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Decomposition Rates of Forest and Steppe Vegetation

Otgonsuren Avirmed

Questions

What is the decomposition rate of larch and pine leaf litter?
The process of decomposition is a critical part of the element fluxes of any ecosystem. Changes in decomposition rate might be affected by the changes of the ecosystem parts. Main reason for setting the experiment was to find the decomposition rate of the dominant litter of the forest zones in study valleys and find out how it differ among different slopes. Different slopes have different permafrost condition and therefore, can have different soil conditions which affect to decomposition process.
What is the decomposition rate of dominant grasses and forbs of the steppe zone? Does high necromass accumulation depend upon decay rate of dominant species of the area?
Grazing is one of the main environmental problems of the six study valleys; each differs by the amount of grazing pressure. The most southern valleys are located far from the settlement areas and are not affected by grazing and necromass accumulates in the ground surface. We believe that necromass is an important insulator for soil temperature and it helps to maintain permafrost, a main characteristic of the Hovsgol watersheds. Therefore, to understand the reason for necromass accumulation we set the experiment in steppe zone that is worth expanded.

Methods

For decomposition experiment we used litterbag methods. Litterbags were made of 1 mm netting and woven polypropylene. Bags filled with different litter were placed above the ground surface. Litterbags with larch (Larix sibirica) and pine (Pinus sibirica) needles were placed in south and north facing slopes of Borsog valley (the most southern valley with no grazing and recent fire impact). Four collections were done since September 2002.

The same methods were used to estimate the rate of decomposition of dominant steppe plants. These are: Koeleria macrantha, Poa attenuata, Carex pedicularis, Artemisia commutata, Artemisia frigida, Thymus gobicus, and Potentilla acaulis.

Experiments were set up in July and August 2004. Collections will be done four times during the course of the experiment; the initial collection was made in September 2004, and will end in 2005.

Results and Discussion

Decomposition experiment results in forest zone suggest that decomposition of larch needles is slower than of pine needles (DF=28, p <.0001). Decomposition rate in south facing slope is always more rapid than on north facing slope (DF=28, Prob>F<.0001). Decomposition rate of the materials depends more on air temperature than on air relative humidity (r2=0.5230, p=0.0296)

Figure 1

Figure 1: Forest Decomposition

Species that dominants in grazed valley have significantly higher rate of decomposition than of species of non-grazed valley (DF=7, p <.0001). Forbs known as dominants of grazed areas and above mentioned results suggest that in addition to grazing effect, high necromass accumulation of grazed areas can be less due to rapid decomposition of forbs and decomposition process have some contribution to less necromass in grazed areas and therefore for less soil moisture.

Figure 2

Figure 2: Decay rate steppe

References:

  • Mark E. Harmon, Knute J. Nadelhoffer, John M.Blair. "Measuring Decomposition, Nutrient Turnover, and Stores in Plant Litter"

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