4. Results
4.2 Plant macrofossil data
4.2.3. Analysis per sample
Below every sample is analysed separately to make a detailed reconstruction of the environment and the changes in it.
Sample 6 (60-50 cm)
The 60-50 cm section contains a smaller number of remains, with 239 remains found. The amount of different taxa is also less than in most samples, with only 32 taxa present. These taxa and remains mostly exists out of Aquatic and Waterside vegetation, which is making up around 70% of the sample. The location of sampling was almost definitely the waterside of a lake, with species such as Nymphaea alba, Salvinia natans, Carex and a great number of Typha present. Nymphaea alba grows in quite deep, relatively calm, preferably still water. It is mostly found at water depths of 1 to 1,5 meters (Weeda et al. 1985, 219).
38
environments. Carex is a plant that pioneers8 in shallow waters and on the waters edge, they can however occur in grasslands, as well as dune valleys and a few types of woodlands (Weeda et al. 1994, 279). These plants together with some other taxa suggest that the location was not an abrupt water edge, but rather a reed marsh like transition into deeper waters.
Some remains of Cenococcum geophilum have been found, indicating the successional stage of a forest, it uses trees and other plants as a host and it has a significant tolerance to water stress. Apart from these remains no indicators have been found of nearby woodlands, meaning the area was relatively open and dominated by pioneering vegetation. Apart from some Poaceaeseeds there are no indicators of a grassland, the water must have stretched and the area was probably swamp like.
Sample 5 (50-40 cm)
Overall section 50-40 cm is similar to the section below, showing clear influence of water, by all the aquatic taxa. The number of taxa slightly increases in this sample and more aquatic taxa appear. Waterside taxa remain the same. Some of the aquatic taxa that occur are several species of Potamogeton. Potamogeton natans, Potamogeton crispus and
Potamogeton trichoides appear in small number in this sample. These are all plants that grow under the water surface and have their roots in soil at the bottom of the water. Interestingly Potamogeton crispus is associated with thriving in water with fluctuation water levels. It can even survive when its habitat runs dry.
Section 50-40 cm contains one species that grows in grasslands, Ranunculus sardous. This species of buttercup grows in full sun and in relatively open vegetation. It mostly occurs in more temperate regions (Weeda et al. 1985, 243).
.
Sample 4 (40-30 cm)
This sampled section shows a significant decrease in taxa as well as remains. The section mostly exists of waterside plants that take up 53% of all the remains, whilst aquatic plants only take up 22% of the assemblage.
Two waterside taxa appear in this section that weren’t found in the section below,
Chenopodium rubrum/glaucum and Cladium mariscus. Chenopodium rubrum is a multiform species, that is spread on the northern hemisphere, mostly in more temperate areas. It is rare in several Pleistocene sand areas in the Netherlands (Probably related to
8 Pioneer species are hardy species that are the first to colonize an ecosystem that was previously static.
39
ice). The plant grows on moist, nitrogen-rich, open areas. It mostly prefers clayey soils and places that are submerged in winter. It occurs naturally in river banks and along brackish sea inlets and creeks, on places where the vegetation is not closed off (Weeda et al. 1985, 158). Cladium mariscus is a cosmolite of the warm-temperate and warm regions, that reaches its northern border at the South of Scandinavia. It was not present in the Netherlands during the last Ice Age and it reappeared in the Atlanticum, a period that was slightly warmer than current temperatures. Furthermore, this species is often situated in areas where water from deeper layers springs up; the consistent temperature of this water ensures a degree of heat in the winter. These warm water temperatures are important for
Cladium mariscus to survive in winter, since it is a heat-loving plant (Weeda et al. 1994, 272-273).
Sample 3 (30-20 cm)
Section 30-20 cm shows a dramatic increase in the amount of taxa, as well as the amount of remains. This sample contains the most taxa and is the most biodiverse. However, it does not contain the most remains. The aquatic and waterside taxa still make up 71% of the assemblage and this indicates that the environment did not change significantly. The increase in organic material is likely a product of taphonomic processes.
There are quite some differences from the last section and this will be discussed per ecological group. In the aquatic taxa there is a notable increase in Zannichellia palustris
and Schoenoplectus lacustris. Zannichellia palustris is a plant that grows in fresh or brackish shallow waters and on soil that contains clay or sand and has a high organic content. In fresh water it mostly appears as a pioneer, in other cases it is supressed by species like Myriophyllum spicatum (Weeda et al. 1991, 264).
Schoenoplectus lacustris is a real pioneer, it cannot survive in denser vegetation. It cannot survive periods of drought and if its water source dries out it can only survive if the soil remains wet. If erosion finds place do to waterflow it will quickly disappear (Weeda et al.
1994, 253).
