Fire Tolerance and the Fire-related Sprouting Characteristics of Two Cool-temperate Broad-leaved Tree Species

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1 Annls of Botny 85: 37 42, 2 Article No. nbo.999.7, vilble online t http: on Fire Tolernce nd the Fire-relted Sprouting Chrcteristics of Two Cool-temperte Brod-leved Tree Species KAZUHIKO MASAKA*, YASUYUKI OHNO nd KENJI YAMADA * Hokkido Forestry Reserch Institute, Dohoku Brnch Sttion, Homre 3, Nkgw, Hokkido , Jpn nd Hokkido Forestry Reserch Institute, Dohoku Brnch Sttion, Otoineppu Sub-Sttion, Otoineppu, Hokkido 98-25, Jpn Received: 3 August 999 Returned for revision: 3 September 999 Accepted: 28 September 999 This study ws conducted in secondry brod-leved forest in northern Hokkido, Jpn, which burned on 2 2 April 998. The study plot, set up on 3 July 998, contined Quercus mongolic vr. grosseserrt nd Betul pltyphyll vr. jponic trees. The ltter were more severely dmged by the fire. Size-dependent survivorship ws observed in both species with lrger trees being more likely to survive the fire. However, mny lrge Betul trees were completely destroyed. Both species developed bundnt root collr sprouts immeditely fter the fire. The number of sprouts rnged from to 296 in Betul nd from to 34 in Quercus. Trees with no sprouts were not necessrily ded. The frequency distribution of the sprouting pttern in Betul ws bimodl. This ws relted to dmge severity, with the most bundnt sprouting mnifest in the most severely dmged trees. This pttern ws not observed in Quercus. Stem dimeter lso ppered to influence the extent of sprouting in Betul, while in Quercus there ws no distinct correltion between bsl re nd the number of sprouts. In Betul, the reltionship between the number of sprouts nd the dmge severity suggests trde-off in resource lloction for sprouting s. shoot flushing in the crown. 2 Annls of Botny Compny Key words: Betul pltyphyll vr. jponic, fire, fire tolernce, Quercus mongolic vr. grosseserrt, resource lloction, root collr sprouting, stem dimeter size. INTRODUCTION Fire commonly disturbs forests worldwide nd mny tree species respond by sprouting, even fter most of their folige hs been destroyed (Kozlowski et l., 99). It is well known tht trees in semi-rid regions re prticulrly well dpted to fire nd hve vigorous sprouting bility tht enbles them to survive recurring fire (Trbud nd Leprt, 98; Uemur et l., 99; Lo pez-sori nd Cstell, 992). On the other hnd, trees of tropicl rinforests, in which nturlly-occurring fires re rre nd where trees re believed to show very few dpttions relted specificlly to post-fire survivl, cn lso sprout nd survive fter n intense fire (Kuffmn, 99). However, there is very little documenttion of the sprouting response of trees following fire in moist temperte forests, where fire is often cused by humn ctivity. The loss of leves in fire generlly releses the dormncy of specilized epicormic buds tht survive under the brk (Kozlowski et l., 99). The bility of trees to sprout from the root collr nd stem is species-specific chrcteristic (Kuffmn, 99; Bellinghm et l., 994, 996; Sonoym et l., 997) tht is closely connected to ptterns of resource deployment (Ski nd Ski, 998). Bellinghm et l. (994) reported sprouting of trees in Jmicn montne forests in response to severe physicl dmge cused by strong wind, nd showed tht broken trunks produced more sprouts thn intct trunks, despite the fct tht there ws no For correspondence. E-mil msk hfri.bibi.hokkido.jp $35. difference between uprooted nd upright trunks. Although the brnches of tree re likely to still be live fter the folige is stripped by strong wind, lmost ll the minor brnches re likely to succumb to crown fire. Tht is, the severity of fire dmge to the crown should hve much greter effect thn wind dmge on sprouting bility. Furthermore, the greter the severity of the crown dmge, the more seriously species- nd size-specific sprouting bility is ffected, since fire tolernce nd resource storge strtegies vry with species nd individul size. Ski