Exposed Mineral Soil Research Articles

Short-term response of the herbaceous layer within leave patches after harvest

Leave patches, uncut areas in a harvested forest, may conserve herbaceous layer species that decline after forest clearcutting. They may also serve to maintain source populations for the recolonization of the harvest area. The main objective of this study is to characterize the short-term response of the herbaceous layer to clearcut harvesting disturbance within and adjacent to leave patches. Four experimental 1 ha patches and two uncut references were established. Within each patch or reference, belts of five 1 m 2 quadrats were placed at 50 m and 5 m outside the patch, at 0 m (edge), and at 25 m, 35 m, and 50 m (centre) inside. These belts of quadrats were replicated at all four aspects (North, South, East, and West). Ground vegetation was sampled yearly for 1 year before harvest and 3 years after harvest in the experimental patches and for 2 consecutive years in the references. Some common residual species declined significantly in the clearcuts, but remained stable inside the patches in the short term (3 years after harvest). Overall species composition changed little in the patch interior and edge after harvest. Colonizing species (those that appeared in quadrats after harvest) in the patch exterior were predominantly early-seral species, whereas colonizers in the patch interior tended to be shade-tolerant forest species. Species were grouped a priori based on two habitat preferences (amounts of canopy cover and disturbed substrate). Species characteristic of a habitat with closed canopy and undisturbed substrates that decreased significantly over time in the patch exterior were negatively correlated with the amount of exposed mineral soil and open canopy. Species characteristic of a habitat with open canopy and disturbed substrates that increased significantly at the patch exterior showed a positive correlation with the amount of exposed mineral soil and open canopy. No species’ habitat preference groups declined significantly in the patch interior or edge over time. Based on species’ responses to forest operations, it appears that at least the common forest species are maintained in the short term within leave patches.

Disturbance history and dynamics of an old-growth mixed species mountain forest in the Slovenian Alps

A long history of human presence in the Alps has made studies of natural forest structure, composition, and disturbance processes difficult. In the Slovenian Alps, we identified a mixed European beech ( Fagus sylvatica L.)-silver fir ( Abies alba Mill.)-Norway spruce ( Picea abies (L.) Karst.) stand with old-growth characteristics that escaped past cutting. We reconstructed the dynamics of the stand using a combination of stand and age structure analyses, dendroecological evidence of past canopy disturbance, and historical evidence of past human activities. The disturbance reconstruction revealed a stand-scale disturbance in the 1850s. Based on the presence of pit-and-mound topography throughout much of the stand and the absence of logging activities found in historical records, we assume this event was caused by strong winds. The current structure and composition of the stand are largely a result of this event. Post-disturbance forest development was dominated by the release of shade tolerant regeneration, especially F. sylvatica. The windthrow also created appropriate conditions (i.e. increased light and exposed mineral soil) for recruitment of less shade tolerant species, including larch ( Larix decidua Mill.) and maple ( Acer pseudoplatanus L.). The results suggest that periodic, intermediate severity wind disturbances, similar to the event documented here, may have had an important influence on pre-settlement forest dynamics in mixed mountain forests of the Alps, and add to the limited available information regarding the historic range of natural variability of disturbance processes. This information may be useful for forest management that attempts to emulate natural processes.

Determinants of riparian fire severity in two Oregon fires, USA

We sought to understand how vegetation indicators and local topographic factors interact to influence riparian fire severity in two recent fires in Oregon, USA. A stratified random sampling design was used to select points in a range of fire severity classes, forest stand ages, and stream sizes in each fire. At each point, plots were sampled in riparian areas and adjacent uplands. Fire severity was assessed in each plot, and measurements were made of factors that have been found to influence riparian fire severity. Understory fire severity (percent exposed mineral soil and bole char height) was significantly lower in riparian areas compared with adjacent uplands in both fires, suggesting a decoupling in understory fire effects in riparian areas versus uplands. However, overstory fire severity (percent crown scorch and percent basal area mortality) was similar in riparian areas and adjacent uplands in both fires. Fire severity in riparian areas was most strongly associated with upland fire severity. In addition, vegetation indicators, particularly those describing riparian fine fuel component and species composition, were strong predictors of riparian fire severity. Consistency in factors controlling fire severity in the two fires suggests that controls on riparian fire severity may be similar in other regions.

