Bare Mineral Soil Research Articles

Assessing soil carbon dynamics following mechanical site preparation in boreal lichen woodlands of Québec, Canada

Soil scarification is a common soil mechanical preparation (MSP) method in forestry aimed to enhance the success of reforestation. However, by turning over and displacing the humus (forming a mound; M), and producing furrows of bare mineral soil (F), it is believed that this method has a substantial effect on soil C stocks. Here, we assessed the influence of this MSP on soil C stocks in two boreal lichen woodlands (LWs) in Québec, Canada, scarified ten and two years before sampling (2012 and 2020 sites, respectively).Carbon stocks averaged 11.8–15.4 kg C m−2 in the undisturbed section of the LWs (IF) with 9–15 % located in the vegetation, 36–42 % in the humus and 42–55 % in the mineral soil (0–30 cm). MSP caused a C concentration decline of ∼105 g C kg−1 in the displaced humus. Unexpectedly, this decrease was similar at both sites, suggesting that most C losses from this horizon occurred within two years. Higher C stock in the mineral horizons of the M than of the IF compartment at the 2012 site, suggests that a fraction of the C lost from the displaced humus may not have been released to the atmosphere but rather translocated to the underlying mineral soil. However, no such phenomenon was detected at the 2020 site, where a net C loss from the mineral soil was observed. Overall, the use of mass balance equations did not show evidence of net C losses at the scale of the whole profile in the disturbed sections of both LWs following MSP. This was partly due to site heterogeneity and a sampling bias, but also to mechanisms such as C translocation from the organic to the mineral soil horizons, and the replenishment of the soil C pool owing to natural regeneration occurring at the surface of the furrows. Overall, this study suggests that MSP may not have as strong an impact on soil C stocks as previously believed. Additionally, it highlights the challenges associated with estimating C changes in the soil following MSP and discusses ways to improve the assessment of C dynamics in such heterogeneous habitats.

Natural seeding as an alternative to planting in black spruce-lichen woodlands

Regeneration failures in the closed-crown boreal forest, which lead to the creation of open lichen woodlands, are expected to increase with climate change due to a rise in burn rates. Past studies have shown that it was possible to restore the productivity of those stands through planting. Since most lichen woodland stands are remotely located, afforestation through planting can be prohibitive. Therefore, the objective of this research was to measure the afforestation efficiency of lichen woodlands through scarification and natural seeding after clear-cutting. Our results showed that clear-cutting, when combined with scarification, promoted seedling establishment more strongly than clear-cutting alone. Scarification was also necessary for creating suitable microsites for germination, which were essentially bare mineral soil and decomposed organic matter. Last, seedling growth was higher in lichen woodlands when logging and scarification were combined, but lower than their counterpart feather moss stands. We conclude that afforestation of lichen woodlands in the closed-crown boreal forest is possible through natural seeding following scarification and could be a cost-effective option compared to planting.

Birch establishes anywhere! So, what is there to know about natural regeneration and direct seeding of birch?

We tested three soil scarification approaches of varying intensity (intensive preparation exposing bare mineral soil, medium intensity with a mixture of organic material and mineral soil, and control without site preparation) on six clear-felled sites in two localities in northern and central Sweden between 2018 and 2021. The effect of soil scarification intensity and soil moisture on the occurrence of naturally regenerated birch seedlings was tested one, two and three years after soil scarification, and the density of direct-seeded birch seedlings one year after seeding. In addition, we tested the effect of the annual seed rain, and differences between the two birch species, on the density of direct-seeded seedlings. Soil scarification and its interaction with soil moisture had a significant positive effect on both the occurrence of naturally regenerated birch seedlings and the density of direct-seeded birch seedlings. There was no significant effect of neither annual natural seed rain nor species choice on direct-seeded seedling density. Time since soil scarification had a significant effect on the occurrence of naturally regenerated birch seedlings. In moist soils with high volumetric water content (≥ 28%), birch seeds germinate at high rates and seedlings survive without soil scarification. In mesic soils, birch seeds germinate with higher rates after soil scarification. In dry soils, birch seeds rarely germinate regardless of any disturbance of the humus layer.

