Monitoring post-wildfire vegetation response with remotely sensed time-series data in Spain, USA and Israel

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1 CSIRO PUBLISHING Interntionl Journl of Wildlnd Fire 21, 19, Monitoring post-wildfire vegettion response with remotely sensed time-series dt in Spin, USA nd Isrel Willem J. D. vn Leeuwen A,B,H, Grnt M. Csdy A, Dniel G. Nery C, Susn Butist D, José Antonio Alloz E, Yohy Crmel F, Le Wittenberg G, Dn Mlkinson G nd Brron J. Orr A A School of Nturl Resources nd the Environment, Office of Arid Lnds Studies, 1955 E 6th Street, University of Arizon, Tucson, AZ 85721, USA. B School of Geogrphy nd Development, University of Arizon, Tucson, AZ 85721, USA. C USDA Rocky Mountin Reserch Sttion, 25 South Pine Knoll Drive, Flgstff, AZ 861, USA. D Deprtmento de Ecologí, Aprtdo 99, Universidd de Alicnte, E-38 Alicnte, Spin. E Fundción Centro de Estudios Ambientles del Mediterráneo, Chrles Drwin, 14, E-4698 Ptern, Spin. F Fculty of Civil nd Environmentl Engineering, Technion, Hif 32, Isrel. G Deprtment of Geogrphy nd Environmentl Studies, University of Hif, Hif 3195, Isrel. H Corresponding uthor. Emil: leeuw@g.rizon.edu Abstrct. Due to the chllenges fced by resource mngers in mintining post-fire ecosystem helth, there is need for methods to ssess the ecologicl consequences of disturbnces. This reserch exmines n pproch for ssessing chnges in post-fire vegettion dynmics for sites in Spin, Isrel nd the USA tht burned in 1998, 1999 nd 22 respectively. Moderte Resolution Imging Spectrordiometer stellite Normlized Difference Vegettion Index () time-series dt (2 7) re used for ll sites to chrcterise nd trck the sesonl nd sptil chnges in vegettion response. Post-fire trends nd metrics for burned res re evluted nd compred with unburned reference sites to ccount for the influence of locl environmentl conditions. Time-series dt interprettion provides insights into climtic influences on the post-fire vegettion. Although only two sites show increses in post-fire vegettion, ll sites show declines in heterogeneity cross the site. The evlution of lnd surfce phenologicl metrics, including the strt nd end of the seson, the bse nd pek, nd the integrted sesonl, show promising results, indicting trends in some mesures of post-fire phenology. Results indicte tht this monitoring pproch, bsed on redily vilble stellite-bsed time-series vegettion dt, provides vluble tool for ssessing post-fire vegettion response. Additionl keywords: drylnds, Moderte Resolution Imging Spectrordiometer, Normlized Difference Vegettion Index, phenology, remote sensing, time series, vegettion recovery. Introduction Recent studies hve shown tht pst mngement prctices nd chnges in climte ply significnt role in the frequency nd severity of wildfires (Swetnm nd Betncourt 1998; Westerling et l. 26), nd tht climte chnge (e.g. CO 2 nd temperture increse) is likely to impct forest fires into the future (Flnnign et l. 2). In prticulr, wildfire disturbnce is becoming more prevlent in mny shrub nd wooded drylnd ecosystems in the south-western USA, the Mediterrnen bsin lndscpe (Swetnm nd Betncourt 1998; Allen et l. 22; Puss 24), nd likely worldwide (IPCC 27). Becuse of the lrge sptil extent nd high sptil nd temporl vribility of drylnd systems, coupled with the potentil for incresing wildfire frequency nd severity, robust post-fire monitoring tools re needed to inform dptive mngement nd dvnce understnding of post-fire vegettion response rtes nd ecosystem helth. Low-cost, rpidly vilble, nd ccurte ssessment of lndscpes following disturbnce will led to improved predictive cpbilities nd more informed mngement decisions (Aronson nd Vllejo 26). Vegettion cover nd pttern re some of the most importnt prmeters for ssessing ecosystem nd lndscpe functioning (Gobin et l. 24; Kéfi et l. 27). The growing demnd for monitoring nd evlution of the impcts of disturbnces such s droughts nd wildfire, s well s the results of restortion nd rehbilittion efforts, re motivting the development of new pproches nd technologies (Tongwy nd Hindley 2; Díz-Delgdo et l. 22; Herrick et l. 25; Kuemmerle et l. 26; Lentile et l. 26; Roder et l. 28; vn Leeuwen 28) tht cn be pplied t different scles nd costs. The longterm evlution of conservtion nd restortion success hs been recognised s one of the mjor deficiencies in lnd conservtion nd restortion efforts (Holl nd Cirns 22). Lndst dt (3-m resolution) hve been used successfully for post-fire vegettion ssessments (Díz-Delgdo et l. 22); however, the opertionl use of these dt cn be IAWF /WF /1/175

