ONSERVATION ISSUE ABSTRACT: We analyzed differences in vertical plant structure and species composition between three sites with different disturbance levels in calden (Prosopis caldenia) forest in the Parque Luro Reserve, Argentina. One of the sites corresponded to a forest affected by a natural fire 15 years before the study. The remaining two sites, an open forest and a closed forest, were areas where wildfires have never been reported. Woody plant diversity, richness, and shrub density were significantly lower in the open forest than in the closed and burned forests, with the closed and burned forests having similar plant diversity • and richness. The burned area also showed the highest percentage of foliage cover in the shrub strata (0.75-3 m height) even when the shrub/sapling density was similar to that of the closed forest. This Changes in Woody suggests that fires in calden forest play an important role in the physiognomy of shrub species. There was little evidence in our study for the establishment of new species as a consequence of wildfires and Plant Structure only one species occurred exclusively in the burned area of the Reserve. Index terms: Argentina, Parque Luro Reserve, Prosopis caldenia, wildfires, woody plant structure and in Fire-disturbed diversity
Calden Forest of the INTRODUCTION American occupation (1787-1879) to once every 7.25 years during the European Colo Parque Luro Reserve, Calden (Prosopis caldenia [Burkart]) for nization period (1911-1993). Medina et al. ests are characteristic of the landscape in (2000) also found that the frequency and Argentina the Espinal biome in the semi-arid pampas the extension of fires in the Caldenal have of central Argentina (Cabrera 1976; Figure increased since 1910, which is supported 1). This 40,000-km2 area of xerophitic by fire records on La Pampa province. vegetation, commonly called Caldenal, Jose Hernan Sarasola1 originally consisted of open forests domi The effects of cattle grazing and natural Department of Applied Biology nated by calden trees, concentrated mostly and prescribed fires on calden forests Estacion Biologica de Donana in valleys, and by grasslands on dunes and have been well documented. However, Avda. de Maria Luisa sin plateau (Cano et al. 1980). Since farming most studies have dealt with the effects Pabellon del Peru began in the early 20th century, calden of these disturbances on ecophysiology 410 13 Sevilla, Espana forests have changed in a number of ways. (Pisani et al. 1999), seed germination (De The most serious landscape modification Villalobos et al. 2002), and seeds bank has been the transition from open forest to (Mayor et al. 1999, Mayor et al. 2003). laura Araceli Bragagnolo shrub land or woodland with a high density There is also considerable information on of young calden trees and brushes. The Ramon Alberto Sosa the ecological implications of these distur history of human use of calden forests is bances on calden forest related to effects acultad de Ciencias Exactas y Naturale related to wood extraction, extensive cattle on plant competition (Pelaez et al. 1994) Universidad Nacional de La Pampa raising, and non-irrigated agriculture after and herbivory (Boo et al. 1993, Peinetti Avenida Uruguay 151 forest cutting. Although large-scale for et al. 1993, Distel et al. 1996). Limited 6300 Santa Rosa est cutting has decreased during the last studies, however, have assessed the ef La Pampa, Argentina decades due to the high economic costs fects of wildfires on its plant composition of such operations, cattle ranching and and structure. Only Dussart et al. (1998) deforestation of small areas for firewood examined calden densities in a comparative • remain as important human activities . study of two areas where fires occurred 18 and 34 years prior to their study, and Wil Accidental wildfires are now the most lard (1973) and Boo et al. (1997) evaluated important factor in the modification of plant survival and abundance in selected calden forests. An estimated 5.6 million species after controlled and accidental fires ha of calden forest were burned in La in southern Caldenal. Pampa province between 1976 and 2002 (Sipowicz 1994, and unpubl. data from In this study, we evaluated the effect of the government of La Pampa province). natural fires on the vertical structure and 1 Corresponding author: Recent dendrochronological studies in woody plant composition of calden forests [email protected]; +3495423 23 40 calden forests (Medina et al. 2000) have in the Parque Luro Reserve, central Argen shown that the fire regime in the area tina. We compared density, richness, and has changed over the last 200 years. The diversity of woody plant species and plant Natural Areas Journal 25:374-380 frequency of fire has increased from once structure in three areas. '!Wo of the areas every 14 years during the interval of Native corresponded to non-burned forests that
374 Natural Areas Journal Volume 25 (4),2005 differed in plant structure and physiognomy as well as in their current use. The other area consisted of a calden forest burned 15 years before the study. N
MATERIAL AND METHODS Study Site * The Parque Luro Reserve is located in east em La Pampa province, central Argentina (Figure 1). The reserve (7604 ha.) consists mainly of xerophytic forests of Prosopis ARG E tl TIN A caldenia. Grasses such as Stipa spp. are the dominant herbaceous species of the PACIFIC lower stratum, and Condalia microphylla OCEAN (Cav.), Lycium chilense (Miers), L. gil liesianum (Miers), and Schinusfasciculatus (Griseb.) are the common shrub species whenever a middle stratum is present. Areas surrounding the reserve consist of agricultural lands planted with crops and perennial and annual pastures. The climate is continental semi-arid with hot summers and cold winters with low humidity and low annual rainfall, typically concentrated in spring and summer. However, unusually high rainfalls have occurred during the last decade. The mean annual rainfall has increased from its historic value of 500-600 ATLANTIC· mm (Cano 1980) up to a mean of 791 mm OCEAN for the last ll-year period.
