Detailed measurements of soil nutri- ents, runoff and sediment discharge were made in two plots about 200 m 2 each in a plantation of Aleppo and Brutia pine in ...
CATENA
vol. 20, p. 129-139
Cremlingen 1993
F i r e I m p a c t s on S o i l N u t r i e n t s a n d S o i l E r o s i o n in a M e d i t e r r a n e a n P i n e F o r e s t P l a n t a t i o n P. K u t i e l & M. I n b a r
Summary Detailed measurements of soil nutrients, runoff and sediment discharge were made in two plots about 200 m 2 each in a plantation of Aleppo and Brutia pine in the Mediterranean climatic region of Israel. One of the plots was affected by a moderate wildfire at the end of summer 1988. The soil nutrient content in the burnt plot was increased significantly. Runoff and erosion rates were low in both plots. However, on the burnt plot they were lower than on the unburnt plot, due to increased infiltration capacity. These results suggest that light and moderate forest fires may increase soil fertility without causing a marked difference in soil runoff and erosion.
1
Introduction
The role of fire has been prominent in Mediterranean forest ecosystems for thousands of years (Naveh 1984). The burning of the vegetation cover affects the water and sediment regimes, the nutrient cycle and the vegetation composition of the damaged areas, causing an adjustment of the ecosystem to the new conditions (Kutiel & Naveh 1987a and b). The alteration of vegetation and soil ISSN 0341-8162 @1993 by CATENA VERLAG, W-3302 Cremlingen-Destedt, Germany 0341--8162/93/5011851/US$ 2.00 + 0.25
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cover by fire affects surface erosion processes in many ways, such as increasing sheetflow and rill formation (McNabb & Swanson 1990). Fire may affect several chemical and physical soil properties, increasing runoff and promoting erosion processes. The major effects are the loss of vegetation and the forest floor litter, which in effect reduce both rainfall intensity and also the proportion of total precipitation that reaches ground level. The degree of alteration of biotic and abiotic factors depends in fire frequency and intensity (Dunn & Debano 1977, Debano et al. 1977, Giovannini et al. 1988, Ferreira 1990, Kutiel & Shaviv 1989). Wildfires in semiarid and Mediterranean forests are thought to increase erosion (Krammes 1960, Laird & Harvey 1986, Diaz-Fierros et al. 1990, White & Wells 1979). However, diversity of lithology, slope steepness, aspects, soil and vegetation types, cover, and other natural factors, as well as the extent and intensity of the fire and the amount and intensity of rainfall create diverse fire effects. The type and magnitude of geomorphic effects depends on two properties - - fire regime and geomorphic sensitivity. Intense fires in high erosion potential areas will dominate sediment production and cause major alternations in the ecosystem (Swanson 1981), while no major effects may be noticed on soil after
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light burning. The objectives of this research are:
100 and 250 m above sea level. The slope gradient is 45% with a north-western aspect. 1. To analyze nutrient release and The planted forest is all-aged with Pisoil chemistry conditions during the nus halepensis and P. brutia trees over first months after fire. 30 years old. A moderate-light wildfire occurred in October 1988, consum2. To determine runoff and sediment ing about 3000 m 2 of the pine forest. yield after a forest fire. The fire moved through the understory and litter layer for 4 hours without caus2 Site description and ing serious damage to the overstory tree canopies. Bark scorch height, measured methodology on the leeward side of the trunk, was The study area is in the Yoqneam for- about 1 m. est, near the Porath rest area in the As a control plot we used an adjaMediterranean region of Israel (fig. 1). cent unburnt forest as close as possible Mean annual rainfall is 550 mm. Aver- to the burnt one, assuming that both age daily minimum temperature of the were similar in their original understory coldest month (February) is 6°C and the vegetation composition. The area of the average daily m a x i m u m temperature of burnt and unburnt plots were 162 m 2 the hottest month (June) is 39°C. and 149 m 2 respectively (fig. 2). The The soil is pale rendzina (Lithic Xe- plots are relatively large and represent rothenth) usually less than 20 em in the area well. Each plot was delimited depth, containing 56% CaCO3 and 6.8% by hard plastic boards, 20 em high and organic matter. The sites are located on about 5 cm below soil surface, which a chalky hillslope with altitudes between joined at a water collector drained by a
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F i g . 2: D e t a i l e d d e s c r i p t i o n of the plots, a - burnt, b - unburnt. A = area; S -- slope; o p e n circles -- trees; b l a c k circle -- u n d r a i n e d d e p r e s s i o n s ; b l a c k s q u a r e s = w a t e r c o l l e c t o r s ; p l a i n l i n e s = e l e v a t i o n c o n t o u r s ; d a s h e d line = p l o t b o u n d a r i e s
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a pipe to a barrel. No accumulation of sediments nor escape of runoff were observed along the plastic boards during the study. A rain gauge was installed near the sites. Total flow and sediment content was collected after each storm. Sediment concentration was determined at the laboratory from the total content of one liter sample. Four soil samples were taken from the burnt and unburnt soils, close to the erosion-runoff plots. This was done in order not to destroy the soil surface structure in these plots, which could affect the runoff and erosion processes. The samples were collected from the upper 5 cm of the mineral soil, where the main effects of the fire occurred (Kutiel & Naveh 1987a, Kutiel & Shaviv 1989). In the unburnt plot, this was done after removal of the litter layer, containing mainly undecomposed needles. The samples were air dried and passed through a four m m sieve. Ammonium and nitrate+nitrite were extracted from each sample with 1 N KC1 solutions and determined by an autoanalyser. Available P was determined using the bicarbonate extraction method (Olsen et al. 1954). Total N and P were determined by the method of Thomas et al. (1967). Cation concentrations (Na, Mg, K and Ca) in extracts of distilled water (1:2 soil water ratio), as well as pH and electrical conductivity (EC) were determined. CaCO3 was determined by evolution of CO2 from soil samples mixed with 5~0 HCI solution. Organic carbon was determined using a potentiometric titration method (Raveh & Avnimelech 1972). Determinations made 1, 4, 5, 6, 7 and 8 months after the fire were performed, each with four replicate soil samples. Differences between burnt and un-
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burnt soils were tested using the model of two way analysis of w~riance with interaction (the factors are time and treatments: burnt and unburnt).
3
Results and discussion
S.1
Soil n u t r i e n t s
No significant changes in soil pH were observed immediately after the fire (tab. 1). Kutiel & Shaviv (1989) conducted a laboratory experiment which simulated a forest fire with a similar soil and found that the soil pH increased by 1 unit when the soil was burnt at 250°C. Therefore, we surmised that the temperature of the soil surface in the pesent fire did not reach 250°C. The EC increased significantly (p0.2
Tot. N % B
0.454.0.03 0,284.0.07 0.334.0.02 0.424-0.04 0.394-0.03 0.394-0.03
133
1.09-t-0.14 0.334.0.14 0.584.0.18 0.52-1-0.11 0.614-0.16 0.434-0.13
U l}
0A9±0.14 0.,164.0.07 0.594.0.14 0.42±0.18 0.34,1.0.02 0.594-0.04
Tot P %
g
UB
0.37,1.0.07 0.384-0.02 0.60,1.0.04 0,374-0.07 0,444-0.09 0.61-I-0.18
g
0.20-t-0.01 0.214-0.01 0,234-0.03 0.224-0.03 0.244-0.03 0.574.0.14
P
