[Temporal dynamics and influencing factors of soil microbes in Larix gmelinii forest soil during spring freezing-thawing period]. / æ˜¥å­£å†»èžæœŸå ´å®‰è½å¶æ¾æž—åœŸå£¤å¾®ç”Ÿç‰©çš„æ—¶é—´åŠ¨æ€åŠå ¶å½±å“å› å­.

Soil microbial community dynamics during the spring freezing-thawing period could affect carbon and nutrient cycling in the subsequent growing season. During spring soil freezing-thawing period, we monitored temporal dynamics of soil microbial community in different soil substrates for Larix gmelinii forest using phospholipid fatty acids (PLFAs) as biomarkers every 3-7 days. The results were as followed: 1) the total PLFAs content, the PLFAs content and relative abundance of each soil microbial group, the ratio of Gram-positive bacteria to Gram-negative bacteria (G+/G-), the ratio of saturated PLFAs to unsaturated PLFAs (S/NS) and the ratio of bacteria to total fungi (fungi + arbuscular mycorrhizal fungi) (B/F) all varied among sampling times; 2) soil total organic carbon (TOC) and nitrogen (TN) were the main factors affecting soil microbial community in the early stage of soil freezing-thawing period; soil moisture, TOC and TN were the main driving factors in the middle stage of soil freezing-thawing period; soil microbes were affected by soil tempera-ture, moisture, TOC, TN and C/N in the late stage of soil freezing-thawing period; 3) the total PLFAs content, the PLFAs content and relative abundance of each soil microbial group (except the relative abundance of bacteria), B/F, G+/G- and S/NS all showed significant difference between soil substrates, and soil TOC, TN and C/N were the key determination factors. Soil temperature, moisture, and nutrient availability were the main factors affecting soil microbial community during the spring soil freezing-thawing period, but the degree of influence varied with the freezing-thawing stages and microbial groups.

[Detecting the moisture content of forest surface soil based on the microwave remote sensing technology.] / 基于微波遥感技术探测森林地表土壤含水率.

The moisture content of forest surface soil is an important parameter in forest ecosystems. It is practically significant for forest ecosystem related research to use microwave remote sensing technology for rapid and accurate estimation of the moisture content of forest surface soil. With the aid of TDR-300 soil moisture content measuring instrument, the moisture contents of forest surface soils of 120 sample plots at Tahe Forestry Bureau of Daxing'anling region in Heilongjiang Province were measured. Taking the moisture content of forest surface soil as the dependent variable and the polarization decomposition parameters of C band Quad-pol SAR data as independent variables, two types of quantitative estimation models (multilinear regression model and BP-neural network model) for predicting moisture content of forest surface soils were developed. The spatial distribution of moisture content of forest surface soil on the regional scale was then derived with model inversion. Results showed that the model precision was 86.0% and 89.4% with RMSE of 3.0% and 2.7% for the multilinear regression model and the BP-neural network model, respectively. It indicated that the BP-neural network model had a better performance than the multilinear regression model in quantitative estimation of the moisture content of forest surface soil. The spatial distribution of forest surface soil moisture content in the study area was then obtained by using the BP neural network model simulation with the Quad-pol SAR data.

[Prediction of litter moisture content in Tahe Forestry Bureau of Northeast China based on FWI moisture codes].

Canadian fire weather index system (FWI) is the most widely used fire weather index system in the world. Its fuel moisture prediction is also a very important research method. In this paper, litter moisture contents of typical forest types in Tahe Forestry Bureau of Northeast China were successively observed and the relationships between FWI codes (fine fuel moisture code FFMC, duff moisture code DMC and drought code DC) and fuel moisture were analyzed. Results showed that the mean absolute error and the mean relative error of models.established using FWI moisture code FFMC was 14.9% and 70.7%, respectively, being lower than those of meteorological elements regression model, which indicated that FWI codes had some advantage in predicting litter moisture contents and could be used to predict fuel moisture contents. But the advantage was limited, and further calibration was still needed, especially in modification of FWI codes after rainfall.

[Selection of advantage prediction model for forest fire occurrence in Tahe, Daxing'an Mountain].

This study chose zero-inflated model and Hurdle model that have been widely used in economic and social fields to model the fire occurrence in Tahe, Daxing'an Mountain. The AIC, LR and SSR were used to compare the models including zero-inflated Poisson model (ZIP), zero-inflated negative binomial model (ZINB), Poisson-Hurdle model (PH) and negative Binomial Hurdle (NBH) (two types, four models in total) so as to determine a better-fit model to predict the local fire occurrence. The results illustrated that ZINB model was superior over the other three models (ZIP, PH and NBH) based on the result of AIC and SSR tests. LR test revealed that the negative binomial distribution was suitable to both the "count" portion of zero-inflated model and hurdle model. Furthermore, this paper concluded that the zero-inflated model could better fit the fire feature of the study area according to the hypotheses of the two types of models.

