How well does a log decay-class system capture the ecology of decomposition? - A case-study from Tasmanian Eucalyptus obliqua forest

The use of decay-class systems in characterising the state of decomposition of a forest’s complement of rotting logs is widespread. While most systems are based on an assessment of logs’ external characteristics, there is an implicit assumption that doing so captures important information on the underlying processes of internal decomposition. However, the validity of this remains largely untested. We explored the relationship between decay-class and internal state of decomposition in logs of Eucalyptus obliqua in the lowland wet eucalypt forests of Southern Tasmania, Australia. We examined rotten-wood samples from a large population of logs across a wide range of diameters. From this we determined that smaller-diameter (<60 cm: regrowth-sized) logs differ from larger-diameter (>60 cm: mature-sized) logs in their pathways of internal decomposition. Decomposition in regrowth-sized logs is characterised by greater activity of surface rots, with white rot-types predominating. Decomposition in mature-sized logs is more concentrated in the interior of the log, with brown rot-types tending to dominate. These differences probably both reflect and help shape the communities of organisms inhabiting logs of different origins. Despite these differences, regrowth and mature-sized logs show the same general progression of internal decomposition across the five decay-classes, to the extent that each class represents logs that have lost a predictable proportion of their original mass. We conclude that a decay-class system that is restricted to a single dimension, such as the five-class system used for E. obliqua, will be quite able to capture the main trajectory of biomass loss, but will not be able to characterise the complexity of the ecological processes giving rise to this loss. Studies that employ single-dimension decay classes, and which aggregate decay-class data across logs, can be given added ecological meaning by first partitioning logs into diameter-classes that reflect the underlying differences in the maturity of the trees giving rise to the logs. For E. obliqua logs, a cut-off diameter of 60 cm offers an appropriate distinction between regrowth-aged and mature-aged trees.     

Legacies from natural forest dynamics: Different effects of forest management on wood-inhabiting fungi in pine and spruce forests

The species composition of wood-inhabiting fungi (polypores and corticoids) was investigated on 1138 spruce logs and 992 pine logs in 90 managed and 34 natural or near-natural spruce and pine forests in SE Norway.Altogether, the study included 290 species of wood-inhabiting fungi. Comparisons of logs with similar properties (standardized tree species, decay class, dimension class) in natural and managed forests showed a significant reduction in species number per log in managed spruce forests, but not in managed pine forests. The species number per log in managed spruce forests was 10-55% lower than on logs from natural spruce forests. The reduction was strongest on logs of large dimensions. A comparison of 200-400 spruce logs from natural and managed forests showed a 25% reduction in species richness corresponding to a conservative loss of ca. 40 species on a regional scale.A closer inspection revealed that species confined to medium and very decayed spruce logs were disfavored in managed forests, whereas species on early decay classes and decay generalists were unaffected. Similarly, species preferring large spruce logs were disfavored in managed forests. Forest management had strongest impact on low-frequent species in the spruce forests (more than 50% reduction), whereas common species were modestly affected. Corticoid fungi were more adversely affected than polypore fungi.These results indicate that wood-decaying fungi in pine forests are more adapted to forest disturbances than spruce-associated species. Management measures securing a continuous supply of dead wood are more important in spruce forests than in pine forests.     

木本油料树种良种选育工作势在必行

良种是生产力发展的基础性、战略性资源,是可持续发展的重要物质基础,是实现优质丰产、增产增收的先决条件.笔者从推动宜昌木本油料产业健康发展的角度,阐述了加强宜昌木本油料良种选育的重要性、必要性和方法.     