The area was declared as aNatural Reserve for the government of La Pampa province km in 1965. Prior uses of the area included 1*""""1 i I introduction of exotic animal species in o 200 400 - 50° 1907 for game and hunting (Amieba 1992). Although many species did not prolifer ate, others, such as the red deer (Cervus - 75" -60" elflphus 1,.) and the V{ild b()ar(Susscroia L.), adapted well to this habitat; and at the present, they are the only large herbivores Figure 1. Distribution of cal den forests in central Argentina (shaded area) and approximate location of the Parque Luro Reserve (solid circle). on it. Wood extraction and cattle raising occurred· in the area between 1920 and 1940 (Arnieba 1992), but these practices was in the visitor use area of the reserve and forest that was burned by a wildfire in have long since been excluded. The Parque consisted of an open forest of calden with January 1987. Luro Reserve is the only protected area in a grassland stratum and a reduced shrub the Caldenal. layer, features that are in part conditioned Only the visitor use area was open to the by soil characteristics (sandy soils); (2) The public. Sampling was conducted during "closed forest" area in the southern portion March and April 2002 in 30 randomly Study design of the reserve has had no human or natural located circular plots of 25 m radius (10 disturbances in the last 60 years; and (3) plots per area). Sampling was conducted in three selected The "burned forest" area consisted of an areas of the Reserve: (1) The "open forest" area of approximately 2000 ha of natural
Volume 25 (4),2005 Natural Areas Journal 375 Plant structure and profile calculated both with and without these few and very old specimens of calden tree specimens. Trees were considered dead concentrate foliage at such heights) rather We used a sampling method developed for when adult trees were scorched and there than to disturbance effects. In terms of Chaco forest by Lopez de Casenave et al. was no evidence of sprouting. relative foliage cover, P. caldenia, Schinus (1995). In the center of each randomly-lo Jasciculatus, Condalia microphyUa, and cated plot, we established a 25 m transect Lycium gilliesianum dominated the ground Statistical analysis in each of the four cardinal directions. We and shrub strata. Only in the burned forest sampled vegetation structure at 10 random did S. Jasciculatus show lower relative val We evaluated differences in horizontal points on each transect by erecting a rod ues than P. caldenia, the dominant species plant cover and vegetation profiles be marker and recording the height of each in the other two areas for the ground-shrub tween the three areas by using one-way plant species that contacted the rod. For strata. The calden also showed the largest ANOVA with Tukey "a posteriori" test for this procedure, we measured at 25 cm values of foliage coverage for the sub paired comparison of means (Zar 1996). intervals in the first 4 m of the rod and at canopy and canopy strata. Logarithm transformation was used when 1 m intervals from 4 to 8 m. We depicted assumption of normality was not achieved. profiles of foliage cover as the percentage When assumptions were not met even Plant density, species richness, and of points with contacts at each interval before logarithm transformation, data diversity and averaged values over the 10 plots in were analyzed using the non-parametric each area. We also included grasses and Kruskal-Wallis and Mann-Whitney U tests Density of woody plant, differed among herbaceous plant species in our analysis (Zar 1996). sites (ANOVA: F . 22.32, P < 0.01), by estimating plant cover at each of the 227 = with the burned forest showing the highest four principal strata present in the forests: density followed by the natural forest and (1) ground, 0-0.5 m, (2) shrub, 0.75-3.00, RESULTS the open forest, respectively (Tukey test: P (3) sub-canopy 3.25-6 m, and (4) canopy < 0.05). Tree density was the same for all from 6 to >8 m. Plant profile and horizontal cover areas (Kruskal-Wallis test: H = 1.11, n =30, P =0.57), with significant differences only Woody plant density and floristic There was a distinct vertical stratification in the shrubs/sapling densities among the composition of vegetation in the three areas with high three forest types (ANOVA: F2.27 = 16.22, foliage cover in the ground layer (i.e., P
376 Natural Areas Journal Volume 25 (4), 2005 >8 :\ : \ 8 ~ \ ". \ Burned forest \ Closed forest \ 7 "- Open forest "- "- 6 \ ..- \ E \ "-"..... 5 \ ..c \ 0> 'Q3 4 \ I 3
2 ...... 1 '-,------0 --- 0 20 40 60 80 100 Cover (%)
Figure 2. Vertical structure expressed as average profile of foliage cover at different heights in the burned, closed, and open calden forests of the Parque Luro Reserve, La Pampa, Argentina.
