Wildfires typically affect multiple forest ecosystem services, with carbon sequestration being affected both directly, through the combustion of vegetation, litter and soil organic matter, and ...indirectly, through perturbation of the energy and matter balances. Post-fire carbon fluxes continue to be poorly studied at the ecosystem scale, especially during the initial window of disturbance when changes in environmental conditions can be very pronounced due to the deposition and subsequent mobilization of a wildfire ash layer and the recovery of the vegetation. Therefore, an eddy-covariance system was installed in a burnt area as soon as possible after a wildfire that had occurred on 13 August 2017 and has been operating from the 43rd post-fire day onwards. The study site was specifically selected in a Mediterranean woodland area dominated by maritime pine stands with a low stature that had burned at high severity.
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•Moss cover developed up to 75% in a hillslope during the first post-fire year.•Moss cover threshold of 67% was effective in reducing soil erosion by 65%.•Runoff response was not ...dependent on moss cover but on other protective layers.
Mosses and wildfires are ubiquitous occurrences. Their correlation has been assessed in few studies. Mosses have been pointed as pioneer species in post-fire environments. However, reasons for moss crusting in post-wildfire soils and their ecosystem role in preventing soil erosion have not been quantitatively assessed. Moss crusts have quickly developed after a wildfire in a hillslope of eucalypt plantations, in central Portugal. This study had as the overarching aim comparing post-fire soil erosion and runoff between different moss cover percentages, combined with other protective cover elements throughout the first year after fire. Overland flow, sediment and organic matter losses were examined at micro-plots presenting different moss cover percentages, both between plots (11–46% in average) and across time (0–75%). While development of moss cover tended to increase the runoff response, a moss cover above 67% significantly reduced sediment and organic matter losses by 65% (0.40 Mg ha−1) and 34% (0.15 Mg ha−1) respectively, especially during the rainiest season. Given that mosses are very fast soil colonizers after wildfires, these results provide clues for considering moss crusts in post-fire management and demonstrate their importance in ecosystem restoration, including prevention of soil loss.
Mankind has built terraces on sloping terrain since pre-historic times, especially for expanding croplands. Widespread terracing for forestry purposes is comparatively recent, presumably linked to ...the advent of fast-growing tree plantations together with technological advances in heavy forestry machinery.
Perhaps not surprisingly therefore, the impacts of terracing on soil properties are poorly studied for forest stands. The present investigation addressed this knowledge gap using eucalypt plantations in north-central Portugal as study case and using a space-for-time approach. In total, 12 pairs of neighbouring, terraced (T) versus non-terraced (NT) plantations were studied, with the terraced plantations equally divided over four time-since-terracing periods: <1 year (recently terraced); 5 years; 10 years; 17 years. As such, the studied chrono sequence covered roughly half of a full eucalypt rotation cycle in the region. All field data and all litter and topsoil (0–5 cm depth) samples were gathered during an 2-weekly campaign, at 5 equidistant transect points per plantation.
Terracing changed all four cover categories most strongly and markedly during the initial time-since-terracing period, while its effects on the averages of vegetation cover (T/NT: 19/37 %) and litter cover (T/NT: 47/62 %) contrasted with those of stone cover (T/NT: 26/1 %) and bare soil cover (T/NT: 8/1 %). Terracing increased dry bulk density across the entire chrono sequence (overall averages T/NT: 1.17/0.84 g cm−3), while it greatly decreased resistance to shear stress but only for the initial post-terracing period (T/NT: 0.8/ 3.2 kg cm−2) and not towards the middle and end of the first rotation cycle (five and ten years after terracing). Total carbon content in soils was significantly affected by terracing, while total nitrogen content not. Both properties revealed similar temporal patterns, with a marked initial decrease (TC: −32 mg C g−1 soil; TN: −0.73 mg N g−1 soil) and a gradual recovery during the first rotation cycle.
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•Terracing changed all four cover categories particularly during the initial period.•Terracing consistently increased dry bulk density across the entire chrono sequence.•Soil resistance to shear stress decreases markedly but only for the initial period.•Terracing imposes reductions in the total carbon content with medium term effects.•Total nitrogen was affected at a lesser degree, presenting a faster recover rate.