nd Ski (998) cut the trunks of severl tree species t vrious heights, nd demonstrted tht the resource storge strtegy nd resource deployment ptterns were strongly relted to sprouting bility. However, there re few studies of the reltionships between fire tolernce, severity of dmge, nd sprouting bility of species nd individul trees. In Hokkido, northern Jpn, lrge-scle fires were frequent following settlement in the Meiji Er (lte 9th century) until erly in the Show Er (erly 2th century) (e.g. Tkok nd Ss, 996). Mny of the forests in the region hve never recovered sufficiently to resume the norml process of succession (e.g. Tkok nd Ss, 996). Smll fires still occur spordiclly nd continue to influence forests in the region. A fire t Nishiokoppe in northern Hokkido in 998 presented n opportunity to document the immedite effects of fire nd to consider their long-term implictions on forest composition. In this study, we ddressed the following questions. () Were there differences in the wys in which trees of different size nd species were ffected during the fire? (2) To wht extent does sprouting bility 2 Annls of Botny Compny

2 38 Msk et l. Fire Tolernce nd Subsequent Sprouting in Brod-le ed Trees differ with size nd species? (3) To wht extent does the severity of dmge ffect the sprouting bility of individul trees? The nswers to these questions should llow us to consider the implictions of fire dmge on the dynmics of cool-temperte brod-leved forests, such s those in northern Hokkido, Jpn. MATERIALS AND METHODS Study site The study ws crried out in secondry cool-temperte brod-leved forest in Nishiokoppe, northern Hokkido, Jpn (43 3 N, E, 22 m.s.l). Betul pltyphyll vr. jponic Hr nd Quercus mongolic vr. grosseserrt Rehd et Wils. re the dominnt species. Other species, such s Populus tremul vr. d idin Schnneid, Acer mono Mxim, Mgnoli obo t Thunb., Sorbus lnifoli C. Koch, nd Klopnx pictus Nki, re sometimes mixed in the forest. The soil is loclly referred to s brown forest soil, nd the forest floor is minly covered with dwrf bmboo, Ss sennensis Rehder. Precipittion in the region is pprox. mm per yer. The men monthly tempertures during the wrmest (August) nd coldest (Jnury) months re 8 5 nd 7 2 C, respectively. A wrmth index of 52 C month indictes tht the region is locted between the cool-temperte nd sub-borel zones (Kir, 977). The forest floor is usully snow-covered from December until the following April. Nishiokoppe belongs to the Okhotsk climtic zone. The foehn ( fo hn) phenomenon in erly spring, just fter the snow cover disppers, is climtic chrcteristic of the region (O kw, 992). The foehn phenomenon involves wrm dry winds tht blow down from the mountins. The study re burned on 2 22 April 998, when the ir temperture reched mximum of 27 9 C with the foehn phenomenon. Almost ll of the vegettion on the forest floor ws burned nd when we surveyed the forest on 22 June 998, there were bundnt sprouts from the root collrs of injured deciduous brod-leved trees. An 8 m m study plot ws estblished in the burned forest on the gentle sloping ridge of hill on 3 July 998. Trees in the study plot were tgged; their stem dimeter t brest height (dbh) ws mesured nd the number of new sprouts counted. The species composition in the study plot is shown in Figure. The principl species studied were B. pltyphyll vr. jponic nd Q. mongolic vr. grosseserrt, the dominnt species in the study plot. Herefter, we will refer to these two species s Betul nd Quercus, respectively. There were no sprouts from the upper trunks, so in this pper, the term sprout is restricted to root collr sprout. There were few sprouts tht hd been dmged by herbivores, such s rodents, nd these were counted together with the current undmged sprouts. Dmge severity ws divided into the following ctegories, scoring crown survivl score by eye mesurement:, no folige in the crown, only stnding trunk remined, which ws considered to be ded;, less thn 25% of the folige survived nd the mjority of the crown ws lost; 2, prtilly dmged, 25 