Variations in the biomass of Eucalyptus plantations at a regional scale in Southern China

We quantified deviations in regional forest biomass from simple extrapolation of plot data by the biomass expansion factor method（BEF） versus estimates obtained from a local biomass model,based on large-scale empirical field inventory sampling data.The sources and relative contributions of deviations between the two models were analyzed by the boosted regression trees method.Relative to the local model,BEF overestimated accumulative biomass by 22.12%.The predominant sources of the total deviation （70.94%） were stand-structure variables.Stand age and diameter at breast height are the major factors.Compared with biotic variables,abiotic variables had a smaller overall contribution （29.06%）,with elevation and soil depth being the most important among the examined abiotic factors.Large deviations in regional forest biomass and carbon stock estimates are likely to be obtained with BEF relative to estimates based on local data.To minimize deviations,stand age and elevation should be included in regional forest-biomass estimation.

Eucalyptus carbon stock estimation in subtropical regions with the modeling strategy of sample plots–airborne LiDAR–Landsat time series data

Updating eucalyptus carbon stock data in a timely manner is essential for better understanding and quantifying its effects on ecological and hydrological processes.At present,there are no suitable methods to accurately estimate the eucalyptus carbon stock in a large area.This research aimed to explore the transferability of the eucalyptus carbon stock estimation model at temporal and spatial scales and assess modeling performance through the strategy of combining sample plots,airborne LiDAR and Landsat time series data in subtropical regions of China.Specifically,eucalyptus carbon stock estimates in typical sites were obtained by applying the developed models with the combination of airborne LiDAR and field measurement data;the eucalyptus plantation ages were estimated using the random localization segmentation approach from Landsat time series data;and regional models were developed by linking LiDAR-derived eucalyptus carbon stock and vegetation age(e.g.,months or years).To examine the models’robustness,the developed models at the regional scale were transferred to estimate carbon stocks at the spatial and temporal scales,and the modeling results were evaluated using validation samples accordingly.The results showed that carbon stock can be successfully estimated using the age-based models(both age variables in months and years as predictor variables),but the month-based models produced better estimates with a root mean square error(RMSE)of 6.51 t⋅ha1 for Yunxiao County,Fujian Province,and 6.33 t⋅ha1 for Gaofeng Forest Farm,Guangxi Zhuang Autonomous Region.Particularly,the month-based models were superior for estimating the carbon stocks of young eucalyptus plantations of less than two years.The model transferability analyses showed that the month-based models had higher transferability than the year-based models at the temporal scale,indicating their possibility for analysis of carbon stock change.However,both the month-based and year-based models expressed relatively poor transferability at a spatial scale.This study provides new insights for cost-effective monitoring of carbon stock change in intensively managed plantation forests.

Effect of Different Soil Regulation Measures on Yield and Soil Fertility of Eucalyptus Plantation in Southern Guangxi

In view of the problems of decreased unit yield,soil acidification,decreased soil organic matter and soil fertility caused by high generation single pure Eucalyptus plantation in southern Guangxi,a field experiment was conducted to study the yield,soil organic matter and soil fertility under six soil conditioning measures[interplanting Tephrosia candida under the forest,interplanting Sesbania cannabina under the forest,organic fertilizer application,residue to woodland,soil testing and formulated fertilization,and applying pure chemical fertilizer(CK)],and the enhancing effects of each treatment on the yield and soil improvement of Eucalyptus plantations were further comprehensively evaluated.The results showed that compared with the control,the five treatments could increase the average stock of Eucalyptus,among which the average stock under the treatment of interplanting T.candida under the forest was the highest,followed by soil testing and formulated fertilization.The soil organic matter content and soil fertility of the forest were significantly improved by interplanting green manure,organic fertilizer application and soil testing and formulated fertilization models,while the short-term(1 a)effect of the residue treatment on the improvement of soil organic matter and soil fertility was insignificant.During the actual production process,interplanting green manure and residue treatment were not effective due to the inoperability,and the applicability were not wide,which still needed further study.Therefore,organic manure application and soil testing and formulated fertilization were suitable choices to promote the improvement of productivity and soil quality of Eucalyptus plantation in Guangxi.

