The place of green leaves in the diet

Green leaves are not equally appreciated in all parts of the tropics and thus play a varied role in the diets of distinct peoples. East and West Africans make frequent use of green vegetables. In parts of Latin America, green leaves are considered food for animals, although local or weedy species may be added to the cooking pot in times of food shortage or in remote regions. In the temperate zone, lettuce is an essential item in salads and is eaten uncooked. Crucifers of many kinds are also well known and used worldwide. The place of green vegetables in the diet is largely a matter of culture, training, and habit.

The role of green leaves in the diet may also be considered by noting how the green food is used. Probably the most common use in all parts of the world is as a boiled vegetable. By boiling, potential pathogens are thus eliminated, sometimes poisonous or irritating substances are neutralized, and spoilage is brought to a halt. Nevertheless, this technique reduces the leaf to a limp and soggy mass, which may not always be appetizing. Some nutrients may be destroyed by heating while others may be leached out. As a general rule, cooking should be as brief as possible. Some leaves may contain mucilaginous substances, which are often, but not always, appreciated. Frying leaves in oil or enveloped in batter preserves some of their unique characteristics and maintains their texture.

Introduction

What is dendrology? The term dendrology is derived from two Greek words meaning trees and discourse or study, or the study of trees. A review of the history of usage of the term has been made by William A. Dayton (Dayton 1945). Perhaps the first use of the word was in the year 1668 as the title of a book or encyclopedia on trees by Ulisse Aldrovandi, Italian physician and naturalist. Originally, dendrology included all aspects of trees, and in that time there was no science of forestry. Now, especially in Europe, dendrology also includes shrubs, but in the United States it is still usually restricted to trees.

In actual use, dendrology is limited to the botany of trees or, more precisely, to the taxonomy of trees. It can be considered as a division of forestry or botany that treats of the taxonomy of trees. In some universities of the United States the subject matter of dendrology is taught by a professor of forestry, and in others by a professor of botany who is a specialist in taxonomy or systematic botany.

A canopy of benefits

Urban trees and forests provide both tangible and less tangible benefits important for a good quality of life. The consumable products include fuelwood, food, fodder, and poles. Trees improve air, water and land resources, provide habitats for wildlife, control erosion, protect watersheds for urban water supply and can be an outlet for safe disposal of urban wastes. Additional benefits to society, including its low-income citizens, are significant and relate to improvement of health, recreation, environmental education, aesthetics, and enhancement of landscape.

Depending on urban forest management objectives, the focus is quite different in wealthier cities and poorer settlements. Multiple purpose urban forests are required for both rich and poor cities. Examples of multi-functional parks can demonstrate how many benefits can be combined in urban improvement projects working with the poor (see table below). Appropriate urban forestry has to focus on those benefits which are desired for local value first.

Forest foods are widely consumed in most agricultural communities and even in many urban areas, particularly in the developing world. In some cases, they provide a regular supplement to the diet; in others they represent a primary source of food. Most often, however, forest foods are consumed when cultivated food supplies are in short supply at the end of the agricultural season, during crop harvesting when there is little time for food preparation, or during emergencies such as famines and wars (Chambers and Longhurst, 1986). Although few studies systematically examine the seasonal importance of forest foods, a number of case-studies from around the world but primarily from Africa illustrate the critical role of forests in reducing seasonal imbalances in food supply, particularly for the rural poor.

Introduction

In most agricultural communities people rely on seasonal crop production. For many rural people, and especially for the poor, these cycles entail periods of food shortage. It is at these critical periods that the importance of forest foods is greatest.

Introduction

Nitrogen gas (N) constitutes four fifths of the world's atmosphere - a virtually inexhaustible supply, yet very few plants and no animals can assimilate nitrogen in its free form. Nitrogen is, though, the essential constituent of the proteins necessary for cell protoplasm, and all organisms are dependent on having it available in a form which they can utilize.

Most plants obtain their nitrogen from the mineralisation of soil organic matter and plant residues, and living organisms and ecosystems are organised to obtain and preserve usable nitrogen. The modern use of synthetic nitrogen fertilisers is fraught with long-term dangers (depleting soil nitrogen reserves, pollution of groundwater, rivers and lakes), and the fertilisers themselves will become increasingly expensive through increasing energy costs.

Introduction

It's a tough world. Trees face a constant battle in competing for light, water and minerals with surrounding plants. As if that were not enough, they also have to fend off the attention of living things, which view trees as good to eat and places to live. Insects chew away on all parts of a tree and are quite capable of completely defoliating it. Larger leaf-eating animals (which are usually on the ground since a belly full of compost heap is a heavy thing to carry around; leaf eating monkeys are an exception) chew away at the lower parts of the tree, although giraffes can reach up around 5.5 m. Whole armies of animals that can climb and fly will feed on the more nutritious flowers, fruits and the sugar-filled inner bark. The grey squirrel, introduced to Britain from N America in the 1880s, is a prime example. This rodent does extensive damage to hardwoods by stripping bark in spring to get at the sweet sap. It seems that dense stands of self-sown hardwoods have little sap and are largely immune (which may be why it does not cause problems in its native home) but well-tended planted trees have thin bark and a high sap content and are mercilessly attacked. So big is the problem that ash, lime and wild cherry may become more common in Britain because of their relatively low palatability to squirrels at the expense of palatable beech and sycamore.