Ectomycorrhizal colonization of naturally regenerating <Emphasis Type="Italic">Pinus sylvestris</Emphasis> L. seedlings growing in different micro-habitats in boreal forest

We investigated the species richness and composition of ectomycorrhizal (EM) fungi colonizing Pinus sylvestris L. seedlings naturally regenerating in boreal forest, in three different microhabitats: on forest ground, on decaying stumps, and within moss layer on erratic boulders. We tested the hypothesis that habitat differences would affect the composition of the EM community of regenerating pine seedlings. In total, 16 EM species were detected, from which none occurred on seedlings growing in all three microhabitats. Piloderma croceum and Cenococcum geophilum were common for seedlings growing in forest ground and on boulders, while Tricholoma aestuans and Suillus luteus were shared between seedlings growing on forest ground and decaying stumps. EM species richness and composition were strikingly different between seedlings regenerating in different microhabitats. Results are discussed as a function of dispersal and niche differentiation of EM fungi.     

Mycobionts of <Emphasis Type="Italic">Salix herbacea</Emphasis> on a glacier forefront in the Austrian Alps

Dwarf willows (e.g. Salix herbacea) are among the earliest ectomycorrhizal (EM) plants colonising primary successional sites such as glacier forefronts in the Tyrolean Alps. EM of S. herbacea were sampled at the Rotmoos glacier forefront (Otz Valley, Austria) three times a year during the growing season and once a year during winter when plants were covered with snow in 2005 and 2006. EM were investigated using morphological methods and by sequencing the rDNA ITS region. The degree of EM mycorrhization was high throughout both years (93%). We distinguished 21 EM morphotypes and identified 19 fungal species. Cenococcum geophilum, Sebacina spp., Tomentella spp. and Cortinarius spp. dominated the mycobiont community of S. herbacea. The observed species richness in this about 150-year-old soil was at least 59% of the estimated species richness. Fungal communities differed significantly between consecutive years, and spatial heterogeneity was high. These differences made it difficult to detect seasonal impacts. Abundances of C. geophilum EM increased throughout the 2-year sampling period. Sebacina incrustans EM were very abundant in 2005, but nearly disappeared in 2006, whilst its fruitbodies were still frequent in the sampling area. This suggests that the mycorrhizae were displaced from the roots by an outcompeting species, whereas the mycelium was still present in the soil.     

Evidence for mutualist limitation: the impacts of conspecific density on the mycorrhizal inoculum potential of woodland soils

The ability of seedlings to establish can depend on the availability of appropriate mycorrhizal fungal inoculum. The possibility that mycorrhizal mutualists limit the distribution of seedlings may depend on the prevalence of the plant hosts that form the same type of mycorrhizal association as the target seedling species and thus provide inoculum. We tested this hypothesis by measuring ectomycorrhizal (EM) fine root distribution and conducting an EM inoculum potential bioassay along a gradient of EM host density in a pinyon–juniper woodland where pinyon is the only EM fungal host while juniper and other plant species are hosts for arbuscular mycorrhizal (AM) fungi. We found that pinyon fine roots were significantly less abundant than juniper roots both in areas dominated aboveground by juniper and in areas where pinyon and juniper were co-dominant. Pinyon seedlings establishing in pinyon–juniper zones are thus more likely to encounter AM than EM fungi. Our bioassay confirmed this result. Pinyon seedlings were six times less likely to be colonized by EM fungi when grown in soil from juniper-dominated zones than in soil from either pinyon–juniper or pinyon zones. Levels of EM colonization were also reduced in seedlings grown in juniper-zone soil. Preliminary analyses indicate that EM community composition varied among sites. These results are important because recent droughts have caused massive mortality of mature pinyons resulting in a shift towards juniper-dominated stands. Lack of EM inoculum in these stands could reduce the ability of pinyon seedlings to re-colonize sites of high pinyon mortality, leading to long-term vegetation shifts.     

Long-Term Effects of Forest Regrowth and Selective Logging on the Seed Bank of Tropical Forests in NE Costa Rica1.

