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The effect of prescribed burning on surface runoff in a pine forest stand of Chihuahua, Mexico
Forest Ecology and Management 137 (2000) 199±207
The effect of prescribed burning on surface runoff in a pine forest stand of Chihuahua, Mexico Hector Alanis Moralesa, Jose NaÂvarb,*, Pedro A. DomõÂnguezb a
Campo Experimental Madera, INIFAP, Madera, Chihuahua, Mexico Professors of Watershed Management and Silviculture, Facultad de Ciencias Forestales-UANL, Km 145 Carr. Nacional, Linares, N.L. 67700, Mexico
b
Received 13 April 1999; accepted 21 November 1999
Abstract During the period from October 1989 to December 1992, the in¯uence of prescribed burning on runoff volumes was investigated within a Pinus arizonica Engelm.-dominated stand in Chihuahua, Mexico. Prescribed burning increased surface runoff, especially in plots treated with prescribed burns applied over two consecutive years. Surface runoff continued to be large one year after ®re application, stressing the temporal effect of prescribed burns. The increment of surface runoff was statistically associated with the reduction of forest fuels and litter-layer depth. Suggestions regarding the application of prescribed burning are given to better safeguard against negative impacts associated with this silvicultural practice. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Prescribed burning; Surface runoff; Pinus arizonica; Residual forest fuel; Litter layer; Northern Mexico
1. Introduction Fule and Covington (1997) suggest that the frequency of human-induced forest ®res is increasing in the coniferous forests of northern Mexico. In addition to economic loss incurred through the reduction of quantity and quality of timber, wild®res also disturb plant succession and, consequently, modify evolutionary processes in these forest ecosystems. Forest ®res also modify wildlife habitat, the local microclimate, and forest soil evolution (Verduzco, 1976; Dyrness, 1976; DeBano, 1981, 1991; Chandler et al., 1983; Ring, 1997).
*
Corresponding author. Tel.: 52-821-24895; fax: 52-821-24251. E-mail address: [email protected] (J. NaÂvar).
Prescribed burning, namely ®re applied under human control, is a silvicultural tool that buffers the potential negative effects of wild®res. The regeneration of desirable plant species, increased plant diversity and wildlife habitat and the creation of temporary forest openings for game and scenic purposes are some of the bene®ts achieved through prescribed burning (Aguirre, 1983; RodrõÂguez, 1994; Ring, 1997). The effects of prescribed burning on soil chemical and physical properties, soil hydrology, soil microfauna, and the budget of several chemicals have been studied by a number of investigators (Ahlgreen and Ahlgreen, 1965; Eivazi and Bryan, 1996; Ring, 1997; Monleon et al., 1997). However, information concerning the ef®ciency of prescribed burning in reducing the amount of forest fuels and what effect this has on surface runoff is lacking. The information is, however, required for the appropriate management
0378-1127/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 9 9 ) 0 0 3 2 8 - X
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of prescribed burns in coniferous forests. The objective of this study was to observe the effect of prescribed burning on forest fuels and surface runoff in a forest stand of Pinus arizonica Engelm. in Madera, Chihuahua, Mexico. 2. Materials and methods 2.1. Study area The study was conducted within the Campo Experimental Madera, Chihuahua, of the Instituto Nacional de Investigaciones Forestales, AgrõÂcolas y Pecuarias (INIFAP) located in the Sierra Madre Occidental mountain range of northwestern Mexico (298080 4000 N and 1088130 0400 W). This area is located within the RH-9 (Sonora-Sur) basin of the RõÂo Yaqui watershed. The study area may be characterized as having a cold-temperate climate, with annual average precipitation and temperature being 838 mm and 9.68C, respectively (SaÂnchez and ChacoÂn, 1986). The experimental area is located at an altitude of 2500 m asl, and has an average slope of 20% with a northeast aspect. The area is located along the continental divide, between the Paci®c Ocean and the interior watersheds. The geology is comprised of volcanic rocks (Irigoyen, 1992). Soils in the area are litosols and rendzins and are characterized as being brownish in color, having medium depth (20±50 cm), with soil horizons A to C present (NarvaÂez, 1990). The soil horizon A11 (0± 30 cm of soil depth) has a sandy texture, with a high organic-matter content. The dominant plant species in the arboreal strata is Pinus arizonica Engelm. Smaller trees are characterized by Quercus sideroxila, Ceanothus fendleri (junco) and Senecio salignus (jarilla). Pteridium aquilinum (helecho), Lupinus mashallianus (hierba loca) and Senecio candidissimum (chucaca) dominate the lower strata (SaÂnchez and ChacoÂn, 1986). 2.2. Experimental design Surface runoff was collected based on the methodology recommended by Morgan (1990). A total of 12 runoff plots (5 20 m each) were established in two groups of six (Fig. 1). Runoff plots were isolated by
wood boards to direct surface ¯ow to two collection drums (each having a capacity of 200 l) by means of a PVC tube. Runoff plots were treated with prescribed burns, employing a randomized block design with four different treatments and three replicates applied in a different manner during the study period. During 1990, treatments consisted of (1) prescribed burning applied during summer (I) (plots 3,7,11, and 4,6,10), (2) control plots (T)(plots 2,5,8), and (3) no prescribed burn (SQ) (plots 1,9,12). During 1991, treatments consisted of (1) prescribed burning during spring (QP) (plots 1,9,12, which were treated as SQ in 1990), (2) prescribed burning in summer (I)(plots 3,7,11, which were treated as I in 1990), (3) no prescribed burning (SQ) (plots 4,6,10, which were treated as I in 1990), and (4) control plots (plots 2,5,8). Treatments during 1992 consisted of (1) no prescribed burn (SQ) (plots 3,7, 11; 4,6,10; and 1,9,12), and (2) control plots (plots 2,5,8) (Fig. 1). The last group of runoff plots was left as controls for the lifetime of the study period. A prescribed burning applied during the summer consisted of burning the dry forest fuel (5% of relative fuel humidity) at midday, with relative air-moisture content of 29%. A prescribed burning applied during spring consisted of burning the dry forest fuel (10% of the relative fuel humidity) early in the morning (7:00 am), with a relative air-moisture content of 40%. Organic forest fuels were inventoried following the methodology of Brown (1974), which is based on a Can®eld line of sampling placed lengthwise in the center of each runoff plot. Coarse forest fuels (branches and stems) intercepting the Can®eld line at discrete spatial intervals were collected. Finer forest fuels were inventoried inside each runoff plot, employing 11 randomly selected sampling sites (0.3 m 0.3 m each). Collected forest fuels were oven-dried at 608C for 24 h. These measurements were conducted before, and after, the application of prescribed burns. Precipitation amount and intensity were recorded in a rain gauge placed in an open clearing in the center of the experimental site. Collected surface runoff was recorded daily with a ruler during a three-year period. The depth of litter layer was also measured with rulers following a Can®eld line placed lengthwise at the center of each plot. Again, these measurements were
H.A. Morales et al. / Forest Ecology and Management 137 (2000) 199±207
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Fig. 1. Schematic drawing of the experimental layout to study the effect of prescribed burns on the efficiency of reducing forest fuels and enhancing runoff in a forest stand in Chihuahua, Mexico.
