The impact of beaver inundation on drained coniferous stands in the Mālpils forest district [Latvia] | Bebru appludinājuma ietekmes novērtējums uz nosusinātajām skujkoku audzēm Mālpils mežniecībā
2009
Gackis, M., Latvia Univ. of Agriculture, Jelgava (Latvia). Forest Faculty. Dept. of Silviculture
The field data were gathered in 2008 in the Mālpils forest district of the Riga Regional Forest District on approximately 6-year-old beaver inundations in previously drained areas in sites where the inundations were next to pine and spruce stands. In each stand round sample plots were established of the total area 500 square m – 6 for the stands under research and 3 for the control. In each plot the stand parameters were surveyed, the tree condition was estimated visually, and holes drilled with M. Presler's increment borer. The size and volume of inundation were instrumentally surveyed. The stand response to beaver activities was evaluated in terms of the loss of additional increment. It was concluded that beaver inundations accumulate a large amount of water available for extinguishing forest fires. Observations prove that the existence of drainage systems and broadleaved stands in the drained and adjoining areas promote the beaver activity. Furthermore, the reaction of smaller dimension trees to the presence of beaver is faster and more pronounced. In the 2008 inventory year, in drained pine stands the radial increment of trees, compared to the estimates, decreased on the average by 62%, and by 70% drained spruce stands. For spruce the greatest increment reduction is in higher density and more extensively inundated stands. In pine stands the cumulative volume increment loss during six years of inundation is on the average 29.7 m**3 haE-1, while in spruce stands it is 54.5 m**3 haE-1. In monetary terms the losses in pine stands from the decrease of additional increment make on the average 87 LVL haE-1 per year, and in spruce stands – 194 LVL haE-1 per year (calculated after the average wood prices in the first part of 2009 in the Vidzeme region). The calculations of this research demonstrate increased negative response of spruce stands against beaver inundation, and in this respect they can be considered as stands of increased risk. In drained pine stands the loss of productivity due to beaver is approximately 2 times less than in spruce stands.
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