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Estimation of forest floor loading is important for many forest management applications, especially those related to fire management and carbon balance. We quantified the physical properties (depth, fuel load, bulk density) and carbon stocks of endemic Dalmatian black pine (Pinus nigra J.F. Arnold subsp. dalmatica [Vis.] Franco) forest floor layers. We also examined how these properties differ with stand age and layer. Forest floor depths ranged from 1.5 cm to 11.5 cm and forest floor fuel (FFF) loads ranged from 11.9 Mg ha-1 in the young stand to 197.3 Mg ha-1 in the old stand. Forest floor carbon (FFC) stocks ranged from 6.4 Mg C ha-1 in the young stand to 85.8 Mg C ha-1 in the old stand. We developed regression equations that can be used to convert the investigated forest floor depth into load in each layer individually and across all layers. These equations, together with the organic carbon (OC) concentration determined here for individual forest floor layers, simplify quantification of carbon stocks in the forest floor. Bulk density (BD) values reported here can also be used to convert depth measurements to loads for each layer and the entire forest floor. The results presented here are suitable for rapid estimation of FFF loads and FFC stocks based solely on forest floor depth, without the need to sample and analyze large amounts of forest floor fuels. Similarly, spatial distribution in FFF loads and carbon stocks can be assessed simply by measuring forest floor depths.

Fuel moisture content (FMC) is the mass of water contained within vegetation in relation to the dry mass. It is one of the most important variables in all wildfire prediction and spread simulation models. FMC has great influence on wildfire ignition and combustion. For accurate wildfire spread simulations and wildfire risk index estimations, fuel moisture is a very important input variable. Since 2016, Croatian firefighters in everyday practice use Web based System for wildfire behaviour modelling and wildfire spread simulation named AdriaFirePropagator. The simulator is based on semi-empirical Rothermel’s surface fire spread model for wildfire behaviour modelling and cellular automata for wildfire spread simulation. Fuel moisture, both live and dead is a very sensitive parameter in wildfire behaviour modelling. Live fuel moisture defines the moisture content of live fuels and dead fuel moisture is defined as moisture of dead fuels with time-lag of 1 hour, 10 hour and 100 hours. In Croatia there is no organised service for daily measurement of fuel moisture content, so values of these variables has to be estimated from meteorological parameters. This paper compares three approaches to fine dead fuel estimation, all implemented in AdriaFirePropagator. The first one, used in most wildfire simulation software, was based on standard mathematical models that relate air temperature, air humidity, 24-hours rainfall and wind speed with fine dead fuel moisture (FFMC). The second one was based on standard Fire Behavior Analysis Tables (FBA Tables) and the third one was based on intensive experimental research of dead fine fuel moisture content of Aleppo pine (Pinus halepenses Mill.). After intensive experimental research new Croatian fine dead fuel models PhFFMC was developed, tested in selected pine species stand and applied in AdriaFirePropagator for fuel regions where this pine species dominate. Croatian model is much better correlated with experimental data, therefore for more accurate wildfire simulations, similar models have to be developed also for other typical vegetation fuel types.

During the last three decades, there has been an increase in the incidence of severe crown fires affecting black pine forests in the sub-Mediterranean area. The objective of this study was to develop and test a model to predict fine fuel moisture content for Dalmatian black pine (Pinus nigra J.F. Arnold subsp. dalmatica (Vis.) Franco) needle litter. We performed laboratory measurements of equilibrium moisture content and response time of dead black pine needles to modify the hourly fine fuel moisture code (FFMC) model, and we compared the predictive ability of the hourly FFMC model with that of modified model (PnFFMC). Field tests showed that although the hourly FFMC model reproduced trends in moisture content of black pine needles quite well, it consistently overestimated moisture content (mean absolute error 3.9%). The PnFFMC model performed better than the hourly FFMC model and was closer to the line of equivalence (mean absolute error 0.9%). This study indicates that the hourly FFMC can easily be modified by incorporating appropriate species-specific equilibrium moisture content and response time values, leading to more accurate predictions of fine fuel moisture content. The need to use recently fallen needles in fuel moisture modelling for Mediterranean pine species is highlighted.