DISCUSSION specimens. Now, however, the plant Prior to the fire, the burned area of the structure and physiognomy of the burned This study provides an initial assessment reserve was similar in appearance to the forest is characterized by a dense cover of of the changes in vegetal structure and closed forest area we analyzed in our study shrubs up to 3 m followed by a decrease composition in a burned calden forest. in that it had well-developed sub-canopy in cover in the sub-canopy and canopy Our results should be considered as pre and canopy strata with a conspicuous but layers. Despite this difference, the burned liminary since only an adequate replication not extremely dense shrub layer (Amieba and closed forests still share some floristic of burned and unburned sites would allow 1992). For example, the density of calden features. The two areas have similar plant a broad generalization of the effects of trees in burned and closed areas is almost diversity and richness and some of the wildfires in the Caldenal. the same when considering the scorched shrub and trees species not observed in the open forest, such as Chuquiraga erinacea (D. Don), Prosopis alpataco (Phil.), and Table 1. Mean horizontal coverage (0/0) ± S.D. for shrub species and tree saplings in ground-shrub Geoffroea decorticans (Gillies ex Hook. strata and for cal den tree in the sub-canopy and canopy strata in Parque Luro Reserve, La Pampa, et Arn.) were recorded in the burned and Argentina. closed forests. Our results agree with those of Talamo and Caziani (2003) that Strata Burned forest Closed forest Open forest also found similar values of plant species Ground-shruba 73.60 ±22.4 64.99 ± 27.50 76.28 ± 38.53 richness among primary and burned areas of Chaco forest. Sub-canopy and canopy 60.37 ± 38.13 88.62 ± 11.33 98.48 ± 2.69 The plant structure and physiognomy of aInclude Condalia microphylla, Lycium chilense, L. gillesianum, Prosopis the open forest reassembles the typical caldenia, Schinus fasciculatus and Geoffroea decorticans. physiognomy of calden forest in deep valleys and plateaus, which are considered
Volume 25 (4), 2005 Natural Areas Journal 377 climax plant communities (Llorens 1995). 100.------, The open forest had the lowest values for species richness and diversity. Species ac _ Burned forest diversity is often greatest at intermediate 80 I,,'~,d Closed forest levels of disturbance (Petraitis et al. 1989) f2ZLI Open forest indicating that the low values we recorded in the open forest could be related to the limited amount of disturbance that has ~ 60 occurred in this habitat. Modification of ~ L.. this area has been related to the alteration of small areas of native forest to facilitate o~ () 40 tourist activities (i.e., the establishment of new roads and recreation areas). The effects of such practices on calden forest could lead to some forest fragmentation 20 and the subsequent increase of the edge area of patches, rather than to a general and broad extended modification of the plant 0-'---- structure. The sampling design used here Ground Shrub Sub-canopy Canopy was more suited to detect general spatially distributed changes on vegetal structure and Strata composition than to record this edge effect on forest fragments (for which further and Figure 3. Mean horizontal coverage (and 1 S.D. indicated by vertical line) ofthe four strata in the burned, specific studies at a minor scale are needed; closed, and open calden forests in Parque Luro Reserve, La Pampa, Argentina. Means with the same see, Lopez de Casenave et al. 1995). letter indicate non-significant differences at P = 0.05 (Mann-Whitney U tests).
3500
3000 ..- ~ I ct:l ..c 2500 x en ct:l - :::::I 2000 "'C :~ "'C C- 1500 >. 'w...... c Q) "'C 1000 ...... C ct:l a.. 500
0 - - Burned forest Closed forest Open forest
Figure 4. Mean tree and shrub densities (± S.D.) in the three areas of cal den forests in Parque Luro Reserve. Open circles are shrub/sapling densities and solid circles are tree densities.
