Modelling the amount of coarse woody debris produced by the new biodiversity-oriented silvicultural practices in Sweden

One of the most important measures adopted in the new biodiversity-oriented forestry in Sweden is to increase the quantity of coarse woody debris (CWD) in commercially managed forests, by leaving existing dead trees as well as ensuring input of new dead trees. We have used a simulation model in order to predict the quantity of CWD of Norway spruce (Picea abies (L.) Karst.) in forest landscapes subject to different management regimes. It is shown that in an average, managed forest landscape in Sweden, where the management regimes are changed in order to follow the current requirements for certification by FSC, the amount of CWD will be more than doubled, but it will take more than 100 years to reach the new level. The increase in the amount of CWD will first be recognised for hard (less decayed) CWD and mainly in young, newly cut stands. Leaving forests unmanaged, retaining living trees and decreasing the destruction of CWD at final cutting, and not removing naturally dying trees are all measures that have a strong positive influence on the amount of CWD.     

Removal of logging residue in Norway spruce thinning stands: Long-term changes in organic layer properties

The aim of this study was to determine whether repeated removal of logging residue in Norway spruce thinning stands causes consistent long-term effects on soil microbial processes in C and N cycling and on soil concentrations of two major groups of plant secondary compounds, phenolic compounds and terpenes. The study sites were four 47-to 70-year-old Norway spruce (Picea abies (L.) Karst) stands, all growing on relatively fertile sites in southern and central Finland. These stands had been thinned twice, the first thinning 22-29 years ago and the second thinning 10 years after the first, 12-19 years ago. After thinnings, the logging residue was either removed (whole-tree harvest, WTH) or left on the site (stem-only harvest, SOH). In one experiment there was also a treatment where a double amount of logging residue was distributed on the plot. Samples were taken from the organic layer (O_fh). Removal of logging residue did not affect the C-to-N ratio or pH much. Removal of logging residue did not affect the amounts of C and N in the microbial biomass but tended to decrease the rates of net N and C mineralization (CO₂ production). It decreased both sesquiterpene and diterpene (mostly resin acids) concentrations but did not affect triterpene (mostly sterols) concentrations. Neither total water-soluble phenolic compounds nor an important group of phenolic compounds, condensed tannins, were affected by removal of logging residue. At these four study sites, the effects of removing logging residue were strongest on the two least fertile sites, whereas the most fertile site did not respond much to removal. In conclusion, with regard to the processes and ratios indicating N availability, stem-only harvest seems generally to be more favorable than whole-tree harvest in long-term.     

Direct estimates of C:N ratios of ectomycorrhizal mycelia collected from Norway spruce forest soils

Direct estimates of C:N ratios of ectomycorrhizal (EM) mycelia growing in situ in forest soils have been obtained for the first time. The mycelial samples were collected from sand-filled mesh bags that were buried in the soil and incubated for 12-18 months in two Norway spruce forests in southern Sweden. At harvest the mesh bags were heavily colonized and the mycelia were extracted from the sand with water. The collected mycelia had earlier been identified as belonging to EM fungi based on their C isotopic composition. The mean value of the C:N ratio for mycelia was 20.2±0.8 (n=25). EM mycelia collected at different soil depths (5, 15 and 30 cm) had similar C:N ratios. C:N ratios of microbial biomass obtained by fumigation-extraction of similar soils have usually been lower (6-13) so possible differences in the extraction efficiency of C and N from bacteria and fungi are discussed.     

Relationships between canopy transpiration, atmospheric conditions and soil water availability—Analyses of long-term sap-flow measurements in an old Norway spruce forest at the Ore Mountains/Germany

