 |
| Titel |
Sensitivity of East African savannah vegetation to historical moisture-balance variation |
| VerfasserIn |
I. Ssemmanda, V. Gelorini, D. Verschuren |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1814-9324
|
| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 10, no. 6 ; Nr. 10, no. 6 (2014-11-28), S.2067-2080 |
| Datensatznummer |
250117079
|
| Publikation (Nr.) |
 copernicus.org/cp-10-2067-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
| Fossil pollen records provide key insight into the sensitivity of terrestrial
ecosystems to climate change. However, tracing vegetation response to
relatively modest historical climate fluctuations is often complicated by the
overriding signature of anthropogenic landscape disturbance. Here we use
high-resolution pollen data from a ~200-year lake-sediment record in
open wooded savannah of Queen Elizabeth National Park (southwestern Uganda)
to assess the sensitivity of the tropical lowland grassland–forest
transition to historical, decade-scale moisture-balance fluctuations.
Specifically we trace vegetation response to three episodes of higher average
rainfall dated to the 1820s–1830s, ca. 1865–1890 and from 1962 to around
2000. Our pollen data indeed reveal a sequence of three wet periods,
separated by two drier periods. During the inferred wetter episodes we find
increases in the percent pollen abundance of trees and shrubs from moist
semi-deciduous forest (Allophylus, Macaranga,
Alchornea, Celtis), riparian forest (Phoenix
reclinata) and wooded savannah (Acalypha, Rhus-type
vulgaris, Combretaceae/Melastomataceae) as well as taxa common in
the local rift-valley grasslands (Acacia, Ficus), together
creating strong temporary reductions in Poaceae pollen (to 45–55% of
the terrestrial pollen sum). During intervening dry periods, Poaceae pollen
attained values of 65–75%, and dryland herbs such as
Commelina, Justicia-type odora and Chenopodiaceae
expanded at the expense of Asteraceae, Solanum-type, Swertia
usambarensis-type, and (modestly so) Urticaceae. Noting that the overall
richness of arboreal taxa remained high but their combined abundance low, we
conclude that the landscape surrounding Lake Chibwera has been an open wooded
savannah throughout the past 200 years, with historical moisture-balance
variation exerting modest effects on local tree cover (mostly the abundance
of Acacia and Ficus) and the occurrence of damp soil areas
promoting Phoenix reclinata. The strong apparent expansion of true
forest trees during wet episodes can be explained partly by enhanced pollen
input via a temporarily activated upland stream. Pollen from exotic trees and
cultural indicators appears from the 1970s onwards, but their combined
influence fails to mask the signature of natural vegetation dynamics in the
pollen record. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|