Effects of overstory tree density, site preparation, and ground vegetation on natural Scots pine seedling emergence and survival in northern boreal pine forests

Natural regeneration is a commonly used forest regeneration method in northern Finland. It is not known, however, what would be the optimal overstory density and ground vegetation composition for seedling emergence and survival, and if site preparation is needed to accompany overstory density manipulation. We studied the effects of overstory density (unthinned control and thinning to 50, 150, and 250 trees·ha−1) and ground vegetation removal (mechanical site preparation with disc trenching) on the number of naturally germinated pine seedlings and survival of individual seedlings over a period of 8 to 11 years. Bare mineral soil was a superior seedbed compared to intact vegetation cover, even though the mortality rate was high on mineral soil. Greater cover of lingonberry, crowberry, and slash had a negative effect on seedling number. Seedling mortality was initially high (60% died during the first 2 years) but decreased throughout the first 5 years. The survival rate of seedlings located in the mineral soil of the upper part of the disc trencher track was twice as high as that of seedlings located in the lower part of the track. High coverage of hair mosses (Polytrichum spp.) was associated with poorer seedling survival. An overstory density of 50–150 trees·ha−1 with site preparation seems to be an efficient treatment to promote regeneration under these circumstances.

Survival and growth of Scots pine (Pinus sylvestris) seedlings in north Sweden: effects of planting position and arginine phosphate addition

ABSTRACT Forest regeneration by tree planting on harvested sites in the boreal forests of northern Europe is frequently preceded by site preparation to increase survival and growth of the seedlings. We studied whether a small addition of arginine phosphate (AP treatment) at the time of planting would further enhance the seedlings’ early performance. Following two growth seasons, we investigated survival and growth of Scots pine (Pinus sylvestris) seedlings on 11 locations between latitudes 61.1°N and 67.1°N in the boreal forest of northern Sweden. The planting positions of seedlings were on capped mounds and bare mineral soil following mechanical site preparation, and in non-prepared soil. We found that seedling survival following site preparation increased with AP treatment. On capped mounds, seedling survival was more variable and appeared more dependent on precipitation during the first month after planting than seedlings positioned in the mineral soil. The positive effect of AP treatment on seedling growth differed between sites and was more pronounced on sites with longer growing seasons. AP treatment had no significant effect on survival of seedlings planted in non-prepared soil, while the positive effect on growth was more pronounced at sites with higher fertility using this planting position.

Processes driving understory community dynamics in Ulleungdo Island broadleaved forest, South Korea

AbstractThe development stage of forest trees has considerable impact on the understory plant species; however, little research has been dedicated to in‐depth investigation of the changes in the ecological processes (deterministic and stochastic) over a mid‐term observational period (≥10 years). We analyzed the forest floor environment, including bare mineral soil, tree communities (density and biomass), understory plant species composition, diversity, cover, and changes in co‐occurring species in the Albongbunji Basin on Ulleungdo Island over an 11‐year period (2009–2019). The forest floor environment exhibited a broad spectrum of changes, beginning in the middle of the observation period and after heavy rainfall, and heavy sediment deposition events were observed. The overstory tree density showed patterns of a general increase and subsequent decline, and the overstory tree biomass increased and then remained steady. The heavy rainfall and sediment deposition as disturbance events also coincided with changes in species composition and the turnover rate of the understory plant communities, causing changes in major ecological processes. The general pattern of species co‐occurrence (zeta diversity) was fitted to an exponential model, indicating the dominance of stochastic processes. The results show a shift in relative importance from deterministic to stochastic processes in the successional stages of understory plant community assembly over a mid‐term observational period.