At the study site Tharandt Anchor Station in Saxony/Germany sap flow measurements are conducted in an old Norway spruce (Picea abies [L.] KARST.) stand. During the study period from 2001 to 2007 several events like thinning, long and short drought periods and a winter storm significantly affected the amount of canopy water use. We show that intra-annual variation of Ec is strongly related to VPD and PPFD. While there is a non-linear relationship between daily Ec and VPD, daily Ec is limited by daily integrated PPFD indicating stomatal control of Ec through photosynthesis. On a monthly or seasonal basis, reduction of Ec is not only related to high VPD and non-saturating PPFD, but also to higher frequencies of precipitation. In comparison to this, nearly 55% of canopy precipitation and 20% of available energy were used for transpiration during the growing season. Intensive seasonal soil water measurements at the site revealed that on average about 74% of soil water removal within the rooting zone can be related to tree water uptake. A good correlation was found between annual Ec and Ec_max, usually occurring in June or July. Further, the monthly sums of June plus July were good predictors of annual Ec. Within the study period, the extreme drought in 2003 revealed a clear threshold of soil water content by 9.5 vol% and had the most pronounced effect on annual Ec followed by a stand thinning. The winter storm “Kyrill” in January 2007 had caused loss of green needles and twigs. It is assumed that the observed reduction in Ec during spring was related to the reduced leaf biomass and potentially to root damage of bended trees. Excluding the effect of extreme drought and forest management, a mean inter-annual variation in Ec of ±15% and in Ec/VPD of ±8% remained. It is concluded that lag-effects of drought and the winter storm add lacking explanation to the inter-annual variability of canopy transpiration besides the typical variation of atmospheric conditions.     

Saprotrophic fungi transform organic phosphorus from spruce needle litter

Fungal decomposition of and phosphorus transformation from spruce litter needles (Picea abies) were simulated in systems containing litter needles inoculated with individual saprotrophic fungal strains and their mixtures. Fungal strains of Setulipes androsaceus (L.) Antonín, Chalara longipes (Preus) Cooke, Ceuthospora pinastri (Fr.) Höhn., Mollisia minutella (Sacc.) Rehm, Scleroconidioma sphagnicola Tsuneda, Currah & Thormann and an unknown strain NK11 were used as representatives of autochthonous mycoflora. Systems were incubated for 5.5 months in laboratory conditions. Fungal colonization in systems and competition among strains were assessed using the reisolation of fungi from individual needles. After incubation, needles were extracted with NaOH and extracts were analysed using ³¹P nuclear magnetic resonance spectroscopy (NMR). Needle decomposition was determined based on the decrease in C:N ratio. Systems inoculated with the basidiomycete S. androsaceus revealed substantial decrease in C:N ratio (from 25.8 to 11.3) while the effect of ascomycetes on the C:N ratio was negligible. We suppose that tested strains of saprotrophic ascomycetes did not participate substantially in litter decomposition, but were directly involved in phosphorus transformation and together with S. androsaceus could transform orthophosphate monoesters and diesters from spruce litter needles into diphosphates, polyphosphates and phosphonates. These transformations seem to be typical for saprotrophic fungi involved in litter needle decomposition, although the proportion of individual phosphorus forms differed among studied fungal strains. Phosphonate presence in needles after fungal inoculation is of special interest because no previous investigation recorded phosphonate synthesis and accumulation by fungi. Our results confirmed that the ³¹P NMR spectroscopy is an excellent instrumental method for studying transformations of soil organic phosphorus during plant litter decomposition. We suggest that polyphosphate production by S. androsaceus may contribute to the phosphorus cycle in forest ecosystems because this fungus is a frequent litter colonizer that substantially participates in decomposition.     

The effect of lime on microbial activity in spruce (Picea abies L.) forests

Summary The use of lime increased heat output and decreased the C:N ratio (global indicators of biological activity) in the organic horizons of a spruce forest (Picea abies L.) soil. These changes were still present after 18 years. During the same period, the muramic acid content increased slightly, while the concentration of both ergosterol and glucosamine decreases. The ratios of ergosterol or glucosamine to muramic acid decreased significantly after 3 years in the plots that had been irrigated and limed, and after 8 years in the limed non-irrigated plots.     

