Effects Of Afforestation Research Articles

Afforestation with Norway spruce on a subalpine pasture alters carbon dynamics but only moderately affects soil carbon storage

There is a strong trend toward reforestation of abandoned grasslands in alpine regions which may impact the carbon balance of alpine ecosystems. Here, we studied the effects of afforestation with Norway spruce (Picea abies L.) on an extensively grazed subalpine pasture in Switzerland on soil organic carbon (SOC) cycling and storage. Along a 120-year long chronosequence with spruce stands of 25, 30, 40, 45, and >120 years and adjacent pastures, we measured tree biomass, SOC stocks down to the bedrock, natural 13C abundances, and litter quality. To unravel controls on SOC cycling, we have monitored microclimatic conditions and quantified SOC decomposability under standardized conditions as well as soil respiration in situ. Stocks of SOC were only moderately affected by the afforestation: in the mineral soil, SOC stocks transiently decreased after tree establishment, reaching a minimum 40–45 years after afforestation (−25 %) and increased thereafter. Soils of the mature spruce forest stored the largest amount of SOC, 13 % more than the pasture soils, mainly due to the accumulation of an organic layer (23 t C ha−1). By comparison, C accumulated in the tree biomass exceeded the SOC pool by a factor of three in the old forest. In contrast to the small impact on C storage, afforestation strongly influenced the composition and quality of the soil organic matter (SOM). With increasing stand age, δ13C values of the SOM became consistently more positive, which can be interpreted as a gradual replacement of grass- by spruce-derived C. Fine roots of spruce were enriched in 13C, in lignin and had a higher C/N ratio in comparison to grass roots. As a consequence, SOM quality as indicated by the lower fraction of readily decomposable (labile) SOM and higher C:N ratios declined after the land-use change. Furthermore, spruce plantation induced a less favorable microclimate for microbial activity with the average soil temperature during the growing season being 5 °C lower in the spruce stands than in the pasture. In situ soil respiration was approximately 50 % lower after the land use conversion, which we primarily attribute to the colder conditions and the lower SOM quality, but also to drier soils (−25 %) and to a decreased fine root biomass (−40 %). In summary, afforestation on subalpine pastures only moderately affected SOC storage as compared to the large C sink in tree biomass. In contrast, SOC cycling rates strongly decreased as a result of a less favorable microclimate for decomposition of SOM, a lower C input by roots, and a lower litter quality.

Afforestation effects on soil microbial abundance, microbial biomass carbon and enzyme activity in dunes of Horqin Sandy Land, northeastern China

In order to investigate the effects of afforestation on soil microbial abundance, microbial biomass carbon and enzyme activity in sandy dunes, 20-year-old Pinus sylvestris var. mongolica Litv. (PSM) and Populus simonii Carriere (PSC) mature forests were selected in Horqin Sandy Land, and mobile dunes was set as a control (CK). Results show that PSM and PSC plantations can improve soil physicochemical properties and significantly increase microbiological activity in mobile dunes. Soil microbial abundance, microbial biomass carbon and enzyme activity show an order of PS>PSM>CK. Total soil microbial abundance in PSM and PSC was respectively 50.16 and 72.48 times more than that in CK, and the differences were significant among PSM, PSC and CK. Soil microbial biomass carbon in PSM and PSC was respectively 23.67 and 33.34 times more than that in CK, and the difference was insignificant between PSM and PSC. Soil enzyme activity, including dehydrogenase (DEH), peroxidase (PER), protease (PRO), urease (URE) and cellobiohydrolase (CEL) in PSM and PSC were respectively 19.00 and 27.54, 4.78 and 9.89, 4.05 and 8.67, 29.93 and 37.46, and 9.66 and 13.42 times of that in CK. P. sylvestris and P. simonii can effectively improve soil physicochemical and microbiological properties in sandy dunes and fix mobile dunes in Horqin Sandy Land. The C mic :C ratio is an applicable indicator to estimate soil stability and soil water availability, and based on an overall consideration of plantation stability and sustainability, P. sylvestris is better than P. simonii in fixing mobile dunes in sandy land.