Effects of Slope Gradient on Runoff and Sediment Yield on Machine-Induced Compacted Soil in Temperate Forests

There has been a severely negative impact on soil water resources in temperate forests caused by the introduction of the type of heavy machinery in the forestry sector used for forest harvesting operations. These soil disturbances increase the raindrop impact on bare mineral soil, decrease infiltration rate, detach soil particles, and enhance surface flow. According to several studies, the role of slope gradient influence on runoff and soil loss continues to be an issue, and therefore more study is needed in both laboratory simulations and field experiments. It is important to define and understand what the impacts of slope gradient in harvesting practices are, so as to develop guidelines for forest managers. More knowledge on the key factors that cause surface runoff and soil loss is important in order to limit any negative results from timber harvesting operations performed on hilly terrains in mountainous forests. A field setting using a runoff plot 2 m2 in size was installed to individualize the effects of different levels of slope gradient (i.e., 5, 10, 15, 20, 25, 30, 35, and 40%) on the surface runoff, runoff coefficient, and sediment yield on the skid trails under natural rainfall conditions. Runoff and sediment yield were measured with 46 rainfall events which occurred during the first year after machine traffic from 17 July 2015 to 11 July 2016 under natural conditions. According to Pearson correlation, runoff (r = 0.51), runoff coefficient (r = 0.55), and sediment yield (r = 0.51) were significantly correlated with slope gradient. Results show that runoff increased from 2.45 to 6.43 mm as slope gradient increased from 5 to 25%, reaching to the critical point of 25% for slope. Also, further increasing the slope gradient from 25 to 40% led to a gradual decrease of the runoff from 6.43 to 4.62 mm. Runoff coefficient was significantly higher under the plot with a slope gradient of 25% by 0.265, whereas runoff coefficient was lowest under the plot with a slope gradient of 5%. Results show that sediment yield increased by increasing the slope gradient of plot ranging 5% to 30%, reaching to the critical point of 30%, and then decreased as the slope gradient increased from 35% to 40%. Runoff plot with a slope gradient of 30% (4.08 g m−2) ≈ plot length of 25% (3.91 g m−2) had a significantly higher sediment yield, whereas sediment yield was lowest under the plot with a slope gradient of 5% and 10%. A regression analysis of rainfall and runoff showed that runoff responses to rainfall for plots with different slope gradients were linearly and significantly increased. According to the current results, log skidding operations should be planned in the skid trails with a slope gradient lower than the 25 to 30% to suppress the negative effect of skidding operations on runoff and sediment yield.

Post-fire regeneration of endangered limber pine (Pinus flexilis) at the northern extent of its range

Limber pine (Pinus flexilis), an understudied tree species important to montane and subalpine ecosystems, is listed as endangered in Alberta. Dispersal of seeds to newly disturbed, open areas by Clark’s nutcracker (Nucifraga columbiana) is expected to facilitate post-disturbance establishment of limber pine. Prescribed burning has thus been proposed as a tool to stimulate natural regeneration, but no studies have yet surveyed limber pine’s regenerative response to disturbance at the northernmost extent of its range. We examined post-fire regeneration in one prescribed burn and one wildfire at the northern edge of limber pine’s distribution and compared this to a regeneration baseline of plots in nearby unburned limber pine acting as seed sources to the burns. Using a likelihood-based approach, we then compared hypotheses of ecological processes influencing seedling occurrence and abundance. Overall, we found only six post-fire limber pine seedlings within the burns, as compared to one hundred twenty-four similarly aged seedlings found in unburned plots. Akaike information criterion (AIC) identified distance to a seed source and absence of canopy cover as hurdles for seedling establishment in the burn. Analysis of seedling abundance was performed on only the unburned dataset due to low regeneration in the burned areas surveyed; model selection here showed that when distance to a seed source is small, substrate variables, including less prevalent bare mineral soil, more rocky cover, and finer soil textures, take on an important role in driving abundance. Substrates important for limber pine abundance in unburned stands were found with similar frequency in the burns, indicating limber pine colonization post-disturbance was not substrate limited but instead constrained by other factors. Our findings suggest that extensive prescribed burns and stand-replacing wildfire events at the northern extent of limber pine’s range may have limited seedling regeneration in the immediate post-fire period. Conservation efforts may be well-served by focusing on fire mitigation efforts, such as thinning and other fuel treatments, in areas surrounding established limber pine stands. Finally, post-disturbance stands could benefit from supplementary seedling plantings to achieve recovery plan restoration goals for this endangered species.

