格氏栲林窗内外土壤理化性质分析

格氏栲（Castanopsis kawakamii）树种的幼苗为适应生长环境的变化,在长期演化过程中在生物量和养分分配等方面渐渐地形成了一些适应生存环境竞争的特征。为了使格氏栲天然林保持群落物种的多样性和促进格氏栲天然林种群的更新与繁殖,对格氏栲林窗内外土壤理化性质进行了试验研究,结果表明：在表层土壤中,林窗的土壤容重高于林内;在下层土壤中,林窗的容重低于林内。在同土壤层次,林窗与林内相比,土壤毛管孔隙度和总孔隙度的数值林窗都要高,而土壤非毛管孔隙度、非毛管孔隙度同毛管孔隙度比值、土壤通气度则低。说明在土壤保水性方面,林窗要好于林内;在通气性与透水性方面,林内要好于林窗。     

Productivity and nutritional value of 20 species of perennial legumes in a low‐rainfall Mediterranean‐type environment in southern Australia

In the rain‐fed mixed‐farming systems of southern Australia, the consistent supply of high‐value forage is limited by a range of climatic, edaphic and systems constraints. Over 2 years, we compared biomass production and nutritional value of 30 accessions of perennial legumes, and predicted intake, grazing days and growth of ewes and lambs. There was significant variation in nutritional value and biomass production between and within species. Lucerne (Medicago sativa) and sulla (Hedysarum coronarium) produced the greatest amount of biomass and energy. There was variability among accessions in digestibility (DMD), acid detergent fibre (ADF) and crude protein, and the rate of change in these traits as plants matured. Trifolium species had the highest DMD across all growth stages. Hairy canary clover (Dorycnium hirsutum), erect canary clover (Dorycnium rectum), greater birdsfoot trefoil (Lotus uliginosus), Australian trefoil (Lotus australis) and running postman (Kennedia prostrata) had energy levels that would not maintain liveweight of mature sheep. In the second year, species differed in response to harvesting treatments. Lucerne and sainfoin (Onobrychis viciifolia) were more productive under a frequent cutting regime. Accessions of white clover (Trifolium repens), red clover (Trifolium pratense), alsike clover (Trifolium hybridum), cullen (Cullen australasicum), strawberry clover (Trifolium fragiferum), sainfoin and birdsfoot trefoil (Lotus corniculatus) showed some promise, while Tedera (Bituminaria bituminosa) and milkvetch (Astragalus cicer) performed poorly under the experimental conditions. We conclude by discussing additional agronomic and nutritional factors that need consideration when developing novel perennial legumes for mixed‐farming systems in the context of a changing climate.     

Analysis of potential yields and yield gaps of rainfed soybean in India using CROPGRO-Soybean model

To assess the scope for enhancing productivity of soybean (Glycine max L. Merr.), the CROPGRO-Soybean model was calibrated and validated for the diverse soybean-growing environments of central and peninsular India. The validated model was used to estimate potential yields (water non-limiting and water limiting) and yield gaps of soybean for 21 locations representing major soybean regions of India. The average water non-limiting potential yield of soybean for the locations was 3020 kg ha⁻¹, while the water limiting potential was 2170 kg ha⁻¹ indicating a 28% reduction in yield due to adverse soil moisture conditions. As against this, the actual yields of locations averaged 1000 kg ha⁻¹, which was 2020 and 1170 kg ha⁻¹ less than the water non-limiting potential and water limiting potential yields, respectively. Across locations the water non-limiting potential yields were less variable than water limited potential and actual yields, and strongly correlated with solar radiation during the season (R² = 0.83, p ≤ 0.01). Both simulated water limiting potential yield (R² = 0.59, p ≤ 0.01) and actual yield (R² = 0.33, p ≤ 0.05) had significant but positive and curvilinear relationships with crop season rainfall across locations. The gap between water non-limiting and water limiting potential yields was very large at locations with low crop season rainfall and narrowed down at locations with increasing quantity of crop season rainfall. On the other hand, the gap between water limiting potential yield and actual farmers yield was narrow at locations with low crop season rainfall and increased considerably at locations with increasing amounts of rainfall. This yield gap, which reflects the actual yield gap in rainfed environment, is essentially due to non-adoption of improved crop management practices and could be reduced if proper interventions are made. The simulation study suggested that conservation of rainfall and drought resistant varieties in low rainfall regimes; and alleviation of water-logging and use of water-logging tolerant varieties in high rainfall regimes will be the essential components of improved technologies aimed at reducing the yield gaps of soybean. Harvesting of excess rainfall during the season and its subsequent use as supplemental irrigation would further help in increasing crop yields at most locations.     