Sa stajališta šumskih požara, šumska prostirka se promatra kao potencijalno gorivo, no njena uloga i značaj u izmjeni tvari i energije, a poglavito ugljika u kontekstu aktualnih globalnih klimatskih promjena su veliki. Zbog toga se informacije o šumskoj prostirci tradicionalno koriste u modelima za procjenu opasnosti od šumskih požara te modelima za predikciju ponašanja i širenja šumskih požara, a u novije vrijeme i za procjenu emisija ugljika i drugih plinova te kvantificiranje zaliha ugljika. Glavni ciljevi ovog rada su: određivanje debljine, gustoće i količine pothorizonata šumske prostirke uz pripadajuće zalihe ugljika u sastojinama alepskog bora te izrada regresijskih modela debljine i količine šumske prostirke te debljine i zalihe ugljika, po pothorizontima i ukupno. Uzorkovanje šumske prostirke obavljeno je na području NP Mljet, u sastojinama alepskog bora, po debljinskim razredima: 0–50 cm, 100–150 cm i 200–250 cm opsega. Uzorkovanje je obavljeno po pothorizontima, a količine i udio organskog ugljika određene su za svaki pothorizont zasebno. Iz dobivenih rezultata vidljivo je da sastojine alepskog bora vežu značajne količine ugljika u svojoj prostirci, no uvjeti i zakonitosti nisu još dovoljno proučeni. U prilog tomu govore značajno veće debljine i količine šumske prostirke u sastojinama alepskog bora od onih do sada poznatih, pa je tako ispod stabala opsega 200–250 cm utvrđena srednja debljina prostirke od 9,0 cm i procijenjena količina od 94,3 Mg ha–1 sa zalihom ugljika od 37 Mg C ha–1. Regresijskom analizom utvrđena je statistički značajna veza debljina šumske prostirke s količinama prostirke i zalihama ugljika, te su dani regresijski modeli za OL pothorizont, zatim za OF1,OF2 i OH zajedno, kao i za ukupnu prostirku. Rezultati ovog istraživanja imaju praktičnu vrijednost u jednostavnijem kvantificiranju količina goriva i zaliha ugljika u šumskoj prostirci sastojina alepskog bora, koje se potom mogu koristiti u navedenim modelima. Inventarizacija šumskih goriva predstavlja osnovu za parametrizaciju i operativnu primjenu navedenih modela u Hrvatskoj.

Pinus halepensis (Mill.) is the most widely distributed and abundant Mediterranean pine, as well as one of the species most affected by wildfires in Europe. The objective of this study was to develop and test an operationally useful fine fuel moisture prediction model for P. halepensis needle litter below the fibre saturation point, where flammability increases rapidly with decreasing moisture content. The predictive ability of the hourly Fine Fuel Moisture Code (FFMC) was also evaluated. Even though the hourly FFMC model is designed for pine litter, it consistently over-predicted moisture content of P. halepensis needle litter and could not track the rapid moisture change during the day. Experimental measurements of equilibrium moisture content and response time of dead P. halepensis needles were used to modify the hourly FFMC model. The modified model performed better than the hourly FFMC model on all evaluation parameters, with a mean absolute error of 1% moisture content. Our results suggest that fine fuel moisture prediction models should be species-specific in order to achieve the accuracy needed for precise prediction of fire behaviour.