To investigate long-term effects of land use on the soil seed bank, we compared the abundance/density, species richness, life form distribution, and species composition of seeds stored in the soil of four 15–20 yr-old second-growth stands, two old-growth stands, and two previously selectively-logged stands in the Caribbean lowlands of Costa Rica. Surface soil (10 cm deep, 4.7 cm diameter) was collected at 10 m intervals along three 120–160 m long transects in each stand (44–48 soil cores, 22–24 combined seed bank samples per site). Seed density was highest but variable in second-growth stands (8331–14535 seeds/m²), low and homogeneous in old-growth stands (2258–2659 seeds/m²), and intermediate and highly variable in selectively-logged stands (1165–6854 seeds/m²), which also had contrasting logging intensities. Species richness was strongly dependent on seed density, but showed less variation. Life form distribution did not differ statistically among or within land-use categories. In each stand, herbs-forbs, shrubs, and vines dominated the seed bank (> 75% of the species richness and abundance), whereas trees were a minor component (< 20% of the species richness and < 5% of the abundance) and were predominandy early successional. Shrubs and vines were most abundant in second-growth stands where regrowth vegetation was repeatedly cut before abandonment, whereas grasses and sedges were most abundant in the only forest stand that was completely surrounded by pastures. In terms of species composition, old-growth stands were more similar to selectively-logged stands than to second-growth stands, but across stands, selectively-logged forests were most distinct from the other two forest types. An inventory of the standing woody vegetation in each site showed little representation of the woody taxa found in the seed bank. We discuss these results in the context of the main factors that have been postulated to influence the abundance, life form, and species composition of tropical forest seed banks, and explore the role of the latter during intermediate phases of tropical forest succession and regeneration.     

The mid-domain effect in ectomycorrhizal fungi: range overlap along an elevation gradient on Mount Fuji,Japan

Mid-domain effect (MDE) models predict that the random placement of species'' ranges within a bounded geographical area leads to increased range overlap and species richness in the center of the bounded area. These models are frequently applied to study species-richness patterns of macroorganisms, but the MDE in relation to microorganisms is poorly understood. In this study, we examined the characteristics of the MDE in richness patterns of ectomycorrhizal (EM) fungi, an ecologically important group of soil symbionts. We conducted intensive soil sampling to investigate overlap among species ranges and the applicability of the MDE to EM fungi in four temperate forest stands along an elevation gradient on Mount Fuji, Japan. Molecular analyses using direct sequencing revealed 302 EM fungal species. Of 73 EM fungal species found in multiple stands, 72 inhabited a continuous range along the elevation gradient. The maximum overlap in species range and the highest species richness occurred at elevations in the middle of the gradient. The observed richness pattern also fit within the 95% confidence interval of the mid-domain null model, supporting the role of the MDE in EM fungal richness. Deviation in observed richness from the mean of the mid-domain null estimation was negatively correlated with some environmental factors, including precipitation and soil C/N, indicating that unexplained richness patterns could be driven by these environmental factors. Our results clearly support the existence of microbial species'' ranges along environmental gradients and the potential applicability of the MDE to better understand microbial diversity patterns.     

Effects of Hurricane Andrew on stands of slash pine (Pinus elliottii var. densa) in the everglades region of south Florida (USA)

