Soil and water nutrients in stem‐only and whole‐tree harvest treatments in restored boreal peatlands

Abstract

In boreal peatlands felling and tree harvest are commonly carried out as part of peatland restoration. Stem-only harvest is the principal harvest method and it leaves the live crown material (felling residue) containing most tree nutrients at the site. Wholetree harvest, where felling residue is removed, is not favored due to higher transport costs, although it might better promote the recovery of nutrient-poor peatlands towards pristine conditions. We investigated whether initial differences in N mineralization and decomposition rates observed between tree harvest methods continued out to 6 years after restoration and whether the spatial variation in water table (WT) level and water nutrient concentrations parallels with the observed pattern in mineralization and decomposition rates. The study was done at 15 peatland sites in Natura 2000 protection areas in Finland during 2007-2013. Concentration of ammonium in soil water was higher in the stem-only harvest treatment compared to that of the whole-tree harvest treatment, whereas the previously observed differences in net N mineralization and decomposition rates had leveled out by the sixth year after restoration. The spatial variation created by the ditch network still affected the hydrology and peatland functions so that the nutrient concentrations were higher near ditches than in other locations, implying potential risk for nutrient leaching. Based on this study, there is no reason to prefer either harvest method over the other in nutrient-poor drained peatlands with low tree volumes, which constitute the majority of available peatland restoration area in Finland.

Separating autotrophic and heterotrophic soil CO<sub>2</sub> effluxes in afforested peatlands

“…Mazzola et al, 2020) and Fennoscandia (e.g. Tolvanen et al, 2020) differ from other types of drained peatlands because this land-use change involves a wholesale shift in the functional composition of the plant community (i.e. replacement of short-statured vegetation with trees), leading to potential interactions or synergistic effects arising from changes to both soil hydrology and plant community composition.…”

Unmanned Aircraft System (UAS) Structure-From-Motion (SfM) for Monitoring the Changed Flow Paths and Wetness in Minerotrophic Peatland Restoration

“…Wetness could have been promoted more by building higher and longer embankments at a lower interval to achieve a sufficient flow dispersion in the strips between the ditches. It is known that the infilled ditches are sensitive to gather flow even after the restoration since the drained organic soil encounters subsidence, lowering the land surface close to the ditch [12,17]; this was observed in Iso Leväniemi. Furthermore, the ditches were deep, making it difficult to gather enough infilling material without lowering the ditch surroundings.…”

“…The first field monitoring visits after restoration typically include subjective visual assessment of factors such as amounts of incoming water, nature-like wetness distribution and effectiveness of ditch infilling and dams in terms of water retention [9]. Furthermore, hydrological changes have been monitored from standpipe wells, either manually or using devices automatically logging the water levels or soil moisture in high temporal resolution [10][11][12]. However, these sensors are restricted to discrete locations.…”

“…Typical restoration actions in peatlands include damming and infilling of ditches and directing the flow away from the drainage network using embankments or by excavating auxiliary ditches [6][7][8][9]. According to discrete standpipe well measurements [10][11][12], the water tables typically rapidly increase after restoration. However, recovering the pristine flow paths may be impossible if the spatial nature of the ecohydrological processes is ignored.…”

Net soil carbon balance in afforested peatlands and separating autotrophic and heterotrophic soil CO<sub>2</sub> effluxes

“…Mazzola et al, 2021) and Fennoscandia (e.g. Tolvanen et al, 2020) differs from other types of drained peatlands because this land-use change involves a wholesale shift in the functional composition of the plant community (i.e. replacement of short-statured vegetation with trees), leading to potential interactions or synergistic effects arising from changes to both soil hydrology and plant community composition.…”