Narrow lenses for capturing the complexity of fisheries: A topic analysis of fisheries science from 1990 to 2016

Despite increased fisheries science output and publication outlets, the global crisis in fisheries management is as present as ever. Since a narrow research focus may be a contributing factor to this failure, this study uncovers topics in fisheries research and their trends over time. This interdisciplinary research evaluates whether science is diversifying fisheries research topics in an attempt to capture the complexity of the fisheries system, or whether it is multiplying research on similar topics, attempting to achieve an in‐depth, but possibly marginal, understanding of a few selected components of this system. By utilizing latent Dirichlet allocation as a generative probabilistic topic model, we analyse a unique dataset consisting of 46,582 full‐text articles published in the last 26 years in 21 specialized scientific fisheries journals. Among the 25 topics uncovered by the model, only one (Fisheries management) refers to the human dimension of fisheries understood as socio‐ecological complex adaptive systems. The most prevalent topics in our dataset directly relating to fisheries refer to Fisheries management, Stock assessment, and Fishing gear, with Fisheries management attracting the most interest. We propose directions for future research focus that most likely could contribute to providing useful advice for successful management of fisheries.     

A 10-year evaluation of the functional basis for regeneration habitat preference of trees in an African evergreen forest

The spatial distribution of tree juveniles in relation to light environments may reflect species differences in growth, survival, and functional traits and will shape the nature of forest regeneration. Long-term field experiments are important to evaluate this issue because of the potentially very long juvenile period in trees. Here, we combine a 10-year seedling survival–growth data with the results of community ordination and multivariate analyses of functional traits to ask how observed juvenile light guilds are related to species functional traits and seedling performance. We transplanted seedlings at a standardized height of 11 cm into the shaded understory and quantified their growth and survival for 10-years. Using the community-wide stem distribution data, we categorized 33 species including the focal 11 species to understory vs. gap/edge guilds. Then, we determined differences between the two guilds in seedling survival, growth, as well as seed size, adult height, and a series of leaf traits, including toughness and chemical traits (fiber, protein, phenolics, tannins, alkaloids, saponins). Among the 11 non-pioneer species whose seedlings were planted into the understory, there was no significant difference in 10-year survival between light guilds, but species in gap/edge guild tended to achieve greater height than species in the understory guild. The leaf chemical traits of 33 species did not differ between the two juvenile light guilds, but gap/edge species had smaller seeds, taller adults, and tougher leaves than understory species. We used logistic regression as a complementary approach to assess the extent to which plant traits varied between light guilds and the most parsimonious model based on AIC_c ranking included only leaf toughness and had an Akaike weight of 0.52. In addition, across the 11 species planted as seedlings, these traits were not significantly related to survivorship or growth over 10 years. A Principle Components Analysis illustrated associations among traits. We conclude that light guilds in terms of juvenile stem distribution could not be explained by long-term field performance of post-establishment seedlings alone. Earlier seedling stage or later sapling stage may be more important in differentiation of light guilds. For the species examined difference in growth rates could be linked to seed size and adult stature, but not to the adult leaf chemical traits considered. These results suggest the importance of examining ontogenetic shifts and relationships among functional traits for a better understanding of regeneration strategies of tropical trees.     

Water relations of pine seedlings in contrasting overstory environments

Overstory conditions influence understory microclimate and resource availability, leading to gradients in evaporative demand and moisture availability that influence seedling water relations. Partial canopies may either reduce seedling moisture stress by ameliorating environmental conditions, or increase moisture stress by reducing soil moisture availability. This study used stable isotope ratios of oxygen (δ¹⁸O) and carbon (δ¹³C) and mass-based foliar nitrogen concentrations to investigate changes in transpiration (E), stomatal conductance (g_s) and intrinsic water use efficiency (iWUE) of pine seedlings across an overstory gradient from open canopy gap environments to closed canopy forest. Foliar δ¹⁸O increased sharply from basal areas of 0–10 m² ha⁻¹ in Pinus banksiana, Pinus resinosa, and Pinus strobus seedlings, followed by a more gradual increase with further increases in basal area. Foliar δ¹³C followed a similar, but less pronounced pattern in P. banksiana and P. strobus seedlings, and had no apparent relationship with overstory basal area in P. resinosa seedlings. The slope of the δ¹⁸O:δ¹³C relationship was positive for every species. Foliar nitrogen concentrations were not correlated with overstory basal area. These results suggest seedling E declined as overstory basal area increased due to reductions in g_s, while iWUE increased slightly from open gaps to partial canopy environments. Open gap environments appear to provide sufficient moisture to sustain high leaf-level gas exchange rates in the species we studied, while relatively small increases in overstory basal area apparently promote rapid declines in g_s, leading to greatly reduced seedling water loss and small increases in iWUE.     

