Increased frequency and new types of disturbances caused by global change calls for deepened insights into possible alterations of successional pathways. Despite current interest in disturbance ...interactions there is a striking lack of studies focusing on the implication of decreasing times between disturbances. We surveyed forest-floor vegetation (vascular plants and bryophytes) in a Pinus sylvestris–dominated, even-aged production forest landscape, unique because of the presence of stands under a precisely dated disturbance interval gradient, ranging from 0 to 123 yr between clearcutting and a subsequent megafire. Despite a dominance of early-successional species in all burned stands 5 yr after fire, progression of succession was linked to time since the preceding clearcutting disturbance. This was most clearly seen in increased frequency with time since clearcutting of the dominant, late-successional dwarf shrub Vaccinium myrtillus, with surviving rhizomes as an important mechanism for postfire recovery. Our results demonstrate the role of legacy species as significant drivers of succession. We conclude that the starting point for succession is modulated by disturbance interval, so that shortened intervals risk reducing development towards late-successional stages. We suggest that a decrease in long successional sequences caused by more frequent disturbances may represent a general pattern, relevant also for other forest types and ecosystems.
Carex humilis is a clonal sedge that can form distinct rings of densely aggregated ramets. We hypothesize that rings form because both production of new ramets and ramet dispersal are positively ...correlated to ramet size. This would lead to an overrepresentation of fast-moving and large ramets with high ramet production at the periphery, whereas slow-moving and small ramets with low ramet production would mainly be found in the interior of rings. We use matrix models to analyse how ramet populations both at the periphery and in the interior develop in the absence of ramet dispersal. We found that the stable size class distributions of ramets predicted by the models were not different from the distributions found in the field. Also, the asymptotic ramet population growth rates (λ₁) were the same. Hence, we conclude that rings would form even in the absence of a link between ramet dispersal and ramet production. Further analysis of the matrix models showed that the ramet population increases at the periphery but decreases in the interior of rings because medium and large ramets produce fewer large ramets in the interior than at the periphery. We also found that the temporal variance in λ₁ and transitions rates during the four study years was much higher at the periphery than in the interior. Our results suggest that rings may form because C. humilis ramets use below-ground resources from a much larger area than the one covered by the shoots. As the clone grows larger, the soil volume available to the ramets in the interior decreases because their access to soil outside the ring is cut-off by the ramets at the periphery. Ramet density in the interior is therefore decreasing.
. The clonal sedge Carex humilis forms rings of densely aggregated ramets in a dry grassland community in Central Europe. We describe the small‐scale spatial variation, both in abiotic factors and ...vegetation, in relation to these rings. Compared to the surrounding vegetation the cover of plants, other than C. humilis, was significantly lower both in the central area of rings and within the rings themselves. The vegetation structure was also different. The soil was more fertile in the central area and within the ring than in the surroundings, measured both directly and by the abiotic response values of the vascular plants. We conclude that neither resource depletion nor competition from other plants were likely to be responsible for the low ramet density in the central area of C. humilis rings. Instead, we suggest that the ring form is caused either by the deposition of growth inhibiting substances or by intrinsic morphological rules.
Including both economic costs and biological benefits of sites in systematic reserve selection greatly increases cost-efficiency. Nevertheless, limited funding generally forces conservation planners ...to choose which data to focus the most resources on; therefore, the relative importance of different types of data must be carefully assessed. We investigated the relative importance of including information about costs and benefits for 3 different commonly used conservation goals: 2 in which biological benefits were measured per site (species number and conservation value scores) and 1 in which benefits were measured on the basis of site complementarity (total species number in the reserve network). For each goal, we used site-selection models with data on benefits only, costs only, and benefits and costs together, and we compared the efficiency of each model. Costs were more important to include than benefits for the goals in which benefits were measured per site. By contrast, for the complementarity-based goal, benefits were more important to include. To understand this pattern, we compared the variability in benefits and in costs for each goal. By comparing the best and the worst possible selection of sites with regard to costs alone and benefits alone for each conservation goal, we introduced a simple and consistent variability measure that is applicable to all kinds of reserve-selection situations. In our study, benefit variability depended strongly on how the conservation goal was formulated and was largest for the complementarity-based conservation goal. We argue that from a cost-efficiency point of view, most resources should be spent on collecting the most variable type of data for the conservation goal at hand.
