short, blunt, and pubescent. Kentucky bluegrass has no auricles and a short, truncate ligule. The final distinguishing morphological feature of turfgrasses is the collar. This is a light-colored band occurring on the abaxial side of the leaf at the junction of the leaf blade and sheath. It can narrow or broad, and continuous or divided. This picture shows the broad, divided collar of redtop. Perennial ryegrass also has a broad, divided collar. In contrast, bermudagrass has a narrow, continuous collar. Finally, St. Augustinegrass has a broad, continuous collar that is also severely constricted.

3、Species Characterization