conducted before, and after, each prescribed burn application. After each precipitation event, surface runoff was summed for all similarly treated plots (in groups of three). Covariance analysis was performed to determine if there was any statistical difference between the surface runoff depths collected under different treatments applied. In addition, the slopes of the linear regression models ®tted to the relationships between surface runoff depth of treated plots were also compared against the depth of surface runoff from the control plots (Steel and Torrie, 1980). The amount of coarse and ®ne forest fuels was summed per sampling site, averaged and statistically tested between treatments employing t tests. The depth of litter layer was also statistically tested using t tests. The source of variation for both t tests was the depth of litter layer and the mass of coarse and ®ne forest fuels before, and after, the application of prescribed burns. To test the statistical dependence of surface runoff on the depth of litter layer, linear and non-linear regression models were ®tted.
3. Results and discussion Total recorded rainfall for the study period of 1990 to 1992, inclusive, was 3988.7 mm distributed over 209 rainfall events. Average rainfall depth was 18.7 mm, with a standard deviation of 15 mm. Average and maximum rainfall intensity recorded were 6.8 and 68.6 mm hÿ1, respectively. The number of rainy days which produced measurable surface runoff was 70 (24, 34, and 12 for the years 1990, 1991, and 1992, respectively), with a total rainfall depth of 1582 mm (516, 520, and 545 mm for the years 1990, 1991, and 1992, respectively). In comparison to the total precipitation, the runoff depth was small (0.45%); however, with the application of prescribed burn, surface runoff approximately tripled to 1.54%. Rainfall events recorded in summer Ð the result of mid-latitude frontal systems and deep convection Ð produced the largest depths of surface runoff. The amounts of forest fuels and depth of litter before, and after, the application of prescribed burn
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Table 1 The total amount of forest fuels and depth of litter before, and after, the application of prescribed burning treatments in a coniferous forest stand in Chihuahua, Mexico Plot No.
2 5 8 1 9 12 4 6 10 3 7 11 Average SD a
Prescribed burning treatmenta
Total forest fuels (kg mÿ2)
Depth of litter (cm)
before
after
before
after
T T T QP QP QP I1990 I1990 I1990 I1991 I1991 I1991
3.20 5.50 4.40 3.80 3.90 5.50 5.80 4.30 5.40 4.20 3.50 3.40 4.41 0.88
3.20 5.50 4.40 2.50 2.70 3.40 0.26 1.90 2.40 0.45 0.40 0.50 2.30 1.62
2.10 6.25 6.40 2.45 4.25 5.70 2.70 3.50 2.25 1.70 2.75 1.80 3.49 1.67
2.10 6.25 6.40 1.25 3.50 2.50 1.50 1.25 1.25 0.50 1.25 0.75 2.38 1.93
QP, prescribed burning applied during spring; T, control; and I, prescribed burning applied during summer.
are reported in Table 1. In individual plots, forest fuels varied from 5.80 to 3.20 kg mÿ2 and from 3.4 to 0.26 kg mÿ2 before, and after, the application of prescribed ®res, respectively. Between treatments, I1991 burned the largest amount of forest fuels (88%) and, thus, resulted in the smallest amount of forest fuels left on the soil surface, on the average 0.45 kg mÿ2. The amount of forest fuels statistically diminished after the application of prescribed burning (p < 0.001). Forest fuels were reduced, on average, by 35% with the QP, by 71% with the I1990, and by 88% with the I1991 treatment. The depth of litter layer varied before the application of forest ®res from 1.7 cm in Plot 3 to 6.4 cm in Plot 8 (Table 1). The application of prescribed burning resulted in a statistical reduction in litter depth (p < 0.01). The mean depth of litter before the application of ®res for all plots was 3.5 cm and it was reduced, after the application of ®res, to 60% in plots treated with I1991. In plots treated with QP and I1990, the depth of litter was reduced to 42 and 52%, respectively. The effect of prescribed burns on surface runoff was more obvious in plots treated with I1991 (Fig. 2). In plots treated with I in 1990, surface runoff increased by 33 and 42% in contrast to surface runoff produced
in control plots. Surface runoff was also larger (31%) in SQ plots in 1990 in contrast to control plots. During 1990, plots treated with prescribed burn produced the largest depth of surface runoff (4.9 mm) in contrast to control plots (3.7 mm). During 1991, plots treated with prescribed burn (I1991), applied in two consecutive seasons (1990 and 1991), produced the largest surface runoff depths (40.2 mm) in contrast to all other plots. During 1992, surface runoff depths continued to be larger (70 mm) in SQ plots, treated before with I1991, (70 mm), in contrast to surface runoff collected in plots treated with SQ, but treated the year before with QP1991 (13.9 mm), or SQ plots, treated the year before with SQ1991 (16.1 mm), or in contrast to control plots (9.6 mm). The proportion of surface runoff/total rainfall depth of runoff-producing events increased from 0.46% in control plots in 1991 to 10.92% in plots treated with I1991 (Table 2). In plots with prescribed burning treatments, the total proportion increased by 0.36% (plots 1,9,12); by 4.13% (plots 3,7,11); and by 0.59% (plots 4,6,10) in contrast to control plots (2,5,8) (Table 2). During 1992, plots treated with I (3,7,11) in 1990 and 1991 produced the greatest proportion of surface runoff depth/total rainfall depth of runoff-producing
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Fig. 2. The average cumulative runoff depths collected in plots treated with different prescribed burning treatments in different periods in Chihuahua, Mexico.
