Wildfire is a major disturbance factor in boreal forests where it is important in rejuvenating soil properties and encouraging tree regeneration and growth. However, the mechanisms behind these effects are poorly understood and little is known as to the ecological effects of charcoal produced by wildfire in these ecosystems. In this study we firstly quantified the mass of charcoal in a chronosequence of twelve forest sites in northern Sweden and found charcoal mass in soil to vary from 984 to 2074 kg ha -1 ; these levels appear to be sufficient for charcoal to have important ecological effect through its sorptive abilities. We then investigated the ability of charcoal from 32 forest stands (representing a range of ages from 1 to 350 yr since last fire) to adsorb phenolic compounds produced by the late successional dwarf shrub Empetrum hermaphroditum ; phenolic compounds from this species have previously been shown to have important phytotoxic effects in boreal forests. Charcoal in soil from forests younger than 100 yr was very effective at reducing these effects while older charcoal was not, suggesting that the sorptive ability is likely to be most important in earlier-successional forests. Experimental reheating of deactivated older charcoal from soil showed that temperatures above 450°C could reactivate charcoal. A microcosm experiment also revealed that soil microbes could effectively reactivate young charcoal that had been saturated with phenolics. Finally we investigated the effects of artificially made charcoal on soil microbial properties at six sites. The microbial biomass was consistently enhanced in humus when it was placed adjacent to charcoal particles. Decomposition of plant litter was sometimes also affected by being in the proximity of charcoal but the dircction of these effects was unpredictable. We conclude that charcoal might catalyse important ecological soil processes in early-successional boreal forests, effects that diminish as succession proceeds, and ultimately may have important long-term consequences for stand productivity and ecosystem function, especially in forests under strict fire control.
Questions It remains unresolved why, despite the obvious functional importance of leaves and roots, co‐existing plant species can display highly contrasting biomass distributions of these organs. Building on the ‘functional equilibrium’ hypothesis, we hypothesize that co‐existing species can each achieve balanced resource acquisition above vs below ground by trading off the biomass vs morphology of structures responsible for resource acquisition, i.e. leaves and fine roots. Methods We tested this hypothesis in a natural field setting by measuring plant above‐ and below‐ground biomass and morphological traits associated with resource uptake – specific leaf area ( SLA ) and specific root length ( SRL ) – of 18 dominant angiosperm species from a sub‐alpine plant community. Location New Zealand South Island. Results We found a significant negative relationship between the species leaf mass to fine root mass ratio and the SLA to SRL ratio when we considered eudicot species only. The SLA to SRL ratio and plant size explained 31% and 34% of the total variation in the species leaf to fine root mass ratio respectively, and 45% when used in combination ( P < 0.05 in all cases). Within a given plant size, 90% of the variation among species in total leaf area was due to differences in SLA , whereas variation in the fine root mass fraction was responsible for 71% of the variation among species in fine root length. Conclusions In support of our hypothesis, part of the difference between co‐occurring species in leaf and fine root biomass distribution could be explained by the variable morphologies of these organs as well as variation in plant size, independent of the plant economic strategy. We expect that this outcome may result from environmental and evolutionary constraints on plant species‐average traits, as well as plastic responses to local environmental conditions. These findings help explain why a diversity of strategies for achieving balanced resource acquisition can co‐exist within a single plant community.
No abstract is provided for this article.
The topic of aboveground–belowground linkages has seen much recent activity, resulting in several conceptual advances regarding plant–soil feedbacks, multitrophic interactions, and how organisms drive ecosystem processes. Although restoration ecology has been rapidly evolving as a scientific discipline, the principles that have developed regarding aboveground–belowground linkages have yet to be thoroughly integrated into it. In this review, we conceptually integrate the role of aboveground–belowground linkages with the principles of restoration ecology through a framework that transcends multiple levels of ecological organization, and illustrate its application through three examples: restoration of abandoned land, reversal of biological invasions, and restoration of natural disturbances. We conclude that this integration can greatly assist restoration ecology, through aiding identification of effective invention practices and prediction of ecosystem recovery.
Wardle, DA Brown, VK Behan-Pelletier, V John, MS Wojtowicz, T Bardgett, RD Brown, GG Ineson, P Lavelle, P van der Putten, WH Anderson, JM Brussaard, L Hunt, HW Paul, EA Wall, DH Workshop of the SCOPE-Committee-on-Soil-and-Sediment-Biodiversity-and-Ecosystem-Function ing Oct, 2002 Estes Pk, CO
Naeem and Li 1 present the results of a microcosm study in which species diversity of organisms within trophic groups was varied. They conclude that the existence of multiple species within these groups enhanced the “reliability” of these systems, that is, the increased likelihood of a consistent level of performance over a given unit of time. But there are problems with their study. For the least diverse communities, one predator species was randomly selected from a selection of two, one autotroph from a selection of three, one consumer of bacteria from a selection of five, and one omnivore from a selection of six. Meanwhile, with the most diverse communities, both predator species and all three autotroph species were used, three consumer bacteria were chosen from the five and three omnivores from the six.