378 Natural Areas Journal Volume 25 (4),2005 Calden trees dominated the forests we alpataco (Phil.). the effect of wildfires on bird species as- . studied in both sub-canopy and canopy semblages in calden forest. strata. The amount of foliage cover of The fire that burned our study area is sus calden in these strata differed among areas, pected to have been very hot and, therefore, Ramon Alberto Sosa is a Professor ofBio with highest foliage cover occurring in the had a more destructive impact on the calden logical Diversity at Universidad Nacional open forest followed by closed and burned forest. The high number of scorched calden de La Pampa, Argentina. His research forests, respectively. In addition to calden, trees, 55%, evidences this even when they focuses on the effects ofcaldenforestfrag foliage coverage also resulted from other all sprouted. Dussart et al. (1998) found mentation on bird species assemblages. tree species (e.g. Geoffroea decorticans) 5.2 % and 1.1 % of dead individuals at two and shrub species (e.g. S. fasciculatus), sites of burned calden forest, and Boo et al. which reach heights two times greater (1997) recorded only 2.5% of dead calden LITERATURE CITED in burned and closed forests than in the after an accidental fire. Willard (1973) re open forest. ported a 50% mortality in calden trees one Amieba, E.O. 1992. El Parque Luro. Su origen, year after a fire (but this estimate may not su historia, su presente. Fundacion Chad Increased light availability resulting from be an accurate representation of the final ileuvu, Santa Rosa, Argentina. canopy removal and the reduction of mortality attributed to the fire). Boo, R.M., L.1. Lindstrom, O.R. Elfa, and competition within plant communities M.D. Mayor. 1993. Botanical composition through the elimination of trees is known and seasonal trends of cattle diets in central ACKNOWLEDGMENTS to stimulate germination and enhance Argentina. Journal of Range Management growth of pioneer species (Keeley 1987). 46:479-482. We than~ D. Caldentey, M. Reyes, and We found supporting evidence for this Boo, R.M., D.V. Pelliez, S.C. Bunting, M.D. N. Sansot for their valuable help during when we studied the burned vs. the closed Mayor, and O.R. Elfa. 1997. Effect of fieldwork and E. Morici for help in plant forest. Although some particular shrub spe fire on woody species in central semi-arid identification. The Direccion de Recursos Argentina. Journal of Arid Environments cies showed densities two and three times Naturales, Gobierno de La Pampa, made 35:87-94. greater in the burned area than the closed this work possible by giving permission to Cabrera, A 1976. Regiones Fitogeognificas forest, the differences in the overall shrubs carry out fieldwork in Parque Luro Reserve. Argentinas. Enciclopedia Argentina de density between these two areas were not The senior author had a fellowship from Agricultura y Ganaderia. Acme, Buenos statistically significant. However, foliage the Consejo Nacional de Investigacio Aires, Argentina. cover for shrub strata differed between nes Cientfficas y Tecnicas de Argentina Cano, E., B. Fernandez, and M. Montes. 1980. these two forests type. This suggests that (CONICET). This study was supported by Vegetation. Pp. 77-78 in INTA, Provincia the increase of foliage cover in the shrub de La Pampa and Universidad Nacional a grant (PI 122) from the Departamento de strata in calden forest after fire distur de La Pampa. Inventario Integrado de los Recursos Naturales, Facultad de Ciencias bance is linked to the dominance in plant Recursos Naturales de La Provincia de La Exactas y Naturales, U niversidad N acional community of species having a sprouting Pampa, Buenos Aires, Argentina. de La Pampa. We thank the Natural Areas strategy in response to fire (sensu Whelan De Villalobos, AE., D.V. Pelaez, R.M. Boo, Journal Editorial Board for helpful review 1995) which may determine highest cover M.D. Mayor, and O.R. Elfa. 2002. Effect comments. of high temperatures on seed germination in the shrub stratum for the burned for of Prosopis caldenia Burk. Journal of Arid est without an increase in the number of Environments 52:371-378. shrubs per area. Our results agree with lose Hernan Sarasola graduatedfrom the Distel, R.A, D.V. Pelaez, R.M. Boo, M.D. those of Boo et al. (1997) who, in their