Fire-enhanced runoff generation and erosion are an important concern in recently burnt areas worldwide but their mitigation has received little public and scientific attention in Portugal. The ...present study addressed this knowledge gap for the two principal fire-prone forest types in Portugal, testing the effectiveness of a type of mulch that is widely available in the study region but has been little utilized and poorly studied so far. For logistic reasons, two somewhat different forest residue mulches were tested in a eucalypt plantation (eucalypt chopped bark) and a nearby Maritime Pine stand (eucalypt logging slash). Arguably, however, more important differences between the two study sites were those in fire severity, resulting in an elevated litter cover prior to mulching at the pine site but not at the eucalypt site, and in experimental design, with eight bounded erosion plots of 16m2 installed at the eucalypt site as opposed to only four at the pine site (due to its limited size). Mulching was applied four months after the wildfire and two months after installation of the plots. Rainfall, runoff and sediment and organic matter losses were measured on a 1- to 2-weekly basis. Mulching proved highly effective at the eucalypt site, on average reducing the runoff coefficient from 26 to 15% and sediment losses from 5.41 to 0.74Mgha−1. This mulching effect was also statistically significant, albeit only for the more important runoff and erosion events, and corresponded to a significant role of litter cover in explaining the variation in runoff and erosion. At the pine site, by contrast, mulching had no obvious effect. In all probability, this was first and foremost due to the comparatively small amounts of runoff and sediments produced by the untreated pine plots (5% and 0.32Mgha−1) and, as such, due to the extensive needle cast following a low severity fire.
► The effectiveness of two forests residue mulching was monitored after a wildfire. ► Chopped bark mulch reduced runoff and erosion in a eucalypt plantation. ► Slash logging mulch in a pine plantation did not show differences. ► Soil water repellency and soil cover were key factors addressing runoff and erosion.
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•Post-fire salvage logging increased soil compaction.•Logging increased sediment production with increasing mechanical disturbance.•Organic matter content of the eroded sediments was ...lower in the disturbed areas.•Logging did not delay post-fire vegetation recovery.•Erosion was positively related with rainfall intensity and reduced by vegetation.
Research has been undertaken on the hydrological and erosional impact of forest fires, but remarkably little work has been conducted on salvage logging operations that often follow them. We assessed the effects of mechanical salvage logging following wildfire on soil physical properties, ground cover, and runoff and erosion response on a eucalypt stand in Portugal. We compared two levels of mechanical disturbance, skid trails by a wheeled forwarder tractor (“skid_low”) and skid trails by the same tractor followed by a tracked feller-buncher (“skid_high”) with control conditions (no mechanical disturbance). Three plots (16 m2) by level of soil disturbance were installed after a moderate intensity fire and subsequent logging operations, and monitored during the first post-fire year. In two control and two skid_low plots runoff was also measured.
Soil bulk density was higher with increasing mechanical disturbance. Soil compaction reduced porosity 7–16%, but as the control porosity was 70%, the reduced porosity still was 60–65%. Soil resistance to penetration significantly increased for the most disturbed area, whereas soil shear strength was significantly reduced in the intermediate disturbance level. Mechanical disturbance did not induce significant effects on soil moisture or ground cover. Initial greater coverage by bare soil in the disturbed plots compared to the control was compensated by a more rapid vegetation recovery in those plots.
Annual runoff amount was not higher at the skid-low than at control plots. Absence of runoff difference was due to high soil porosity of 65%, even after tractor trafficking, and a greater surface roughness on the skid_low plots compared to the control. Sediment production increased with increasing soil disturbance. The mean sediment rate was 1.6–3 times greater for the disturbed than the control plots. This increase could be explained by the higher soil compaction and reduced soil shear strength on the mechanically disturbed plots and initial differences in ground cover. Organic matter content of the eroded sediments was higher on the control than the disturbed plots, due to initial higher ash cover on the control plots.
Overall, sediment production was significantly related to rainfall intensity and reduced by vegetation regrowth. Sediment rates tend to decrease with time since the initial fire and logging disturbance, highlighting the importance of a rapid implementation of erosion control measures. Specific management practices are needed to minimize the impacts of logging in burnt soils which are already subject to greater erosion risk and soil degradation.
•Forest terracing had an immediate reduction on soil carbon, nitrogen, and phosphorus.•The construction of terraces negatively affects the soil labile and plant available fractions.•After terracing ...the soil nutrient concentrations in the interpatch were strikingly lower.•Terracing imposes reductions in the soil CO2 effluxes, particularly in the interpatch.
Over the last decades, eucalypt plantations have increasingly involved intensive soil mobilization by heavy machinery. In north-central Portugal, bench terracing with bulldozers has become a common practice for eucalypt re-/afforestation. Its impacts on soil properties and functions, however, have received little research attention so far.
The present study aimed to address the changes in topsoil fertility from immediately before to immediately after the construction of terraces. This was done for two contrasting micro-sites (tree-patch and inter-patch). Topsoil fertility was characterized in terms of both total and labile carbon and nitrogen as well as available phosphorous. In addition, this study aimed to assess the short-term impacts of terracing on soil respiration, as an indicator of soil biological activity. Soil respiration was monitored at monthly intervals during the first year following terracing at the terraced as well as at a nearby, non-terraced eucalypt plantation.