Effectiveness of Coastal Bio-Shield for Reduction of the Energy of Storm Surges and Cyclones

Abstract Vegetation bio-shield has been widely recognized as a natural method to reduce the energy of cyclones and storm surges. The effectiveness of coastal vegetation in reducing storm surge has been investigated in this study. This study includes three types of analysis such as satellite image analysis, numerical model simulation and laboratory experiment. In satellite image analysis, two SPOT images are analyzed to investigate the damages caused by the super cyclone SIDR which occured on the 15th of November, 2007. From this analysis it is studied that the densely populated vegetation areas were less damaged than the exposed areas without vegetation barriers. About 3% of the total study area was damaged by the SIDR. A two dimensional hydrodynamic model named Bay of Bengal model was applied for Sandwip island to study the effect of afforestation in reducing storm waves and current speed. Three scenarios of 200m, 400m and 600m distance of vegetation from embankment and two specific points were considered at the east side of Sandwip island. Results show that the water level decreases slightly but the current speed increases significantly as the distance of vegetation barrier increases from the embankment towards the sea. The laboratory experiment shows that the wave height is reduced up to 46% behind the vegetation zone, 43% within the barrier and 41% in front of vegetation for wave period of 1.6 sec when the vegetation barrier is placed at 1m from embankment.

Woody Vegetation Removal Stimulates Riparian and Benthic Denitrification in Tallgrass Prairie

Expansion of woody vegetation into areas that were historically grass-dominated is a significant contemporary threat to grasslands, including native tallgrass prairie ecosystems of the Midwestern United States. In tallgrass prairie, much of this woody expansion is concentrated in riparian zones with potential impacts on biogeochemical processes there. Although the effects of woody riparian vegetation on denitrification in both riparian soils and streams have been well studied in naturally wooded ecosystems, less is known about the impacts of woody vegetation encroachment in ecosystems that were historically dominated by herbaceous vegetation. Here, we analyze the effect of afforestation and subsequent woody plant removal on riparian and benthic denitrification. Denitrification rates in riparian soil and selected benthic compartments were measured seasonally in naturally grass-dominated riparian zones, woody encroached riparian zones, and riparian zones with woody vegetation removed in two separate watersheds. Riparian soil denitrification was highly seasonal, with the greatest rates in early spring. Benthic denitrification also exhibited high temporal variability, but no seasonality. Soil denitrification rates were greatest in riparian zones where woody vegetation was removed. Additionally, concentrations of nitrate, carbon, and soil moisture (indicative of potential anoxia) were greatest in wood removal soils. Differences in the presence and abundance of benthic compartments reflected riparian vegetation, and may have indirectly affected denitrification in streams. Riparian soil denitrification increased with soil water content and NO3 - . Management of tallgrass prairies that includes removal of woody vegetation encroaching on riparian areas may alter biogeochemical cycling by increasing nitrogen removed via denitrification while the restored riparian zones return to a natural grass-dominated state.

Afforestation effects on vegetation structure and diversity of grasslands in southern Brazil: The first years

We evaluated the effects of afforestation on the composition and structure of southern Brazilian subtropical grasslands directly beneath tree plantations, in pastures, and in permanent protection areas near watercourses. Cover of plants was registered in 120 plots of 1m2 in grasslands located at two distances from small watercourses in pasture and eucalypt plantation areas within a livestock ranching landscape. Livestock density is reduced in plantation areas. Species composition beneath tree plantations was significantly different from both pasture and nearby permanent protection areas. Permanent protection areas near plantations were also compositionally different from pastures. Eucalypt plantation was the environment type where ruderals were most abundant. Growth form cover distribution in pasture areas showed a consistent pattern, with graminous herbs being the most common growth form followed by prostrate herbs, prostrate subshrubs, and standing subshrubs. In plantation areas, the dominance of the graminoid herb growth form increased markedly, as well as standing herbs. These increases occurred mainly at the expense of prostrate herbs and subshrubs, which were significantly reduced. Plot-level species density was significantly affected by distance from watercourse and, more importantly, was significantly influenced by the interaction between management regime and distance to watercourse. It was reduced in eucalypt plantations relative to permanent protected areas. Current management of eucalypt plantations in southern Brazil produce unsuitable conditions for grassland species to thrive within plantations. Livestock densities <1.0animalunitha−1 in eucalypt plantations undermines the ability of surrounding permanent protection areas to act as ecological networks for biodiversity conservation.

