Interpreting the vegetational and environmental changes at Marathousa 1

changes at Marathousa 1

In order to make a clear assessment of the change in the vegetation and environment at Marathousa 1, it is necessary to portray the landscape that maintained unchanged throughout the section. It is important to note that it is not known over what time span these changes happened. As the sequence is not very long it can be assumed that it does not spans over much more time than 100 years. Important to note is that a big part of the archaeological remains, most importantly, the straight tusked elephant, were found on top of the sediment that was sampled at the 40-50 cm section and this was buried by the 30-40 cm section.

5.1.1.

The landscape of Marathousa 1

From the data derived of macrofossils and pollen from the section at Marathousa 1, the following can be implied. The site is located near the water’s edge of a lake. This can be concluded from the high numbers of aquatic and waterside plants found in the samples throughout the section. From the aquatic taxa ecological factors of the lake can be deducted, which is useful to understand the nature of the lake. The taxa show that throughout the section at the point of sampling the environment consisted of shallow water at the edge of a lake. Species like Nymphaea alba and Potamogeton cannot survive in deep water since they need their roots in the sediment at the bottom of the water and Nymphaea alba has her leaves floating on the water. These plants together with Characeaealso imply that the water was clear, since they use photosynthesis and if the water is muddy or too deep the light would not reach the plants. The aquatic plants overall need sun and grow in warm and consistent water temperatures, especially Salvinia natans is a good example of this, since it has its leaves on the surface of the water and it can only grow in sunny and warm places in shallow water (Szmeja and Gałka 2013, 114). Most of the plants found in the assemblage grow in a freshwater environment, but a number of them can survive a more saline environment as well. It is not very likely the lake was influenced by the sea, since the site is not located close enough to the sea. The water in the lake must have been mesotrophic to eutrophic with a neutral pH. Species like Schoenoplectus lacustris need a nutrient rich environment and thrive in weak acidic waters. However, Characeaecannot form its oospoores (reproductive systems) in acidic water conditions. Zannichellia

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palustris, a submerged species similar to Potamogeton grows in nutrient rich water, that is neutral in pH as well. These do occur together throughout the sample, suggesting the pH level of the lake was neutral.

The waterside plants growing on the edge of the lake show reed swamps, with species like

Typha and Carex dominating. These plants thrive on waterlogged soils and some are even standing in the water. Plants such as Typha, Carex and Juncus grow quite tall and can overshadow other plants easily. Cyperus longus is one of these species that grows tall and in dense clusters. It prefers nutrient rich soils and grows in sunny warm places on moist to wet soils. Most of the waterside taxa do not tolerate shade and need to grow in full sunlight, meaning that there were almost no trees at the waters edge. The majority of the waterside taxa are pioneer species.

The dense reed swamps would probably grow in clusters and sometimes open up, in order for other plants can grow. Mentha aquatica is one of these waterside plants that grows lower to the ground, together with species like Lycopus europeus, Eupatorium cannabium

and Alisma. The soils at the edge of the lake must have been rich in nutrients and neutral in pH to even calcareous, in order for these plants to grow and thrive. Regular flooding can be seen from several taxa that thrive in regular flooding conditions, such as Butomus umbellatus, Cyperus longus, Epilobium hirsutum, Lycopus europeaus, Lythrum salicaria

and Mentha aquatica. In the geological record regular flooding is visible by sediment deposited by mudflows. The sediments that were used in this research were analysed as being part of mudflow deposition, thus it is very logical that this is reflected in the plant assemblage as well.

In the pollen data, which is complimented by some of the macrofossil data, a grassland becomes apparent in a more regional setting. Presumably further away from the lake a dry grassland was present, dominated by Artemisia and some Poaceaespecies. Species like

Ranunculus sardous and Polygonum lapathifolium grow in disturbed grasslands around the lake. This grassland is more present in the pollen data, than in the macrofossil data, suggesting this is of a regional nature, instead of local. However, in some cases grasses and grassland species must have grown closer to the lake margin, indicating an overlap in these two ecologies.

Further away from the lake and probably in combination with the grassland, is woodland, that mostly consists of Quercus trees. Quercus is generally a species that grows in warm temperate regions. Combinations of Quercus woodlands, with a more open dry environment is not uncommon, this can be seen for example in modern day Mediterranean oak forests, such as that of the Zagros mountains. Trees like Alnus and Salix grew closer

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to the waters edge, since they need more moisture and cannot survive on open dry grassland. However, they were probably not abundant, since the other waterside vegetation does not tolerate shade.

In summary, the landscape at Marathousa 1 consisted of a reed swamp at the edge of a lake with tall grasses and reeds in patches and lower lying plants at the edges in more open areas. Submerged plants grew in clear water that would be still or in some cases slow moving. On the water surface plants grew that float on the water surface and have their roots in the soil, so the water level was not too deep at the edge of the lake. Further away from the waters edge the landscape changed into open, dry grassland that was sometimes disturbed, with oak trees scattered around the landscape.

