Native Broadleaved Species Research Articles

Effects of mixed broadleaved tree species with pure Pinus massoniana plantation on soil microbial necromass carbon and organic carbon fractions

Mixing native broadleaved tree species is a widely used method for renovating Pinus massoniana plantations. Soil microbial necromass carbon and organic carbon fractions are important parameters for evaluating the impacts of tree species mixing and soil organic carbon (SOC) stability. However, their responses to the mixing and renovation of P. massoniana plantation has not been understood yet. Here, we selected a pure P. massoniana plantation (PP) and a mixed P. massoniana and Castanopsis hystrix plantation, with ages of 16 (MP16) and 38 years (MP38), respectively, as the research objects. We quantified soil physical and chemical properties, microbial necromass carbon content, and organic carbon components at different soil layers to reveal whether and how the introduction of C. hystrix into P. massoniana plantation affected soil microbial necromass carbon and organic carbon components. The results showed that the mixed P. massoniana and C. hystrix plantation significantly reduced fungal necromass carbon content and the ratio of fungal/bacterial necromass carbon in the 0-20 cm and 20-40 cm soil layers. There were no significant differences in microbial necromass carbon contents, bacterial necromass carbon contents, and their contributions to SOC among the different plantations. The contribution of fungal necromass carbon to SOC was higher than that of bacterial necromass carbon in all plantation types. The contribution of soil mineral-associated organic carbon (MAOC) to SOC was higher than that of occluded particulate organic carbon (oPOC) and light-free particulate organic carbon (fPOC) for all plantation types. Mixing the precious broadleaved tree species (i.e., C. hystrix) with coniferous species (P. massoniana) significantly increased MAOC content and the contribution of MAOC, oPOC, and fPOC to SOC in the 0-20 cm and 20-40 cm soil layers. The MAOC of MP38 was significantly higher than that of PP in all soil layers and the MAOC of MP38 stands were significantly higher than MP16 stands in the 20-40 cm, 40-60 cm, and 60-100 cm soil layers, indicating that hybridization enhanced SOC stability and that the SOC of MP38 stands were more stable than MP16 stands. SOC and total nitrogen contents were the main environmental factors driving the changes in soil microbial necromass carbon, while soil total nitrogen and organically complexed Fe-Al oxides were the primary factors affecting organic carbon fraction. Therefore, SOC stability can be enhanced by introducing native broadleaved species, such as C. hystrix, during the management of the P. massoniana plantation.

Growth and Adaptive Capacity of Douglas Fir Genetic Resources from Western Romania under Climate Change

The most recent climate change scenarios show that Southern and Eastern Europe will be affected by a significant increase in temperature and drought frequency by the end of the 21st century. Romania has already recorded very high temperatures and long periods of drought over recent decades, the most affected regions being the south, west and east of the country. Considering that successful forest management requires suitable species and high-quality reproductive material for reforestation, the aim of this study was to evaluate and compare the growth and drought response of Douglas fir (Pseudotsuga menziessi var. menziesii) and Norway spruce (Picea abies) in two stands installed at the end of the 19th century in western Romania. The growth traits, wood characteristics and drought parameters (resistance, recovery, resilience and relative resilience) of Douglas fir and Norway spruce trees have been analyzed and compared. The climate–growth relationship was determined using growth response functions over the period 1938–2017. Additionally, to simulate the potential impact of climate change on Douglas fir in this region, the RCP4.5 scenario was used over two periods: 2041–2070 and 2071–2100. The results reveal that Douglas fir has an exceptional growth capacity, overcoming the Norway spruce since the early ages in both site conditions. The highest growth performances were seen in the low-productivity site. From analyzing the responses to drought events, considerable differences were found between species. The results highlight the high resistance and relative resilience to extreme droughts of Douglas fir compared to Norway spruce. However, autumn–winter temperatures play an important role in the adaptation of Douglas fir to site conditions in Romania. The use of appropriate provenances of Douglas fir in mixed stands with native broadleaved species may be an option for climatically exposed sites, thus increasing the value of these stands.