木本泥炭添加比例对猪粪堆肥腐熟度和污染及温室气体排放的影响

针对当前猪粪好氧堆肥过程中存在的腐熟度低、氮素损失严重、污染气体排放量大等问题,该研究以木本泥炭作为添加剂与猪粪进行联合堆肥,研究了不同木本泥炭添加量(添加比例依次为占物料湿基质量的5%、10%、15%和20%的4个处理)对猪粪好氧堆肥产品腐熟度和堆肥过程中CH4、NH3和H2S等污染气体排放变化的影响。结果表明:在猪粪堆肥中添加木本泥炭作为调理材料,堆体可成功启动升温,在第2~4天堆体可进入高温期,并持续7 d以上,达到无害化卫生标准;经28 d好氧堆肥以后,堆肥产品p H值为8.0左右,电导率值为1.47~1.82 m S/cm,发芽指数均大于80%,达到腐熟标准;木本泥炭添加量增加至15%以上时,有机质分解程度高,物料干质量降解率达22%左右,28 d堆体含水率下降35%左右,CH4、NH3和H2S排放量分别减少82.12%~89.48%、53.47%~63.31%、50.98%~62.76%,总温室气体排放当量减少70.34%~83.26%,堆体总氮损失减少率达44%~63%,保氮效果显著。因此,建议木本泥炭用作猪粪堆肥添加剂的最优添加量为15%~20%(以物料总湿重计)。     

台湾土石流研究综述

 台湾地狭人稠,平地开发趋于饱和。随着社会经济快速发展,使得山坡地陆续开发,破坏原有之水土保持,且台湾岛之山脉地质大多属沉积岩及变质岩,性质脆弱且易断裂,再加上年平均雨量高达2500mm,其中78%的降雨集中于5—10月的台风季节,因此台湾地区土石流频繁。为了解台湾地区土石流之研究沿革,搜集相关土石流之研究成果,并配合台湾地区重大灾害,分析土石流特性、土石流成分分析、危险评估与重建、抑制工程及现场调查仿真等方面的研究进展。     

Conservation-oriented forestry and early successional saproxylic beetles: Responses of functional groups to manipulated dead wood substrates

New conservation-oriented forestry aims to maintain intact populations of forest organisms by improving the conservation value of managed forests and providing protected areas. We tested the conservation value of treatments of dead wood for assemblages of early successional saproxylic beetles. In nine areas in northern Sweden, we selected one clear-cut, one mature managed forest and one reserve. In 2001-2002, we placed three blocks of spruce logs, each containing control, burned and shaded logs and a high stump (“snag”) at each site. Saproxylic beetles emerging from the dead wood were collected using emergence traps and beetles flying close to it were collected using flight-intercept traps. After one year of exposure, assemblage composition was examined, with respect to nutritionally-defined functional groups, red-listed species and fire-favoured species. Experimental snags were most complementary to control logs, supporting different assemblages of cambium consumers and fungivores and supporting more red-listed individuals. Burned logs supported depauperate assemblages, particularly with respect to cambium consumers, while shading of logs affected assemblages of fungivores, but only on clear-cuts. Despite containing less dead wood, managed forests provided valuable habitat, supporting similar assemblages of saproxylic beetles to reserves. Most functional groups were less abundant on clear-cuts than in older forests, but fire-favoured species were more common on clear-cuts, suggesting that clear-cuts may support assemblages of species associated with natural disturbances, if suitable substrates are available. Utilization of logs by saproxylic beetles changes over time, so long-term monitoring of our experimental logs will determine their lifetime conservation value.     

Density loss and respiration rates in coarse woody debris of Pinus radiata, Eucalyptus regnans and Eucalyptus maculata

