E. Luis-Calabuig

Seed banks of Erica australis and Calluna vulgaris in a heathland subjected to experimental fire

Soil samples were collected before and after an experimental fire on a heathland in the province of Le6n (Spain). The seed banks were assessed by counting the num- bers of seedlings appearing of Erica australis and Calluna vulgaris. A total of 2285 germinable seeds/m2 before burning and 1177 germinable seeds/m2 after the fire were estimated for Erica australis, and 90 and 690 germinable seeds/m2, respec- tively, for Calluna vulgaris. After the fire the number of germinable seeds/m2 of Erica australis had decreased, whilst there was a considerable increase in the number of germinable seeds/m2 of Calluna vulgaris. Neither seedlings nor sprouts of Calluna vulgaris had appeared in the field plots 10 months after the fire. Erica australis did recover mainly by sprouting after fire.

Comparative Analysis of Runo and Sediment Yield with a Rainfall Simulator After Experimental Fire

Changes produced in runoff and sediment levels before and after fire and during the revegetation process were examined using a rainfall simulator. The area was burned in an experimental fire, reaching temperatures from 35° to 563° C. Then it was revegetated using different species combinations. Fifteen permanent plots were established in the burnt area (4 treatments and a control replicated three times). Simulated rainfall of 15 mm per 5 min was applied in each treatment. No significant differences were found in sediment yield and runoff between treatments, but greatest runoff was observed to occur immediately after the fire. A significant relationship was found between runoff and woody cover, and a decrease in runoff can be observed as cover increases. The relationship between sediment yields and runoff rates was also positive. The low rates observed during rainfall simulation are due to the effect of natural vegetation rather than revegetation treatments. The high organic matter content also had an influence on the low rates of runoff and sediment.

Space-time heterogeneity in the recovery after experimental burning and cutting in a Cistus laurifolius shrubland

Recovery after experimental burning and cutting in a shrubland of Cistus laurifolius in NW Spain has been studied. The community was homogeneous prior to the disturbances, and tended to recover through a process of autosuccession. It was tested whether in a small space (two 100 m2 plots) there was a greater similarity among individual subplots (12) in five consecutive years, or among the five subplots considered in each plot in the same year. By comparing space and time beta diversity using analysis of variance, no significant differences were observed, which indicates that temporal changes are not of a greater magnitude than space heterogeneity, even on such a small scale. Changes in time are characterized by an increase in cover by woody species, mainly Cistus laurifolius, or a decrease in the diversity and richness of species. Space heterogeneity (differences between subplots) does not seem to be determined by environmental gradients, since the sampling surface is very small, and may be due to the effect of some annual or perennial species, which are not dominant and only appear in some subplots, probably due to random dispersal.

Effects of fertilization and cutting on the chemical composition of vegetation and soils of mountain heathlands in Spain

Abstract In the mountains of northern Spain, patches dominated by Calluna vulgaris are scarce and they may disappear or change as a result of continued lack of management and possibly increasing nutrient availability through atmospheric deposition. The effects in the soil properties and in the composition of Calluna vulgaris and Erica tetralix shoots on heathlands dominated by Calluna and Erica subjected to fertilization and experimental cutting were studied in three mountain passes in northern Spain. A total of 90 1-m2 plots received different combinations of cutting and twice the estimated atmospheric deposition of nitrogen (5.6 g.m−2.yr−1) as ammonium nitrate. One of the dominant ericaceous species (Calluna and Erica) was selectively cut by hand at ground level and their nitrogen shoot content were compared in the presence or absence of the other. Treatments were carried out in April 1998. In each plot one soil sample was taken in the original situation and 12, 24 and 36 months after the treatments. Soil properties such as organic matter, total nitrogen, available phosphorus and pH were determined. In every plot five shoots of Calluna and Erica were also taken to analyse total nitrogen content in the original situation and 12, 24 and 36 mo after the treatments. Nitrogen addition does not necessarily lead to increased levels in the soil, and a clear pattern was not found in the three areas. A gradual decrease in available phosphorus content was detected in the three areas until two years after treatment, although values tend to recover in two of the areas in the third study year. An increase in organic matter content was observed in all areas. It is concluded that increased nutrients alone, at twice the rate of the estimated current atmospheric deposition for the area, which is relatively low, will not alter significantly the soil characteristics of the mountain heathland stands. A clear increase in plant N-content is observed in the fertilized plots in comparison with the non-fertilized ones and Calluna always has higher nitrogen content than Erica. This increase is most pronounced one year after the treatments started in one of the areas and after two years in the other two areas. In some cases the elimination of one species is seen to favour nitrogen increase in the other.

Eleven years of recovery dynamic after experimental burning and cutting in two Cistus communities

Recovery after cutting and burning in two series of experimental shrubland plots dominated by Cistus laurifolius and Cistus ladanifer, respectively, was studied over 11 years. The two communities tend to recover by an autosuccession process after disturbances, with Cistus species being dominant from the first or second year. The greatest diversity is recorded in the first few years after the disturbances, with higher species richness, basically herbaceous ones, and lower dominance effect. Cover by woody species tends to increase but from the fourth year the differences are not significant. The highest herbaceous cover is after one year and the peak is more marked in the cut plots. Herbaceous species cover decreases afterwards and there are small changes in the different years but without clear trends. When all the samplings are compared by a TWINSPAN, the first division separates both communities and the second division the initial and the final phases from each community. The separation between cut and burnt plots is only observed in the final phases.