2 76 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. chllenging becuse of persistent cloud cover, dt continuity, cquisition nd processing costs, tsking nd dt vilbility. Mny studies hve used the Normlized Difference Vegettion Index ( = (ρ NIR ρ red )/(ρ NIR + ρ red ), where ρ red is the surfce reflectnce vlue for the red wvelength nd ρ NIR is the reflectnce vlue for the ner-infrred wvelength; Tucker 1979) to exmine post-wildfire vegettion response processes (Mlingreu et l. 1985; Viedm et l. 1997; Díz-Delgdo nd Pons 21; Mlk nd Puss 26; Hudk et l. 27). Timeseries dt of remotely sensed spectrl vegettion indices, such s, hve been extensively used to evlute trends in vegettion dynmics (Gowrd et l. 1985; Justice et l. 1985; Lovelnd et l. 1995), but evluting post-wildfire vegettion response with redily vilble 25-m Moderte Resolution Imging Spectrordiometer (MODIS) (Justice et l. 1998) time series nd phenology dt (vn Leeuwen 28) hs been explored much less. Biweekly corse sptil resolution (8 km) time-series dt from the Ntionl Ocenic nd Atmospheric Administrtion s (NOAA) Advnced Very High Resolution Rdiometer (AVHRR) Pthfinder hve been used to derive temporl nomlies for burned nd unburned res nd rtes of recovery for forests in Cnd (Goetz et l. 26), Borneo nd north-estern Chin (Idris et l. 25), but might be too corse for more locl nd regionl post-fire monitoring pproches. Abrupt chnges in the vegettion growth cycle or lnd surfce phenology cused by drought nd wildfire disturbnce often result in nomlous vegettion growth trjectories tht cn be monitored with MODIS 25-m time-series dt (vn Leeuwen 28). Mny studies hve pointed to the need for long-term monitoring nd the development of tools to evlute ecosystem response to wildfires (US Government 23; Myor et l. 27; Wittenberg et l. 27; Rollins 29). This reserch exmined severl novel pproches for the evlution of post-fire vegettion response trjectories t the lndscpe scle. These pproches hve the potentil to be pplied to ny vegettion monitoring or restortion effort, yet lso llow for comprtive nlyses mong different sites s well s the evlution of the success nd sustinbility of the mngement ctions pplied. Structurl, functionl nd lndscpe qulity indictors to monitor post-fire vegettion response nd restortion projects cn be derived from the remotely sensed dt. In the present study specil effort ws mde to ensure the generlity of this reserch, nd its pplicbility worldwide. To ccomplish this, post-fire vegettion trends in three countries (Spin, USA nd Isrel) were evluted, covering vriety of ecosystems nd lndscpes, nd wide rnge of drylnd environments. This reserch focussed on the potentil of the following remotely sensed sesonl nd sptil metrics for monitoring nd evluting post-wildfire vegettion response: (1) Sesonl greenness or signtures, showing the mount of vegettion cover, cn be used for monitoring on biweekly bsis (Goetz et l. 26). These signtures cn provide informtion on the sesonlity, trend nd pttern of vegettion dynmics. (2) Trends in sptil heterogeneity t the lndscpe scle cn be ssessed through the ppliction of sptil sttistics (e.g. coefficient of vrition, COV) (Brbos et l. 26) on the greenness imgery. COV represents mesure of site heterogeneity tht cn be clculted bsed on the presence nd bsence of vegettion cover nd cn serve s mens to ssess frgmenttion nd connectivity. (3) Phenologicl metrics derived from time-series stellite dt cn show the timing of vegettion ctivity in sptil nd lndscpe context, including: beginning, pek nd end of the growing seson, s well s the mount of vegettion greenness for ech of these (Reed et l. 1994). The integrtion of these sesonl curves cn then provide the reltive mount of productivity for ech growing seson in the time series. Both the timing nd mgnitude of the vegettion greenness will provide insight into the vegettion response to environmentl conditions nd mngement tretments. Most of these metrics re even more useful when they re combined with ground-bsed observtions. Although ground-bsed observtions re generlly limited in their sptil extent, the remotely sensed dt llow for extrpoltion once the metrics re verified in the field by locl experts. Objectives The primry gol of this reserch ws to evlute the effectiveness of stellite-bsed sptilly explicit time-series dt nd derived vegettion phenology metrics for ssessing post-fire ecosystem dynmics with respect to vegettion types, environmentl controls nd stndrd or reference conditions. To tht end, the following objectives were identified: (1) Compre dt to ground dt to provide context for subsequent post-fire vegettion response nlyses using the time-series stellite dt. (2) Chrcterise unburned reference nd post-fire vegettion sesonlity in response to environmentl controls like temperture nd precipittion events with time-series dt. (3) Evlute how time-series dt cn be used to monitor post-fire vegettion cover trjectories. (4) Assess the post-fire chnges in sptil lndscpe heterogeneity using time-series dt. (5) Evlute whether vegettion phenology cn be used to ssess post-wildfire vegettion dynmics nd response. In order to ddress these objectives, reserch pproch ws designed tht tested three hypotheses (H) cross three drylnd environments. Nmely, tht post-fire vegettion response: H 1 : is correlted with positive trend or slope of the time-series dt; H 2 : results in decrese in the stndrd devition of the signl over time, indicting declining sptil heterogeneity; H 3 : cn be described by using trends in vegettion phenologicl metrics. Our pproch included the collection nd pre-processing of MODIS time-series vegettion dt, precipittion nd temperture dt, nd ground-bsed vegettion coverestimtes for ech of the three study res. The pre- nd post-fire vegettion dt were exmined to evlute both the temporl (H 1 ) nd sptil (H 2 ) vegettion dynmics with time-series dt of the burned nd unburned sites, using unburned sites s reference. Phenologicl metrics (phenometrics) were generted for ll sites

3 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 77 using the time-series dt, fter which the post-fire phenometrics were evluted to determine their utility for describing post-fire vegettion dynmics not cptured by the time series lone (H 3 ). This reserch should result in better understnding of the sptil nd temporl ptterns in greenness nd phenology metrics cross ecosystems. By evluting this pproch in multiple ecosystems, the most useful post-fire monitoring techniques nd informtion cn be evluted. Dt nd methods Study res Two study sites were chosen in ech of three study res (Spin, USA nd Isrel) to investigte temporl nd sptil vegettion dynmics s well s the performnce of phenologicl metrics for detecting differences nd similrities in burned nd unburned (bseline or reference) sites between nd within ech re (Fig. 1). Study res were selected in order to represent vriety of precipittion nd temperture combintions, including the mount nd timing of those combintions. Tble 1 provides n overview of the site ttributes including the time of the fire, burned re, temperture nd precipittion vribles. Note tht the site in Isrel prtilly burned second time. Monthly precipittion nd minimum nd mximum temperture dt were obtined for ech of the three sites from wether sttions ner the study sites. Dt for the Indin fire were obtined from sttion in Prescott, Arizon, USA, 7 km from the burned site. Precipittion dt for the Gudlest site in estern Spin were obtined from the Gudlest reservoir wether sttion, locted in the study re. Temperture dt were obtined from sttion in Cllos, Alicnte, Spin, 15km from the burned site. Mt Crmel dt were from wether sttion t Hif University, locted on the edge of the burned site in north-western Isrel. Temperture dt t the Mt Crmel site were only vilble since 23. Study res consisted of one burned site nd one unburned (reference) site (Figs 2 4). All three fire studies were intense crown fires in forests nd shrublnds. In ech cse the burned re ws defined by the perimeter of the burn, nd the reference site ws selected bsed on close proximity, similr size, vegettion composition, nd topogrphic context. Criteri used to select the specific burned sites were: (1) sufficient size to encompss t lest ten 25-m MODIS pixels; nd (2) burn dte within 2 yers of the beginning of the MODIS record in Februry 2, to llow for sufficient coverge of the post-fire lnd cover chnge trjectories nd phenology. Ground-bsed vegettion dt were collected for sites in Spin nd the USA to llow for comprtive nlysis between ground-bsed vegettive cover nd MODIS dt. Gudlest fire re, Alicnte, Spin The Gudlest re is locted on the south-fcing slopes of the Xortà mountin rnge, which drin to the Gudlest reservoir in the Alicnte province of estern Spin. The dominnt soil type is Clcric Cmbisol (FAO 1988), developed over white mrls nd limestone. Steep slopes nd nrrow crop terrces chrcterise the re, locted t 4 6 m elevtion. The climte is dry subhumid Mediterrnen. The site represents common mosic lndscpe in Mediterrnen drylnds. Most of the terrces re currently bndoned nd covered by pine forest or shrublnd, depending on the ge of bndonment. Old terrces re covered by Pinus hlepensis (Aleppo pine) forest tht nturlly colonised the bndoned fields. These forest ptches include dense understorey dominted by Rosmrinus officinlis (Rosemry), Eric multiflor (Hether) nd Ulex prviflorus (Gorse), nd n herbceous lyer dominted by Brchypodium retusum (Flse Brome). The vegettion of recently bndoned terrces is dominted by tree crops, including Certoni siliqu (Crob tree) nd Ole europe (Olive tree), together with Aleppo pine splings, nd dense herbceous lyer of Brchypodium retusum nd vriety of legumes. Post-fire vegettion cover t the Gudlest site ws mesured by the point intercept method (Greig-Smith 1983) in 1 5-m 2 plots, using.5.5-m grid covering the entire plot. Totl plnt cover ws mesured 1, 2, 28, 34, 46, 57 nd 7 months fter the fire. These dt were used to perform comprtive nlysis between ground-bsed vegettive cover nd MODIS dt. Indin fire re, Prescott Ntionl Forest, Arizon, USA The Indin fire site is locted inside the Prescott Ntionl Forest, which lies in mountinous section of centrl Arizon (south-western USA) between forested plteus of the Mogollon Rim to the north nd est nd rid Sonorn desert to the south. Soils re derived from Pleozoic sndstones nd limestones interspersed with quternry nd upper tertiry igneous intrusions. The re is dominted by cnopy of Pinus ponderos (Ponderos pine) nd Quercus emoryi (Emory ok), with n understorey of interior chprrl species (Quercus turbinell, Shrub live ok; Arctostphylos pungens, Pointlef mnznit). Elevtion of the two sites rnges from 169 to 192 m, representing rnge of spects, with slopes of up to 35 degrees. Wildfires in conjunction with high-intensity monsoon rin storms cuse extensive erosion in the lndscpes of the Prescott Ntionl Forest (DeBno et l. 1998; Nery nd Ryn 25). The Indin fire strted on 15 My 22 ner Indin Creek Rod in the Prescott Ntionl Forest nd burned into the Prescott city limits. Vegettion cover dt were collected every spring nd fll (utumn) following the Indin fire (eight collections in totl). A series of three trnsects were mesured cross n untreted wtershed within the burned re, one locted mid-slope on ech side of the min dringe nd one in the center of the dringe. Ech trnsect ws 5 m long nd consisted of 1 subplots, seprted by 5 m long the length of tpe, for totl of 3 subplots per wtershed. The dt were collected s n oculr estimte of the percentge bundnce of live vegettion for herbceous, shrub nd tree cover clsses. These clsses were summed for the purpose of this study. In ddition to the cover mesurements, dominnt species were recorded for the burned nd reference sites (J. L. Byers, pers. comm.). Mt Crmel fire, Isrel Mount Crmel Ntionl Prk includes distinctive mountin ridge in north-western Isrel nd covers 25 km 2 with its highest pek t 546 m. In the pst, severl res on Mt Crmel hve been ffected by wildfire events tht burned reltively smll res ( 4km 2 ). The lithology is minly composed of chlk limestone nd dolomite. The slopes re steep nd the strems hve slopes

