Ice storm damage to oak forests in subtropical China

Ice storms,as important sources of frequent and injurious disturbances,drive forest dynamics in the Northern Hemisphere.However,stand-level differential vulnerability to ice storms and the associated factors that predispose forest stands remain unclear.This is particularly concerning in the subtropics where the frequency of ice storms is predicted to increase with global warming.Here we assessed how the impact on three forest stands(early and late secondary-growth forests,and old-growth forests)differed after an extreme ice storm during 20–21 March 2022,and identified the abiotic and biotic factors that determine the damage intensity in the Shennongjia World Natural Heritage Site,a biodiversity conservation hotspot in central China.We found a stand-specific‘middomain effect’where the late secondary-growth forest sustained the most severe damage,the early secondarygrowth forest sustained the least,and the old-growth forest suffered an intermediate amount.‘Crown broken’was the most severe damage type across all three forest stands,although the proportion of‘branch broken’was also high in the old-growth forest.Topography played a significant role in determining the vulnerability of the early secondary-growth forest to severe ice storms whereas the forest structure and composition were important factors in explaining the damage rates in the old-growth forest,although they differed among the damage categories.In contrast,topography,forest structure and composition generally explain the intensity of damage in the late secondary-growth forests.Our results highlight that,in subtropical forests,the intensity of damage caused by severe ice storms and related determining factors are stand-level dependent.We also suggest exploring potential management strategies(e.g.,slow-growing hardwood species that can resist storms should be the main species for reforestation in early secondary-growth forests)to mitigate the risk of future severe ice storms,as well as other wind-related climatic extremes.

Effect of competition on spatial patterns of oak forests on the Chinese Loess Plateau

Reforestation or natural forest regeneration is an alternative measure for controlling soil erosion in degraded land on the Chinese Loess Plateau（CLP）. However, our understanding of the temporal dynamics and the spatial patterns of forest regeneration remains inadequate. Two oak forests at different development stages were investigated to determine the spatial patterns of competitions（intraspecies and interspecies） during different successional stages. The intraspecies and interspecies spatial relationships among different tree diameters at breast height were analyzed at multiple scales by Kriging interpolation method and univariate and bivariate O-ring statistics. Our analytical results indicated that self-correlation and competition intensity were relatively high between oak and pine trees in the early development stage of oak forests due to their clumped distributions of heavy seeds. Birch trees had a lower competition in comparison to oak trees although birch was the dominant species. Therefore, asymmetric competition of oak trees was most likely to have led to their edge dispersal and their success in replacing the pioneer species. Asymmetric competition means that larger individuals obtained a disproportionately large share of the resources and suppressed the growth of smaller individuals. Kriging interpolation analysis showed a tendency towards homogenization caused by interspecies competition during the succession of oak forests. Our results demonstrated that the competition was the driving factor in the spatial distribution of oak forests on the CLP.

Effect of land-use changes on chemical and physical properties of soil in western Iran(Zagros oak forests)

The consequence of land-use change from forest to agriculture and other uses has become one of the world’s greatest concerns.The soil,one of the most important components of forests and containing all the required plant nutrients as soluble ions,is highly impacted by these changes.Because vast areas of the Zagros forests in western Iran have changed in use during the last few decades,the present study investigated the effects of landuse changes of forest area to agriculture,orchard,and agroforestry on soil chemical and physical properties.Soil was sampled at four land-use areas:less-disturbed forest areas(control)and agricultural,orchard,and agroforestry areas.Among each of the two forest-use areas(agroforestry and orchard),we selected five trees with similar-sized crowns and sampled under each tree crown at 0-15 and>15-30 cm depths.Five soil samples also were taken in agriculture area at each depth.The findings indicated that during land-use changes,soil sand particles decreased,and clay and silt particles of soil increased,resulting in a fine soil texture.Moreover,the amount of nitrogen(N),phosphorus(P),organic carbon(OC),and electrical conductivity(EC)of soil decreased at both depths due to the decrease in organic matter.Soil pH and magnesium(Mg)level rose during land-use change at both depths except at agricultural sites.Soil potassium(K)content decreased during agricultural use due to the elimination of tree cover.The level of K decreased only at the depth of 0-15 cm because of K dependency on parent materials.Generally,most soil nutrients were affected by plant removal in the conversion.Forest and agricultural soil are distinguishable by their properties,while land-uses such as agroforestry-orchard separated from the others.Soil nutrients were severely affected by the decrease and elimination of tree cover,plowing,and continuous harvesting,resulting in a decline in soil quality and fertility.