Effects of Afforestation with Pines on Collembola Diversity in the Limestone hills of Szárhalom (West Hungary)

Abstract - We investigated the responses of collembolan communities to pine afforestation in an area formerly characterized by a mosaic of autochthonous downy oak woodland and steppe meadows. Study sites were selected in mixed stands of black pine and Scots pine and control samples were taken from downy oak stands and open steppe meadows. A total of 1884 Collembola specimens belonging to 66 species were collected. Three species, namely Protaphorura pannonica (Onychiuridae), Tomocerus mixtus (Tomoceridae) and Isotoma caerulea (Isotomidae) proved to be new to the Hungarian fauna. There are typical Collembola communities which are specific to different habitat types where species of a given composition can only or predominantly be found in that habitat, as well as some basic common species which occur in every habitat. The highest species richness (41) was found in steppe meadows, considerably lower (34) in downy oak forests, reaching the lowest value (25) in pine plantations. Although several forest species present in the oak woodland were completely missing from the pine forests, there was no significant difference between the Collembola diversities of the two forest habitats. The difference became more prominent in collembolan abundance which resulted in less than half of individuals/m2 in pine plantations compared to the soils of downy oak forests, most likely due to the changed soil conditions, especially of humus characteristics, caused by the pine needle litter. Jaccard similarity measure indicated approximately equal similarity (0.24-0.28) for paired comparison, suggesting that a relatively constant 'basic Collembola community' determined by the soil type typical for the area is present; while dissimilarity in communities between sites are partly provided by spatial heterogeneity of open and forest habitats and by the difference of the vegetation type.

Simulated impacts of afforestation in East China monsoon region as modulated by ocean variability

Using the National Center for Atmospheric Research Community Climate System Model Version 3.5, this paper examines the climatic effects of afforestation in the East China monsoon region with a focus on land–atmosphere interactions and the modulating influence of ocean variability. In response to afforestation, the local surface air temperature significantly decreases in summer and increases in winter. The summer cooling is attributed to enhanced evapotranspiration from increased tree cover. During winter, afforestation induces greater roughness and weaker winds over the adjacent coastal ocean, leading to diminished latent heat flux and increased sea-surface temperature (SST). The enhanced SST supports greater atmospheric water vapor, which is accompanied by anomalous wind, and transported into the East China monsoon region. The increase in atmospheric water vapor favors more cloud cover and precipitation, especially in the eastern afforestation region. Furthermore, the increase in atmospheric water vapor and cloud cover produce a greenhouse effect, raising the wintertime surface air temperature. By comparing simulations in which ocean temperature are either fixed or variable, we demonstrate that a significant hydrologic response in East China to afforestation only occurs if ocean temperatures are allowed to vary and the oceanic source of moisture to the continent is enhanced.

Can hybrid poplar plantations accelerate the restoration of forest understory attributes on abandoned fields?