Few hurricanes affect intact stands of subtropical pines. We examined effects of winds in the eyewalls of Hurricane Andrew, where wind speeds were >200 km h^–1, on all remaining large mainland stands of Pinus elliottii var. densa (south Florida slash pine) on limestone outcroppings (rocklands) in the everglades region of southern Florida. We measured densities and sizes of trees and assessed damage and mortality in plots in old-growth stands in the Lostman's Pines (LOP) region of Big Cypress National Preserve and in second-growth stands in the Pines West (PIW) and Long Pine Key (LPK) regions of Everglades National Park. We also examined age-size relationships using sections from trees killed by the hurricane in LOP and LPK. We used the data to predict effects of recurrent hurricanes on the structure and dynamics of the old-growth stand and to compare effects of hurricanes on old- and second-growth stands.Slash pine was resistant to hurricane winds. Most trees in stands (68–76%) were not severely damaged; mortality in the three regions averaged 17–25% shortly after the hurricane and 3–7% during the following year. Mortality was positively associated with tree size; mean tree sizes decreased and size-selective thinning occurred in all stands. Nonetheless, local mortality ranged from 3–4% to 50–60% among plots in all stands. Such local variation in mortality resulted from clustering of large trees, especially in old-growth stands, and from microbursts during the hurricane, which affected all stands. Recurrent, intense hurricanes are predicted to kill larger trees, slowly opening new patches and increasing sizes of extant patches, thus resulting in almost continual presence of openings suitable for recruitment in old-growth stands. Age-size relationships also indicated that large trees in old-growth stands may survive 2–3 centuries. The combination of frequent openings and wind resistance of large trees is predicted to result in old-growth stands that are highly uneven aged, with trees locally distributed in similar-aged patches. The extent to which such stands deviate from demographic equilibrium, as well as turnover rates within stands, are likely to increase as the frequency of recurrent, intense hurricanes increases.Damage and mortality differed in old- and second-growth stands. Large trees were more, but small trees less likely to be damaged in old- than second-growth stands. In contrast, mortality was significantly lower in old- (LOP: 16.9% ± 3.1 [mean ± s.e.]) than second-growth stands (PIW: 22.5% ± 2.0; LPK: 25.2% ± 2.7). Total hurricane-related mortality was 30–60% higher in second- than old-growth stands. Size class structure, more uneven in old- than second growth stands prior to the hurricane, diverged even more afterwards. Hurricane Andrew removed     

云南松（Pinus yunnanensis）林外生菌根真菌的时空分布

2000年至2005年,调查了滇中及其附近云南松林下外生菌根真菌的生态分布,共采集、鉴定标本834号,计有27科39属211种（含变种、变型）。结果表明,红菇属（Russula）、牛肝菌属（Boletus）、乳菇属（Lactarius）、乳牛肝菌属（Suillus）、口蘑属（Tricholoma）、鸡油菌属（Cantharellus）和革菌属（Thelephora）等为云南松林下的主要外生菌根菌类群。它们的发生与分布受到气候（如：气温和降水）、植被（如：林龄、林地郁闭度和草本植被）、地形特征（如：海拔、坡向和坡度）、土壤条件（如：pH值、地表腐殖质和枯枝落叶层等）和人为干扰（比如：商业化采集、林木采伐、火烧和地表物清理）诸多因素的影响。总结为如下：(1）5a的调查结果显示,云南松外生菌根菌的分布表现出季节性变化的规律;其中以每年1、2、3月份的物种多样性为最低,雨季期间急剧增加,至中夏和秋末达到顶峰,种类最为繁多。(2）在海拔1500～2100 m,云南松外生菌根菌种类随着海拔的升高而逐渐增加,至顶峰后,又呈缓慢下降趋势。海拔因素不但对其物种多样性,而且对于类群的组成也具有重要的影响。特定的类群往往发生在特定海拔范围。(3）随着云南松林龄的增加,外生菌根菌呈现由少至多的演替过程。外生菌根菌多样性随云南松林生长而逐渐增加的演替方式,可能与宿主光合作用产物、根部分泌物和土壤条件的逐渐变化有关。(4）人类干扰是云南松外生菌根菌物种多样性和类群组成的主要负影响因子。大规模的商业化采集可破坏或枯竭地下菌丝体,打破各物种之间的竞争平衡,减少孢子释放影响资源再生能力,进而直接影响到子实体的产生。外生菌根菌物种多样性的减少趋势会随林木砍伐和火烧强度的增加而加剧。地表枯枝落叶层与杂草密度也会影响子实体的产生,其中枯枝落叶层的厚度与云南松外生菌根菌子实体的发生呈负相关性,而被紫茎泽兰覆盖的云南松林地内也很少会发现相应的子实体。     

Ectomycorrhizal fungal communities in late-successional Swedish boreal forests, and their composition following wildfire