Reduced-impact logging: Challenges and opportunities

Over the past two decades, sets of timber harvesting guidelines designed to mitigate the deleterious environmental impacts of tree felling, yarding, and hauling have become known as “reduced-impact logging” (RIL) techniques. Although none of the components of RIL are new, concerns about destructive logging practices and worker safety in the tropics stimulated this recent proliferation of semi-coordinated research and training activities related to timber harvesting. Studies in Southeast Asia, Africa, and South and Central America have clearly documented that the undesired impacts of selective logging on residual stands and soils can be substantially reduced through implementation of a series of recommended logging practices by crews that are appropriately trained, supervised, and compensated. Whether reducing the deleterious impacts of logging also reduces profits seems to depend on site conditions (e.g., terrain, soil trafficability, and riparian areas), whether the profits from illegal activities are included in the baseline, and the perspective from which the economic calculations are made. A standardized approach for calculating logging costs using RILSIM software is advocated to facilitate comparisons and to allow uncoupling RIL practices to evaluate their individual financial costs and benefits. Further complicating the matter is that while there are elements common to all RIL guidelines (e.g., directional felling), other components vary (e.g., slope limits of 17–40° with ground-based yarding). While use of RIL techniques may be considered as a prerequisite for sustaining timber yields (STY), in particular, and sustainable forest management (SFM), in general, RIL should not be confounded with STY and SFM. This confusion is particularly problematic in forests managed for light-demanding species that benefit from both canopy opening and mineral soil exposure as well as where harvesting intensities are high and controlled primarily by minimum diameter cutting limits. These qualifications notwithstanding, since logging is the most intensive of silvicultural treatments in most tropical forests managed for timber, some aspects of RIL are critical (e.g., protection of water courses) whether forests are managed for STY, SFM, or even replacement by agricultural crops.

Storage and mobility of black carbon in permafrost soils of the forest tundra ecotone in Northern Siberia

AbstractBoreal permafrost soils store large amounts of organic carbon (OC). Parts of this carbon (C) might be black carbon (BC) generated during vegetation fires. Rising temperature and permafrost degradation is expected to have different consequences for OC and BC, because BC is considered to be a refractory subfraction of soil organic matter. To get some insight into stocks, variability, and characteristics of BC in permafrost soils, we estimated the benzene polycarboxylic acid (BPCA) method‐specific composition and storage of BC, i.e. BPCA‐BC, in a 0.44 km2‐sized catchment at the forest tundra ecotone in northern Siberia. Furthermore, we assessed the BPCA‐BC export with the stream draining the catchment. The catchment is composed of various landscape units with south‐southwest (SSW) exposed mineral soils characterized by thick active layer or lacking permafrost, north‐northeast (NNE) faced mineral soils with thin active layer, and permafrost‐affected raised bogs in plateau positions showing in part thermokarst formation. There were indications of vegetation fires at all landscape units. BC was ubiquitous in the catchment soils and BPCA‐BC amounted to 0.6–3.0% of OC. This corresponded to a BC storage of 22–3440 g m−2. The relative contribution of BPCA‐BC to OC, as well as the absolute stocks of BPCA‐BC were largest in the intact bogs with a shallow active layer followed by mineral soils of the NNE aspects. In both landscape units, a large proportion of BPCA‐BC was stored within the permafrost. In contrast, mineral soils with thick active layer or lacking permafrost and organic soils subjected to thermokarst formation stored less BPCA‐BC. Permafrost is, hence, not only a crucial factor in the storage of OC but also of BC. In the stream water BPCA‐BC amounted on an average to 3.9% of OC, and a yearly export of 0.10 g BPCA‐BC m−2 was calculated, most of it occurring during the period of snow melt with dominance of surface flow. This suggests that BC mobility in dissolved and colloidal phase is an important pathway of BC export from the catchment. Such a transport mechanism may explain the high BC concentrations found in sediments of the Arctic Ocean.

