Forest floor fuel loads and carbon stocks in aleppo pine forests on island of Mljet

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

Količine goriva u šumskoj prostirci sastojina hrasta crnike (Quercus ilex L.) i hrasta medunca (Quercus pubescens Willd.)

The application of newer remote sensing methods, such as aerial and terrestrial lidar scanning and the use of "Structure-from-motion" (SfM) photogrammetry, complemented field data collection and enabled 3D mapping of forest fuel layers, greatly simplifying and improving their characterization. However, these methods are not suitable for quantifying forest floor characteristics. For this purpose, it is still necessary to collect data using classical field methods, determining the presence of subhorizons and their depth, while the characteristics of the forest floor: bulk density, load, carbon concentration and carbon stock are determined in the laboratory. Therefore, it is still common practice to create regression equations that allow operatives to determine the amount of available forest floor fuel and the carbon stock it contains based on the depth of the forest floor, which is an easily measurable variable, or to determine forest floor loading by subhorizon and overall. Forest floor information is used in models for predicting forest fire behavior and spread, in fire effects models, in planning and monitoring mechanical fuel reduction, in quantifying fuel consumption and smoke emissions, in quantifying carbon stocks, in describing habitat and its productivity, and in planning for preparedness. As stands of holm oak (Quercus ilex L.) and pubescent oak (Quercus pubescens Willd.) are located in the Mediterranean part of Croatia, where the risk of forest fires is the highest, and the previously published data on the forest floor are not suitable for the models, the main objectives of the research were to determine the depth, bulk density and load of individual subhorizons of the forest floor and to create regression equations that allow estimating the amount of available fuel in the forest floor based on its depth. Sampling of forest floor in holm oak stands (60, 90 and 100 years old) was conducted on the islands of Lastovo and Mljet, while sampling in pubescent oak stands (53 and 90 years old) was conducted in Dugopolje and Biograd na Moru. The amount of forest floor and OC stock in old stands of holm oak and pubescent oak is twice as small as in old stands of Aleppo pine and Dalmatian black pine. This suggests that pine stands have a significantly greater amount of potentially available fuel in the forest floor and are therefore potentially more at risk from fire, but also that they store twice as much carbon in the forest floor. In this study, for the first time in Croatia, bulk densities of individual subhorizons of the forest floor were determined for holm oak and pubescent oak and regression equations were created that allow estimating the amount of available fuel in the forest floor based on its depth per subhorizon and overall. The results of this research have practical value in simpler quantification of forest floor fuel loading, which is important for operational use of models to predict