ANATOMICAL CHANGES INDUCED by FIRESDAMAGED CAMBIUM in TWO NATIVE TREE SPECIES of the CHACO REGION, ARGENTINA Sandra Bravo This

Home , Aspidosperma, Schinopsis, Schinopsis lorentzii

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 cambium 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 parenchyma 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 vegetation 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 summer, 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, discoloured 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. 3C, D). The wood present at the time of fire damage showed considerable accumulation of dark substances. Wood formed after fire damage differed from the wood formed before the damage and consequently when samples dried the two zones separated. In fire scars, the discoloured wood was compartmentalized by the secretion of dark substance, likely tannins or gums, between the unaltered and the altered wood tissue. The secretion products were deposited in the axial and radial parenchyma, vessels, and fibres of S. lorentzii, whereas in A. quebracho-blanco only parenchyma accumulated secretion products (Fig. 3E). The wood formed after cambium damage showed a callus on the edge of the fire scar, barrier zones and ribs of wound wood (Fig. 3, 4). This callus was formed by a proliferation of parenchyma cells. The altered wood zone cells spread forming a convex mass of tissue, from the fire scar edges to the damaged surface (Fig. 4A, B). Subsequently, the cambium produced ribs of wound wood with atypical wide growth rings (Fig. 3A, B). The wound altered wood zone showed a decrease in the percentage of vessels and fibres, an increase in the percentage of axial parenchyma cells and grouped rays (Fig. 4A, B; Table 1). This zone accumulated secretion substances similar to the ones observed at the boundary between normal and discoloured wood. In S. lorentzii the ray parenchyma percentage and the ray width were reduced significantly (p < 0. 05) in response to cambium damage. The number of rays/mm and ray height in this species increased as did the crystal abundance. Aspidosperma quebracho- blanco did not show significant differences in the ray parenchyma percentage. However, it showed a significant increase in ray height and width (Table 1; Fig. 4C). The tangential diameter of vessels was reduced in both species. The fibres had thin- ner cell walls and atypically wide lumens (Fig. 4E). In addition the axial system was disoriented (Fig. 4F). In the fire mark zone, the wood formed after the fire appears similar to that of wound altered zone. The thickness of this zone varied between 200 and 250 µm in A. quebracho-blanco and between 200 and 400 µm in S. lorentzii. A large accumulation of dark substances occurred in response to cambium damage (Fig. 5B).

DISCUSSION

The fire scars observed in Aspidosperma quebracho-blanco and Schinopsis lorentzii are similar to those described in other species (e.g. Barret & Arno 1988; Agee 1993; Larson 1994; Gill 1995; Smith & Sutherland 2001; Kitzberger et al. 2000; Grau et al.

Downloaded from Brill.com09/30/2021 05:30:20AM via free access Bravo — Fire-damaged cambium 289

Table 1. Anatomical features of the normal and wound altered wood in Aspidosperma quebracho-blanco and Schinopsis lorentzii. A = average, SD = standard deviation. * = marginally significant, ** = significant, *** = highly significant.

A. quebracho-blanco S. lorentzii –––––––––––––––––––––––––––– ––––––––––––––––––––––––––– Variables Normal wood Wound altered Normal wood Wound altered wood wood ––––––––––– ––––––––––– ––––––––––– ––––––––––– A SD A SD A SD A SD

% of vessels 14.6 5.3 7.8 5.3** 11.2 2.7 7.4 2.6** % of fibres 57.6 4.5 25.8 7.3*** 65.5 4.1 17.4 3.9*** % of axial parenchyma 8 3.1 46.8 12.2*** 4.9 2.6 68 7.1*** % of radial parenchyma 19.8 2.7 19.6 5.9 18.4 2.9 6.4 3.7*** Tangential diameter of vessels (µm) 68.8 13.5 53.3 14*** 81 17.5 52.5 15.2*** No. of vessels per ocular area (×40) 3.4 1.0 2.4 1.5 5.8 2.5 5 2.1* No. of rays/mm 12.3 1.7 10.9 1.5 9.8 1.6 13 2*** Ray width (No. of cells) 2.9 0.4 5 1.2*** 3.6 1.0 3.2 0.9* Ray height (µm) 246.8 77.5 256.5 109.3* 240.3 48.8 263.3 60.9* Ray width (µm) 40.2 6.1 62 22.1*** 24.3 4.8 19.3 4.8***