Seed rain and soil seed bank in Chinese fir plantations and an adjacent natural forest in southern China: Implications for the regeneration of native species.

The natural regeneration of native broadleaved species underneath forest monoculture plantations is important to recover ecosystem functions and to mitigate adverse environmental effects. To understand how seed rain and soil seed bank facilitate natural regeneration, we surveyed their density and composition in a monoculture Chinese fir plantation, a mixed Chinese fir–broadleaf plantation, and an adjacent natural broadleaved forest for two years in southern China. Twenty‐eight species (16 families) were in seed rain, and 45 species (27 families) were in soil seed bank. Seed rain density did not differ significantly across stands; however, the number of taxa in seed rain was highest in the mixed plantation and lowest in the natural forest. Seed bank density was significantly higher in the mixed plantation than in the other stands (p < .05). The Sørensen similarity index of species composition between seed sources and aboveground vegetation were relatively low (<.50). The seeds of various native tree species were common in the seed bank of the plantations, indicating that seed rain and seed bank played an important role in native forest regeneration. We recommend that managers interested in sustainable forestry should take into consideration the presence of existing soil seed bank when developing their management strategies. In addition, with regard to forest regeneration process, we also recommend supplementation of the species composition by direct seeding or planting of desired species.

Impact of forest degradation and reforestation with Alnus and Quercus species on soil quality and function in northern Iran

Abstract Forest degradation causes soil carbon losses and affects soil C and N cycling. However, it is not clear how reforestation of degraded areas with different species affects soil and ecosystem restoration, particularly in northern Iran. The aim of this study was to evaluate the effect of forest degradation and reforestation with two contrasting species: Alnus and Quercus as N2-fixing and non N2-fixing tree species, respectively, on soil quality and function after 30 years in the northern Iran region. We selected four forest stands: Carpinus betulus-Parrotia persica natural forest (NF), Alnus subcordata (AP) and Quercus castaneifolia (QP) plantations as rehabilitated areas, and a degraded natural forest (DNF). We examined the main litter and soil chemical properties and soil C and N microbial fractions. Litter and soil physico-chemical properties and microbial activity differed among land covers. As expected, deforestation caused a decrease in most soil C and N fractions as well as in soil microbial activity with an increase in metabolic quotient-qCO2. The plantation with Quercus spp. improved substrate induced respiration, as well as microbial biomass carbon and dissolved organic carbon compared to the Alnus plantation, whereas mineral N was similar in the natural site and the Alnus plantation. Although forest plantations had not reached the same values of microbial activity as the natural forest soils, soil C and N fractions were similar to the natural site after 30 years. The findings of this study support the importance of preserving natural forests for soil conservation. In addition, employing of N2 fixing trees such as Alnus spp. or, Quercus spp., suitable native broadleaved species, is proposed for the rehabilitation of degraded natural forests. Although both forest plantations led to soil recovery after 30 years, Quercus plantations were more efficient in restoring microbial communities than Alnus plantations indicating that litter quantity is more important than litter quality for soil recovery.

Long-term afforestation effect and help to optimize degraded forest lands and reducing climate changes

