Unburnt Treatment Research Articles

Harvest residue recycling rather than slash-burning results in the enhancement of soil fertility and bacterial community stability in Eucalyptus plantations

Deforestation and slash combustion have substantial adverse impacts on the atmosphere, soil and microbe. Despite this awareness, numerous individuals persist in opting for high-intensity Eucalyptus planting through slash-burning in pursuit of immediate profits while disregarding the environmental significance and destroying the soil. Slash-unburnt agriculture can effectively safeguard the ecological environment, and compared with slash-burning, there remains a limited understanding of its regulatory mechanisms on soil fertility and microbial community. Also, large uncertainty persists regarding the utilization of harvest residues. Thoroughly investigating these questions from various perspectives encompassing physical soil characteristics, nutrient availability, bacterial community structures, and stability is crucial. To explore the ecological advantages of slash-unburnt techniques on microorganisms and their associated ecosystems, we used two slash-unburnt (Unburnt) planting techniques: Spread (naturally and evenly covering the forest floor after logging) and Stack (residues are piled along contour lines) as well as the traditional slash Burnt method (Burnt) in a Eucalyptus plantation. A comparative analysis was conducted between the two methods. We observed that over a span of 4 years, despite the initial lower application of fertilizer in the Unburnt treatments compared with the Burnt treatment during the first 2 years, the Unburnt treatment gradually caught up or even surpassed and attained similar nutrient levels as the Burnt treatment. Alphaproteobacteria was the main phyla that indicated the difference in soil bacterial communities between Burnt and Unburnt treatments. The microbial networks also highlighted the significance of the Unburnt method, as it contributed to the preservation of crucial network nodes and the stability of soil bacterial communities. Therefore, rational utilization of harvest residue may effectively avoid the vast damage caused by slash-burning to Eucalyptus trees and the soil environment but may also increase the potential for restoring soil fertility, improving fertilizer utilization efficiency, and maintaining microbial community stability over time.

Temporal variations in litterfall biomass input and nutrient return under long-term prescribed burning in a wet sclerophyll forest, Queensland, Australia

Litterfall helps maintaining nutrient return in forest ecosystems. However, the influence of long-term prescribed burning on the dynamics of litterfall biomass and carbon (C) and nitrogen (N) cycling is poorly understood. A 39-year old prescribed burning field trial in a wet sclerophyll forest, southeast Queensland, Australia, was used to investigate the interactive effects of prescribed fire regimes and temporal variation on the quantity and quality of litterfall and C and N return. Treatments included no burning (NB) since 1969, 2 yearly burning (2yrB; burned 19 times) and 4 yearly burning (4yrB; burned 9 times) since 1972. Litterfall was collected monthly on 32 occasions between 2011 and 2013. Significant temporal variation was observed in monthly and annual litterfall biomass. Both burning treatments had lower monthly inputs of total litterfall and leaf litter, mean annual cumulative litter biomass, litter C concentrations and C return via leaf litter, compared with the NB treatment. Most significant reductions in litter N concentrations and N return via litter were associated with 2yrB treatment. The 4yrB and the NB treatments did not differ significantly in terms of twig biomass, litterfall C:N ratios and N return via leaf litter. Despite both long-term prescribed burning treatments negatively impacting C return to the soil by reducing the quantity and quality of litter inputs, previous studies at the site suggest no difference in 0–10 cm soil organic carbon levels between the 4yrB treatment and the unburnt treatment. Hence a longer period of prescribed burning at the 4yrB frequency is likely required before lower C return translates to differences in ecosystem productivity in this wet sclerophyll forest ecosystem. The 2yrB can potentially alter forest C and N cycling and net primary productivity, but these alterations are unlikely to be detected through short-term studies.