Evaluation of the composite burn index for assessing fire severity in Alaskan black spruce forests

We evaluated the utility of the composite burn index (CBI) for estimating fire severity in Alaskan black spruce forests by comparing data from 81 plots located in 2004 and 2005 fire events. We collected data to estimate the CBI and quantify crown damage, percent of trees standing after the fire, depth of the organic layer remaining after the fire, depth of burning in the surface organic layer (absolute and relative), and the substrate layer exposed by the fire. To estimate pre-fire organic layer depth, we collected data in 15 unburned stands to develop relationships between total organic layer depth and measures of the adventitious root depth above mineral soil and below the surface of the organic layer. We validated this algorithm using data collected in 17 burned stands where pre-fire organic layer depth had been measured. The average total CBI value in the black spruce stands was 2.46, with most of the variation a result of differences in the CBI observed for the substrate layer. While a quadratic equation using the substrate component of CBI was a relatively strong predictor of mineral soil exposure as a result of fire (R2 = 0.61, P < 0.0001, F = 60.3), low correlations were found between the other measures of fire severity and the CBI (R2 = 0.00–0.37). These results indicate that the CBI approach has limited potential for quantifying fire severity in these ecosystems, in particular organic layer consumption, which is an important factor to understand how ecosystems will respond to changing climate and fire regimes in northern regions.

Effects of forest floor disturbances by mechanical site preparation on floristic diversity in a central Ontario clearcut

The effects of forest floor disturbance by six mechanical site preparation (MSP) treatments on structural and compositional diversity of early successional communities were examined in a clearcut in central Ontario. Periodic assessment of floristic diversity and abundance was performed to quantify treatment effects on species richness and abundance of three discrete plant life forms (cryptogam, herbaceous and woody) in the first five growing seasons after MSP. Botanical surveys of the surrounding uncut forest provided an estimate of pre-harvest forest species composition of the clearcut study site. Intensity of forest floor disturbance differed significantly among MSP treatments, creating a variety of microsites. The percentage of mineral soil exposure and abundance of downed woody material ranged from 7% to 52% and 18% to 1%, respectively, from the least to most severe treatments. Five years after MSP, 134 species (50 cryptogams, 47 herbaceous, 37 woody) were present in the clearcut study site, compared with 102 species (54 cryptogams, 25 herbaceous, 23 woody) in the uncut forest. Species richness and abundance of cryptogam, herbaceous and woody plant species increased with time after MSP, except for herbaceous species richness. MSP treatment significantly influenced species richness of cryptogams, herbaceous and woody plants, and abundance (percent cover) of woody plants. Treatment differences in richness and abundance were strongly correlated with intensity of forest floor disturbance. Scalping treatments that created the most mineral soil exposure and removed the most downed woody material typically supported the lowest species diversity and lacked several native forest species. Cryptogams were most affected by MSP, with higher richness and abundance where forest floor disturbance was relatively low. MSP did not affect the incidence of alien plant species: only two alien species were observed on the study site, representing less than 1% of total cover. Evaluation of MSP effects on early successional plant communities based on beta diversity in an ordination analysis revealed several distinct species groups associated with specific treatments. The relative amount of forest floor disturbance and downed woody material among treatments were strong predictors of species groupings within the ordination. Plant communities in slash piles were distinct from those resulting from MSP and contained several remnant forest species. Examination of species’ autecology provided supporting evidence that the displacement of downed woody material and forest floor organic layers was the leading cause of changes in species richness and abundance on this site.

