RESTRICTION ENDONUCLEASE ANALYSIS OF RIBOSOMAL DNA SEQUENCE VARIATION IN LAMINARIA (PHAEOPHYTA)1

The taxonomy and evolutionary relationships of species in the genus Laminaria are poorly understood. Previous studies have demonstrated significant plasticity of morphological characters used to describe taxa, and interfertility has been reported among putative species. We analyzed nuclear ribosomal DNA (rDNA) sequence variation in eight species of Laminaria (L. agardhii Kjell., L. digitata (Huds.) Lamour., L. groenlandica Rosenv. [sensu Druehl 1968], L. longicruris De la Pyl., L. longipes Bory, L. saccharina (L.) Lamour., L. setchellii Silva, and L. yezoensis Miyabe) to elucidate evolutionary relationships in this genus. Restriction maps were constructed using a small subunit rDNA probe from Costaria costata (Turn.) Saunders, an rDNA repeat from the nematode Caenorhabditis elegans, and 11 hexameric restriction endonucleases in an annealing analysis of genomic DNA. Laminaria rDNA restriction maps were compared to each other and to that of the outgroup taxon, C. costata. rDNA restriction maps of Laminaria species and C. costata were similar. Restriction fragment length polymorphisms mapped to both the coding regions and the nontranscribed spacer of rDNA. Laminaria species were distinguished with this method. The restriction maps of L. agardhii, L. saccharina, and L. longicruris were identical, supporting a previous hypothesis that these species are conspecific. Comparison of restriction maps of Laminaria species suggested that the generic subdivision of Sections Simplices and Digitatae may be invalid.     

Single-copy DNA-DNA hybridizations among five species ofLaminaria (Phaeophyceae): Phylogenetic and biogeographic implications

DNA-DNA hybridizations between single-copy nuclear DNA fromLaminaria digitata and total DNA fromL. saccharina, L. Hyperborea, L. rodriguezii, L. ochroleuca andChorda filum, respectively, show that these species ofLaminaria are genotypically closely related.Chorda filum is only distantly related withL. digitata. Based on the thermal elution patterns of the DNA hybrids, as quantified by ΔT_m(e) values, it is hypothesized that all five species ofLaminaria evolved at about the same time from their most recent common ancestor some 15–19 Ma ago. This phylogenetic hypothesis is discussed in relation to the history of modern laminarialean distribution patterns. Paper presented at the XIV International Botanical Congress (Berlin, 24 July–1 August, 1987), Symposium 6-15, “Biogeography of marine benthic algae”.     

Current state of seaweed resources in Spain

Commercial seaweeds in Spain are harvested on the north and northwest coasts. They are mainly agarophytes and carrageenophytes (Gelidium spp. and some Irish moss-like species, respectively), although some Phaeophyceae species (Fucus spp. and Laminaria spp.) are also exploited for alginates. No industrial seaweed cultivation is carried out in Spain at present. Spain's total commercial seaweed harvest can be estimated at 6,528 ± 2,076 t dry wt year^–1. Gelidium spp. are by far the most harvested, attaining 5,135 ± 1,761 t dry wt y^–1. To date, Spain's commercial seaweed harvest is low compared with that of other countries, but data on field standing crops and productivities of commercial taxa suggest that harvesting could be increased greatly.     

Gelidium pristoides in South Africa

Gelidium pristoides has been harvested commercially from the eastern Cape, South Africa, since 1951, with 40–80 t y^–1 (dry wt) collected in recent years. This species has been intensively studied since 1983, and we briefly review knowledge of its biology in relation to harvesting. We describe a new study of intertidal epiphytic animals, showing that none is specific to G. pristoides, and that only 2.8% of these animals (numbers) inhabit this agarophyte, while the rest are found in other intertidal algal communities: harvesting is considered to have negligible effects on epifauna. Over the past 3 y, we have monitored, at two sites, the effects of the harvesting of G. pristoides on other benthic algae and animals. In only two of the seven main components analysed, did we find any difference between harvested and control plots. At one site only, the number of limpets and percentage cover of Gelidium was higher in harvested plots. These results show that harvesting has no significant biological effect. Regulations governing seaweed exploitation in South Africa were amended in 1988, to encourage local processing of products, and these changes are discussed in relation to the local Gelidium industry. Despite experimental results predicting a higher yield per unit effort if harvesting is limited to summer, harvesting continues throughout the year for practical reasons.     