Forest wildfire and 12 years of post-disturbance succession of saprotrophic macrofungi (Basidiomycota, Ascomycota)

Saprotrophic macrofungi are key decomposers of plant biomass in forests. These fungi form ecologically diverse group where different species specialize in specific substrates. Wildfires produce massive amounts of heterogeneous dead substrates. The postfire succession of saprotrophic fungi on these substrates may have major consequences on how carbon and nutrients are released back to forest ecosystems after a fire.We studied the effects of a wildfire (covering 143 ha) on saptroptrophic macrofungi (Basidiomycota and Ascomycota) in a Scots pine (Pinus sylvestris) dominated forest in eastern Finland during 12 years after the wildfire. In particular, we focused on the consequences that within-fire variation in fire severity had on fungal assemblages. Twenty-two permanent sample plots (10 × 10 m2 each) were monitored annually. Plots were located on sites with four different fire severity classes and on two unburned control sites. A total of 43 102 sporocarps of macrofungi were collected. Based on fungal life histories, we separated four different groups in the analyses: (1) wood-associated fungi on decayed wood, (2) decomposers of organic matter in soil or that live on bare mineral soil in forest floor, (3) biotrophic macrofungi that are associations between algae and fungi and that may also be symbiotic with mycorrhizae fungi, and (4) parasites on a living host plant or other fungi.In total, 219 species were observed. Fire severity affected species richness and composition, and fire always increased fungal diversity in comparison with unburned control sites. On the burned sites, species richness was highest on sites of medium burn severity (114 species in total, vs. 88–106 spp. on other burned sites). Substrate association of species was closely connected to assemblage dynamics: on soil and humus substrates, the succession of fire-associated pyrophilous species was rapid when compared to the succession of aphyllophoroid wood-associated macrofungi (AWAM). Pyrophilous and AWAM assemblages comprised many indicator species that occurred only ephemerally during the few years after the fire.In previous studies, AWAM assemblages often respond negatively to forest fires in short-term. Our results, however, show that if also other than AWAM macrofungi are included, there are several species typical for immediate post-fire habitats. The role that these species have on forest ecosystem and – for example – on carbon dynamics after a wildfire remains an important topic for future studies. From the conservation viewpoint, the finding emphasizes that post-fire young successional forests are important habitats for specialized and rare fungi.

Root system origin and structure influence planting shock of black spruce seedlings in boreal microsites

Planting shock can last for several years during which seedling growth may significantly slow down. This duration depends upon the time that is required for the root system to acclimatize to its new environment. We hypothesized that characteristics of the root system are important factors for black spruce (Picea mariana [Mill.] BSP) seedling establishment. To test this hypothesis, we compared growth and physiology of three stock types: containerized seedlings, with a dense initial root system restricted to the volume of a root plug; deeply planted containerized seedlings, with the stem buried during production to develop dense adventitious and initial root systems; and bareroot seedlings, with a less developed but unrestricted initial root system. The three stock types were planted on three microsites that are typical of reforestation sites found in eastern Canadian boreal forest: (1) bare mineral soil; (2) in presence of ericaceous shrubs; or (3) in presence of Sphagnum spp. and ericaceous species. Labelled nitrogen fertilizer was added to half of the seedlings to compare nitrogen uptake. We measured seedling growth (height, diameter, above- and belowground biomass), nutrition (including 15N uptake) and 13C discrimination (as an indicator of water stress) at the end of the second growing season. Except at the root level, there were few interactions between stock types and microsites. For fertilized microsites, we speculate that ericaceous species captured most added nutrients since seedlings that were planted directly on mineral soil had greater height and diameter increments than seedlings with competing vegetation. In unfertilized microsites, Sphagnum spp. and ericaceous species had significant negative effects on seedling growth. For stock type, the presence of a root plug allowed containerized and deeply planted seedlings to have a lower δ13C, suggesting less water stress compared to bareroot seedlings. Strong initial root system development of containerized seedlings resulted in greater total biomass. We hypothesized that the presence of adventitious roots in deeply planted seedlings positively influenced nutrient uptake, particularly N. As nutrient availability is one of the most limiting factors in the boreal forest, we suggest using deeply planted containerized seedlings to reduce planting stress.