The Relationship of Multispectral Satellite Imagery to Immediate Fire Effects

The Forest Service Remote Sensing Applications Center (RSAC) and the U.S. Geological Survey Earth Resources Observation and Science (EROS) Data Center produce Burned Area Reflectance Classification (BARC) maps for use by Burned Area Emergency Response (BAER) teams in rapid response to wildfires. BAER teams desire maps indicative of fire effects on soils, but green and nonphotosynthetic vegetation and other materials also affect the spectral properties of post-fire imagery. Our objective was to assess how well satellite image-derived burn severity indices relate to a suite of immediate post-fire effects measured on the ground. We measured or calculated fire effects variables at 418 plots, nested in 50 field sites, located across the full range of burn severities observed at the 2003 Black Mountain, Cooney Ridge, Robert, and Wedge Canyon wildfires in western Montana, the 2003 Old and Simi wildfires in southern California, and the 2004 Porcupine and Chicken wildfires in interior Alaska. We generated the Normalized Burn Ratio (NBR), differenced Normalized Burn Ratio (dNBR), Relative dNBR (RdNBR), Normalized Difference Vegetation Index (NDVI), and differenced NDVI (dNDVI) burn severity indices from Landsat 5 Thematic Mapper (TM) imagery across these eight wildfires. The NBR correlated best with the fire effects measures but insignificantly, meaning other indices could act as suitable substitutes. The overstory (trees in Montana and Alaska, shrubs in California) measures appear to correlate best to the image variables, followed by understory and surface cover measures. Exposed mineral soil and soil water repellency were poorly correlated with the image variables, while green vegetation was most highly correlated. The BARC maps are more indicative of post-fire vegetation condition than soil condition. We conclude that the NBR and dNBR, from which BARC maps of large wildfires in the United States are currently derived, are sound choices for rapid assessment of immediate post-fire burn severity across the three ecosystems sampled. Our future research will focus on spectral mixture analysis (SMA) because it acknowledges that pixel reflectance is fundamentally a mixture of charred, dead, green and nonphotosynthetic vegetation, soil, rock and ash materials that are highly variable at fine scales.

Mapping Ground Cover Using Hyperspectral Remote Sensing after the 2003 Simi and Old Wildfires in Southern California

Wildfire effects on the ground surface are indicative of the potential for post-fire watershed erosion response. Areas with remaining organic ground cover will likely experience less erosion than areas of complete ground cover combustion or exposed mineral soil. The Simi and Old fires burned ∼67,000 ha in southern California in 2003. Burn severity indices calculated from pre- and post-fire multispectral imagery were differenced (i.e., differenced Normalized Burn Ratio (dNBR)) to highlight fire-induced changes to soil and vegetation. Aerial and field hyperspectral data were also collected together with field ground cover measurements soon after the fires. Spectral endmembers representing green vegetation, nonphotosynthetic vegetation (NPV), charred NPV, and charred and uncharred inorganic materials (soil, ash, and rock) were used in a constrained linear spectral unmixing process to determine the post-fire fractional ground cover of each component on the ground surface. The spectral unmixing results, dNBR, and a Relative dNBR (RdNBR) were validated using field-measured fractional ground cover estimates to determine which product best predicted the conditions on the ground. The spectral unmixing results were significantly correlated to all classes of charred and uncharred organics and inorganics, and the dNBR was the best indicator of charred soil and green vegetation. The RdNBR had several significant correlations with the ground data, yet did not consistently correlate well with any specific ground cover types. A map of post-wildfire ground cover and condition, especially exposed soil and remaining vegetative cover, is a good indicator of the fire’s effect on the ground surface and the resulting potential for hydrologic response.