forest fire behavior and spread, but they can also be used in other models mentioned earlier.Primjena novijih metoda daljinskih istraživanja, kao što su zračno i terestričko skeniranje lidarom te primjena „Structure-from-motion“ (SfM) fotogrametrije nadopunila je terensko prikupljanje podataka i omogućila 3D kartiranje slojeva šumskih goriva čime se značajno pojednostavnila i unaprijedila njihova karakterizacija. Ove metode, međutim, nisu uporabive za kvantificiranje značajki šumske prostirke za koju se podatci i dalje trebaju prikupljati klasičnim terenskim metodama pri čemu se određuje prisutnost podhorizonata i njihova debljina dok se značajke prostirke: gustoća, količina, udjel i zaliha ugljika određuju u laboratoriju. Stoga je i dalje standardna praksa izrada regresijskih jednadžbi koje operativcima omogućuju da na temelju debljine šumske prostirke koja je lako mjerljiva varijabla, odrede količine raspoloživog goriva te zalihe ugljika u njoj, odnosno da na temelju debljina i gustoća pojedinih podhorizonata šumske prostirke odrede količine po podhorizontima i ukupno. Informacije o šumskoj prostirci koriste se u modelima za predikciju ponašanja i širenja šumskih požara, modelima učinka požara, zatim kod planiranja i praćenja mehaničke redukcije goriva, kvantificiranja potrošenog goriva i emisije dima, kvantificiranja zaliha ugljika, za opisivanje staništa i njegove produktivnosti te planiranje pripravnosti. S obzirom na to da sastojine hrasta crnike (Quercus ilex L.) i hrasta medunca (Quercus pubescens Willd.) pridolaze u mediteranskom dijelu Hrvatske gdje je opasnost od šumskih požara najveća, a podatci koji su o šumskoj prostirci do sada publicirani nisu prikladni za navedene modele glavni ciljevi istraživanja bili su utvrditi debljine, gustoće i količine pojedinih podhorizonata šumske prostirke te izraditi regresijske jednadžbe koje omogućuju procjenu količine raspoloživog goriva u šumskoj prostirci temeljem njene debljine. Uzorkovanje šumske prostirke u sastojinama hrasta crnike (starosti 60, 90 i 100 god.) obavljeno je na otocima Lastovu i Mljetu, dok je uzorkovanje u sastojinama hrasta medunca (starosti 53 i 90 god.) obavljeno u okolici Dugopolja i Biograda na Moru. Količina šumske prostirke i zaliha OC u starim sastojinama hrasta crnike i hrasta medunca dvostruko je manja u odnosu na stare sastojine alepskog bora i dalmatinskog crnog bora. Na osnovu toga može se reći da borove sastojine imaju značajno veću količinu potencijalno raspoloživog goriva u šumskoj prostirci te su zbog toga potencijalno ugroženije požarima, ali i da pohranjuju dvostruko više ugljika u šumskoj prostirci. U ovoj su studiji za sastojine hrasta crnike i hrasta medunca, po prvi puta za Hrvatsku, određene gustoće pojedinih podhorizonata šumske prostirke te su izrađene regresijske jednadžbe koje omogućuju procjenu količine raspoloživog goriva u šumskoj prostirci temeljem njene debljine po podhorizontima i ukupno. Rezultati ovog istraživanja imaju praktičnu vrijednost u jednostavnijem kvantificiranju količina goriva, što je važno u operativnoj primjeni modela za predikciju ponašanja i širenja šumskih požara, ali se mogu koristiti i u ostalim, prethodno spomenutim modelima