The present study examined the forest floor, soil properties, and dynamics of greenhouse gas fluxes in 23-years old stands of alder (Alnus subcordata C. A. M.), maple (Acer velutinum Bioss.), cypress (Cupressus sempervirens L. var. horizontalis), and pine (Pinus nigra) sites in northern Iran. A degraded natural forest (DNF) with sparse trees including Parrotia persica C. A. M., Carpinus betulus L., and Diospyros lotus L. located near the afforested stands was selected as the control region. Fifteen forest floor and topsoil (0–15 cm) samples per site were taken and analyzed in the laboratory. In addition, the seasonal changes in the fluxes of CO2, CH4, and N2O were studied over a year. The quality of the forest floor differed among the sites, indicating the highest N, and the lowest C concentrations in the alder stand. The soil bulk density, pH, available nutrients (P, Ca, and Mg), earthworm activities and microbial biomass N were significantly higher in the alder stand with organic C being the least. The microbial biomass C did not differ among the studied sites, whereas the total N was significantly higher in the alder ≈ maple sites having the minimum C/N ratios. High contents of water were found in the DNF site. The highest CO2 (0.31 mg CO2 m−2 d−1) and N2O (0.42 mg N2O m−2 d−1) fluxes were observed in the DNF site. The CH4 flux showed higher amounts in the DNF ≈ cypress ≈ pine (0.12, 0.11 and 0.07 mg CH4 m−2 d−1, respectively) sites than in the maple ≈ alder (−0.05, and − 0.04 mg CH4 m−2 d−1, respectively) plantations. The highest values of all fluxes were measured in August, whereas the lowest were detected in February. This research recommends a plantation with suitable native broad-leaved species along with a forestation management plan to rehabilitate the forests of the DNF area.

Estimating Rainfall Interception of Vegetation Canopy from MODIS Imageries in Southern China

The interception of rainfall by vegetation canopies plays an important role in the hydrologic process of ecosystems. Most estimates of canopy rainfall interception in present studies are mainly through field observations at the plot region. However, it is difficult, yet important, to map the regional rainfall interception by vegetation canopy at a larger scale, especially in the southern rainy areas of China. To obtain a better understanding of the spatiotemporal variation of vegetation canopy rainfall interception with regard to the basin scale in this region, we extended a rainfall interception model by combining the observed rainfall data and moderate resolution imaging spectroradiometer leaf area index (MODIS_LAI) data to quantitatively estimate the vegetation canopy rainfall interception rate (CRIR) at small/medium basin scales in Guangdong Province, which is undergoing large changes in vegetation cover due to rapid urban expansion in the area. The results showed that the CRIR in Guangdong declined continuously during 2004–2012, but increased slightly in 2016, and the spatial variability of CRIR showed a diminishing yearly trend. The CRIR also exhibited a distinctive spatial pattern, with a higher rate to the east and west of the mountainous areas and a lower rate in the central mountainous and coastal areas. This pattern was more closely related to the spatial variation of the LAI than that of rainfall due to frequent extreme rainfall events saturating vegetation leaves. Further analysis demonstrated that forest coverage, instead of background climate, has a certain impact on the canopy rainfall interception, especially the proportion of broad-leaved forests in the basin, but more in-depth study is warranted in the future. In conclusion, the results of this study provide insights into the spatiotemporal variation of canopy rainfall interception at the basin scale of the Guangdong Province, and suggest that forest cover should be increased by adjusting the species composition to increase the proportion of native broad-leaved species based on the local condition within the basin. In addition, these results would be helpful in accurately assessing the impacts of forest ecosystems on regional water cycling, and provide scientific and practical implications for water resources management.

Impacts of forest conversion on soil bacterial community composition and diversity in subtropical forests

Forest conversion may affect the soil microbial community through impacts on soil properties. However, our understanding of the effects on the soil bacterial community remains limited. The objective of this study was to understand the impacts of forest conversion of native broad-leaved species on soil bacterial structure and diversity. The phylogeny structure and diversity of the soil bacterial communities were compared among four forest types. We found that the soil total nitrogen (TN) and C:N ratios were significantly different between a mixed forest and other forest types. The native forest and mixed forest contained a higher relative abundance of Actinobacteria, Gammaproteobacteria, and Acidimicrobiia compared with the Chinese fir and Bamboo forests, but more unique operational taxonomic units (OTUs) were found in the Chinese fir and Bamboo forests. Soil bacteria in bamboo forest and Chinese fir forest showing a higher diversity but a lower total sequencing number than native forest and mixed forest. Among the soil properties, pH was an important variable that contributing to both soil bacterial communities and soil alpha diversities. Our work suggests that after a long-tern forest conversion, both land-use history and vegetation species strongly influence soil bacteria communities, and soil pH is a main factor that influences soil bacterial structure.