Sa stajališta šumskih požara, šumska prostirka se promatra kao potencijalno gorivo, no njena uloga i značaj u izmjeni tvari i energije, a poglavito ugljika u kontekstu aktualnih globalnih klimatskih promjena su veliki. Zbog toga se informacije o šumskoj prostirci tradicionalno koriste u modelima za procjenu opasnosti od šumskih požara te modelima za predikciju ponašanja i širenja šumskih požara, a u novije vrijeme i za procjenu emisija ugljika i drugih plinova te kvantificiranje zaliha ugljika. Glavni ciljevi ovog rada su: određivanje debljine, gustoće i količine pothorizonata šumske prostirke uz pripadajuće zalihe ugljika u sastojinama alepskog bora te izrada regresijskih modela debljine i količine šumske prostirke te debljine i zalihe ugljika, po pothorizontima i ukupno. Uzorkovanje šumske prostirke obavljeno je na području NP Mljet, u sastojinama alepskog bora, po debljinskim razredima: 0–50 cm, 100–150 cm i 200–250 cm opsega. Uzorkovanje je obavljeno po pothorizontima, a količine i udio organskog ugljika određene su za svaki pothorizont zasebno. Iz dobivenih rezultata vidljivo je da sastojine alepskog bora vežu značajne količine ugljika u svojoj prostirci, no uvjeti i zakonitosti nisu još dovoljno proučeni. U prilog tomu govore značajno veće debljine i količine šumske prostirke u sastojinama alepskog bora od onih do sada poznatih, pa je tako ispod stabala opsega 200–250 cm utvrđena srednja debljina prostirke od 9,0 cm i procijenjena količina od 94,3 Mg ha–1 sa zalihom ugljika od 37 Mg C ha–1. Regresijskom analizom utvrđena je statistički značajna veza debljina šumske prostirke s količinama prostirke i zalihama ugljika, te su dani regresijski modeli za OL pothorizont, zatim za OF1,OF2 i OH zajedno, kao i za ukupnu prostirku. Rezultati ovog istraživanja imaju praktičnu vrijednost u jednostavnijem kvantificiranju količina goriva i zaliha ugljika u šumskoj prostirci sastojina alepskog bora, koje se potom mogu koristiti u navedenim modelima. Inventarizacija šumskih goriva predstavlja osnovu za parametrizaciju i operativnu primjenu navedenih modela u Hrvatskoj., From the aspect of forest fires, the forest floor is considered a potential fuel: however, in the context of current global climate change it plays an exceptionally important role in the exchange of matter and energy and of carbon in particular. For this reason, forest floor data are traditionally used in forest fire danger rating and in fire behavior and spread models. More recently they have also been used to estimate emissions of carbon and other gasses and to gasses and to quantify carbon stocks. The main objectives of this study are to a) determine the depth, bulk density and fuel load for each forest floor horizon with the associated carbon stock in Aleppo pine stands and b) develop regression models that relate forest floor depth to forest floor fuel load and forest floor depth to forest floor carbon stock, for horizons and for the entire forest floor. Forest floor sampling was carried out in Aleppo pine stands situated in Mljet National Park, per 0-50 cm, 100-150 cm and 200-250 cm circumference classes. Each forest floor horizon was sampled separately, and fuel load and organic carbon content were determined for each horizon. Our results suggest that Aleppo pine stands contain significant carbon stocks in the forest floor, but relations and processes that influence these stocks have not been sufficiently studied. This is supported by significantly greater forest floor depths and fuel loads in Aleppo pine stands than previously reported. Thus, the mean depth of forest floor of 9.0 cm, fuel load of 94.3 Mg ha-1, and carbon stock of 37 Mg C ha–1 were determined under trees with a 200-250 cm circumference class. Regression analysis revealed a statistically significant relationship between depth and fuel load and between depth and carbon stock. Regression models were given for the OL horizon, the OF1,OF2 and OH horizons, as well as for the entire forest floor. Our results have practical value as they will allow reliable quantifications of forest floor fuel loads and carbon stocks in Aleppo pine stands by using easily measurable fuel characteristic, which can then be applied in the aforementioned models. The forest fuel inventory provides the basis for parameterization and operational use of a number of forest resource management applications in Croatia.

