Undisturbed Plots Research Articles

Biotic constraints on the establishment and performance of native, naturalized, and invasive plants in Pacific Northwest (USA) steppe and forest

Factors that cause differential establishment among naturalized, invasive, and native species are inadequately documented, much less often quantified among different communities. We evaluated the effects of seed addition and disturbance (i.e., understory canopy removal) on the establishment and seedling biomass among two naturalized, two invasive, and two native species (1 forb, 1 grass in each group) within steppe and low elevation forest communities in eastern Washington, USA. Establishment within each plant immigrant class was enhanced by seed addition: naturalized species showed the greatest difference in establishment between seed addition and no seed addition plots, native and invasive species establishment also increased following seed addition but not to the same magnitude as naturalized species. Within seed addition plots, understory canopy disturbance resulted in significant increases in plant establishment (regardless of plant immigration class) relative to undisturbed plots and the magnitude of this effect was comparable between steppe and adjacent forest. However, regardless of disturbance treatment fewer invasive plants established in the forest than in the steppe, whereas native and naturalized plant establishment did not differ between the habitats. Individual biomass of naturalized species were consistently greater in disturbed (canopy removed) versus undisturbed control plots and naturalized species were also larger in the steppe than in the forest at the time of harvest. Similar trends in plant size were observed for the native and invasive species, but the differences in biomass for these two immigration classes between disturbance treatments and between habitats were not significant. We found that strong limitations of non-native species is correlated with intact canopy cover within the forest understory, likely driven by the direct or indirect consequences of low light transmittance through the arboreal and understory canopy. Considered collectively, our results demonstrate how seed limitation and intact plant ground cover can limit the abundance and performance of naturalized species in Pacific Northwest steppe and low elevation forest, suggesting that local disturbance in both habitats creates microsites for these species to establish and survive. Future studies evaluating interactions between multiple barriers to establishment using more representatives from each immigration class will further reveal how biotic interactions ultimately influence the demography and distribution of non-native plants within these communities.

Effects of forest management and climatic variables on the mycelium dynamics and sporocarp production of the ectomycorrhizal fungus Boletus edulis

The effect of forest management practices (cutting for timber production and intensive seasonal sporocarp collection) on extraradical soil mycelium and sporocarp production of the king bolete (Boletus edulis Bull.) has been evaluated in a Pinus sylvestris L. forest in Soria (central Spain) from 2011 to 2015. Extraradical soil mycelium of B. edulis was quantified by real-time PCR from soil samples taken in plots submitted to clearcutting and partial cutting in 2012, and in undisturbed areas. In a parallel experiment, the B. edulis mycelium biomass was also measured in fenced plots where all the fruiting bodies of this species were removed weekly along the fruiting season of five years (2011–2015), and compared to plots in which no collection of B. edulis was done.Clearcutting and partial cutting of trees resulted in a sharp decrease of B. edulis mycelium biomass in all the sampled plots. The differences between control and cut plots were significant from the 7th month after cutting until the last measurement in September 2015. The cut plots showed a reduced amount of B. edulis mycelium biomass as compared to undisturbed plots and no recovery was observed three years after cutting. No significant differences in fungal biomass between clearcutting and partial cutting plots were observed.Intensive collection of B. edulis sporocarps along four productive seasons (September to November) did not significantly affect the soil mycelium biomass as compared to non-collected plots. The mean mycelium biomass varied significantly among the different sampling times but no significant interaction between the sporocarp collection and sampling time was detected.The obtained dataset allowed to establish correlations between soil mycelium biomass, sporocarp production, and climatic parameters (monthly mean precipitation and temperature). Monthly mean precipitation measured two, three, four and five months before sampling was negatively correlated with B. edulis mycelium biomass. No correlations were detected between monthly mean temperature and mycelium biomass. Mean precipitation in autumn (September to November) was significant and positively correlated with sporocarp productivity. No significant effects of mean precipitation in previous summer, spring and winter on sporocarp production were detected. No significant effect of temperature in the fruiting of B. edulis was observed.We concluded that mycelium surveys are useful indicators of the fungal response to management practices and may provide complementary information to sporocarps surveys towards an integrated forest management considering sustainability and multiproductive criteria.