events. Surface runoff increased in 1992 in all plots, but the increment was greater in plots treated before with prescribed burns (Table 2). Surface runoff was noted in plots 1,9,12 (Q1991) several months after the prescribed burn was applied. However, when I1991 was applied to plots 3,7,11, its effect on surface runoff was immediately noted. Since this set of plots had been treated in 1990 with I1990, the Table 2 The proportion of surface runoff/rainfall depth of runoff-producing storms for plots treated with prescribed burns in a forest stand in Chihuahua, Mexico Plots 2,5,8 (%)
Plots 1,9,12 (%)
Plots 3,7,11 (%)
Plots 4,6,10 (%)
0.80(T a1990) 0.46(T1991) 1.01(T1991) 0.76(Total)
0.91(SQ1990) 0.86(QPc1991) 1.55(SQ1992) 1.12(total)
1.04(Ib1990) 10.92(I1991) 2.83(SQ1992) 4.89(total)
1.15(I1990) 0.76(SQ1991) 2.10(SQ1992) 1.35(total)
a
Control. Prescribed burning applied during summer. c Prescribed burning applied during spring. b
cumulative effect of prescribed burns appeared to contribute to increased runoff depths (Fig. 2). Surface runoff proportions started to diminish in 1992 in plots treated with I1990 and I1991 and increasing in plots treated with I1990 and QP1991, indicating the temporal effect of prescribed burning on runoff and the time delay required to increase surface runoff. Linear regression models were found to ®t the relationships between the sums of surface runoff depths from control and treatment plots (p < 0.0001), with the exception of 1992 (p < 0.1791). The coef®cients of determination ranged from 0.40 to 0.97. The regression slope was 4.5 times larger in plots treated with I1990 in contrast to control plots (T1990) (Table 2). In plots treated with prescribed burn (I1991), the regression slope increased 87 times in contrast to control plots (T1991). The effect of prescribed burning on the depth of surface runoff was still noted in 1992 in plots treated with QP in 1991, I in 1990, and I in 1991 because the slopes of the regression models continued to be statistically larger and did not return to their original values (Table 3 and Fig. 3).
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Table 3 Slope comparison for several regression models fitted to the sum of surface runoff depth produced in experimental plots with different prescribed burning treatments in Chihuahua, Mexico Relationships Y vs. Xa
T1990 ÿ SQ1990 vs. T1990 ÿ I11990 T1990 ÿ SQ1990 vs. T1990 ÿ I21990 T1990 ÿ SQ1990 vs. T1991 ÿ QP1991 T1990 ÿ SQ1990 vs. T1991 ÿ I1991 T1990 ÿ SQ1990 vs. T1991 ÿ SQ11991 T1990 ÿ SQ1990 vs. T1992 ÿ SQ31992 T1991 ÿ RI1991 vs. T1991 ÿ QP1991 a
Regression slope
Student t-test
p
1
2
tcal
test
0.4151 0.4151 0.4151 0.4151 0.4151 0.4151 36.057
1.0877 1.8826 1.7961 36.057 1.2221 2.1059 1.7961
2.101 3.522 2.971 4.868 2.645 9.005 4.870
2.021 2.021 2.021 2.010 2.010 2.000 2.000
0.021 0.001 0.003 0.001 0.006 0.001 0.001
QP, prescribed burning applied during spring; T, control; and I, prescribed burning applied during summer.
The volume of surface runoff was not statistically different in plots treated with I1990, SQ1991, and SQ21992, indicating the persistence of the ®re effect. This implies that the prescribed burns conducted in spring or summer had a similar effect on the depth of surface runoff. However, these experimental plots recorded slightly larger depths of surface runoff than those collected in control plots in 1990. By far, plots treated with I1991 recorded the largest depth of runoff proportions (Table 2). At the plot scale, surface runoff was statistically related to the depth of litter (Fig. 4). In 1990, the
relationship between surface runoff and litter depth was found to be a negative linear relationship, indicating that surface runoff depths decreased with increased litter layer depth. For example, average surface runoff depths of 0.3 cm were produced when the litter layer depth was 1 cm, and when the litter depth increased to 6.0 cm the depth of runoff reduced to 0.07 cm (Fig. 4a). In 1991, the relationship between surface runoff depth and litter layer depth shifted to a negative power regression model (Fig. 4b), emphasizing the effect of I1991 treatment. Following the relationship, a litter
Fig. 3. The regression models between the sum of runoff depths for plots treated with prescribed burns and plots treated as controls in a forest stand in Chihuahua, Mexico.
H.A. Morales et al. / Forest Ecology and Management 137 (2000) 199±207
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Fig. 4. The statistical relationships between the depth of litter and the depth of runoff for 12 experimental plots with prescribed burn treatments in a forest stand in Chihuahua, Mexico.