Effects of litter removal on plant species diversity: a case study in tropical Eucalyptus forest ecosystems in South China

The removal of litterfall in the Eucalyptus plantations in South China affected the plant biodiversity in these ecosystems was found based on the field observation and lab analysis. The protection times of species diversity of three Eucalyptus communities were different (Community Ⅰ with no protection, Community Ⅱ with 7-year-protection, Community Ⅲ with 35-year-protection). The total numbers of species in these communities (from Community Ⅰ to Ⅱ to Ⅲ) are 1, 6, and 17, respectively. The results showed that the protection of litterfall from being taken out of the ecosystem is important and can increase plant species diversity. This study combined biomass data, the chemical and physical properties of the soil, and the diversity of microbes in the communities. It is concluded that the mechanism of the effects of litter removal on biodiversity includes three factors: removing the suitable habitat of microbe and animal, decreasing the soil nutrient, and changing the special habitat for the germination and growth of invading plants. These results should have important implications for managing these Eucalyptus forest ecosystems in South China.

Introduction of Dalbergia odorifera enhances nitrogen absorption on Eucalyptus through stimulating microbially mediated soil nitrogen-cycling

Background:There is substantial evidence that Eucalyptus for nitrogen(N)absorption and increasing the growth benefit from the introduction of N-fixing species,but the underlying mechanisms for microbially mediated soil N cycling remains unclear.Methods:We investigated the changes of soil pH,soil water content(SWC),soil organic carbon(SOC),total N(TN),inorganic N(NH_(4)^(+)-N and NO_(3)^(-)-N),microbial biomass and three N-degrading enzyme activities as well as the biomass and N productivity of Eucalyptus between a pure Eucalyptus urophylla×grandis plantation(PP)and a mixed Dalbergia odorifera and Eucalyptus plantation(MP)in Guangxi Zhuang Autonomous Region,China.Results:Compared with the PP site,soil pH,SWC,SOC and TN in both seasons were significantly higher at the MP site,which in turn enhanced microbial biomass and the activities of soil N-degrading enzymes.The stimulated microbial activity at the MP site likely accelerate soil N mineralization,providing more available N(NH_(4)^(+)-N in both seasons and NO_(3)^(-)-N in the wet-hot season)for Eucalyptus absorption.Overall,the N productivity of Eucalyptus at the MP site was increased by 19.7% and 21.9%,promoting the biomass increases of 15.1% and 19.2% in the drycold season and wet-hot season,respectively.Conclusion:Our results reveal the importance of microbially mediated soil N cycling in the N absorption on Eucalyptus.Introduction of D.odorifera enhances Eucalyptus biomass and N productivity,improve soil N availability and increased soil C and N concentration,which hence can be considered to be an effective sustainable management option of Eucalyptus plantations.

Effects of Litter Removal and Addition on Soil Nitrogen Mineralization of Eucalyptus Plantation

[Objectives]This study was conducted to understand the process of soil nitrogen mineralization in Eucalyptus plantations,and to identify the characteristics of soil nitrogen mineralization with different litter inputs.[Methods]With the soil of the Eucalyptus plantation in Fusui County,Guangxi as the research object,the soil nitrogen mineralization of the Eucalyptus plantation under different litter treatments(removing litter,adding litter and retaining litter)was studied by PVC tube closed-top in-situ incubation.[Results]①After 1 year of litter treatment,the inorganic nitrogen(NH_(4)^(+)-N+NO_(3)^(-)-N)in the soil of different treatments ranked as adding litter(20.15 mg/kg)>retaining litter(16.02 mg/kg)>removing litter(11.60) mg/kg),and the differences reached a significant level(P<0.05).②After 30 d of in-situ incubation,there were significant differences in soil nitrate nitrogen content before and after incubation in the three treatments(removing litter,adding litter,and retaining litter)before and after incubation(P<0.05),but no significant differences were observed in soil ammonium nitrogen content(P>0.05).Soil nitrate nitrogen contents increased from 1.47,2.01 and 1.72 mg/kg before incubation to 3.66,6.73 and 5.02 mg/kg,respectively,and soil ammonium nitrogen content increased from 11.60,20.15 and 16.02 mg/kg before incubation to 13.65,21.54 and 17.18 mg/kg,respectively.The net nitrogen mineralization quantities of the three treatments were 4.24,6.11 and 4.46 mg/kg,respectively,and the net nitrogen mineralization rates from large to small were adding litter[0.180 mg/(kg·d)]>retaining litter[0.141 mg/(kg·d)]>removing litter[0.125 mg/(kg·d)].Therefore,both removal and addition of litter affected the soil nitrogen input and nitrogen mineralization rate of the Eucalyptus plantation,thereby affecting soil nitrogen availability and the ability of soil to maintain plant-available nitrogen.[Conclusions]This study provides a theoretical basis for nutrient management in Eucalyptus plantations,especially nitrogen nutrient management.

