Fire Ecology S. P. Singh FRI , Dehradun, India E. Mail: firstname.lastname@example.org
All lands affected by naturalfires• Globally 5,130 Tg biomass consumedannually by fire, emitting 8,200 Tg/yr CO 2, 413Tg/yr CO and 19.4 Tg/yr methane.• Lightning• Sparks from falling rocks• Volcanic activity• Natural combustion
Human evolution and domination linked to fire , and so are some ecosystems• Mediterranean xeric shrub communities- chapparal, fynbos, mattorals• African savannas, Brazil’s cerrado, prairies, Himalayan Chir pine , they together account for 40% of vegetation.
In India most fires are man-made ;affect 3.7 million ha annually• To grow grasses• Shifting cultivation• Collection of NTFPs• Due to stay in fringe areas• To keep wild animals away
CO2 emission due to forest fires in India Tg CO2 emission Years
Black carbon (BC) concentration at a mountain site (Nainital), IndiaNote: The black carbon concentration is lowest during the months of thesummer monsoonSource: Dumka et al. (2010)
Types of fireSurface -• Spreads over ground, generally burns only litter, seedlings,herbs, and lower parts of trees partially.• Ground temp. 90-1200 CCrown-• Ignited by a surface fire flame; flame travels from one treecrown to another; common in coniferous forests;• A windy condition more damagingGround-•Flameless, consumes organic matter below litter layeraccumulated over hundreds of years, can consume rhizomes,roots and seeds,causing lasting damages
• El Nino- Southern Oscillation (ENSO) caused bycyclic climate variability can lead to widespread fires inSouth Asia; In seasonal tropical forests (monsoon) ofquite common• Agricultural burning causing catastrophic fires inCentral America, Indonesia, Mexico.• Shifting cultivation in tropical forest areas• Savannas
Fire behaviour• Fuel- amount and quality (dry or wet)fuel size, C:Nratio, higher surface to volume ratio of litter; lesscompaction (means more O2 and more inflammability)e.g. some Australian eucalypts highly flammable dueto oil• Fire intensity (I) = Heat (H, Kcal g/ dry matter)XFuel availability (g dry matter m-2) X Rate of spread(R, m sec-1) (Wakimoto 1977)• A wind can bring a fresh supply of oxygen
Effect of fire on air• Combustion is generally incomplete• Releases CO2, H2O, CO, CH4, N2O, NH3, trace hydrocarbon, volatile organic compounds, ozone (Crutzen & Goldmmer 1993)• Black carbon, other aerosols
Effect of fire on soil• Soil temperature raised- e.g., 6900 C in intense burn 4100 C in moderate burn 2400 C in light burn at surface,but the rise at 5 cm soil depth being 11.6%, 17.1% and 25% of surface respectively also persistent rise due to the reduced albido
Some nutrients and organic matter lost• N& K compounds volatilized, released and lost by distillation; N loss little up to 2000C, but up to 60% at 7000C ; also lost are Fe, Zn, Na at high temperatures• Moderate rise in temperate region raises the release of Ca, Na, Mg, hence cycling enhanced (De Bano et al. 1977).• Organic matter - Cation Exchange Capacity - Capacity to hold nutrients -• N2 fixers increase: Alnus, Robinia, Lespedeza, Desmodium• Erosion loss- Annual sediment yield after a wild fire 14- 28 fold of pre-burn stage (Helvey et al. 1985), cascade range, Washington P-14 times, Ca, Mg- 26 times, K-38 times.
Soil and nutrient losses after a wildfire in NWPacific, USAAltitudes 610 m to 2,135 m, with average slope ~ 50%a mature forest of Ponderosa Pine (P. Ponderosa) andDouglas fire( Pseudotsuga menziesii) Precipitation average 58 cm, only 10% from June toSeptember, 70% snow. No fire for last 40 years. Changes after fire in 5 km 2 watershed Pre fire (1967- 1970) Post fire (1971- 1977) 1972Sediment 21- 100 269-4003 3800yield (kg)
Sediment transport increased due to wildfire and result in the loss of nutrients Total N increased 40 times Available P increased form 0.001 to 0.014kg/ha/yr. Ca, Mg, K, Na combined loss in sedimentincreased from 1.98 kg/ha/yr to 54.3 kg/ha/yr.Ca, Mg, K, Na solution loss for 19.3 to 42.3kg/ha/yr.But the solution loss occurs from a larger area,while sediment transport is limited to riparianareas; then solution losses of nutrients are inavailable from.
Losses of nutrients through Debris flow(torrents) losses• 13.9 kg/ha/yr N• 3.4 kg/ha/yr P• 3,851 kg/ha/yr Ca, K, Na, MgCompared to suspended sediment debrisflow losses were 83 times greater for total N,243 times for available P, 71 times for cations.Debris torrents occur occasionally, channelsare scoured to bedrock in most places,limiting vegetation establishment.