Summary 1. Despite recent interest in linkages between above‐ and below‐ground communities and their consequences for ecosystem processes, much remains unknown about their responses to long‐term ecosystem change. We synthesize multiple lines of evidence from a long‐term ‘natural experiment’ to illustrate how ecosystem retrogression (the decline in ecosystem process rates due to long‐term absence of major disturbance) drives vegetation change, and thus above‐ground and below‐ground carbon (C) sequestration, and communities of consumer biota. 2. Our study system involves 30 islands in Swedish boreal forest that form a 5000‐year, fire‐driven retrogressive chronosequence. Here, retrogression leads to lower plant productivity and slower decomposition and a community shift from plants with traits associated with resource acquisition to those linked with resource conservation. 3. We present consistent evidence that above‐ground ecosystem C sequestration declines, while below‐ground and total C storage increases linearly for at least 5000 years following fire absence. This increase is driven primarily by changes in vegetation characteristics, impairment of decomposer organisms and absence of humus combustion. 4. Data from contrasting trophic groups show that during retrogression, biomass or abundance of plants and decomposer biota decreases, while that of above‐ground invertebrates and birds increases, due to different organisms accessing resources via distinct energy channels. Meanwhile, diversity measures of vascular plants and above‐ground (but not below‐ground) consumers respond positively to retrogression. 5. We show that taxonomic richness of plants and above‐ground consumers are positively correlated with total ecosystem C storage, suggesting that conserving old‐growth forests simultaneously maximizes biodiversity and C sequestration. However, we find little observational or experimental evidence that plant diversity is a major driver of ecosystem C storage on the islands relative to other biotic and abiotic factors. 6. Synthesis. Our study reveals that across contrasting islands differing in exposure to a key extrinsic driver (historical disturbance regime and resulting retrogression), there are coordinated responses of soil fertility, vegetation, consumer communities and ecosystem C sequestration, which all feed back to one another. It also highlights the value of well‐replicated natural experiments for tackling questions about above‐ground–below‐ground linkages over temporal and spatial scales that are otherwise unachievable.
Phosphorus (P) is an important macronutrient in arctic and subarctic tundra and its bioavailability is regulated by the mineralization of organic P. Temperature is likely to be an important control on P bioavailability, although effects may differ across contrasting plant communities with different soil properties. We used an elevational gradient in northern Sweden that included both heath and meadow vegetation types at all elevations to study the effects of temperature, soil P sorption capacity and oxalate-extractable aluminium (Alox) and iron (Feox) on the concentration of different soil P fractions. We hypothesized that the concentration of labile P fractions would decrease with increasing elevation (and thus declining temperature), but would be lower in meadow than in heath, given that N to P ratios in meadow foliage are higher. As expected, labile P in the form of Resin-P declined sharply with elevation for both vegetation types. Meadow soils did not have lower concentrations of Resin-P than heath soils, but they did have 2–fold and 1.5–fold higher concentrations of NaOH-extractable organic P and Residual P, respectively. Further, meadow soils had 3-fold higher concentrations of Alox + Feox and a 20% higher P sorption index than did heath soils. Additionally, Resin-P expressed as a proportion of total soil P for the meadow was on average half that in the heath. Declining Resin-P concentrations with elevation were best explained by an associated 2.5–3.0°C decline in temperature. In contrast, the lower P availability in meadow relative to heath soils may be associated with impaired organic P mineralization, as indicated by a higher accumulation of organic P and P sorption capacity. Our results indicate that predicted temperature increases in the arctic over the next century may influence P availability and biogeochemistry, with consequences for key ecosystem processes limited by P, such as primary productivity.
Several recent studies have claimed to present experimental evidence from synthesised plant communities in which diversity was varied as a treatment that diversity reduces community invasibility by other plant species. This type of result contrasts from that of many observational studies which find diversity and invasibility to be positively correlated in nature, but some recent literature has claimed that these observational studies are confounded by extrinsic covarying factors while experimental studies are not. In this article I evaluate each of eight experiments from six recent publications in which the effect of varying plant diversity on the success of invasive species was investigated. In each case that invasibility was identified by the authors as being adversely affected by plant species richness, the result can be explained by factors that covaried with diversity in the experiment, most notably as a consequence of “sampling effect” (in which the most competitive species or species combination in the total species pool has a greater probability of occurring as species richness is increased), or through the incorrect use of statistical techniques. It is proposed that the apparent discrepancy between the results of many observational and experimental studies at least in grasslands is because: (1) in observational studies competitive dominant species are often associated with the most productive plots, and these dominants both reduce diversity through competitive exclusion of subordinates and competitively suppress invasive species; and (2) in recent experimental studies “sampling effect” results in the most competitive species (and therefore those most likely to suppress the invader) occurring with greater frequency as diversity is increased. Both observational and experimental studies therefore point to the role of competitive dominants in reducing invasibility, and in both situations species richness of the plant community need not be invoked as an explanation for the results.
This study investigates how burrow-nesting, colonial seabirds structure the spatial patterns of soil and plant properties (including soil and leaf N) and t
Summary The study of interactions and feedbacks between plants and soils is a rapidly expanding research area, and a primary tool used in this field is to perform glasshouse experiments where soil biota are manipulated. Recently, there has been vigorous debate regarding the correctness of methods for carrying out these types of experiment, and specifically whether it is legitimate to mix soils from different sites or plots (mixed soil sampling, MSS ) or not (independent soil sampling, ISS ) to create either soil inoculum treatments or subjects. We performed the first empirical comparison of MSS vs ISS approaches by comparing growth of two boreal tree species ( Picea abies and Pinus sylvestris ) in soils originating from 10 sites near the boreal forest limit in northern Sweden, and 10 sites in the subarctic region where boreal forests may potentially expand as a result of climate change. We found no consistent differences in the conclusions that we reached whether we used MSS or ISS approaches. We propose that researchers should not choose a soil handling method based on arguments that one method is inherently more correct than the other, but rather that method choice should be based on correct alignment with specific research questions and goals.
