Source: NASA Studies on late Quaternary environmental ...
Transcript of Source: NASA Studies on late Quaternary environmental ...
Lisa Schüler & Hermann Behling
Studies on late Quaternary environmental dynamics on Mt Kilimanjaro - �rst results
Department of Palynology and Climate Dynamics
Corresponding author: Lisa Schü[email protected]
Göttingen Center for Biodiversity & Ecology
This project is funded by:
Introduction Study Site
Method
First Results
References:1 Hemp 2006 4 Verschuren et al. 20092 Hemp 2006 5 Marchant et al. 20063 Feagri & Iversen 1989
NORTH SOUTH
6000m
5000m
4000m
3000m
2000m
1000m
100
200
Depthcm
0
10000
20000
30000
2200±96
6100±86
7400±47
8900±100
10600±65
13800±144
18900±224
21700±365
32700±335
14C ages (yr B
P)
%
0
Savanna
0
Submontane Forest
0 10
Afromontane Forest
0 10 20
Ericace
ous Belt
0 10 20
Alpine Grassl
and
0 10 20 30 40 50 60 70
Herbs
0
Aquatics
0 10 20 30
Fern Spores
0 10 20
Fungal Spores
0
Euphorbia
0
Abrus
0
Leonitis
0
Cissampelos
0
Ulmace
ae
0
Vitex
0
Araliace
ae
0
Ilex
0
Senecio hadienese
0
Olea
0
Podocarp
us
0
Clematis
0
Artemisi
a
0 10
Erica
0 10
Myrsine
0 10 20
Ranunculus
0 10
Alchemilla
0
Iridace
ae
Main Taxa
Mt Kilimanjaro is an inactive stratovolcano located in NE Tanzania. It rises from savanna plains at 700m to an ice-capped summit at 5895m asl. It was formed in the spreading zone of the East African Rift System.Our study site, Maundi Crater, is located at 2780m asl on the SE side of Mt Kilimanjaro in the transition between upper montane forest and the subalpine heathland zone. The climate is tropical diurnal and influenced by the Asian Monsoon penetrating into East Africa and causing two pronounced wet seasons. Annual mean temperature is 10°C and annual precipitation is around 1900mm1.
Fig 1: The study site, Maundi Crater, surrounded by Erica bush Photo: Rob Marchant
In our project, we study pollen, charcoal and chemical composition derived from peat and sediment cores from different key areas at Mt. Kilimanjaro in order to reconstruct former and to predict future landscape dynamics. We would like to better understand local and regional ecosystems, climate and fire dynamics in a larger context as well as ecosystem dynamics and their reaction on environmental changes. Further, we would like to investigate their role for the development of the biodiversity hot spots in East Africa. Here, we are presenting the results of the pollen analysis of our first study site, the Maundi Crater.
We sampled every 10cm of the 6m long sediment core derived from the center of the Maundi Crater. The samples were prepared applying the standard method3. So far, we have determined and counted 100 pollen grains of the uppermost 32 samples which are dated back to ~38000 14C yrs BP. We assigned every pollen taxa to a vegetation zone known from the present and calculated percentages.
Our first results reveal that the vegetation belt composition, classified as savanna, submontane forest, Afromontane forest, Ericaceous belt, and alpine grassland, has remained rather stable during the past 38,000 yrs. The taxa composition within the vegetation types has varied. The increase in Ericaceous vegetati-on in the late Holocene indicates more frequent (anthropogenic?) fire events. Three phases with no pollen records may be related to droughts that disabled pollen preser-vation. The high percentage of herbs and Ericaceous vegetation inbetween these periods also suggest dry conditions causing a decline of montane forest vegetation.The dry period between 6200 and 7400 14C yr BP coincides with low lake level stands recorded from a lake at the foot of Mt Kilimanjaro4. The increase of aquatics and spores during the late Holocene proposes increasingly humid conditions.
Conclusion and Future Perspective Based on our pollen analytical results, we assume that the ecosystems on Mt Kilimanjaro have been rather stable during the past 38,000 yrs. Despite pronounced past climate events which impacted other parts of the African continent, such as Heinrich Events and African Humid period, we can notice very little change in vegetation composition at our study site. This leads to the conclusion that this East African Mountain system must be predominantly influenced by a different climate driver, possibly the Asian Monsoon activity and its associated precipitation intensities and patterns5.We will analyse further pollen, charcoal and chemical composition to investigate more samples of the Maundi core, and follow-up cores along the slopes of Mt Kilimanjaro. Modern vegetation and pollen rain data will help us calibrate, interpret and model our results.
Mt Kilimanjaro
Fig 2. Ericaceous vegetation at 3200m asl on the S slope of Mt Kilimanjaro
Fig 3. Alpine grassland vegetation at 4000m asl with Poaceae species and Dendrosenecio.
Fig 4. Afromontane Forest between 1500 and 3000m asl
Fig 5. Submontane forest between 1100m and 1500m asl
Fig 6. Savanna vegetation composed of many grass species (Poaceae) and drought resistent trees such as Acacia (Acacia sp.) and Baobab (Adansonia digitata)
Fig 7. The vegetation belts on Mt Kilimanjaro. Due to the moist air of the SE Asian Monsoon, the vegetation belts are shifted downslope on the N side. At the foot of the mountain savanna vegetation dominates the landscape. On the southern slope, agricultural plants such as bananas or coffee are cultivated. Further uphill, we find submontane forest between 1100 to 1500m asl (S slope) with different species depending on the exposition of the slope. From 1500m to 3000m asl (S slope) the vegtation is composed of Afromontane Forest species. Above ~3000m asl on (S slope), occasional frost and decreasing precipitation only allow Ericaceous shrubland to grow; in the areas higher than 4000m asl, exclusively afroalpine grassland can be found up to the rock and snow line2 (after Hemp 2006).
Fig 8. Percentage pollen diagram of the samples from the Maundi Crater peat core. Pollen and spore percentages are plotted against core depth (cm) and age (14C yr BP). The pollen taxa are grouped into vegetation zones found today at Mt Kilimanjaro. The main taxa composing the different vegetation zones are shown in more detail.
Artemisia sp.
Senecio hadiense
Alchemilla sp.
Hagenia abyssinica
Helichrysum spec.Helichrysum sp.
Erica spec.Erica sp.
PoaceaePoaceae
Podocarpus spec.Podocarpus
Mt Kilimanjaro
no pollen record
no pollen record
no pollen record
Source: NASA