Adapting the pair-correlation function for analysing the spatial distribution of canopy gaps

Forestry around the world has been experiencing a paradigm shift towards more nature-oriented forest management leading foresters to emulate natural disturbances by their silvicultural treatments. Important characteristics of all disturbances are their size, severity, temporal and spatial distribution. This study focuses on the spatial distribution of gaps in the forest canopy which are typically caused by small-scale, low intensity disturbances.     

Nitrogen dynamics across silvicultural canopy gaps in young forests of western Oregon

Silvicultural canopy gaps are emerging as an alternative management tool to accelerate development of complex forest structure in young, even-aged forests of the Pacific Northwest. The effect of gap creation on available nitrogen (N) is of concern to managers because N is often a limiting nutrient in Pacific Northwest forests. We investigated patterns of N availability in the forest floor and upper mineral soil (0–10 cm) across 6–8-year-old silvicultural canopy gaps in three 50–70-year-old Douglas-fir forests spanning a wide range of soil N capital in the Coast Range and Cascade Mountains of western Oregon. We used extractable ammonium (NH₄⁺) and nitrate (NO₃⁻) pools, net N mineralization and nitrification rates, and NH₄⁺ and NO₃⁻ ion exchange resin (IER) concentrations to quantify N availability along north-south transects run through the centers of 0.4 and 0.1 ha gaps. In addition, we measured several factors known to influence N availability, including litterfall, moisture, temperature, and decomposition rates. In general, gap-forest differences in N availability were more pronounced in the mineral soil than in the forest floor. Mineral soil extractable NH₄⁺ and NO₃⁻ pools, net N mineralization and nitrification rates, and NH₄⁺ and NO₃⁻ IER concentrations were all significantly elevated in gaps relative to adjacent forest, and in several cases exhibited significantly greater spatial variability in gaps than forest. Nitrogen availability along the edges of gaps more often resembled levels in the adjacent forest than in gap centers. For the majority of response variables, there were no significant differences between northern and southern transect positions, nor between 0.4 and 0.1 ha gaps. Forest floor and mineral soil gravimetric percent moisture and temperature showed few differences along transects, while litterfall carbon (C) inputs and litterfall C:N ratios in gaps were significantly lower than in the adjacent forest. Reciprocal transfer incubations of mineral soil samples between gap and forest positions revealed that soil originating from gaps had greater net nitrification rates than forest samples, regardless of incubation environment. Overall, our results suggest that increased N availability in 6–8-year-old silvicultural gaps in young western Oregon forests may be due more to the quality and quantity of litterfall inputs resulting from early-seral species colonizing gaps than by changes in temperature and moisture conditions caused by gap creation.     

木兰围场华北落叶松人工林林隙对天然更新的影响

为了阐明华北落叶松人工林不同林隙大小对更新的影响规律,对木兰围场低效华北落叶松人工林林隙内苗木更新特性进行了研究。结果表明:林隙内更新苗的主要种类有华北落叶松、山杨和油松。华北落叶松和山杨的密度在林隙面积为120~140m2时最大,达到2 411株/hm2;而油松的密度在林隙面积为20~40m2时最大,为196株/hm2。随着林隙面积的增大,华北落叶松和山杨大径级和大高度级更新幼苗数量基本呈现增加的趋势,在林隙面积达到160~180m2时达到最大值;而油松在40~60m2时达到最大,径级大于2cm的更新苗密度为69株/hm2。     

热带森林林窗湿热季气温分布特征的初步研究

林窗是群落演替的起始地，其本身的特征影响着环境因子，进而影响森林的结构、物种组成、种群动态等.利用西双版纳湿热季次生林林窗的实测气温资料，探讨该林窗气温的分布特征.结果表明热带次生林林窗4个方位不同位置的气温日变化具有2～3个峰值；日平均气温的高低顺序是林窗边缘＞扩展林窗边缘＞林内；林窗内气温日较差较小；林窗内不同位置相对林窗中央具有增加低温和降低高温的效应，这种增温效应(0.4～0.6℃)较降温效应(-1.4～-1.5℃)弱.其结果可为林窗小气候形成机制及森林群落的演替与更新等提供科学依据.