layer depth of 6 cm would generate 0.0 mm of surface runoff, while total burning of the litter would produce a runoff depth of 2.0 mm. This indicates, as already noted, that plots treated with I1991 produced the largest depths of surface runoff by an average of 2 mm. Finally, in 1992, a negative exponential regression model best ®tted the surface runoff depth vs. litter layer depth relationship (Fig. 4c). This further illustrates the persistence of the effect of ®re on runoff. During this period, a litter layer depth of 6 cm would produce 0.1 mm of runoff, whereas the total burning of litter would produce a runoff of 1.6 mm. Prescribed burning produced signi®cant volumes of surface runoff and this effect was noted mainly in plots treated with prescribed burning in two consecutive years. This is in agreement with the research conducted by Ahlgreen and Ahlgreen (1965) and Williams and Melack (1997). The partial reduction of litter or the partial elimination of forest fuels statis-
tically controlled the depth of surface runoff. Onda and Yukawua (1994) observed that mineral forest soils developed a compacted layer at the surface when the organic layer was eliminated and partially controlled the volume of runoff. Surface crusting processes have also been observed in soils lacking litter on the soil surface (Hillel, 1980). Observations, consistent with values reported by Dunne and Leopold (1978), indicated that litter intercepts 15% of its depth. Thus, a reduction of 50% (from 6 to 3 cm) of litter depth could have explained the additional runoff depths generated in plots treated with prescribed burn (0.45 cm). The non-linear relationships between runoff depth and litter depth after the application of prescribed burning indicate that there may be additional processes in¯uencing the generation of runoff. Development of soil hydrophobicity could be one of these factors (DeBano, 1991). This effect appeared to be
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more important after the application of prescribed burn in two consecutive years for plots 3,7,11 (note the power regression model) and tended to disappear in 1992 (note the exponential regression model, which appeared to return to the linear relationship established before the application of prescribed burns). Litter possesses hydrophobic properties (DeBano et al., 1979; DeBano, 1981), which are enhanced by heating, burning, in®ltrating, and condensing organic distillates below the soil surface. Soil temperature during ®res, soil texture, and the type of burning material are important factors controlling the volume of distilling substances and depth of condensation (Letey et al., 1962). Soil temperatures of 4508C completely destroy organic matter and, thus, inhibit the development of hydrophobicity (DeBano et al., 1979; DeBano, 1981, 1991), while soil temperatures between 100±2008C promote hydrophobicity. Hydrophobicity is of utmost importance in sandy soils (DeBano et al., 1979), the soil texture found within the study area. Condensing organic litter distillates controls sealing of soil pores, reducing in®ltration and promoting runoff (Letey et al., 1962; DeBano et al., 1979; DeBano, 1981). The application of prescribed burns, to eliminate the risk of wild®res, should be conducted to reduce the depth of litter to 2 cm. This depth of litter would increase the volume of surface runoff to 30% of the potential volume when the litter is completely eliminated. The frequency of application should also be >3 years to allow the soil to recover from the potential development of hydrophobicity, or any other soil physical processes enhancing surface runoff. These issues are of paramount importance to protect watersheds from disturbing processes such as soil erosion, river channel modi®cation, and siltation of reservoirs. 4. Conclusions The application of prescribed burning reduced forest fuels and increased the depth of surface runoff in a pine forest stand dominated by Pinus arizonica Engelm. in Madera, Chihuahua, Mexico. This effect was noted in plots treated with prescribed burning during two consecutive years, and diminished one year after the application of the treatment, stressing the
relative importance of ®re frequency in hydrologically related processes. The depth of organic litter statistically controlled the depth of runoff, but other processes appeared to enhance the production of surface runoff. Acknowledgements The INIFAP and CONACyT funded this research through grant 2452 P-N. M.Sc. Darryl Carlyle-Moses of University of Toronto is recognized by the revision of the manuscript. References Aguirre, B.C., 1983. Labores silvõÂcolas complementarias al suelo. Bol. TeÂc. No. 93. Inst. Nal. de Invest. Ftales. SARH. MeÂxico, D.F., pp. 7±13. Ahlgreen, I.F., Ahlgreen, C.E., 1965. Ecology of prescribed burning on soil microorganisms in a Minnesota Jack pine forest. Bot. Rev. 46, 304±310. Brown, J.K., 1974. Handbook for Inventory Owned Woody Material. United States Department of Agriculture. Forest Service. General Technical Report. INT-16, 24 pp. Chandler, C., Cheney, P., Thomas, P., Trabaud, L., Williams, D., 1983. Fire in Forestry. Forest Fire Management and Organization. Wiley, New York. 450 pp. DeBano, L.F., 1981. Water repellent soils: a state-of-the-art. General Technical Report PSW-46. Illus. Pacific Southwest Forest and Range Exp. Stn. USDA. Forest Service. Berkeley, CA, USA. 25 pp. DeBano, L.F., 1991. The effect of fire on soil properties. Proc. on Management and Productivity of Western Montane Forest Soils. USDA. Forest Service. General Technical Report INT280. Boise, ID, USA, pp. 151±156. DeBano, L.F., Rice, R.M., Conrad, C.E., 1979. Soil in chaparral fires: Effects on soil properties, plant, nutrients, erosion and runoff. USDA: Forest Service. Pacific Southwest Forest and Range Experiment Station. USA. 21 pp. Dunne, T., Leopold, L.B., 1978. Water in Enviromental Planning. W.H. Freeman and Company, New York. 815 pp. Dyrness, C.T., 1976. Effect of wildfire on soil wettability in the high cascades of Oregon. USDA. For. Serv. Res. Pap. PNW202, 18 pp. Eivazi, F., Bryan, M.R., 1996. Effects of long-term prescribed burning on the activity of selected soil enzymes in an oakhickory forest. Can. J. For. Res. 26 (10), 1799±1804. FuleÂ, P.Z., Covington, W.W., 1997. Fire regimes and forest structure in the Sierra Madre Occidental, Durango, MeÂxico. Acta BotaÂnica Mexicana 41, 43±79. Hillel, D., 1980. Fundamentals of Soil Physics. Academic Press. San Diego, CA, 413 pp.
