Post-fire Sites Research Articles

Post-Pyrogenic Successions in Oak-Korean Pine Forests with Schisandra chinensis and Corylus mandshurica in Sikhote-Alin

This article discusses the results of long-term stationary studies of the formation and development of oak-cedar pine forests with magnolia berry and hazel growing in the Southern and Middle Sikhote-Alin. Considered here are the peculiarities of stands decline, seed-based reforestation, as well as the tree species growth and development courses during the process of reforestation successions in areas with different intensity of fire exposure. Following persistent ground fires, the stands decline is most intensive in the first 5 years, with decay rates and the number of surviving trees varying in different types of burnt areas. The most active seed-based reforestation occurs on post-fire sites mainly during the first 2 years, with birch, aspen and other early stage species predominating. The rate of annual growth of the young generation of trees is the most intensive on plots significantly damaged by fire, in serial species (birch, aspen, Maak’s bird cherry, etc.) they are an order of magnitude higher than in climax broadleaved and coniferous species. Determination of dominance indices, equally dependent on the numbers of undergrowth, thin and large trees, showed that during reforestation successions after both rapid and persistent lowland fires, the phytocenotic importance dynamics in Korean pine, Mongolian oak and other forest forming species has its own peculiarities.

Response of vulnerable karst forest ecosystems under different fire severities in the Northern Dinaric Karst mountains (Slovenia)

BackgroundThis study deals with wildfires in marginal areas of the Mediterranean climatic and biogeographical regions (Northern Mediterranean) where fires were not common. The aim of the research was to determine the differences in floristic composition and traits at different intensities of fire damage and to analyze the changes in forest ecosystems during the wildfires that took place in the summer of 2022. The study included both the zonal forests and non-native black pine (Pinus nigra) forests. Remote sensing techniques linked to the vegetation data sampled in the field during the 2023 vegetation season, the very first season after the fires, were also used in the fire assessment.ResultsThe study confirmed that satellite data analysis, orthophoto interpretation, and on-site vegetation sampling provide equivalent information on fire severity, opening up the possibility of transferring knowledge to similar post-fire sites without field sampling in the future. TWINSPAN classification analysis divided the sampled plots into clusters based on tree species prevalence and fire severity. The diagnostic species of the clusters were calculated using a fidelity measure. Ordination revealed that the first axis on the detrended correspondence analysis (DCA) correlated with wildfire severity. Ecological conditions and strategies, life forms, chorotypes, seed dispersal classes, and regeneration traits were analyzed along this gradient. We found that post-fire sites became warmer, drier, and lighter, which favored the growth of ruderal, theropytic, cosmopolitan, anemochorous and post-fire emergent species. After the fire, a “wave” of annual ruderal species was observed.ConclusionsThe results indicate that post-fire recovery can be left to natural processes without human intervention, except in the case of non-native pine stands where planting or seeding may be necessary. Otherwise, it is essential to control the possible occurrence of invasive species. Isolated adaptations of species to fire have also been observed, such as heat-stimulated germination. Such adaptations could develop in regions exposed to frequent fires and where fires act as an evolutionary factor.

Two new species of Achaeta (Enchytraeidae, Oligochaeta) from afforested post-mining and post-fire sites in Poland

Achaeta (Enchytraeidae, Oligochaeta, Clitellata) is a genus of small, soil-dwelling annelids, peculiar by the absence of chaetae in all species. Here two new species of this genus are described from afforestation sites in southern Poland. Descriptions are based on the investigation of living and preserved material. The species are also characterized at the DNA level, using fragments of the COI and ITS genes, sequenced from the holotypes and paratypes. The worms are not longer than 4–6 mm, with about 30 to 35 segments, and with medium-large male and female reproductive organs. Achaeta florens sp. nov., discovered at a post-mining site, has four segmental pyriform glands, an oesophageal appendage restricted to segment V, a clitellum with distinct transverse rows and dorsal and ventral interruption, and spermathecae with blossom-like fields of vesicular gland cell apices around the ventrally located ectal pores. The species is without peculiar characters but the combination of characters is diagnostic. Its morphological distinction from A. nurmineni, described from the Indian subcontinent, is difficult due to the poor description of that species; A. nurmineni is therefore considered a species inquirenda. Achaeta gemmata sp. nov., discovered in high abundance at a post-fire site, is without pyriform glands but with conspicuous, gem-like lateral papillae in all preclitellar segments. The papillae are modified and enlarged epidermal gland cells that protrude into the body cavity. The species is without oesophageal appendage and has a dorsally closed clitellum and lateral spermathecal pores. It is superficially similar to Achaeta camerani, found at the same site, but can be distinguished based on sexual and non-sexual characters. A comparison of COI sequences showed 100% identity with a specimen from Sweden, erroneously identified as A. cf. brevivasa. Genetic distance between the two new species based on COI differences is 20%, distances to other species of Achaeta with publicly available COI sequences range from 16% to 26%.