4 78 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. Legend No dt Wter km km km km km km Fig. 1. Study res for the post-wildfire vegettion response nlysis in Spin (upper two imges), USA (middle two imges) nd Isrel (lower two imges). The bse mps re Normlized Difference Vegettion Index () dt derived from Moderte Resolution Imging Spectrordiometer imgery. Burned sites re outlined in yellow, nd reference sites re in blue. exceeding 5% in plces. The climte is Mediterrnen, with dry summers nd riny winters. Fig. 4 shows representtive photos of the unburned reference site nd the burned site on Mt Crmel, Isrel. Nveh (1973) defined the re s Mediterrnen fire bioclimte. Vegettion on the terrros soils is chrcterised by complex of P. hlepensis Pistci plestin (Pistchio) Cistus spp. (Rock rose) ssocitions on south-fcing slopes nd Quercus clliprinos (Plestine Ok) P. plestin ssocitions on northfcing slopes, forming Mediterrnen evergreen sclerophyll woodlnd. Most of the pines re not nturl nd were plnted in the region, dting from 8 yers go. Currently the forest tht covers the re is ptchwork of nturl Mediterrnen vegettion nd plnted non-ntive trees of vrious ges.

5 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 79 Tble 1. Summry descriptions of the three study res, including dte nd re of the burned site, minimum nd mximum monthly tempertures, nnul precipittion nd dominnt seson, nd the dominnt species found t the study sites Sources: Gudlest dt, University of Alicnte; Indin dt, USDA Forest Service; Mt Crmel dt, University of Hif (Inbr et l. 1997); temperture dt, Ntionl Climte Dt Center Are chrcteristics Gudlest Indin Mt Crmel Burn dte Aug My 22 Dec. 1999; Apr. 25 Burned re (h) ; 135 Temperture ( C) Monthly minimum Monthly mximum Annul Annul precipittion (cm) Precipittion seson Winter Summer nd winter Winter Tble 2. Coefficients nd ssocited P-vlues for the lest-squres model = β + β 1 period, where period indictes the number of MODIS periods since burn Regression results re shown for burned sites, reference sites, nd the difference (reference burned) between the two for burned res in Spin, USA nd Isrel Site Burned Reference Difference β 1 P-vlue β 1 P-vlue β 1 P-vlue Gudlest E Indin E E E-14 Mt Crmel E E-15 () (b) Fig. 2. Unburned mosic of pine forest shrublnd ptches () nd post-wildfire vegettion growth (b) (December 24; 6 yers fter the Gudlest wildfire). Vegettion cover in the region rnges between 5 nd 7% on south-fcing slopes, nd between 6 nd 1% on north-fcing slopes. MODIS time-series dt This study exmined the use of 25-m sptil MODIS time-series dt to evlute post-fire vegettion response using some of the methods in the literture tht were developed in the context of Lndst-bsed wildfire reserch. Lndst imgery (often cquired few times yer t 3-m resolution) hs been shown to be useful for identifying nd mpping res ffected by wildfire, becuse fire cuses vlues to decrese (Ksischke et l. 1993; Ksischke nd French 1995; White et l. 1996; Fernndez et l. 1997; Slvdor et l. 2). MODIS time-series dt from Mrch 2 through Februry 27 were obtined for northern Arizon, southestern Spin, nd the Mt Crmel region of north-western Isrel.

6 8 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. () (b) Fig. 3. Unburned mixed ok pine forest () nd post-wildfire vegettion growth (b) (9 September 26; 2 yers fter the Indin fire). () (b) Fig. 4. Unburned mixed ok pine forest () nd the post-wildfire sitution (b) t the Mt Crmel site (October 26). The primry MODIS product obtined for this study ws the 16-dy dt t 25-m resolution, resulting in dy composite imges (periods) per yer. is successful s vegettion mesure in tht it is sufficiently stble to permit meningful comprisons of sesonl nd internnul chnges in vegettion growth nd ctivity (vn Leeuwen et l. 26). Dt for ll three countries were downloded from the Lnd Processes Distributed Active Archive Center in Sioux Flls, South Dkot, USA, nd were mosicked nd reprojected into projections tht mtched mpping stndrds pproprite for ech of the three countries. This resulted in time series of 138 imges for ech of the three study res. Following this preprocessing of the dt, the time series ws summrised for burned site nd reference site selected in ech country six sites in totl (Fig. 1). The men nd stndrd devition of ll pixels within the boundries of ech site were clculted for ech time step in the time series nd recorded in n ASCII text file. These text files provided the bsis for the evlution of sptil nd temporl trends in nd the ssocited phenology dt. Extrcting phenologicl metrics from time series To dte, the min pproch tht hs been used to derive phenology for lnd surfces from stellite imgery is bsed on curve derivtives (Reed et l. 1994; Jönsson nd Eklundh 22), whereby criticl points re identified in the nnul Vegettion Index curve tht correspond to sesonl phenomen. The vilbility of high temporl resolution stellite dt, coupled with the techniques for the nlysis of sesonl nd internnul vegettion dynmics, fcilitte the evlution of vribility nd trends

