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 particlcs tend to scattcr sunlight. Dust is really a product of vegetation covcr, or rather a lack of vegetation cover areas with lots of bare soil between...

Direct C02 Effects And The Ecology Of The Past

There are some fairly good indications that the C02 concentration of the atmosphere has undergone natural variations in the past, before humans began to affect it. The best substantiated changes in C'02 were those that occurred between glacial and interglacial periods during the last 650.000 years, where bubbles trapped in ice caps preserve samples of the ancient atmosphere that can be analyzed (Chapter 7). The evidence of such fluctuations in CO has set ecologists wondering what these might...

The Two Direct Effects Of Co On Plants Photosynthesis And Water Balance

Carbon dioxide may affect plants by changing the climate, but it can have another more subtle and quite separate influence, through its direct effects on plant physiology. Since CO is fundamental to photosynthesis, it makes sense that increasing the amount of CO in the atmosphere will tend to allow plants to photosynthesize faster. This then is one-half of the direct C02 effect on plants. But there is also another less straightforward direct effect of C02 on the water balance of plants. Why...

Humans And The Carbon Store Of Plants

No single species alters the world's habitats as much as humans do. Even in distant prehistory, the arrival of people in a particular part of the world could be heralded by an increase in burning. For example, in Australia there was a sudden jump in fire frequency around 45.000 years ago, right around the time when humans first show up in the archaeological record. From what we know of the Australian Aborigines and other hunter-gatherers when they were first contacted by Europeans, humans...

Wiiat 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 Figure...

Microclimates and vegetation

Climate on the broad scale, across hundreds of kilometers, brings about the broad-scalc distribution of vegetation types (Chapters 1 and 2). However, even looking at the world much more locally, wc see that there arc also very substantial differences in the average climatc. For example, a south-facing slope has a different climate from a north-facing one. The year-round temperature and rainfall conditions under a tree will be different from those just a few meters away in the open. The...

Box 81 Q C3 and CAM plants

Many plants in arid environments decrease the problem of water loss through stomata by chemical tricks that help them take up CO with less water loss. These are known as C4 and CAM plants. Most plants are known as C3 plants. They take CO up into leaf cells which handle the whole photosynthetic reaction in the same cells. The C02 gets fixed into a three-carbon chain (hence the name C3), and then in the same cell the water-splitting part of photosynthesis gives the hydrogen needed to tack on to...

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...

Plants on the move

3.1 VEGETATION CAN MOVE AS THE CLIMATE SHIFTS Bionics arc fundamentally determined by climate, as arc the ranges of most individual plant species. Whenever the global climate changed in the past, so did the form and species composition of vegetation in each part of the world. In the past couple of decades, geologists have become increasingly aware just how much the earth's climate can change, and often on far shorter timescales than would have been thought possible. Each of these changes must...

Seasons As Well As Vegetation Distribution Are Changing

For a long time, naturalists and gardeners have recorded dates of flowering and leafing of the plants around them. These records happen to provide another interesting measure of responses to climate change. In Europe, it is quite evident that the seasonal patterns in vegetation have been shifting in response to warmer temperatures. In Britain, for example, a long tradition of amateur natural history has ensured an abundance of information on the detailed distribution and behavior of plants,...

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...