择伐对吉林蛟河阔叶红松林群落结构及动态的影响

科学的森林经营能够优化林分结构,是调控森林生产力和生物多样性的有效手段。择伐作为森林经营的重要方式之一,其对森林结构以及群落动态的影响一直未有定论,因此迫切需要利用更加全面的数据对择伐及伐后林分特征的变化进行长期监测。根据森林大样地建立规范,2010年在吉林蛟河建立了42hm~2阔叶红松林动态监测样地,2011年冬季截取部分面积进行择伐经营,以经营样地为研究对象,运用数值变量描述采伐活动并分析择伐前后群落结构的变化;同时结合2015年的二次调查数据,以立地条件基本一致的对照样地为参照,比较林分水平和物种水平上死亡率、更新率的差异,并利用线性混合效应模型探究择伐活动对个体径向生长的影响。研究结果显示:经营样地的择伐强度为5.4%,受采伐干扰影响较大的物种主要包括色木槭、白牛槭、裂叶榆、胡桃楸、千金榆、水曲柳以及紫椴,采伐主要集中于林冠层树种,亚林层和灌木层个体很少涉及。择伐前后物种组成、径级结构等并未发生明显改变。5年间,经营样地和对照样地的林分密度都降低,对比对照样地,经营样地的死亡率较低,但其更新状况并未优于对照样地。从胸高断面积来看,经营样地整体的年平均生长量高于对照样地,表明择伐导致的稀疏对个体生长和存活起到了一定的促进作用。将采伐强度纳入线性混合效应模型中分析发现,胸径始终是影响个体生长的最重要因素,其次是树木个体之间的非对称竞争;采伐所涉及到的7个主要树种的年平均生长量均高于对照样地,但仅有紫椴的径向生长表现出对采伐干扰的显著响应。综合来看,低强度择伐对群落结构和动态的影响较小,不同物种的径向生长对择伐的响应存在一定差异。     

鼎湖山退化马尾松林、混交林和季风常绿阔叶林土壤全磷和有效磷的比较

土壤全磷和有效磷浓度的变化随林型和季节不同而异,总的来说,其大小顺序为:季风常绿阔叶林> 混交林>马尾松林(林型);夏季>冬季>春季>秋季(季节),有效磷浓度为:秋季>春季>冬季>夏季(季 节)。收割林下层和凋落物这种人为干扰活动对土壤全磷含量的影响不明显,但对土壤有效磷含量具有显著 的影响。在试验开始时(1990年5月),土壤全磷和有效磷浓度在马尾松林保护样地(停止人为干扰)和处理样 地(按当地习惯继续收割林下层和凋落物)间的差异均不显著。经七年多的试验后,土壤全磷浓度在保护样地 和处理样地间仍十分相似,但土壤有效磷浓度在保护样地显著高于处理样地,说明保护样地在停止人为干扰 后相对于继续受干扰的处理样地其林地条件得到了改善,从而使土壤有效磷含量也得到提高。只要停止人为 干扰,鼎湖山退化马尾松林土壤有效磷供应力是可以自然恢复到季风常绿阔叶林的水平。     

Evaluating different harvest intensities over understory plant diversity and pine seedlings,in a <Emphasis Type="Italic">Pinus pinaster</Emphasis> Ait. natural stand of Spain

Although modern forestry takes into consideration the analysis of the effects of forest management on plant structure, diversity and seedlings, little is known about how those parameters respond to harvest techniques in the Mediterranean region. We investigated the effect of three different harvest intensities, respect to uncut controls, on understory plant species functional groups, richness, diversity and pine seedlings in a natural Maritime pine stand in Spain, three years after harvesting. The harvest treatments produced a reduction of the number of Pinus pinaster seedlings and woody species cover, and an increase of species richness (total and of annual species) and plant cover of annual species respect to control plots (CO). The Shannon diversity values showed no differences between treatments. These results emphasize that the tree harvest treatments analyzed are not suitable for the management of this P. pinaster stand. Otherwise, the reduction of pine seedling density by harvest treatments and the changes in richness and cover of functional groups would not induce the natural regeneration of this stand maintaining the understory plant layer.     