75% of the folige survived; 3, dmged, but Frequency (no.) dbh clss (cm) FIG.. Size-clss frequency histogrms in the study plot. ( ) Betul pltyphyll vr. jponic; ( ), Quercus mongolic vr. grosseserrt; ( ) Acer jponic nd A. mono; ( ) Klopnx pictus; ( ) Mgnoli obo t, Prunus srgentii nd Tili jponic. more thn 75% of the folige survived; 4, intct, unscthed crown. Lrge trees re expected to tolerte fire better thn smll trees, becuse their crown is more elevted nd their brk is thicker. One-wy ANOVA ws conducted to test the differences in stem size (dbh) nd survivl score. The mortlity of ech dbh clss ws defined s the proportion of trees with survivl score compred to the number of trees in the dbh clss. The resource potentil of the surviving body of the tree ws therefore ssessed lrgely in reltion to the size of tree. A regression nlysis ws lso conducted to evlute the reltionship between trunk size expressed s the log-trnsformed bsl re (BA π[dbh 2] ) to the logtrnsformed (number of sprouts ) for different survivl scores. These nlyses were pplied to both Betul nd Quercus. RESULTS Sur i l mode during fire The reltionship between survivl score nd tree size ws positive in both species (Fig. 2A nd B; one-wy ANOVA nd Tukey s HSD test, P 5). As expected, these results indicted tht fire dmged smll trees more intensively thn lrge trees. The mortlity of Betul ws higher thn tht of Quercus in ll size-clsses (Fig. 3). Mny lrge Betul trees were ded, while few lrge Quercus trees died, mking the mortlity of the lrge Betul much higher thn tht of Quercus (Fig. 3). The crown position of ech species seemed to hve no effect on the dmge severity, since the brk of brnches in the crown ws not chrred. Sprouting chrcteristics We observed vigorous sprouting in both species. The mximum number of sprouts in Betul ws 296, while in Quercus it ws 34. The sprouting frequency distribution ws bimodl in Betul, nd L-shped in Quercus (Fig. 4A nd 3

3 Msk et l. Fire Tolernce nd Subsequent Sprouting in Brod-le ed Trees 39 dbh (cm) A B b 2 b b 3 4 Number of trees A 2 2 < 2 2 < 2 3 < 2 4 < 2 5 < 2 6 < 2 7 < 2 8 < 2 9 B 2 b b b < 2 2 < 2 3 < 2 4 < 2 5 < 2 6 < 2 7 < 2 8 < 2 9 Number of sprouts FIG. 4. Log-scled number-clss frequency histogrm of sprouts per tree for B. pltyphyll vr. jponic (A) nd Q. mongolic vr. grosseserrt (B). Survivl scores: ( ) ;( ) ;( )2;( ) 3;( ) Survivl score FIG. 2. Boxplots of the dbh of B. pltyphyll vr. jponic (A) nd Q. mongolic vr. grosseserrt (B) for different survivl scores. The smple is represented s box whose top nd bottom re drwn t the upper nd lower qurtiles, respectively. The box is divided t the medin. Verticl lines re drwn from the top nd bottom of the box to the 9th nd th percentiles, respectively. The closed squre indictes the men dbh. Mens tht shre the sme letter do not differ significntly within species (P 5). Mortlity (%) Betul Quercus 2 dbh size-clss (cm) FIG. 3. Mortlity of trees in ech size clss. B). In Betul, the two peks suggest lterntive responses of sprouting or not sprouting. The men number of sprouts is likely to increse with dmge severity. These fetures were 3 not observed in Quercus (Fig. 4 B). The stem dimeter ppered to influence sprouting in Betul (Fig. 5A; R 8, F 928, P 2, n 56), especilly in the ded trees (survivl score ) (R 755, F 4 7, P, n 5). However, there ws no significnt correltion between bsl re nd the number of sprouts when the trees without sprouts were excluded from the nlysis. In Quercus, there ws no correltion between bsl re nd the number of sprouts (Fig. 5B; R 49, F 74, P 2, n 35). In Quercus, the mximum number of sprouts ws seen in slightly lrger nd prtilly surviving trees. Tolernce to fire DISCUSSION In the study plot, the fire tolernce nd sprouting bility of Betul differed mrkedly from tht of Quercus. The fire only slightly dmged lrge Quercus trees (Fig. 2 B), which suggests tht the brk of these trees ws thick enough to resist the fire. The brk of oks contins bundnt sclerenchym tissue, especilly interlocking fibres. Consequently, cells outside the periderm remin coherent, resulting in very thick brk nd, hence, high tolernce to fire (Krmer nd Kozlowski, 979). On the other hnd, lthough size-dependent tolernce lso pplied in Betul, mny lrge trees were completely burned (Fig. 2A). The brk of birch species is thin nd contins lrge mounts of terpene, contributing to its low criticl temperture for ignition. The reltively inflmmble Betul brk probbly contributes to the bimodl distribution of dmge severity (Fig. 2 A). A difference in fire tolernce relted to brk thickness is lso recognized in fire prone ecosystems such s Siberin tig