2003). Comparable fire injuries have been observed also in other native woody species of the Chaco region (Giménez et al. 1997, 1998; Bravo et al. 2001a, b; Bravo et al. 2006). Fire marks were described as minor fire wounds in Prosopis alba and P. nigra (Bravo et al. 2001a) and they seem to be frequent in species with a thick bark, such as A. quebracho-blanco and S. lorentzii (Bravo et al. 2008). Bark can be effective in

A B

Figure 5. Wood altered by fire marks. – A:C ross section with wood formed before and after fire in Aspidosperma quebracho-blanco. – B: Cross section of barrier zone associated to fire mark in Schinopsis lorentzii. — Scale bars = 150 µm.

Downloaded from Brill.com09/30/2021 05:30:20AM via free access 290 IAWA Journal, Vol. 31 (3), 2010 preventing fire damage to the cambium because it reduces thermal shock (Hengst & Dawson 1994; Gill 1995; Sutherland & Smith 2000). In the fire marks described in this work, the cambium remained functionally active allowing continuity of wood production. However, when the wood is dried, fissures would develop between the wood formed before and after fire damage and this would be a serious defect. The discoloration observed in the wood present at the time of injury in A. quebracho- blanco and S. lorentzii could be related to changes in moisture content caused by wounds or heat transference during the fire. Rademacher et al. (1984) and Smith and Sutherland (2001) stated that these changes favour reactions such as the breakdown of phenolic compounds and the growth of pathogenic microorganisms, which can cause discoloration. Discoloration associated with fire wounds has been observed in other native species of the Chaco region and cited as a common wood defect (Giménez et al. 1997; Bravo et al. 2001a, 2006; Giménez 2003). The accumulation of dark substances in the boundary layer between discoloured and normal wood is a part of the compartmentalization process (Schmitt et al. 1995; Rademacher et al. 1984). Compartmentalization reduces water loss and minimises the spreading of wood decay (Sutherland & Smith 2000). Widespread tannin accumulation in wood of S. lorentzii could be associated with the radial canals present in this species and which likely react to fire damage (Giménez & Moglia 1995). Aspidosperma quebracho-blanco normally does not produce coloured heartwood (Moglia & López 2001), but wounds caused by fire are dark-coloured indicating the synthesis of new compounds or changes in common wood compounds (Fig. 3B). The nature of these chemical changes is yet to be analyzed. The callus observed in fire-scar edges could originate from living wood parenchyma and phloem cells (Smith & Sutherland 2001). In these two Chaco species the barrier zone consisted of parenchyma cells, fibres and larger rays. The increase in axial parenchyma in the barrier zone and wound altered wood zone probably resulted from enhanced cell divisions of vascular cambium and phellogen (Larson 1994). The decrease in ray parenchyma percentage in S. lorentzii (Table 1) differs from the response observed in other species in which the percentage of ray parenchyma increases after cambial damage (Rademacher et al. 1984; Gourlay & Grime 1994). The ray parenchyma percentage and number of rays per mm in the barrier zone and wound altered wood of A. quebracho-blanco was not significantly different from ‘normal wood’, but ray height and width were greater than in ‘normal wood’. The increase of parenchyma in response to cambial damage has been interpreted as forming an anatomical and chemical boundary to resist the moisture loss and to avoid the spread of wood-inhabiting fungi (e.g., Rademacher et al. 1984; Smith & Sutherland 2001). The parenchyma secretes substances such as tannins, gums and others into vessels and fibres as a response to damage (Schmittet al. 1995). The significant decrease in the percentage of vessels and their tangential diameter in A. quebracho-blanco and S. lorentzii is a response that would reduce water transport and axial spread of pathogens (e.g., Rademacher et al. 1984). The atypical appearance of the fibres could represent cells that are a transitional state between parenchyma and fibres (Larson 1994). It has been suggested that the tree prioritises new cell production