7 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 81 ( 1 ) t strt, strt Smll Int Green-up rte Pek Observtions SG model Begin end Lrge Int. Amplitude t end end Senescence rte dy time periods (23/yer) Fig. 5. Grphicl exmple of the phenologicl metrics tht cn be derived from Normlized Difference Vegettion Index () time series. Int, integrl; SG, Svitsky Goly..45 ().55 (b) 9/24 5/23 1/23.4 4/2 6/ /24 6/22 1/ /21 y.13x R Frctionl cover.35 1/22 6/23 8/22 y.34x R Frctionl cover Fig. 6. Site-representtive vegettion frctionl cover dt plotted ginst the men Normlized Difference Vegettion Index () vlues for the Gudlest () nd Prescott (b) sites. Smple dtes re indicted bove ech point. of vegettion phenology s they relte to lndscpe nd climte chnges, disturbnces nd vribility. MODIS -bsed phenologicl metrics s described by Reed et l. (1994) nd Jönsson nd Eklundh (22) were extrcted yerly (bsed on 23 MODIS observtions) to evlute post-wildfire vegettion response for ll three countries. Vegettion phenometrics of the burned sites nd unburned reference sites were derived using Svitsky Goly filter to fit curve to ech time series of dt usingtimest softwre (Jönsson nd Eklundh 22, 24). The phenometrics were compred to determine whether they could be used to ssess post-wildfire response (H 3 ). The sesonl phenometrics tht were compred re depicted in Fig. 5, nd include: Strt of the growing seson: The time (t strt ) where strt vlues strt to increse is defined s the point in time for which the vlue hs incresed by 2% of the distnce between the left minimum vlue nd the mximum vlue. End of the growing seson: The time (t end ) where end vlues level off nd re t 2% of the pek vlue nd the lowest end of the seson vlue.

8 82 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. Time of pek growing seson: The time where pek vlues re t mximum.the ssocited vlue is relted to the sesonl highest mount of greenness or vegettion cover. Length of the growing seson: The length is often indictive of the difference between the beginning nd end of fvourble growing conditions (e.g. precipittion nd temperture limited systems in rid nd semi-rid lndscpes). Amplitude of the growing seson: The mplitude is obtined s the difference between the pek nd bse vlues. bse is the verge of the strt nd end vlues. This is mesure of sesonl vegettion dynmics. Lrge integrl: This metric integrtes vlues between the zero-bseline ( = ) nd sesonl fitted curve during the length of the growing seson for ech yer. It is n indiction of totl vegettion biomss (tvb). Smll integrl: This metric integrtes vlues during the length of the growing seson tht re between bse nd the fitted curve, nd is n indiction of new sesonl vegettion growth or productivity (svp). Left (l) derivtive nd right (r) derivtive: These metrics re relted to the rte of green-up nd plnt growth, nd the rte of senescence respectively. MODIS time-series dt were summrised for ech of the burned nd reference sites using Timest to generte 11 phenometrics for ech yer, lthough Timest did not generte metrics for the lst yer of the record due to insufficient dt to complete the sesonl determintions (Fig. 5). This resulted in totl of 6 yers of metrics for ech of the sites. Dt nlysis pproch Comprison of field-bsed vegettion cover to MODIS Vegettion cover dt were collected to evlute the bility of rdiometric dt in the form of to represent groundbsed biophysicl dt such s percentge vegettion cover for two of the three ecosystems under investigtion. Field dt collected t the Spin nd USA field sites were compred with MODIS vlues for dtes corresponding to the field collection dtes. The degree of correltion between field nd stellite dt ws ssessed by clculting the coefficient of determintion (R2) between the two dtsets. Visul interprettion of time-series dt As first step in understnding the vlue of MODIS timeseries dt for monitoring post-fire response, the dt for the three sites were evluted by visul interprettion in conjunction with precipittion nd temperture dt for ech of the study res. Such visul interprettion cn revel nunced responses in temporl vegettion ptterns to climtic events such s drought or unusul periods of precipittion, s demonstrted by Ksischke et l. (1993), who used Lndst-bsed dt for visul nlysis of pre- nd post-fire response. These observtions cn further n understnding of chnges in wildfire risk or post-wildfire vegettion response. The cuses of some differences in sesonl ptterns between regions cn lso be seen by interpreting the MODIS time-series dt, s differences in the timing of precipittion nd temperture between regions result in unique sesonl vegettion ptterns. Evluting post-fire trends In order to test the hypothesis tht post-fire vegettion response is ssocited with positive trend of the MODIS time-series dt (H 1 ), trends in time-series dt were evluted for ech of the three countries, similr to Viedm et l. (1997) nd Díz-Delgdo et l. (22). Viedm et l. (1997) clculted Lndst-bsed recovery rtes bsed on the reltionship between the nd time. Díz-Delgdo et l. (22) showed tht the rtio between the men of burned nd unburned res cn be used to evlute post-fire recovery in Ctloni, Spin, bsed on severl Lndst scenes. The post-fire MODIS time-series dt for the burned res were evluted by testing for significnt post-fire response slope. To do this the post-burn dt were fitted using the simple liner regression model: = β + β 1 period, where period indictes the number of MODIS periods since burn. The reltionship ws tested for significnce t α =.5. This sme test ws repeted for the reference sites nd fter subtrcting the time series of the burned sites from tht of the reference sites. Coefficients (β 1 ) for ech reltionship were tested for significnce in order to evlute the use of reference site to ccount for vritions in vegettion communities to locl environmentl conditions. Sptil heterogeneity nlysis Post-wildfire lndscpes re typiclly chrcterised by high degree of sptil vribility in the erly stges of post-fire vegettion dynmics due to vritions in burn severity nd the distribution of biotic nd biotic fctors nd legcies (Turner et l. 1999). Over time, however, dominnt vegettion types my exert n incresing degree of control over the function of the ecosystem (Holling nd Gunderson 22), resulting in n overll decline in sptil heterogeneity within the burn perimeter. The COV (stndrd devition divided by the men) hs been used with stellite-bsed time-series dt to indicte chnges in sptil heterogeneity over time (Brbos et l. 26). We used the COV trjectories to provide mesure of the chnge in reltive heterogeneity of ech of the selected sites. To compre nd evlute the trends in sptil heterogeneity for the three countries (H 2 ), the COV for both the burned nd unburned sites for ech MODIS composite period between 2 nd 27 were clculted. The COV ws computed by tking the rtio of the stndrd devition to the men (Gotelli nd Ellison 24) of the vlues of ll pixels within ech site s perimeter. The corresponding differences between the COV burned nd COV reference sites were then computed for ech period. As with the men dt, we used the post-fire simple liner regression model COV = β + β 1 period, where period indictes the number of MODIS periods since burn, to quntify the rte of chnge in sptil heterogeneity. Phenologicl comprison nd nlysis pproch The evlution of phenometrics for use in post-fire vegettion ssessment involved the nlysis of three primry reltionships, defined by the metrics derived for ech study site. First, phenometrics were compred between the reference sites in the three regions. This ws done in order to evlute the bility of the derived phenometrics to discern differences between the