This study was conducted to evaluate the effects of wildfires on ectomycorrhizal (EM) fungal communities in Scots pine ( Pinus sylvestris ) stands. Below- and above-ground communities were analysed in terms of species richness and evenness by examining mycorrhizas and sporocarps in a chronosequence of burned stands in comparison with adjacent unburned late-successional stands. The internal transcribed spacer (ITS)-region (rDNA) of mycobionts from single mycorrhizas was digested with three restriction enzymes and compared with an ITS–restriction fragment length polymorphism (RFLP) reference database of EM sporocarps. Spatial variation seemed to be more prominent than the effects of fire on the EM fungal species composition. Most of the common species tended to be found in all sites, suggesting that EM fungal communities show a high degree of continuity following low-intensity wildfires. Species richness was not affected by fire, whereas the evenness of species distributions of mycorrhizas was lower in the burned stands. The diversity of EM fungi was relatively high considering that there were only three EM tree species present in the stands. In total, 135 EM taxa were identified on the basis of their RFLP patterns; 66 species were recorded as sporocarps, but only 11 of these were also recorded as mycorrhizas. The species composition of the below-ground community of EM fungi did not reflect that of the sporocarps produced. EM fungal species present in our ITS–RFLP reference database accounted for 54–99% of the total sporocarp production in the stands, but only 0–32% of the mycorrhizal abundance.     

Woody vegetation structure of xeric forest stands under different edaphic site conditions and disturbance histories in the Biosphere Reserve 'Parque Costero del Sur', Argentina

We studied stand structures and soil properties in an old-growth forest and two 30-yr-old second-growth stands. In the old-growth forest, the total density and basal area average 1566 trees > 1.25 m height ha^-1 and 46.73 m² ha^-1. The dominant trees are Scutia buxifolia and Celtis tala. Using multivariate techniques we distinguished three stands: PS1, dominated by S. buxifolia, is 1000 m far from the river. Its soil is shallow and loamy. PS2 and PS3, co-dominated by S. buxifolia and C. tala, are over 1200 m distant from the river. There the soil is deeper and has thicker texture and higher phosphorus and calcium concentrations than the near-the-river forest soil. Scutia buxifolia shows reverse J-shaped size-distributions and has morphological features of stress-tolerant species. Celtis tala shows oscillating decay size-curves that suggest recruitment pulses related to small gaps and it has morphological features of competitive species. Celtis tala was selectively cut in the past in the second-growth stands SNRD and SRD. The stand SNRD, 1000 m far from the river, is dominated by S. buxifolia. The second species is Schinus polygamus which presents the bell-shaped size-structure of the pioneer species. SNRD does not differ from its old-growth counterpart PS1 in total tree density, basal area and tree branching. The stand SRD, over 1200 m distant from the river, is co-dominated by S. buxifolia and by C. tala trees regenerated from stumps. SRD does not differ from its old-growth counterparts PS2 and PS3 in total tree density and basal area. As to tree branching, it does not differ from PS3, but differs from PS2. All the stands are being invaded by the exotic tree Ligustrum lucidum.The differences between the old-growth stands seem to be related to the gradients of soil texture and nutrient concentrations raising edaphic stress towards the river. In SNRD, the stress, the stress-tolerance of S. buxifolia, and the aptitude of S. polygamus to recruit in disturbed habitats seem to have prevented the post-logging recruitment of C. tala. In SRD, C. tala regenerated possibly due to a better competitive performance in a more favorable site. Under protection the second-growth stands recovered the old-growth quantitative features. We recommend the restoration of the qualitative features and the control of L. lucidum.     

Influence of aspect and stand age on ground flora of southeastern Ohio forest ecosystems

The species composition and diversity of the ground flora (vascular plants less than one meter in height excluding tree seedlings) were compared between sixteen mesic northeast-facing and sixteen dry southwest-facing middle slopes in southeastern Ohio. On each aspect, eight of the plots were located in second-growth forest stands (70 to 90 years in age) and eight of the plots were located in old-growth forest stands (greater than 150 years in age) in order to determine how the ground flora on opposing slopes varies with time since major disturbance. Physiographic and A horizon characteristics were measured to select comparable plots. Multi-response permutation procedures (MRPP) detected significant differences in the ground-flora species composition of second-growth and old-growth plots on both northeast-facing and southwest-facing slopes. In addition, the ground-flora species composition of northeast-facing plots differed significantly from that of southwest-facing plots. Northeast-facing plots were significantly higher in species richness and Hill's diversity (N1) than southwest-facing plots. Northeast-facing second-growth plots were also significantly higher in species richness and Hill's diversity than northeast-facing old-growth plots. No significant differences in these measures were found between southwest-facing second-growth and old-growth forests plots. Twenty-one species were identified as potential indicators of age, based on their distribution across the plots. Certain species with similar ecological characteristics were found to have similar patterns of occurrence. Further research is needed to determine the extent to which differences in the ground flora of second-growth old-growth reflect the sensitivity of individual species to past disturbance.     