Exploring the factors affecting carbon and nutrient concentrations in tree biomass components in natural forests, forest plantations and short rotation forestry

BackgroundCoupling biomass models with nutrient concentrations can provide sound estimations of carbon and nutrient contents, enabling the improvement of carbon and nutrient balance in forest ecosystems. Although nutrient concentrations are often assumed to be constant for some species and specific tree components, at least in mature stands, the concentrations usually vary with age, site index and even with tree density. The main objective of this study was to evaluate the sources of variation in nutrient concentrations in biomass compartments usually removed during harvesting operations, covering a range of species and management conditions: semi-natural forest, conventional forest plantations and short rotation forestry (SRF). Five species (Betula pubescens, Quercus robur, Eucalyptus globulus, Eucalyptus nitens and Populus spp.) and 14 genotypes were considered. A total of 430 trees were sampled in 61 plots to obtain 6 biomass components: leaves, twigs, thin branches, thick branches, bark and wood. Aboveground leafless biomass was pooled together for poplar. The concentrations of C, N, K, P, Ca, Mg, S, Fe, Mn, Cu, Zn and B were measured and the total biomass of each sampled tree and plot were determined. The data were analysed using boosted regression trees and conventional techniques.ResultsThe main sources of variation in nutrient concentrations were biomass component > > genotype (species) ≈ age > tree diameter. The concentrations of Ca, Mg and K were most strongly affected by genotype and age. The concentrations of P, K, Ca, Mg, S and Cu in the wood component decreased with age, whereas C concentrations increased, with a trend to reach 50% in the older trees. In the SRF, interamerican poplar and P. trichocarpa genotypes were comparatively more efficient in terms of Ca and K nutrient assimilation index (NAI) (+ 65–85%) than eucalypts, mainly because leafless biomass can be removed. In the conventional eucalypt plantations (rotation 15 years), debarking the wood at logging (savings of 225% of Ca and 254% of Mg for E. globulus) or the use of selected genotypes (savings of 45% of P and 35% of Ca) will provide wood at a relatively lower nutrient cost. Considering all the E. globulus genotypes together, the management for pulp with removal of debarked wood shows NAI values well above (× 1.7–× 3.9) the ones found for poplar or eucalypt SRF and also higher (× 1.6–× 4.0) than the ones found for oak and birch managed in medium or long rotations. The annual rates of nutrient removal were low in the native broadleaved species but the rates of available soil nutrients removed were high as compared to poplar or eucalypts. Management of native broadleaved species should consider nutrient stability through selection of the biomass compartments removed.ConclusionsThe nutrient assimilation index is higher in poplar grown under short rotation forestry management than in the other systems considered. Nutrient management of fast growing eucalyptus plantations could be improved by selecting efficient genotypes and limiting removal of wood. The values of the nutrient assimilation index are lower in the natural stands of native broadleaved species than in the other systems considered.

Tree species could have substantial consequences on topsoil fauna: a feedback of land degradation/restoration

The characteristics of the faunal community in the soil are closely related to soil quality and function. Land degradation, which reduces vegetation cover, may affect the soil surface-active fauna because both the above ground and below ground invertebrates depend on complex plant communities. In this study, we evaluated the effect of land degradation/restoration and factors affecting soil fauna in northern Iran. The studied land uses were virgin natural forest (VNF), Alnus subcordata C.A.M. plantation (ASP), Quercus castaneifolia C.A. Mey plantation (QCP), Cupressus sempervirens var. horizontalis plantation (CSP) and degraded natural forest (DNF). VNF and ASP enhanced soil earthworm density (2.43 and 2.12 ind. m−2) and dry mass (27.44 and 23.39 mg m−2) with more ratio of epigeic. The activities of acarina (91,851.37 and 85,810.43 ind. m−2), collembola (83,009.50 and 74,996.18 ind. m−2) and protozoa [921.25 and 851.81 (× 102 g soil)] were increased under VNF ≈ ASP, respectively. Nematode population (650 in 100 g soil) significantly improved under VNF. In general, good quality forest floor, alkaline soil and accumulation of macro-element nutrients improved biological activities under the VNF and ASP sites, while low-quality forest floor, acidic soil, less macro-elements nutrients decreased biological activities imposed by the QCP, CSP and DNF sites. More activities of the studied soil fauna were found in autumn and spring. The findings of this study support the importance of preserving natural forests. In addition, employing N2-fixing and suitable native broadleaved species have been proposed in a bid to rehabilitate DNFs.