Changes in the population structure of Ascophyllum nodosum (L.) Le Jolis due to mechanical harvesting

The use of a Norwegian suction cutter to harvest populations of the brown alga Ascophyllum nodosum (L.) Le Jolis in southwestern Nova Scotia started in 1985. The impact of this type of mechanical harvest on the algal population structure was evaluated. Changes in the length and density of individual plants (clumps) within 0.25 m^–2 quadrats, as well as the length of individual shoots within clumps were monitored before and after an experimental harvest. The mechanical harvest cut mainly the longer plants, thus changed the initial bimodal size structure of the population to unimodal. There was a 20 to 36% plant mortality, reducing the plant density from 92.6 to 73.6 individuals m^–2. Pre-harvest size distribution of the tagged shoots was skewed to the right and became more normal after the harvest. Tagged shoots in the harvested quadrats suffered a 42% mortality as compared to 11% of those in the control quadrats. An understanding of the impact of the mechanical harvesting on the harvested population is essential in the design of a management strategy. Sources of variation in the impact of mechanical harvest include the tide level at time of harvest, length of time the machine operated in one site, skill of the machine operator, and sharpness of the machine cutting blades.     

Response of a Wild Edible Plant to Human Disturbance: Harvesting Can Enhance the Subsequent Yield of Bamboo Shoots

Wild edible plants, ecological foodstuffs obtained from forest ecosystems, grow in natural fields, and their productivity depends on their response to harvesting by humans. Addressing exactly how wild edible plants respond to harvesting is critical because this knowledge will provide insights into how to obtain effective and sustainable ecosystem services from these plants. We focused on bamboo shoots of Sasa kurilensis, a popular wild edible plant in Japan. We examined the effects of harvesting on bamboo shoot productivity by conducting an experimental manipulation of bamboo shoot harvesting. Twenty experimental plots were prepared in the Teshio Experimental Forest of Hokkaido University and were assigned into two groups: a harvest treatment, in which newly emerged edible bamboo shoots were harvested (n = 10); and a control treatment, in which bamboo shoots were maintained without harvesting (n = 10). In the first year of harvesting (2013), bamboo shoot productivities were examined twice; i.e., the productivity one day after harvesting and the subsequent post-harvest productivity (2–46 days after harvesting), and we observed no difference in productivity between treatments. This means that there was no difference in original bamboo shoot productivity between treatments, and that harvesting did not influence productivity in the initial year. In contrast, in the following year (2014), the number of bamboo shoots in the harvested plots was 2.4-fold greater than in the control plots. These results indicate that over-compensatory growth occurred in the harvested plots in the year following harvesting. Whereas previous research has emphasized the negative impact of harvesting, this study provides the first experimental evidence that harvesting can enhance the productivity of a wild edible plant. This suggests that exploiting compensatory growth, which really amounts to less of a decline in productivity, may be s a key for the effective use of wild edible plants.     

The influence of drainage and soil phosphorus on the vegetation of Douala-Edea Forest Reserve,Cameroun

