Arid Australia as a source of plant diversity: the origin and climatic evolution of Ptilotus (Amaranthaceae)

Paleoecological studies in Patagonia provide information about vegetation and climate changes occurred during the Holocene. The climatic evolution of this region offers a unique opportunity to study the environmental variability as well as the ecosystem variations. The dynamic of the forest ecosystems is modulated by the occurrence of disturbances. Fires are one of the most important disturbances in temperate forest ecosystems, and its study allows contrasting independently about the changes experienced by ecosystems. In addition, in Patagonia, environmental and postglacial vegetation changes have been determined by variations in the temperature and westerlies winds. In order to reconstruct changes experienced by the forest ecosystem and patterns of plant diversity during the Holocene, in relation to Postglacial dynamics, natural and anthropic disturbances in the Lake Argentino, pollen and charcoal were studied in a sedimentary sequence at Península Avellaneda. Pollen assemblages suggest non-cyclic changes in plant diversity during the Holocene. The highly diverse cold grass-shrub communities dominated the area up to the Early Holocene, when they were displaced upland by less diverse forest and steppes. Also, The Early and Midd-Holocene was characterized by opposite variations of hydric balance between Andean and extra-andean plant communities present between 48° and 50° S, whereas fire activity occurs synchronously between forest (Andean) and steppe communities (Extra-andean). Late Holocene is characterized by different proxy signals depending on the geographical location of the paleoecological records. To conclude, this work provides a better understanding of the fossil pollen record by its comparison with modern surface pollen samples along an altitudinal vegetation gradient.

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Plant diversity and species richness of Ljubljana marsh grasslands under the influence of different cutting and fertilizing regimes

Acta Agronomica Hungarica ◽

10.1556/aagr.57.2009.2.11 ◽

2009 ◽

Vol 57 (2) ◽

pp. 197-203 ◽

Cited By ~ 2

Author(s):

T. Sinkovč

Keyword(s):

Species Richness ◽

Plant Diversity ◽

Grassland Management ◽

Botanical Composition ◽

Significant Negative Effect ◽

Negative Effect ◽

Cutting Regimes ◽

N Rates ◽

Exploitation Intensity ◽

Plot Design

The botanical composition of grasslands determines the agronomic and natural values of swards. Good grassland management usually improves herbage value, but on the other hand it frequently decreases the plant diversity and species richness in the swards. In 1999 a field trial in a split-plot design with four replicates was therefore established on the Arrhenatherion type of vegetation in Ljubljana marsh meadows in order to investigate this relationship. Cutting regimes (2 cuts — with normal and delayed first cut, 3 cuts and 4 cuts per year) were allocated to the main plots and fertiliser treatments (zero fertiliser — control, PK and NPK with 2 or 3 N rates) were allocated to the sub-plots. The results at the 1 st cutting in the 5 th trial year were as follows: Fertilising either with PK or NPK had no significant negative effect on plant diversity in any of the cutting regimes. In most treatments the plant number even increased slightly compared to the control. On average, 20 species were listed on both unfertilised and fertilised swards. At this low to moderate level of exploitation intensity, the increased number of cuts had no significant negative effect on plant diversity either (19 species at 2 cuts vs. 20 species at 3 or 4 cuts). PK fertilisation increased the proportion of legumes in the herbage in the case of 2 or 3 cuts. The proportion of grasses in the herbage increased in all the fertilisation treatments with an increased numbers of cuts. Fertiliser treatment considerably reduced the proportion of marsh horsetail ( Equisetum palustre ) in the herbage of the meadows. This effect was even more pronounced at higher cut numbers. The proportion of Equisetum palustre in the herbage was the highest in the unfertilised sward with 2 cuts (26.4 %) and the lowest in the NPK-fertilised sward with 4 cuts (1.4%).

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