Explaining temporal variation in soil CO2 efflux in a mature spruce forest in Southern Germany

An open dynamic chamber system was used to measure the soil CO₂ efflux intensively and continuously throughout a growing season in a mature spruce forest (Picea abies) in Southern Germany. The resulting data set contained a large amount of temporally highly resolved information on the variation in soil CO₂ efflux together with environmental variables. Based on this background, the dependencies of the soil CO₂ efflux rate on the controlling environmental factors were analysed in-depth. Of the abiotic factors, soil temperature alone explained 72% of the variation in the efflux rate, and including soil water content (SWC) as an additional variable increased the explained variance to about 83%. Between April and December, average rates ranged from 0.43 to 5.15 μmol CO₂ m⁻² s⁻¹ (in November and July, respectively) with diurnal variations of up to 50% throughout the experiment. The variability in wind speed above the forest floor influenced the CO₂ efflux rates for measuring locations with a litter layer of relatively low bulk density (and hence relatively high proportions of pore spaces). For the temporal integration of flux rates for time scales of hours to days, however, wind velocities were of no effect, reflecting the fact that wind forcing acts on the transport, but not the production of CO₂ in the soil. The variation in both the magnitude of the basal respiration rate and the temperature sensitivity throughout the growing season was only moderate (coefficient of variation of 15 and 25%, respectively). Soil water limitation of the CO₂ production in the soil could be best explained by a reduction in the temperature-insensitive basal respiration rate, with no discernible effect on the temperature sensitivity. Using a soil CO₂ efflux model with soil temperature and SWC as driving variables, it was possible to calculate the annual soil CO₂ efflux for four consecutive years for which meteorological data were available. These simulations indicate an average efflux sum of 560 g C m⁻² yr⁻¹ (SE=22 g C m⁻² yr⁻¹). An alternative model derived from the same data but using temperature alone as a driver over-estimated the annual flux sum by about 7% and showed less inter-annual variability. Given a likely shift in precipitation patterns alongside temperature changes under projected global change scenarios, these results demonstrate the necessity to include soil moisture in models that calculate the evolution of CO₂ from temperate forest soils.     

Carbon dioxide emissions of soils under pure and mixed stands of beech and spruce, affected by decomposing foliage litter mixtures

Soil respiration is the largest terrestrial source of CO₂ to the atmosphere. In forests, roughly half of the soil respiration is autotrophic (mainly root respiration) while the remainder is heterotrophic, originating from decomposition of soil organic matter. Decomposition is an important process for cycling of nutrients in forest ecosystems. Hence, tree species induced changes may have a great impact on atmospheric CO₂ concentrations. Since studies on the combined effects of beech-spruce mixtures are very rare, we firstly measured CO₂ emission rates in three adjacent stands of pure spruce (Picea abies), mixed spruce-beech and pure beech (Fagus sylvatica) on three base-rich sites (Flysch) and three base-poor sites (Molasse; yielding a total of 18 stands) during two summer periods using the closed chamber method. CO₂ emissions were higher on the well-aerated sandy soils on Molasse than on the clayey soils on Flysch, characterized by frequent water logging. Mean CO₂ effluxes increased from spruce (41) over the mixed (55) to the beech (59) stands on Molasse, while tree species effects were lower on Flysch (30-35, mixed > beech = spruce; all data in mg CO₂-C m⁻² h⁻¹). Secondly, we studied decomposition after fourfold litter manipulations at the 6 mixed species stands: the O_i - and O_e horizons were removed and replaced by additions of beech -, spruce - and mixed litter of the adjacent pure stands of known chemical quality and one zero addition (blank) in open rings (20 cm inner diameter), which were covered with meshes to exclude fresh litter fall. Mass loss within two years amounted to 61-68% on Flysch and 36-44% on Molasse, indicating non-additive mixed species effects (mixed litter showed highest mass loss). However, base cation release showed a linear response, increasing from the spruce - over the mixed - to the beech litter. The differences in N release (immobilization) resulted in a characteristic converging trend in C/N ratios for all litter compositions on both bedrocks during decomposition. In the summers 2006 and 2007 we measured CO₂ efflux from these manipulated areas (a closed chamber fits exactly over such a ring) as field indicator of the microbial activity. Net fluxes (subtracting the so-called blank values) are considered an indicator of litter induced changes only and increased on both bedrocks from the spruce - over the mixed - to the beech litter. According to these measurements, decomposing litter contributed between 22-32% (Flysch) and 11-28% (Molasse) to total soil respiration, strengthening its role within the global carbon cycle.     