To protect land from commercial exploitation is a common conservation practice. However, this requires large financial resources and it is therefore important to evaluate the cost-effectiveness of ...different strategies used in the selection of these conservation areas. In this study we compare four strategies and relate the differences in cost-effectiveness to differences in the selection process. We measure conservation benefits both as the amount of three tree structures and as the number of species in three species groups. We also estimate both the information cost associated with selecting conservation areas and the opportunity cost. We found the key habitat strategy to be the over-all most cost-effective. In this strategy, the areas have a flexible size and are selected by the authorities in a national field survey. The least cost-effective strategy was one where the selection was based only on forest classes in a satellite map. Intermediate were the retention group strategy, where small areas are left by the forest owner at harvesting, and the nature reserve strategy, where large areas are selected by the authorities. We emphasize that the differences we found are associated with the selection process and that other aspects, such as long-term survival of species, may rank the strategies differently. We conclude that the cost-effectiveness of a selection strategy depends on the size of the planning area for selection of conservation areas, the size of the conservation areas, the objective of the agent making the selection, and the amount and type of information on which the selection is based.
1 In a calcareous dry grassland community in central Europe genets of the clonal sedge Carex humilis form very distinct rings of densely aggregated ramets. As genet growth form is generated by ramet ...population dynamics, ramet demography must be studied in order to understand how rings develop. We analysed how ramet demography in C. humilis depends on ramet position within the ring and how this is linked to ramet size. 2 The per ramet population growth rate was > 1 at the periphery of rings but < 1 in the interior, meaning that the population increases at the periphery but decreases in the interior. The population growth rate differed mainly because ramets were smaller in the interior and because smaller ramets produced fewer vegetative ramets. It is unlikely that the smaller ramet size is caused by negative density dependence, interspecific competition, internal control or resource depletion. 3 The study covered four growing seasons and we found considerable variation in ramet demography between years. The net result for the 4 years was that the total number of C. humilis ramets in the population increased. However, both production of vegetative ramets and ramet size decreased during the study period and if this trend continues population size will instead decrease.
The clonal sedge Carex humilis forms rings of densely aggregated ramets in a dry grassland community in Central Europe. We describe the small-scale spatial variation, both in abiotic factors and ...vegetation, in relation to these rings. Compared to the surrounding vegetation the cover of plants, other than C. humilis, was significantly lower both in the central area of rings and within the rings themselves. The vegetation structure was also different. The soil was more fertile in the central area and within the ring than in the surroundings, measured both directly and by the abiotic response values of the vascular plants. We conclude that neither resource depletion nor competition from other plants were likely to be responsible for the low ramet density in the central area of C. humilis rings. Instead, we suggest that the ring form is caused either by the deposition of growth inhibiting substances or by intrinsic morphological rules. Nomenclature: Tutin et al. 1964–1993.
In clonal organisms the distribution of a genet is potentially unlimited in space and time. Fitness, defined as the rate of change in number of units carrying a certain allele or allele complex, can ...be calculated using life cycle graph analysis. The units used should be self-replicating, limited in space and time, and not unnecessarily small. The distribution of looping times (the time required for a unit to come back to the same stage) should be used rather than the mean looping time when calculating fitness. Whether vegetative and sexual reproduction are mutually exclusive or not depends on the life history of the studied population.
Data on the clonal sedge, Carex bigelowii, from three sites along an altitudinal gradient in Swedish Lapland were analysed at two levels: 1) between tiller systems within sites and 2) between tiller ...populations at different sites. At the tiller system level we studied the components of fitness (measured as the finite rate of increase in the number of tillers), and found that the two main components (mean daughter tiller production and tiller generation time) were positively correlated at two of the sites. They are hence counteracting each other in their effects on fitness. At the same two sites, higher mean daughter tiller production was mainly caused by a decrease in the proportion of tillers without daughter tillers, together with an increase in the proportion of tillers with more than one daughter tiller. At the third site the same phenomena were observed but, in addition, the proportion of tillers with one daughter tiller was slightly reduced as well. Tiller systems at this site also differed from the others by showing a positive correlation between fitness and variation in daughter tiller production. At no site was mean rhizome length of tiller systems correlated with fitness. At the population level, the tiller densities at the lower and intermediate sites appeared to have been stationary (no net trend) during the past 10-20 years. At the upper site, the number of tillers in the sampled quadrats had increased, either due to high mobility of the tiller systems or to an actual increase in overall population density. We also measured the flowering rates in the populations and found no major differences between the sites. No seedling establishment of C. bigelowii has been recorded in this area and the costs of sexual reproduction, in terms of decreased vegetative reproduction, are therefore expected to be low. This expectation was in accordance with an earlier study finding no such costs associated with flowering and seed set.
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