Soil moisture loss• Organic matter destroyed bulk density raised increased runoff/ reduced infiltration drier soil• Ash and charred crust resulting from fire reduce micropores.
In some conifer forests a non-wettable / water repellent layer resulting from decomposition is established below soil surface restricting water infiltration e.g., Sequoiadendron giganteum, Pinus ponderosa, Abies concolor
pH increases• Because of loss of litter which is acidic• Greater loss of N P and Cl which form anions than of Ca, K and Mg which form cations
Soil biota reduced• Because of: direct killing: reducing their food bases• But can increase after a few years• Higher pH favour bacteria than fungi (Ahlgren 1974)• Grasses turn more nutritious (more protein)• But frequent burning can bring down biota permanently
Fire Impacts on Plants and Vegetation (based onHeinselman 1993; Pyne et al.1996)• Recurrent fires herbs +, woody plants –• Creates bare soil, a seed bed required by many species.• Temporary reduction in competition for light, moisture, nutrients, and some species have competitive advantage.• Influences community composition and succession• Release of seeds in lodge pole pine, jack pine, some birch, eucalypts
Fire Impacts on Plants and Vegetation…….• Stimulates flowering and fruiting in some species• Promotes sprouting from root collar in Oaks , maples, alders; roots sucking in aspen• Creates patchy condition• In prairies, prevents invasion of woody species• The Californian Chaparral depends on fire for thenutrient generation and reduction in litter andallelochemicals
Plant Adaptation and Response to Fire• Enhanced seed setting and reproduction e.gCyndon dactylon (Bermuda grass), gives competitiveadvantage• Serotiny (late to open) closed cone produced overseveral years, opens only with burn: lodgepole pinerequiring 45-500C, knobane pine 2000C; otherexamples are P. Attenuata, P. Banksiana, P.contorta, P. muricata, Cupressus macrocarpa,Sequoiadendron giganteum (Biswell 1989)• Fire burn resin and thus open cones.
• Fire induced upsurge in height growth due tothe mobilization of stored carbohydrates inroots.
Seed Germination Promoted• Seed requiring Scarification for germination e.g.legumes such as Astragalus and Trifolium – fireruptures and splits seed coat, thus water andoxygen permeates germinates• Seeds of grasslands like Bromus mollis can survive>2000C for 2 minutes (Daubenmire 1968); Avenaseeds can germinate even after getting charred.
• Heat shocks stimulates germination in manyspecies of Fabiaceae, Rhamnaceae,Convolvulaceae, Sterculiaceae. (Khurana &Singh 2001)• Long seed viability in fire adapted communitylike chaparral ;remains dormant between twofire events e.g. Ceanothus velutinus remainviable in litter for up to 575 years (Zavitkovskiand Newton 1968)
Bud Protection and Re-sprouting• Dormant buds enclosed in litter in grasses and shrub ofchaparral communities survive fire and resprout due toburn.• Sprouts from burls or ligno-tubers (turnip shaped ortubular swellings, up to 4 m across in some eucalypts)which have buds below ground surface is anotheradaptation to fire.
• Thick bark particularly a sapling/ young tree stage helps trees to survive e.g. pines.• High crowns, open stands, large buds, long needles in pines, deep roots give fire resistance e.g. Larix occidentalis, an extremely fire resistant conifer Pinus roxburghii
Fire resilience (capacity of species to come back after fire) (based on Brown et al. 2000)Short fire cycle- favours species which have juvenilesprouting, can store seeds in soil, can invade a bruntside from outside, short lifecycle, bear seeds at anearly stage (precocious seed bearers)Intermediate fire- favours species- the matureindividual of which resist fire.• Stores seeds in crown• Sprout well• Colonize a site
Long interval fire- favours species less resistant tofire and regenerates through seeds.Some ecosystem characters promote fire andspecies that have them- e.g. high flammability due to a high proportion ofdead woods, high volatile compounds, loose andflaky barks.- Get burned and burns and other, and thencomeback.
Fire in Indian forest ecosystems• States vary from having 30% to 80% fire proneareas• Largely man-made• Pine and Sal forests particularly fire tolerant• Between two major pines, P. roxbughii is fire tolerantand P. wallichiana is fire resilient.• Jhum, which involves man-made fires is quite commonin North-east Himalaya
Fire as Management Tool• To promote desired species e.g., grasses many ofwhich have buds protected by soil and litter; pines, or toremove unpalatable grasses which dominate heavilygrazed grasslands.• To maintain species diversity periodic burning is donee.g. Kwongan, a shrub community.In this area near crop-field is burned frequently to keepshrubs away; far off areas burned after a longer interval(~20 years) so that shrubs grow and flower and maintainpollinators populations- crop yield increased.
-To produce succulent grass tissues- To keep fuel load low, to pre-empt big fires.- To provide bed for seedling establishment andgrowth.- To control insects and pests.- To create breeding grounds for some birds whichrequire specific shrubs.