Influence of harvest residues and vegetation on microsite soil and air temperatures in a young conifer plantation

Soil temperature influences many processes in young forest stands including growth and phenology of trees, water uptake, and nutrient mineralization. Effects of harvest residue management and other site preparation techniques on soil and air temperatures have previously been reported at the treatment level, but there is little information on temperature patterns in the various microsites created by these treatments. This study examines the effects of bole-only harvesting with and without vegetation control (BO + VC; BO − VC) and total-tree harvesting plus removal of legacy woody debris with vegetation control (TTP + VC) on microsite temperature in a young Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) plantation. Hourly soil temperatures were recorded at a 10-cm mineral soil depth for 5 years post-planting, and near-ground (25 cm) air temperatures were recorded for 1 year. In the TTP + VC treatment, mean soil temperature and diurnal range in soil temperature during the growing season differed by microsite surface condition in the following sequence: exposed mineral soil > intact forest floor > decaying wood over soil > shade of stumps. In the BO treatments, soil temperature differences among microsites were smaller, and only the stump-shade microsite differed significantly from the others. Near-ground air temperature did not differ by microsite. A sine-wave model showed that diurnal warming of soil beneath decaying wood occurred more slowly than for other microsites. Total annual soil degree-day accumulation was 25–37% greater in the TTP + VC treatment than in the BO + VC treatment; the greatest difference occurred in the year with the warmest spring air temperature. Vegetation control treatments had little effect on soil temperature in the BO harvest treatment. The reduced microsite variability and diurnal fluctuation in soil temperature in the BO harvest treatment may be beneficial where summer temperature extremes are a concern. Alternatively, the warmer spring and early summer soil temperatures of the TTP harvest treatment may be advantageous for early seedling development.

The role of environmental factors and tree injuries in soil carbon respiration response to fire and fuels treatments in pine plantations

The need to understand how forest management practices affect soil CO2 exchange with the atmosphere (soil respiration) has increased with the recognition of a likely feedback effect of climate warming on soil respiration rates. Previous research addressing the mechanisms driving soil respiration has yielded inconsistent and/or conflicting results. This study looked to alternative above-ground forest characteristics to help explain spatial variability in soil respiration in a 30-year-old Sierra Nevada pine plantation. Fire hazard mitigation is one of the predominant management goals in these and other western US forests. Therefore, this analysis examined how fuels treatments, including shredding of understory vegetation (mastication), prescribed fire, and a combination thereof, affected soil respiration and its relationship to environmental factors and post-fire tree injuries. Multiple regression models indicated that mastication had no significant impact on soil respiration, but the roles of soil temperature and forest floor depth (O horizons) in the models increased after the treatment. Burning reduced soil respiration by ∼14%, and increased its sensitivity to tree proximity and the exposure of bare mineral soil. Scorch height in burned stands was negatively correlated with soil respiration. Models incorporating only tree injury or tree proximity parameters explained between 63% and 91% of the variability in burned plantations. This work suggests that measures of above-ground forest features can increase understanding of management impacts on soil respiration, and the mechanisms by which these impacts occur. These results are especially applicable in Mediterranean climates, where moisture stress reduces the effectiveness of soil microclimate in explaining soil respiration.

Effects of vegetation control on nutrient removal and Fagus orientalis, Lipsky regeneration in the western Black Sea Region of Turkey

Dense Rhododendron ponticum (L.) understories of eastern beech ( Fagus orientalis Lipsky) stands in the Black Sea Region (BSR) of Turkey create challenging forest vegetation management problems relative to beech regeneration. Rhododendron traditionally is controlled in Turkish forests with grubbing and bulldozing. The effects of these practices on nutrient removal and natural beech regeneration have not been quantitatively studied. Two woody vegetation control treatments (bulldozing and hand-grubbing) were installed during late summer, 2002 in three mature beech stands with dense rhododendron understories in the Düzce Forest Management Directorate, in the Turkish western BSR. Aboveground biomass of each vegetation component, total aboveground vegetation biomass, nutrient concentrations, organic matter (OM) removal, and total amount of OM nutrients were determined for each woody vegetation control treatment. Soil bulk density and nutrient content, and beech seedling biomass, nutrient content, and natural regeneration also were studied. One year after treatment, the machine site preparation by bulldozing (MSP) that removed understory vegetation and attached roots, reduced mean forest floor OM content by about 84%, when compared to hand-grubbing. Mean soil C, N, K and Mg concentrations on the bulldozed sites were 36, 27, 50 and 55% less, respectively, than those on the grubbed sites. Total C and Mg amounts at the 5–10 cm soil depth were 24 and 47% lower, respectively, for mechanical site preparation (MSP) sites, when compared to grubbed sites. Overall, soil bulk density did not differ significantly between the grubbing and MSP treatments. Frequent passes on designated transects on MSP sites resulted in a significant ( P < 0.01) one-third increase in bulk density of the first 20 cm soil depth, when compared to grubbed sites. No natural beech regeneration occurred on untreated control sites. Mineral soil exposure on the MSP sites increased beech seedling germination substantially. One year after treatment, the mean number of naturally regenerated seedlings for MSP sites was 2.5 times greater than for grubbed sites. Woody control treatments had significant effects upon beech seedling chemistry, with N, P, K, Ca and Mg concentrations averaging 35, 47, 12, 33 and 25% lower, respectively, for MSP sites, when compared to grubbed sites. However, mean seedling biomass and nutrient content were significantly greater ( P < 0.05) on MSP sites. Long-term effects from windrowing on MSP site residues, associated topsoil and nutrients need to be evaluated.