H.A. Morales et al. / Forest Ecology and Management 137 (2000) 199±207 Irigoyen, S.M., 1992. DeterminacioÂn de las curvas-nuÂmero bajo doce condiciones de cobertura arboÂrea/hojarasca, en el macizo forestal del municipio de Madera, Chihuahua. Tesis de MaestrõÂa en IngenierõÂa. Universidad AutoÂnoma de Chihuahua, 152 pp. Letey, J., Osborn, J., Delishek, R.E., 1962. The influence of the water-solid contact angle on water movement in soil. Bull. Int. Assoc. Sci. Hydrol. 3, 75±81. Monleon, V.J., Cromack, K., Landsberg, J.D., 1997. Short and long-term effects of prescribed underburning on nitrogen availability in Ponderosa Pine stands in Central Oregon. Can. J. For. Res. 27 (3), 369±378. Morgan, R.P.C., 1990. Soil Erosion and Conservation. Longman Scientific & Technical. Essex, UK, 298 pp. NarvaÂez, F.R., 1990. El suelo en relacioÂn con los tipos de vegetacioÂn y su productividad en el aÂrea experimental forestal Madera, Chihuahua. Tesis de MaestrõÂa en Ciencias. Universidad AutoÂnoma de MeÂxico. MeÂxico, D.F. pp. 22±73. Onda, Y., Yukawua, N., 1994. The influence of understories and litter layer on the infiltration of forested hillslopes. Proc. of the
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International Symposium on Forest Hydrology. Tokyo, Japan. pp. 107±114. Ring, E., 1997. Environmental impact of forest fires in forest ecosystems Ð a study of the literature with the focus on Scnadinavia. Forest Research Institute No. 2, Sweden, 58 pp. RodrõÂguez, T.D.A., 1994. La lucha contra el fuego. GuõÂa para la prevencioÂn, presupresioÂn y supresioÂn de incendios forestales. Universidad AutoÂnoma Chapingo. SubsecretarõÂa Forestal y de la Fauna Silvestre. SARH. MeÂxico, 171 pp. SaÂnchez, C.J., ChacoÂn, J.M., 1986. RelacioÂn suelo-vegetacioÂn del aÂrea experimental Madera. Ciencia Forestal 69, 39±64. Steel, D., Torrie, J.H., 1980. Principles and Procedures of Statistics. A Biometrical Approach. 2a. McGraw±Hill, USA, pp: 239±269 and 401±434. Verduzco, G.J., 1976. ProteccioÂn Forestal. PATENA, A.C, 369 pp. Williams, M.R., Melack, J.M., 1997. Effects of prescribed burning on drought on the solute chemistry of mixed-conifer forest streams of Sierra Nevada, CA. Biogeochemistry 39 (3), 225± 253.
The effect of prescribed burning on surface runoff in a pine forest stand of Chihuahua, Mexico Hector Alanis Moralesa, Jose NaÂvarb,*, Pedro A. DomõÂnguezb a
Campo Experimental Madera, INIFAP, Madera, Chihuahua, Mexico Professors of Watershed Management and Silviculture, Facultad de Ciencias Forestales-UANL, Km 145 Carr. Nacional, Linares, N.L. 67700, Mexico
b
Received 13 April 1999; accepted 21 November 1999
Abstract During the period from October 1989 to December 1992, the in¯uence of prescribed burning on runoff volumes was investigated within a Pinus arizonica Engelm.-dominated stand in Chihuahua, Mexico. Prescribed burning increased surface runoff, especially in plots treated with prescribed burns applied over two consecutive years. Surface runoff continued to be large one year after ®re application, stressing the temporal effect of prescribed burns. The increment of surface runoff was statistically associated with the reduction of forest fuels and litter-layer depth. Suggestions regarding the application of prescribed burning are given to better safeguard against negative impacts associated with this silvicultural practice. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Prescribed burning; Surface runoff; Pinus arizonica; Residual forest fuel; Litter layer; Northern Mexico
1. Introduction Fule and Covington (1997) suggest that the frequency of human-induced forest ®res is increasing in the coniferous forests of northern Mexico. In addition to economic loss incurred through the reduction of quantity and quality of timber, wild®res also disturb plant succession and, consequently, modify evolutionary processes in these forest ecosystems. Forest ®res also modify wildlife habitat, the local microclimate, and forest soil evolution (Verduzco, 1976; Dyrness, 1976; DeBano, 1981, 1991; Chandler et al., 1983; Ring, 1997).
*
Corresponding author. Tel.: 52-821-24895; fax: 52-821-24251. E-mail address: [email protected] (J. NaÂvar).
Prescribed burning, namely ®re applied under human control, is a silvicultural tool that buffers the potential negative effects of wild®res. The regeneration of desirable plant species, increased plant diversity and wildlife habitat and the creation of temporary forest openings for game and scenic purposes are some of the bene®ts achieved through prescribed burning (Aguirre, 1983; RodrõÂguez, 1994; Ring, 1997). The effects of prescribed burning on soil chemical and physical properties, soil hydrology, soil microfauna, and the budget of several chemicals have been studied by a number of investigators (Ahlgreen and Ahlgreen, 1965; Eivazi and Bryan, 1996; Ring, 1997; Monleon et al., 1997). However, information concerning the ef®ciency of prescribed burning in reducing the amount of forest fuels and what effect this has on surface runoff is lacking. The information is, however, required for the appropriate management
0378-1127/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 9 9 ) 0 0 3 2 8 - X
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of prescribed burns in coniferous forests. The objective of this study was to observe the effect of prescribed burning on forest fuels and surface runoff in a forest stand of Pinus arizonica Engelm. in Madera, Chihuahua, Mexico. 2. Materials and methods 2.1. Study area The study was conducted within the Campo Experimental Madera, Chihuahua, of the Instituto Nacional de Investigaciones Forestales, AgrõÂcolas y Pecuarias (INIFAP) located in the Sierra Madre Occidental mountain range of northwestern Mexico (298080 4000 N and 1088130 0400 W). This area is located within the RH-9 (Sonora-Sur) basin of the RõÂo Yaqui watershed. The study area may be characterized as having a cold-temperate climate, with annual average precipitation and temperature being 838 mm and 9.68C, respectively (SaÂnchez and ChacoÂn, 1986). The experimental area is located at an altitude of 2500 m asl, and has an average slope of 20% with a northeast aspect. The area is located along the continental divide, between the Paci®c Ocean and the interior watersheds. The geology is comprised of volcanic rocks (Irigoyen, 1992). Soils in the area are litosols and rendzins and are characterized as being brownish in color, having medium depth (20±50 cm), with soil horizons A to C present (NarvaÂez, 1990). The soil horizon A11 (0± 30 cm of soil depth) has a sandy texture, with a high organic-matter content. The dominant plant species in the arboreal strata is Pinus arizonica Engelm. Smaller trees are characterized by Quercus sideroxila, Ceanothus fendleri (junco) and Senecio salignus (jarilla). Pteridium aquilinum (helecho), Lupinus mashallianus (hierba loca) and Senecio candidissimum (chucaca) dominate the lower strata (SaÂnchez and ChacoÂn, 1986). 2.2. Experimental design Surface runoff was collected based on the methodology recommended by Morgan (1990). A total of 12 runoff plots (5 20 m each) were established in two groups of six (Fig. 1). Runoff plots were isolated by