Forest fires as an ecological and landscape factor in the Dalmatian hinterland

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\u27s. 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

A potential risk of fire on open space in the Republic of 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

Forest floor and soil properties of silver fir and european hop hornbeam forests (Ostryo-abietetum /Fukarek 1963/Trinajstić 1983) on Biokovo mountain

SažetakBrojna istraživanja pokazuju da su šume obične jele ugrožene klimatskim promjenama, posebice na južnim rubovima njihova rasprostranjenja gdje su negativni učinci zatopljenja izraženiji. Šume jele i crnoga graba rastu od 850 m do 1150 m nadmorske visine na kontinentalnoj padini planine Biokovo na karakterističnom vrtačastom reljefu, koji utječe na mozaični raspored golih stijena, tla, vegetacije i šumske prostirke. Cilj ovoga istraživanja je, po prvi puta, za termofilne i najjužnije šume jele i crnoga graba u Hrvatskoj utvrditi fiziografske značajke šumske prostirke i tla te sadržaj teških metala u površinskom sloju tla, pa usporediti dobivene podatke za šumsku prostirku i tlo s podacima za ostale jelove zajednice Hrvatske. Terenskim opažanjima u nizu vrtača utvrđeno je da ljeti (sušno i toplo razdoblje) iz jamskih otvora i pukotina struji hladan zrak, stvarajući u vrtačama specifične mikroklimatske uvjete koji pogoduju jeli i mogu potencijalno biti važan čimbenik njenog opstanka. U šumi jele i crnoga graba utvrđene su značajne količine šumske prostirke i zalihe ugljika, koje su u rasponu od 2,86 kg m–2 do 11,59 kg m–2, odnosno od 1,13 kg m–2 do 4,89 kg m–2 uz izrazitu prostornu varijabilnost. Po fiziografskim značajkama površinskog sloja tla šume jele i crnoga graba grupiraju se uz bukovo-jelove šume sjevernog Velebita i Gorskog kotara, što upućuje na dominantan pedogenetski utjecaj (karbonatnog) matičnog supstrata. Osnovni limitirajući čimbenik tla šuma jele i crnoga graba njegova je mala dubina. U površinskom sloju tla utvrđen je povišen do vrlo visok sadržaj teških metala Cu, Pb, Zn, Ni i Cd.SummaryClimate change is affecting the availability of resources and conditions critical to the life and survival of forest communities and the species that inhabit them, especially at the edges of their distribution. Numerous studies indicate that fir forests are threatened by climate change, especially at the southern edges of their range where the negative effects of warming are more pronounced.The aim of this study was to determine for the first time for the thermophilic and southernmost fir and hornbeam forests (Ostryo-Abietetum) in Croatia the physiographic characteristics of the forest floor and soil, as well as the content of heavy metals in topsoil layer, and to compare the obtained data for the forest floor and soil with data for other fir communities in Croatia. These forests grow from 850 m to 1150 m a.s.l. on the continental slope of Biokovo Mountain on a characteristic sinkhole relief which influences the mosaic arrangement of soil, vegetation and forest floor.Field observations in a number of sinkholes have shown that in summer (the dry and hot period) cold air flows in from caves and cracks and creates specific microclimatic conditions in the sinkholes that are favourable for fir and could be a key factor for its survival.At the bottom of the sinkholes, fir trees dominate, rockiness is less pronounced and Mollic Leptosol and Leptic Cambisol alternate. The forest floor mass (load) is higher. On the other hand, at the edges of the sinkholes, the rockiness is more pronounced, the soil is either very shallow (Mollic Leptosol) or absent, and the forest floor mass is lower. Thermophilic tree species dominate, while firs are sporadic or absent.Considerable amounts of forest floor and carbon stocks were determined in the fir and hornbeam forests, ranging from 2.86 kg m-2 to 11.59 kg m-2 and 1.13 kg m-2 to 4.89 kg m-2, respectively, with high spatial variability. According to the physiographic characteristics of the surface layer of the soil, fir and hornbeam forests are grouped together with the beech-fir forests of the northern Velebit and Gorski kotar, indicating the dominant pedogenetic influence of the (carbonate) parent substrate. The basic limiting factor of the soil of fir and hornbeam forests is its shallow depth. Elevated to very high content of the heavy metals Cu, Pb, Zn, Ni and Cd were found in the topsoil