Meta-analysis shows the impacts of ecological restoration on greenhouse gas emissions

International initiatives set ambitious targets for ecological restoration, which is considered a promising greenhouse gas mitigation strategy. Here, we conduct a meta-analysis to quantify the impacts of ecological restoration on greenhouse gas emissions using a dataset compiled from 253 articles. Our findings reveal that forest and grassland restoration increase CH4 uptake by 90.0% and 30.8%, respectively, mainly due to changes in soil properties. Conversely, wetland restoration increases CH4 emissions by 544.4%, primarily attributable to elevated water table depth. Forest and grassland restoration have no significant effect on N2O emissions, while wetland restoration reduces N2O emissions by 68.6%. Wetland restoration enhances net CO2 uptake, and the transition from net CO2 sources to net sinks takes approximately 4 years following restoration. The net ecosystem CO2 exchange of the restored forests decreases with restoration age, and the transition from net CO2 sources to net sinks takes about 3-5 years for afforestation and reforestation sites, and 6-13 years for clear-cutting and post-fire sites. Overall, forest, grassland and wetland restoration decrease the global warming potentials by 327.7%, 157.7% and 62.0% compared with their paired control ecosystems, respectively. Our findings suggest that afforestation, reforestation, rewetting drained wetlands, and restoring degraded grasslands through grazing exclusion, reducing grazing intensity, or converting croplands to grasslands can effectively mitigate greenhouse gas emissions.

Impact of Native Quercus robur and Non-Native Quercus rubra on Soil Properties during Post-Fire Ecosystem Regeneration

Following disturbances, ecosystems are more susceptible to invasion by non-native species. Furthermore, it is important to determine the impact of alien tree species on soil regeneration processes during secondary succession. In this study, we analyzed the effect of native and late successional common oak (Quercus robur) and non-native red oak (Q. rubra) on soil physicochemical (pH, carbon, and nutrient content) and microbial properties (microbial biomass [Cmic] and respiration [RESP]) nearly 30 years after severe fire disturbance. Post-fire soils under Q. rubra had organic horizons with a greater mass, lower pH values, and depleted nutrient (N, Ca, K, Mg, and P) contents than soils under Q. robur. The impact of Q. robur as a late successional species on soil properties 30 years after a disturbance was similar to that of pioneer species (Scots pine, European larch, common birch, and black alder), as is indicated in previous studies. Most of the studied physicochemical (bulk density, soil organic carbon, N, Ca, K, and P content) and microbial (RESP and Cmic) soil parameters under Q. robur were within the ranges found for post-fire soils under pioneer tree species. Only the pH and Mg and Na contents in organic horizons were higher under Q. robur than under pioneer species. Our results indicate that Q. robur could be a valuable addition to reforestation sites after fire disturbance, especially in more fertile microhabitats. Due to the depletion of soil nutrients, care should be taken when introducing Q. rubra during the reforestation of post-fire sites, especially in larger groups.

Recovering of soil organic matter and associated C and N pools on regenerated forest ecosystems at different tree species influence on post-fire and reclaimed mine sites