Multi-functional plantations using fast-growing tree species can potentially be used to accelerate the restoration of forest habitat on abandoned farmland. However, few studies have directly compared the ecological effects of active afforestation using plantations to natural afforestation. The present study compares the effects of the establishment and the first 10years of growth of two different hybrid poplar clones to adjacent abandoned fields and natural second-growth forests, in terms of abiotic attributes and understory vegetation communities. Experimental plantations of a Populus maximowiczii×P. balsamifera (M×B) hybrid and a P. deltoides×P. nigra (D×N) hybrid were established in 2000 on abandoned fields at 8 sites in southern Quebec, Canada. In 2009, soil chemical properties, soil moisture, canopy openness, leaf litter biomass, and understory vegetation communities were sampled in the plantations and in neighboring unmanaged abandoned fields and second-growth woodlots. Canopy development was greatly accelerated by the plantations of both hybrid poplar clones, compared to the unplanted portions of abandoned fields, and in the more productive plantations of both clones, canopy openness and leaf litter biomass were similar to those measured in the woodlots. No difference was detected in soil chemical properties between the abandoned fields and either type of plantation. The plantation soils were drier than those of both the abandoned fields and the secondary forests, possibly due to increased transpiration by the hybrid poplars. The plantations favored the colonization of the sites by native tree seedlings compared to the unmanaged fields, producing a nurse stand effect. Among herbaceous and shrub species, native species richness was slightly higher in the plantations than in the fields. The understories of the fastest growing plantations had species in common with both the fields and the woodlots, while the understory of the slowest growing plantations was very similar to the field vegetation. The plantation understories had lower covers of open-habitat species than the fields, while the M×B plantations had slightly greater covers of native, shade-tolerant species. Plantations of the M×B clone were more distinct from the abandoned fields than were plantations of the D×N clone. In conclusion, hybrid poplar plantations appear capable of accelerating the restoration of certain understory attributes, which in turn favors their colonization by tree seedlings and suppresses competition from light-demanding herbaceous species.

Land use change in a temperate grassland soil: Afforestation effects on chemical properties and their ecological and mineralogical implications

The current change in land use of grassland in the temperate region of South America is a process associated with the worldwide expansion of annual crops and afforestation with fast growing exotic species. This last cultivation has particularly been the subject of numerous studies showing its negative effects on soil (acidification, loss of organic matter and base cations, among others). However its effects on the mineral fraction are not yet known, as it is generally considered as one of the slowest responses to changes. This stimulated the present study in order to assess whether the composition of clay minerals could be altered together with some of the physicochemical parameters affected by afforestation. This study compares the mineralogical composition of clays by X-ray diffraction (XRD) in a grassland soil (Argiudolls) under natural coverage and under Eucalyptus grandis cultivation implanted 25years ago in a sector of the same grassland. The tendency of some physicochemical parameters, common to other studies was also compared. XRD results showed, as a most noticeable difference in A11 and A12 subhorizons (~20cm) under eucalyptus, the fall of the 10Å spectrum minerals (illite-like minerals), which are the main reservoir of K in the soil. Meanwhile, the physicochemical parameters showed significant changes (p<0.01) to highly significant ones under eucalyptus, particularly in these subhorizons, where on average soil organic matter decreased by 43%; K+ by 34%; Ca2+ by 44%, while the pH dropped to this level by half a point. Our results show that the exportation of some nutrients is not compensated due to the turnover of organic forestry debris; the process of soil acidification was not directly associated with the redistribution of cations, but with an incipient podzolization process; the loss of potassium together with soil acidification, leads to a drastic change in clay mineralogy, which would be irreversible.

Changes in soil carbon sequestration and soil respiration following afforestation on paddy fields in north subtropical China

Aims Although many studies have reported net gains of soil organic carbon (SOC) after afforestation on croplands, this is uncertain for Chinese paddy rice croplands. Here, we aimed to evaluate the effects of afforestation of paddy rice croplands on SOC sequestration and soil respiration (Rs). Such knowledge would improve our understanding of the effectiveness of various land use options on greenhouse gas mitigation in China. Methods

Afforestation effects on soil carbon stocks of low productivity grassland in New Zealand

AbstractSoil carbon stock change between two major land uses in New Zealand was measured by sampling paired plots across the boundaries of low productivity grassland and forest planted pre‐1990. The national soil carbon monitoring system uses low productivity grassland as a benchmark to evaluate soil carbon stock change for other land uses. The goal was to validate earlier estimates of the effect of pre‐1990 afforestation and to reduce their level of uncertainty. We selected a set of sites to represent the national stocks of forests planted pre‐1990. Previous studies derived estimates of the land‐use effect on soil carbon for afforestation ranging from +1.6 to −8.5 t/ha to 30 cm depth. For all estimates, the 95% confidence interval spanned zero. Our study used nine of the previous paired‐plot sites and sampled and analysed 21 new sites. The land‐use effect of change from grassland to forest planted pre‐1990 was estimated at −17.4 t/ha. The 95% confidence interval ranged from −10.1 to −24.6 t/ha and did not include zero change. The result supported the soil carbon monitoring system assumption that forests planted pre‐1990 have significantly lower soil carbon stocks than the low‐productivity‐grassland standard. Evidence of stock change occurred in depth increments to 0.2 m but with no significant change for the 0.2–0.3 m increment. This suggests that the sampling depth of 0.3 m was adequate for the estimation of soil carbon stock change.