Influence of Anthropogenic Disturbances on Stand Structural Complexity in Andean Temperate Forests: Implications for Managing Key Habitat for Biodiversity.

Forest attributes and their abundances define the stand structural complexity available as habitat for faunal biodiversity; however, intensive anthropogenic disturbances have the potential to degrade and simplify forest stands. In this paper we develop an index of stand structural complexity and show how anthropogenic disturbances, namely fire, logging, livestock, and their combined presence, affect stand structural complexity in a southern Global Biodiversity Hotspot. From 2011 to 2013, we measured forest structural attributes as well as the presence of anthropogenic disturbances in 505 plots in the Andean zone of the La Araucanía Region, Chile. In each plot, understory density, coarse woody debris, number of snags, tree diameter at breast height, and litter depth were measured, along with signs of the presence of anthropogenic disturbances. Ninety-five percent of the plots showed signs of anthropogenic disturbance (N = 475), with the combined presence of fire, logging, and livestock being the most common disturbance (N = 222; 44% of plots). The lowest values for the index were measured in plots combining fire, logging, and livestock. Undisturbed plots and plots with the presence of relatively old fires (> 70 years) showed the highest values for the index of stand structural complexity. Our results suggest that secondary forests < 70-year post-fire event, with the presence of habitat legacies (e.g. snags and CWD), can reach a structural complexity as high as undisturbed plots. Temperate forests should be managed to retain structural attributes, including understory density (7.2 ± 2.5 # contacts), volume of CWD (22.4 ± 25.8 m3/ha), snag density (94.4 ± 71.0 stems/ha), stand basal area (61.2 ± 31.4 m2/ha), and litter depth (7.5 ± 2.7 cm). Achieving these values will increase forest structural complexity, likely benefiting a range of faunal species in South American temperate forests.

Potential and Determinants of Carbon Storage of Freshwater Swamp Forests in the Niger Delta

There has been an increase in carbon assessments across global ecosystems, but some ecosystem types remain woefully understudied-freshwater swamp forests are one such ecosystem. Results of the above ground carbon estimates are derived from 16, one-hectare forest plots divided evenly across four forest sites. Results on carbon storage are compared with results on forest use and ownership from interviews with communities living in the area. Since forest use determined the composition, structure and the capacity of the ecosystem to sequester carbon; its above ground carbon decreased from the undisturbed forest plots to the disturbed (modified) sites across the sites. Forest units under communal ownership demonstrated possibilities of actualizing targeted/ restricted use of tree species, as well as targeted carbon storage capacities. Even though joint ownership and management schemes are likely to regulate the use of the ecosystem, and possibly enhance better carbon sequestration, achieving this still seems elusive due to a long existing land tenure system and generational inheritance of (forest) lands across the region. Carbon sequestration across the region will remain under threat unless suitable awareness on forest management is backed up with alternative sources of livelihood, incentives and compensation to the custodians of the forest resources.

Effects of different disturbance regimes on grass and herbaceous plant diversity and biomass in Zimbabwean dambo systems

ABSTRACTThis study examined the species richness, diversity, biomass of grasses and herbaceous plants and seed germination in plots with contrasting disturbance regimes established in a dambo garden, in Chiota, Zimbabwe. The disturbance regimes were burning, clipping, clearing and conventional tillage and were applied annually to each subplot from 2010 to 2012. It was hypothesised that burning increases biomass, species richness and diversity of plants while reducing seed bank diversity. Clearing, clipping and conventionally tilling negatively affect biomass, species richness and diversity. The Shannon–Wiener Index was used to estimate species diversity and the average values obtained ranged 0.53, 0.85, 0.91, 1.3 and 1.70, for the undisturbed, burnt, conventionally tilled, clipped and cleared plots, respectively. The biomass in the experiment ranged from 0.92t ha–1 for the ploughed plot to 20.92t ha–1 for the undisturbed plot. The species richness for the plants decreased in the following order; clearing>conventional tillage>burning>clipping>undisturbed. These results show that disturbance regimes increased species richness but however decreased plant biomass. It is apparent that the management practice that ensures maximum biomass of grasses and herbs in dambos is maintaining them in their natural state. However, clearing seemed to improve species diversity compared to maintaining the dambo in its natural state.EDITED BY Alexander van Oudenhoven and Patricia Balvanera