Organic and inorganic soil phosphates and acid phosphatase activity in the rhizosphere of 80-year-old Norway spruce [Picea abies (L.) Karst.] trees

Summary Inorganic and organic phosphates (P) were measured in bulk soil, rhizosphere soil and mycorrhizal rhizoplane soil of Norway spruce. Various methods of P extraction and estimation were compared. In addition, acid phosphatase activity and mycelial hyphae length were determined. In soil solutions from various locations, about 50% (range 35%–65%) of the total P was present as organic P. Compared to the bulk soil, the concentrations of readily hydrolysable organic P were lower in the rhizosphere soil and in the rhizoplane soil; this difference was particularly marked in the humus layer. In contrast, the concentrations of inorganic P either remained unaffected or increased. A 2- to 2.5-fold increase was found in the activity of acid phosphatase in the rhizoplane soil in comparison to the bulk soil. There was a positive correlation (r = 0.83^***) between phosphatase activity and the length of mycelial hyphae. The results stress the role of organic P and of acid phosphatase in the rhizosphere in the P uptake by mycorrhizal roots of spruce trees grown on acid soils.     

Parasitoids (Hymenoptera, Ichneumonoidea) of Saproxylic beetles are affected by forest successional stage and dead wood characteristics in boreal spruce forest

The habitat requirements and effects of forest management on insects belonging to higher trophic levels are relatively unknown in forest ecosystems. We tested the effect of forest successional stage and dead wood characteristics on the saproxylic parasitoid (Hymenoptera, Ichneumonoidea) assemblage in boreal spruce-dominated forests in northern Sweden. Within each of nine areas, we selected three sites with different management histories: (1) a clear-cut (2) a mature managed forest and (3) an old-growth forest. Parasitoids were collected in 2003 using eclector traps mounted on fresh logs, which were either untreated (control), burned, inoculated with fungi, or naturally shaded, and on artificially-created snags.Both forest type and dead wood characteristics had a significant effect on parasitoid assemblages. Grouped idiobionts and some species, such as Bracon obscurator and Ontsira antica, preferred clear-cuts, while others, such as Cosmophorus regius (Hym., Braconidae) and other koinobionts, were associated with older successional forest stages. No single dead wood substrate was sufficient to support the entire community of parasitoids in any forest type, even when the regular host was present. In particular, snags hosted a different assemblage of species from other types of dead wood, with parasitoids of Tetropium spp. such as Rhimphoctona spp. (Hym., Ichneumonidae) and Helconidea dentator (Hym., Braconidae) being abundant. These results indicate that a diversity of dead wood habitats is necessary to support complete assemblages of beetle-associated parasitoids from early successional stages of dead wood and that parasitoids may be more sensitive to habitat change than their hosts.     

Orangutan population density, forest structure and fruit availability in hand-logged and unlogged peat swamp forests in West Kalimantan, Indonesia

We investigated the population density of Bornean orangutans Pongo pygmaeus pygmaeus and aspects of habitat quality in a selectively hand-logged peat swamp forest in West Kalimantan, Indonesia, and in a comparable unlogged forest nearby. We conducted orangutan nest surveys, measured different parameters of forest structure, recorded monthly changes in fruit availability, and noted the sex and the stage of maturity of orangutans encountered. Nest density, an index of orangutan population density, was 21% lower in the logged area. The forest, logged 2 years previously, had fewer large food trees and a greater number of canopy gaps. We discuss these differences in relation to the lower orangutan nest density in the logged forest. Significantly fewer adult orangutans were observed in the logged study area. We hypothesize that fully adult orangutans, particularly females, are the most severely affected by hand-logging.     