Does afforestation of pastures increase sequestration of soil carbon in Mediterranean climates?

Afforestation of agricultural land to mitigate climate change and other environmental degradation has been increasingly implemented around the world. However, the effects of afforestation on soil carbon and particularly nitrogen content remain unclear. We conducted a hierarchical Bayesian meta-analysis of published data on the effects of afforestation of pastures on soil carbon and nitrogen stocks in a Mediterranean climate. We found no evidence for substantial changes in soil carbon, nitrogen or C:N ratio across three decades of afforestation. However, a lack of data on the carbon content of the litter underestimates the potential for afforestation to sequester carbon in the soil. We investigated soil carbon content under remnant woodlands and found that it was higher than under the afforested pastures suggesting that afforestation has the potential to increase soil carbon over longer time scales. Targeted studies that measure carbon content and form within soils over an extended chronosequence are much needed to improve predictions of the potential for afforestation to increase soil carbon storage.

Effects of rainwater harvesting and afforestation on soil properties and growth of Emblica officinalis while restoring degraded hills in western India

Effect of rainwater harvesting (RWH) structures like Contour trench (CT), gradonie (GD), box trench (BT), V-ditch (VD) and afforestation with Emblica officinalis Gaertn (planted in August, 2005) were studied in 20% slopes with a view to improve soil status, plant growth, sequester carbon and rehabilitate hills for local benefits. Soil pH and EC decreased and percent soil, SOC, NO3-N and PO4-P increased in June 2010 over 2005. Enhanced soil water and nutrients in 20% and <10% slopes, respectively than in 10-20% slope, whereas it was 17.8, 16.1, 24.2 and 14.0% greater in CT, GD, BT and VD treatments, respectively over control. The highest plant growth was in CT plots in all slopes. Second best treatment was BT in <10% slope and VD in other slopes.Conclusively, RWH and afforestation facilitated soil improvement but CT/BT treatments were more efficient in conserving soil and water facilitating plant growth and helped restore the degraded hill. However, further research is required on soil water use and its partitioning in different vegetation component and the benefits accrued from it for the local people. Key words: Plant growth, hill restoration, soil carbon, soil nutrients, water dynamics

Simulated Local and Remote Biophysical Effects of Afforestation over the Southeast United States in Boreal Summer*

Abstract Afforestation has been proposed as a climate change mitigation strategy by sequestrating atmospheric carbon dioxide. With the goal of increasing carbon sequestration, a Congressional project has been planned to afforest about 18 million acres by 2020 in the Southeast United States (SEUS), the Great Lake states, and the Corn Belt states. However, biophysical feedbacks of afforestation have the potential to counter the beneficial climatic consequences of carbon sequestration. To assess the potential biophysical effects of afforestation over the SEUS, the authors designed a set of initial value ensemble experiments and long-term quasi-equilibrium experiments in a fully coupled Community Climate System Model, version 3.5 (CCSM3.5). Model results show that afforestation over the SEUS not only has a local cooling effect in boreal summer [June–August (JJA)] at short and long time scales but also induces remote warming over adjacent regions of the SEUS at long time scales. Precipitation, in response to afforestation, increases over the SEUS (local effect) and decreases over adjacent regions (remote effect) in JJA. The local surface cooling and increase in precipitation over SEUS in JJA are hydrologically driven by the changes in evapotranspiration and latent heat flux. The remote surface warming and decrease in precipitation over adjacent regions are adiabatically induced by anomalous subsidence. Our results suggest that the planned afforestation efforts should be developed carefully by taking account of short-term (local) and long-term (remote) biophysical effects of afforestation.