Understanding the processes in soils after disturbances could be helpful in better designing restoration practices. The labile fraction of soil organic carbon (LSOC) plays a vital role in recovering soil properties and quality. This study compared labile C and N fractions, including microbial biomass C (MBC), cold-water-soluble C (WSC), water-soluble N (WSN), hot-water-extractable C (HWC), hot-water-extractable N (HWN), particulate organic carbon (POC), and particulate organic nitrogen (PON) in post-mining, post-fire, and undisturbed soils under different tree cover (Scots pine, common birch, and black alder). Nearly 30 years after the disturbance, post-mining soils were characterized by lower soil organic carbon (SOC) and total nitrogen (TN) as well as their labile fractions compared to those of post-fire and undisturbed soils. Disturbed soils had less stable SOC than undisturbed soils. Compared to the post-fire site, the higher proportion of WSC in SOC in post-mining soils suggests higher SOC turnover and leaching potential during primary succession compared to secondary succession. The post-fire soils had a similar SOC stock to undisturbed soils but differed in the C and N labile fractions stock. Post-fire soils were characterized by higher POC stocks due to charcoal admixture and lower WSN, HWC, and HWN fractions than undisturbed soils. The studied tree species differently affected the recovery of SOM properties after disturbances. Post-mining soils under alder had higher SOC, TN, and labile fractions (except MBC) than soils under birch and pine cover. However, this was not true for the post-fire site, where only WSN was higher under the alder. The soils under birch stands had the highest MBC stocks across all sites. The soils under pine had less stable SOM than those under birch and alder, which may accelerate podzolization processes. Results indicate a longer time for the recovery of C and N pools during primary succession than in secondary succession on sandy soils. Alder, as phytomelioration species that increases the C and N pools in post-fire sites, has limited usefulness.

Effects of Post-Fire Management on a Mediterranean Small Mammal Community

Wildfires simplify ecosystems, modifying the ecological niches of the fauna living in the recently burned areas. Small mammals respond rapidly to changes in habitat structure and composition after fire, but the effects of fire can be ameliorated by some management strategies (e.g., salvage logging). Hence, it is necessary to explore whether alternative management strategies may be able to return the ecosystem to its initial state. We studied the small mammal community by live trapping on eight plots under different post-fire treatments in Sant Llorenç del Munt i l’Obac Natural Park (Barcelona province, NE Spain). At the community level, an increase in overall relative abundance and species density was observed in the burned areas. Apodemus sylvaticus, the most abundant mammal in study area, used woody debris piles as a shelter against predators. Mus spretus was more abundant in post-fire sites with large open areas interspersed with woody debris piles. Crocidura russula steadily increased its presence in later successional stages when ground cover became more complex. Our results suggest that combining different management strategies may be appropriate to improve the habitat suitability and biodiversity of small mammals and other key open-land species throughout the burned area.

Fire Severity Controls Successional Pathways in a Fire-Affected Spruce Forest in Eastern Fennoscandia

Tree stand dynamics, changes in the ground vegetation and soils, and species diversity of wood-decaying fungi were studied in pristine middle boreal spruce forests affected by a surface fire in the Vodlozersky National Park (Arkhangelsk Region, Russia) in 2011. In the third year after the fire, the burnt area was dominated by birch, which contributed an average of 72% to the total amount of major tree species regeneration. In sites affected by a high-severity fire, the ground vegetation cover did not exceed 40%, with Chamaenerion angustifolium (L.) Scop. and Marchantia polymorpha L. dominating in the first years after. By the tenth year, the diversity of the newly forming tree layer increased from 5 to 11 species and natural thinning of deciduous tree regeneration was already underway, although its amount was still over 100,000 plants per hectare throughout. By the end of the first post-fire decade, Picea abies (L.) H. Karst. and Pinus sylvestris L. accounted for 11% of the total regeneration. The occurrence and cover of pyrogenic species Chamaenerion angustifolium and Marchantia polymorpha declined sharply at this stage. Vegetation in sites affected by mid-severity fire was mostly regenerating through propagation of the survivor Avenella flexuosa (L.) Drejer, Vaccinium myrtillus L., V. vitis-idaea, etc. In the burnt area, the species diversity of wood-destroying fungi was reduced compared to the adjacent unburned areas, and it was the same in both heavily and moderately burnt areas. This is probably due to the fact that the downed deadwood in post-fire sites was trunks of the same age and in the same degree of decay whereas the total amount of downed deadwood in the control (unburnt forest) was lower but featuring all stages of decay and, furthermore, there were plenty of fungi-populated dead standing and weakened overmature trees.