All living trees (30 cm gbh) were enumerated in 104 80×80 m plots arranged along four transects in the Douala-Edea Forest Reserve Cameroun, a system of low-lying ancient coastal sand dunes interspersed by numerous streams and swamps. The extent of permanent and seasonal swamps was recorded for each plot. Two hundred thirty taxa were recognized of which 63% were identified to species. Mean tree density was 376 ha^–1, basal area 31.0 m² ha^–1 and number of species per plot 39. The Olacaceae were the most abundant family in terms of basal area, but the Euphorbiaceae the most frequently represented. The most abundant species wasCoula edulis (Olacaceae). Twenty-two plots had most of their area permanently or seasonally swamped. Percentage sand, silt and clay ranged between 32–100, 0–64, 0–21% respectively. The ranges for other variables recorded were: pH (2.7–5.4), organic carbon (1.5–12.4%), available phosphorus (7–90 ppm) and potassium (28–188 ppm), and nitrogen (ammonium 4–40 ppm, nitrate 1–12 ppm).Classification of the plots on the basis of six soil variables provided three large distinct groups: swamp plots and non-swamp plots, the latter divided into plots of low and high available soil phosphorus. Swamp plots were distinguished by high abundances ofProtomegabaria stapfiana andLibrevillea klainei, though correspondence ordination of plots in these groups showedP. stapfiana associated with more clayey soils andLibrevillea klainei (andGluema ivorensis) on the very sandy soils. Direct gradient analysis highlighted several species associated with these lower phosphorus soils. Available soil phosphorus is not as low at Douala-Edea as in parts of Korup, and the association of these Douala-Edea soils with the Caesalpinioideae is correspondingly weaker.Nomenclature follows Aubréville (1963–1983).The field work was supported by grant numbers RR00167-14, RR00167-15 and RR0167-16 from the National Institutes of Health for the operation of the Wisconsin Regional Primate Research Center, and N.A.T.O. Scientific Affairs grant number 1748 (to PGW and JSG). It was greatly facilitated by the skill and dedication of Ferdinand Namata. R. M. Polhill and D. W. Thomas assisted considerably in the identification of plant species. Sue Gartlan collected and collated the meteorological data, besides other field support. In the field phase J.S.G., P.G.W. and D.B.McK. were researches attached to the National Office of Scientific and Technical Research (ONAREST), Yaoundé. We thank M. D. Swaine for comments on earlier drafts, R. Letouzey for checking species nomenclature, the Computer Unit at Stirling University for facilities, M. Burnett for the typing at Stirling, and the Department of Soil Science, University of Wisconsin, for undertaking the soil chemical analyses.Reprint requests to D.McC.N. at Stirling.Publication No. 23-025 of the Wisconsin Regional Primate Center.     

Seasonal changes in the relationship between plant species richness and community biomass in early succession

We analysed the relationship between plant species richness and productivity on first-year-old fields at two similar sites in central Europe. At both sites, a wide range of productivity levels was available resulting from different long-term fertilisation. In order to identify underlying mechanisms of the species richness–productivity relationship we included the seasonal dynamics and the number of individuals of each species in our analysis. We sampled 10 and 21 plots, respectively, at the two sites in May, June and July by harvesting all aboveground parts of vascular plants in 0.25 m² subplots. Species richness, number of individuals of each species and community biomass as a surrogate of productivity were recorded in each sample.At one site, the relationship between species richness and biomass was significantly positive in the May and June harvest. This relationship disappeared in the July harvest due to a reduction in species richness at high productivity levels. The relations between species richness and number of individuals and between number of individuals and biomass paralleled the species richness–productivity relation but the individual number–biomass relationship remained positive until the last harvest. Between-species differences in individual number–community biomass relationships and their seasonal dynamics revealed “interspecific competitive exclusion” even though the species richness–biomass relationships were not negative or hump-shaped. At the second site, species richness was not related to productivity or to number of individuals. Our study demonstrated the importance of temporal dynamics and regional processes in understanding species richness–productivity patterns.     

Multispecies resource management of economically important marine plant communites of eastern Canada

The annual 45,000 t harvest of six marine plant taxa, consisting principally of the algaChondrus crispus, is worth $ 5 million annually to maritime fishermen. The harvesting techniques enable capture of associated biota and alter the abiotic structure of the habitat. Methods developed to assess ecological impact include permanent transects which are sampled for vegetation composition and dry biomass.C. crispus represents 80% of the plant biomass in commercial beds; 27 other genera comprise the remainder. Thirty-five associated invertebrate species include only one of direct economic importance, the lobster,Homarus americanus. On commercialChondrus beds off western Prince Edward Island, lobsters were captured in basket dragrakes up to 5.4 h⁻¹ during 1975 and 1976. Of the total lobster catch, the percentage injured byChondrus dragrakes was 2.7% in 1975 and 1.3% in 1976.Chondrus dragrakes, as used in southwestern Nova Scotia, disrupt the drumlin substrate. Controlled dragraking for 2-h periods disrupted 0.25% to 1.5% of the bottom area. One month of normal harvest activity displaced 0.5% to 2.9% of the bottom of surveyed sites. A harvest of 1000 t ofLaminaria spp. is projected for 1979. Dragrakes harvest entire plants averaging 5.0 ± 2.3 m in length. The residual population averaged 2.3 ± 1.9 m. Indirect effects of kelp harvesting on the benthic community are the subject of ongoing research.     