[Carbon density and production in valley spruce-fir forest in Xiaoxing'an Mountains, China].

The carbon density and production were measured using both forest inventory and allometry approaches in the declining valley spruce-fir forest in Xiaoxing' an Mountains. Results showed that the total carbon density of the forest was 268. 14 t C · hm(-2) in 2011, and carbon densities of the vegetation, detritus and soil were 74.25, 16.86 and 177.03 t C · hm(-2), respectively. From 2006 to 2011, tree layer carbon density decreased from 80.86 t C · hm(-2) to 71.73 t C · hm(-2). The average decrease proportions per year of carbon density were 0.5%, 1.2%, 2.7% and 3.7% for Abies nephrolepis, Betula platyphylla, Picea spp., and Larix gmelinii, respectively. However, carbon densities were increased by 2.9%, 3.9% and 7.2% per year for Alnus sibirica, Pinus koraiensis and Acer ukurunduense, respectively. Net primary production (NPP) of the forest was 4.69 t C · hm(-2) · a(-1). The ratio of belowground NPP to aboveground NPP was 0.56. Litterfall accounted for the largest proportion of the NPP of forest with a value of 34.5%. As the two most important carbon output approaches of forest ecosystems, the fluxes of heterotrophic respiration and coarse woody debris decomposition were 293.67 and 119.29 g C · m(-2) · a(-1), respectively. Net ecosystem production (NEP) of the forest was 55.90 g C · m(-2) a(-1). The results indicated that the valley spruce-fir forest in the declining state still had a certain carbon sink capacity.

[Prediction models for ground surface fuels moisture content of Larix gmelinii stand in Daxing'anling of China based on one-hour time step].

By using the equilibrium moisture content-time lag methods of Nelson and Simard and the meteorological element regression method, this paper studied the dynamics of the moisture content of ground surface fine dead fuels under a Larix gmelinii stand on the sunny slope in Daxing' anling with a time interval of one hour, established the corresponding prediction models, and analyzed the prediction errors under different understory densities. The results showed that the prediction methods of the fuels moisture content based on one-hour time step were applicable for the typical Larix gmelinii stand in Daxing' anling. The mean absolute error and the mean relative error of Simard method was 1.1% and 8.5%, respectively, being lower than those of Nelson method and meteorological element regression method, and close to those of similar studies. On the same slopes and slope positions, the fuel moisture content varied with different understory densities, and thus, it would be necessary to select the appropriate equilibrium moisture content model for specific regional stand and position, or establish the fuel moisture content model based on specific stand when the dynamics of fuel moisture content would be investigated with a time interval of one hour.

[Research progress in post-fire debris flow].

The occurrence of the secondary disasters of forest fire has significant impacts on the environment quality and human health and safety. Post-fire debris flow is one of the most hazardous secondary disasters of forest fire. To understand the occurrence conditions of post-fire debris flow and to master its occurrence situation are the critical elements in post-fire hazard assessment. From the viewpoints of vegetation, precipitation threshold and debris flow material sources, this paper elaborated the impacts of forest fire on the debris flow, analyzed the geologic and geomorphic conditions, precipitation and slope condition that caused the post-fire debris flow as well as the primary mechanisms of debris-flow initiation caused by shallow landslide or surface runoff, and reviewed the research progress in the prediction and forecast of post-fire debris flow and the related control measures. In the future research, four aspects to be focused on were proposed, i. e., the quantification of the relationships between the fire behaviors and environmental factors and the post-fire debris flow, the quantitative research on the post-fire debris flow initiation and movement processes, the mechanistic model of post-fire debris flow, and the rapid and efficient control countermeasures of post-fire debris flow.

[Fire behavior of Quercus mongolica leaf litter fuelbed under zero-slope and no-wind conditions. II. Analysis and modelling of fireline intensity, fuel consumption, and combustion efficiency].