wood boards to direct surface ¯ow to two collection drums (each having a capacity of 200 l) by means of a PVC tube. Runoff plots were treated with prescribed burns, employing a randomized block design with four different treatments and three replicates applied in a different manner during the study period. During 1990, treatments consisted of (1) prescribed burning applied during summer (I) (plots 3,7,11, and 4,6,10), (2) control plots (T)(plots 2,5,8), and (3) no prescribed burn (SQ) (plots 1,9,12). During 1991, treatments consisted of (1) prescribed burning during spring (QP) (plots 1,9,12, which were treated as SQ in 1990), (2) prescribed burning in summer (I)(plots 3,7,11, which were treated as I in 1990), (3) no prescribed burning (SQ) (plots 4,6,10, which were treated as I in 1990), and (4) control plots (plots 2,5,8). Treatments during 1992 consisted of (1) no prescribed burn (SQ) (plots 3,7, 11; 4,6,10; and 1,9,12), and (2) control plots (plots 2,5,8) (Fig. 1). The last group of runoff plots was left as controls for the lifetime of the study period. A prescribed burning applied during the summer consisted of burning the dry forest fuel (5% of relative fuel humidity) at midday, with relative air-moisture content of 29%. A prescribed burning applied during spring consisted of burning the dry forest fuel (10% of the relative fuel humidity) early in the morning (7:00 am), with a relative air-moisture content of 40%. Organic forest fuels were inventoried following the methodology of Brown (1974), which is based on a Can®eld line of sampling placed lengthwise in the center of each runoff plot. Coarse forest fuels (branches and stems) intercepting the Can®eld line at discrete spatial intervals were collected. Finer forest fuels were inventoried inside each runoff plot, employing 11 randomly selected sampling sites (0.3 m 0.3 m each). Collected forest fuels were oven-dried at 608C for 24 h. These measurements were conducted before, and after, the application of prescribed burns. Precipitation amount and intensity were recorded in a rain gauge placed in an open clearing in the center of the experimental site. Collected surface runoff was recorded daily with a ruler during a three-year period. The depth of litter layer was also measured with rulers following a Can®eld line placed lengthwise at the center of each plot. Again, these measurements were
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Fig. 1. Schematic drawing of the experimental layout to study the effect of prescribed burns on the efficiency of reducing forest fuels and enhancing runoff in a forest stand in Chihuahua, Mexico.
conducted before, and after, each prescribed burn application. After each precipitation event, surface runoff was summed for all similarly treated plots (in groups of three). Covariance analysis was performed to determine if there was any statistical difference between the surface runoff depths collected under different treatments applied. In addition, the slopes of the linear regression models ®tted to the relationships between surface runoff depth of treated plots were also compared against the depth of surface runoff from the control plots (Steel and Torrie, 1980). The amount of coarse and ®ne forest fuels was summed per sampling site, averaged and statistically tested between treatments employing t tests. The depth of litter layer was also statistically tested using t tests. The source of variation for both t tests was the depth of litter layer and the mass of coarse and ®ne forest fuels before, and after, the application of prescribed burns. To test the statistical dependence of surface runoff on the depth of litter layer, linear and non-linear regression models were ®tted.
3. Results and discussion Total recorded rainfall for the study period of 1990 to 1992, inclusive, was 3988.7 mm distributed over 209 rainfall events. Average rainfall depth was 18.7 mm, with a standard deviation of 15 mm. Average and maximum rainfall intensity recorded were 6.8 and 68.6 mm hÿ1, respectively. The number of rainy days which produced measurable surface runoff was 70 (24, 34, and 12 for the years 1990, 1991, and 1992, respectively), with a total rainfall depth of 1582 mm (516, 520, and 545 mm for the years 1990, 1991, and 1992, respectively). In comparison to the total precipitation, the runoff depth was small (0.45%); however, with the application of prescribed burn, surface runoff approximately tripled to 1.54%. Rainfall events recorded in summer Ð the result of mid-latitude frontal systems and deep convection Ð produced the largest depths of surface runoff. The amounts of forest fuels and depth of litter before, and after, the application of prescribed burn
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Table 1 The total amount of forest fuels and depth of litter before, and after, the application of prescribed burning treatments in a coniferous forest stand in Chihuahua, Mexico Plot No.
2 5 8 1 9 12 4 6 10 3 7 11 Average SD a
Prescribed burning treatmenta
Total forest fuels (kg mÿ2)
Depth of litter (cm)
before
after
before
after
T T T QP QP QP I1990 I1990 I1990 I1991 I1991 I1991
3.20 5.50 4.40 3.80 3.90 5.50 5.80 4.30 5.40 4.20 3.50 3.40 4.41 0.88
3.20 5.50 4.40 2.50 2.70 3.40 0.26 1.90 2.40 0.45 0.40 0.50 2.30 1.62
2.10 6.25 6.40 2.45 4.25 5.70 2.70 3.50 2.25 1.70 2.75 1.80 3.49 1.67
2.10 6.25 6.40 1.25 3.50 2.50 1.50 1.25 1.25 0.50 1.25 0.75 2.38 1.93
QP, prescribed burning applied during spring; T, control; and I, prescribed burning applied during summer.