Fine Root Dynamics in Three Forest Types with Different Origins in a Subalpine Region of the Eastern Qinghai-Tibetan Plateau

Fine roots play a crucial role in plant survival potential and biogeochemical cycles of forest ecosystems. Subalpine areas of the Eastern Qinghai-Tibetan Plateau have experienced different forest re-establishment methods after clear-cutting primary forest. However, little is known about fine root dynamics of these forests originating from artificial, natural and their combined processes. Here, we determined fine root traits (biomass, production and turnover rate) of three subalpine forest types, i.e., Picea asperata Mast. plantation forest (artificial planting, PF), natural secondary forest (natural without assisted regeneration, NF) and P. asperata broadleaved mixed forest (natural regeneration after artificial planting, MF) composed of planted P. asperata and naturally regenerated native broadleaved species. At the soil depth of 0–30 cm, fine root biomass was the highest in PF and fine root production was the highest in NF, and both were the lowest in MF. Fine root dynamics of the three forest types tended to decrease with soil depth, with larger variations in PF. Fine root biomass and production were the highest in PF in 0–10 cm soil layer but were not significantly different among forest types in the lower soil layers. There were positive correlations between these parameters and aboveground biomass across forest types in soil layer of 0–10 cm, but not in the lower soil layers. Fine root turnover rate was generally higher in mixed forests than in monocultures at all soil depths. In conclusion, the natural regeneration procedure after clear-cutting in the subalpine region of western Sichuan seems to be superior from the perspective of fine root dynamics.

C and N cycle monitoring under Quercus castaneifolia plantation

In temperate forests, oak (Quercus castaneifolia) is an important species that grows along an elevation gradient from the flood prone plains to high topographical positions of the landscape. This study was aimed to monitor the effect of oak plantation on the soil C and N cycles and dynamics in the north of Iran. We tested the following hypotheses: (i) reclamation of deforested areas, planting of oak can improve topsoil fertility via forest floor inputs in the long-term, (ii) soil C and N microbial indices can be enhanced under oak plantation, 25 years after planting. For this purpose, three afforested oak stands with 15, 20, and 25 years old, besides a site without plantation, were selected and thirty samples per each site were taken from forest floor and soil (20 × 20 × 10 cm) layers and their physicochemical, biological, and enzymatic properties were assessed. The acquired data demonstrated that forest floor quality, physicochemical and biological properties and enzymatic activities (i.e. urease, acid phosphatase, arylsulfatase and invertase) have been changed over time of oak plantation. Moreover, the microbial activity of soil C and N include basal respiration (BR), substrate inducted respiration (SIR), microbial biomass carbon (MBC), Metabolic quotient (qCO2), microbial entropy (MBC/C), carbon availability index (CAI), carbon management index (CMI), particle organic carbon (POC) and dissolved organic carbon (DOC) were significantly higher in the plantation areas than without plantation site. Oak plantation significantly improved the N microbial characteristics [NH4+, NO3−, N mineralization, microbial biomass nitrogen (MBN), particle organic nitrogen (PON) and dissolved organic nitrogen (DON)]. Under different land covers, soil microbial activities were more affected by variations in forest floor and soil chemical properties with higher ratio of C, N and available nutrients. Taken together, plantation with suitable native broadleaved species could be considered to rehabilitate degraded natural forests through improving soil quality. Findings also highlighted the importance of understanding C and N cycles in the plantation areas which could involve in global warming phenomena.