Effects of Afforestation on the Abundance,Biomass Carbon and Enzymatic Activities of Soil Microorganism in Sandy Dunes

In order to investigate the effects of afforestation on soil microbial abundance,microbial biomass carbon and enzymatic activities in sandy dunes,around 20-year-old Pinus sylvestris var.mongolica(PSM) and Populus simonii Carr.(PSC) mature forests were selected in Horqin Sandy Land,and mobile dunes were set as controls(CK).The results showed that PSM and PSC plantation could improve soil physiochemical properties and increase microbiological activities significantly.Soil microbial abundance,microbial biomass carbon and enzymatic activities showed an order of PSCPSMCK.Soil total microbial abundance in PSM and PSC were 50.16 and 72.48 times of that in CK,and the differences were significant among PSM,PSC and CK.Soil microbial biomass carbon in PSM and PSC were 23.67 and 33.34 times of that in CK,and the difference was insignificant between PSM and PSC.Soil enzymatic activities,including dehydrogenase(DEH),peroxidase(PER),protease(PRO),urease(URE) and cellobiohydrolase(CEL) activities in PSM and PSC were 19.00 and 27.54,4.78 and 9.89,4.05 and 8.67,29.93 and 37.46,9.66 and 13.42 times,repectively,of that in CK.Pinus sylvestris var.mongolica and Populus simonii Carr.are both efficient tree species to improve soil physiochemical and microbiological properties in sandy land,and moreover,they are both efficient tree species to fix mobile dunes in Horqin Sandy Land.Cmic∶C ratio is an efficient indicator to estimate soil stability and availability,and based on an overall consideration of plantation stability and sustainability,Pinus sylvestris var.mongolica was better than Populus simonii Carr.to fix mobile dunes in sandy land.

Effects of afforestation on soil respiration in an arid shrubland in Chile

We studied the effects of afforestation on soil respiration (Rs) in an arid shrubland in northern Chile. We sampled Rs monthly for three years in two adjacent plots, one left as control in natural condition, and one afforested with Acacia saligna. Sampling occurred 3–6 years after afforestation. Soil temperature (Ts) was a good predictor of Rs on certain periods of the year, although we could not relate this to specific levels of soil moisture (θ). Seasonal Rs variation related more to θ than to Ts, which could be explained by extremely low annual precipitation (138mm), concentrated during winter months. The correlation between Ts and Rs was higher when measured under plants compared to bare ground. The afforested site had in average 17% lower annual Rs (p=0.06) than the control site. During some months of the third year of measurements, the afforested site showed greater Rs than the control, suggesting that in the near future, Rs might be higher for the afforested site than for the natural condition, depending on the effect that trees may have on soil carbon stability, temperature and hydrological conditions.

Effects of afforestation with four unmixed plant species on the soil–water interactions in a semiarid Mediterranean region (Sicily, Italy)

Purpose An assessment of the effect of plant cover on the properties of four afforested soils in central Sicily was performed with the aim of discriminating among them after 60 years of afforestation.

Soil Texture and Forest Species Condition the Effect of Afforestation on Soil Quality Parameters

The objective of the present study was to evaluate the effect of afforestation of degraded agricultural soils on soil organic carbon (OC) stocks and related soil physical properties. We assumed that forest species and soil texture would have a strong effect on C stabilization and thus would also affect some physical properties. The study was composed of two experiments to evaluate (i) the effect of different tree species and (ii) the effect of soil texture on OC and physical properties. In the first case, soil samples were taken in 40-year-old plantations of Pinus haleppensis, P. haleppensis inoculated with ectomycorrhiza at planting, Pinus pinea, Eucalyptus spp., and Gleditsia triacanthos. For the second experiment, soils under three land-use types, namely, agriculture, P. haleppensis forest, and native savanna virgin were sampled at seven different sites in La Pampa, Argentina, that represented a climatic gradient from 850- to 600-mm annual rainfall and a textural gradient ranging from loam, sandy loam, to sand. The measured variables were bulk density, particle density, water retention at field capacity water content, structural stability index, total OC, large-aggregate C, intermediate-aggregate C, and small-aggregate C. Forest species had a differential effect on physical properties, especially bulk density, and OC contents. The forest species with the most favorable effects were P. haleppensis inoculated with ectomycorrhiza and G. triacanthos, whereas P. pinea and Eucalyptus were least effective, confirming the beneficial role of mycorrhizal fungi and symbiotic N fixation for restoring C stocks in a semiarid temperate environment. In all sites, we found significant differences in total OC and large-aggregate C contents between agriculture and forest treatments, thus indicating that afforestation with P. haleppensis would favor C sequestration in any of the three textural classes.