Moisture of dead forest fuel as a factor influencing forest fire occurrence

Udio vlage mrtvog sitnog šumskog goriva je središnja komponenta gotovo svih modela za procjenu opasnosti od šumskih požara te modela za predikciju ponašanja šumskih požara. Glavni cilj ovoga rada bio je izraditi operativno primjenjive modele procjene udjela vlage otpalih iglica alepskog bora (Pinus halepensis Mill.) i dalmatinskog crnog bora (Pinus nigra Arnold subsp. dalmatica (Vis.) Franco), u uvjetima ispod točke zasićenosti vlakanaca. Ravnotežni udio vlage i vrijeme reakcije eksperimentalno su određeni u komori rasta, za obje vrste. Temeljem rezultata navedenih laboratorijskih eksperimenata i strukture HFFMC (Hourly Fine Fuel Moisture Code) modela, izrađeni su modeli za procjenu udjela vlage sitnog goriva na bazi sata, koji su u odabranim sastojinama navedenih vrsta i testirani, zajedno s izvornim HFFMC modelom. Rezultati testiranja su pokazali da HFFMC model, iako namijenjen za listinac bora, nije prikladan za operativnu primjenu u šumama alepskog i dalmatinskog crnog bora. S druge strane, izrađeni modeli su postigli bolje rezultate i prikladni su za operativnu primjenu jer srednja apsolutna pogreška modela za alepski bor iznosi 1 % udjela vlage, a modela za dalmatinski crni bor 0,86 % udjela vlage. Dobiveni rezultati sugeriraju da ovi modeli moraju biti specifični za pojedinu vrstu kako bi postigli točnost potrebnu za preciznu predikciju ponašanja šumskog požara. U ovom su radu prvi put, za obje vrste, određeni ravnotežni udio vlage i vrijeme reakcije, ali i izrađen ovakav tip modela. Ravnotežni udio vlage prvi put je određen i za lišće hrasta crnike (Quercus ilex L.) te hrasta medunca (Quercus pubescens Willd.). Osim izrađenih modela za procjenu udjela vlage sitnog goriva, u radu je regresijskom analizom definirana povezanost debljine šumske prostirke s njenom količinom. Za sastojine alepskog bora, dalmatinskog crnog bora, hrasta crnike i hrasta medunca dani su regresijski modeli za OL-podhorizont, zatim za OF i OH podhorizonte zajedno, te za ukupnu količinu šumske prostirke. Izrađeni regresijski modeli omogućuju jednostavno kvantificiranje količine goriva, što je jako važno u operativnoj primjeni modela za predikciju ponašanja šumskih požara. Regresijski modeli, zajedno s izrađenim modelima za procjenu udjela vlage sitnog goriva, predstavljaju temelj za usvajanje postojećih ili izradu vlastitih modela za predikciju ponašanja šumskih požara.The moisture content of dead fine forest fuels is a central component of nearly all fire behaviour and fire danger rating systems. The main objective of this thesis was to develop operationally applicable fine fuel moisture prediction models for Aleppo pine (Pinus halepensis Mill.) and Dalmatian black pine (Pinus nigra (Arnold) subsp. dalmatica ((Vis.) Franco)) needle litters below the fibre saturation point. Experimental measurements of equilibrium moisture content and response time of dead needles were carried out in a growth chamber for both species. The results of these laboratory experiments and the structure of the HFFMC (Hourly Fine Fuel Moisture Code) model were used to develop hourly fine fuel moisture prediction models, whose predictive ability was tested in selected pine species stands. The predictive ability of the HFFMC model for both litter types was also evaluated. Although the HFFMC model was designed for pine litter, the results suggest that it is unsuitable for operational use in Aleppo pine and Dalmatian black pine forests. In contrast, new models performed better and can be used operationally because the mean absolute error of fine fuel moisture prediction model for Aleppo pine is 1% moisture content, and for Dalmatian black pine it is 0.86 % moisture content. The results suggest that these models should be species-specific in order to achieve the accuracy needed for precise prediction of fire behaviour. This thesis is the first to report equilibrium moisture content and response time data for both species, as well as develop this type of model. Equilibrium moisture content was also determined for the first time for the leaves of holm oak (Quercus ilex L.) and pubescent oak (Quercus pubescens Willd.). The other objective of this thesis, in addition to developing fine fuel moisture prediction models, was to develop regression models that relate forest floor depth to forest floor fuel load. Regression models were given for the OL horizon, the OF and OH horizons, and for the entire forest floor in Aleppo pine, Dalmatian black pine, holm oak and pubescent oak stands. These regression models allow for reliable quantifications of forest floor fuel loads, which is very important in the operative application of fire behaviour prediction models. Regression models, together with fine fuel moisture prediction models, provide a basis for the adoption of existing or development of our own fire behaviour prediction models