4 4 Msk et l. Fire Tolernce nd Subsequent Sprouting in Brod-le ed Trees Number of sprouts + 5 A 5 B Number of sprouts brek point = 2 35 Bsl re (cm 2 ) FIG. 6. Simultion of tree-size sprouting reltionship for different survivl scores in B. pltyphyll vr. jponic. The survivl score is shown in the inset box. Bsl re (cm 2 ) FIG. 5. Reltionship of bsl re to sprouts per tree for different survivl scores in B. pltyphyll vr. jponic (A) nd Q. mongolic vr. grosseserrt (B). A regression line could only be fitted for the trees with survivl score inb. pltyphyll vr. jponic (R 755, F, 4 7, P, n 5). Survivl scores: ( ) ; ( ) ; ( ) 2;( ) 3;( ) 4. (Chugnov, 979; Uemur et l., 99) nd Austrlin euclyptus (Gill nd Ashton, 968). Sprouting bility nd resource lloction All the sprouts observed in the study plot were clerly disturbnce-induced. Heting per se, rther thn chrring, ws likely to be responsible for cusing dormnt buds to germinte, since mny sprouts were observed on intct, unchrred Betul trees (Fig. 4A). Whether sprouting occurs in Betul (Fig. 4A) should lrgely reflect the mount of resources vilble in the tree. These chrcteristics of sprouting led us to expect there to be criticl size for sprouting bility, since there is positive correltion between bsl re nd number of sprouts. In ddition, the men number of sprouts in Betul is likely to increse with dmge severity, since the most bundnt sprouting ws observed in the most severely dmged trees (Fig. 4A). Such obvious differences in sprouting strtegy suggest the presence of switch in the lloction of resources to sprouting nd wy from shoot flushing in the crown. Therefore, we compred the log-trnsformed (number of sprouts ) (ln N S ) with both the log-trnsformed bsl re (ln B) nd the survivl score (S) by piecewise regression nlysis in order to consider the lterntives. The following significnt reltionships were derived: ln N S ln B 4 S for N S 2 35 nd ln N S ln B 27 S for N S 2 35 (R 84, F 67 42, P, n 56; Fig. 6). Tree size nd dmge severity explined t lest 84% of the vrition in the sprouting bility of Betul. This shows tht sprouting occurs bove criticl size. Although positive correltion between individul tree size nd the number of sprouts hs been recognized in severl tree species (Jones nd Rynl, 987; Giovnnini et l., 992), little hs been reported on criticl size for sprouting. The dormnt bsl buds of birch species re likely to form clusters (Kuppi et l., 987), nd the number of clusters is positively correlted with tree size (Kuppi et l., 988). The reltionship between the number of clusters of dormnt buds nd tree size would be one of the cuses of criticl size for sprouting bility. In ddition, we showed tht the greter the dmge tree sustined, the more sprouts tht subsequently emerged. This suggests tht trees without living brnches in the crown re still ble to llocte resources to initite sprouting, while trees with some surviving brnches re ble to llocte resources to both new sprouts nd shoot flushing in the crown. Kuffmn (99) investigted survivl by sprouting of tropicl rin forest trees following fire, nd reported tht the more severe the fire, the greter the proportion of trees which produced sprouts. On the other hnd, sprouts from broken stems must rech certin minimum size to disply sufficient photosynthetic surfce to support the root system (Peterson nd Pickett, 99). Therefore, there re thought to be trde-offs in resource lloction between sprouting nd shoot flushing in the crown. By contrst, lterntive sprouting strtegies were not observed in Quercus, nd there ws no reltionship between ln N s nd ln B or S s observed with Betul. In generl, ok