Relationships between microsite type and the growth and nutrition of young black spruce on post-disturbed lowland black spruce sites in eastern Canada

The surface of the soil in recently harvested or burned lowland black spruce (Picea mariana (Mill.) BSP) sites is composed of a fine mosaic of different bryophytes (mostly Sphagnum spp. and feathermosses), disturbed organic material originating mostly from mosses at different stages of decay, and exposed mineral soil. Growth substrates were compared in lowland black spruce stands regenerating after either careful logging or wildfire. The 3-year annual increment for black spruce seedlings was greatest with substrates of feathermosses, mainly Pleurozium schreberi (Brid.) Mitt., fibric material of P. schreberi origin, and a mixture of fibric P. schreberi and humic materials; it was least with fibric Sphagnum spp., mineral soil, and decaying wood substrates. The most favourable substrates for growth were characterized by better black spruce N and P foliar status. Our results also suggest that categories of growth substrates in the rooting zone reflect nutritional quality better than categories of growth substrates on the soil surface. To maintain or increase black spruce growth following careful logging of sites prone to paludification, we recommend fill-planting of seedlings in substrates originating from P. schreberi; management techniques that favour P. schreberi over Sphagnum mosses should also be developed.

Conventional and Mechanized Logging Compared for Ozark Hardwood Forest Thinning: Productivity, Economics, and Environmental Impact

Abstract Replicate 4-ac plots in a 70-year-old upland oak forest on slopes averaging 30 percent in southeastern Missouri were harvested by conventional (chainsaw + skidder) and mechanized (small tracked skid steer + feller-buncher and harvester + forwarder) logging equipment.The heavy thinning prescribed by a crop tree management approach removed an average of 1,300 ft3 or 40 tons per acre of pole wood and sawlogs, leaving an average basal area of 36 ft2/ac. The harvester/forwarder was the most productive (ft3/production hour),and the small feller-buncher the least, being the only system whose (unreplicated) production cost exceeded revenue. Production costs (excluding mobilization, overhead, and profit) of the conventional and harvester/forwarder systems were not statistically different on average, but the lowestcost of the latter was 14% less than that of the conventional system. The frequency of residual trees experiencing substantial bole damage was not significantly different among logging technologies, but the harvester/forwarder did have a higher incidence of substantial crown damage.The area of exposed mineral soil did not differ significantly among technologies, and soil compaction sufficient to impede rooting was rare. Lack of site and operator replication and incomplete cost analyses over a limited time prohibit generalization of these conclusions. North. J. Appl. For. 23(4):264 –272.

Are mineral soils exposed by severe wildfire better seedbeds for conifer regeneration?