Comparison of the regeneration after burning, cutting and ploughing in a Cistus ladanifer shrubland

The recovery of a Cistus shrubland after experimental treatments (cutting, burning and ploughing) was studied to determine qualitative and quantitative differences in the secondary succession. The study was carried out in three experimental plots of 100 m2 each, in which five 1 m2 sampling units were fixed and surveyed for five years, estimating cover percentage of each plant species. The data were analysed by means of affinity indexes (Sorensen and Steinhaus Indexes). The results indicated that the cover of the woody species increased progressively, but the degree of recovery depended on the treatment, as well as on the time afterwards. The number of these species remained almost constant throughout the whole period. The herbaceous species diversity was higher in the two first years in all treatments. When treatments were compared, the greatest diversity occurred after cutting. The regeneration of the community occurred by autosuccession in which the diversity decreased when the dominance of Cistus increased, unlike the general trend of the classical theories. The recovery was very quick after all three treatments, which can be interpreted as a great resilience of this ecosystem.

Effects of sowing native herbaceous species on the post-fire recovery in a heathland

Erica australis heathlands in Leon province (NW Spain) have high resilience to disturbances and their post-fire recovery is very fast. The risk of soil erosion is high in the first few months after fire. The aim of this study is to investigate the effects on post-fire succession of sowing grass (Agrostis capillaris and Festuca rubra) and legume (Lotus corniculatus) seeds in a heathland burned by a summer wildfire, and to determine the most suitable native herbaceous species combination for protecting the soil in the first few phases of recovery. Fifteen permanent 4 m2 plots are established in the burned area; four treatments and a control (unsown) are applied, each with three replicates. Three similar unburned plots are also considered (unburned control). Total cover is significantly higher in the sown plots in relation to the control in the first few months after sowing, but there are no differences after 18 months. Lotus corniculatus appears only in the first year and has no effect on the total cover. F. rubra appears earlier than Agrostis capillaris, but decreases significantly in cover after 18 months. Shrub species have the highest cover in the control plots and the lowest in the Agrostis plots. The correspondence analysis shows that the trend for vegetation in all plots reaches similar species composition by the time of final sampling. The last sampling of sown plots shows greater similarity to the control plots than the sampling of these plots within the first year. The fast initial growth of F. rubra, together with its decrease and subsequent low cover from the second year, make it more preferable than Agrostis capillaris for purposes of soil protection. However, additional research, both species- and site-specific, is necessary, as different responses due to different post-fire conditions and pre-fire species composition can have important implications on community dynamics.

Interactions between mediterranean shrub species eight years after experimental fire

This paper is part of a wider study in which different combinations of species were assayed for the revegetation of experimentally burnt heathlands. In this particular case, we determined whether there was any interaction between the dominant species, Erica australis, which recovered by vegetative resprouting, and the only successful woody species sown, Cytisus sp., eight years after fire and seven years after sowing. A detailed study was carried out on each square metre of cover and height of both species in three 160 m2 plots. Total cover exceeded 100% in all subplots sown with Cytisus, whereas it did not reach 65% in the others, when both species coexist together. There was an inverse correlation between the covers of both species and a positive correlation between the height of Erica australis and the cover and the height of Cytisus. There was no significant difference in Erica cover in plots sown with Cytisus and plots not sown. There could be some competition for light, but both species are capable of coexisting with high canopy overlap, for at least some time. Cytisus is expanding from the seeded subplots, suggesting that the dense cover of Erica australis does not impede the establishment of Cytisus.

Does fire regime affect both temporal patterns and drivers of vegetation recovery in a resilient Mediterranean landscape? A remote sensing approach at two observation levels

We investigate how fire regime may influence both temporal patterns and drivers of vegetation regeneration in a Natural Park (NW Spain) affected by a long history of fire events and human activities. To address this issue, we evaluate the suitability of five spectral indices derived from Landsat imagery (for the period 1992–2005) for estimating biophysical properties of vegetation and monitoring post-fire recovery. Complementarily, we assess the role of the observation level (pixel and patch) on the results, identifying which of them is more informative for land management. Tasselled Cap Wetness was the best-performing index and total cover was the vegetation property more closely related to spectral data. Most post-fire recovery occurred within the 2 years following the fire event. Fire recurrence did not influence patch extent or shape nor did it affect ecosystem resilience. However, patch extent and shape affected resilience. The relevance of the environmental drivers behind vegetation recovery was not related to fire recurrence and changed over time. Prior vegetation status and rainfall were the most important drivers, while topography and vegetation type had a more secondary role. Our results advocate the consideration of patches as the most appropriate organisational unit when monitoring vegetation recovery.

Temporary changes of the edaphic characteristics during the first year of postfire regeneration in two oak groves

Changes in chemical composition of surface 5 cm soil were examined during I year following a fire in two Quercus pyrenaica ecosystems. The soils were analyzed for available Ca, Mg, P, K, total N, organic C, and pH. The principal component analysis, including the magnitudes and rates of increases or decreases of the chemical components, showed that the postfire soils of the two ecosystems had a markedly different behavior. The reasons for the differences were ascribed primarily to the intensity of the fire, caused by different understory vegetation and climatic situations.