This study compared field and laboratory decomposition rates of coarse woody debris (CWD) (>10 cm diameter) from three tree species: Pinus radiata, Eucalyptus regnans, and Eucalyptus maculata. For this purpose, the density loss of logs on the ground sampled from chronosequences of sites following harvesting was determined using the water replacement technique. P. radiata logs were sampled 1, 2.5, 6, and 9 years following harvesting, and logs of E. regnans and E. maculata were collected from sites that were harvested 1, 3.5, 6.5, and 12 and 1.5, 6.5, and 11.5 years ago, respectively. In addition, the C/N ratio of wood was determined and current respiration rates of logs from these different age classes were measured through laboratory incubation. The times for loss of 95% of material (t_0.95) determined from density loss for these species were 24 years for P. radiata, 43 years for E. regnans, and 62 years for E. maculata. The decomposition rates of CWD derived from laboratory respiration were 6.1, 5.9 and 11.9 times higher than the decay rates from density loss in P. radiata, E. regnans, and E. maculata, respectively. This points to severe constraints of decomposition through adverse conditions in the field. The changes in respiration rates and C/N ratio with age of decaying logs indicated that the single component, negative exponential decay model could be applied satisfactorily only to P. radiata. In the case of the eucalypt species, substrate quality (expressed through respiration rates) declined in the oldest samples. This may be explained by the loss of rapidly decomposing sapwood and the retention of more decay-resistant heartwood. In these cases, a two-component model will be more suitable to describe the density loss of decaying wood.     

Effect of agroforestry woody species on earthworm activity and physicochemical properties of worm casts

The effects of five agroforestry woody species (Dactyladenia barteri, Gliricidia sepium, Leucaena leucocephala, Senna siamea andTreculia africana) on the surface aasting activity ofHyperiodrilus africanus were studied in an Alfisol (Oxic Paleustalf) in southwestern Nigeria. Casting activity under the woody species decreased in the following order:Dactyladenia sp. (26.4 Mg ha^-1 year^-1)>Gliricidia sp. (24.4 Mg ha^-1 year^-1)>Treculia sp. (22.9 Mg ha^-1 year^-1)>Leucaena sp. (18.6 Mg ha^-1 year^-1)>Senna sp. (18.3 Mg ha^-1 year^-1). These differences in casting activity were partly explained by microclimatic effects. Irrespective of the woody species, the worm casts were higher in clay and silt contents, bulk density, water-stable aggregates, pH, organic C, exchangeable cations, effective cation exchange capacity, and extractable P levels than the corresponding surface soils. The woody species did affect the physicochemical properties and P sorption of the worm casts. The content of water-stable aggregates of worm casts decreased in the following order:Dactyladenia sp.>Treculia sp.>Senna sp.>Leucaena sp.>Gliricidia sp. Large differences in extractable P levels were observed.Senna sp. was associated with the highest extractable P level (11.5 mg kg^-1) andTreculia sp. the lowest (4.9 mg kg^-1). P sorption was highest on worm casts underDactyladenia sp. and lowest on those underTreculia sp. Without fertilizer application, there were no significant differences in the dry weight of maize grown in the different worm casts. With NPK applications, the dry weight of maize grown in worm casts associated withTreculia sp. was significantly lower than that of maize grown in the other worm casts, mainly due to the low extractable P level. Despite a high organic C and exchangeable K status, maize grown in the worm casts still responded significantly to N and K applications. The N uptake by maize grown in worm casts associated withTreculia sp. was lower than that in the other treatments.     

Soil niche effect on species diversity and catabolic activities in an ectomycorrhizal fungal community

The species of an ectomycorrhizal (ECM) community were investigated in a temperate oak forest by morphotyping and ITS rDNA sequencing. Thirty-six ECM morphotypes were found at the site. The niche effect (as organic soil, mineral soil or dead woody debris artificially introduced in the soil) on the ECM community structure and on the potential catabolic activities of the most abundant morphotypes was studied. The morphotypes in each niche were subjected to enzymatic tests developed for hydrolytic and oxidative enzymes involved in the decomposition of organic compounds. The ECM community structure varied widely depending on the soil horizon or habitat patch. The species richness was higher in the A1 horizon than in the other niches. Different ECM species had different activity patterns for the eight enzymatic tests while co-occurring in the same niche. Catabolic activities also changed within species between niches. Dead woody debris were extensively colonized by two saprotrophic fungi (Megacollybia platyphylla and Armillaria sp.) and, in this particular niche, ECM morphotypes predominantly belonged to the genera Lactarius and Tomentella. These morphotypes showed high chitinase activities. This study suggested also that some ECM fungi could obtain nutrients via the chitin degradation of dead or live saprobes.