Trees of the People

This book is about the importance of trees to people as sources of fuel, shelter, timber, and recreation. It is developing as short chapters covering varied aspects of forestry and natural woodlands.

Chapters

Forests migrated to survive ice-ages    

 

Oak tree isolated in farmland. Long ago this region had a dominant vegetation of oaks and similar broad-leaf trees. Woods remain here, and nearby is a major plantation of non-native conifer trees, also a large timber-yard and associated wood processing industry.

This introductory chapter follows the story of how trees and forests responded to the end of the last major ice-age by extensive expansion of their range. As people also increased in number and ability to grow crops, maintain livestock, and use wood for construction and fuel, the forests diminished. Now new relationships between people, trees and forests are developing, to the benefit of both.

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Energy of sunlight harvested as wood

 

Leaves of beech, a tree of great value as timber and aesthetically. The carbon stored in trees is extracted from air by leaves the incorporated into the woody parts of trees. 

Life on Earth is powered by sunlight and trees predominate in capturing this energy. Trees use this energy to incorporate carbon from the atmosphere to synthesize organic matter, mainly as wood. This chapter describes the pathways of energy and matter from green leaves through to harvested timber.

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Leaves: when should they fall?

 Maple tree deciduous leaf during fall when the green photosynthetic pigments have been withdrawn by the tree.

How do some deciduous broad-leaf tree species manage to flourish in regions that seem suitable only for coniferous needle-leaf species? Why do some needle-leaf conifers shed all their leaves before the onset of every winter? Answers to these questions may be found in recent studies showing how all types of leaves are adapted so that their gain of energy and materials is optimal under a wide range of physical and biological constraints upon photosynthesis.

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Roots and their fungal partners

 

Base of a larch tree with a fly-agaric mushroom. This fungus forms mycorrhizal relationships with many species of tree.

How roots of trees in woodlands function can only be understood fully in the context of the fungi they are symbiotic with. These are the mycorrhizal fungi that are a large and active component of many soils. Threads of these fungi wrap around tips of roots and there extract sugars from the sap of the trees. In exchange the trees gain mineral nutrients from the fungal threads. But where does the balance lie between the cost to the tree of losing these sugars and its gain from the nutrients?

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Trees to store carbon

Accumulating carbon storage in a plantation forest over 80 years. These three compartments of storage and one category of fuel substitution, all increase the tonnage of carbon stored at a rising level.

Plants grow by transforming the carbon of carbon dioxide gas in the atmosphere into the structures of their bodies. Trees with their woody roots, stems and branches store huge amounts of carbon. The wood is long lasting and it stores carbon away from the atmosphere for decades to centuries. Tree planting is now promoted worldwide as an important contribution to mitigating the climate crisis. 

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People making wooden buildings

 

A spiral staircase made with types of engineered wood. This method allows new structures of great strength and utility to be made.

This chapter describes the growing trend of using wood as the main structural material for tall buildings as apartment blocks and offices, also the enhanced use of wood for internal structures of aesthetically pleasing form. One advantage is to reduce the carbon dioxide emissions from manufacture of steel, concrete and brick for conventional buildings; another is to store carbon within the structure of the building.

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 Wood as fuel: from cooking to electrical energy

A modern style of kiln for the small-scale production of charcoal. Globally the use of charcoal for cooking remains large and essential.

Crucial stages in the development of human society were the inventions of how to use fire and of cooking our food. Harvesting of woody fuel became essential, and when manufacture of charcoal was invented our ability to produce metal tools and ceramics developed. Demand for wood based fuel was so great that tree coppicing and sustainable forestry were invented. Now we incorporate wood as fuel into methods to remove carbon dioxide from the atmosphere and to substitute for fossil fuels.

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Regeneration woodlands

 

Natural growth of trees on an island (a refugium) gives information on what to plant in the community regeneration project nearby, as well as providing dispersed seeds.

Regeneration of woods and forests is increasingly popular and this topical subject is broad and varied worldwide. This chapter provides an overview ranging from community projects to restore areas of disused land to a former wooded character, through to questions of how to protect such woods from damage by herbivores, and regeneration for sustainability of woodlands used for multiple purposes.

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Tree reproduction

Female cones of a spruce tree Picea sitchensis, ripening in mid-summer to produce seed. This species produces huge numbers of small light seeds that can be carried far on the wind.

Trees devote a large proportion of their resources each year to produce seeds but few seeds survive to become the next generation of mature trees. Mechanisms of reproduction by both conifers and flowering trees are complex but can be followed through the structure of cones and flowers as they develop toward producing seeds and fruits. Adaptations of seeds and fruits for dispersal are also used for breeding and horticulture of food crops.

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How did this pine forest arrive here?

Stand of Scots pine trees, Pinus sylvestris in a national park. This is a remnant of a large forest that slowly migrated to north western Europe from small populations that had survived the last major ice-age in southern Europe.

Scots pine probably originated as a separate species somewhere central to eastern Europe and from there spread across Eurasia to reach the seaboards of the Atlantic and Pacific Oceans. This tree species is one of the world's most widespread naturally. The ecological processes, constraints, and adaptations that enabled this vast migration is the theme of this chapter. The example of the small population that came naturally to inhabit northern Scotland is a focus and this chapter concludes with the story of the loss of much of this local population followed by the current enthusiasm for large scale regeneration and reconnection of the fragments into a healthier and more enjoyable whole.

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Forests with animals eating their trees

A moose, the largest species of deer. They inhabit forests of North America and Eurasia and feed on many types of vegetation during summer but depend heavily on foliage of conifer trees during winter. Credit: Diego Delso, Wikimedia

All plants are at risk from many kinds of organisms that will feed on them, from bacteria to fungi to insects and mammals. So many of them that here two examples of herbivorous animals of conifer forests are used to introduce ecological factors that influence their populations, and defences plants use against herbivores. An insect pest of forests of North America, a species of moth, the eastern spruce budworm, is described with emphasis on the caterpillar stage that eats needle-leaves. These insects devastate large areas of forest when their populations grow rapidly. In the same forests there are many deer with feeding habits that inhibit regeneration of trees. Of these moose are the largest, often common, and feed on leaves of conifers during winter. Moose are also common in Scandinavian countries and are well studied in relation to the management of timber forests and how their populations are affected by wolves living in the same forests.

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