Ectomycorrhizas associated with a relict population of Dryas octopetala in the Burren, western Ireland II. Composition, structure and temporal variation in the ectomycorrhizal community

The composition, structure and temporal variation of ectomycorrhizal (EM) communities associated with mountain avens (Dryas octopetala) in grass heaths of the Burren, western Ireland were assessed by using soil core sampling in two permanent plots and 30 other sites (196 cores in total). Of the 34 different EM types observed, 11 were common and constituted over 80% of the EM biomass. Four EM types, Craterellus lutescens, Tomentella sp., Dryadirhiza fulgens and Cenococcum geophilum were the most abundant as measured by EM length and frequency of occurrence in cores. The species profile and relative abundances were very similar in cores from the permanent plots and different sites in the Burren, indicating that they were all representative of the same EM community. The below-ground EM community in both plots was compared with production of basidiomes, and the latter was found to be an unreliable indicator of EM community structure. Temporal variation in the EM community was assessed by repeated core sampling of the two permanent plots over a 14-month period (between March 1998 and May 1999). No statistically significant shifts in EM abundance were found between sampling dates, probably as a consequence of the large variation in EM abundance between core samples over the sampling period. No significant relationship was found between rainfall, soil moisture or soil temperature and fluctuations in EM abundance. Patterns of total EM abundance and fluctuations in EM diversity were strongly correlated between the two permanent plots over the sampling period. Temporal fluctuations in the dominant EM type, Craterellus lutescens, were similar in both plots with respect to mycorrhizal length, biomass and relative abundance, and the patterns between both plots were positively correlated. EM diversity was negatively correlated with biomass of ectomycorrhizas of Craterellus lutescens in both plots, but it was significant only in plot 1.     

Riverscape-level patterns of riparian plant diversity along a successional gradient, Willamette river, Oregon

Riparian forest communities dominated by Populus balsamifera ssp. trichocarpa L. (Torr. and Gray ex Hook.) Brayshaw are important contributors to biodiversity in terrestrial and aquatic ecosystems of the Western United States. Species composition along a successional gradient from stand initiation to late-succession of P. balsamifera-dominated riparian forests was investigated along 145 km of the Willamette River, Oregon. There were 151 total species encountered across 28 stands and a mean species richness of 33.3 species per stand. Young stands were dominated by P. balsamifera and Salix tree spp. and opportunistic herbaceous species. Understory trees, shrubs, and herbaceous species as well as late-successional tree species established 12–15 years after stand initiation. Fraxinus latifolia Benth. was the dominant late-successional tree species. Vertical structural diversity, P. balsamifera mean diameter at breast height, large tree biomass, and stand age were strongly correlated with understory species presence and abundance based on non-metric multidimensional scaling (NMS) ordination. There were no young stands on mid and high terraces and this was reflected in geomorphic position being strongly correlated with the stand age gradient. Abundance of Phalaris arundinacea L. an invasive grass species, was also significantly correlated with plant species composition and abundance. This study indicates that Willamette River riparian forests are diverse and therefore important to the biodiversity of the Willamette River valley and that their presence as a mosaic of communities of different successional stages may be threatened by human interventions, including influences exerted by introduced plant species.     

Changes in Different Trophic Levels of Litter-dwelling Macrofauna Associated with Giant Knotweed Invasion

Abstract The highly invasive giant knotweed (Reynoutria spp.) often displaces nettle (Urtica dioica) dominated stands in European floodplains. Urtica-dominated stands differ from the monospecific Reynoutria stands in plant species richness and stand structure. We thus hypothesize that Reynoutria invasion profoundly alters ecosystem structure and function, with negative effects cascading up through the food chain. We performed a paired sampling design in six sites belonging to two different locations and studied effects on the soil and the litter-dwelling fauna. Reynoutria stands differed in habitat structure and were characterized by decreased soil pH and potassium depletion. The faunal analysis is based on model groups of herbivore generalists (Gastropoda), detritivores (Isopoda and Diplopoda), and predators (Opiliones). The gastropod assemblages from Reynoutria stands were severely impoverished subsets of those from Urtica stands with reduced densities, species richness and diversity. In general, snails were more sensitive to Reynoutria invasion than slugs such as the invasive Arion 'lusitanicus’. Among detritivores, the abundance of the Isopoda decreased, whereas Diplopoda were not affected by Reynoutria invasion. Yet, the relative abundance of detritivores was significantly higher within the Reynoutria stands. Abundance, species richness and diversity of the predatory Opiliones were higher in the relatively sparse Reynoutria stands. We conclude that ecosystem changes associated with Reynoutria invasion are characterized by shifts from a plant-based to a detritus-based food chain and that Reynoutria invasion primarily enhances predators that profit from the simplified vegetation structure. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Molecular approaches to ectomycorrhizal diversity studies: variation in ITS at a local scale