Harvesting of the Kelp Ecklonia Maxima in South Africa Affects Its Three Obligate, Red Algal Epiphytes

In South Africa, more than 7000 t (f wt) of kelp (Ecklonia maxima) fronds are harvested annually to feed cultured abalone. Carpoblepharis flaccida, Gelidium vittatum and Polysiphonia virgata are conspicuous red algal epiphytes on older kelps and provide habitat and food for numerous animals. Over 4.5 y, we examined the effects of one destructive harvest of E. maxima on these 3 epiphytes. Two 20 × 20 m plots of kelp with similar epiphyte loads were demarcated. In one, all E. maxima sporophytes with stipes longer than 50 cm were harvested. The other plot served as a control. After 2.5 y the biomass of E. maxima in the harvested plot had recovered to control levels, but the epiphyte load (g epiphytes. Kg kelp⁻¹) was statistically lower in the harvested plot after 2.5 and 3.5 y, and only recovered after 4.5 y. While most commercial harvesters cut through the “heads” (primary blades) of the kelp, effectively killing them, a new, non-lethal method removes secondary blades 20–30 cm from their bases, leaving the meristems and primary blades intact. At 5 sites studied, G. vittatum and P. virgata were found almost entirely on stipes and primary blades, and harvesting only distal parts of secondary blades limited losses to about 50% of C. flaccida biomass. To protect epiphytes, non-lethal harvesting is recommended and permanent non-harvest zones have been established in addition to limiting kelp yields and disallowing harvesting in Marine Protected Areas.     

Mineral nitrogen and microbial dynamics in the forest floor of clearcut or partially harvested successional boreal forest stands

The effects of clearcut and partial harvesting of early-seral trembling aspen plots were compared to conventional clearcut harvesting in mid-seral mixedwood and late-seral conifer plots. Twice a year, for three consecutive years, we assessed mineral N and microbial dynamics in the forest floor of these plots to test three hypotheses related to the higher litter quality of aspen leaves and to the sustained inputs of available C on partially harvested plots: (1) the post-clearcutting mineral N flush and the net [(NO₃^–): (NO₃^– + NH₄⁺)] production ratio (RNI) are higher in aspen plots than in black spruce plots, with intermediate values occurring in mixedwood plots; (2) net N mineralization rates in aspen plots are higher in spring than in autumn; and (3) compared to clearcutting, partial harvesting reduces potential ammonification and nitrification rates. Initial NH₄⁺ and NO₃^– concentrations respectively ranged between 1.7–4.4 and 0.2–1.5 g N kg^–1 N_total, net ammonification and nitrification rates (30 d incubations) respectively ranged between 5.3–17.8 and 0.1–27.6 g N kg^–1 N_total, basal respiration ranged between 20.9–38.9 mg CO₂-C kg^–1 h^–1, and microbial biomass ranged between 6.1–8.7 g C_mic kg^–1. Although clearcutting increased NO₃^– concentrations in aspen plots, the balance of our results did not support our first hypothesis, because NH₄⁺ concentrations increased in conifer plots only, potential ammonification was unaffected by clearcutting, potential nitrification increased in mixedwood plots only, and RNI increased in all plots. In each seral stage, basal respiration, microbial biomass, and metabolic quotient either increased or were unaffected by clearcutting, suggesting that increases in RNI after disturbance were not related to lower microbial immobilisation of NO₃^– due to lower available C. Forest floors in mid-seral mixedwood plots exhibited a distinct combination of mineral N and microbial properties, suggesting that the functional richness of the forest is enhanced not only by the number of species, but also by the diversity of assemblages that are present. Results supported our second hypothesis and showed, furthermore, that net N mineralization in conifer stands is greater in autumn than in spring. Partial harvesting in aspen stands resulted in lower potential mineralization of N and lower RNI, compared to clearcutting. Further lysimetry studies are needed to confirm whether partial harvesting mitigates NO₃^– leaching following disturbance.     

