An Example Of A Biome Or Broadscale Vegetation Type Tropical Rainforest

In each biome, vegetation looks the way that it does because of selection by the environment. Natural selection has killed plants which had the wrong characteristics, and allowed others that had the right features to survive. By this mechanism, plants from many different lineages have evolved to "suit" the climate, often in quite subtle

NATURAL LAND

Figure 2.1. (b) Areas of the most intense human alteration of vegetation. Agriculture ("dry" croplands that depend on rainfall, plus irrigated croplands watered by farmers) is extensive. In the mid-latitudes temperate forests tend to be harvested on a rotational basis so they can often be regarded as semi-natural and are called forest-crop here. Source: Chase et al. (2000).

NATURAL LAND

FOREST CROP

IRRIGATED CROP

ORY CROP

FOREST CROP

IRRIGATED CROP

ORY CROP

Figure 2.1. (b) Areas of the most intense human alteration of vegetation. Agriculture ("dry" croplands that depend on rainfall, plus irrigated croplands watered by farmers) is extensive. In the mid-latitudes temperate forests tend to be harvested on a rotational basis so they can often be regarded as semi-natural and are called forest-crop here. Source: Chase et al. (2000).

ways. One example that can be used to illustrate the link between form and function in vegetation is the tropical rainforest biome, which is scattered across several land-masses close to the equator. The distribution of tropical rainforest closely follows the equatorial climate zone with year-round rain and warm conditions, occurring in the Amazon Basin, in central Africa, central America and South-Hast Asia (Figure 2.1a*).

If you were placed in tropical rainforest anywhere in the world, it would look much the same, even though many of the groups of plants are quite different between the regions. This overall resemblance occurs because similarity in climate has selected for various features of the vegetation; evergreen forest with hard glossy leaves, "buttress" roots on the trees that splay out near the ground, an abundance of climbing vines in the forest, and leaves with elongated ends known as drip tips. Another characteristic of tropical rainforest is the presence of epiphytes—plants which grow perched on the branches of large trees. Close similarity in the vegetation between different lands is true within each of the bionics, and it occurs because plants require the same characteristics to exploit the opportunities and survive the challenges presented by the climate.

For example, in the tropical moist climate, the soil is often soggy with rain, and the clays that form in tropical soils tend to be particularly slick when they are wet.

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Figure 2.2. Buttress roots in a tropical rainforest tree. Source: Author

The intense chemical breakdown of rocks in the warmth and the damp (a process known as chemical weathering; see Chapter 7) tends to give deep soils without any laver of rocks near the surface which the trees could hold onto with their roots. Hence the trees need extra anchorage to avoid falling over in these slippery conditions. The evolutionary response to these unstable soil conditions has been buttress roots-splayed out trunks (Figure 2.2*) that resemble the buttresses on the side of a medieval cathedral. But, instead of propping up the tree, as buttresses on a building would do, these act as points of entry for wide-set roots that anchor the tree more effectively into the ground, much as the ropes on a tent would do.

Long drawn-out tips to the leaves are another very common feature that has a function in the climate of the tropics (Figure 2.3*). Where it rains frequently, the surface of a leaf often accumulates water. Since the rainforest leaves arc long-lived, often lasting three or four years, if leaves stayed wet over time they would accumulate fungi and lichens that would eventually chokc the leaf. The answer to this problem is to drain the water off a leaf each time it rains, and these drip tips (as they arc known) help this by concentrating the weight of the surface water down to this central point until its tension breaks and it drips or trickles away.

Epiphytes (Figure 2.4*) occur in the tropical rainforest because of the high humidity and frequent rainstorms. A plant that grows perched high on a tree branch

Rainforest Leaf Waxy And Drip Tip
Figure 2.3. Drip tips on leaves of a rainforest tree shortly after a thunderstorm, with drops of water still draining from them. Source: Author.
Figure 2.4. An epiphyte growing on a tropical rainforest tree. Source: Author.

has not got much to root into, usually just some rotted leaf litter and moss. So the supply of water around its roots is very precarious. Only in a very moist environment, where it will be re-supplicd with water every couple of days, can such a plant survive.

In other parts of the world outside the equatorial zone, there are different climatic combinations of hot and cold, wet and dry. Similar sets of conditions result in similar types of vegetation. Even though the particular plant species found in the various parts of a biome may be unrelated, they look and behave similarly to one another. This is because natural selection has pressured them in same direction, by selecting plants which had the "right" features, and killing those that did not.

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Emergency Preparedness

Emergency Preparedness

Remember to prepare for everyone in the home. When you are putting together a plan to prepare in the case of an emergency, it is very important to remember to plan for not only yourself and your children, but also for your family pets and any guests who could potentially be with you at the time of the emergency.

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