Динамика населения мелких млекопитающих пирогенных сообществ в степном бору

In 2008–2021 we studied small mammals annually using zoological ditches in the Tsasucheysky steppe pine forest (Zabaikalsky Region, Russia). Before the 2012 high-severity fire we captured small mammals in a typical pine forest, either old-growth or old-burnt sites, and after the 2012 fire—in sites of fresh primary and repeated burns as well as in survived areas. The undisturbed steppe pine forest was characterised by small numbers of mammals, dominated by Myodes rutilus. In the first-burnt sites mainly Cricetulus pseudogriseus individuals were captured during the first decade after the fire. This species also rapidly invaded the re-burnt sites; however, in the third or fourth year the small mammal community became polydominant. In the old post-fire area (more than 10 years after the fire) small mammals were most abundant and the community was more diverse. In the post-fire sites С. pseudogriseus, Lasiopodomys raddei, Sorex tundrensis and S. minutissimus were the most numerous; Alexandromys mongolicus was also common in the old burnt sites. The total number of small mammals decreased significantly only in the first year after the fire. The total abundance of small mammals in the sites of old and repeated burns was significantly higher than in the undisturbed pine forests and first burned areas. In parallel, the total numbers of small mammals in the pyrogenic and relevant preceding communities were not statistically different. The number of M. rutilus decreased and the number of C. pseudogriseus increased in the burns compared to the pine forest. Despite the changes in the composition and structure of the community, the fire led to no significant changes in the overall abundance of small mammals in the Tsasucheysky Pine Forest during the first following decade. Subsequently, when the burns became overgrown, the small mammal community became richer in both number of species and their abundance. This indicates the resilience of small mammal populations to fires in the forest-steppe and, thus, the stability of the food base for small mammal predator populations.

Do bird communities differ with post-fire age in

Prescribed fire is a widespread management practice in fire-prone ecosystems that can have significant effects on fauna. To inform the development of appropriate prescribed burning regimes, we explored bird responses to time since fire in threatened Banksia woodlands in south-western Australia. We used area searches to estimate bird densities on 20 plots ranging from 1 to 26 years post fire. Fire had no significant effect on the overall bird community or any foraging guilds and there was no clear post-fire succession. Of the 26 frequently occurring species analysed, only two showed responses to fire, with yellow-rumped thornbills more abundant in early and late post-fire sites and scarlet robins more abundant in either early, or early and late post-fire habitats. Our study suggested that bird communities in Banksia woodlands are quite adaptable to a range of prescribed burning regimes. However, owing to late-successional reptiles, Carnaby’s black cockatoo and mammals in Banksia woodlands, we recommend prescribed burning regimes that reduce early and increase late successional habitat. Phytophthora dieback, urbanisation and associated habitat fragmentation and a drying climate may have important synergistic effects and the role of these in structuring bird communities needs to be further considered in developing appropriate fire regimes.

Effect of tree species and soil texture on the carbon stock, macronutrient content, and physicochemical properties of regenerated postfire forest soils

AbstractMany countries are having increased frequency and severity of wildfires, including mega‐fires. The revegetation of postfire sites and tree species selection are the most important counteracting measures. In this study, we analyzed the effect of tree species (Scots pine, European larch, common birch) on the C stock, macronutrient content, and physicochemical parameters (pH, sorption complex properties) of regenerated soil of different textures (sands and loams) in a large, postfire site. Nearly, 30 years after the fire, soils differed among the species. The carbon stock under larch was higher in litter (Oi + Oe) horizons than under birch. In mineral horizons (0–5 cm), the C stock was highest under birch. Litter layers under birch had a higher pH, a lower C:N ratio, and higher N, P, Ca, and Mg content compared to layers under pine and larch. In the A‐horizons (0–5 cm), soils under birch was higher in soil organic carbon (SOC), cation exchange capacity (CEC), and acidity than soils under conifers. Soil texture in the studied range—from sands to loams—had only a limited effect on the properties of the studied postfire soils. Thus, our results indicate that the tree species used for the reforestation of postfire sites are crucial to the properties of regenerating soils and restoring the ecological functions of soils. Among the studied tree species, common birch had the most pronounced effect on soil properties, and this is especially significant because the species has appeared by spontaneous succession.

