2019

LVM is Investigating the Impact of Forest Machinery on Groundwater Flow

 In the photo: Groundwater inflow into a ditch

In order to transport timber from a felling site to a log yard, forest machines often move across ditch beds or between standing trees. JSC “Latvia's State Forests” (LVM), in cooperation with the Latvian State Forestry Research Institute “Silava”, conducted a study to determine whether the weight of forest machinery compacts the soil and alters the groundwater flow to such an extent that it affects tree growth.

Water level and flow in the soil is one of the most important factors for providing trees with favourable growing conditions, namely that excess water in the roots of the tree impedes oxygen access and impedes the release of carbon dioxide, while water scarcity impedes cell proliferation and growth.

The tasks of the research included determination of the water filtration rate on forest machinery routes and the rest of the stand, monitoring of groundwater level within 12 months and laboratory determination of the effect of soil compaction on the water filtration rate.

In order to study the impact of forest machinery on groundwater flow, areas where forest soil could potentially have a negative impact on water flow were selected. Therefore, the study was carried out in forest stands on glacial moraine sediments and glacial sediment basins, as well as in forest stands alongside newly constructed forest paths, where ditches have been excavated and the removed soil layer has been used for pavement construction.

Results in thinning areas

The study found that in forest thinning areas along forest roadways, soil densities in different soil layers were increased by an average of 10-27%. In sandy sediments the soil density can increase up to 18-54%. In turn, soils with a higher proportion of clay particles can be compacted by 16-63%.

However, the preliminary results of the study show that significant soil compaction does not adversely affect groundwater flow on either side of forest machinery pathways or changes in the water filtration rate in the soil below them.

Results concerning ditch beds

Groundwater level measurements show that ditch bed compaction affects groundwater level fluctuations after rainfall. Under such weather conditions, in the ditch beds used for timber transportation, time periods with a faster rise in water level and longer fall periods compared to control areas can be observed.

The results show that the soil freezing and thawing cycle improves the rate of soil water filtration after the soil has been compacted. However, in order to evaluate the restoration of water filtration properties of compacted soil, the study should preferably be conducted over a longer period. This, in addition to the current knowledge, would give an idea of the duration of the compaction effect and the residual effect of repeated compaction.

With a view to developing high-value and sustainable forest management, LVM regularly collaborates with scientists to determine how forestry decisions affect the quality of future forest stands.