are reported in Table 1. In individual plots, forest fuels varied from 5.80 to 3.20 kg mÿ2 and from 3.4 to 0.26 kg mÿ2 before, and after, the application of prescribed ®res, respectively. Between treatments, I1991 burned the largest amount of forest fuels (88%) and, thus, resulted in the smallest amount of forest fuels left on the soil surface, on the average 0.45 kg mÿ2. The amount of forest fuels statistically diminished after the application of prescribed burning (p < 0.001). Forest fuels were reduced, on average, by 35% with the QP, by 71% with the I1990, and by 88% with the I1991 treatment. The depth of litter layer varied before the application of forest ®res from 1.7 cm in Plot 3 to 6.4 cm in Plot 8 (Table 1). The application of prescribed burning resulted in a statistical reduction in litter depth (p < 0.01). The mean depth of litter before the application of ®res for all plots was 3.5 cm and it was reduced, after the application of ®res, to 60% in plots treated with I1991. In plots treated with QP and I1990, the depth of litter was reduced to 42 and 52%, respectively. The effect of prescribed burns on surface runoff was more obvious in plots treated with I1991 (Fig. 2). In plots treated with I in 1990, surface runoff increased by 33 and 42% in contrast to surface runoff produced
in control plots. Surface runoff was also larger (31%) in SQ plots in 1990 in contrast to control plots. During 1990, plots treated with prescribed burn produced the largest depth of surface runoff (4.9 mm) in contrast to control plots (3.7 mm). During 1991, plots treated with prescribed burn (I1991), applied in two consecutive seasons (1990 and 1991), produced the largest surface runoff depths (40.2 mm) in contrast to all other plots. During 1992, surface runoff depths continued to be larger (70 mm) in SQ plots, treated before with I1991, (70 mm), in contrast to surface runoff collected in plots treated with SQ, but treated the year before with QP1991 (13.9 mm), or SQ plots, treated the year before with SQ1991 (16.1 mm), or in contrast to control plots (9.6 mm). The proportion of surface runoff/total rainfall depth of runoff-producing events increased from 0.46% in control plots in 1991 to 10.92% in plots treated with I1991 (Table 2). In plots with prescribed burning treatments, the total proportion increased by 0.36% (plots 1,9,12); by 4.13% (plots 3,7,11); and by 0.59% (plots 4,6,10) in contrast to control plots (2,5,8) (Table 2). During 1992, plots treated with I (3,7,11) in 1990 and 1991 produced the greatest proportion of surface runoff depth/total rainfall depth of runoff-producing
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Fig. 2. The average cumulative runoff depths collected in plots treated with different prescribed burning treatments in different periods in Chihuahua, Mexico.
events. Surface runoff increased in 1992 in all plots, but the increment was greater in plots treated before with prescribed burns (Table 2). Surface runoff was noted in plots 1,9,12 (Q1991) several months after the prescribed burn was applied. However, when I1991 was applied to plots 3,7,11, its effect on surface runoff was immediately noted. Since this set of plots had been treated in 1990 with I1990, the Table 2 The proportion of surface runoff/rainfall depth of runoff-producing storms for plots treated with prescribed burns in a forest stand in Chihuahua, Mexico Plots 2,5,8 (%)
Plots 1,9,12 (%)
Plots 3,7,11 (%)
Plots 4,6,10 (%)
0.80(T a1990) 0.46(T1991) 1.01(T1991) 0.76(Total)
0.91(SQ1990) 0.86(QPc1991) 1.55(SQ1992) 1.12(total)
1.04(Ib1990) 10.92(I1991) 2.83(SQ1992) 4.89(total)
1.15(I1990) 0.76(SQ1991) 2.10(SQ1992) 1.35(total)
a
Control. Prescribed burning applied during summer. c Prescribed burning applied during spring. b
cumulative effect of prescribed burns appeared to contribute to increased runoff depths (Fig. 2). Surface runoff proportions started to diminish in 1992 in plots treated with I1990 and I1991 and increasing in plots treated with I1990 and QP1991, indicating the temporal effect of prescribed burning on runoff and the time delay required to increase surface runoff. Linear regression models were found to ®t the relationships between the sums of surface runoff depths from control and treatment plots (p < 0.0001), with the exception of 1992 (p < 0.1791). The coef®cients of determination ranged from 0.40 to 0.97. The regression slope was 4.5 times larger in plots treated with I1990 in contrast to control plots (T1990) (Table 2). In plots treated with prescribed burn (I1991), the regression slope increased 87 times in contrast to control plots (T1991). The effect of prescribed burning on the depth of surface runoff was still noted in 1992 in plots treated with QP in 1991, I in 1990, and I in 1991 because the slopes of the regression models continued to be statistically larger and did not return to their original values (Table 3 and Fig. 3).
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Table 3 Slope comparison for several regression models fitted to the sum of surface runoff depth produced in experimental plots with different prescribed burning treatments in Chihuahua, Mexico Relationships Y vs. Xa
T1990 ÿ SQ1990 vs. T1990 ÿ I11990 T1990 ÿ SQ1990 vs. T1990 ÿ I21990 T1990 ÿ SQ1990 vs. T1991 ÿ QP1991 T1990 ÿ SQ1990 vs. T1991 ÿ I1991 T1990 ÿ SQ1990 vs. T1991 ÿ SQ11991 T1990 ÿ SQ1990 vs. T1992 ÿ SQ31992 T1991 ÿ RI1991 vs. T1991 ÿ QP1991 a
Regression slope
Student t-test
p
1
2
tcal
test
0.4151 0.4151 0.4151 0.4151 0.4151 0.4151 36.057
1.0877 1.8826 1.7961 36.057 1.2221 2.1059 1.7961
2.101 3.522 2.971 4.868 2.645 9.005 4.870
2.021 2.021 2.021 2.010 2.010 2.000 2.000
0.021 0.001 0.003 0.001 0.006 0.001 0.001
QP, prescribed burning applied during spring; T, control; and I, prescribed burning applied during summer.
The volume of surface runoff was not statistically different in plots treated with I1990, SQ1991, and SQ21992, indicating the persistence of the ®re effect. This implies that the prescribed burns conducted in spring or summer had a similar effect on the depth of surface runoff. However, these experimental plots recorded slightly larger depths of surface runoff than those collected in control plots in 1990. By far, plots treated with I1991 recorded the largest depth of runoff proportions (Table 2). At the plot scale, surface runoff was statistically related to the depth of litter (Fig. 4). In 1990, the
relationship between surface runoff and litter depth was found to be a negative linear relationship, indicating that surface runoff depths decreased with increased litter layer depth. For example, average surface runoff depths of 0.3 cm were produced when the litter layer depth was 1 cm, and when the litter depth increased to 6.0 cm the depth of runoff reduced to 0.07 cm (Fig. 4a). In 1991, the relationship between surface runoff depth and litter layer depth shifted to a negative power regression model (Fig. 4b), emphasizing the effect of I1991 treatment. Following the relationship, a litter
Fig. 3. The regression models between the sum of runoff depths for plots treated with prescribed burns and plots treated as controls in a forest stand in Chihuahua, Mexico.