Changes in mineral nitrogen, phosphorus availability and salt-extractable aluminium following the application of green manure residues in two weathered soils of South Vietnam

Phosphorus deficiency and aluminium toxicity in weathered soils can be amended by applying organic residues. Nitrogen mineralization, changes in P-availability and changes in salt-extractable Al following the incorporation of residues of various green manures (Flemingia congesta, Mucuna pruriens, Pueraria phaseoloides, Tithonia diversifolia) were quantified in a field core incubation experiment. Dried residues were added at an application rate of 45 kg P ha⁻¹ to two soils representative for the main soil groups of the South Vietnamese uplands, set up in incubation cores in an experimental field near Ho Chi Minh City, Vietnam.Decomposition of the residues proceeded at high rates. Mineralized nitrogen from the residues was recovered mainly as ammonium during the first 2 weeks of incubation. Nitrogen release from Tithonia residues with the highest lignin content and lignin:N ratio occurred more gradually compared to the three legumes. Resin-extractable P was significantly increased by residue treatments. Largest and sustained increases in resin-extractable P (0.67 and 2.06 mg P kg⁻¹ in the two soils) were observed in samples amended with Tithonia, which was related to the large P-content (0.37%) and small C:P ratio (110) of the residues. The P-concentration in the residues, rather than the total amount of P applied through the residues, affected the increase in P-availability. The increase in resin-extractable P was correlated to the P-content (R=0.64) and C:P ratio (R=−0.65) of the residues. Salt-extractable Al-concentrations were considerably reduced by the organic amendments, up to 70 and 50% in the two soils. At the rate of 45 kg P ha⁻¹, no significant differences between the residue treatments to reduce soil acidity were observed.As such, the application of high quality residues that are rich in P, in particular T. diversifolia, may enhance crop production by creating favourable soil conditions during the initial stages of plant development of the main crop.     

Declines in forage availability for bumblebees at a national scale

We assessed national scale changes in the forage plants of bumblebees in Britain, as a means of providing quantitative evidence for the likely principal cause of declines in bumblebee species. We quantified the relative value of native and long-established plant species as forage (nectar and pollen) resources for bumblebees by collating visitation data from 14 field sites across Britain. Twentieth Century changes in range and frequency of these forage plants were assessed using data from the New Atlas of the British and Irish Flora (1930-1969 to 1987-1999) and the Countryside Surveys of Britain (1978-1998). Forage plants declined in both large-scale range and local-scale frequency between the two survey periods. These changes were of greater magnitude than changes in other native plant species, reflecting serious reductions in quality of foraging habitats for bees as well as a general decline in insect-pollinated plants. Seventy-six percent of forage plants declined in frequency within 1-km squares, including those (e.g. Trifolium pratense) of particular value for threatened bumblebee species. We consider how our findings relate to other recorded changes in the British flora, how they may help to explain declines in bumblebees and how they could contribute to a conservation strategy.     

Wild bee species increase tomato production and respond differently to surrounding land use in Northern California

Pollination provided by bees enhances the production of many crops. However, the contribution of wild bees remains unmeasured for many crops, and the effects of anthropogenic change on many bee species are unstudied. We experimentally investigated how pollination by wild bees affects tomato production in northern California. We found that wild bees substantially increase the production of field-grown tomato, a crop generally considered self-pollinating. Surveys of the bee community on 14 organic fields that varied in proximity to natural habitat showed that the primary bee visitors, Anthophora urbana Cresson and Bombus vosnesenskii Radoszkowski, were affected differently by land management practices. B. vosnesenskii was found primarily on farms proximate to natural habitats, but neither proximity to natural habitat nor tomato floral abundance, temperature, or year explained variation in the visitation rates of A. urbana. Natural habitat appears to increase B. vosnesenskii populations and should be preserved near farms. Additional research is needed to determine how to maintain A. urbana. Species-specific differences in dependency on natural habitats underscore the importance of considering the natural histories of individual bee species when projecting population trends of pollinators and designing management plans for pollination services. Thus, to maintain an entire bee community, multiple approaches, including maintaining natural habitat, should be implemented.     