Species composition and richness of viable seed bank after fire events in Mount Ciremai National Park and Kuningan Botanic Gardens, West Java, Indonesia

Abstract. Ekasari I, Sadono R, Marsono D, Witono JR. 2021. Species composition and richness of viable seed bank after fire events in Mount Ciremai National Park and Kuningan Botanic Gardens, West Java, Indonesia. Biodiversitas 22: 3437-3447. Forest fire is an environmental disaster that can decline ecosystem function and restoration efforts must be considered to restore forest ecosystems after fire events. Natural regeneration using existing soil seed banks is a promising approach in restoration due to its advantage in terms of minimizing cost. This study aimed to examine the species composition and richness of germinable seed banks in several post-fire sites in Mount Ciremai National Park (MNCP) and Kuningan Botanic Gardens (KGB), West Java, Indonesia. One hundred fifty-eight soil samples were collected from the study sites representing fire events (i.e., four post-fire sites and one non-fire site), and soil depths (i.e., upper, middle, and lower). The collection of soil samples and identification of seedlings emergence were conducted from September 2019 to February 2020. Data were analyzed using ANOVA and correspondence analysis using SPSS Version 22. In total, 4626 emergence seedlings were recorded, belonging to 158 species and 58 families in which 41 families in the upper soil layer, 35 families in the middle soil layer, and 33 families in the lower soil layer. The results showed that Poaceae, Asteraceae, and Euphorbiaceae as the most dominant families. The upper soil layer of post-fire site 2018 had the highest species richness (R=11.98), while the lower soil layer of post-fire site 2012 had the lowest species richness (R=2.64). Our findings suggest that when carrying out restoration activities in post-fire areas, it is preferable to use native species that do not compete with species persisted in soil seed banks.

Soil factors determining the fine-root biomass in soil regeneration after a post-fire and soil reconstruction in reclaimed post-mining sites under different tree species

For this study, we analyzed the increase in fine root biomass under pine, birch, and larch (Pinus sylvestris, Betula pendula, and Larix decidua, respectively) plantings growing in regenerated (postfire sites) and reconstructed (reclaimed mine soils) forest ecosystems. The control sites were located in natural habitats on podzolic soils in managed forests of the Olkusz Forest District, Poland. The objective of the manuscript included determination of the chemical properties of soils that influence the biomass of fine roots of different tree species under the conditions of regenerated and reconstructed forest ecosystems. We found that there was no difference in the biomass of the fine roots of the studied species in the reconstructed forest system. The afforestation of forest ecosystems with birch may be particularly beneficial to environment because of its higher fine root biomass. Additionally, the fine root biomass increased with pH. Factors reducing the growth of fine root biomass were the availability of magnesium and the total soil carbon content. These results confirm the vulnerability of fine roots to site conditions and highlight the utility of fine root biomass evaluation when studying the dynamics and regeneration of soils.

Drivers of understory species richness in reconstructed boreal ecosystems: a structural equation modeling analysis

Understory vegetation accounts for the most diverse part of the plant community in boreal forests and plays a critical role in stand dynamics and ecosystem functions. However, the ecological processes that drive understory species diversity are poorly understood and largely unexplored for reconstructed boreal ecosystems. The current study explored the relationships between understory species richness and biotic and abiotic factors in sites reclaimed after oil sands mining in northern Alberta, Canada, three and six growing seasons post-reclamation. Reclaimed sites with two main surface soils, forest floor mineral soil mix (FFMM) and peat mineral soil mix (PMM), were used along with post-fire benchmarks. A number of soil physicochemical (including nutrients) and vegetation properties were measured and considered in the a-priori hypothesis framework. Structural equation models (SEM) were used to evaluate the multivariate relationships. In general, the FFMM sites had greater species richness than the PMM sites, even six growing seasons after reclamation. A maximum 254% increase in graminoid and shrub cover was observed on FFMM between year 3 and 6 post-reclamation, whereas a maximum 137% increase in forb and bryophyte cover was recorded on PMM. The post-fire sites showed a significant increase (70%) only in shrub cover. Major driving factors of understory species richness varied among soil types. The SEM revealed a strong interdependency between species richness and soil and vegetation factors on FFMM with a positive control from soil N on species richness. In contrast, on PMM soil nutrients had a negative effect on species richness. Temporal changes in the drivers of species richness were mostly observed on FFMM through a negative vegetation control on species richness. The models and significant causal paths can be used in monitoring changes in understory species relationships in reclaimed sites and in identifying future research priorities in similar systems.