Assessment of Cork Oak Decline Using Digital Multispectral Imagery in Relation with in Situ Crown Condition

Cork oak in Maamora forest is experiencing the dieback phenomenon. The evaluation of the latter in this forest has gained the importance over time and with the solicitation of managers to objectify its phytosanitary situation. Aiming at prioritizing management actions, remote sensing seems to be an effective tool to inquire about stands’ health conditions and their evolution. To this end, this study aims at mapping and validating health status of cork oak stands in Maamora. Sentinel 2 images in 2015 and 2020 were processed to calculate the differential normalized difference water index (NDWI), revealing vegetation moisture variation caused by drought. A statistical method based on thresholds was used to map cork oak dieback stands, those with no changes and those recovered. Results have shown that 54.63% of cork oak in Maamora forest have not changed in terms of phytosanitary situation between 2015 and 2020, 31.10% of oak stands are afflicted by a slight decline and 12.97% by a severe decline. Areas with slight or strong recovery remain minimal and represent 1.04% and 0.25% respectively. Ground data indicated that the map generated displayed a good distinction between stands severely and slightly declined with a global accuracy of 66.66%. Therefore, further research elaborating an advanced vegetation index reflecting the various factors of dieback would be of much importance.

Analysis of soil moisture variation by forest cover structure in lower western Himalayas, India

Soil moisture affects various hydrological processes, including evapotranspiration, infiltration, and runoff. Forested areas in the lower western Himalaya in India constitute the headwater catchments for many hill streams and have experienced degradation in forest cover due to grazing, deforestation and other human activities. This change in forest cover is likely to alter the soil moisture regime and, consequently, flow regimes in streams. The effect of change in forest cover on soil moisture regimes of this dry region has not been studied through long term field observations. We monitored soil matric potentials in two small watersheds in the lower western Himalaya of India. The watersheds consisted of homogeneous land covers of moderately dense oak forest and moderately degraded mixed oak forest. Observations were recorded at three sites at three depths in each watershed at fortnightly intervals for a period of three years. The soil moisture contents derived from soil potential measurements were analyzed to understand the spatial, temporal and profile variations under the two structures of forest cover. The analysis revealed large variations in soil moisture storage at different sites and depths and also during different seasons in each watershed. Mean soil moisture storage during monsoon, winter and summer seasons was higher under dense forest than under degraded forest. Highest soil moisture content occurred at shallow soil profiles, decreasing with depth in both watersheds. A high positive correlation was found between tree density and soil moisture content. Mean soil moisture content over the entire study period was higher under dense forest than under degraded forest. This indicated a potential for soil water storage under well managed oak forest. Because soil water storage is vital for sustenance of low flows, attention is needed on the management of oak forests in the Himalayan region.

Effect of forest fire on soil microbial biomass and enzymatic activity in oak and pine forests of Uttarakhand Himalaya, India