Increasing tree diversity enhances microbial and enzyme activities in temperate Iranian forests

Our findings show the differential impacts of tree types (hornbeam–ironwood natural forest and plantations of ash, maple, cypress and pine) on soil physical–chemical characteristics and how dominant tree species regulate the size and activity of soil microbial and enzymes. Soil microbial and enzyme activities have an important influence on nutrient cycling. The variation in soil carbon (C) and nitrogen (N) microbial indices as well as enzyme activities were determined under hornbeam–ironwood natural forest and 25-years old plantations of ash, maple, cypress and pine in northern Iran. Four soil profiles were dug along the four parallel transects in the central part of each forest stand, resulting in 16 soil samples for each stand at a depth of 0–15 cm. The results showed significant differences in most of studied soil physico-chemical properties among different land covers. Soil microbial basal respiration (MR) and substrate induced respiration (SIR) were found to be significantly higher under natural forest than in the plantation stands. Microbial biomass C (MBC) did not differ for the forest stands, whereas natural forest had significantly higher qCO2 (MR: MBC), microbial entropy (MBC: Corg) and C availability index (MR: SIR) values. The establishment of plantations reduced the values of soil microbial biomass N, mineral nitrogen (NH4–N and NO3–N) and N mineralization with the least under coniferous stands of cypress and pine, while greater amounts were observed under natural forest. With replacement in the type of tree species from natural forest to plantations, acid phosphatase, arylsulphatase and invertase enzyme activities decreased significantly in the topsoil, whereas like natural forest, ash plantation improved urease enzyme. This research recommends conservation of natural forests for increase of soil quality and plantation of suitable native broad-leaved species for rehabilitation of degraded natural forests.

Ophiostomatoid fungi isolated from three different pine species in Argentinian Patagonia

SummaryPine plantations in Argentinian Patagonia cover ca. 95,000 ha in Chubut, Río Negro and Neuquén provinces. Exotic bark beetles (Orthotomicus laricis, Hylastes ater and Hylurgus ligniperda) commonly occur in freshly cut logs, stumps and slash. These beetles are vectors of “ophiostomatoid” fungi which include primary tree pathogens as well as important agents of blue stain. The aim of this study was to identify these beetle‐associated fungi. Sawing mills and pine plantations were surveyed three consecutive years. Fungal isolates from stained logs, processed wood and insect galleries were identified based on morphological and DNA sequence comparisons of ITS and β‐tubulin gene regions. Two Grosmannia, one Graphilbum and three Ophiostoma species were identified. Ophiostoma piliferum and O. peregrinum sp. nov. were the most frequently isolated taxa. O. peregrinum occurred in all provinces, colonizing different conifer species and, interestingly, also the native broadleaved species Nothofagus dombeyi. Pine plantation forestry in southern South America includes Argentina, Brazil, Chile, Paraguay and Uruguay. Emerging data from Argentina, Chile and Uruguay revealed some coincidences between these countries, but also several differences, probably, as a result of multiple introduction events.

Impacts of changes in land use/cover on soil microbial and enzyme activities

Microbial and enzyme activities are increasingly being recognized as sensitive indicators of soil quality. This study aims to determine the impacts of different kinds of land use/cover, i.e. virgin natural forest (VNF), degraded natural forest (DNF), alder plantation (AP), sequoia plantation (SP), improved fallow (IF) and home garden (HG) areas on soil properties in northern Iran. Five composed samples per land use/cover were taken from the top 10cm of the soil.Soil microbial respiration was found to be in the ranked order of AP>VNF>HG>DNF>IF≈SP areas, being more than one-and-a-half-fold under AP compared with SP. The values of microbial biomass carbon were almost two times higher under SP≈VNF than under IF≈HG areas. Microbial biomass nitrogen was found to be significantly higher under AP≈VNF than in the other kinds of land covers. AP≈VNF significantly increased the activities of urease and acid phosphatase, whereas greater activities of invertase occurred in AP≈VNF≈SP sites. Arylsulphatase activity was significantly higher to be significantly higher under AP in comparison with VNF>HG>DNF>SP>IF areas. As a conclusion, alder (Alnus subcordata C. A. Mey.) plantation improved the soil quality to levels similar to natural forest ecosystems. This research recommends the preservation of natural forests to increase soil quality and a plantation with suitable native broad-leaved species and forestation plan management to rehabilitate degraded natural forests.