Lichens Contribute to Open Woodland Stability in the Boreal Forest Through Detrimental Effects on Pine Growth and Root Ectomycorrhizal Development

In the boreal forest, open lichen woodlands have been described as an alternative stable state to closed-crown feather moss forest. In this study, we addressed the role of terricolous lichens in stabilizing open woodlands by hindering tree regeneration and/or growth. Based on field and greenhouse experiments, we compared germination and growth of jack pine (Pinus banksiana) on feather mosses (primarily Pleurozium schreberi) and lichens (primarily Cladonia stellaris), using bare mineral soil as a control. Drivers were investigated by (1) manipulating nutrient supply, (2) simulating shade of a closed canopy on the ground layer with the assumption this would mitigate lichen influence on pine growth, and (3) examining pine root ectomycorrhizal colonization and diversity as indicators of pine ability to take up nutrients. Total growth of 6-month-old greenhouse and 2–3-year-old field seedlings, as well as belowground growth of 2-year-old greenhouse seedlings, was significantly greater in moss than in lichen. Seed germination was not affected by ground cover type. Although field phosphorus and base cation availability was greater in mosses than in lichens, fertilization did not entirely compensate for the negative effects of lichens on pine growth in the greenhouse. Ground layer shading had no impact on pine growth. Lichens were associated with reduced abundance and modified composition of the root ectomycorrhizal community. By suggesting that terricolous lichens constitute a less favorable growth substrate than mosses for pine, our results support the hypothesis that lichens contribute to open woodland stability in the potentially closed-crown feather moss forest.

Local Seed Source Availability Limits Young Seedling Populations for Some Species More Than Other Factors in Northern Hardwood Forests

Light is generally regarded as the most important factor affecting tree regeneration in selection managed forests. For decades this paradigm guided forestry in the Great Lakes region, where small harvest gaps were used to promote shade-tolerant species. However, recent attempts to regenerate a more diverse forest community, by varying harvest gap size, have been less successful, bringing the predominance of light into question. Here, we investigate the influence of light availability along with local seed production potential [Σ(diameter2/distance2)] (SPP), substrate availability, site quality, and nontree vegetation (NTV) on 8 tree species' initial density and survival in 19 stands located throughout the Northern Lower and Eastern Upper Peninsula of Michigan. Larger-seeded, shade-tolerant to mid-tolerant sugar maple, red maple, and white ash seedlings were at least twice as abundant as those of any other species. Light availability was not a strong factor predicting seedling density, except for sugar maple, which showed a negative response to increasing light. In contrast, SPP had a strong positive influence on yellow birch, eastern hemlock, black cherry, and white ash seedling density, with evidence of local and regional seed source limitations. Substrate availability was an important factor influencing white pine and paper birch seedling density, as each species was significantly more abundant in plots dominated by bare mineral soil than in plots dominated by leaf litter. Collectively, these results suggest that from seed through two growing seasons, SPP and substrate availability can exert a stronger influence on seedling layer diversity than light availability created by harvest gaps.

Regeneration Niche of Whitebark Pine in the Canadian Rocky Mountains: The Basis to Restoring an Endangered Species

ABSTRACTKnowledge of regeneration processes of the endangered whitebark pine (Pinus albicaulis Engelm.) is critical for developing approaches for recovery and restoration of the species. We investigated biophysical associates of whitebark pine seedling occurrence and density in different mesohabitats (defined by community type and elevation) within the northern Rocky Mountains of Alberta. We developed candidate linear models to examine factors influencing occurrence and abundance. Occurrence was positively related to bare mineral soil and species richness in forest mesohabitats, while in both open and alpine-treeline environments it was positively related to prostrate shrub cover. Negative associates included tree cover, rocky substrates, and seedling cover of other conifers. Model validation showed a strong correlation between observed and predicted occurrence (correlations of 0.60, 0.56, and 0.56 for forest, open, and alpine-treeline mesohabitats, respectively). Climate models best predicted seedling density; abundance was highest on south-facing slopes in all mesohabitats. Correlations between observed and predicted density were 0.83, 0.92, and 0.72 for forest, open, and alpine-treeline mesohabitats, respectively. Our study identifies biophysical parameters to consider when planting blister rust—resistant seedlings and suggests that open mesohabitats along south-facing slopes may be best for regeneration of whitebark pine, particularly near the northern limits of its range.