Background:Forest fire incidences in the Himalayan region of Uttarakhand,India are very common in summers.Pine and oak are the principal and dominant species of Himalayan subtropical forest and Himalayan temperate forest,respectively.Forest vegetation influences the physicochemical and biological properties of soil and forest fire in pine and oak forests may have a different effect on the physicochemical and biological properties of soil.Therefore,the present study was carried out to assess the impact of forest fire on soil microbial properties,enzymatic activity,and their relationship with soil physicochemical properties in the advent of forest fire in the pine and oak forests of the Garhwal region of Uttarakhand Himalaya,India.Results:The soil microbial biomass carbon and nitrogen,soil basal respiration,and acid phosphatase activity decreased,whereas dehydrogenase activity increased at burnt sites of both forest types.The overall change in soil microbial biomass carbon was 63 and 40%at the burnt oak forest and burnt pine forest,respectively.Dehydrogenase activity and acid phosphatase activity showed a strong positive correlation with soil organic matter(r=0.8)and microbial indices,respectively.The ratio of soil microbial biomass carbon/nitrogen was reduced at burnt sites of both forest types.Factor analysis results showed that fire had a significant impact on soil characteristics.The soil basal respiration was linked with macro-and micronutrients at burnt sites,whereas at control sites,it was linked with physicochemical properties of soil along with nutrients.Conclusion:Forest fire had a significant impact on soil properties of both forest types.The impact of forest fire on soil microbial biomass carbon was stronger in the oak forest than in the pine forest.Forest type influenced soil enzymatic activity at burnt sites.The bacterial community was dominated over fungi in burnt sites of both forests.Soil microbial indices can be used as a selective measure to assess the impact of fire.Furthermore,forest type plays an important role in regulating the impact of forest fire on soil properties.

Scleroderma nastii sp.nov.,a gasteroid mushroom from Phulchoki hill,Nepal

A new species of Scleroderma is described from temperate Oak forest of Phulchoki hill,at the highest peak(2,762 m)ringing the Kathmandu valley,Nepal.Smooth to velvety,pseudostipitate basidiome,smaller and sub-reticulate basidiospores in comparison to its close relatives,are key diagnostic features of this newly discovered mushroom.The novelty of the taxon was also confirmed based on phylogenetic analysis using the data sets of the internal transcribed spacer region(ITS)of nuclear rDNA sequences along with the analysis of scanning electron micrographs of its basidiospores.A comprehensive description,illustrations,and comparisons with phenetically similar species are provided in this study.Additional surveys are needed to verify the species diversity and clarify their geographic distribution.

Variations in leaf litter decomposition across contrasting forest stands and controlling factors at local scale

Aims litter decomposition is a critical pathway linking the above-and belowground processes.However,factors underlying the local spatial variations in forest litter decomposition are still not fully addressed.We investigated leaf litter decomposition across con-trasting forest stands in central China,with objective to determine the spatial variations and controlling factors in forest floor leaf lit-ter decomposition in relation to changes in forest stands in a tem-perate forest ecosystem.Methods leaf litter decomposition was studied by using litterbag method across several typical forest stand types in baotianman Nature reserve,central China,including pure stands of Quercus aliena var.acuteserrata,Q.glandulifera var.brevipetiolata and Q.vari-abilis,respectively,and mixed pine/oak stands dominated by Pinus armandii and Q.aliena var.acuteserrata,as well as stands of pure Q.aliena var.acuteserrata trees ranging in stand age from~40 to>160 years.measurements were made on litter mass remaining and changes in litter chemistry during decomposition over a 2-year period,along with data collections on selective biotic and environmental factors.a reciprocal transplant experiment involv-ing Q.aliena var.acuteserrata and Q.variabilis was concurrently carried out to test the occurrence of‘home-field advantage(HFa)’in local forests when only considering contrasting oak tree spe-cies.Correlation analyses and path analyses were performed to identify the dominant drivers and their relative contributions to variations in leaf litter decomposition.Important findingssignificant variations were found in the rate of leaf litter decomposi-tion among stands of different tree species but not among stand age classes.The values of decay constant,k,varied from 0.62 in Q.aliena var.acuteserrata stands to 0.56 in Q.variabilis stands.The reciprocal litter transplant experiment showed that the rate of leaf litter decom-position was on average 5%slower in home-fields than on recipro-cal sites.Path analysis identified litter acid-unhydrolyzable residue(AUR)to N ratio,soil microbial biomass carbon(MBC),soil pH and soil organic carbon(SOC)as most prominent factors controlling the rate of leaf litter decomposition,collectively accounting for 57.8%of the variations;AUR/N had the greatest negative effect on k value,followed by weaker positive effects of SOC and MBC.our findings suggest that tree species plays a primary role in affecting forest floor leaf litter decomposition by determining the litter quality,with site environment being a secondary factor contributing to the local vari-ations in leaf litter decomposition in this temperate forest ecosystem.