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Fig. 4. The statistical relationships between the depth of litter and the depth of runoff for 12 experimental plots with prescribed burn treatments in a forest stand in Chihuahua, Mexico.
layer depth of 6 cm would generate 0.0 mm of surface runoff, while total burning of the litter would produce a runoff depth of 2.0 mm. This indicates, as already noted, that plots treated with I1991 produced the largest depths of surface runoff by an average of 2 mm. Finally, in 1992, a negative exponential regression model best ®tted the surface runoff depth vs. litter layer depth relationship (Fig. 4c). This further illustrates the persistence of the effect of ®re on runoff. During this period, a litter layer depth of 6 cm would produce 0.1 mm of runoff, whereas the total burning of litter would produce a runoff of 1.6 mm. Prescribed burning produced signi®cant volumes of surface runoff and this effect was noted mainly in plots treated with prescribed burning in two consecutive years. This is in agreement with the research conducted by Ahlgreen and Ahlgreen (1965) and Williams and Melack (1997). The partial reduction of litter or the partial elimination of forest fuels statis-
tically controlled the depth of surface runoff. Onda and Yukawua (1994) observed that mineral forest soils developed a compacted layer at the surface when the organic layer was eliminated and partially controlled the volume of runoff. Surface crusting processes have also been observed in soils lacking litter on the soil surface (Hillel, 1980). Observations, consistent with values reported by Dunne and Leopold (1978), indicated that litter intercepts 15% of its depth. Thus, a reduction of 50% (from 6 to 3 cm) of litter depth could have explained the additional runoff depths generated in plots treated with prescribed burn (0.45 cm). The non-linear relationships between runoff depth and litter depth after the application of prescribed burning indicate that there may be additional processes in¯uencing the generation of runoff. Development of soil hydrophobicity could be one of these factors (DeBano, 1991). This effect appeared to be
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more important after the application of prescribed burn in two consecutive years for plots 3,7,11 (note the power regression model) and tended to disappear in 1992 (note the exponential regression model, which appeared to return to the linear relationship established before the application of prescribed burns). Litter possesses hydrophobic properties (DeBano et al., 1979; DeBano, 1981), which are enhanced by heating, burning, in®ltrating, and condensing organic distillates below the soil surface. Soil temperature during ®res, soil texture, and the type of burning material are important factors controlling the volume of distilling substances and depth of condensation (Letey et al., 1962). Soil temperatures of 4508C completely destroy organic matter and, thus, inhibit the development of hydrophobicity (DeBano et al., 1979; DeBano, 1981, 1991), while soil temperatures between 100±2008C promote hydrophobicity. Hydrophobicity is of utmost importance in sandy soils (DeBano et al., 1979), the soil texture found within the study area. Condensing organic litter distillates controls sealing of soil pores, reducing in®ltration and promoting runoff (Letey et al., 1962; DeBano et al., 1979; DeBano, 1981). The application of prescribed burns, to eliminate the risk of wild®res, should be conducted to reduce the depth of litter to 2 cm. This depth of litter would increase the volume of surface runoff to 30% of the potential volume when the litter is completely eliminated. The frequency of application should also be >3 years to allow the soil to recover from the potential development of hydrophobicity, or any other soil physical processes enhancing surface runoff. These issues are of paramount importance to protect watersheds from disturbing processes such as soil erosion, river channel modi®cation, and siltation of reservoirs. 4. Conclusions The application of prescribed burning reduced forest fuels and increased the depth of surface runoff in a pine forest stand dominated by Pinus arizonica Engelm. in Madera, Chihuahua, Mexico. This effect was noted in plots treated with prescribed burning during two consecutive years, and diminished one year after the application of the treatment, stressing the
relative importance of ®re frequency in hydrologically related processes. The depth of organic litter statistically controlled the depth of runoff, but other processes appeared to enhance the production of surface runoff. Acknowledgements The INIFAP and CONACyT funded this research through grant 2452 P-N. M.Sc. Darryl Carlyle-Moses of University of Toronto is recognized by the revision of the manuscript. References Aguirre, B.C., 1983. Labores silvõÂcolas complementarias al suelo. Bol. TeÂc. No. 93. Inst. Nal. de Invest. Ftales. SARH. MeÂxico, D.F., pp. 7±13. Ahlgreen, I.F., Ahlgreen, C.E., 1965. Ecology of prescribed burning on soil microorganisms in a Minnesota Jack pine forest. Bot. Rev. 46, 304±310. Brown, J.K., 1974. Handbook for Inventory Owned Woody Material. United States Department of Agriculture. Forest Service. General Technical Report. INT-16, 24 pp. Chandler, C., Cheney, P., Thomas, P., Trabaud, L., Williams, D., 1983. Fire in Forestry. Forest Fire Management and Organization. Wiley, New York. 450 pp. DeBano, L.F., 1981. Water repellent soils: a state-of-the-art. General Technical Report PSW-46. Illus. Pacific Southwest Forest and Range Exp. Stn. USDA. Forest Service. Berkeley, CA, USA. 25 pp. DeBano, L.F., 1991. The effect of fire on soil properties. Proc. on Management and Productivity of Western Montane Forest Soils. USDA. Forest Service. General Technical Report INT280. Boise, ID, USA, pp. 151±156. DeBano, L.F., Rice, R.M., Conrad, C.E., 1979. Soil in chaparral fires: Effects on soil properties, plant, nutrients, erosion and runoff. USDA: Forest Service. Pacific Southwest Forest and Range Experiment Station. USA. 21 pp. Dunne, T., Leopold, L.B., 1978. Water in Enviromental Planning. W.H. Freeman and Company, New York. 815 pp. Dyrness, C.T., 1976. Effect of wildfire on soil wettability in the high cascades of Oregon. USDA. For. Serv. Res. Pap. PNW202, 18 pp. Eivazi, F., Bryan, M.R., 1996. Effects of long-term prescribed burning on the activity of selected soil enzymes in an oakhickory forest. Can. J. For. Res. 26 (10), 1799±1804. FuleÂ, P.Z., Covington, W.W., 1997. Fire regimes and forest structure in the Sierra Madre Occidental, Durango, MeÂxico. Acta BotaÂnica Mexicana 41, 43±79. Hillel, D., 1980. Fundamentals of Soil Physics. Academic Press. San Diego, CA, 413 pp.
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