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

Published source details Tárrega R., Luis-Calabuig E. & Alonso I. (1997) Space-time heterogeneity in the recovery after experimental burning and cutting in a Cistus laurifolius shrubland. Plant Ecology, 179-187.
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Summary

Many garigue and maquis (shrub) habitats in the Mediterranean region are derived from degradation of the original forests by human activity and constitute stages of secondary succession which appear after fire, cutting of forests, or abandonment of grasslands or cultivated fields. A characteristic of many of the woody shrub species in these habitats is their capacity to resprout after cutting or burning. However, most of the species of the genus Cistus, Mediterranean shrubs typical of garigue and maquis, can only regenerate from seeds. This study compared the changes in the floristic composition of a laurel-leaved cistus Cistus laurifolius-dominated community after burning or cutting treatments. The study also investigated the extent of spatial heterogeneity by comparing spatial with temporal changes after these disturbances; such knowledge may contribute to appropriate evidence-based management to maintain the biodiversity of these dry Mediterranean shrublands.

Study area: The study took place in a shrubland situated at about 900 m in the southwest of the province of Leon, northwest Spain. A uniform area dominated by Cistus laurifolius (average cover 75%) was selected. Other shrub species present were two leguminous shrubs i.e. broom Chamaespartium tridentatum (average cover <8%) and Adenocarpus complicatus (<4%), and white-flowered sun-rose Halimium umbellatum (2%) and gum cistus Cistus ladanifer (1%). Total herbaceous species cover averaged <1%.

Disturbance treatments: Two 100 m² plots, each separated by a 2 m wide corridor were established and the following treatments were applied in July 1989:

i) cutting of woody species using a mechanical cutter and pruning scissors;

ii) burning aerial biomass by simulating a wildfire;

(No further treatment details are given in the original paper).

Vegetation monitoring: Vegetation was surveyed annually each June from 1990 to 1994. Five subplots of 1 m²/plot were randomly selected and marked in the first year. Each June all species present, cover of each species, and the percentage bare soil were recorded within the quadrats.

Woody species cover: After burning or cutting, the most obvious change consisted of an increase of woody species cover overtime, mainly due to C. laurifolius. Woody cover recovery was more rapid in the burnt plot over the first three years (c.14%; 48% and 67% respectively - values read from graphs) than in the cut plot (c. 6%, 17% and 40%). After in the fourth and fifth years woody cover was relatively stable and similar in both plots (around 60-70%).

Herbaceous cover: Herbaceous cover, both of annuals and perennials, was much greater in the first year in the cut plot (perennials c. 40%; annuals c. 38%) than in the burnt plot (perennials c.19%; annuals c. 2%). In the second year and subsequently however, perennial cover remained fairly constant in the cut plot (6-10%), whilst generally dropping (c.15% in year 2; 3% year 3; 4% year 4; and 7% year 5) in the burnt plot. Annual herb cover was consistently low in the burnt plot (presumably in part at least, due to seed mortality due to burning and the open xeric environment initially created) reaching peak cover in year 2 (c. 3%) and declining subsequently. In the cut plot, after the initial rapid increase to c. 38% in year 1, herb cover rapidly reduced to c.6% in year 2, and by year 5 was only around 1%, similar to cover values recorded prior to treatment.

Furthermore, higher plant diversity and species richness was observed in the cut plot, although differences tended to diminish over time. The increase in C. laurifolius cover and concurrent decrease in herbaceous species cover, was highly correlated.

Spatial heterogeneity: Practically no changes in spatial heterogeneity appeared in the cut plot, but heterogeneity was higher in the burnt plot in the first year, decreasing in the second year and maintaining itself without any great changes in the following three years.

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