Effects of stump harvest and site preparation on N2O and CH4 emissions from boreal forest soils after clear-cutting

Harvesting stumps after clear-cutting can increase bioenergy supplies and thus reduce needs for fossil fuels, but more knowledge is required about associated changes in greenhouse gas emissions from forest soils to assess the climatic impact of extracting stumps for this purpose. The soil disturbance caused by harvesting stumps may alter soil processes, including N mineralization. N availability is an important determinant of emissions of the potent greenhouse gases N2O and CH4. Effects of stump harvest on these gases are largely unknown. Therefore, they were explored in this study by monitoring differences in N2O and CH4 emissions associated with different types of disturbance during two years following stump harvest and site preparation (as well as their overall effects) at three mesic sites, using the chamber technique. N2O emissions at two of the sites were affected by the type of soil disturbance, but not at the other site. At one site, the N2O emissions were highest from undisturbed soil and mounds and significantly lower from mixed soil, bare mineral soil and wheel ruts. At this site the emission rates were clearly correlated with N availability across the disturbances. At the second site showing significant treatment effects, N2O emissions were higher from the bare mineral soil after site preparation than from other types of disturbed soil. At the third site there were no significant N2O emissions, possibly due to reductions in nitrogen availability caused by the fast establishment of vegetation at that site. The CH4 fluxes included both uptakes and losses, but were generally low following all types of soil disturbances, although they were substantial from wheel ruts and soil pits. In conclusion there were no, or minor, between-treatment differences in N2O and CH4 emissions. Furthermore, the radiative forcing potential of these emissions was small compared to mean CO2 emissions from Swedish clear-cuts. Thus, our results indicate that stumps can be harvested without causing elevated emissions of N2O and CH4 on mesic sites. The effects on wetter sites remain to be illuminated.

Finding balance between fire hazard reduction and erosion control in the Lake Tahoe Basin, California–Nevada

The 2007 Angora Fire served as a stark reminder of the need for fuel reduction treatments in the Lake Tahoe Basin, California–Nevada, USA. Concerns exist, however, that the corresponding removal of forest floor fuels could increase erosion rates, negatively affecting the clarity of Lake Tahoe. To quantify trade-offs between fuel reduction and erosion, we conducted field-based snowmelt runoff simulation experiments at 16 sites within the Lake Tahoe Basin that had received mechanical mastication or prescribed fire treatments. Erodibility was measured to determine if thresholds of litter, duff, and woody fuel cover could be established that are sufficient for trapping sediment and increasing infiltration, without contributing to fire hazard. Field snow-melt simulations revealed that as little as 25% of the ground surface covered with masticated fuels over duff was sufficient to mitigate erosion. The post-prescribed fire environment characterized by heterogeneous patches of exposed bare mineral soil interspersed with unburned patches mitigated erosion by increasing infiltration. Considerable increases in sediment yield were observed in plots with >35% of ground area burned; the highest total sediment yields (values) occurred in plots where between 66% and 100% of the soil surface burned. Our field results suggest that erosion and wildfire severity can be simultaneously mitigated through the use of masticated fuel reduction treatments or prescribed fire treatments that leave sufficient organic matter to trap sediment but have sufficiently low fuel loading and/or enough fuel discontinuity or patchiness to limit fire spread.

