ANATOMICAL CHANGES INDUCED by FIRESDAMAGED CAMBIUM in TWO NATIVE TREE SPECIES of the CHACO REGION, ARGENTINA Sandra Bravo This
Total Page：16
File Type：pdf, Size：1020Kb
IAWA Journal, Vol. 31 (3), 2010: 283–292 ANATOMICAL CHANGES INDUCED BY FIRE-DAMAGED CAMBIUM IN TWO NATIVE TREE SPECIES OF THE CHACO REGION, ARGENTINA Sandra Bravo Cátedra de Botánica, Facultad de Ciencias Forestales, Universidad Nacional de Santiago del Estero, Avenida Belgrano 1912 (s), 4200 Santiago del Estero, Argentina [E-mail: [email protected]] SUMMARY This study examined anatomical responses to fire damage of the cam- bium in Schinopsis lorentzii and Aspidosperma quebracho-blanco. Bole cross sections were extracted from specimens with external signs of fire damage. Samples were taken from zones designated normal, discoloured and wound altered. The vessel, fibre, axial and ray paren- chyma percentages, tangential vessel diameter, vessels per mm2, rays per mm, and ray width and height of these zones were compared. Fire scars and fire marks were identified on cross sections ofS. lorentzii and A. quebracho-blanco. The fire marks reflect minor wounds that did not affect wood formation. The fire scars, on the other hand, are the result of wounds that interrupted cambial activity thus affecting the shape of the bole and causing discolouration of pre-existing wood adjacent to wounds. The wood formed after fire damage included callus, barrier zones at fire scar edges and the formation of ribs of wound wood. The wound altered zone was characterised by a decrease in the percentage of vessels and fibres, an increase in the percentage of axial parenchyma, the formation of grouped rays, a decrease in vessel tangential diameter, and occurrence of fibres with atypical structure. Disorientation in the axial xylem system was observed in the barrier zone. The anatomical responses to cambium damage and formation of discoloured wood and woundwood ribs suggest that wood quality and utilisable volume of bole in the studied species is affected by fire. Key words: Schinopsis, Aspidosperma, cambium, fire damage, barrier zone, discoloured wood. InTroDucTIon Scars and/or marks resulting from fire that occur in woody plants are useful for dating past fires (Agee 1993; Kitzberger et al. 2000; Smith & Sutherland 2001; Bravo et al. 2001a). After fire damage plants begin physiological processes important for defense against pathogen attack and recovery from wounding. These processes can vary with fire characteristics, plant species and individuals. The most common responses to Associate Editor: Susan Anagnost Downloaded from Brill.com09/30/2021 05:30:20AM via free access 284 IAWA Journal, Vol. 31 (3), 2010 cambial damage are the formation of barrier zones and the compartmentalization of the Argentine injured area (Larson 1994; Gill 1995; Smith Chaco Region & Sutherland 2001). Injuries caused by fire Santiago usually lead to wood decay, reduced com- del Estero mercial value and also may affect tree health (e.g., Rademacher et al. 1984; Gill 1995; Sutherland & Smith 2000; Bravo et al. 2001a; 2006). The Chaco region extends through Ar- gentina, Paraguay, Bolivia and a small part of Brazil. In Argentina, the chaco region is approximately 600,000 km2 and includes the provinces of Salta, Tucumán, Jujuy, ca- tamarca, Santiago del Estero, Córdoba, chaco, Santa Fe and Formosa (Hueck 1978; de la Balze et al. 2004; Fig. 1). The vegeta- tion of the chaco is a mosaic of forests, woodlands, savannas and shrublands (Mo- rello & Adámoli 1968; Bucher 1982). Fire and floods are the major disturbances in the region (Bucher 1982; Bravo et al. 2001b; Tálamo & caziani 2003). Fires usually start in savannas and may spread to forests and Figure 1. Location of the study area in the woodlands when environmental conditions Argentine Chaco region. are extreme (Kunst & Bravo 2003). The forests in the western chaco region, Argentina, are dominated by the decidu- ous species Schinopsis lorentzii (Griseb.) Engler (quebracho colorado santiagueño) of the Anacardiaceae and the evergreen Aspidosperma quebracho-blanco Schltdl. (quebracho blanco) of the Apocynaceae. Both species are 16–20 m tall, produce high quality diffuse porous wood and form annual growth rings (Giménez & ríos 1999; Moglia 2000). Schinopsis lorentzii has been overexploited during the last century for tannin extraction, firewood, posts, railway sleepers and carpentry materials, and thus may be at risk (Hueck 1978). Aspidosperma quebracho-blanco has been exploited for similar uses although with lesser intensity. Wood defects such as fire scars and fire marks are common in the wood of native species of the chaco region (Giménez et al. 1998; Moglia 2000; Bravo et al. 2001a; 2006) and make the woods unsuitable for many uses because the anatomical structure and physical properties are altered. The volume and degree of wood discolouration and pathogen attack may be affected by the size and severity of the wounds and the vigour and age of individuals (Lee et al. 1988). Bravo