The response of cerambycid beetles (Coleoptera: Cerambycidae) to long‐term fire frequency regimes in subtropical eucalypt forest

AbstractFire has a varied influence on plant and animal species through direct (e.g. fire‐induced mortality) and indirect (e.g. modification of habitat) effects. Our understanding of the influence of fire regime on invertebrates and their response to fire‐induced modifications to habitat is poor. We aimed to determine the response of a beetle family (Coleoptera: Cerambycidae) to varying fire treatments and hypothesised that the abundance of cerambycid beetles is influenced by fire frequency due to modifications in habitat associated with the fire treatments. Arthropods were sampled across 3 months in annually and triennially burnt areas (treatments starting in 1952 and 1973 respectively), an area unburnt since 1946, and a former unburnt treatment, burnt by wildfire in 2006. Eleven different cerambycid taxa were collected using flight intercept panel traps, dominated by three species (Ipomoria tillides, Adrium sp. and Bethelium signiferum) which made up 99% of individuals collected. Over the sampling period the long unburnt treatment had significantly lower species richness than the triennial and wildfire treatments. Cerambycid abundance was significantly higher in the triennially burnt treatment than in all other fire treatments. Ipomoria tillides was more abundant in both frequently burnt treatments, Adrium sp. was more common in triennially burnt areas, whereas B. signiferum, was more common in the wildfire affected treatment. Some, but not all, cerambycid beetles were more common in areas with a more open understorey (i.e. resulting from frequent burning), and lower tree basal area, as this likely influences their ability to fly easily between food sources. Cerambycid abundance was positively related to the volume of coarse woody debris and healthy tree crowns. Cerambycid beetles were clearly influenced by historic fire regime, suggesting that changes in fire regime can potentially have a profound influence on arthropod assemblages, and subsequent influences on ecosystem processes, which are currently poorly understood.

Response of Soil Denitrifying Communities to Long-Term Prescribed Burning in Two Australian Sclerophyll Forests

Low-intensity prescribed burning is a common forest management tool and plays a major role in modifying biogeochemical cycling through the alteration of substrate availability and microbial communities. In this study, we assessed the response of microbial community to repeated prescribed burning in two sclerophyll forests (the Bauple site, dry, annual rainfall 1000 mm; and the Peachester site, wet, 1711 mm) in southeast Queensland, Australia. At the dry sclerophyll forest (the Bauple site), annual and triennial burning did not significantly alter the soil carbon (C) and nitrogen (N) content, while at the wet scleophyll forest (the Peachester site), two yearly burnings resulted in significantly lower soil total C and N contents compared to the long unburnt treatment. In spite of these different responses, prescribed burning regimes did not significantly influence the abundance of 16S rRNA or denitrifying gene (narG, nirK, nirS, nosZ) at both sites. These results indicated that, long-term prescribed burning has little effect on the denitrifying communities, while it has varying effects on soil chemical properties at the two sites, which are likely to be explained by differences in vegetation type and soil moisture regime.

The effect of long‐term repeated burning and fire exclusion on above‐ and below‐ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

AbstractWe used a long‐term fire experiment in south‐east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soil‐stored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 1971–1972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil‐stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 3–7.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil‐stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.

Short-term response of the encroacher shrub Seriphium plumosum to fire

Quantification of the short-term impact of burning in terms of the encroacher shrub Seriphium plumosum and grass tuft mortality, seed germination of the shrub (field and seed bank), aboveground phytomass production, plant density and basal cover of the grass sward was conducted in semiarid grassland following an accidental fire. These variables were determined along a terrain morphological unit where S. plumosum density increased with altitude. On average 57% of S. plumosum seedlings were killed by fire, but fire had no significant (P > 0.05) influence on the mortality of mature shrubs. Fire significantly (P ≤ 0.01) stimulated seedling emergence of S. plumosum, to such an extent that an average of 510 seedlings ha−1 occurred on the foot slope, while only 9.14 seedlings ha−1 emerged in the unburnt treatment. Seedling emergence showed greater association with protection from direct sunlight and seedlings emerged not closer than 281 mm from the nearest leaves (canopy) of a mature S. plumosum shrub. The aboveground phytomass production of the unburnt grass sward was nearly double that of the burnt areas over the first season following the fire. Fire as a control measure should be carefully handled because it can lead to increased encroachment of S. plumosum.