Mongolian oak (Quercus mongolica) is an important constructive and accompanying species in mixed broadleaf-conifer forest in Northeast China, In this paper, a laboratory burning experiment was conducted under zero-slope and no-wind conditions to study the effects of fuel moisture content, loading, and thickness on the fireline intensity, fuel consumption, and combustion efficiency of the Mongolian oak leaf litter fuelbed. The fuel moisture content, loading, and thickness all had significant effects on the three fire behavior indices, and there existed interactions between these three affecting factors. Among the known models, the Byram model could be suitable for the prediction of local leaf litter fire intensity only after re-parameterization. The re-estimated alpha and beta parameters of the re-parameterized Byram model were 98.009 and 1.099, with an adjusted determination coefficient of 0.745, the rooted mean square error (RMSE) of 8.676 kW x m(-1), and the mean relative error (MRE) of 21%, respectively (R2 = 0.745). The re-estimated a and b by the burning efficiency method proposed by Albini were 0.069 and 0.169, and the re-estimated values were all higher than 93%, being mostly overestimated. The Consume model had a stronger suitability for the fuel. The R2 of the general linear models established for fireline intensity, fuel consumption, and burning efficiency was 0.82, 0.73 and 0.53, and the RMSE was 8.266 kW x m(-1) 0.081 kg x m(-2), and 0.203, respectively. In low intensity surface fires, the fine fuels could not be completely consumed, and thus, to consider the leaf litter and fine fuel in some forest ecosystems being completely consumed would overestimate the carbon release from forest fires.

[Fire behavior of ground surface fuels in Pinus koraiensis and Quercus mongolica mixed forest under no wind and zero slope condition: a prediction with extended Rothermel model].

A laboratory burning experiment was conducted to measure the fire spread speed, residual time, reaction intensity, fireline intensity, and flame length of the ground surface fuels collected from a Korean pine (Pinus koraiensis) and Mongolian oak (Quercus mongolica) mixed stand in Maoer Mountains of Northeast China under the conditions of no wind, zero slope, and different moisture content, load, and mixture ratio of the fuels. The results measured were compared with those predicted by the extended Rothermel model to test the performance of the model, especially for the effects of two different weighting methods on the fire behavior modeling of the mixed fuels. With the prediction of the model, the mean absolute errors of the fire spread speed and reaction intensity of the fuels were 0.04 m X min(-1) and 77 kW X m(-2), their mean relative errors were 16% and 22%, while the mean absolute errors of residual time, fireline intensity and flame length were 15.5 s, 17.3 kW X m(-1), and 9.7 cm, and their mean relative errors were 55.5%, 48.7%, and 24%, respectively, indicating that the predicted values of residual time, fireline intensity, and flame length were lower than the observed ones. These errors could be regarded as the lower limits for the application of the extended Rothermel model in predicting the fire behavior of similar fuel types, and provide valuable information for using the model to predict the fire behavior under the similar field conditions. As a whole, the two different weighting methods did not show significant difference in predicting the fire behavior of the mixed fuels by extended Rothermel model. When the proportion of Korean pine fuels was lower, the predicted values of spread speed and reaction intensity obtained by surface area weighting method and those of fireline intensity and flame length obtained by load weighting method were higher; when the proportion of Korean pine needles was higher, the contrary results were obtained.

[Fire behavior of Mongolian oak leaves fuel-bed under no-wind and zero-slope conditions. I. Factors affecting fire spread rate and modeling].

Aimed to understand the fire behavior of Mongolian oak leaves fuel-bed under field condition, the leaves of a secondary Mongolian oak forest in Northeast Forestry University experimental forest farm were collected and brought into laboratory to construct fuel-beds with varied loading, height, and moisture content, and a total of 100 experimental fires were burned under no-wind and zero-slope conditions. It was observed that the fire spread rate of the fuel-beds was less than 0.5 m x min(-1). Fuel-bed loading, height, and moisture contents all had significant effects on the fire spread rate. The effect of fuel-bed moisture content on the fire spread had no significant correlations with fuel-bed loading and height, but the effect of fuel-bed height was related to the fuel-bed loading. The packing ratio of fuel-beds had less effect on the fire spread rate. Taking the fuel-bed loading, height, and moisture content as predictive variables, a prediction model for the fire spread rate of Mongolian oak leaves fuel-bed was established, which could explain 83% of the variance of the fire spread rate, with a mean absolute error 0.04 m x min(-1) and a mean relative error less than 17%.

[Change trends of summer fire danger in great Xing' an Mountains forest region of Heilongjiang Province, Northeast China under climate change].