Effect of Planting Eucalyptus Trees on Runoff Depth and Its Processes of Forestland Natural Watersheds

The runoff and runoff process of Eucalyptus plantations natural watershed were studied to provide guidance for scientific evaluation of water conservation capacities of Eucalyptus plantations,compared with the Pinus massoniana forest natural watershed. The runoff volumes of Eucalyptus plantations and P. massoniana forest natural watersheds were continuously monitored using the small watershed runoff monitoring method and the automatic data collection devices from August,2013 to December,2016,and effects of heavy rainfall and continuous rainfall on the runoff process were studied. Results showed that the annual runoff coefficient of Eucalyptus plantations natural watershed was 0. 050,and 55. 4% lower than P. massoniana forest（ 0. 112）,with the difference being significant（ P 〈 0. 01）. Total runoff duration,time of maximum runoff lagging behind rainfall peak,and runoff duration caused by a heavy rainfall process（ amounting to 147. 5 mm） between the two kinds of forest watersheds were significant different,those of Eucalyptus plantations were 35. 6 mm,0. 2 h and 13. 8 h,respectively,while those of P. massoniana forest were28. 5 mm,0. 7 h and 35. 5 h,respectively. Eucalyptus plantations natural watershed produced only 4-days runoff,and runoff depth amounted to3. 8 mm with a 7-days continuous precipitation process of rainfall with 125. 0 mm,while P. massoniana forest natural watershed produced continuously 13-days runoff,and the runoff depth was 10. 1 mm. In conclusion,water conservation capacity of Eucalyptus plantations is obviously lower than P. massoniana forest.

Legume Green Manuring Improves Soil Fertility and Plant Growth of Eucalyptus Plantation in South Subtropical China

Legume green manure is extensively planted to improve soil fertility in crop field.However,the application of legume in Eucalyptus plantation is still limited and depends on site specific and species.Therefore,the objective of this study was to determine the effects of green manure interplantation on soil fertility and plant growth of Eucalyptus plantation in a short term.A field experiment of one year was established to investigate the green manure growth,forest soil nutrients and Eucalyptus plant growth inter-planted with two legume species(Tephrosia candida,TC and Sesbania cannabina,SC)at south subtropical China.Legumes were inter-planted in linear among the tree space of Eucalyptus stand.Result showed that the green manure inter-plantation increased soil organic matter by 9.66%of TC and 18.44%of SC.Soil available nitrogen,phosphorus and potassium were improved significantly by the legume treatments as well.The increment of height and diameter at breast height of Eucalyptus during the experiment was significant in legume treatments.Thus,the timber volume increment was improved significantly by 46.81%of TC and 35.47%of SC compared with the control treatment.Therefore,the inter-plantation of legume green manure under the Eucalyptus plantation is effective to improve soil fertility and tree growth.Such a measure is potential and referenced for the sustainable forest management.

Effects of forest cover types and environmental factors on soil respiration dynamics in a coastal sand dune of subtropical China

Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration(Rs) for secondary natural Litsea forest and plantations of casuarina,pine, acacia and eucalyptus. Results show that significant diurnal variations of Rsoccurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of Rswere found in all five forest stands. Rschanged exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of Rs variations. Positive relationships between seasonal Rsand soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter(Q10 value) of Rsranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual Rswas highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter,and soil properties(pH, total N, available P, and exchangeable Mg) were also significant factors.

Linear programming approach for optimal forest plantation

The aim of this research was to identify species suitable for plantation. We first identified species for potentially suitable for plantation based on ecological capabilities regarding soil properties. We determined the area of plantation for different species based on ecological capabilities. Then, we collected relevant data such as growth patterns of different species, labor requirements for plantation and plantation cost. A linear programming model and two integer linear programming models were used for optimization. The appropriate species based on ecological capabilities were ash, elm, maple, oak and bald cypress. A linear programming model was used based on ecological capabilities classification to determine the land area of different species for plantation. Then, two integer linear programming models were employed to select the species for plantation. We set ecological properties unequal for all of the species in the first run of the integer programming model. Two groups were classified： group one included maple and ash; group two included bald cypress,oak and elm. The second integer programming model assumed equal ecological properties for all the species.Results of linear programming showed that maple and bald cypress were appropriate for plantation at the site and their plantation areas should be 151.3 and 355.3 ha, respectively. Results of the first integer linear programming model showed that maple and bald cypress would be economically profitable for plantation. The results of the second integer linear programming model showed that only bald cypress would be appropriate for plantation.