The Accessibility of Post-Fire Areas for Mechanized Thinning Operations

In 1992, in Southern Poland, large areas of Silesian forests were affected by the country’s largest forest fire. Stands introduced in the 9000-ha post-fire region are currently undergoing early thinning. Due to the scope of these treatments, the chance for their timely implementation is ensured only by the application of cut-to-length (CTL) technologies, i.e., with the use of harvesters and forwarders. The use of CTL technologies may, however, be difficult due to the fire history of these stands, which could affect the bearing capacity of their soils. The objective of this study is to determine the accessibility of stands for forest machines in relation to the bearing capacity of the soils and changes in soil compaction in the post-fire sites. Soil compaction was measured in terms of penetrometer resistance in the stands introduced in the post-fire area in question, as well as in control stands growing on five different soil types. It was shown that in the topsoil layer—from 8 to 18 cm thick depending on the soil type—differences in soil compaction in the post-fire and control areas were relatively small. The impacts of the forest fire—manifested as a significant increase in the compaction of the forest soils—were still visible, but only in the deeper layers of the soil profile. In all of the compared pairs of forest compartments located in the stands regenerated after the fire, significantly higher values of cone indexes (CI) were found. The average value of this index in the post-fire stands was 2.15 MPa, while in the control stands it was 1.60 MPa, which indicates that in both groups of stands the bearing capacity of the soils should not limit the accessibility for vehicles used for timber harvesting and extraction.

Monitoring of post-fire forest scars in Serbia based on satellite Sentinel-2 data

This study aims to improving long-term post-fire environment assessment. It proposes a method for monitoring fire impact using Sentinel-2 satellite data by combining spectral and textural features of land cover types inside a post-fire study sites. Specific objectives were to 1) test stability of the burnt area index for Sentinel-2 (BAIS2) for identification of burn in study sites, 2) investigate the optimal feature combination for mapping land covers inside study sites, and 3) assess and analyse dynamic in land covers of study sites. BAIS2 was shown independent on date acquisition of satellite images to distinguish forest burn from other land covers over the analysed May–September vegetation period. Texture of study site improved the classification results. The most accurate classification method for identification of study sites land covers (with 0.84 Kappa coefficient and 0.86 overall accuracy) was based on combination of Sentinel-2 bands, BAIS2, and texture by Fourier transform. Analysis of vegetation recovery within the study sites demonstrated different recovery rates. Natural regeneration of pine was not observed, during three to six years of observations following fire events. The proposed method and findings can support planning of forest management measures needed to effectively restore forest cover.

Postfire Effects in Siberian Larch Stands on Multispectral Satellite Data

This work considers the dynamics of vegetation indices and surface temperature of postfire areas of different ages in larch forests of the permafrost zone of Siberia obtained using long-term Terra/MODIS satellite imagery. Landsat/ETM and OLI satellite images were preliminarily classified to analyze the degree of pyrogenic disturbance in the sample of postfire sites. An increase in the average temperature of the underlying surface of the postpyrogenic areas by 3.9–4.6°C was recorded, depending on the degree of disturbance of the litter, which is 15–30% of the average background values. Compared with background values, the deviation (decrease) in the next postfire year was 22% for the NDVI and 72% for the NBR index. Recovery of the NDVI to background values required 7–10 years after the fire. The recovery period for the surface temperature and the NBR index are significantly higher, that is, 15 years and more. Moreover, for 15–20 years after the fire, the temperature anomalies of the underlying surface remain significant.

Impact of wildfire on 137Cs and 90Sr wash-off in heavily contaminated forests in the Chernobyl exclusion zone