Laboulbenia exigua and related taxa (Ascomycetes,Laboulbeniales)

TheLaboulbenia exigua group comprises seven species. Three of these species are described as new to science, and two new varieties ofL. exigua and one new variety ofL. balazucii are distinguished and described. New taxa areL. yamadae, L. consobrina, L. gebleri, L. exigua var.yaeyamae, L. exigua var.melanolabiata andL. balazucii var.exilis. This fungus group is characterized by grayish yellow to gray-brown thalli with simple inner and outer appendages, dark-spotted or streaked receptacles, and perithecia containing narrow ascospores 3–4–(–5) µm in width; the species and varieties occur onChlaenius (Carabidae) and closely allied taxa. The bilobed apex of mature perithecium, owing to the rounded apices of the posterior apical cells of the outer wall cell rows, and 3-celled, curved inner appendage in young thalli, and the deciduous antheridium are also characteristic of this group.     

Seasonal variation in Laminaria digitata and its impact on biochemical conversion routes to biofuels

Laminaria digitata is a highly prevalent kelp growing off the coast of the UK but has rarely been considered as a source of biomass to date. This study shows it can be used as a feedstock in both ethanol fermentation and anaerobic digestion for methane production. The study optimised several parameters in the fermentation of L. digitata and investigated the suitability of the macroalgae through the year using samples harvested every month. For both methane and ethanol production, minimum yields were seen in material harvested in March when the carbohydrates laminarin and mannitol were lowest. July material contained the highest combined laminarin and mannitol content and maximum yields of 167 mL ethanol and 0.219 m³ kg⁻¹L. digitata.     

Soil nitrogen mineralization in plantations ofJuglans nigra interplanted with actinorhizalElaeagnus umbellata orAlnus glutinosa

Nitrogen mineralization rates were estimated in 19-year-old interplantings of black walnut (Juglans nigra L.) with dinitrogen fixing autumn-olive (Elaeagnus umbellata Thunb.) or black alder (Alnus glutinosa L. Gaertn.) and in pure walnut plantings at two locations in Illinois USA. N mineralization rates were measured repeatedly over a one year period usingin situ incubations of soil cores in oxygen-permeable polyethylene bags at 0–10 and 10–20 cm soil depths, and also by burying mixed-bed ion-exchange resin in soil. Mineralization rates were highest in summer and in plots containing actinorhizal Elaeagnus and Alnus in contrast with pure walnut plots. Elaeagnus plots at one location yielded 236 kg of mineral N ha^–1 yr^–1 in the upper 20 cm of soil, a value higher than previously reported for temperate decidous forest soils in North America. The highest mean plot values for N mineralization in soil at a location were 185 kg ha^–1 yr^–1 for Alnus interplantings and 90 kg ha^–1 yr^–1 for pure walnut plots. Plots which had high N mineralization rates also had the largest walnut trees. Despite low pH (4.1 and 6.5) and low extractable P concentrations (1.4 and 0.7 mg kg^–1 dry mass) at the two locations, nitrification occurred in all plots throughout the growing season. NO ₃ ^– –N was the major form of mineralized N in soil in the actinorhizal interplantings, with NH ₄ ⁺ –N being the major form of mineral N in control plots. Walnut size was highly correlated with soil nitrogen mineralization, particularly soil NO ₃ ^– –N production in a plot.     

