Forests

Forests temper a stern climate, and in countries where the climate is milder, less strength is wasted in the battle with nature Uncle Vanya, by Anton Chekov Since the beginning of agriculture, 12,000 years ago, humans have had an uneasy relationship with forests. On one hand, the forests provided timber, and good hunting for game. But they also took up space where crops might be grown, and provided a refuge for malevolent creatures both real and imaginary. As farming spread out from its first...

Under the canopy

In the cooler forest understory, out of the direct sun, overheating is not a problem and leaves can grow bigger than at the top of the canopy. Many of the types of plants that grow down near the floor of the forest have large plate-like leaves 30 cm or more across undivided leaves this size are hardly ever seen up in the forest canopy. On the forest floor, the overwhelming impression is of stillness and quiet. The calls of birds up in the canopy are muffled by the leaves. There may be barely...

From Microclimates To Macroclimates

The same factors which affect microclimates, including the plants themselves, translate into larger effects on the heat balance and moisture balance of the earth's surface. In many respects, the macroclimate (over hundreds of kilometers) is the sum total of all the microclimates across broad areas. For example, the local effect of a boreal forest canopy heating up in the sun because it has shed the snow from its branches can make a great difference to regional climate if it occurs on a broad...

How Plants Make the Global Environment

Assistant Professor in Biological Sciences Seoul National University Gwanak-Ro Seoul SPRINGER-PRAXIS BOOKS IN ENVIRONMENTAL SCIENCES SUBJECT ADVISORY EDITOR John Mason, M.B.E., B.Sc., M.Sc., Ph.D. ISBN 978-3-642-00880-1 Springer Berlin Heidelberg New York Springer is part of Springer-Science + Business Media (springer.com) Library of Congress Control Number 2009933599 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the...

Box 41 James Lovelock and Gaia

James Lovelock (b. 1919) is an independent scientist whose work has inspired a whole new way of thinking about the world. Of his many important contributions to science, probably the greatest has been the message that earth's environment is to a large extent controlled by life itself. Much of this book is about the ways that living organisms have seized control of climate and atmosphere. Although there have always been scientists who worked on the effects of life at the broad scale, in the last...

The Present Increase In C02

Since the late 1700s, the carbon dioxide level in the atmosphere has been increasing (Figure 7.10). The record of air bubbles trapped in polar ice shows the 18th century beginning stages of this rise, which has gently accelerated over time into a steep increase of about 1 a year. The change in CO2 levels is also recorded in the stomatal densities of the leaves of trees preserved in herbaria leaves collected around 1750 have a lower number of stomatal pores per unit number of epidermal cells in...

Utilization of microclimates in agriculture

Many of the aspects of microclimates that affect plant ecology also apply to agriculture. Good farmers plan their planting to avoid unfavorable microclimates avoiding frost pockets for sensitive crops, and allowing for the effect of aspect on temperature or water balance. They can also try to make new microclimates which will favor the plants they are growing. Shelter belts of planted trees or bushes create a drag that slows down the drying or cooling winds that blow across farmland. The effect...

The Ocean

Out in the open ocean, the store of living carbon as plants is tiny less than in a desert on land. The floating cells of phytoplankton have lifetimes of only a few days before they sink and die or are eaten, so biomass cannot build up near the top of the ocean. The material that rains down from the surface into the deep ocean slowly rots and disperses into the water as it sinks, in a journey that may take a month. Often it clumps together as it sinks into what is aptly named marine snow''. What...

Bumps and hollows in the landscape have their own microclimate

As I mentioned above, a group of rocks that provides shelter can allow a pocket of still air to form on an exposed mountain slope. Small bowl-shaped hollows in the landscape, a few meters or even just a few centimeters across, can also act as solar energy collectors (like a parabolic satellite dish which concentrates the signal into the middle), gathering heat into the center to give a warmer microclimate. In tundra the grassy or shrubby vegetation which exists in very cold Arctic and alpine...

Plants As A Control On C02

Since the beginning of photosynthetic life on earth, plants have likely had a big influence on the C02 level in the atmosphere. Green and (especially) blue-green bacteria, the precursors and distant cousins of modern-day green plants, began to spread through the oceans about 3.5 billion years ago. They were a source of oxygen, pouring out this highly reactive corrosive gas, which gives life to us but acts as a poison for many of the more primitive bacteria. At the same time, these...