5 Msk et l. Fire Tolernce nd Subsequent Sprouting in Brod-le ed Trees 4 species hve well-developed tp root contining bundnt crbohydrtes (Ski et l., 997), nd it hs been ssumed tht there is tp root storge strtegy for surviving fires (Crow, 988). The wek trend in sprouting bility of Quercus in the study site is probbly due to tp root development; Betul develops rootlets rther thn tp root (Kozlowski, 97). The resource storge strtegy of the root should therefore ffect the sprouting bility of trees (Ski nd Ski, 998); however, we hve no informtion on the extent of strch reserves in these species nd whether this might explin the greter sprouting of Betul. The mortlity nd recruitment rte of sprouts must be studied for further discussion. In ddition, the ok involved in our study is considered to be well dpted to fire, since lrge trees re well protected by virtue of their thick brk. Indeed, in this species, mild fires might be insufficient to stimulte the sprouting of dormnt buds. With regrd to resource lloction, the impct of fire on the plnt community is lso likely to be determined by the seson in which the fire occurs. For exmple, it is well documented tht sprouting is lest bundnt in stumps when newly fully-lefed-out tree is swn down in spring, when crbohydrte reserves re likely to be t lowest level, wheres there is bundnt sprouting from stumps of trees which hve been cut during the dormnt seson (Crwley, 986; Mlnson nd Trbud, 988). In the study plot, the fire occurred before the trees lefed out, nd the prolific sprouting tht followed the fire must hve been relted to the seson in which it occurred (Clrk nd Liming, 953; Mlnson nd Trbud, 988; Bbeux nd Muffette, 994 ). In conclusion, we suggest tht the reltively high tolernce to fire shown by Quercus will llow it to become progressively dominnt in res where there re frequent fires. Conversely, the mortlity of lrge Betul trees in the study re suggests tht its bundnce will decline under similr fire regimes (Fig. 2A nd B). In similr mnner in the estern United Sttes, fire is considered to hve plyed vitl role in mintining ok dominnce before Europen settlement (Abrms, 992). Fire should fvour oks becuse of their thick brk, sprouting bility, resistnce to rotting fter fire scrring, nd the suitbility of fire-creted seedbeds for corn germintion (Lorimer, 985). In our study site, however, the sprouting bility of Betul ws much higher thn tht of Quercus (Fig. 3). The surviving Quercus cnopy trees ppered to be shding their own sprouts, wheres the sprouts of Betul were not shded by mother trees which hd lost their crowns. Therefore Betul, in contrst, seems to hve greter dvntge for regenertion by sprouting thn Quercus, unless fires occur t high frequency. These differences might be relted to post-fire seed estblishment. The dynmics of sprout popultions under heterogeneous light regimes on the forest floor would be n interesting spect for further study. ACKNOWLEDGEMENTS We re grteful to Drs M. D. Abrms, J. S. Pte, nd n nonymous referee for their invluble comments nd suggestions on the mnuscript, nd for correcting the English. We re lso grteful to Dr K. Umeki, T. Egw, M. Hond nd Y. Tkhshi for their help in the field survey; Y. Kwi for trnslting the Russin text; nd Hokkiryokk Inc. for permission to conduct our survey in the compny-owned forest. LITERATURE CITED Abrms MD Fire nd the development of ok forests. BioScience 42: Bbeux P, Muffette Y The effects of erly nd lte spring cuts on the sprouting success of red mple (Acer rubrum) in northwestern Quebec. Cndin Journl of Forest Reserch 24: Bellinghm PJ, Kohym T, Aib S The effects of typhoon on Jpnese wrm temperte rinforest. Ecologicl Reserch : Bellinghm PJ, Tnner EVJ, Heley JR Sprouting of trees in Jmicn montne forests, fter hurricne. 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