9 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 83 three regions, unrelted to wildfire disturbnce events. Second, the metrics derived for ech re for the burned nd unburned sites were compred in order to identify those metrics tht best described trends in post-wildfire vegettion dynmics. Third, the phenometrics for the burned sites cross the three regions were evluted by pooling the post-burn metrics of ll three, fter tking into ccount the behviour of the reference sites for ech region. This ws done in order to determine the vlue of using reference site, s well s the degree to which post-fire response cross regions is similr or different. To compre reference sites between the three regions, ech metric ws verged cross the 7 yers to crete representtive description of the phenology for ech of the three study res. For ech metric, differences in the mens of the metric cross regions were tested using pirwise comprison of the mens (α =.5), fter ccounting for multiple comprisons using Tukey Krmer djustment (Rmsey nd Schfer 1997). Chnges in post-fire phenometrics were evluted by testing the rte of chnge in ech metric s function of yer since burn. This ws done first for ech study re seprtely, nd then by pooling the dt from the three res. In ech cse the reltionships were evluted using the burned re lone, s well s using the reference re to ccount for differences in locl dynmics nd vrible climtic conditions. In the cse of the timing-bsed metrics (strt, end, nd pek timing, s well s length of the growing seson), nd the two metrics relted to the rte of green-up nd senescence (left nd right derivtives), the burned re metrics were subtrcted from those of the reference re, s interpreting differences for these metrics is more intuitive by considering simple difference. For the mgnitude-, svp- nd tvb-relted metrics (bse, pek, mplitude, nd the smll nd lrge integrls), burned metrics were divided by reference metrics to ccount for the potentil for non-linerity in the increses in differences between burned nd reference metrics given increses in overll productivity of both burned nd reference sites. These metrics re lso esily interpreted in terms of percentge of the reference vlues. All results from the Isrel fire were presented for the period of record before the occurrence of the 25 fire. The second recurrent fire in 25 prtilly overlpped with the 1999 fire nd ws therefore treted seprtely in the nlysis. Results nd discussion Comprison of field-bsed vegettion cover to MODIS vlues Fig. 6 shows n exmple of how the vlues incresed with higher frctionl vegettion cover t the Gudlest nd Prescott fire sites. Although the reltionships of nd biophysicl prmeter like the frctionl vegettion cover re often site specific nd vry with the opticl properties of soil nd vegettion, nd with phenologicl stges, usully increses with increses in cover. Vribility in the position of the sensor nd sun cn lso diminish the strength of the reltionship between the nd frctionl vegettion cover (vn Leeuwen et l. 1994). Fig. 6 shows firly strong liner reltionship for the Prescott site nd indictes tht the mximum frctionl cover (peking in September October) nd corresponding were higher ech consecutive yer fter the fire. The reltionship between the nd frctionl cover for the Gudlest site is less strong becuse the MODIS monitoring period strted 2 yers fter the fire, with vegettion lredy covering more thn 5% of the surfce, chnging slowly during the following yers, nd with sesonl nd internnul vrition msking the slight response trend of vlues. Strting in 22, plnt cover stbilises round 8%, wheres vlues continues to vry until the end of the monitoring period, probbly reflecting the response of the vegettion to climtic vrition (Figs 6, 7). In ddition, totl vegettion cover ws mesured, including both senescent nd live vegettion. Senescent vegettion hs low response nd cn obscure green vegettion, which by itself results in high vlues (vn Leeuwen nd Huete 1996). These results suggest tht MODIS vlues re highly sensitive to chnges in vegettion cover for low to moderte cover vlues. Visul interprettion of wether nd MODIS time-series dt Time-series, precipittion nd temperture dt show the post-wildfire sesonl vegettion dynmics between 2 nd 8 yers fter the wildfire s well s their response to climte vribles t the Gudlest study re; time-series dt for the reference site with similr originl vegettion re depicted s well (Fig. 7). The mounts nd sesonlity of vegettion, s indicted by the vlues, re similr for both res nd re still firly close in levels, with the re tht burned hving slightly but consistently lower levels of thn the reference re over the course of the study period. This consistent difference cn be ssocited with the shift in the vegettion community tht occurred fter the wildfire, with pre-fire pine forest ptches moving to gorse shrublnd (U. prviflorus) communities fter the fire. Moreover, during regulr field visits fter the fire, it ws observed tht the vegettion in the shrublnd ptches recovered rpidly, wheres vegettion in the pine forest res recovered more slowly, showing very poor regenertion of pines nd moving to more gorse-dominted shrublnd. The timing of the lowest vlues re observed to occur in the summer months, wheres the highest vlues re observed during the fll nd spring, which re the periods combining wet soils nd wrm tempertures. The dynmic rnge of the is lower for the Gudlest region thn for either the Prescott (Fig. 8) or Mt Crmel (Fig. 9) regions. Time-series, precipittion nd temperture dt re shown for the Prescott region in Fig. 8 to demonstrte the prend post-wildfire vegettion dynmics. The Indin fire strted on 15 My 22. Fig. 8 shows the time series for the region of the fire just before the burn, shortly fter the burn, nd for some time fter the event. The trjectories re similr for the two sites before the time of the fire, including consistent decline in ctively photosynthesising vegettion over the nerly 5-month period immeditely before the fire (Fig. 8). The drought trend t the Indin fire re most likely indictes tht the lrge mount of vegettion present in Jnury hd dried up just before the fire. The drought in the spring of 22 is pronounced in the precipittion dt shown (Fig. 8). For most yers more spring rinfll ws mesured compred with 22. Prior to the fire the res hve similr levels, with the re eventully consumed

10 84 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. () Gudlest fire nd reference site 1998-fire Burned Reference (b) 4 Gudlest temperture nd precipittion Precipittion Min temperture Mx temperture 4 Precipittion (mm) Temperture ( C) Fig. 7. Moderte Resolution Imging Spectrordiometer 25-m Normlized Difference Vegettion Index () time-series dt for the burned (1998 fire) nd reference sites from nerby Gudlest () nd precipittion, minimum nd mximum temperture dt (bottom) from nerby Gudlest, Spin (b). in the wildfire hving slightly higher vlues thn the reference re just before the fire. It is importnt to note tht the Indin fire strted on 15 My, yet the compositing process of MODIS dt selects for the mximum vlue cross the 16-dy composite period. Therefore, the fire ws detected in the composite imge of the following period. One yer fter the pek in the previous yer s growth the difference between the peks in vegettion of the burned nd unburned res cn be clerly seen. Four yers following the fire the difference remins cler, lthough the time-series curves indicte tht the gp between the two res hs diminished. After the 22 drought, the unburned reference site continued to hve lower vlues thn before the 22 drought (Fig. 8). Investigtion on the ground hs shown, however, tht lthough the burned region is being restored by plnting ponderos pine seedlings (in 26), it is not returning quickly to its prior stte of pine forest, but is rther moving to n interior chprrl vegettion type. Field visits in 25 nd 26 showed tht post-fire vegettion ws dominted by resprouting shrub species, including Q. turbinell (Shrub live ok) nd Juniperus deppen (Alligtor juniper), with herbceous component of grsses nd forbs (Fig. 3). The timing of the lowest minimum nd mximum tempertures coincide with the lowest vlues. During these times, the overstorey ok nd pine growth stops nd herbceous vegettion senesces or is covered by snow. vlues for pixels covered with snow or senescent vegettion tend to be.15 or lower. The Mt Crmel fire strted in Time-series, precipittion nd temperture dt re shown for the Mt Crmel region in Fig. 9 long with the pre- nd post-wildfire vegettion dynmics nd their response to wether vribles. The time-series dt for the reference site with similr originl vegettion tht ws not burned is shown s well.the mounts nd sesonlity of vegettion, s indicted by the vlues, hve similr ptterns for both res. The differences between the yerly minimum nd mximum vlues re lrger for the burned site thn the reference site. Nine yers following the fire, the difference is still cler, lthough the time-series curves indicte tht the gp between the two res is diminishing, especilly in 23. The timing of the lowest precipittion nd mximum tempertures coincide with the lowest vlues. The timing of the minimum vlues usully occurs lter in the yer t the burned site thn t the unburned reference site (Fig. 9). Evluting post-fire trends Regression of the post-fire for burned sites, reference sites, nd the difference between the two (Tble 2) shows tht nlysis of the burned site lone cn led to confusing nd misleding results. When looking t the burned sites lone,