Downloaded from Brill.com09/30/2021 05:30:20AM via free access Bravo — Fire-damaged cambium 291 at the expense of cell differentiation (wall thickness) so as to quickly close wounds. The locally wide growth rings of woundwood ribs are interpreted as important for closing the wounds and reducing notch stresses (Smith & Sutherland 2001). The results of this research indicate that fire scars reduce the utilisable volume of the tree bole due to the formation of discoloured wood, interruption in wood formation, and production of barrier zones. The anatomical changes in the barrier zone and wound altered wood surely affect wood quality and the wood’s technological properties such as durability, strength, and dimensional changes during drying. Although fire marks represent minor wounds and do not represent interrupted cambial activity, the wood in this region differs and can be considered a defect. These results suggest that, if fire is used as a management tool in native forests or commercial plantations, the risk of affecting wood quality needs to be considered. The relation between fire wounds and the health of the tree (e.g., susceptibility to bacterial, fungal and insects attacks) needs further research in the Chaco region.

REFERENCES

Agee, J.K. 1993. Fire ecology of Pacific Northwest forests. Island Press, Washington, DC. Barret, S. & S. Arno. 1988. Increment-borer methods for determining fire history in coniferous forests. Intermountain Research Station. General Technical Report INT-244. Forest Service, United States, Department of Agricultural, Ogden, UT. Boletta, P., A. Ravelo, A. Planchuelo & M. Grilli. 2006. Assessing deforestation in the Argen- tine Chaco. Forest Ecology and Management 228: 108–114. Bravo, S., A. Giménez & J. Moglia. 2001a. Efectos del fuego en la madera de Prosopis alba Griseb. y Prosopis nigra (Griseb.) Hieron. Mimosaceae. Bosque 22: 51–63. Bravo, S., A. Giménez & J. Moglia. 2006. Caracterización anatómica del leño y evolución del cre-cimiento en ejemplares de Acacia aroma y Acacia furcatispina en la Región Chaqueña, Argentina. Bosque 27: 146–154. Bravo, S., C. Kunst, A. Giménez & J. Moglia. 2001b. Fire regime of an Elionorus muticus (Spreng.) Kuntze savanna, western Chaco region, Argentina. Intern. J. Wildland Fire 10: 65–72. Bravo, S., C. Kunst & H. Grau. 2008. Aptitude of native woody species of Chaco region for den- droecological studies about fire regimes. Dendrochronologia 26: 43–52. Bucher, E. 1982. South American arid savannas, woodlands and tickets. Ecology of Tropical Savannas. Ecological Studies 42: 48–79. Springer Verlag, Berlin. de la Balze, V. 2004. El Chaco americano: consideraciones iniciales. In: Fundación Hábitat y Desarrollo (eds.), El gran Chaco americano. Buenos Aires, Argentina. Gill, A.M. 1995. Stems and fires. In: B.L. Gartner (ed.), Plant stems. Physiology and functional morphology: 323–342. Academic Press, Inc. Giménez, A. 2003. El fuego y el crecimiento de Prosopis nigra. In: C. Kunst, S. Bravo & J. Pani- gatti (eds.), Fuego en los ecosistemas Argentinos: 157–165. Ediciones INTA, Argentina. Giménez, A. & J. Moglia. 1995. Estructura cortical de Anacardiáceas argentinas. Investigación Agraria y Recursos Forestales 4: 189–203. Giménez, A. & N. Ríos. 1999. Crecimiento de Schinopsis quebracho-colorado (Schlecht.) Barkl. et Meyer, Anacardiaceae. Madera y Bosques 5 (2): 36–51. Giménez, A., N. Ríos & J. Moglia. 1997. Leño y corteza de Itín Prosopis kuntzei (Harms) en rela- ción a algunas magnitudes dendrométricas. Investigación Agraria Sistema y Recursos For- estales 6: 163–182.