Native species richness buffers invader impact in undisturbed but not disturbed grassland assemblages

Many systems are prone to both exotic plant invasion and frequent natural disturbances. Native species richness can buffer the effects of invasion or disturbance when imposed in isolation, but it is largely unknown whether richness provides substantial resistance against invader impact in the face of disturbance. We experimentally examined how disturbance (drought/burning) influenced the impact of three exotic invaders (Centaurea stoebe, Linaria dalmatica, or Potentilla recta) on native abundance across a gradient of species richness, using previously constructed grassland assemblages. We found that invaders had higher cover in experimentally disturbed plots than in undisturbed plots across all levels of native species richness. Although exotic species varied in cover, all three invaders had significant impacts on native cover in disturbed plots. Regardless of disturbance, however, invader cover diminished with increasing richness. Invader impacts on native cover also diminished at higher richness levels, but only in undisturbed plots. In disturbed plots, invaders strongly impacted native cover across all richness levels, as disturbance favoured invaders over native species. By examining these ecological processes concurrently, we found that disturbance exacerbated invader impacts on native abundance. Although diversity provided a buffering effect against invader impact without disturbance, the combination of invasion and disturbance markedly depressed native abundance, even in high richness assemblages.

Characterization of ectomycorrhizal communities of Asteropeia mcphersonii seedlings spontaneously growing in natural forest and in open disturbed areas

Forest ecosystem disturbances generate changes including soil changes, generally with loss of topsoil and loss of much of the diversity of microorganisms, which are usually replaced by others that are more adapted to the new conditions. We describe the effect of rainforest clear-cutting in Madagascar, with stripping of surface soil horizons among ectomycorrhizal fungal communities associated with natural Asteropeia mcphersonii seedlings. An experimental device was placed on four sites, each including an undisturbed plot with litter and a plot in clear-cut areas on a soil composed of a homogeneous mineral substrate. On each of these eight plots the ectomycorrhizal infection rate was determined and root tips were collected to sequence the internal transcribed spacer. 219 sequences grouped into 59 operational taxonomic units (OTUs) were obtained. The main taxonomic groups were Russulaceae, Boletales and Thelephoraceae. Marked spatial aggregation was observed for OTUs. The disturbance significantly affected the ectomycorrhizal infection rate of A. mcphersonii seedlings and the OTU composition of mycorrhizal communities. However, some OTUs were found in both types of environments. We discuss the effect of the disturbance on mycorrhizal communities associated with natural ectomycorrhizal A. mcphersonii seedlings, particularly in view of its application to ecological restoration of disturbed forest environments.

Intraspecific interactions shift from competitive to facilitative across a low to high disturbance gradient in a salt marsh

Disturbances are ubiquitous among salt marshes, and disturbances such as litter removal may form stressful environmental conditions. The stress-gradient hypothesis (SGH) predicts that the relative importance of facilitation and competition between species will vary inversely to each other across abiotic stress gradients. However, how intraspecific interactions vary across disturbance levels, and whether they follow the SGH has not been investigated. To test the SGH with intraspecific interactions within Suaeda salsa individuals, we assessed individual survival in established fully mapped salt marsh plots with two treatments, disturbed, litter removal and control, undisturbed plots. Recently developed spatial statistics were applied to distinguish between random processes, intraspecific facilitation, scramble competition, and contest competition underlying the spatial patterns at different spatial scales, growth stages, and disturbance levels. We found evidence that intraspecific interactions among S. salsa individuals across disturbance levels tended to support the SGH, but this support depended on time and space. Intraspecific interactions were more likely to show positive density dependence in disturbed plots, particularly at the seedling period and when individuals were separated by < 9 cm. However, positive density dependence was not detected in undisturbed plots. The protective effects of litter on seedlings, which were lost in undisturbed sites, may have been at least partly simulated at high seedling densities. Mortality in disturbed sites was not random, and facilitation had a more important influence than competition on population dynamics in high disturbance sites. However, the influence of competition on population dynamics, specifically scramble competition was also clearly important.