In most ectomycorrhizal (EM) community studies involving molecular identification methods there is a poor correspondence between fungi that appear dominant as sporocarps and those that appear dominant on EM roots and the species richness belowground is higher than that above ground. As a consequence, many fungi from root tip samples remain unidentified. In most studies, genetic data from multiple samples of an EM morphotype collected from various sampling locations are compared to genetic data from one to a few sporocarps of each species for identification purposes. The mismatch between above- and belowground species richness may be influenced by these different sampling efforts. To address this, intra-specific variation in the ITS region first investigated in Kårén et al. (1997) is revisited here, but at a spatial scale in which variation is expected to be low. Sporocarps were collected across a 7 km region of the Oregon Dunes National Recreation Area in western North America. ITS–RFLP data are presented for 3-18 sporocarps from each of 44 EM species in 18 genera. A total of 311 sporocarps were analyzed. Fifty-three ITS–RFLP types were observed. Of the 44 species, 38 (86% of total) yielded a single, species specific, RFLP type. No 2 species had the same RFLP type. Polymorphic ITS–RFLP types were observed in six species (14%). The following three species had two ITS-RFLP types with one type dominating: Inocybe lacera, Laccaria proxima, and Rhizopogon subcaerulescens. The following three species had three RFLP types with no type dominating: Laccaria laccata, Lactarius deliciosus, and Tricholoma flavovirens. A phylogenetic analysis of ITS sequences in Tricholoma revealed that two of the RFLP types in T. flavovirenswere apparently the result of intra-specific variation, while the third RFLP type was likely a cryptic species. All the other RFLP types observed in Tricholoma represented unique phylogenetic species. These results suggest that ITS–RFLP data from single samples (sporocarp or EM) are robust for characterizing most of the species at this scale. However, restriction endonucleases detect a limited amount of existing nucleotide variation and thus have limited value to detect cryptic species. Therefore, additional analyses of sequence data should be added to the RFLP matching technique to identify unknown RFLP types. These data also suggest that polymorphic RFLP types within species do not adequately explain the mismatch between above- and belowground views of EM species richness.     

Reduction of solar UV-B mediates changes in the Sphagnum capitulum microenvironment and the peatland microfungal community

The influence of near-ambient and reduced solar UV-B radiation on a peatland microfungal community was assessed by exposing experimental plots to UV-selective filtration. Replicate plots were covered with special plastic films to effect treatments of near-ambient and attenuated solar UV-B. The microfungal community from the top 1 cm of Sphagnum capitulum in a Tierra del Fuego peatland was censused throughout three growing seasons, between 1999 and 2002. Sphagnum capitula under near-ambient UV-B were more compressed and held more water than capitula under reduced UV-B. This water had a greater conductivity and was more acidic under near-ambient UV-B, as would be expected with increased leaching from the Sphagnum leaves. Nine regularly occurring hyphal fungi from the peatland were identified, at least to genus. Over three field seasons, no treatment effect on total fungal colony abundance was recorded, but individual species abundance was increased (Mortierella alpina), decreased (Penicillium frequentans), or was unaffected (P. thomii, Aureobasidium) by near-ambient UV-B. Species richness was also slightly lower under near-ambient UV-B. These treatment differences were smaller than seasonal or inter-annual fluctuations in abundance and species richness. In a growth chamber experiment, lamp UV-B treatments indicated that realistic fluxes of UV-B can inhibit fungal growth in some species. In addition to this direct UV-B effect, we suggest that changes in the peatland fungal community under near-ambient solar UV-B may also result from increased nutrient and moisture availability in the Sphagnum capitulum. The subtle nature of the responses of peatland fungi to solar UV-B suggests that most fungal species we encountered are well adapted to current solar UV-B fluxes in Tierra del Fuego.     

