Responses of Mediterranean plant species to different fire frequencies in Garraf Natural Park (Catalonia, Spain): field observations and modelling predictions

Published source details Lloret F., Juli G. Pausas J.G. & Vila M. (2003) Responses of Mediterranean plant species to different fire frequencies in Garraf Natural Park (Catalonia, Spain): field observations and modelling predictions. Plant Ecology, 167, 223-235.
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Summary

Dynamics in response to fire history of a Mediterranean garrigue plant community comprising Aleppo pine Pinus halepensis, Kermes oak Quercus coccifera, Mediterranean heath Erica multiflora, rosemary Rosmarinus officinalis, white cistus Cistus albidus, sage-leaved cistus C.salviifolius and the grass Ampelodesmos mauritanica, were studied following two approaches: i) field surveys in areas unburned for the last 31 years, once burned (1982), and twice burned (1982 and 1994), and ii) modelled simulations with different fire recurrence. Here results from the field surveys are summarised.

Study site: The study was undertaken at Garraf Natural Park located 30 km south of Barcelona, northeast Spain (41°15'N, 2°0' E). The vegetation is dominated by evergreen, sclerophyllous shrubs up to 1.5 m high and open P.halepensis forest. Grazing by livestock, mainly sheep and goats, over many centuries has been important in influencing the vegetation in the region, however, this has not been historically intensive in Garraf due to the mostly superficial stony soils overlying limestone bedrock, with frequent rocky outcrops.

Field surveys: Survey were conducted from January to March 1996 in three areas: an unburned area - 31 years at least since the last fire; once-burned area - 14 years after the last fire; and twice-burned (1982 and 1994) two years after the most recent fire.

A subset of 92 quadrats from a 500 — 500 m grid map covering the Park was selected, 30 in the unburned and the twice-burned areas, and 32 in the once burned areas. Within each quadrat a 10 x 10 m sampling plot was established, there location selected to balance the combinations of aspect (north or south), topographical location (steep or flat), and soil type (presence of rock outcrops in c.30% of the total soil surface).

Vegetation cover of six dominant perennial species selected for study (i.e. Aleppo pine Pinus halepensis, Kermes oak Quercus coccifera, Mediterranean heath Erica multiflora, rosemary Rosmarinus officinalis, white cistus Cistus albidus, sage-leaved cistus C.salviifolius and Ampelodesmos mauritanica) in each plot was estimated by point intercept sampling. The presence of these species every 0.5 m along the four sides each sampling plot and in a 10 m transect running through the middle of each.

Ampelodesmos cover was more than 1.5 times as high in the twice-burned areas than in the once-burned areas and over twice that in the unburned areas; this post-fire cover increase is attributed to the ability of this grass to resprout after fire. Quercus cover was twice as high in burned areas than in the unburned areas; Erica and Rosmarinus showed little difference between unburned and once-burned areas. Cover of Pinus, Erica, Rosmarinus and Cistus was lower in the twice-burned area, although this was not significant for the Cistus species (which regenerate by seed after fire, rather than by resprouting). The generally lower vegetation cover on the twice burned area is easily explained by the time since the burn (only 2 years).

Average (+ SE) percent cover of each of the six study species
Ampelodesmos: unburned - 15.6 (3.5); once burned - 22.9 (4.0); twice-burned - 35.8 (3.3)
Pinus: unburned - 42.1 (5.3); once burned - 5.9 (1.9); twice-burned - 0.5 (0.2)
Quercus: unburned - 11.6 (3.0); once burned - 23.8 (4.1); twice-burned - 23.9 (3.4)
Erica: unburned - 7.7 (2.0); once burned - 4.3 (1.0); twice-burned - 1.6 (0.4)
Rosmarinus: unburned - 6.6 (1.4); once burned - 9.8 (2.1); twice-burned - 0.6 (0.2)
Cistus (both spp.): unburned - 1.1 (0.9); once burned - 0.8 (0.4); twice-burned - 0.4 (0.2)

Conclusions: Higher fire frequency was associated with an increase in A.mauritanica (by resprouting) and a decrease in abundance of P.halepensis. The species that regenerate by seed after fire i.e. R.officinalis and Cistus, achieved maximum abundance in areas with intermediate fire recurrence. E.multiflora exhibited slower recovery (by resprouting).

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