Artificial canopy gaps in the restoration of boreal conservation areas: long-term effects on tree seedling establishment in pine-dominated forests

Creation of canopy gaps can be used as a restoration measure to aid in the diversification of structural variability and tree species composition in forests. However, it is not generally known how the specific properties of gaps influence restoration success. In this study, we examined tree seedling regeneration in 94 small canopy gaps that were established for restoration purposes in two protected Pinus sylvestris (Scots pine)-dominated forests in eastern Finland 10 years earlier. In particular, we assessed the effect of gap size, within-gap position, and soil preparation (exposure of the mineral soil) within the gaps (soil disturbance) on seedling establishment. We found that tree species composition in the sample plots consisted mainly of P. sylvestris (73 %) and Betula spp. (16 %) seedlings. Most Pinus and Betula seedlings were found in the disturbed plots, and only 6 % of the seedlings were found in the undisturbed plots (no soil preparation applied). The mean number of pooled Pinus and Betula seedlings per disturbed plot (40 × 60 cm) was 0.5 and 0.1, respectively. Mean height of the Pinus and Betula seedlings was 9.2 cm and 51.5 cm, respectively, which suggests that seedling development in the disturbed plots was very slow and is probably hindered by an insufficient amount of solar radiation reaching the forest floor, as well as by root competition with the trees that surround the gap. Both factors are affected by gap size, which was probably not large enough (mean diameter ≤23 m) in our study forests to reach a threshold value that meets the requirements of Pinus and Betula seedlings. We conclude that the creation of small canopy gaps does not appear to be an effective method to restore the age class structure and tree species composition in boreal pine-dominated forests. Further studies that manipulate the gap size more widely than this current study are needed.

Windthrows increase soil carbon stocks in a central Amazon forest

Abstract. Windthrows change forest structure and species composition in central Amazon forests. However, the effects of widespread tree mortality associated with wind disturbances on soil properties have not yet been described in this vast region. We investigated short-term effects (7 years after disturbance) of widespread tree mortality caused by a squall line event from mid-January of 2005 on soil carbon stocks and concentrations in a central Amazon terra firme forest. The soil carbon stock (averaged over a 0–30 cm depth profile) in disturbed plots (61.4 ± 8.2 Mg ha−1, mean ±95 % confidence interval) was marginally higher (p = 0.09) than that from undisturbed plots (47.7 ± 13.6 Mg ha−1). The soil organic carbon concentration in disturbed plots (2.0 ± 0.17 %) was significantly higher (p &lt; 0.001) than that from undisturbed plots (1.36 ± 0.24 %). Moreover, soil carbon stocks were positively correlated with soil clay content (r2 = 0.332, r = 0.575 and p = 0.019) and with tree mortality intensity (r2 = 0.257, r = 0.506 and p = 0.045). Our results indicate that large inputs of plant litter associated with large windthrow events cause a short-term increase in soil carbon content, and the degree of increase is related to soil clay content and tree mortality intensity. The higher carbon content and potentially higher nutrient availability in soils from areas recovering from windthrows may favor forest regrowth and increase vegetation resilience.