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

Abstract:A fire-mediated recruitment bottleneck provides a possible explanation for the coexistence of trees and grasses in mesic savannas. The key element of this hypothesis is that saplings are particularly vulnerable to fire because they are small enough to be top-killed by grass fires, but unlike juveniles, they take several years to recover their original size. This limits the number of recruits into the adult size classes. Thus savanna vegetation may be maintained by a feedback whereby fire restricts the density of adult trees and allows a grass layer to develop, which provides fuel for subsequent fires. Here, we use results from a landscape-scale fire experiment in tropical Australia, to explore the possible existence of a recruitment bottleneck. This experiment compared tree recruitment and survival over 4 y under regimes of no fire, annual early and annual late dry-season fire. Stem mortality decreased with increasing stem height in the fire treatments but not in the unburnt treatment. Tree recruitment was 76–84% lower in the fire treatments than the unburnt treatment. Such fire-induced stem loss of saplings and reduced recruitment to the canopy layer in this eucalypt savanna are consistent with the predictions of the fire-mediated recruitment bottleneck hypothesis.

Fire Regimes and Tree Growth in Low Rainfall Jarrah Forest of South-west Australia

Regular fuel reduction burning is an important management strategy for reducing the scale and intensity of wildfires in south-west Australian native forests, but the long term effects of this on tree and stand growth are not well understood. Five fire treatments, including application of frequent and infrequent low intensity burns, and 25 years of fire exclusion, were applied to small (4 ha) experimental plots in a low rainfall mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest to investigate the effects of these treatments on tree stem diameter growth, stand basal area increment and tree mortality. Mean tree stem growth measured over 20 years was lowest in the long unburnt treatment compared with the burn treatments, although surface soil nutrient levels were generally higher in the unburnt treatment, suggesting these sites may be moisture limited. There was no clear pattern of the effects of the burn treatments, including the number of fires and the interval between fires, on tree stem growth, stand basal area increment, crown health or mortality. These factors were strongly influenced by dominance condition, with dominant and co-dominant trees growing most and suppressed trees growing least and experiencing the highest mortality levels. There was no evidence of deteriorating tree or stand health that could be attributed to either regular low intensity burning or to a long period (25 years) of fire exclusion.

Response of vegetation and vertebrate fauna to 23 years of fire exclusion in a tropical Eucalyptus open forest, Northern Territory, Australia

Abstract This opportunistic study compares the vegetation, fuel loads and vertebrate fauna of part of a 120‐ha block of tropical open forest protected from fire for 23 years, and an adjacent block burnt annually over this period. Total fuel loads did not differ significantly between the unburnt and annually burnt sites, but their composition was markedly different, with far less grassy fuel, but far more litter fuel, in the unburnt block. There were major differences between treatments in the composition of trees and shrubs, manifest particularly in the number of stems. There was no overall difference in plant species richness between the two treatments, but richness of woody species was far higher in the unburnt treatment, and of annual and perennial grasses, and perennial herbs in the annually burnt treatment. Change in plant species composition from annually burnt to unburnt treatment was directional, in that there was a far higher representation of rainforest‐associated species (with the percentage of woody stems attributable to ‘rainforest’ species increasing from 24% of all species in the annually burnt treatment to 43% in the unburnt treatment, that of basal area from 9% to 30%, that of species richness from 8% to 17%, and that of cover from 12 to 47%). The vertebrate species composition varied significantly between treatments, but there was relatively little difference in species richness (other than for a slightly richer reptile fauna in the unburnt treatment). Again, there was a tendency for species that were more common in the unburnt treatment to be rainforest‐associated species. The results from this study suggest that there is a sizeable and distinct set of species that are associated with relatively long‐unburnt environments, and hence that are strongly disadvantaged under contemporary fire regimes. We suggest that such species need to be better accommodated by fire management through strategic reductions in the frequency of burning.

Fire and biodiversity: responses of grass‐layer beetles to experimental fire regimes in an Australian tropical savanna