The value of timber quality forests for insect conservation on Tierra del Fuego Island compared to associated non-timber quality stands

Insect community studies related to forest management focus principally on timber-quality stands, and often omit the remainder of the landscape. This study aimed mainly to compare insect communities of primary timber-quality forests (Nothofagus pumilio) with associated non-timber-quality stands (wetland, edge, riparian and N. antarctica forests), and secondarily to characterize these insect assemblages throughout the growing season and at different vertical strata to evaluate the importance of each habitat type for insect conservation. A total of 18,800 individuals belonging to 231 RTUs (recognizable taxonomic units) were identified, of which Diptera, Hymenoptera, Lepidoptera and Coleoptera were the dominant orders. Lepidoptera RTUs were mostly generalists, while the other main orders were most frequently found in timber-quality forests and included many RTUs with specific environmental requirements. Timber-quality stands had higher richness and abundance than associated non-timber-quality forests and possessed more exclusive species (18%), while 39% of RTUs were shared between all sites. The spatial heterogeneity of timber-quality stands generated different niches and favored insect diversity, which would not have been maintained by protecting non-timber-quality stands alone. Consequently, the proper management of subantarctic Nothofagus forests must include the conservation of timber-quality stands, as protection of non-timber-quality areas alone will not be sufficient for insect conservation at the landscape scale.     

云南松(Pinus yunnanensis)林外生菌根真菌的时空分布

2000年至2005年,调查了滇中及其附近云南松林下外生菌根真菌的生态分布,共采集、鉴定标本834号,计有27科39属211种（含变种、变型）。结果表明,红菇属（Russula）、牛肝菌属（Boletus）、乳菇属（Lactarius）、乳牛肝菌属（Suillus）、口蘑属（Tricholoma）、鸡油菌属（Cantharellus）和革菌属（Thelephora）等为云南松林下的主要外生菌根菌类群。它们的发生与分布受到气候（如：气温和降水）、植被（如：林龄、林地郁闭度和草本植被）、地形特征（如：海拔、坡向和坡度）、土壤条件（如：pH值、地表腐殖质和枯枝落叶层等）和人为干扰（比如：商业化采集、林木采伐、火烧和地表物清理）诸多因素的影响。总结为如下：（1）5a的调查结果显示,云南松外生菌根菌的分布表现出季节性变化的规律;其中以每年1、2、3月份的物种多样性为最低,雨季期间急剧增加,至中夏和秋末达到顶峰,种类最为繁多。（2）在海拔1500-2100m,云南松外生菌根菌种类随着海拔的升高而逐渐增加,至顶峰后,又呈缓慢下降趋势。海拔因素不但对其物种多样性,而且对于类群的组成也具有重要的影响。特定的类群往往发生在特定海拔范围。（3）随着云南松林龄的增加,外生菌根菌呈现由少至多的演替过程。外生菌根菌多样性随云南松林生长而逐渐增加的演替方式,可能与宿主光合作用产物、根部分泌物和土壤条件的逐渐变化有关。（4）人类干扰是云南松外生菌根菌物种多样性和类群组成的主要负影响因子。大规模的商业化采集可破坏或枯竭地下菌丝体,打破各物种之间的竞争平衡,减少孢子释放影响资源再生能力,进而直接影响到子实体的产生。外生菌根菌物种多样性的减少趋势会随林木砍伐和火烧强度的增加而加剧。地表枯枝落叶层与杂草密度也会影响子实体的产生,其中枯枝落叶层的厚度与云南松外生菌根菌子实体的发生呈负相关性,而被紫茎泽兰覆盖的云南松林地内也很少会发现相应的子实体。     

Conservation value of timber quality versus associated non-timber quality stands for understory diversity in Nothofagus forests