Functional diversity of microbial communities in the mixed boreal plain forest of central Canada

This study was designed to examine whether or not specific tree species (Picea glauca, Picea mariana, Pinus banksiana, Populus tremuloides), their post-fire stand age, or their position in a successional pathway had any significant effect on the functional diversity of associated soil microbial communities in a typical mixed boreal forest ecosystem (Duck Mountain Provincial Forest, Manitoba, Canada). Multivariate analyses designed to identify significant biotic and/or abiotic variables associated with patterns of organic substrate utilization (assessed using the BIOLOG™ System) revealed the overall similarity in substrate utilization by the soil microbial communities. The five clusters identified differed mainly by their substrate-utilization value rather than by specific substrate utilization. Variability in community functional diversity was not strongly associated to tree species or post-fire stand age; however, redundancy analysis indicated a stronger association between substrate utilization and successional pathway and soil pH. For example, microbial communities associated with the relatively high pH soils of the P. tremuloides-P. glauca successional pathway, exhibited a greater degree of substrate utilization than those associated with the P. banksiana-P. mariana successional pathway and more acidic soils. Differences in functional diversity specific to tree species were not observed and this may have reflected the mixed nature of the forest stands and of their heterogeneous forest floor. In a densely treed, mixed boreal forest ecosystem, great overlap in tree and understory species occur making it difficult to assign a definitive microbial community to any particular tree species. The presence of P. tremuloides in all stand types and post fire stand ages has probably contributed to the large amount of overlap in utilization profiles among soil samples.     

Habitat selection of the Eurasian woodcock in winter in relation to earthworms availability

The Eurasian woodcock (Scolopax rusticola) is a game species experiencing high hunting pressure, long-term modifications of its habitats, and with questions regarding its current conservation status. Winter is a season of highest concentration of birds and hunting pressure but woodcock precise habitat requirements are poorly known. It is crucial to assess threats and to develop sustainable management options for the conservation of woodcock populations. During three consecutive winters, we monitored 65 individual woodcocks fitted with radio-tags in Brittany, France. Habitat selection was analysed using GIS and compositional analysis, in relation to vegetation types, soil variables (humus types) and the abundance of their main prey (earthworms). Woodcocks used different habitats diurnally and nocturnally, generally preferring areas with high earthworm biomass. Diurnal habitat selection in forests was associated with humus type (preference for mulls, rich in earthworms) and dense shrub strata (better protection). Hedges with a high density of trees and shrub were also important habitat. At night, grazed meadows were the preferred habitat, containing five times higher biomass of earthworms compared to cultivated fields. Sustainable management of populations requires protection and management of habitats that incorporates food and cover. Forestry practices should preserve rich humus types and coppices by choosing tree species that ameliorate the soil and soil tilling. Changes in landscapes and intensive agricultural practices are current threats to woodcock populations: destruction of hedges, decrease of permanent grazed meadows, impoverishment of soils fauna biomasses from ploughing and chemical applications. However, woodcocks may benefit from the recent development of set-asides, grass field-borders and simplified farm practices (no-tillage and direct sowing).     

‘Ecological forestry’ and eucalypt forests managed for wood production in south-western Australia

The model of ‘ecological forestry’ has evolved as a part of the development of the concept of ecosystem management. ‘Ecological forestry’ emphasises that manipulation of a forest ecosystem should consider, and as far as practicable work within the limits of, natural disturbance patterns prior to extensive human alteration of the landscape. This paper evaluates the extent to which forest management practices in jarrah (Eucalyptus marginata) and karri (Eucalyptus diversicolor) forests of south-western Australia align with this view of the characteristics and appropriate silviculture of ‘ecological forestry’. Characteristics and appropriate silviculture of ‘ecological forestry’ are evaluated in relation to (i) the stand level decisions of stand structure and harvest timing and (ii) the landscape level decisions of harvest levels and age structures, and spatial patterns of harvest. Forest management in south-western Australia is found to align with appropriate silviculture under this model of ‘ecological forestry’. Additionally, the landscape triad of areas managed to ‘ecological forestry’ principles, conservation reserves and areas managed to production forestry is in place in the south-western forests of Australia. Strengths and weaknesses in the model of ‘ecological forestry’ and the ability to interpret consistency of practices in the forests of south-western Australia with the characteristics of ‘ecological forestry’ are identified.     