Soil microbial community composition does not predominantly determine the variance of heterotrophic soil respiration across four subtropical forests.

To explore the importance of soil microbial community composition on explaining the difference in heterotrophic soil respiration (Rh) across forests, a field investigation was conducted on Rh and soil physiochemical and microbial properties in four subtropical forests in southern China. We observed that Rh differed significantly among forests, being 2.48 ± 0.23, 2.31 ± 0.21, 1.83 ± 0.08 and 1.56 ± 0.15 μmol m−2 s−1 in the climax evergreen broadleaf forest (BF), the mixed conifer and broadleaf forest (CF), the conifer plantation (CP), and the native broadleaved species plantation (BP), respectively. Both linear mixed effect model and variance decomposition analysis indicated that soil microbial community composition derived from phospholipid fatty acids (PLFAs) was not the first-order explanatory variable for the Rh variance across the forests, with the explanatory power being 15.7%. Contrastingly, vegetational attributes such as root biomass (22.6%) and soil substrate availability (18.6%) were more important for explaining the observed Rh variance. Our results therefore suggest that vegetation attributes and soil carbon pool size, rather than soil microbial community composition, should be preferentially considered to understand the spatial Rh variance across the subtropical forests in southern China.

Invasive Tree Species Robinia pseudoacacia: A Potential Biomass Resource in Nagano Prefecture, Japan

The introduced tree species, Robinia pseudoacacia (black locust), has spread extensively in many countries. Because of its active regeneration and rapid initial growth, R. pseudoacacia has not been successfully eradicated despite many efforts. To manage this species, developing information on the growth of R. pseudoacacia as a biomass resource is desirable, and this will motivate logging and could contribute to the extermination or sustainable use of this species. In the present study, the stand volume and growth of R. pseudoacacia forests in riverbeds along the Chikumagawa River in Nagano Prefecture in Japan were examined by tree ring and stem analyses. Seven plots were established in R. pseudoacacia riparian forests of varying ages, and 611 measurements of diameter at breast height and 386 measurements of tree height were made. Stand volumes, which were estimated using equations of stem volume curve based on the results of stem analysis of 47 sample trees, were almost the same as or higher than those of native broadleaf forests in Japan. Stand volumes continued to increase for more than 20 years. Current annual increments of four plots (aged 13–22 years) indicated that it could take <5 years after regeneration for the annual increment of R. pseudoacacia forests to reach a maximum level. Growth of R. pseudoacacia was comparable to or faster than native broadleaved species in Japan, showing the possibility of short rotation harvesting.

Regeneration of native broadleaved species on clearfelled conifer plantations in upland Britain

In upland areas of Great Britain, large tracts of non-native conifer plantations have been established on poor quality agricultural land. There is now considerable interest in the conversion of some of these plantations to a more natural woodland comprised of native tree species. We studied the tree regeneration and ground flora on 15 upland sites (altitudes ranging from 120m to 380m above sea level) that had been clearfelled of conifers. Regeneration of native tree species was successful where a clearcut site was adjacent to mature native trees, which acted as a seed source. Mean regeneration densities of native tree species on clearcut sites were typically greater than 1000stems/ha, exceeding minimum recommended planting densities for the establishment of new native woodland. Whilst 10 native woody tree species were recorded, the regeneration was dominated by birch species. Regeneration densities were significantly higher on clearcut sites than on adjacent areas of unplanted moorland, probably due to the lack of a dense ground flora following the clearfelling operations. Our results indicate that where local native seed sources exist, clearfelling upland conifer plantation sites to allow natural regeneration has the potential to be an effective method of establishing native woodland.