In the aquatic taxa a new species appears, Groenlandia densa. This species of plant is similar to plants from the genus Potamogeton. Groenlandia densa can only grow in carbonate-rich and thus basic water. It grows in sweet, clear, somewhat chalk- and nutrient- rich, however fosfate poor water with a fosfate poor soil, that exists of sand or riverclay. It seems to be bound to waters with a uniform temperature, so cold in the summers and unfrozen in the winters. It is a pioneer plant that prefers moving water, but can also occur in newly dug puddles (Weeda et al. 1991, 241-242).
40
Several taxa appear that fit under the grassland ecology. These are, Ranunculus sardous, Polygonum, Euphorbia exigua and Chenopodium ficifolium. Euphorbia exigua is a field plant that grows on chalk-rich clay, chalk and loess. She can be found on open spaces that are disturbed (Weeda et al. 1988, 17-18). Euphorbia exigua occurs in temperate regions of Eurasia. It can only be found at places were the soil is reworked and in open roadside verges, in building areas and on agricultural fields. It grows on chalk holding sands (Weeda
et al. 1985, 163). A large quantity of Poaceae become apparent in this section, further suggesting that grasslands became more prominent.
Apart from the seemingly increasing grassland a high quantity of Cenoccum geophilum
appears, indicating a larger presence of woodland in the region. Next to that the remains of Rubus fructicosus have been found, which is a species that thrives in woodlands with sandy soil. They prefer damp soils, but also occur in drier environments (Weeda et al.
1987, 66).
Sample 2 (20-10 cm)
In section 20-10 cm the amount of taxa decreases and the amount of remains decreases slightly as well. The Aquatic and Waterside taxa make up 75% of the assemblage, which means the environment stayed relatively similar to the sections before.
The taxa remain relatively similar to the section below, with some minor changes. In the aquatic taxa Potomogeton coloratus appears. Potamogeton coloratus is a plant that is bound to high corbonate content and nutrient poor water. It subsides in cool, chalck-rich groundwater and a uniform temperature is very important for this plant to survive (Weeda
et al. 1991, 246-247).
In the grassland taxa the species Linum perenne appears for the first time. This plant is a perennial herb that grows in open, well-drained areas on base-rich substrates, including lightly-grazed grassland, dry banks and roadsides (www.brc.ac.uk).
There is an increase visible in remains of most of the waterside taxa and this is especially visible in Mentha aquatica. This species is native to the temperate regions of Europe. It grows on places where the water reaches the surface all year around. It thrives in sunny to light shaded areas, with carbonate- and nutrient-rich soils (Weeda et al. 1988, 179-181).
Cenoccocum geophilum is not present in this sample, but Rubus fructicosus is. Nothing can be said about the woodland increasing or decreasing in size.
Sample 1 (10-0 cm)
Section 10-0 cm shows a slight decrease in the amount of taxa present, whilst a significant increase is present of the amount of remains in the section. This section has the most remains preserved.
41
The aquatic taxa in this section are less represented, with them making up 19% of the sample. 39% of the sample is waterside taxa, which means that only 58% of the taxa are related to a waterbody. This suggests that there might be a slight change in the vegetation in this level. This can also be seen by the increase of grassland taxa, with species like
Linum perenne, Polygonum lapathifolium, Ranunculus sardous and Verbena officinalis.
Polygonum lapathifolium usually grows on reworked sandy soil in moist areas at the edge of water bodies (Weeda et al. 1985, 138). Verbena officinalis originates from the Mediterranean and is nowadays a cosmolite of warm temperate regions. It prefers sunny places and grows on moist to relatively dry, nitrogen-rich, chalky soils. It is a heath-loving plant that does not occur in the Northern parts of Europe (Weeda et al. 1988, 141-142). The significantly increased number of Poaceaeremains is also an indicator of increased grasslands surrounding the area.
In the waterside taxa there is an increase in most of the taxa that were also present in the section below. There is especially an increase in Menta aquatica and Eupatorium cannabium. Eupatorium cannabium occurs in Europe up till southern Scandinavia and is characteristic for places with a high organic content and moist and/or chalk-rich environments. It mostly occurs at the higher zones of riparian vegetation (Weeda et al. 1991, 33-34).
A few taxa appear or reappear such as Oenanthe aquatica and Urtica kioviensis. Oenanthe aquatica is characteristic of fluctuating waterlevels, it is an outspoken pioneer that only germinates in areas that fall dry every year. Nowadays it pioneers at riparian vegetation that is strongly visited and trampled by cows (Weeda et al. 1987, 265-268).
Interesting is the appearances of Alnus glutinosa and Sambucus. Alnus glutinosa is a tree species that thrives in wet to damp, nutrient rich to moderately nutrient rich soil. It mostly grows in swamp forests and at watersides. For good growth it needs nutrient and mineral rich permanently damp soil. The roots can grow into the groundwater. It cannot resist strong water flow in the summer. Sambucus is a genus of fast growing small trees that occur in a number of environments, but often in woodlands.
There is a small amount of Cenoccocum geophilum remains present in this section.