5.1.2. Changes in the landscape of Marathousa 1

The landscape of Marathousa 1 has already been interpreted as a reed swamp surrounding the edge of a lake with nearby grasslands and woodland consisting mostly of oak trees in the nearby area. In the lowest part of the section (sample 6, 50-50 cm), the lake seems to have a number of plant species surrounding it, but it is relatively small and it indicates an open landscape dominated by pioneering vegetation, like Schoenoplectus lacustris.

In the following section the overall plant composition remains extremely similar, however there is a slight increase in remains and more aquatic taxa appear. Especially the appearance of several Potamogeton species is interesting. Potamogeton crispus occurs in temperate and tropical areas, whilst Potamogeton natans occurs in temperate and cooler areas. The species occur together suggesting a temperate climate in this part of the section. Pollen zone 1 shows similar vegetation, but in the area surrounding the reed swamp it shows an abundance of Artemisia, suggesting a cold, dry environment outside of the lake margins.

A major change is visible in pollen zone 2 (45-20 cm) and this is visible in the macrofossil sample 3 (20-30 cm) as well. In macrofossil sample 4 (30-40 cm) there is sudden decline in vegetation, that is probably related to taphonomic issues, rather than vegetation change. The change is mostly attested by an increase in remains and in taxa in general. The aquatic and waterside taxa still make up 71% of the assemblage, indicating no change in the water levels. The site remained at the edge of the lake in a reed swamp, but it provided for a greater number of species at this time. There is an increase in pioneering taxa such as

Zannichellia palustris and Schoenoplectus lacustris, which are both species thriving in nutrient rich soils/waters, thus indicating more eutrophic conditions in the lake.

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The macrofossil and the pollen data both show an increase in grassland vegetation, however, there is a decrease in Artemisia pollen, suggesting a less dry environment. The grassland species found in the macrofossils all show the presence of disturbed and moist soils, which further strengthens the idea of the surrounding landscape getting less dry. An increase in woodland is also apparent in both the pollen and the macrofossil data. In the pollen an increase in Quercus is visible and Ulmus also shows a slight increase. In the macrofossil data this is strengthened further by the number of Cenococcum geophilum

found and Rubus fruticosus. The vegetation around the lake became denser and the water’s edge moved further away. Species like Salix and Alnus grew near the water edge providing shade in certain areas.

Further up in the profile the grassland and woodlands become more prominent. Several species of grasslands are now visible in the macrofossil remains as well as in the pollen. In the uppermost macrofossil sample the aquatic and waterside taxa only make up 58% of the remains. This means that the edge of the lake was moving away from the sampling location, due to catchment dynamics. Trees like Salix and Sambucus are now visible in the macrofossil record, suggesting these grew very close to the location of sampling. In the pollen data Artemisia pollen declined and are only limitedly present. The new grassland taxa only grow on moist soils, so the environment must have been wetter than before. In summary, the vegetation started as a reed swamp surrounding a fresh lake, with a dry woodland in the distance. It became richer in vegetation and biodiversity was higher half way through the section. Grassland and woodland become more apparent higher in the section, suggesting the margins of the lake subtracted slightly and the vegetation seems to become more dense, even though pioneer species are still thriving.

5.1.2.

Trampling and its effect on the vegetation

In chapter 2 the data of the large mammal finds has been presented and from this it became clear that large mammals were present in the area of Marathousa 1. Especially the find of a partially complete skeleton of a straight tusked elephant that was scavenged by hominins is a big indicator of large mammal presence. Multiple elephant remains were found in the layers and other large mammals such as Hippos were also found. These large mammals must have had an effect on their environment, not only were they likely to drink and bathe in the water of the lake and eat the vegetation surrounding it, they also trampled the vegetation surrounding the lake with their large masses.

The effect of trampling by large mammals on the vegetation has been studied numerous amounts. One of those studies is an experimental one on the effects of trampling in a national park in Rwanda (Plumptre 1993). The results of this research showed that the

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impact of the african elephants (Loxodonta Africana) was biggest on the vegetation, resulting in the killing of many plants. However, this effect did not decrease the biodiversity in the region and it can be suggested that it actually maintained biodiversity, by securing the survival of plants that are ruled out by faster growing taller plants (Plumptre 1993, 125). Elephants do not only trample soil, but have also seen to use their tusks and trunks to dig in the soil, looking for water (Haynes 1988, 149). By doing this they disturb soils and uproot plants.

At Marathousa 1 a number of plants are found that only grow in reworked/disturbed soil. It is likely that this disturbance in the soil comes from animal activities such as the digging activities of elephants. It is important to note, however, that the elephants used in the example above are of a different species than the extinct elephant from Marathousa 1. The presence of tall growing plants, next to lower lying plants that compete for sunlight, could indicate that taller plants were regularly trampled, making room for the smaller plants to grow. This probably helped to stabilize the ecosystem, rather than making it decrease in biodiversity.