Restocking with broadleaved species during the conversion of Tsuga heterophylla plantations to native woodland using natural regeneration

The removal of conifers planted during the twentieth century on sites that had been woodland for many centuries, with the intention of restoring native broadleaved species, is an important aim of forestry policy in Great Britain. Current guidance generally advocates gradual removal of plantation trees using continuous cover silviculture and restocking by natural regeneration, but methods are largely untested. This study investigated natural regeneration of trees and shrubs at sites where western hemlock had been established either pure or in mixture with native broadleaved species. Western hemlock had been cleared from 70% of the sites. There were c. 10–300 stems ha−1 providing canopy cover of 10–90%; the predominant broadleaved canopy trees were ash, beech, birch and oak. The ground flora of all sites was species poor; bramble was the predominant vegetation type overall, but grasses, rushes and shrubs were relatively more abundant on open sites. A total of 15 native tree species were regenerating, birch was most common and at most sites there were few valuable broadleaved timber species. Although combined numbers of seedlings and saplings varied from 200 to 20,000 ha−1, large areas of most sites had few regenerating trees and <10% of their area was becoming restocked with timber species. Relationships between seedling numbers and site characteristics were complex and varied with species, but there was a consistent positive relationship between the presence of nearby parent trees and the frequency and abundance of seedlings. The results indicate that the current reliance on natural regeneration may be unwise especially for those broadleaved species such as oak and beech which are valued for their timber.

Assessments of the impacts of Chinese fir plantation and natural regenerated forest on soil organic matter quality at Longmen mountain, Sichuan, China

Three soil labile organic carbon indicators, i.e., particulate organic carbon (POC) by size fractionation, light fraction organic carbon (LFOC) by density fractionation and permanganate-oxidizable carbon (MnoxC) oxidized by 333 mM KMnO 4, were employed to identify the soil organic carbon (SOM) pools of a Chinese fir plantation (CF) and a regenerated forest (RF) that were converted originally from the natural evergreen broad-leaved forest (NF) 18 years ago after clear cutting on an upland yellow soil in Longmen mountain, southwest China. Bulk soil organic carbon and nitrogen concentration at the soil depth of 0–20 cm were significantly lower in CF and RF than in NF, while no significant C/N ratio change was found. Top soil MnoxC concentration of CF showed a significant increase while RF demonstrated a slight decline compared to NF, whereas, non-MnoxC of CF and RF both presented a significant decline compare to NF. A different indication between chemical oxidization and physical fractionation method was found. POC, particulate organic nitrogen (PON), mineral-associated organic carbon (MOC) and mineral-associated organic nitrogen (MON) were significantly reduced in CF and RF compared to NF. CF, POC and PON showed significant reductions than that in RF. The losses of TOC and N in the particulate separates were more than that in the mineral-associated separates for both CF and RF. A significant decline of LFOC at 0–10 cm, 10–20 cm and 20–30 cm soil depths were found in CF and RF compared to NF, and a significant larger loss of LFOC in CF than in RF was also found. The heavy fraction organic carbon (HFOC) at the 0–10 cm soil depth was also significantly reduced in CF and RF, while there was no significant difference between CF and RF. The absence of vegetation cover in CF and RF, especially at the early stage of restoration, was contributed to the reductions in both labile and non-labile carbon. Timely thinning after canopy closure or establishing CF mixing with native broad-leaved species should be encouraged to mitigate the labile carbon loss.

Multiple mineral deficiencies in forest plantations in Liberia

Mineral deficiencies are often responsible for growth abnormalities, growth inhibition and the decline of tree plantations in the rain forest zone of Liberia. Foliar analyses of Pinus caribaea, P. oocarpa and several exotic as well as native broad-leaved species show obvious differences in the nutrient status of fast-growing, healthy trees and slowly growing trees with deficiency symptoms. Besides phosphorus, foliar levels of potassium, magnesium, and nitrogen seem to be below the critical range in pines. On the other hand, high aluminium and iron concentrations occur frequently.