We examined jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) BSP), and white spruce (Picea glauca (Moench) Voss) seed germination and seedling recruitment in aspen (Populus tremuloides Michx.) and conifer mixedwood stands following the 1999 Black River fire in southeastern Manitoba, Canada. Three postfire seedbed types were tested: scorched (surface litter only partially consumed), lightly burned (surface litter consumed with little or no duff consumption), and severely burned (complete consumption of litter and duff exposing mineral soil). Seeds were sown in 1999, 2000, and 2001, and each cohort was monitored for 3 years. In 1999, severely burned seedbeds had poor germination, while scorched seedbeds had the highest germination. The reverse was true in 2001. After the first growing season, continued survival of seedlings was greater on severely burned seedbeds for all three cohorts. However, better survival on severely burned seedbeds was not sufficient to overcome poor germination in 1999 and 2000. When using artificial seeding to promote conifer regeneration, we recommend a delay of one full year after a severe spring fire for jack pine and two full years for black spruce and white spruce on boreal aspen and conifer mixedwood sites.

Influence of soil scarification on reindeer foraging and damage to planted Pinus sylvestris seedlings

The effects of soil scarification on reindeer lichen cover and re-establishment, reindeer foraging and damage possibly caused by reindeer to planted Scots pine seedlings were studied during six growing periods in a field experiment established in a reindeer lichen site that was grazed by a herd of 500–600 reindeer each winter. Seedlings (at a density equivalent to 2000 ha−1) were planted in mounds with mineral soil on top, in tracks with exposed mineral soil, in tracks with mixed organic material and mineral soil and in intact lichen mat (control) with no soil disturbance. The disturbed area varied from 0 to 28%. After six growing periods, the reindeer lichen cover and volume were 10–20% lower in the scarified plots than in the control plots. There was no clear evidence that the reindeer avoided foraging even in plots with the highest levels of soil disturbance. However, the behaviour of the reindeer during winter grazing seemed to be affected by both coverage of reindeer lichen (positively) and the proportion of exposed mineral soil (negatively). Damage possibly caused by reindeer trampling affected 8.2% of the living seedlings each year and approximately 50% of these seedlings were subsequently infected by fungal diseases (compared with 20% of viable undamaged seedlings). Scarification treatments that exposed mineral soil mildly resulted in higher survival and growth rates than the other treatments, especially the control.

Concepts about Forests and Water

Abstract Six concepts concerning forests, forestry, and water resources are discussed: (1) the role of the forest canopy in erosion control; (2) the impact of disturbance on soils; (3) the variability of natural water quality; (4) the impact of harvesting on water quality; (5) the role of extreme experiments; and (6) the effectiveness of forestry best management practices (BMP). The literature shows that the forest floor, not the canopy, protects soils from erosion. Harvesting can be conducted in ways that limit compaction and essentially confine overland flow to areas of exposed mineral soil on roads, trails, and log landings. Overland flow from these areas can be controlled and converted to subsurface flow before it reaches streams and lakes. Thus, effects to watershed hydrology are small. Undisturbed watersheds tend to have better quality water than highly disturbed watersheds, but the undisturbed character of a catchment does not assure high-quality water. Undisturbed forests vary greatly in sediment and chemical exports that are controlled by variables such as streamflow, soils, geology, air pollution, and land use history. Conversely, timber harvesting does not necessarily have measurable or biologically meaningful negative effects on water quality. Forestry BMP have proven effective in controlling adverse changes to in-stream sediment and water chemistry. Many studies that have reported large changes in water quality often represent extreme treatments not associated with typical forest operations, or they have not employed BMP. Properly and adequately used forestry BMP protect watershed resources while allowing the removal of wood products.

