Historical background

At the 19th century plant macrofossils was the only technique available for reconstructing past vegetation, and it was used to outline the vegetational development from Tertiary to present day in North-West Europe and the British Isles. However, shortly after its presentation by von Post in1916, pollen analysis was recognised as a powerful tool in studies of long-term vegetation history and it replaced plant macrofossils almost completely. Then again, in the 1960s the advantages of plant macrofossils were rediscovered and it became more common to integrate it with pollen analysis. Today plant macrofossils has been recognised as an indispensable method when unravelling many of the questions in palaeoecology, especially concerning tree-line studies.

 What is a macrofossil?

Any potentially identifiable (sub-)fossil preserved in the sediments which can be seen by the naked eye.
 

  Which plant groups can we excpect to find?

            Vascular plants are most common, because they are usually more hardy

        e.g.            Betula fruit                  Leaves                 Fern sporangia
                                                                                           with spores                  Roots

                         Betula female
                           catkin scale
 

             Bryophytes are quite common, especially the leafmosses (Musci and Anthocerotae). Liverworths (Hepaticae) are
                rare, since they are more fragile.

                e.g.  Sphagnum

 
 

             Fungi (mainly mychorrhiza)and large algae, and rarely also lichen fragments can be found.

However, often there is a mixture of more or less whole seeds and other plant (and animal) remains in the sediments.

1. The macrofossil production of the species and how this is influenced by the environment.
2. How it is spread (by wind, water, animals, mechanical) and how far
3. How good the preservations is (in different environments).
4. If the seeds are eaten (e.g. Potmogeton by ducks).
 

and further, the sedimentation in water depends on:

1. Size and shape of the lake.
2. Draining system (out or inlets)
3. The vegetation around (forested or open)

Advantages of plant macrofossil analysis

Compared to pollen analysis macrofossils can often be identified to a lower taxonomic level. For instance, macrofossils of dwarf and tree-birch can be separated, and several families (Brassicaceae, Caryophyllaceae, Cyperaceae, Ericaceae, Rosaceae, Poaceae, Rosaceae) and genera (e.g. Salix, Pinus, Potamogeton) can be identified down to species or genera level.

In addition, many species are either poorly represented as pollen due to low production (e.g Dryas and aquatics) or poor preservation in the sediments (e.g. Juncus, Luzula, Najas, Ceratophyllum, Callitriche), or not represented by pollen or spores (e.g. bryophytes or Characeae).

Since macrofossils are less readily dispersed, being heavier than pollen, they tend to represent the local flora. This is very important when reconstruction past vegetation, since the pollen always will be a mixture of local and long-distance transport, which are very difficult to separate. Especially in treeless environments, such as the arctic and alpine areas of today, plant macrofossils have their advantage over the long transported pollen (from e.g. Alnus, Betula, Pinus).

Terrestrial plant macrofossils are also indespendable when it comes to dating of cores from calcareous areas. Since bulk-dates will be too old (due to the reservoir effect).

Disadvantages of plant macrofossil analysis

However, some plants produce soft and fragile parts, that do not preserve very well (e.g. Alnus, Corylus avellana, Tilia cordata, Ulmus glabra), except under very favourable catchment conditions. Also, a few pollen taxa can be identified to a lower taxonomic level than macrofossils (e.g. Typha latifolia).

In addition, macrofossils tend to be produced in much less quantitative amounts than pollen and other microfossils, hence larger samples are required for analysis. And (as for pollen) absence of macrofossils cannot be taken as evidence for not having grown there.
 

Conclusion

For reconstructions of vegetation history in general and tree-lines in particular, plant macrofossils provide the best approach in non-forested areas.

MAKROFOSSIL I KLIMAFORSKING

§ Kva er eit makrofossil?

§ Tolking av makrofossil
 Bruk av artar

· Spreiing; speglar makrofossila den lokale floraen, dersom ikkje, kor langt unna voks den?
· Representasjon; kva tyder dei verdiane vi får, med omsyn på kor mange plantar som produserte dei?
· Bevaring; vil fråveret av ein plante tyde at den ikkje voks der? Kor mykje har bevaring av plante- materialet å seie.

Vegetasjonen i dag

§Makrofossil i ”fleirdisiplin- studiar”
 makrofossil og pollen
 makrofossil, diatomear og fjøremygg