Summary Up to 50% or more of the savanna landscapes of northern Australia are burnt each year, but the effects of these fires on savanna faunas are poorly known, especially for arthropods. We investigated the responses of grass‐layer beetles to three fire regimes (unburnt – fires excluded; early – annual fires lit early during the dry season; late – annual fires lit late during the dry season) as part of a landscape‐scale fire experiment at Kapalga in Australia’s Northern Territory, where replicated fire regimes were applied to 15–20‐km2 landscape units over a 5‐year period. We also sought to identify beetle species that might act as indicators of particular fire regimes, and examined the extent to which analysis at the family level is sufficient to reveal patterns evident from species‐level analysis. Beetles were sampled using sweep nets during February (mid‐wet season) and May (end of wet season) each year, from 1989 (18 months prior to the imposition of fire treatments) to 1995 (after 5 years of treatments). A total of 3865 beetles from 233 species was recorded, with the dominant families Chrysomelidae (leaf beetles) and Curculionidae (weevils) contributing 91% of all beetles and 57% of total species. Total beetle abundance, species richness, family richness and the abundances of one of the 10 most common species were significantly affected by fire treatment according to anova. In all cases, beetle abundance and richness were similar in the two burning treatments, but greater than in the unburnt treatment. These differences were only apparent during the second half of the experiment. The responses were mirrored by changes in composition at species, family and guild levels, according to multivariate analysis. According to indicator analysis, five beetle species were significant indicators of late fires, and one of early fires. All these species were infrequently recorded and therefore of limited use for management. However, two common species were indicative of burnt habitats if early and late treatments are considered together. Family richness was highly correlated (r2 = 0·615) with species richness, and multivariate analysis of family‐level abundances revealed the compositional changes in relation to fire that were evident in species‐level analysis. Family was therefore a reliable surrogate of species for detecting beetle responses. Although we found significant effects of our experimental treatments, in the broader context of overall beetle dynamics the assemblages appeared to be remarkably resilient to fire. This reflects a long history of association with frequent fire, and is consistent with many other components of the northern Australian fauna, where fire appears to be of secondary importance to variation in rainfall and soil type. The lack of effect of fire timing on grass‐layer beetles calls into question a management paradigm that focuses largely on fire intensity, and suggests that fire management needs to be more mindful of fire frequency.

The impact of experimental fire regimes on seed production in two tropical eucalypt species in northern Australia

Abstract This study investigated the effect of three experimental fire regimes on the fecundity, ovule development and seedfall of two common wet‐dry tropical savanna eucalypts, Eucalyptus minima and Eucalyptus tetrodonta, in northern Australia. Both species flower early in the dry season and ovule development occurs during the dry season. This coincides with a period of frequent fires. The three fire regimes considered were applied for four years between 1990 and 1994. These regimes were (i) Unburnt, (ii) Early, fires lit early in the dry season, and (iii) Late, fires lit late in the dry season. The treatments were applied to nine catchments (15–20 km2) with each fire regime replicated three times. Fire intensity typically increases as the dry season proceeds. Therefore, early dry season fires generally differ from late dry season fires in both their intensity and their timing in relation to the reproductive phenology of the eucalypts. Late dry season burning significantly reduced the fecundity of both species, whereas Early burning had no significant effect. Ovule success was significantly reduced by the Early burning for both species. The Late burning significantly reduced ovule success in E. tetrodonta, but not in E. miniata. The results suggest that fire intensity and fire timing may both be important determinants of seed supply. Fire intensity may be a determinant of fecundity, whereas fire timing in relation to the reproduction phenology may have a significant impact on ovule survival. Both fire regimes resulted in a substantial reduction in seed supply compared with the Unburnt treatment. This may have a significant impact on seedling regeneration of these tropical savanna eucalypts.

Growth of eucalypt regeneration established with and without slash burns in Tasmania

Summary Early height growth of mixed eucalypt species regeneration established by clearfall, burn and sow treatments at four locations taking in a range of different forest sites in eastern and north-eastern Tasmania has been compared with that of natural regeneration on adjoining areas which were clearfelled at the same time but not burnt. The natural regeneration was of various origins but was generally still quite small at the time of the burn and sow treatments, which it pre-dated by up to 12 years. Height has been measured several times at each site during the period 2–10 years post-burn. On two relatively wet sites (approximately 1250 mm and 1000 mm mean annual rainfall) the burn and sow treatments produced significantly faster early height growth than the unburnt treatments, but on the two drier sites (approximately 850 mm and 800 mm mean annual rainfall) growth rates did not differ significantly between treatments. On the drier sites the unburnt treatment allowed vigorous coppice shoots to establish an initial height advantage which has so far been maintained. These early results suggest that, on productivity grounds, the case for slash burning is not so strong in Tasmania's drier, more open, lower quality forests as in the wetter, higher quality forests. Nevertheless, in the drier forests slash burns are still used more often than not, mainly to facilitate future fire protection.