Fire reintroduction increased longleaf pine (Pinus palustris L.) recruitment and shifted pine demographics in a long-unburned xeric sandhill assemblage

Adaptive management methods are best for ensuring management goals are met when implementing prescribed fire to areas of fire exclusion. Prior to intense logging and subsequent fire suppression efforts of the early 1900s, longleaf pine (Pinus palustris) woodlands dominated the southeastern United States. As a pyrogenic forest type, natural wildfires occur with a 2–15year fire return interval. Remaining longleaf forests are predominantly second-growth, with current vegetation structure reflecting decades of fire exclusion resulting from continued suppression efforts. Research in longleaf savannas has demonstrated that hardwood encroachment, reduced floristic diversity, and reduced longleaf yearling establishment occurs in the absence of fire. However, few studies have examined the potential role of prescribed fire management in moderating longleaf pine regeneration in second-growth xeric sandhill assemblages. Over a seven year period of fire reintroduction, we examined the effects of prescribed fire on longleaf pine demographics and structure in a forest that experienced a significant reduction in fire frequency during the 20th century. We observed no difference in overstory composition or hardwood density between burned and adjacent unburned areas. Understory woody stem density (DBH<2cm) was dominated by juvenile longleaf plants, which likely caused greater variability in light reaching the forest floor in unburned vs. burned areas. Significant shifts in demographic structure were evident in juvenile longleaf plants that initiated height growth following the onset of prescribed fire treatments. Longleaf yearling density (<1year old) averaged 5plantsm−2 (unburned <1plantm−2) and was positively correlated with fire frequency. Greater accumulation of leaf litter in unburned (10cm) vs. burned areas (5cm) likely influenced yearling recruitment, as expected given the species’ need for contact with bare mineral soil for germination. Unlike pine savannas where reduction of hardwoods is often the target of management, intraspecific interactions (i.e. negative density dependence) likely play a greater role in successful longleaf recruitment and population demography in this sandhill assemblage. This study further highlights the utility of implementing and observing a range of fire applications when reintroducing fire to long unburned systems.

Bryophytes and their microhabitats in coniferous forest pastures: should they be considered in the pasture management?

Forest pastures, like many other semi-natural (traditional) rural biotopes, have undergone a drastic decline both in area and quality during the last century in many areas. We explored the bryophyte flora of Finnish coniferous forest pastures on acidic soil and aimed to recognize the most important microsites (rocks, coarse woody debris, tree bases, mineral soil patches and closed vegetation) for bryophyte diversity. The effects of microhabitat heterogeneity (microsite entropy) on bryophytes was also examined. We found altogether 83 bryophyte species. The only red-listed species, Tayloria tenuis, was frequently found on dung patches and a few rare ruderal species grew exclusively on bare mineral soil. Rocks comprised the most species rich microsite and many common forest floor species showed preference for this microsite. Microhabitat heterogeneity explained bryophyte species richness on both alpha (plot average) and gamma (pasture total) scales. The results suggest that certain individual bryophyte species and their microsites should be taken into account in the management of this biotope, rather than guiding the management solely on the basis of the overall bryophyte diversity.

Strategies for preventing invasive plant outbreaks after prescribed fire in ponderosa pine forest

Land managers use prescribed fire to return a vital process to fire-adapted ecosystems, restore forest structure from a state altered by long-term fire suppression, and reduce wildfire intensity. However, fire often produces favorable conditions for invasive plant species, particularly if it is intense enough to reveal bare mineral soil and open previously closed canopies. Understanding the environmental or fire characteristics that explain post-fire invasive plant abundance would aid managers in efficiently finding and quickly responding to fire-caused infestations. To that end, we used an information-theoretic model-selection approach to assess the relative importance of abiotic environmental characteristics (topoedaphic position, distance from roads), pre-and post-fire biotic environmental characteristics (forest structure, understory vegetation, fuel load), and prescribed fire severity (measured in four different ways) in explaining invasive plant cover in ponderosa pine forest in South Dakota’s Black Hills. Environmental characteristics (distance from roads and post-fire forest structure) alone provided the most explanation of variation (26%) in post-fire cover of Verbascum thapsus (common mullein), but a combination of surface fire severity and environmental characteristics (pre-fire forest structure and distance from roads) explained 36–39% of the variation in post-fire cover of Cirsium arvense (Canada thistle) and all invasives together. For four species and all invasives together, their pre-fire cover explained more variation (26–82%) in post-fire cover than environmental and fire characteristics did, suggesting one strategy for reducing post-fire invasive outbreaks may be to find and control invasives before the fire. Finding them may be difficult, however, since pre-fire environmental characteristics explained only 20% of variation in pre-fire total invasive cover, and less for individual species. Thus, moderating fire intensity or targeting areas of high severity for post-fire invasive control may be the most efficient means for reducing the chances of post-fire invasive plant outbreaks when conducting prescribed fires in this region.