Effects of a clearcut on the net rates of nitrification and N mineralization in a northern hardwood forest,Catskill Mountains,New York,USA

The Catskill Mountains of southeastern New York receive among the highest rates of atmospheric nitrogen (N) deposition in eastern North America, and ecosystems in the region may be sensitive to human disturbances that affect the N cycle. We studied the effects of a clearcut in a northern hardwood forest within a 24-ha Catskill watershed on the net rates of N mineralization and nitrification in soil plots during 6 years (1994–1999) that encompassed 3-year pre- and post-harvesting periods. Despite stream NO₃^– concentrations that increased by more than 1400 mol l^–1 within 5 months after the clearcut, and three measures of NO₃^– availability in soil that increased 6- to 8-fold during the 1^st year after harvest, the net rates of N mineralization and nitrification as measured by in situ incubation in the soil remained unchanged. The net N-mineralization rate in O-horizon soil was 1– 2 mg N kg^–1 day^–1 and the net nitrification rate was about 1 mg N kg^–1 day^–1, and rates in B-horizon soil were only one-fifth to one-tenth those of the O-horizon. These rates were obtained in single 625 m² plots in the clearcut watershed and reference area, and were confirmed by rate measurements at 6 plots in 1999 that showed little difference in N-mineralization and nitrification rates between the treatment and reference areas. Soil temperature increased 1 ± 0.8 °C in a clearcut study plot relative to a reference plot during the post-harvest period, and soil moisture in the clearcut plot was indistinguishable from that in the reference plot. These results are contrary to the initial hypothesis that the clearcut would cause net rates of these N-cycling processes to increase sharply. The in situ incubation method used in this study isolated the samples from ambient roots and thereby prevented plant N uptake; therefore, the increases in stream NO₃^– concentrations and export following harvest largely reflect diminished uptake. Changes in temperature and moisture after the clearcut were insufficient to measurably affect the net rates of N mineralization and nitrification in the absence of plant uptake. Soil acidification resulting from the harvest may have acted in part to inhibit the rates of these processes. The US Governments right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

The macrofauna and macroflora associated withLaminaria digitata andL. hyperborea at the island of Helgoland (German Bight,North Sea)

This paper describes the macroflora and macrofauna associated with two bull kelp species,Laminaria hyperborea andL. digitata, at the island of Helgoland, North Sea. During a study period of seven months (March–September 1987), 29 macroflora species and 125 macrofauna species were found. The dominant taxonomic groups were Polychaeta (25 species), Bryozoa (17), Amphipoda (14), Hydrozoa (10) and Ascidiae (8). The species maximum was in July. In general,L. hyperborea was preferred as a substrate for settlement toL. digitata. Composition of the communities associated with kelp changed during the season according to exposure to wave action, and according to location on the kelp thallus. The rhizoid community of both kelps bore more species at exposed locations. Wave-exposedL. digitata lacked obvious faunal settlement on both phylloid and cauloid. Phylloid and cauloid ofL. hyperborea were chosen as an attractive substrate at both sheltered and wave-exposed locations, showing an association of encrusting bryozoan and hydrozoan colonies.     

On the distribution patterns and population dynamics of sublittoral and profundal oligochaeta fauna from Lake Banyoles (Catalonia,NE Spain)

Oligochaeta assemblages from Lake Banyoles were composed of one species of Naididae and eight species of Tubificidae, Potamothrix heuscheri (8–1350 ind. m^–2) being the most abundant and widely distributed species, followed by Limnodrilus hoffmeisteri (25–858 ind. m^–2) and Psammoryctides barbatus (12–792 ind. m^–2). The remaining species were Potamothrix hammoniensis, Potamothrix bavaricus, Limnodrilus claparedeanus, Branchiura sowerbyi, Aulodrilus pigueti and Dero digitata, all of which occurred at lower densities and with restricted distributions.Regardless of sampling depth, maximum densities of oligochaetes were found in winter (up to 5,142 ind. m^–2 in December) and secondarily in June. Immature Tubificidae with hair setae and mature P. heuscheri were present and dominant throughout the year. Cestode parasites were recorded infesting L. hoffmeisteri and P. heuscheri populations.Oligochaeta densities increased with depth, but low oxygen concentrations (less than 1 mg l^–1) during a long period (4 months) in some basins of the lake acted as a key factor in reducing the density of worms and the species richness to one species, Potamothrix heuscheri.