By using Delta and WGEN downscaling methods and Canadian Forest Fire Weather Index, this paper analyzed the variation characteristics of summer fire in Great Xing' an Mountains forest region of Heilongjiang Province in 1966-2010, estimated the change trends of the summer fire danger in 2010-2099, compared the differences of the forest fire in summer, spring, and autumn, and proposed the prevention and control strategies of the summer fire based on the fire environment. Under the background of climate warming, the summer forest fire in the region in 2000-2010 showed a high incidence trend. In foreseeable future, the summer forest fire across the region in 2010-2099, as compared to that in the baseline period 1961-1990, would be increased by 34%, and the increment would be obviously greater than that of spring and autumn fire. Relative to that in 1961-1990, the summer fire in 2010-2099 under both SRES A2a and SRES B2a scenarios would have an increasing trend, and, with the lapse of time, the trend would be more evident, and the area with high summer fire would become wider and wider. Under the scenario of SRES A2a, the summer fire by the end of the 21st century would be doubled, as compared to that in 1961-1990, and the area with high summer fire would be across the region. In the characteristics of fire source, attributes of forest fuel, and fire weather conditions, the summer forest fire was different from the spring and autumn forest fire, and thus, the management of fire source and forest fuel load as well as the forest fire forecast (mid-long term forecast in particular) in the region should be strengthened to control the summer forest fire.

[Fire behavior of Mongolian oak leaves fuel bed under no-wind and zero-slope conditions. II. Analysis of the factors affecting flame length and residence time and related prediction models].

Taking fuel moisture content, fuel loading, and fuel bed depth as controlling factors, the fuel beds of Mongolian oak leaves in Maoershan region of Northeast China in field were simulated, and a total of one hundred experimental burnings under no-wind and zero-slope conditions were conducted in laboratory, with the effects of the fuel moisture content, fuel loading, and fuel bed depth on the flame length and its residence time analyzed and the multivariate linear prediction models constructed. The results indicated that fuel moisture content had a significant negative liner correlation with flame length, but less correlation with flame residence time. Both the fuel loading and the fuel bed depth were significantly positively correlated with flame length and its residence time. The interactions of fuel bed depth with fuel moisture content and fuel loading had significant effects on the flame length, while the interactions of fuel moisture content with fuel loading and fuel bed depth affected the flame residence time significantly. The prediction model of flame length had better prediction effect, which could explain 83.3% of variance, with a mean absolute error of 7.8 cm and a mean relative error of 16.2%, while the prediction model of flame residence time was not good enough, which could only explain 54% of variance, with a mean absolute error of 9.2 s and a mean relative error of 18.6%.

[Prediction on the changes of forest fire danger rating in Great Xing'an Mountain region of Northeast China in the 21st century under effects of climate change].

Based on the A2a and B2a climatic scenarios for both the baseline period (1961-1990) and the future scenario periods (2010-2039, 2040-2069, and 2070-2099) from the Hadley Centre's General Circulation, and by using Delta method, WGEN downscaling methods, and Canadian Forest Fire Danger Rating System, this paper classified the forest fire dangers in Great Xing' an Mountains region of Heilongjiang Province, Northeast China, predicted the changes of the forest fire danger rating in the period 2010-2099 relative to baseline period (1961-1990), and analyzed the uncertainty of the long-term prediction of forest fire danger rating. It was predicted that under the background of climate warming, the mean annual days of extremely high, very high, and medium forest dangers in study region in the 21st century all showed an increasing trend, while the mean annual days of high and low forest dangers were in adverse. Relative to the baseline period of 1961-1990, the mean annual days of extremely high and very high forest dangers in the 2040-2069 and 2070-2099 under the scenarios of SRES A2a and B2a would be increased by 43 and 36, and 62 and 61, respectively.

[Dynamics of forest fire weather indices in Tahe County of Great Xing' an Mountains region, Heilongjiang Province].

Based on the 1974-2008 forest fire and meteorological data in Tahe County of Great Xing' an Mountains region, and with the help of Canadian Forest Fire Weather Index System (CFFWIS), this paper qualitatively and quantitatively analyzed the dynamics of forest fire weather indices in the region. In 1974-2008, the mean annual fire occurrence in the region showed an increasing trend, and the increment in 2000-2008 was 72.2%, compared with that in 1974-1999. The fuel moisture codes, fire behavior indices, and fire severity indices in 1974-2008 had an overall increasing trend, which was more evident with time extended. In the future, the probability of forest fire occurrence in the region would be increasing, fuels would be getting drier, fire intensity would be increased, fire weather would be more serious, and fire control would be more difficult. Therefore, more efforts should be made to improve the capability of forest fire control, especially in summer. As a fundamental technique, prescribed burning should be applied to reduce the fuel load. From this doing, the probability of fire occurrence and the fire potential intensity could be reduced.