What is Amber?

It is probably only from the Carboniferous onwards that land based plant species evolved capable of producing resin which subsequently turned into amber. From that time on various tree species have produced different deposits of amber.

Tree Sources
The worlds two current major deposits of amber; Dominican Republic and Baltic had two separate tree types which produced the original resin. The Baltic source tree has been named Pinites succinifer. In appearance it would have probably resembled a pine or spruce tree and the forests in which it grew were sub tropical in nature. It may not have looked unfamiliar today. Here a photograph of a fir and spruce forest may well give a good indication of what the Baltic amber forest would have looked like.

From amongst the numerous inclusions found in Baltic amber other trees species have been identified as being present. Here are just some of the trees which must have grown in the ancient amber forest:

Cycadacea (Ferns & Palms)
Coniferae (Cypresses, Cedars, Pine, Thujas)
Juniperinae (Junipers)
Fagaceae (Beeches, Oaks)
Salicaceae (Willows)
Santalaceae (Sandalwoods)
Magnoliaeae (Magnolias)
Lauraceae (Laurels)
Aceraceae (Maples)

Grimaldi in his latest book ‘Amber - Window to the Past’ refers to current research (not specified) which casts a shadow of doubt onto the Baltic Amber tree species.. Most Baltic amber possesses Succinic acid. This is a problem when attributing Baltic fossil resin to a species of pine, as up until recently no extant pine tree resin was known to contain succinic acid. But, two recent pine tree genera’s have been found which do possess succinic acid in their resin, they are Keteleeria and Pseudolarix. The latter has been discovered in the Eastern mountain ranges of China. An important and relevant observation is that the ecological systems which are supported by the Pseudolarix trees in China appear to reflect those presumed and extrapolated from the inclusions discovered in Baltic amber.

What is equally interesting is the presence of Pseudolarix pine cones in a fossil resin discovered on the Axel Heiburg island in Canada which also has succinic acid present. From this it can safely be presumed that this tree was capable of producing the resin which would transform over millions of years into amber. Pseudolarix is therefore beginning to look more likely as the true source of the Baltic Amber deposits.

The Dominican Republic resin tree was Hymenaea protera (Alternate link Hymenaea protera) for which had its origins in Africa. Close relatives of this tree (Hymenaea verrucosa) still exist within the sub continent of Africa and on some of the West Indian islands.The following link discusses in a little more detail Hymenaea protera .

Many of the major amber deposits have had their tree source identified. Key amongst them are:

Country / Species Family
Alaska / Agathis Undetermined plant family
Baltic / Pinites succinifer
Burma / Nummulites biaritzensis
Canada - Cedar Lake / Agathis Undetermined plant family
Dominican Republic / Hymenaea protera
Germany - Bitterfield / Cupressospermum saxonicum (Now disputed)
Mexico - Chiapas / Hymenaea Undetermined plant family
Middle East / Agathis Undetermined plant family
Romania - Colti / Sequoioxylon gypsaceum

In nearly all of these cases the climate under which these trees grew was sub tropical. The climatic conditions where amber is now found may have changed dramatically since the time of the resin bearing trees. The Baltic for instance is no longer sub tropical.

It is interesting to note that few potential amber forming forests now exist. The North Island of New Zealand had in the earlier part of this year one of the most extensive resin bearing forests in the world. This location produced the famous kuari gum and the tree responsible for these massive deposits was Agathis australis. Few of these trees now remain of the once huge forests.

Current day forests of spruce and pine produce small quantities of resin, none of it is likely to lead to fossilised amber. Their form of resin degrades and breaks down into other compounds before becoming copal or amber.

A book published in 1491; 'Hortus Sanitatus' shows the earliest representation of the fabled amber tree in the form of a woodcut illustration. As you can see the tree appears to bearing some unusual fruit, as well as resin being exuded from the trunk.

Purpose of the Resin

The reason for the exudation of the resin from various species of trees is not fully understood. Research suggests one of five reasons:

1. a defence mechanism against fungal or insect attack;
2. a bi-product of some form of growth process;
3. a form of desiccation control via the resin covering of leaves and bark;
4. an aid to reproduction and the attraction of insect pollinators;
5. a reaction to storm or weather damage.

Of these 5 processes the world's major amber deposits are most likely to be a product of insect or fungal assault. Amber therefore could be a reaction to attack from external forces. For example, an insect bores a hole into a branch or twig and a stream of resin is exuded to prevent further intrusion and to repair and reinforce the damage done.

Seasonal growth may also induce a flux of resin into the plant at certain times of year. Research has been undertaken which analysed inclusions which would indicate at what time of the year the fresh resin had been produced. The result of this research centred mostly on the presence of stellate hairs. Stellate hairs are a product of the oak trees and are produced predominantly during the spring and early summer, the results of this work indicated that up to 60% of the Baltic amber would have been fresh at the time these inclusions were trapped.

Dr Jean Langenheim is probably one of the foremost resaearchers into ancient tree resin, a small web page giving biographical details can be reached here.

It is a common misconception that resin was only vented onto the tree’s external surfaces; branches, trunk and surface roots, as in the picture of a cherry tree trunk (to the left). Resin was in fact also exuded within the tree its self forming moats or channels of hardening resin within the wood matrix. What the purpose of these formations were for is unknown. It might be speculated that it was a reaction in some cases to termite or wood boring insect attack?

The diagram (Alternative External Diagram) shows a cut away tree trunk with typical amber channels and pools which formed within the trunks or branches as well as on their surfaces. Each of these resins formed by the tree had a unique chemical constituency and was not uniform in nature.

The resin was formed in resin canals or ducts within the wood itself. It is not part of the trees sap, which is a watery substance containing complex sugars. Specialist cells which form the resin are distributed throughout the body of the tree itself.