INFLUENCE OF FIRE ON SOIL RESPIRATION RATES IN FOREST STANDS ADJACENT TO MADRID. SPAINCarla Uribe1. Rosa Inclán1. Dolores M. Sánchez1. Ramón Morante1. Ana María Fernández1. Ángeles Clavero1. Ana Cardeña1. Daniel De la Torre1 and Helga Van Miegroet2

1Department of environment. CIEMAT. MADRID. SPAIN.2Department of Wildland Resources. Utah State University. LOGAN. USA.

INFLUENCE OF FIRE ON SOIL RESPIRATION RATES IN FOREST STANDS ADJACENT TO MADRID. SPAINCarla Uribe1. Rosa Inclán1. Dolores M. Sánchez1. Ramón Morante1. Ana María Fernández1. Ángeles Clavero1. Ana Cardeña1. Daniel De la Torre1 and Helga Van Miegroet2

1Department of environment. CIEMAT. MADRID. SPAIN.2Department of Wildland Resources. Utah State University. LOGAN. USA.

INTRODUCTION

Mediterranean forests are vulnerable to numerous threats including wildfires due to a combination of climatic factors and increased urbanization. In the last decades the number of wildfires has doubled around Madrid. Increased temperatures and summer drought lead to increased risk of forest fires (IPCC 2007).This may have important consequences for the C dynamics and the C balance in these ecosystems. Soil respiration represents ~67-76% of total ecosystem respiration and changes in this flux can have a major impact on the global C cycle.

In this study we characterize the effects of fire on soil respiration and physic-chemical and biological soil properties in three ecosystem type characteristic of the Central System in Spain: Quercus ilex subsp. Ballota. Quercus pyrenaica Willd. and Pinus sylvestris L.

In each forest type we established two study plots one burned and one in the unburned control. Near each plot a pit was dug to determine the soil characteristics. In addition we took soil samples (0-10cm) to characterize carbon content and the microbial community structure using the PLFA technique (Phospholipids Fatty Acids). In 2008 the following monthly measurements were made:

• Soil respiration (12 random locations): closed dynamic system LI-6400 (LI-COR INC. Lincoln. NE. USA); no measurements after rain to avoid inhibition of CO2 diffusion due to saturation of soil pore space or CO2 pulse with rehydration of the soil (Rey et al. 2002). • Temperature: thermocouple (Omega Engineering). • Soil moisture: TDR (Time Domain Reflectometry ; System TRIMEG IMKO GmbH). • Litterfall: collected in 4 boxes per plot (0.29 m2 each).Differences were analyzed using Statistic 6.0 software (StatSoft. Inc.. Tulsa USA).

RESULTS

STUDY OBJECTIVES

EXPERIMENTAL METHODS

LOCATION

CONCLUSIONS

Quercus ilex Quercus pyrenaica Willd Pinus Sylvestris L.

Figure 1. Seasonal variation of the soil respiration by the three species of trees: CO2 flows are generally greater in unburned than in burned treatments. Also most burned treatments have higher temperatures (ºC) and lower moisture (vol%) than the unburned.

Figure 2. Differences in soil carbon pools are small and species/location dependent.

Table1. Soil characteristics under the tree species of study.

Species Treatment Gram + Bacteria(%) Gram – Bacteria(%) Actinomycetes(%) Fungi(%)

Quercus ilexUnburned 58.51 33.43 7.54 34.81

Burned 66.66 30.52 8.94 32.87

Quercus pyrenaicaUnburned 58.13 33.87 9.49 25.52

Burned 61.99 30.86 8.04 24.67

Pinus sylvestrisUnburned 57.18 21.10 8.09 20.68

Burned 75.55 15.99 14.40 21.39

Table 2.The only change in the microbial community structure in the

burned site is a decline in Gram – bacteria and an increase in Gram + bacteria.

DATE OF FIRE:2004

DATE OF FIRE: 2002

DATE OF FIRE:2001

SOIL RESPIRATION(Quercus pyrenaica )

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Fire affects soil temperature, moisture and soil respiration. The most significant effect (decline in respiration) is observed in the most recent fire (Quercus ilex in 2004).In the other two locations (Quercus pyrenaica and Pinus sylvestris) the effects are more heterogeneous, possibly to longer time since fire. The lower soil respiration in the burned treatment of Quercus ilex coincides with a lower soil carbon content and lower C/N.

Future directions: To investigate the interaction of all parameters involved in carbon dynamics and better interpret the complex effects of fires on forest soils and on the overall carbon balance of these ecosystems.

Quercus ilex Soil classification (FAO1998): UMBRISOL HÁPLICO

Depth (cm) C/N pH Silt and Clay% (Fine fraction)

Unburned Burned Unburned Burned Unburned Burned Unburned Burned

0-23 0-23 8.32 5.75 5.70 5.56 50.20 35.07

23-40 23-48 5.83 4.51 5.82 5.54 59.43 30.43

40-62 48-67 6.24 3.96 5.92 5.49 53.27 60.07

  67-97   2.21   5.79   35.54Quercus pyrenaica Soil classification (FAO1998): CAMBISOL ÉUTRICO

Depth (cm) C/N pH Silt and Clay% (Fine fraction)

Unburned Burned Unburned Burned Unburned Burned Unburned Burned

0-20 0-22 10.68 8.19 6.58 5.90 21.89 14.52

20-51 22-40 7.25 11.43 6.83 5.80 20.94 37.74

51-75 40-68 3.38 10.85 6.68 5.78 4.08 40.95

75-105 68-98 3.62 8.20 6.16 5.88 0.74 22.83

SOIL RESPIRATION (Quercus ilex )

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Pinus sylvestris Soil classification (FAO1998): UMBRISOL HÁPLICO

Depth (cm) C/N pH Silt and Clay% (Fine fraction)

Unburned Burned Unburned Burned Unburned Burned Unburned Burned

0-20 0-25 11.85 6.76 5.14 4.33 9.35 8.99

20-45 25-46 6.83 4.96 5.17 4.60 28.46 10.15

45-75 46-75 1.95 2.66 5.57 4.69 3.81 20.46

75-105 75-105 1.89 0.35 5.38 4.75 0.27 19.85