Mongolian pine plantations enhance soil physico-chemical properties and carbon and nitrogen capacities in semi-arid degraded sandy land in China

Horqin Sandy Land is a seriously desertified and an ecologically fragile region of China. Soil degradation and desertification in this region are the result of several decades of overgrazing, non-manure cropping with short fallow, and arbitrary land use and management. We investigated whether the afforestation of active sand dunes with Mongolian pine (Pinus sylvestris var. mongolica Litv.) enhances the carbon (C) and nitrogen (N) storages and the overall soil quality. We compared soil physico-chemical properties, and C and N storages in the total and light fraction soil organic matter of active sand dunes, and of 25- and 35-year-old plantations. Soil water holding capacity, fine particle content and nutrients were significantly higher in plantations than in active sand dunes, with greater improvements occurring in the top 5cm than in the 5–15cm layer of the soil profile. Soil C and total N storages were 6.1 and 3.7 folds in 25-year-old, and 10.2 and 5.3 folds in 35-year-old plantations compared to active sand dunes, respectively. Carbon and N storages in the light fraction were 20.9 and 15.8 folds in 25-year-old, and 36.1 and 25.0 folds in 35-year-old plantations, respectively, relative to active sand dunes. The light fraction played an important role in soil C sequestration and its amount is an indicator of the effects of afforestation on C storage in sandy soil. The upper 15cm of the soil profile in the 35-year-old plantations of Mongolian pine has the capacity to sequester significant amount of C in the region, potentially offsetting part of the carbon that has been lost due to desertification over the past century in the Horqin Sandy Land. Our results conclude that afforestation with Mongolian pine has had positive impacts on soil quality and has increased the capacity for soil C sequestration in semi-arid degraded areas.

The effects of afforestation on soil organic and inorganic carbon: A case study of the Loess Plateau of China

The determination of the changes in soil organic carbon (SOC) and inorganic carbon (SIC) in the subsoil following afforestation is meaningful and necessary for assessing carbon sequestration, but such knowledge is limited. In this case study, a paired-site approach was used to determine the differences in the SOC and SIC stock in the topsoil and subsoil, respectively, between a black locust (Robinia pseudoacacia L.) forest site (converted from cropland 30 years ago) and a cropland site in the middle of the Loess Plateau of China. Compared with the cropland, the SOC stock was significantly greater under the forest in both the top 20 cm and the subsoil (30–60 cm layer). The annual litter input under the forest was more than twice that of the cropland, and the fine root biomass was significantly higher in the forest. We conclude that the higher litter input and fine root biomass may partly contribute to the greater SOC in the forest. In addition, the soil nitrogen (N) content changed in synchronicity with SOC during afforestation, which indicates that SOC accumulation in the top/subsoil may be determined by the increase in soil N in these layers. In contrast, the SIC stock in the top 20 cm of the forest was significantly lower than that of the cropland. However, this decrease in the SIC level in the topsoil of the forest was offset by an increase in SIC in the subsoil (60–100 cm). The change in SIC along the soil profile following afforestation could be explained by the dissolution and leaching of SIC from the topsoil and subsequent precipitation in the subsoil. The dissolution and leaching of SIC in the forest topsoil were due to the high biological activity associated with the high aboveground litter input, fine root biomass and SOC stock as well as the high soil water content, whereas the precipitation of the leached SIC in the subsoil was a result of the dramatic decrease in the soil water content and fine root biomass in the subsoil. These findings suggest that soil can accumulate organic carbon in the topsoil and subsoil following black locust plantation establishment on cropland (as in the Loess Plateau study area) and that this type of cropland to forest plantation conversion in this area can redistribute SIC along the soil profile without affecting the net SIC accumulation.