11 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 85 () Indin fire nd reference site.8.7 Burned Reference.6.5 Drought fire (b) 15 Prescott temperture nd precipittion Drought 4 3 Precipittion (mm) Temperture ( C) Precipittion Min temperture Mx temperture Fig. 8. Moderte Resolution Imging Spectrordiometer 25-m Normlized Difference Vegettion Index time-series dt for the Indin fire site nd the unburned reference site on the Prescott Ntionl Forest ner Prescott, AZ, USA () nd wether dt from nerby Prescott, AZ, USA (b). The 22 drought nd fire events re indicted with rrows. results show significntly positive slopes for ll three burned sites. However, the slope for the post-fire period t the reference site for Gudlest is very similr to tht of the burned site. This cn be seen visully in the time-series dt (Fig. 1) nd quntittively in the vlues of the model coefficients (Tble 2). The difference between the burned nd reference sites does not indicte significnt post-fire slope for the Gudlest fire. This my suggest tht there is trend in the vegettion tht is independent of the effects of the fire, nd tht the index is unble to detect difference between tht trend nd ny post-fire effects tht my exist. This trend could lso be ssocited with climte vrition. During the first 3 yers fter the fire (until 21), n extremely dry period occurred in the re, resulting in stressful conditions for vegettion performnce, followed by reltively wet period nd the ssocited response of vegettion in both burned nd unburned sites. Dt for the Mt Crmel fire does not show significnt trend when the burned site lone is observed. This is most likely due to the lrge sesonl mplitude t tht site, which dds to the vribility of the site nd mkes significnce more difficult to estblish (Fig. 1). By subtrcting the reference site, these sesonl differences re lrgely eliminted, nd highly significnt trend is seen for the difference between the burned nd reference sites. Results from the regression models for the difference between burned nd reference sites in ll three countries re illustrted in Fig. 1. According to the trjectories for the difference between reference nd burned sites (Fig. 1, Tble 2), the Gudlest site nd, to lesser extent, the Indin site re still very fr from closing the gp between their pre- nd post-fire timeseries curves. In both cses, chnge in the type of vegettion community is observed fter the fire. Mediterrnen plnt communities generlly include mny species tht hve the bility to resprout from stumps or hve the cpcity to successfully regenerte from seed fter fires. The most common post-fire pttern is the utosuccession of the plnt community, so tht burned sites rech stte similr to the preexisting (unburned) one (Trbud nd Leprt 198). However, it hs lso been reported tht vegettion structure nd biomss my become dominted by few shrub species, prticulrly when fire disturbnce returns within short time intervls (Díz- Delgdo et l. 22). This type of shift in plnt communities hs lso been observed fter lrge wildfires in some pine forests in south-western USA (Nrog 28) where previously shdesuppressed ok shrubs vigorously resprout fter fire wheres pine regenertion is prevented becuse of the distnce to seed sources.

12 86 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. () Mt Crmel fire nd reference site fire Second 25-fire Burned Reference (b) 4 Mt Crmel temperture nd precipittion Drought Precipittion (mm) Temperture ( C) Precipittion Min temperture Mx temperture Fig. 9. Moderte Resolution Imging Spectrordiometer 25-m Normlized Difference Vegettion Index timeseries dt for burned nd reference sites on Mt Crmel, Isrel (). Note tht second fire occurred on prt of the site tht ws burned in Precipittion dt re shown for yers 2 6, nd minimum nd mximum tempertures were plotted from the second hlf of 23 through 26 (b). Wether dt were collected from nerby Mt Crmel, Isrel. The Mt Crmel fire site first burned in 1999 nd burned gin in 25. Drought nd fire events re indicted with rrows. Post-fire sptil heterogeneity trends Anlysis of the post-fire COV show significnt post-fire trends in declining sptil heterogeneity using the burned re lone, without comprison to reference site (Tble 3). Results for the reference sites show some very smll, yet significnt, trends in heterogeneity for the Gudlest site, but not for the Mt Crmel or Indin sites (Tble 3). The results for the difference between COV of the burned nd reference sites ll show decrese in heterogeneity over time (Tble 3). These results suggest tht the reference sites cn be considered stble with respect to sptil heterogeneity in response to environmentl conditions over time. Plots of the COV over time for the three burned sites re shown in Fig. 11. Our results show consistent decresing trend in the lndscpe-scle vegettion heterogeneity with time fter fire. This my indicte tht the differences in between ptch, interptch nd intrptch res re highest fter the fire nd slowly diminish with time fter the fire. Therefore, t the lndscpe level, fire lters the ptch structure of the burned re. Similrly, Turner et l. (1999) found tht vritions in burn severity nd the redistribution of resources cross the burned re resulted in heterogeneous post-fire lndscpe. Rtes of regenertion of the pre-existing sptil reltionships mong vegettion ptches vry cross the presented post-fire ecosystems. Ricott et l. (1998) found tht the post-wildfire recovery of the sptil distribution of vegettion ptches cn be quite rpid, especilly for ecosystems with resilient vegettion

13 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 87 () fire Gudlest difference (reference burned) y 5.857E-5x.4985 P-vlue (b).4.2 Indin difference (reference burned) 22-fire y.8335x.2144 P-vlue 9.415E (c) Mt Crmel difference (reference burned) fire y.1435x.2383 P-vlue 6.883E-15.2 Second 25-fire Fig. 1. Time-series Normlized Difference Vegettion Index difference, showing the trends of post-fire burned sites subtrcted from reference sites. Post-fire liner trends re significnt (α =.5) for the Indin (b) nd Mt Crmel (c) sites, but not for the Gudlest site (). Note tht the Mt Crmel dt from the time fter the second fire occurred were excluded from the trend nlysis. such s those found in Mediterrnen ecosystems. At the Gudlest site it is found tht the wildfire fvours the spred of gorse shrublnd, prticulrly in those lnd-use ptches most severely ffected by the fire due to the rpid coloniztion of U. prviflorus on disturbed soils (Bez et l. 23). Thus, in south-estern Spin, the wildfire fcilitted shift from pine forest ptches into gorse shrublnd communities, nd rejuventing lredy existing gorse shrublnds, possibly resulting in weker trends in post-fire lndscpe heterogeneity compred with the Mt Crmel nd Indin sites. Evlution of lnd surfce phenologicl metrics Species composition often chnges fter recurring nd severe wildfire events. For exmple, the regenertion ptterns of three Mediterrnen pine forests chnged significntly fter lrge wildfire in north-estern Spin, resulting in trnsition to okdominted communities nd shrublnds (Retn et l. 22). In mixed P. ponderos (Ponderos pine), Quercus gmbelii nd Q. emoryi (Gmbel nd Emory ok) forests, mjor crown fire results in mny chrred sngs (Pssovoy nd Fule 26) fter which ntive orgnisms nd plnts often vigorously return or