The construction of bench terraces led to a significant immediate reduction in topsoil contents of total and labile carbon and nitrogen as well as available phosphorus. The reductions were inferred to result from the mixing of the A, B, C and R horizons, in combination with a priming effect due to soil aeration and resulting exposure of carbon and nitrogen compounds to soil micro-organisms. Bench terrace construction furthermore increased spatial heterogeneity in topsoil fertility, turning differences in carbon, nitrogen and phosphorus contents between tree and inter-patches significant immediately afterwards. Likewise, soil respiration tended to be significantly different between tree-patches and inter-patches at the terraced site but not between tree-patches and inter-patches at the neighbouring non-terraced site. These short-term impacts of bench terracing on the spatial patterns in soil respiration are likely to reflect its immediate impacts on the spatial patterns in soil fertility. The present findings plainly justified further research on the medium and long-terms« impacts of bench terracing on eucalypt soil properties and functions.
•We compared three seed provenances of A. unedo under contrasting water contents.•Seedling development was analysed using morphological and physiological parameters.•Low water content was negative ...for aboveground and positive for belowground biomass.•Different provenances revealed different adaptations to contrasting water regimes.
In the last decades, several studies have reported the increase of land degradation and desertification in the Mediterranean Basin. Depending on degradation severity, ecological restoration might be needed in order to promote ecosystem recovery. The ecology of the selected species and intra specific variability should be considered in order to improve restoration options, especially facing climate change.
The present study tested the hypothesis that seedlings from drier provenances would be better adapted to low water content conditions. Seeds were germinated under controlled temperature after which seedlings were grown in a phytotron under two contrasting watering regimes. Seedling performance was analysed using morphological and physiological parameters.
Low water content had a clear negative effect on the seedlings’ aboveground biomass (total dry weight, root collar diameter, leaf dry weight and leaf weight ratio) and a positive effect on belowground biomass (root weight and root:shoot ratio). This response was not unequivocal, since provenances differed in morphological adaptations to low water content. Seedlings from the wettest provenance revealed a higher relative growth rate under high water content but a poor adaptation to limited water availability when compared to the other two provenances. This was observed by the absence of a significant belowground investment in this provenance. Seedlings from the wettest provenance also presented a significant reduction of total leaf area that was not observed in the other two provenances. This can however be hardly considered as a successful adaptation to cope with drought since this provenance produced less sclerophyllous leaves, less belowground biomass and also lower sapwood to leaf area ratio independently from the water content conditions. By contrast, seedlings from the dry provenance with the hottest summer had similar root collar diameter, leaf dry weight and physiological performance under both watering regimes.
The observed adaptations to water regimes seem to be related with the climate of the seed source and highlighted the importance of seed provenance in ecological restoration actions using Mediterranean species. This knowledge could improve early establishment success predictions for different plant populations, allowing more reliable and cost-effective management decisions under climate change scenarios.
This study addressed the impacts of wildfire and, in particular, its severity on the seed bank of the litter/ash layer and the topsoil of a Mediterranean pine plantation (Pinus pinaster Ait.) in ...north-central Portugal. The study location was selected for presenting a homogeneous pine cover before the fire, on the one hand, and, on the other, heterogeneous patches with distinct degrees of damage to the pine crowns immediately after the fire. The experimental design involved the selection, from the opposite valley side, of three zones with adjacent strips of Low and High Canopy Consumption (L/HCC). Within each of these strips, a transect was laid out along which three plots were established at 10m intervals. The same was done in the unburnt area immediately outside the fire perimeter. At each plot, samples were collected within the first two weeks after the fire to: (i) asses viable seed densities for three sampling layers, using the indirect method for a 10-month period; (ii) estimate maximum temperature reached (MTRs) at 0–3cm depth, on the basis of Near Infrared Spectroscopy (NIR). Fire severity at the plots was further determined by verifying, in situ, pine canopy consumption (FCC) as well as by measuring the minimum diameter of remaining shrub twigs (TDI). In comparison with the unburnt area, the recently burnt area as a whole revealed a substantial increase in overall densities of viable seeds. Seed bank composition, however, varied markedly within the burnt area but this could be explained reasonably well by differential effects of the wildfire associated with its severity, in terms of the two crown consumption classes as well as the TDI index but not the MTRs. The inclusion of the litter/ash layer and the separation of two soil depths were amply justified by providing clear support for the important role of fire severity, in particular for the two principal taxa (Calluna vulgaris and Erica spp., presumably mainly E. australis).
► We studied the effect of fire severity on the soil seed bank – density seedlings. ► Severity - crown consumption (Low-LCC, High-HCC), twig diam-TDI, soil temp-MTR. ► LCC areas had more seedling density than HCC areas. ► MTR indicated low to moderate heating and did not relate to seed bank density. ► TDI-significant relation to post-fire total seedlings density.
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