A review of the effects of forest fire on soil properties

Forest fires are key ecosystem modifiers affecting the biological,chemical,and physical attributes of forest soils.The extent of soil disturbance by fire is largely dependent on fire intensity,duration and recurrence,fuel load,and soil characteristics.The impact on soil properties is intricate,yielding different results based on these factors.This paper reviews research investigating the effects of wildfire and prescribed fire on the biological and physico-chemical attributes of forest soils and provides a summary of current knowledge associated with the benefits and disadvantages of such fires.Low-intensity fires with ash deposition on soil surfaces cause changes in soil chemistry,including increase in available nutrients and pH.High intensity fires are noted for the complete combustion of organic matter and result in severe negative impacts on forest soils.High intensity fires result in nutrient volatilization,the break down in soil aggregate stability,an increase soil bulk density,an increase in the hydrophobicity of soil particles leading to decreased water infiltration with increased erosion and destroy soil biota.High soil heating(> 120℃) from high-intensity forest fires is detrimental to the soil ecosystem,especially its physical and biological properties.In this regard,the use of prescribed burning as a management tool to reduce the fuel load is highly recommended due to its low intensity and limited soil heating.Furthermore,the use of prescribed fires to manage fuel loads is critically needed in the light of current global warming as it will help prevent increased wildfire incidences.This review provides information on the impact of forest fires on soil properties,a key feature in the maintenance of healthy ecosystems.In addition,the review should prompt comprehensive soil and forest management regimes to limit soil disturbance and restore fire-disturbed soil ecosystems.

Study on Soil Nutrient Fertility of Cultivated Land in Laos

[Objectives] This study was conducted to explore the differences in soil nutrient contents of cultivated land in different regions of Laos,and to provide a basis for soil nutrient management and scientific fertilization in Laos. [Methods] By collecting 166 samples of the 0-20 cm cultivated soil layer from farmland in the farming areas of Luang Namtha Province in the northern part of Laos and Vientiane Province in the middle of the country,the contents of soil organic matter,total nitrogen,available phosphorus,available potassium,available calcium and available magnesium were analyzed,so as to evaluate the current status of soil nutrient fertility and explore the differences in soil nutrient contents of regional cultivated land. [Results] The soil organic matter was relatively abundant,the total nitrogen and available potassium contents were at the lower-middle level,and the available phosphorus,available calcium and available magnesium were insufficient or extremely insufficient. The soil nutrient contents of cultivated land were different in different regions. [Conclusions] It is suggested that lime or other alkaline fertilizers should be applied on the farmland with acid soil,and nitrogen,phosphorus,and potassium fertilizers should be added at the same time to improve soil nutrient fertility.

Leaf nutrient dynamics and nutrient resorption:a comparison between larch plantations and adjacent secondary forests in Northeast China

Aims Conversion of secondary forests to pure larch plantations is a common management practice driven by the increasing demand for timber production in Northeast China,resulting in a reduction in soil nutrient availability after a certain number of years following conversion.Nutrient resorption prior to leaf senescence was related to soil fertility,an important nutrient conservation strategy for plants,being especially significant in nutrient-poor habitats.However,the seasonal dynamics of leaf nutrients and nutrient resorption in response to secondary forest conversion to larch plantations is not well understood.Methods A comparative experiment between larch plantations(Larix spp.)and adjacent secondary forests(dominant tree species including Quercus mongolica,Acer mono,Juglans mandshurica and Fraxinus rhynchophylla)was conducted.We examined the variations in leaf nutrient(macronutrients:N,P,K,Ca and Mg;micronutrients:Cu and Zn)concentrations of these tree species during the growing season from May to October in 2013.Nutrient resorption efficiency and proficiency were compared between Larix spp.and the broadleaved species in the secondary forests.Important Findings Results show that the seasonal variation of nutrient concentrations in leaves generally exhibited two trends,one was a downward trend for N,P,K,Cu and Zn,and another was an upward trend for Ca and Mg.The variations in foliar nutrient concentrations were mainly controlled by the developmental stage of leaves rather than by tree species.Resorption of the observed seven elements varied among the five tree species during leaf senescence.Nutrient resorption efficiency varied 6–75%of N,P,K,Mg,Cu and Zn,while Ca was not retranslocated in the senescing leaves of all species,and Mg was not retranslocated in Larix spp.Generally,Larix spp.tended to be more efficient and proficient(higher than 6–30%and 2–271%of nutrient resorption efficiency and resorption proficiency,respectively)in resorbing nutrients than the broadleaved species in the secondary forests,indicating that larch plantations had higher leaf nutrient resorption and thus nutrient use efficiency.Compared with Larix spp.,more nutrients would remain in the leaf litter of the secondary forests,indicating an advantage of secondary forests in sustaining soil fertility.In contrast,the larch plantation would reuse internal nutrients rather than lose nutrients with litter fall and thus produce a positive feedback to soil nutrient availability.In summary,our results suggest that conversion from secondary forests to pure larch plantations would alter nutrient cycling through a plantmediated pathway.