Moisture of dead forest fuel as a factor influencing forest fire occurrence

Udio vlage mrtvog sitnog šumskog goriva je središnja komponenta gotovo svih modela za procjenu opasnosti od šumskih požara te modela za predikciju ponašanja šumskih požara. Glavni cilj ovoga rada bio je izraditi operativno primjenjive modele procjene udjela vlage otpalih iglica alepskog bora (Pinus halepensis Mill.) i dalmatinskog crnog bora (Pinus nigra Arnold subsp. dalmatica (Vis.) Franco), u uvjetima ispod točke zasićenosti vlakanaca. Ravnotežni udio vlage i vrijeme reakcije eksperimentalno su određeni u komori rasta, za obje vrste. Temeljem rezultata navedenih laboratorijskih eksperimenata i strukture HFFMC (Hourly Fine Fuel Moisture Code) modela, izrađeni su modeli za procjenu udjela vlage sitnog goriva na bazi sata, koji su u odabranim sastojinama navedenih vrsta i testirani, zajedno s izvornim HFFMC modelom. Rezultati testiranja su pokazali da HFFMC model, iako namijenjen za listinac bora, nije prikladan za operativnu primjenu u šumama alepskog i dalmatinskog crnog bora. S druge strane, izrađeni modeli su postigli bolje rezultate i prikladni su za operativnu primjenu jer srednja apsolutna pogreška modela za alepski bor iznosi 1 % udjela vlage, a modela za dalmatinski crni bor 0,86 % udjela vlage. Dobiveni rezultati sugeriraju da ovi modeli moraju biti specifični za pojedinu vrstu kako bi postigli točnost potrebnu za preciznu predikciju ponašanja šumskog požara. U ovom su radu prvi put, za obje vrste, određeni ravnotežni udio vlage i vrijeme reakcije, ali i izrađen ovakav tip modela. Ravnotežni udio vlage prvi put je određen i za lišće hrasta crnike (Quercus ilex L.) te hrasta medunca (Quercus pubescens Willd.). Osim izrađenih modela za procjenu udjela vlage sitnog goriva, u radu je regresijskom analizom definirana povezanost debljine šumske prostirke s njenom količinom. Za sastojine alepskog bora, dalmatinskog crnog bora, hrasta crnike i hrasta medunca dani su regresijski modeli za OL-podhorizont, zatim za OF i OH podhorizonte zajedno, te za ukupnu količinu šumske prostirke. Izrađeni regresijski modeli omogućuju jednostavno kvantificiranje količine goriva, što je jako važno u operativnoj primjeni modela za predikciju ponašanja šumskih požara. Regresijski modeli, zajedno s izrađenim modelima za procjenu udjela vlage sitnog goriva, predstavljaju temelj za usvajanje postojećih ili izradu vlastitih modela za predikciju ponašanja šumskih požara.The moisture content of dead fine forest fuels is a central component of nearly all fire behaviour and fire danger rating systems. The main objective of this thesis was to develop operationally applicable fine fuel moisture prediction models for Aleppo pine (Pinus halepensis Mill.) and Dalmatian black pine (Pinus nigra (Arnold) subsp. dalmatica ((Vis.) Franco)) needle litters below the fibre saturation point. Experimental measurements of equilibrium moisture content and response time of dead needles were carried out in a growth chamber for both species. The results of these laboratory experiments and the structure of the HFFMC (Hourly Fine Fuel Moisture Code) model were used to develop hourly fine fuel moisture prediction models, whose predictive ability was tested in selected pine species stands. The predictive ability of the HFFMC model for both litter types was also evaluated. Although the HFFMC model was designed for pine litter, the results suggest that it is unsuitable for operational use in Aleppo pine and Dalmatian black pine forests. In contrast, new models performed better and can be used operationally because the mean absolute error of fine fuel moisture prediction model for Aleppo pine is 1% moisture content, and for Dalmatian black pine it is 0.86 % moisture content. The results suggest that these models should be species-specific in order to achieve the accuracy needed for precise prediction of fire behaviour. This thesis is the first to report equilibrium moisture content and response time data for both species, as well as develop this type of model. Equilibrium moisture content was also determined for the first time for the leaves of holm oak (Quercus ilex L.) and pubescent oak (Quercus pubescens Willd.). The other objective of this thesis, in addition to developing fine fuel moisture prediction models, was to develop regression models that relate forest floor depth to forest floor fuel load. Regression models were given for the OL horizon, the OF and OH horizons, and for the entire forest floor in Aleppo pine, Dalmatian black pine, holm oak and pubescent oak stands. These regression models allow for reliable quantifications of forest floor fuel loads, which is very important in the operative application of fire behaviour prediction models. Regression models, together with fine fuel moisture prediction models, provide a basis for the adoption of existing or development of our own fire behaviour prediction models