Natural pest control in citrus as an ecosystem service: Integrating ecology, economics and management at the farm scale

While we were completing a year-long survey of soil invertebrates in eight citrus orchards in South Australia, there was an outbreak of Kelly’s citrus thrips (Pezothrips kellyanus). Four growers in our survey reported their orchards were free of thrips, while the others reported suffering serious economic damage. A retrospective analysis, using data from the invertebrate survey, showed that orchards without thrips damage all had dense ground cover (perennial grasses, diverse forbs and with a deep litter layer), whereas orchards with thrips damage all had patchy ground cover (bare mineral soil with scattered annual weeds or a sparse monoculture of lucerne or oats and no litter layer). Orchards with dense ground cover and no thrips damage had far denser populations of predatory mesostigmatid mites (mean 6471±692m−2 1 SE) compared with orchards with patchy ground cover and thrips damage (1097±126m−2). Most Mesostigmata (total 17 spp.) were generalist predators, capable of feeding on thrips larvae when they move from the fruit to the soil to pupate. We suggest the absence of thrips damage is causally related to the presence of a diverse, abundant fauna of natural enemies, enhanced by good quality ground cover habitat and that growers with no thrips damage are benefitting from the ecosystem service of natural pest control. Using three scenarios of increasing severity of thrips damage (10%, 20% and 40%), we estimated the mean value of natural pest control of thrips as an ecosystem service was A$ 2640, A$ 4610 and A$ 8540 per hectare for those orchards that benefited from the service, whereas those orchards that received no such benefit potentially lost A$ 1970, A$ 3260 and A$ 5850 respectively. Our findings led to the planting of improved ground cover as habitat for predators by three growers, and the development of a commercial predator biocontrol agent for thrips by a fourth, based on mites harvested from his orchard. Growers who had effective natural pest control of thrips are more likely to have greater economic resilience in relation to price volatility shocks than those growers who do not benefit from this ecosystem service.

Long-term effects of chaining treatments on vegetation structure in piñon–juniper woodlands of the Colorado Plateau

Over the last half-century a range of methods have been utilized to reduce trees and shrubs in order to reduce wildfire risk and promote herbaceous vegetation to support livestock and wildlife. We examined the long-term (20–40year) effects of past tree-reduction treatments on vegetation and ground cover in piñon–juniper woodlands, which is the third most extensive vegetation type in the continental United States. Tree-reduction treatments were conducted between 1963 and 1988 in Grand Staircase-Escalante National Monument, Utah by the US Bureau of Land Management and involved chaining followed by seeding to remove trees and often shrubs. Treatments were effective at increasing perennial grass cover and reducing tree cover over multiple decades. The increase in perennial grass cover was predominantly due to a nonnative species that was seeded, Agropyron cristatum (crested wheatgrass). Surface fuel loads were nearly twice as high in treated areas, likely changing fire behavior and increasing habitat complexity. Treated areas had higher bare mineral soil cover and lower biocrust cover, which may influence soil erosional processes. Interestingly, treated areas had significantly less Pinus edulis (piñon pine) recruitment compared to untreated areas, while there was no change in Juniperus osteosperma (Utah juniper) recruitment. These results indicate that treated areas may become more J. osteosperma dominated in the future due to increased establishment of J. osteosperma compared to P. edulis. Our results show that while treatments were effective at reducing tree cover and increasing herbaceous cover, there were long-term (40year) treatment effects on vegetation composition and ground cover that need to be taken under consideration when developing future management strategies.