Posljednjih nekoliko desetljeća na području Mediterana, uslijed povećanja temperaturnih ekstrema i povećanja učestalosti toplinskih valova s maksimalnom dnevnom temperaturom zraka većom od 30 °C, prisutan je generalni trend povećanja opožarene površine, učestalosti požara, njihovog intenziteta i žestine. U Hrvatskoj je taj trend također uočljiv, a osobito na području krša. U radu je prikazana i prostorna razdioba područja ugroženih toplinskim stresom na području Hrvatske koja potvrđuje da je upravo jadransko područje najugroženije s obzirom na klimatske promjene kod nas. Dodatno zabrinjava činjenica da se područje ugroženosti od požara za vrijeme sušnih i vrućih razdoblja širi od jadranske obale prema unutrašnjosti Hrvatske. Analiza klimatskih pokazatelja prikazana u radu ukazuje na činjenicu da u budućnosti možemo očekivati sve veću opasnost od požara otvorenog prostora u Republici Hrvatskoj po prostornoj i sezonskoj ugrozi. Prema raznim klimatskim scenarijima u Europi se očekuju intenzivniji, češći i dugotrajniji valovi vrućine u drugoj polovici 21. stoljeća pa će zasigurno najveći izazov održivog gospodarenja šumskim ekosustavima na području Mediterana biti borba protiv šumskih požara., The past few decades in the Mediterranean, due to the increase of temperature extremes and increased frequency of heat waves with maximum daily air temperature above 30 ° C, there is a general trend of increasing fire-affected areas, the frequency of fire, their intensity and severity. In Croatia, this trend is also evident, especially in the field of rubble. The paper describes the spatial distribution of the areas at risk of heat stress on the Croatian territory which confirms that it was the Adriatic region the most vulnerable with respect to climate change in our country. An additional problem is the fact that the area of fire risk in dry and hot period extending from the Adriatic coast to the Croatian inland. Analysis of climate indicators presented in the paper indicates that in the future we can expect an increasing risk of fire of open space in the Republic of Croatia in terms of spatial and seasonal endanger. According to various climate scenarios in Europe are expected to be more intense, more frequent and longer-lasting heat waves in the second half of the 21st century and will certainly the greatest challenge of sustainable management of forest ecosystems in the Mediterranean will be the fight against forest fires.

Šumski požari predstavljaju veliku opasnost za šumska zemljišta i šume u Republici Hrvatskoj, a naročito u Dalmaciji, na otocima i u Dalmatinskoj zagori. Sve veći broj požara u značajnoj mjeri degradira ekosustav i narušava njegovu stabilnost što dovodi do smanjenja bioraznolikosti i povećanja opustošenih prostora. U posljednja dva desetljeća 20. stoljeća, godišnja izgorena površina u mediteranskim zemljama procijenjena je na oko 600 000 ha, što je gotovo dvostruko više nego tijekom 1970-tih godina. U razdoblju od 1998. do 2004. godine bilo je ukupno 115 666 požara kojim je bilo obuhvaćeno ukupno 1 250 892 ha. Od 1996. godine do 2005. godine u Republici Hrvatskoj bilo je ukupno 3 324 šumskih požara, od čega su na krškom području bila 2 792 šumska požara ili 84,00 %. Ukupna izgorena površina na krškom i kontinentalnom području Hrvatske je 183 015 ha, od čega na krško područje otpada 175 199 ha ili 95,73 %. Prosječna izgorena površina po požaru na krškom području iznosi 62,75 ha. U istom razdoblju na području Dalmatinske zagore (šumarije: Drniš, Vrgorac, Knin, Sinj, Imotski) bio je ukupno 831 požar, odnosno 29,76 % od ukupnog broja požara na krškom području, a čime je izgoreno 44 164 ha površine, odnosno 25,21 % od ukupno izgorene površine krškog područja u promatranom razdoblju. Usavršavanje metoda prevencije i borbe protiv šumskih požara omogućuje bitno smanjenje opožarenih površina. Poznavati čimbenike koji uvjetuju nastanak šumskih požara kao i čimbenike koji započinju širenje vatrene stihije bitno je zbog pripreme i vođenja preventivnih aktivnosti. Jedna od najvažnijih preventivnih mjera jest poznavanje obilježja šumskih goriva, u prvom redu njihove zapaljivosti, gorivosti i sadržaja vlage. Uzroci nastanka požara mogu biti različiti, od