Humans Altering The Natural Vegetation Shifting Biomes

In some areas the natural vegetation has been almost totally removed such as where there are now ploughed fields or cityscapes. But, in many other places, the effect of human actions has been more subtle. Often the result of anthropogenic influence seems to be a downgrading of the vegetation to something that might be found in a rather drier or colder climate. For example, a meadow in the English countryside can only exist under human influence the forest that once covered the land has been...

Predicting Where Vegetation Types Will Occur

Knowing that biomes are in a general way related to climate, ecologists have wondered if it is possible to predict which biome will occur in a particular place, using some simple set of rules based on climatic conditions. As well as providing a satisfying explanation of the present-day world, these predictive schemes are useful in enabling ecologists to look both forwards and backwards in time. They can be used (1) to predict how biomes will shift in the future in response to human disruption...

Will a high CO2 world favor C3 species over C4 species

Probably the most generally held principle in forecasting raised C02 effects is that plants using the more water-efficient and C02-efficient C4 photosynthetic system will lose out by competition to the normal C3 plants which have more to gain from raised C02. When C4 plants growing alone are fertilized with extra C02, they tend to show little gain from it. There is almost no enhancement of photosynthesis, although they do lose a little less water because they can get the C02 they need quicker...

But Deserts Make Themselves

In addition to all of the more traditional climatology, there is another factor whose importance is only now becoming understood. Deserts partly owe their existence to the fact that they themselves exist. The desert makes the desert, internally modifying its own climate so that less rain falls So the link from climate to vegetation, in Chapter 1, has been turned on its head. A fundamental fact of the earth system, that climate scientists are only now becoming fully aware of, is that vegetation...

Nutrients And Evergreenness

Evergreenness is not only determined by climate soils can have a lot to do with it too. Part of the reason why boreal forests tend to have evergreen conifers may be that the soils underneath them are nutrient-deficient. Each time a plant changes its leaves, some nutrients fail to be re-absorbed before the leaves are dropped, and are lost. If nutrients are in short supply, other plants that keep their leaves will grow faster and overtop this plant, and their roots will also grow fast and grab...

Dust

So far, we have considered albedo, roughness and evaporation of water in the feedbacks between vegetation cover and climate. Another potentially important vegetation-climate feedback comes from dust. The dust in the atmosphere mostly consists of particles of soil, fragments of the sorts of minerals that make up rocks and clays. These tiny particles tend to scatter sunlight. Dust is really a product of vegetation cover, or rather a lack of vegetation cover areas with lots of bare soil between...

Life within rocks endolithic lichens and algae

Even in the coldest places on earth there is life, and favorable microclimates make it possible. For example, in the Antarctic mountains, where the air never gets above freezing, a north-facing rock surface on a sunny day can get much warmer. Although temperatures right on the rock surface can rise above freezing in the direct sunlight, the very dry air and rapid fluctuations in temperature prevent any form of life from growing there. Over just a few minutes, the temperature can rise above...

Response Of Vegetation To The Present Warming Of Climate

There are of course many aspects of plant ecology that seem tightly controlled by temperature the broad-scale distribution of biomes across the continents is one example (Chapter 2). Temperature also determines exactly how high up a mountain trees can grow, and the precise time of year that trees start to leaf out, or when spring flowers appear. It also determines how fast a tree can grow, with variations in climate showing up in the width of the annual rings. Because of the amplifying factors...

Big plants make the microclimates of smaller plants

The plants that live on the forest floor at low light levels, milder temperatures and higher humidity are specialized to a microclimate made for them by the canopy trees that absorb most of the sunlight. Their photosynthetic chemistry is specialized to low light levels and they cannot cope with direct sunlight. These forest floor plants tend to have soft leaves, because leaves underneath the canopy have no need to be tough they are not blown about by the wind, nor are they dehydrated in direct...

Patterns in species richness

Erica Tetralix Range

When the ranges of individual species are superimposed on one another and counted up, striking patterns in the total numbers of species become clear. Species richness, as it is called, tends to be greater at the warmer end of each biome in the mid and high latitudes, and in the wetter parts in the tropics. In general, there is a strong trend towards more species of trees in forests at lower latitudes. This trend is most obvious in eastern Asia where the climate is uniformly moist from north to...