不同经营模式对川西亚高山天然次生林林地水文效应的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同经营模式对川西亚高山天然次生林林地水文效应的影响 DOI: 10.5846/stxb201503050431 作者: 作者单位: 四川省林业科学研究院,四川省林业科学研究院,四川农业大学旅游学院,四川农业大学旅游学院,四川省林业科学研究院,四川省林业科学研究院,中国林业科学研究院森林生态环境与保护研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家“十二五”科技支撑计划项目（2012BAD22B0104）；四川省基本科研业务费项目（JB2015-04）；林业公益性行业专项（201104109-01） Effects of different forest management regimes on woodland hydrological effects of natural secondary forests in a sub-alpine region of western Sichuan, China Author: Affiliation: Sichuan Academy of Forestry,Sichuan Academy of Forestry,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:天然次生林是川西亚高山林区经历大规模砍伐后形成的主要森林类型之一，是我国西南林区水源涵养林的重要组成部分。以不同经营模式（抚育经营、清林+补植经营以及封育经营）的川西亚高山次生桦木林和桦木、岷江冷杉混交林为研究对象，通过样方取样法获取和分析了林地苔藓、枯落物和土壤的水文指标。结果表明，与封山育林经营相比，抚育经营下的两种林型的苔藓最大持水率均显著升高（F=8.147，P=0.010；F=15.525，P=0.006）、桦木林的蓄积量显著降低（F=4.979，P=0.022），而苔藓最大持水量变化不显著；混交林则均无显著变化。在清林+补植经营下，混交林苔藓水文效应变化不显著（F=2.280，P=0.183），而桦木林虽然苔藓最大持水率无显著变化（F=4.072，P=0.098），但蓄积量的显著降低（F=3.536，P=0.044）导致了其最大持水量的降低（F=3.782，P=0.042）。两种经营方式基本上促进了天然林的枯落物最大持水率、降低了林下枯落物蓄积量；其中抚育经营效果更显著，但两种经营方式下枯落物最大持水量变化不显著。两种经营方式下，桦木林和混交林的林下土壤容重均降低（F=10.715，P<0.01；F=5.148，P<0.05），同时桦木林土壤最大持水量增加（F=4.499，P<0.05），其中抚育经营的影响程度都更显著。从4年来的短期效应来看，两种经营方式均对天然林的林地持水能力具有促进作用，抚育经营较清林+补植经营更显著，但这仅是短期的结果，两种经营方式对于退化天然林水文以及其他生态功能恢复的长期影响还有待于进一步的观测研究。 Abstract:In the wake of the large-scale logging of its sub-alpine region, natural secondary forest is one of dominant forest types of western Sichuan, and plays an important role in water conservation in the forests of southwestern China. The moss, litter, and soil produced by different management regimes (e.g., clearing and pruning, clearing and replanting, and no disturbance) have been measured and sampled, and their hydrological effects on Betula spp. forests and mixed forests with Abies faxoniana and Betula spp. have been analyzed. The results of this study revealed that the maximal water holding rate (MWHR) of moss from clearing and pruning was significantly higher than that from no disturbance, but the cumulated mass (CM) of moss from clearing and pruning was significantly lower than that from no disturbance, and the maximal water holding capacity (MWHC) of moss was no different between forest types or between clearing and pruning mode and no disturbance mode. In Betula spp. forests managed by clearing and replanting, the MWHR and CM of moss was lower, but not significantly so, while the MWHC of moss was significantly lower than that in the undisturbed plots of the same forest type. In addition, there was no significant difference between the hydrological effects of both mixed forests with Abies faxoniana and Betula spp. Under the two regimes including active management, the MWHR of the litter and the soil water holding capacity both increased, the CM of the litter and soil bulk density decreased, but MWHC of litter was not significantly different between artificial mode and undisturbed mode. The performance of the clearing and pruning regime was more significantly better than that of clearing and replantation regime. From short-term effects for 4 years, the woodland's capacity to facilitate water conservation was increased by both the clearing and pruning regime and the clearing and replantation regime, in both Betula spp. forests and fixed forests with Abies faxoniana and Betula spp. The performance of the clearing and pruning regime was more significant than those of the other management regimes. Over the long term, the hydrological and ecological effects of different management regimes on natural secondary forests requires further investigation. 参考文献 相似文献 引证文献

Nutrient distribution and cycling in a subtropical rainforest in New South Wales

Subtropical rainforests in New South Wales (NSW) are distributed on the more fertile forest soils and are nutritionally distinct from the Eucalyptus forests in the same areas. The distribution, cycling of organic matter and nutrients and nutrient use efficiency in an Australian subtropical rainforest were studied and aspects were compared with reported Eucalyptus studies. The available nutrients were greatly in excess of the stand uptake or requirement. A single undisturbed plot within a research trial in mature forest was selected for the study. At the beginning of the study, the aboveground forest biomass was ~334 t ha–1 of organic matter and, 22 years later, there was 357 t ha–1, giving a net accumulation rate of 1.03 t ha–1 year–1, and net primary productivity of 13.0–14.6 t ha–1 year–1. Litterfall and forest-floor analyses indicated a very rapid turnover of organic matter, with an estimated half-life of ~0.5 years. The quantity of nutrients in the stand was high relative to other forest types in the area, with 1109.2 kg N ha–1, 62 kg P ha–1, 1999 kg Ca ha–1, 591 kg Mg ha–1 and 901 kg K ha–1. Nutrient requirement estimated as nutrient content of the current tissue was estimated to be 107, 5.3, 99, 26 and 61 kg ha–1 year–1 for N, P, Ca, Mg and K, respectively, and uptake defined as removal from the soil was estimated to be 112, 4.7, 128, 37 and 49 kg ha–1 year–1 for the same nutrients, the difference between these being net nutrient redistribution. Nutrient use efficiency (NUE), defined as net primary productivity (NPP) per requirement (t kg–1), was calculated to be 0.12, 2.43, 0.13, 0.50 and 0.21 for N, P, Ca, Mg and K, respectively; these values were low, for example, compared with mature E. pilularis, for which NPP was 0.20, 6.5, 0.43, 1.04 and 0.52 t kg–1 for N, P, Ca, Mg and K, respectively. Using NUE defined as NPP per uptake provided comparable estimates. The rainforest represents a forest growing with basically no nutrient limitations, and, as such, is a benchmark for forest nutrient distribution, cycling and NUE.