14 88 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. Tble 3. Coefficients nd ssocited P-vlues for the lest-squres model COV = β + β 1 period, where period indictes the number of MODIS periods since burn Regression results re shown for burned sites, reference sites, nd the difference (reference burned) between the two for burned res in Spin, USA nd Isrel Site Burned Reference Difference β 1 P-vlue β 1 P-vlue β 1 P-vlue Gudlest E E-11 Indin E E-14 Mt Crmel E E-8 () fire Gudlest burned coefficient of vrition P-vlue 5.28E-5 y.485x.2654 COV.3 (b) Indin burned coefficient of vrition 22-fire P-vlue 1.163E-1 y.1221x.3368 COV (c) fire Mt Crmel burned coefficient of vrition P-vlue 2.727E-11 y.926x.2134 Second 25-fire COV Fig. 11. Time-series coefficient of vrition (COV) showing the trends of post-fire burned sites. Post-fire liner trends re significnt (α =.5) for the Gudlest (), Indin (b) nd Mt Crmel (c) sites, indicting decrese in sptil heterogeneity since the burn t ll three sites. Note tht the Mt Crmel dt from the time fter the second fire occurred were excluded from the trend nlysis.

15 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 89 Period number Periods Integrted Strt period b b 25 3 b Gudlest Indin Mt Crmel Gudlest Indin Mt Crmel Gudlest Indin Mt Crmel Length of seson Gudlest Indin.1 Gudlest Indin Amplitude 8 Gudlest Indin b Mt Crmel Mt Crmel Totl vegettion biomss b Mt Crmel Period number /period.4 Pek period Gudlest Indin Mt Crmel Mt Crmel Mt Crmel Period number End period Mt Crmel Bse Pek c.6 c c.8 b b.5.7 b Integrted Rte of green-up Gudlest Indin Sesonl vegettion productivity Gudlest Indin b b /period Rte of senescence Gudlest Indin Gudlest Indin b b Mt Crmel Fig. 12. Boxplots showing the medin nd stndrd devitions (lower nd upper qurtiles) for ech of the eleven metrics tested between reference sites (Gudlest, Indin nd Mt Crmel). Any dt observtion tht lies more thn 1.5 interqurtile rnge (IQR) lower thn the first qurtile or 1.5 IQR higher thn the third qurtile ws considered n outlier, indicted with + sign. The smllest vlue nd lrgest vlue tht re not outliers were mrked by horizontl line connecting by verticl line to the box. Boxplots lbeled with the sme letters (, b, c, or combintion thereof) for ech metric indicte tht the medin for tht metric does not differ significntly between sites. resprout t the site nd initite recovery. On the other hnd, in mny of these chrred res, invsive species re ble to estblish themselves (Crwford et l. 21), often crowding out ntive species. Becuse the phenology of vegettion community reflects the species tht re most dominnt, we expect tht the chnges in species distribution nd communities cused by wildfire disturbnces (Btineh et l. 26) will be observble with time series of vegettion greenness. Evlutions of phenologicl metrics cross the three regions show both similrities nd differences between the three reference sites representing the regions (Fig. 12). In prticulr, the timing of phenologicl events, including the strt nd end time for the growing sesons, re significntly different (α =.5) between the two Mediterrnen regions (Gudlest nd Mt Crmel) nd the USA site (Indin fire), wheres these metrics re very similr for the two Mediterrnen sites. It is interesting to note, however, tht the durtion of the growing seson does not differ significntly between the three regions. These differences in phenology between the three regions re most likely due to differences in the mount nd timing of precipittion nd temperture ptterns t ech of these sites. Rinfll in the Mediterrnen regions comes primrily in the winter but tempertures remin high enough for yer-round growth, thus resulting in strting periods in the lte fll. In contrst, precipittion in centrl Arizon, USA occurs in both the summer nd winter months, with dry period in the erly spring, ccounting for the differences in strt of growing seson from the Mediterrnen sites. Site-specific differences in the rtes of green-up (left derivtive) nd rtes of senescence (right derivtive) re lrgely inconclusive. Phenologicl metrics relted to mgnitude, in prticulr the mplitude, bse, pek, nd proxies for totl vegettion biomss (lrge integrl; tvb ) nd sesonl vegettion productivity (smll intergrl; svp ) lso show significnt differences mong the three res. Gudlest generlly shows the lowest vlues, lthough it receives higher verge nnul precipittion thn the Indin fire site (Tble 1). Bsed on tvb nd svp dt, the productivity t the Gudlest site ws lower thn the productivity t the Mt Crmel site, nd the productivity of the Indin site flls mostly in between these two. It my

16 9 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. Period number Strt period 1 P-vlue (burned reference) Period number 1 1 Pek period P-vlue p-vlue = (burned reference) Period 1 1 End period P-vlue Yers (burned reference) Periods Length of seson 1 P-vlue p-vlue = (burned reference) /period Rte of green-up.1 P-vlue p-vlue = (burned reference) /period Rte of senescence.1 P-vlue p Yers (burned reference) Amplitude Bse Pek P-vlue p-vlue =..542 P-vlue p-vlue =.26 P-vlue p-vlue = Yers Rtio(burned/reference) Rtio(burned/reference) Rtio(burned/reference) Totl vegettion biomss Sesonl vegettion productivity P-vlue.38 P-vlue p-vlue = Yers Rtio(burned/reference) Rtio(burned/reference) Fig. 13. Pooled differences between burned nd reference re phenometrics, where timing-bsed metrics (strt, pek nd end periods, length of seson) nd rtes of green-up nd senescence were clculted s differences of the burned minus the reference metrics nd the bse Normlized Difference Vegettion Index (), pek, mplitude, biomss nd productivity were clculted by dividing the burned by the reference metrics. From these metrics, only the bse showed significnt (P-vlue =.26) post-fire trend. The x-xis represents the number of yers fter the fire event., Gudlest;, Indin;, Mt Crmel. be tht higher tempertures t the predomintely south-fcing slopes t the Gudlest site result in more nnul evpotrnspirtion nd thus less productivity compred with the Indin fire site. Differences in soil properties could lso ply role in site-specific productivity. The phenometrics tht re ssocited with the burned sites were normlised with the phenometrics of the reference site for the Gudlest, Indin nd Mt Crmel study res in order to ssess trends nd vribility in the phenometrics s they chnge over time fter the fire event (Fig. 13). Visul interprettion suggests some trends nd site-specific vribility. However, sttisticlly significnt post-wildfire trends re not observed for the mjority of the site-specific phenometrics. Exceptions to this include n nnul increse of the pek t the Indin fire site when compred with the reference site (P =.22), nd increses in totl vegettion biomss (lrge integrl;