Moisture of dead forest fuel as a factor influencing forest fire occurrence

Udio vlage mrtvog sitnog šumskog goriva je središnja komponenta gotovo svih modela za procjenu opasnosti od šumskih požara te modela za predikciju ponašanja šumskih požara. Glavni cilj ovoga rada bio je izraditi operativno primjenjive modele procjene udjela vlage otpalih iglica alepskog bora (Pinus halepensis Mill.) i dalmatinskog crnog bora (Pinus nigra Arnold subsp. dalmatica (Vis.) Franco), u uvjetima ispod točke zasićenosti vlakanaca. Ravnotežni udio vlage i vrijeme reakcije eksperimentalno su određeni u komori rasta, za obje vrste. Temeljem rezultata navedenih laboratorijskih eksperimenata i strukture HFFMC (Hourly Fine Fuel Moisture Code) modela, izrađeni su modeli za procjenu udjela vlage sitnog goriva na bazi sata, koji su u odabranim sastojinama navedenih vrsta i testirani, zajedno s izvornim HFFMC modelom. Rezultati testiranja su pokazali da HFFMC model, iako namijenjen za listinac bora, nije prikladan za operativnu primjenu u šumama alepskog i dalmatinskog crnog bora. S druge strane, izrađeni modeli su postigli bolje rezultate i prikladni su za operativnu primjenu jer srednja apsolutna pogreška modela za alepski bor iznosi 1 % udjela vlage, a modela za dalmatinski crni bor 0,86 % udjela vlage. Dobiveni rezultati sugeriraju da ovi modeli moraju biti specifični za pojedinu vrstu kako bi postigli točnost potrebnu za preciznu predikciju ponašanja šumskog požara. U ovom su radu prvi put, za obje vrste, određeni ravnotežni udio vlage i vrijeme reakcije, ali i izrađen ovakav tip modela. Ravnotežni udio vlage prvi put je određen i za lišće hrasta crnike (Quercus ilex L.) te hrasta medunca (Quercus pubescens Willd.). Osim izrađenih modela za procjenu udjela vlage sitnog goriva, u radu je regresijskom analizom definirana povezanost debljine šumske prostirke s njenom količinom. Za sastojine alepskog bora, dalmatinskog crnog bora, hrasta crnike i hrasta medunca dani su regresijski modeli za OL-podhorizont, zatim za OF i OH podhorizonte zajedno, te za ukupnu količinu šumske prostirke. Izrađeni regresijski modeli omogućuju jednostavno kvantificiranje količine goriva, što je jako važno u operativnoj primjeni modela za predikciju ponašanja šumskih požara. Regresijski modeli, zajedno s izrađenim modelima za procjenu udjela vlage sitnog goriva, predstavljaju temelj za usvajanje postojećih ili izradu vlastitih modela za predikciju ponašanja šumskih požara.The moisture content of dead fine forest fuels is a central component of nearly all fire behaviour and fire danger rating systems. The main objective of this thesis was to develop operationally applicable fine fuel moisture prediction models for Aleppo pine (Pinus halepensis Mill.) and Dalmatian black pine (Pinus nigra (Arnold) subsp. dalmatica ((Vis.) Franco)) needle litters below the fibre saturation point. Experimental measurements of equilibrium moisture content and response time of dead needles were carried out in a growth chamber for both species. The results of these laboratory experiments and the structure of the HFFMC (Hourly Fine Fuel Moisture Code) model were used to develop hourly fine fuel moisture prediction models, whose predictive ability was tested in selected pine species stands. The predictive ability of the HFFMC model for both litter types was also evaluated. Although the HFFMC model was designed for pine litter, the results suggest that it is unsuitable for operational use in Aleppo pine and Dalmatian black pine forests. In contrast, new models performed better and can be used operationally because the mean absolute error of fine fuel moisture prediction model for Aleppo pine is 1% moisture content, and for Dalmatian black pine it is 0.86 % moisture content. The results suggest that these models should be species-specific in order to achieve the accuracy needed for precise prediction of fire behaviour. This thesis is the first to report equilibrium moisture content and response time data for both species, as well as develop this type of model. Equilibrium moisture content was also determined for the first time for the leaves of holm oak (Quercus ilex L.) and pubescent oak (Quercus pubescens Willd.). The other objective of this thesis, in addition to developing fine fuel moisture prediction models, was to develop regression models that relate forest floor depth to forest floor fuel load. Regression models were given for the OL horizon, the OF and OH horizons, and for the entire forest floor in Aleppo pine, Dalmatian black pine, holm oak and pubescent oak stands. These regression models allow for reliable quantifications of forest floor fuel loads, which is very important in the operative application of fire behaviour prediction models. Regression models, together with fine fuel moisture prediction models, provide a basis for the adoption of existing or development of our own fire behaviour prediction models