Assessing burn severity and comparing soil water repellency, Hayman Fire, Colorado

An important element of evaluating a large wildfire is to assess its effects on the soil in order to predict the potential watershed response. After the 55 000 ha Hayman Fire on the Colorado Front Range, 24 soil and vegetation variables were measured to determine the key variables that could be used for a rapid field assessment of burn severity. The percentage of exposed mineral soil and litter cover proved to be the best predictors of burn severity in this environment. Two burn severity classifications, one from a statistical classification tree and the other a Burned Area Emergency Response (BAER) burn severity map, were compared with measured ‘ground truth’ burn severity at 183 plots and were 56% and 69% accurate, respectively. This study also compared water repellency measurements made with the water drop penetration time (WDPT) test and a mini-disk infiltrometer (MDI) test. At the soil surface, the moderate and highly burned sites had the strongest water repellency, yet were not significantly different from each other. Areas burned at moderate severity had 1·5 times more plots that were strongly water repellent at the surface than the areas burned at high severity. However, the high severity plots most likely had a deeper water repellent layer that was not detected with our surface tests. The WDPT and MDI values had an overall correlation of r = −0·64(p < 0·0001) and appeared to be compatible methods for assessing soil water repellency in the field. Both tests represent point measurements of a soil characteristic that has large spatial variability; hence, results from both tests reflect that variability, accounting for much of the remaining variance. The MDI is easier to use, takes about 1 min to assess a strongly water repellent soil and provides two indicators of water repellency: the time to start of infiltration and a relative infiltration rate. Copyright © 2005 John Wiley & Sons, Ltd.

Seedbed variation from the interior through the edge of a large wildfire in Alberta

Despite the importance of seedbeds in the life histories of many plant species, there has been little study of the seedbeds created by wildfire in fire-prone vegetation types such as the boreal forest. Both within the interior and at the edge of a very large (&gt;100 000 ha) 2001 wildfire in the mixedwood boreal region of Alberta, we examined the postfire duff depth and the percent coverage of seedbed types. Minimizing the effect of site and forest composition, we looked only at Picea glauca (Moench) Voss – Populus tremuloides Michx. sites burned during a single day of high fire intensity. Good seedbeds (thin humus and exposed mineral soil, with or without ash) averaged 35% coverage within the interior of the fire but varied enormously among stands. There was a weak but significant positive correlation between prefire percent white spruce basal area and percent mineral soil exposure; that is, there is some tendency for conifer stands to create the seedbeds best suited for their own germinants. Fire severity played a clear role in mineral soil exposure, which was greatest in areas with 100% canopy mortality. Mineral soil exposure was far less at the edges of the fire, averaging only 5% even in areas where all trees had been killed; the burn edge was characterized by superficial flaming combustion with no evidence of substantial duff removal via smoldering combustion. In short, the areas where white spruce seed will be most common after the fire, the edges, are where the worst seedbeds in the burn will be found. Regeneration microsites at fire edges appear to be better suited to regeneration of broadleaf species, via suckering; the persistence of white spruce in fire-prone landscapes continues to be difficult to explain.

Effects of Light Gaps and Litter Removal on the Seedling Performance of Six African Timber Species1

ABSTRACTValuable timber tree species frequently show poor regeneration after selective logging in tropical forests. Small size of logging gaps, lack of soil disturbance, and limited seed availability have each been blamed for observed regeneration failures. We investigated seed germination and seedling performance using a split‐plot factorial design involving light availability and litter removal for six Central African timber tree species, hypothesizing that canopy gaps and litter removal would improve seedling establishment, and that less shade‐tolerant species would show stronger responses to both factors. Contrary to our expectations, significantly more germinants established on intact litter than on exposed mineral soil 3 mo after seeding. After 18 mo, seedling survival, height and diameter growth, leaf area, and rooting depth were all much higher in gap plots than in the understory for all species, with the exception of Gilbertiodendron dewevrei, a highly shade‐tolerant species whose survival was higher in the understory. Leaf production was negatively influenced by litter removal in the least shade‐tolerant species, Nauclea diderrichii, with weak or positive effects in other species. G. dewevrei, while displaying a low‐light threshold for growth, exhibited a surprisingly high growth response to increasing light comparable to more shade‐intolerant species, a response that may help explain its local competitive dominance in the region. Due to the rapid closure of small gaps, we suggest that shade‐intolerant species such as N. diderrichii, Khaya anthotheca, and Entandrophragma utile might benefit from more intensive silvicultural practices that create larger canopy gaps.