The Green Sahara Of The Past

Evidence from a whole range of sources shows that only a few thousand years ago, the climate of the whole Sahara region was very different from now. Animal bones in the desert sands show that giraffes and elephants once walked where there is now no vegetation and no water. The people who lived in the central Sahara at that time even recorded the animals they saw in rock paintings and engravings, vividly illustrating just how completely this place has changed in a few thousand years. A more...

Modeling Direct C02 Effects

How can we predict how plants around the world will respond to raised C02 levels Plant physiologists and global ecosystem modelers have put a great deal of emphasis on short-term observations of the effects of increased C02 on photosynthesis. They have also tended to make a lot of use of a set of principles together known as the Farquahar Model, put together by Graham Farquahar at the Australian National University. This model reduces the complex process of assimilation of C02 into the plant to...

The importance of sun angle

Just as sun angle makes the difference overall between temperatures at different latitudes of the earth, it makes a significant difference on a local scale too. If a slope is angled towards the sun when the sun is low in the sky, it gets more of a full beam and so the surface temperature of soil or leaves (and the air just above) will be warmer. On a slope that is in the wrong direction relative to the sun, much of the day is spent in shadow or being sunlit at an angle, so it will be colder...

Co2 Fertilization Effects Across Trophic Levels

What sort of effects might increasing C02 have on broader community structure How will the animals and the fungi that feed off living plants respond to changes in the growth and composition of plants that are C02-fertilized Most of the work on how increased C02 can affect such interactions has focused on crop plant systems, although the findings might also apply to more natural communities. Several studies of herbivory on C02-fertilized crops have suggested there might be an increase in insect...

Vegetation Of Cold Climate Trees

2.1 BIOMES THE BROAD VEGETATION TYPES OF THE WORLD On the broadest scale, certain forms of vegetation occur again and again, scattered between different places around the planet. Depending on how finely you might choose to subdivide them, there are between five and twenty fundamental vegetation types in the world. They include, for example, tropical rainforest and savanna in the tropics, and in the high latitudes temperate forest and steppe. Such broad-scale vegetation types are known as...

Amplification Of Change By Vegetation Cover

So far, relatively little modeling has been done on other grassland and desert regions of the world, but the suspicion must be that some of these also show instability in climate that is amplified by vegetation. Apart from the Sahara and Arabia, there are certainly some regions that have a history of large, repeated changes in climate over the past 10,000 years or so. One example is semi-arid northwestern China, which shows great instability in climate on the timescale of millennia. At various...

Deforestation and the Little Ice

Little Ice Age

Between 1000 and 1900 ad, forests in many areas of the northern mid-latitudes retreated under the onslaught of a growing population. The most dramatic episode of deforestation occurred after 1600 in North America, as European settlers arrived Figure 6.8. Global temperature history of the last 2,000 years from several sources of tree ring data, showing the Little Ice Age dip after about 1300 ad. Source CDIAC. 0 00 400 800 00 1000 '400 1R0H 1S00 000 and began clearing land for fields. By 1850,...

Scrub Biomes

In climates that are too dry for forest but wetter than desert, one can either have scrub or grassland. Whether scrub or grassland vegetation actually occurs in a particular place depends on a range of factors including soil type, the time of year when rain occurs, fire frequency and the abundance of grazing mammals. It also depends partly on what species of plants happen to have evolved locally whether they are mostly grasses or mostly bushes. Also, if the soils are thin, infertile and rocky,...

Experiments With Raised C02 And Whole Plants

Earth When Relaese C02

A leaf studied in high C02 concentration over a few minutes is not necessarily at all representative of nature. This statement might seem obvious, but modelers have not always been prepared to acknowledge it Because there are many factors that could potentially change plants' responsiveness to C02, a good way to get a firmer idea of how wild or crop plants will behave is to do experiments on whole plants grown over weeks, months or years. For about 20 years now, plant biologists have been...

The Strength Of The Seasonal Wiggle In Co2

The seasonal wiggle the difference between summer and winter CO2 concentra-tion also shows some variability over time. Seen from the CO2 monitoring stations in some places (e.g., from Mauna Loa in Hawaii and from Barrow in northern Alaska), the strength of this wiggle seems to be increasing. When it was first noticed, this increase in the seasonal oscillation in CO2 was explained in terms of increasing CO2 fertilization (Chapter 8) allowing more green leaves and other seasonal material to build...