Canopy structure of woody landscape modulators determines herbaceous species richness along a rainfall gradient

Landscape modulators are ecosystem engineers that create distinct patches that differ from their surroundings in abiotic conditions and species composition. Woody plants are principal landscape modulators in many terrestrial ecosystems. The effects of woody landscape modulators on herbaceous species richness have been studied at the site level in Israel. Here we examine the effect of woody landscape modulators on the general pattern of herbaceous species richness over a large spatial scale along a rainfall gradient, and develop a novel quantitative model to explain that pattern. A uniform experimental design was implemented at five sites along a rainfall gradient in Israel. Herbaceous species richness was determined in woody (modulated) patches and in their surrounding (unmodulated) areas, both in undisturbed (control) plots and in plots in which the canopies of the woody plants had been removed. Herbaceous species richness increased asymptotically with increasing rainfall in the unmodulated areas, but not in the modulated patches of the no-removal plots. Removal of woody plant canopies resulted in a similar pattern of herbaceous species richness to that of the unmodulated areas. Woody landscape modulators modify the pattern of herbaceous species richness along rainfall gradients by creating a biotically induced gradient of abiotic conditions, mainly via their canopy structure. The proportion of species in the site-level species pool that are filtered into the modulated patches declines in strong negative correlation with increasing LAI of the landscape modulator. The combination of climatic and biotically induced gradients determines the overall pattern of herbaceous species richness in two-phase landscape mosaics.

Carbon Dynamics in Central US Rockies Lodgepole Pine Type after Mountain Pine Beetle Outbreaks

Mountain pine beetle-caused tree mortality has substantially changed live tree biomass in lodgepole pine ecosystems in western North America since 2000. We studied how beetle-caused mortality altered ecosystem carbon (C) stocks and productivity using a central US Rockies age sequence of ecosystem recovery after infestation, augmented with growth-and-yield model simulations. Field measurements showed that total C stocks were reduced by beetle outbreaks, although differences compared with undisturbed stands were not easily distinguished. Simulations with outbreaks showed long-term C losses of 1–30%. Field data indicated that aboveground C productivity was reduced among plots infested within 25 years of measurements, but productivity levels of plots with older infestations were indistinguishable from those of undisturbed plots. Simulations indicated that outbreaks reduced C productivity for 20 – 60 years, but rates recovered such that 100-year postoutbreak averages were similar among infested and undisturbed stands. Simulations also showed that C dynamics are affected by outbreak severity and that C productivity might be stimulated by outbreaks relative to that of undisturbed stands. Outbreaks redistributed C from live (sinks) to dead pools (sources), but slow decomposition of snags combined with recovered tree growth resulted in resilience of aboveground C stocks.