The responses of leaf litter invertebrates to environmental gradients along road edges in subtropical island forests

Knowledge of how roads affect forest biodiversity can be improved by measuring the responses of indicator species to complex environmental gradients caused by these infrastructures. We studied litter invertebrate species responses to road edges in laurel and pine forests in Tenerife, Canary Islands. We sampled invertebrates from litter and assessed the environmental variation related to road proximity. We also assessed the effect of relevant environmental predictors on a diverse array of potential indicator species. We applied canonical ordination and non-parametric regression (Lowess) to classify invertebrate species responses to roads and their associated gradients. Three types of responses to road edge proximity were defined for the most common invertebrate taxa: edge-preferring or edge specialists, interior-preferring or edge-avoiders, and edge-indifferent or neutral species. Those species appearing most frequently and with higher population density between 1 and 20 m from the edge (commonly peaking at 10 m from the road) were categorized as edge-preferring. We classified taxa attaining peak population densities at or beyond 60 m from the edge (and most commonly 100 m) as interior species. Edge-neutral species were those without an evident pattern of stabilization in abundance along the gradient and with peaks in abundance at varying distance intervals. These edge litter communities contain a high native and endemic diversity but also a significant density of alien fauna. The specific patterns of penetration of road edge effects on invertebrate species should be seen as having a pervasive and cumulative impact considering the exceptionally large number of roads in these forests and the high population densities of alien invertebrates. Future management plans for forest conservation on the Canary Islands should include the highly altered but valuable litter communities along road edges.     

Response of soil microbial biomass dynamics to quality of plant materials with emphasis on P availability

Soil microbial biomass is a major sink and source of plant available P and transformer of soil organic P. The dynamics of microbial biomass P (B_P) and C (B_C) and resin extractable P (P_ex) in a sandy loam soil (Kandic Rhodustalf) after amending with plant materials of diverse quality were examined in a laboratory incubation study. Quality variables of the plant materials were described by the proportion of dry matter as total P, total N, lignin (LIG), and soluble polyphenolics (Pp). The materials were added to the soil at a rate equivalent to 10 t ha⁻¹ (dry weight) and kept at 50% field moisture capacity and 25 °C. Included was an unamended control soil. During incubation of up to 56 d, soil samples were periodically analyzed for P_ex, B_P and B_C. Quality variables affecting P_ex, B_P, B_C and B_P-to-B_C ratio were total P, total N, N-to-P and C-to-P ratios. Total P appeared to be the most important quality factor affecting P_ex, B_P, B_C and B_P-to-B_C ratio. There was no consistent significant correlation between P_ex and B_P or between B_P and B_C. This was attributed to the complexity of the dynamics of P_ex and B_P pools and the absence of a significant microbial turnover due to the short incubation periods assessed in the study. By virtue of the high P content and resulting in a low B_P-to-B_C ratio, leaves of the shrubby non-legume Tithonia diversifolia (Hemsley) A. Gray, had a distinct advantage of replenishing P_ex in the short-term and yet maintain a high potential to release P through microbial turnover. The tree legume Sesbania sesban, on the other hand, resulted in a low B_P-to-B_C ratio but also had a low P content and may be useful for the build up of soil organic matter (SOM) and P release in the long term. Exploiting plant materials with quality variables exhibited by T. diversifolia might create the potentials for fast replenishment of solution P as well as improving SOM.     

沙地云杉在河西地区的适应性及发展潜力

[目的]探讨沙地云杉在河西沙区的适应性及其影响因子,为该区生态建设中树种的选择提供依据。[方法]通过对河西地区沙地云杉生长情况的观测研究,以及搜集沙地云杉原产地和其他引种地相关资料,从气候、种子育苗、苗木移栽成活率及生长速度等方面比较分析沙地云杉在河西地区的适应性。[结果]河西地区温度条件适宜沙地云杉生长发育,但降水不足造成的土壤水分亏缺问题必须要通过人工灌水措施加以解决;7a后的沙地云杉生长速度超过原产地白音敖包,适应性强,在农田防护林建设中发展潜力大。[结论]沙地云杉在河西地区具有较大的发展潜力。