prirodnih (suša, visoka temperatura, niska relativna vlaga zraka, vjetreni režim, udar groma) do onih uzrokovanih ljudskim nemarom (paljenje korova na poljoprivrednim površinama, bačen neugašen opušak, neugašena izletnička vatra, razni ekološki incidenti) koji su i najčešći. Dosadašnjim spoznajama vezanim uz problematiku šumskih požara utvrđeno je da pozornost treba posvetiti pedološkim, klimatskim i vegetacijskim uvjetima nastanka i širenja požara, te svekolikim uvjetima obnove šuma poslije požara. Odluka o tome kako pristupiti obnovi šuma ili šumskog zemljišta koje je bilo zahvaćeno šumskim požarom ili je njime uništeno, ovisi o nizu biološko-ekoloških i gospodarskih činitelja. Sam požar, u pravilu, uzrokuje regresiju vegetacije te se na opožarenim površinama, ovisno o tipu vegetacije prije požara i biološko-ekološkim uvjetima javljaju specifični degradacijski tipovi vegetacije. Međutim, na brzinu, kvalitetu i uspjeh progresivne sukcesije izgorenih površina pozitivno može utjecati čovjek u vidu izbora vrsta i metoda sanacije. Uvažavanjem svega navedenog zasigurno bi se znatno pridonijelo očuvanju biološke i krajobrazne raznolikosti uz načelo održivog razvoja prirodnih ekosustava., Forest fires represent a major threat to forests and forest land in Croatia, especially in Dalmatia, the islands and the Dalmatian hinterland. An increasing number of fires significantly degrade the ecosystem and disrupt its stability, leading to a decrease in biodiversity and increase the devastated area. In the last two decades of the 20th century, the annual burned areas in Mediterranean countries is estimated at around 600 000 ha, which is almost twice as much during the 1970's. From 1998 to 2004. there were a total of 115 666 fire which included a total of 1,250,892 hectares. Since 1996. year until 2005. in the Republic of Croatia had a total of 3324 forest fires, of which the karst area was 2792 forest fire, or 84.00%. The total burned area in the continental karst and Croatian territory is 183 015 ha, of which the karst area of waste 175 199 hectares or 95.73%. The average area burned per fire in the karst area is 62.75 hectares. In the same period in the Dalmatian hinterland (Forestry office: Drniš Vrgorac, Knin, Sinj, Imotski) was a total of 831 fires, or 29.76% of the total number of fires in the karst area, which burned 44 164 ha, or 25 , 21% of total burn surface area of the karst areas in the period. Improving methods of prevention and fight against forest fires allows significantly reducing the burnt areas. Knowing the factors that condition the occurrence of forest fires as well as factors that start spreading the blaze is essential for the preparation and conduct of preventive activities. One of the most important preventive measure is to know the characteristics of forest fuels, primarily their flammability, combustibility, and moisture content. Causes of fire may be different from natural (drought, high temperatures, low relative humidity, wind regime, lightning) to those caused by human negligence (burning weeds on agricultural land, thrown unquenched butt, unquenched fire excursion, various environmental incidents) which are most common. Current state of knowledge concerning the problem of forest fires has been found that attention should be paid pedological, climatic and vegetation conditions of occurrence and spread of fire, and the overall conditions of regeneration after fire. The decision on how to approach restoration of forests or forest land that was affected by forest fires or it is destroyed depends on a number of biological, ecological and economic factors. The fire, normally, causing regression of the vegetation on the burnt areas, depending on the type of vegetation before the fire and the biological and ecological conditions occurring specific degradation of vegetation types. But, however, the speed, quality and success of the progressive succession of burned areas can positively affect a man in mind the choice of types and methods of rehabilitation. Appreciating all this would certainly contribute significantly to the preservation of biological and landscape diversity with the principle of sustainable development of natural ecosystems.