Functional response of lignicolous fungal guilds to bark beetle deforestation

Conifer-dominated forests in the northern hemisphere are prone to large-scale natural disturbances, yet our understanding of their effects beyond changes in species diversity is limited. Bark beetle disturbances provide dead wood for lignicolous fungal guilds and increase insolation but also desiccation. We investigated whether species richness of these guilds increases and functional diversity decreases after bark beetle disturbance, which would promote through habitat filtering the coexistence of species adapted to harsh conditions, i.e. light stress for lichens and substrate desiccation for wood-inhabiting fungi.We sampled epixylic and epiphytic lichens (primary producers) and wood-inhabiting fungi (mainly wood decomposers, some form ectomycorrhizas) in the Bohemian Forest (Long Term Ecological Research – LTER – Site Bavarian Forest National Park), an area in Central Europe most heavily affected by the bark beetle Ips typographus, on undisturbed plots and disturbed plots with spruce (Picea abies) dieback 8 years ago. We analysed species diversity, functional diversity (optimized by phylogeny), and functional compositions.Species richness of lichens but not that of wood-inhabiting fungi was higher on disturbed plots than on undisturbed plots. Community compositions of both guilds differed considerably on disturbed and undisturbed plots. On both types of plots, lichen communities were clustered according to functional diversity, which indicated habitat filtering, and fungal communities were overdispersed, which indicated competition. Disturbance increased the strength of these two patterns only slightly and was significant only for fungi. Single-trait analysis revealed changes in the functional composition; on disturbed plots, lichenous species with larger and more complex growth forms and fungi with large, perennial fruit bodies were favoured. Although the forest canopy changed tremendously because of the bark beetle disturbance, the most important driver of lichen and fungal diversity and mean trait assemblages seemed to be the enrichment of dead wood. The changes in insolation and moisture did not act as habitat filters for either guild. This indicated that the assembly patterns of lichen and fungal communities in coniferous forests are not affected by stand-replacing disturbances in contrast to the predictions for other disturbance regimes.

Early vegetation control for the regeneration of a single-cohort, intimate mixture of white spruce and aspen on upland boreal sites – 10thyear update

In Canada's boreal forest region, mixedwood stands dominated by trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca [Moench] Voss) are prominent and provide important timber and non-timber values. A paucity of silvicultural tools for regenerating mixedwood conditions prompted the establishment of an experiment in 2002, replicated in west-central Alberta and northeastern Ontario, to test a strategy for regenerating a single-cohort, intimate mixture of aspen and white spruce. After ten growing seasons, spruce planted at 5-m spacing, each free of woody and early (first two years) herbaceous competition within a 2-m radius, had equivalent or better survival, height growth and health status than spruce growing competition-free for the duration of the experiment (α = 0.05). Select aspen situated in the vicinity of these spruce were at least as large as aspen crop trees situated in undisturbed plots. The year-10 results of this long-term experiment suggest the hypothesized mixedwood regeneration strategy may offer a practical means of establishing mixedwoods capable of producing an early fibre rotation of aspen (~ age 30) and long term (> 60- years) sawlog crop of spruce.

Small-scale spatial heterogeneity of soil properties in undisturbed and reclaimed sagebrush steppe

The sagebrush (Artemisia tridentata) steppe is inherently heterogeneous, both above- and belowground disturbances that manipulate vegetation and soil may result in homogenization of soil properties. Our objective was to examine the spatial distributions of soil properties in a sagebrush steppe of south-central Wyoming following disturbance and reclamation. We predicted that soil properties in undisturbed sagebrush steppe would display patchiness, while reclaimed soils would be more uniform. At the experimental scale (<10m2), we examined the spatial correlation structure and patterns of soil properties in a recently disturbed and reclaimed pipeline scar and adjacent undisturbed sagebrush steppe in 2009. In each treatment, we sampled soil (0–0.05m depth, calcareous fine sand Regosol) using a spatially explicit design, and used geostatistics to quantify, interpolate, and visualize spatial patterns of soil chemical and biological properties. Soil nitrogen and organic carbon in the undisturbed plot showed spatial associations with the vegetation, which were not apparent in the reclaimed plot. Our predictions about homogenization were true for soil properties that are known to have strong spatial associations with shrubs. Soil organic carbon concentration, total nitrogen concentration, and microbial abundance experienced homogenization, while soil salinity and alkalinity became patchier after disturbance. In addition to changes in spatial patterns, most soil properties were elevated in the reclaimed soil, compared with the undisturbed soil. This case study illustrates that the degree of soil heterogeneity in this patchy system may change with disturbance. Belowground spatial patterns should be considered when restoring characteristically heterogeneous shrub lands.