et al. (2008) found that fire wounds observed in some native woody species of the chaco region generally affect up to 20% of the bole perimeter. The objective of this study was to determine how fire damage affected the anatomy and wood quality of S. lorentzii and A. quebracho-blanco. Downloaded from Brill.com09/30/2021 05:30:20AM via free access Bravo — Fire-damaged cambium 285 MaterIALS AnD METHoDS The research area was located in La Maria Experimental Ranch belonging to the Instituto Nacional de Tecnologia Agropecuaria, Santiago del Estero, Argentina (28° 3' S and 64° 15' n). The vegetation is composed of patches of forests, savannas and grasslands and could be considered typical of the chaco region, Santiago del Estero (Fig. 1). The climate is semiarid and strongly seasonal. rainfall occurs mainly in sum- mer, and the dry season extends from April to october. Average rainfall is 550 mm. The average temperature is 26.9 °c for the hottest month and 12.4 °c for the coldest. Extreme temperatures range between 42 and 45 °c in summer and -7 and -8 °c in winter (Boletta et al. 2006). Sampling was carried out in an ecotonal band located between the forests and the savannas. This area was selected because fires that start in the savannas usually end in the ecotone (Kunst & Bravo 2003). cross sections of the bole of six specimens of Schinopsis lorentzii and six specimens of Aspidosperma quebracho-blanco that had external signs of fire damage (fire scars or scorched barks) were taken at 0.3 m height. It was not feasible to core trees because of the species’ high density. Moreover, cross sections allowed better views of fire injuries. Samples defined as normal wood, dis- coloured wood, and altered wood were extracted from the cross sections (Fig. 2). The wood defined as normal was formed before the fire, it has an anatomy that is typical for the species. Discoloured wood is wood affected by heat transference and with less coloration than normal wood. The altered wood zone included the barrier zone and wound wood ribs generated by fire scars. Discoloured wood Wound altered wood zone Normal wood Figure 2. Sample extraction zones for microscopic sections in woody species boles. Transverse, radial longitudinal and tangential longitudinal sections from each zone were made using a Leitz sliding microtome following the methodology proposed by Johansen (1940). The sections had a thickness of 10–15 µm and were stained with safranin and fast green. Percentages of vessels, fibres, axial and radial parenchyma, tangential diameter of vessels (µm), number of vessel per mm2, number of rays per mm, maximum ray width (cell number) and height (µm) were measured as per the Downloaded from Brill.com09/30/2021 05:30:20AM via free access 286 IAWA Journal, Vol. 31 (3), 2010 recommendations of rademacher et al. (1984) and Gourlay and Grime (1994). The percentages of vessels, fibres, parenchyma and rays were obtained following Quirk and Smith’s methodology (1975). Photomicrographs were taken using Leitz-oM 100 equipment. A parametric t test for matched samples was used to assess the significance of the anatomical differences between the normal wood and the wound-altered wood. Analyses were done using the statistical program Statistica 6.0. A B C D E F Figure 3. Fire-altered wood. – A: Fire scar in Schinopsis lorentzii. – B: Fire scar in Aspidosperma quebracho-blanco. – c: Fire mark in S. lorentzii. – D: Fire mark in A. quebracho-blanco. – E: Tannin secretion in compartmentalizated wood of S. lorentzii. – F: Cicatricial callus in A. quebracho-blanco.— Scale bars in E & F = 50 µm. Downloaded from Brill.com09/30/2021 05:30:20AM via free access Bravo — Fire-damaged cambium 287 A B C D E F Figure 4. Wood altered by fire scars. – A:c ross section of callus and barrier zone in Schinopsis lorentzii. – B: cross section of barrier zone in S. lorentzii. – C: Longitudinal radial section with aggregated rays in Aspidosperma quebracho-blanco. – D: cross section of barrier zone with crys- tals in S. lorentzii. – E: cross section of bar zone with atypical fibres in S. lorentzii. – F: Longitudinal radial section with disorientation in axial xylem system in A. quebracho-blanco. — Scale bars for A & c = 150 µm, for B, D–F = 50 µm. Downloaded from Brill.com09/30/2021 05:30:20AM via free access 288 IAWA Journal, Vol. 31 (3), 2010 RESULTS Fire scars and fire marks were identified on transverse sections of both species (Fig. 3A, B). Due to death of the cambium cells, wood formation was interrupted and fire scars formed in both species. Fire scars altered the bole shape and remained open long after the fire. Very close to the fire injury, the wood tissue became discoloured (Fig. 2, 3). Evidence of pathogen attacks (e.g. by insects and fungi) were also observed on the discoloured wood (Fig. 3A, B). Fire marks were minor wounds affecting isolated sectors of growth rings. Here the fire did not kill the cambium or interrupt bole growth and, only occasionally, the wood was discoloured (Fig.