Conservation strategies of forested landscapes must consider biodiversity of the included site types, i.e. timber-quality forests and associated non-timber-quality stands. The objectives were to characterize forest overstory structure in timber-quality versus associated non-timber-quality stands; and to compare their understory communities. Six forest types were sampled in Nothofagus forests of Tierra del Fuego (Argentina): two timber-quality N. pumilio forests, and four associated non-timber-quality stands (edge, N. antarctica, wetlands and streamside forests). Overstory structure and understory vegetation (species richness, frequencies, cover and biomass) were characterized during spring and summer seasons. Analysis of variance and multivariates were carried out. Overstory structure differed across the site types, with higher tree size, canopy closure and tree volume in timber-quality stands. Fifty-one understory plant species were observed, but understory variables varied with site types, especially wetlands (highest native and exotic richness, cover and biomass, and 25% of exclusive species). Site types were grouped in three: N. antarctica stands, streamside stands and the other N. pumilio forests according to multivariate analysis. Forty three percent of plants were distributed in all site types, and all timber-quality forest understory species were present in some associated non-timber-quality stands. Timber-quality N. pumilio forests have a marginal value for understory conservation compared to associated non-timber-quality stands, because these last include all the plants observed in timber-quality forests and also possess many exclusive species. Therefore, protection of associated non-timber-quality stands during forest management planning could increase understory conservation at landscape level, and these could be better reserves of understory diversity than retentions of timber-quality stands.     

Influence of Aspen on Forest Floor Properties in Black Spruce-dominated Stands

In the absence of fire in black spruce-feathermoss stands, a thick forest floor layer dominated by bryophytes and sphagnum accumulates. This layer is associated with wet, cool and nutrient-poor soil conditions conducive to the paludification process and pushing the ecosystem towards an unproductive open black spruce forest. The presence of Populus tremuloides in theses stands may halt this process because this species has a high nutrient cycling rate and a litter that represses moss cover. The main hypothesis of this study is that, despite similar abiotic conditions (slope and drainage), the presence of Populus tremuloides in a stand dominated by Picea mariana affects surface soil nutrient availability, total N, pH as well as the decomposition process. The abundance of Populus tremuloides trees was associated with higher exchangeable cations, cationic exchangeable capacity and pH of the forest floor layer on all sites. A decrease in organic matter thickness with increasing aspen presence was also found on all sites, suggesting that this species affects the decomposition process by the quality of its litter as well as by a general improvement of soil physical and chemical properties. The decomposition rate of a standard substrate as well as in vitro potential net nitrogen mineralization were positively related to Populus tremuloides on only one of the three sites, and non-significant on the other sites. Strong immobilization of added nitrogen during incubation was observed on all sites and was not related to aspen, which suggested that in these stands, the soil microbial community is uniformly and strongly nitrogen limited. The zone of influence of Populus tremuloides was evaluated in areas around the soil sampling plot ranging from 3 to 7 m. The results revealed that this zone varies with soil properties. The results suggest that the presence of Populus tremuloides accelerate nutrient cycling, which could affect stand productivity to some extent.     

Post-fire, seasonal and annual dynamics of the ectomycorrhizal community in a Quercus ilex L. forest over a 3-year period

Two study plots, burned and control, were established in autumn 1998 in a Quercus ilex forest located in northern Spain, part of which had been affected by a low intensity fire in 1994. Soil samples for ectomycorrhizae (ECM) were taken over a 3-year period in each study plot in spring, summer, autumn and winter. ECM morphotypes were identified and the relative abundance of each morphotype in each soil sample calculated, along with species richness, Shannon diversity index and percentage of mycorrhization in each soil sample. The relative abundance of certain ECM morphotypes differed between burned and control plots, and the percentage of mycorrhizal tips was significantly lower in the burned than in the control plot. Nevertheless, there were no significant differences in the diversity, species richness or species composition of the ECM community in the burned and control plots. The dominant ECM morphotypes in both stands were Cenococcum geophilum and several thelephoroid fungi. Sphaerosporella brunnea and Pisolithus tinctorius thrived especially in the burned plot, whereas three ectomycorrhizal morphotypes assigned to the genus Hebeloma were especially abundant in the control plot. There was no significant variation in the relative abundance of the ECM morphotypes between seasons, but ECM community species richness was highest in autumn and lowest in summer. The percentage of mycorrhizal tips reached a maximum in winter, with its minimum in autumn. Collection of samples over the 3-year period also enabled us to detect a significant increase in percentage of ECM colonisation in the burned stand over time.