Downloaded from Brill.com09/30/2021 05:30:20AM via free access 292 IAWA Journal, Vol. 31 (3), 2010

Giménez, A., N. Ríos, J. Moglia & C. López. 1998. Leño y corteza de Prosopis alba Griseb., algarrobo blanco, Mimosaceae, en relación con algunas magnitudes dendrométricas. Bosque 19: 53–62. Gourlay, I. & G. Grime. 1994. Calcium oxalate cristals in African Acacia species and their anal- ysis by scanning proton microprobe. IAWA J. 15: 137–148. Grau, H., T. Easdale & L. Paolini. 2003. Subtropical dendroecology. Dating disturbances and forest dynamics in northwestern Argentina montane ecosystems. Forest Ecology and Man- agement 177: 131–143. Hengst, G.E. & J. Dawson. 1994. Bark properties and fire resistance of selected tree species from central hardwoods region of North America. Can. J. For. Res. 24: 668–696. Hueck, K. 1978. Los bosques de Sudamérica. Ecología, composición e importancia económica. Sociedad Alemana de Cooperación Técnica (GTZ), Munich. Johansen, D.H. 1940. Plant michotechnique. McGraw-Hill, New York. Kitzberger, T., T. Veblen & R.Villalba. 2000. Métodos dendroecológicos y sus aplicaciones en estudios de dinámica de bosques templados de Sudamérica. In: F.A. Roig (ed.), Dendro- cronología de América Latina: 17–78. EDIUNC, Mendoza, Argentina. Kunst, C. & S. Bravo. 2003. Ecología y régimen de fuego en la región chaqueña argentina. In: C. Kunst, S. Bravo & J. Panigatti (eds.), Fuego en los Ecosistemas Argentinos: 109–118. Ediciones INTA, Argentina. Larson, P. 1994. Vascular cambium. Development and structure. Springer Verlag, Berlin. Lee, S., S. Teng, M. Lim & A. Rasali. 1988. Discolouration and heart rot of Acacia mangium - some preliminary results. Journal of Tropical Forest Science 1 (2): 170–177. Moglia, J.G. 2000. Variabilidad de los caracteres anatómicos del leño de Aspidosperma quebracho-blanco (Schlecht.), Apocynaceae. Tesis Doctoral, Universidad Nacional de Tucumán, Argentina. Moglia, J. & C. López. 2001. Variabilidad radial de algunos caracteres anatómicos de Aspido- sperma quebracho-blanco. Bosque 22: 3–14. Morello, J. & J. Adámoli. 1968. Las grandes unidades de vegetación y ambiente del Chaco ar- gentino. Primera Parte. Objetivos y metodología. Serie Fitogeográfica 10. Ediciones INTA, Argentina. Quirk, J. & D. Smith. 1975. Comparison of dual linear and dot grid eyepiece methods for esti- mating wood properties of Douglas fir. Wood Science 8: 92–96. Rademacher, J., J. Bauch & A. Shigo. 1984. Characteristics of xylem formed after wounding in Acer, Betula and Fagus. Development and characteristics of discoloured woods. IAWA Bull. n.s. 5: 141–151. Schmitt, U., W. Liese, H. Thong & W. Killmann. 1995. The mechanism of wound response in Acacia mangium. IAWA J. 16: 425–432. Smith, K. & E.K. Sutherland. 2001. Terminology and biology of fire scars in selected Central Hardwoods. Tree-Ring Research 57: 141–147. Sutherland, E.K. & K. Smith. 2000. Resistance is not futile: The response of hardwoods to fire- caused wounding. In: Proceedings Workshop on Fire, People and the Central Hardwoods Landscape. General Technical Report NE274: 111–115. USDA Forest Service. Tálamo, A. & S. Caziani. 2003. Variation in woody vegetation among sites with different distur- bance histories in the Argentine Chaco. Forest Ecology and Management 184: 79–92.

Downloaded from Brill.com09/30/2021 05:30:20AM via free access