UniversidadNacional de La Pampa, Argen Mayor, and O.R. Ella. 1996. Growth of study area on southern Caldenal, observed tina, in Natural Resources and is currently Prosopis caldenia seedlings in the field as little variation on shrub abundance of the related to grazing history of the site and in a PhD student at the Dofiana Biological principal woody species following fire a greenhouse related to different levels of Station, Spain. He has been conducting events. There was little evidence for the competition from Stipa tenuis. Journal of research works on Parque Luro Reserve establishment of new colonizing species Arid Environments 32:251-257. since 1998, studying the breeding biology, after fire in our study and we only found Dussart, E., P. Lerner, and R. Peinetti. 1998. foraging ecology, and habitat selection of one species, Senna aphylla, to occur ex Long term dynamics of two popUlations of birds of prey in this protected area. Prosopis caldenia Bukart. Journal of Range clusively in the burned area. Other species, Management 51:685-691. when we compared their densities among Laura Araceli Bragagnolo also graduated Keeley, J.E. 1987. Role of fire in seed germina burned and unburned areas, seem to have from the Universidad Nacional de La tion of woody taxa in California chaparral. a pioneer-type behavior: lodina rhom Pampa, Argentina, in Natural Resources. Ecology 68:434-443. bifolia (Hook et Am; occurring as trees She is currently involved in the Master Llorens, E.M. 1995. Viewpoint: the state and and saplings), Geoffroea decorticans and Program on Conservation Biology of the transition model applied to the herbaceous Prosopis flexuosa (DC.; saplings), and all Universidad Internacional de Andalucfa layer of Argentina's calden forest. Journal the shrub species with the exemption of of Range Management 48:442-447. (Spain). Her thesis project is focused in Ephedra ochreata (Miers) and Prosopis Lopez de Casenave, J., J.P. Pelotto, and J.
Volume 25 (4),2005 Natural Areas Journal 379 Protomastro. 1995. Edge-interior differences Peinetti, R., M. Pereyra, A. Kin, and A. Sosa. Sipowicz, A.H. 1994. Ecologia y manejo de in vegetation structure and composition in 1993. Effects of cattle ingestion on viability fuego en el ecosistema del caldenal. Bo a Chaco semi-arid forest, Argentina. Forest and germination rate of calden (Prosopis letin de Divulgacion Tecnica No. 51. EEA Ecology and Management 72:61-69. caldenia) seeds. Journal of Range Manage Anguil, Instituto Nacional de Tecnologia Magurran, A.B. 1989. Diversidad Ecologica y ment 46:483-486. Agropecuaria, Argentina. su Medicion. Vedra, Barcelona, Spain. Pelaez, D.V., R.A. Distel, R.M. Boo, O.R. Elfa, Talamo, A., and S.M. Caziani. 2003. Variation Mayor, M.D., R.M. Boo, D.V. Pelaez, and O.R. and M.D. Mayor. 1994. Water relations in woody vegetation among sites with dif Elfa. 1999. Seasonal variation of seed bank between shrubs and grasses in semi-arid ferent disturbance histories in the Argentine ofMedicago minima and Erodium cicutarum Argentina. Journal of Arid Environments Chaco. Forest Ecology and Management as related to grazing history and presence of 27:71-78. 184:79-92. shrubs in central Argentina. Journal of Arid Petraitis, P.S., R.E. Latham, and R.A. Niesen Whelan, R.J. 1995. The Ecology of Fire. Cam Environments 43:205-212. baum. 1989. The maintenance of species bridge University Press. Cambridge, U.K. Mayor, M.D., R.M. Boo, D.V. Pelaez, and O.R. diversity by disturbance. Quarterly Review Willard, E.B. 1973. Effect of wildfires on woody Elfa. 2003. Seasonal variation of the soil of Biology 64:393-418. species in the Monte Region of Argentina. seed bank of grasses in central Argentina as Pisani, J.M., and R.A. Distel. 1999. Production Journal of Range Management 26:97-100. related to grazing and shrub cover. Journal of phenols and spines in response to shoot Zar, J.H. 1996. BioestatisticalAnalysis, 3rd ed. of Arid Environments 53:467-477. damage in Prosopis caldenia and Proso Prentice Hall, Princeton, N.J. Medina, A., E.G. Dussart, H.D. Estelrich, and pis flexuosa. Journal of Chemical Ecology E.A. Morici. 2000. Reconstruccion de la 5:1141-1150. historia de fuego en un bosque de Prosopis caldenia (Burk.) de Arizona, sur de la pro vincia de San Luis. Multequina 9:91-98.
380 Natural Areas Journal Volume 25 (4), 2005