The Quaternary The Last 24 Million Years

Even before we humans began our grand experiment with greenhouse gases, we had always lived in a time of dramatically unstable climate. Such variability was unusual even against the standards of the changeable history of the earth. The impression of ever-lasting stability one might get from seeing the world over a few decades is an illusion on the timescale of a several thousand years, the climate in any place in the mid-latitudes can plunge to near-Arctic temperatures, and then after a few...

What Deforestation Does To Climate Within A Region

What will happen if a forest is removed and replaced with much more open vegetation, such as grassland or fields of crops In a general way, there will be two competing effects on local climate. First, albedo will be greater over the more open grassland or cropland with patches of lighter soil between the leaves. This will tend to cool down the surface because solar energy is reflected straight back to space. However, the smoother surface of a grassland or crop cover and the smaller total amount...

Human Effect On Climate The Grasslands Of The Great Plains In The

There may be some places in the world where climate-engineering by humans altering vegetation cover has already occurred, albeit unintentionally. In the 1800s the grasslands of the central USA were transformed at a pace and on a scale unmatched in any other region in history. Settlers poured westwards in their millions, ploughing up the deep prairie soils to plant wheat and corn fields stretching for hundreds of miles. Did this affect the climate The debate about it goes back a long way, to the...

Volatile Organic Compounds And Climate

It is known that tree leaves evaporate many different organic compounds (VOCs) out into the air around them, especially when they are heated under a hot sun. There are several groups of compounds, including monoterpenoids and isoprene, which are thought to play some sort of protective role within the leaves, though no-one is quite sure what (it might, for example, be against insects, fungi or heat). The rate at which these chemicals are emitted depends on the particular forest type, and also...

What Causes Microclimates

Temperature Alpine Rner Silene

Microclimates are caused by local differences in the amount of heat or water received or trapped near the surface. A microclimate may differ from its surroundings by receiving more energy, so it is a little warmer than its surroundings. On the other hand, if it is shaded it may be cooler on average, because it does not get the direct heating of the sun. Its humidity may differ water may have accumulated there making things damper, or there may be less water so that it is drier. Also the wind...

What Will Happen As The Warming Continues

Eventually, global warming may get to the point where the present distribution ranges of species of plants and animals are left far behind the areas that they could potentially live in. For example, the potential range of sugar maple Acer saccharum might shift hundreds of kilometers to the north, way up into Canada towards the Figure 3.13. Sugar maple extends from southeastern Canada to the south-central USA a . By 2090, sugar maple may be able to grow way up to the southern Hudson Bay lighter...

The Future Direct Co2 Effect A Good Or A Bad Thing For The Natural World

If direct C02 fertilization turns out to have significant effects on the natural world, will these effects be good or bad The effects are likely to be complex and multi-faceted, and whether they are, on balance, likely to be good or bad is a subjective issue that depends on one's priorities. Some scientists, and groups supported by the fossil fuel lobby, have argued that C02 fertilization might turn out to be a very good thing for nature in general. By allowing plants to thrive on less water,...

Deciduous Or Evergreen The Adaptive Choices That Plants Make

Deciduous Trees Midlatitudes

In some areas forests keep their leaf cover all year round. In others they drop their leaves part of the year and grow a new set after a few weeks or months. So one finds temperate deciduous forests in the northern temperate zone, but temperate evergreen forests in eastern Australia, southern China, New Zealand and parts of Chile Figure 2.1 . In some parts of the tropics, mainly near the equator, the forests are evergreen. In other places mainly the outer tropics the forests are deciduous. The...

Vegetation Cope With Dry Climate North India

How the monsoon rains move north then south of the equator during the year, following the zone where the sun is directly overhead. even more tightly, so there is no chance of rain falling from it. These bands of descending air, north and south of the Equator, tend to give desert climates with hardly any rainfall. Hence the same mechanism that produced very wet climates along the equator also produces arid climates to the north and south. The ITCZ does not just stay...

Which Current Moves Cold Water To Warm Latitudes

The Ekman Spiral Describes

Intertropical convergence zone, a belt of rising air heated by the equatorial of maximum heating from sun being directly overhead the earth is rotating, and in every 24 hour rotation the equator has a lot farther to travel round than the poles. So, the closer you are to the equator, the faster you are traveling as the earth turns. When wind comes from a slightly higher latitude, it comes from a part of the earth that is rotating more slowly. As it nears the equator, it gets left behind and the...