Fire effects on invasive and native warm‐season grass species in a North American grassland at a time of extreme drought

AbstractQuestionCan the timing of cutting or burning be used to selectively damage an invasive C4 grass species while limiting collateral damage to dominant native C4 grass species in a grassland community?LocationA medium to short grass prairie in central Texas, US.MethodsWe conducted six cut and burn trials between June 2011 and January 2012 during an exceptional drought year. Target species were the native, perennial, C4 grass Schizachyrium scoparium (little bluestem) and the introduced, perennial, C4 grass Bothriochloa ischaemum (yellow bluestem). Burn trials were conducted inside a steel barrel using standardized fuel loads. To assess recovery, we counted the first cohort of new tillers that emerged after treatment and tillers that grew in the subsequent spring. We also recorded phenological status, meteorological variables and burn temperatures to determine if tiller recovery was predictable.ResultsBothriochloa ischaemum responded more negatively to burning than to cutting, but these treatments were no different for S. scoparium. Both species produced the smallest number of tillers after the summer burns, and the burn date × species interaction was insignificant. On average, peak fire temperature inside tussocks was 100 °C higher in B. ischaemum than in S. scoparium. Judging from the reduction in tiller densities in undisturbed plots from spring 2011 to spring 2012, B. ischaemum was also more sensitive to drought. Multivariate models were significant and related burn recovery to peak fire temperature, among other factors, and recovery from cutting to ambient temperature on the day of cutting. In B. ischaemum, plants with higher investment in early reproductive growth suffered more burn damage.ConclusionsWe identified no optimal burn time that maximized discrimination between the two species. Nonetheless, the invasive species was more sensitive to both drought and fire, possibly due to higher heat exposure of growing points. Thus, burning during the summer of a drought year may constitute the sought‐after treatment that selectively favours native species. Ultimately, successful management will involve fuel and temperature management combined with assessment of the relative phenologies of the target species prior to burning. This study suggests that a hot fire at a time when the invasive species has a larger investment in early reproductive growth will provide the best control.

Changes in soil biogeochemistry following disturbance by girdling and mountain pine beetles in subalpine forests.

A recent unprecedented epidemic of beetle-induced tree mortality has occurred in the lodgepole pine forests of Western North America. Here, we present the results of studies in two subalpine forests in the Rocky Mountains, one that experienced natural pine beetle disturbance and one that experienced simulated disturbance imposed through bole girdling. We assessed changes to soil microclimate and biogeochemical pools in plots representing different post-disturbance chronosequences. High plot tree mortality, whether due to girdling or beetle infestation, caused similar alterations in soil nutrient pools. During the first 4 years after disturbance, sharp declines were observed in the soil dissolved organic carbon (DOC) concentration (45-51 %), microbial biomass carbon concentration (33-39 %), dissolved organic nitrogen (DON) concentration (31-42%), and inorganic phosphorus (PO4(3-)) concentration (53-55%). Five to six years after disturbance, concentrations of DOC, DON, and PO4(3-) recovered to 71-140 % of those measured in undisturbed plots. Recovery was coincident with observed increases in litter depth and the sublitter, soil O-horizon. During the 4 years following disturbance, soil ammonium, but not nitrate, increased to 2-3 times the levels measured in undisturbed plots. Microbial biomass N increased in plots where increased ammonium was available. Our results show that previously observed declines in soil respiration following beetle-induced disturbance are accompanied by losses in key soil nutrients. Recovery of the soil nutrient pool occurs only after several years following disturbance, and is correlated with progressive mineralization of dead tree litter.

Effects of Human Disturbance on Mountain Vegetation Communities

The changes in species diversity follow-ing disturbance can give us insights into the pro-cesses governing the assembly and coexistence of species. In this study, we investigate different grassland community and calculate measures of taxonomic diversity, phylogenetic diversity, trait diversity within communities and among com-munities. The results showed disturbed plots have lower values in terms of their taxonomic, phylogenetic, and functional trait diversity. This suggests that disturbance acts as a filter by cre-ating a harsh environment that selects for spe-cies. NMDS ordination also supported the pat-tern that the two habitat types differ in their species composition. In addition, variation in ordination scores was larger in disturbed plots than undisturbed plots. This was mainly due to different type and extent of disturbance. Further-more, disturbance weakened the strength of competition in communities by reducing the number of species and thus freeing resources, which provides the opportunity for immigration of alien species. It was also not difficult to get recruitment for disturbed communities from neighboring communities. Thus this disturbance of patchiness did not produce significant harm for mountain communities.