Wildfires may play a role in redistributing radionuclides in the environment in combination with hydrological processes such as surface runoff and soil erosion. We investigated plot-scale radionuclide wash-off at forest sites affected by wildfires in the Chernobyl Exclusion Zone (CEZ). We also compared speciation of the washed-off radionuclides with those in previous studies conducted just after the accident in 1986. We observed the surface runoff and the radionuclide wash-off with a soil erosion plot at forest and post-fire sites during May–September 2018. In the post-fire site, 2.81 mm of surface runoff was observed in at least three flow events resulting from 285.8 mm total rainfall. The fluxes of dissolved and particulate 137Cs were estimated as 4.9 and 161 Bq m−2, respectively. The dissolved phase 90Sr flux was estimated as 214 Bq m−2. At the forest site, a single surface runoff (0.67 mm) event was generated by rainfall of 182.2 mm. The fluxes of dissolved and particulate 137Cs wash-off values were 6.2 and 8.6 Bq m−2, respectively. The flux of dissolved 90Sr wash-off from the forest was estimated as 45.1 Bq m−2. The distribution coefficient, which indicates the dissolved-particulate form of radionuclides, in the post-fire site was 30 times higher than that in the forest site, indicating the importance of particulate 137Cs wash-off after fire in the CEZ. The entrainment coefficients for dissolved and particulate 137Cs concentrations were around 50 times lower than those obtained in the corresponding position within the CEZ immediately after the accident in 1987. The effect of downward migration of 137Cs over 30 years led to decreased entrainment coefficients for dissolved and particulate 137Cs. The effect of downward migration of radionuclides was considered sufficient to indicate changes in normalized liquid and solid radionuclides wash-off entrainment coefficient and the distribution coefficient in this study.

Effects of invasive plants on fire regimes and postfire vegetation diversity in an arid ecosystem.

We assessed the impacts of co‐occurring invasive plant species on fire regimes and postfire native communities in the Mojave Desert, western USA. We analyzed the distribution and co‐occurrence patterns of three invasive annual grasses (Bromus rubens, Bromus tectorum, and Schismus spp.) known to alter fuel conditions and community structure, and an invasive forb (Erodium cicutarium) which dominates postfire sites. We developed species distribution models (SDMs) for each of the four taxa and analyzed field plot data to assess the relationship between invasives and fire frequency, years postfire, and the impacts on postfire native herbaceous diversity. Most of the Mojave Desert is highly suitable for at least one of the four invasive species, and 76% of the ecoregion is predicted to have high or very high suitability for the joint occurrence of B. rubens and B. tectorum and 42% high or very high suitability for the joint occurrence of the two Bromus species and E. cicutarium. Analysis of cover from plot data indicated two or more of the species occurred in 77% of the plots, with their cover doubling with each additional species. We found invasive cover in burned plots increased for the first 20 years postfire and recorded two to five times more cover in burned than unburned plots. Analysis also indicated that native species diversity and evenness as negatively associated with higher levels of relative cover of the four invasive taxa. Our findings revealed overlapping distributions of the four invasives; a strong relationship between the invasives and fire frequency; and significant negative impacts of invasives on native herbaceous diversity in the Mojave. This suggests predicting the distributions of co‐occurring invasive species, especially transformer species, will provide a better understanding of where native‐dominated communities are most vulnerable to transformations following fire or other disturbances.

Moisture content variations in soil and plant of post-fire regenerating forests in central Yunnan Plateau, Southwest China

Plant moisture content (PMC) is used as an indicator of forest flammability, which is assumed to be affected by climate drought. However, the fire-induced drought stress on PMC and its spatial and temporal variations are unclear. Based on a parallel monitoring experiment from 2014 to 2015, this study compared the PMCs and soil moisture contents (SMC) at five post-fire sites in central Yunnan Plateau, Southwest China. The number of years since last fire (YSF), season, topographic position, plant species and tissue type (leaf and branch) were selected as causal factors of the variations in PMC and SMC. A whole year parallel monitoring and sampling in the post-fire communities of 1, 2, 5, 11 and 30 YSF indicated that drought stress in surface soils was the strongest in spring within the first 5 years after burning, and the SMC was regulated by topography, with 64.6% variation in soil moisture accounted for by YSF (25.7%), slope position (22.1%) and season (10.8%). The temporal variations of PMC and SMC differed at both interannual and seasonal scales, but the patterns were consistent across topographic positions. PMC differed significantly between leaves and branches, and among three growth-forms. The mean PMC was lower in broad-leaved evergreen species and higher in conifer species. Season and soil temperature were the primary determinants of PMC, accounting for 19.1% and 8.3% of variation in PMC, respectively. This indicated phenology-related growth rather than drought stress in soil as the primary driver of seasonal changes in PMC. The significant variations of PMC among growth forms and species revealed that seasonal soil temperature change and dominant species in forest communities are useful indicators of fire risk assessment in this region.