17 Multicountry monitoring of post-wildfire vegettion response Int. J. Wildlnd Fire 91 P =.376) nd bse vlues (P =.289) for the Mt Crmel fire. Similrly, no significnt trends re evident for most of the phenometrics fter pooling the three res. The one exception to this is the bse vlues, which increse with time since burn when pooled. Visul observtion of the dt tht contribute to this reltionship between svp nd number of yers fter burn (Fig. 13) revels tht the Indin nd Mt Crmel fire dt contributed to liner reltionship throughout the post-burn period, but the Gudlest fire do not show the sme linerly incresing reltionship. Overll, lthough the phenometrics seem to differentite well between vegettion communities in diverse sites (Fig. 12), the dt used here do not demonstrte tht there is greement in the trends for ll of the sites or tht the phenometrics revel the more subtle shifts tht might indicte chnges in post-wildfire community phenology. Conclusions The rpid rte t which ecosystems re being degrded by both nturl disturbnces nd humn ctivities is the impetus for ecologicl restortion nd conservtion efforts worldwide. This is especilly true in drylnds, where the synergy of nthropogenic nd climtic drivers hs led to desertifiction processes nd presents serious thret to nturl resource mngement for ecologicl nd societl sustinbility (IPCC 27). Monitoring the effect of disturbnces such s wildfires is especilly importnt in drylnds, s these sensitive ecosystems re being degrded nd desertified t fst rte worldwide. However, lrge-scle monitoring of post-fire vegettion response is very costly nd time consuming. There is need for common methodology for bseline evlutions of post-wildfire effects t the stnd nd lndscpe scles. Field nd multiscle stellite observtions re both vluble nd often synergistic. Cre should be tken tht these dt sources re used judiciously to fit the specific chrcteristics of ny prticulr mngement effort nd llow for comprtive nlyses between different ctions or inctions. Although post-wildfire vegettion response is ffected by fire severity, vegettion community chrcteristics nd environmentl controls (DeBno et l. 1998; Turner et l. 1999), future reserch will need to ddress how the presented remotely sensed sesonl nd sptil metrics for monitoring nd evluting post-wildfire vegettion re impcted by differences in fire severity. This reserch demonstrtes how moderte-resolution stellitebsed sptilly explicit time-series dt nd derived vegettion phenology metrics cn be used for ssessing post-wildfire ecosystem dynmics with respect to mixed shrub nd forest vegettion types. The inclusion of stndrd or reference site to normlise for environmentl controls tht ffect both burned nd unburned sites is shown to be criticl for quntifying trjectories in sptil nd temporl vegettion response metrics of ll three sites recovering fter recent wildfires. MODIS time-series dt (25-m resolution) re successfully used to chrcterise unburned reference nd post-fire vegettion sesonlity in response to environmentl controls like temperture nd precipittion. Time-series dt re shown to be n effective tool for monitoring both unburned nd post-fire vegettion cover trjectories. In ddressing the first hypothesis, it is demonstrted tht post-fire vegettion response trends hd positive trend or slope of the time-series dt for the Mt Crmel nd Indin sites. The Gudlest site shows consistent difference between the burned nd unburned reference sites, but without ny trend or slope in the time-series dt fter the fire. Anlysis of the post-fire chnges in sptio-temporl heterogeneity using time-series dt confirms the second hypothesis, showing decrese in the stndrd devition of the signl over time for ll three sites, indicting declining sptil heterogeneity with time. The evlution of remotely sensed vegettion phenology for ssessing post-wildfire vegettion dynmics nd response shows some promising results. Trends in vegettion phenologicl metrics tht described postfire vegettion response trjectories re observed for the Indin nd Mt Crmel sites but re less cler for the Gudlest site. The vribles relted to the timing of the growing seson show few trends mong ll three sites with respect to chnges in the timing of vegettion response fter wildfires. These results lso show tht nlysis of both the originl time-series dt, s well s summries of such dt in the form of phenometrics, cn provide useful insights into differences between vegettion communities. For both the time series nd the phenometrics, more mesic sites seem to lend themselves more redily to post-disturbnce nlysis compred with xeric sites, possibly due to n incresed signl mplitude reltive to the noise inherent in MODIS time-series dt. In mking inferences regrding the generl pplicbility of phenology in evluting post-disturbnce vegettion dynmics, we noticed two potentil chllenges. First, the MODIS product used here is 16-dy composite. It is quite possible tht subtle shifts in the timing of phenologicl events due to disturbnces re not detectble t this temporl resolution. Further work should be done with dtsets of finer time scles before concluding tht chnges in the timing of biologicl events ssocited with the disturbnce of plnt communities re not discernble using phenometrics. Second, this nlysis involved nrrow time window of t most 8 yers since burn, which ws limited by the period of record for the MODIS sensor. Thus smple sizes were smll reltive to the mount of internnul vribility one might nticipte for nturl systems. This resulted in chllenges in estblishing significnce for post-fire phenologicl trends. Further ttention to these nd other burned sites my revel trends over longer term thn is seen here. This then constitutes generl constrint to the use of nnul phenology metrics derived from remote sensing dtsets of limited durtion in the determintion of trends in res of recent disturbnce. Post-fire mngement units need tools to both monitor the effect of wildfires on ecosystem helth nd evlute the effect of post-fire vegettion mngement. There re severl structurl, functionl nd lndscpe qulity indictors required for mking informed decisions. This reserch provides few promising monitoring protocols tht cn potentilly ugment the indictors nd tools vilble to post-fire mngement. Mngement ctivities could include, mong others, replnting, slvge-logging, grss-seeding, ppliction of mulch, pellets or strw. The ctul pplictions of these protocols for the evlution of mngement prctices needs further evlution nd must tke into ccount sptil scles nd frequency of required observtion (e.g. Lndst nd MODIS). The proposed monitoring tools

18 92 Int. J. Wildlnd Fire W. J. D. vn Leeuwen et l. nd presented results suggest tht these protocols cn provide informtion bout sesonl nd internnul trends in the postwildfire vegettion response nd llow for comprtive nlysis mong countries. These reserch results suggest tht the presented monitoring tools for post-wildfire vegettion response ssessment bsed on 25-m MODIS time-series dt could contribute to nd be n integrted prt of post-wildfire monitoring protocols. The presented tools re cost effective, nd could provide ner-rel-time ssessments of post-fire vegettion response, ddressing vitl need in fire-prone ecosystems worldwide (Aronson nd Vllejo 26). These tools lso need to be explored to evlute the effectiveness of pre- nd post-wildfire forest restortion tretments nd ssess the effect of recurrent fires nd environmentl conditions on ecosystem dynmics. Acknowledgements MODIS dt re distributed by the Lnd Processes Distributed Active Archive Center, locted t the USA Geologicl Survey Center for Erth Resources Observtion nd Science ( The USDA Forest Service, Pcific South-west Reserch Sttion nd the Prescott Ntionl Forest contributed site nd GIS dt. We thnk Rosrio López- Pom, Jon Llovet nd Ángeles G. Myor for their useful contributions to the field survey t the Gudlest site. We thnk Dr Sturt E. Mrsh for his constructive feedbck nd fcilitting prt of this reserch through the Arizon Remote Sensing Center. The input provided by three nonymous reviewers is very much pprecited nd gretly contributed to this pper. This reserch ws supported by grnt from the Interntionl Arid Lnds Consortium (4R-2). References Allen CD, Svge M, Flk DA, Suckling KF, Swetnm TW, Schulke T, Stcey PB, Morgn P, Hoffmn M, Klingel JT (22) Ecologicl restortion of Southwestern ponderos pine ecosystems: A brod perspective. 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