Short-term effects of fire on soil properties inPinus densiflora stands

This study was performed to investigate a short time change (one week after fire) on soil properties due to the fire inPinus densiflora Sieb. et Zucc stands of the Kosung area in Kangwon Province in Korea. Twenty seven sampling plots [16 burned (8 low intensity fire, 8 high intensity fire) and 11 unburned plots] were chosen. Mineral soil samples from three depths (0–5, 5–15, and 15–25 cm) under the forest floor were collected. Forest fire in the area affected soil chemical properties. Soil pH, total nitrogen, available phosphorus, potassium, calcium, and magnesium in the surface soil (0–5 cm) of the burned area compared with the unburned area increased, but there was no marked change in the subsurface soil (5–25 cm). Organic matter, total nitrogen, available phosphorus, and exchangeable cations in the surface soil were generally lower in the high than in the low intensity fire areas. This indicates that these nutrients on the high intensity fire may be volatilized. The results suggest that change in soil chemical properties in the area was restricted mainly to the surface soil and was different between the high and the low intensity fire types.     

Changes and effects of a natural fire on ectomycorrhizal inoculum potential of soil in a Pinus halepensis forest

A typically mediterranean forest of Pinus halepensis wass tudied. During two years following fruiting fungal species, the number of sclerotia in soil, and the percentages and types of mycorrhizas present were determined. In burned stands ascomycetes were typical carbonicolous while basidiomycetes were strongly reduced. The sclerotia extracted from soils were mainly Cenococcum. The number of sclerotia in burned stands was greater than in unburned stands. Seven types of mycorrhizas were recognized in Pinus halepensis root systems from bioassays: Cenococcum, E-strain, Rhizopogon, Suillus, Tuber, Xerocomus, and one non-identified. Nearly 100% of the roots were colonized by mycorrhizal fungi. Ectendomycorrhizas represented 50–90% of the total number. The predominant type is ectendomycorrhizas formed by ascomycetes included in the E-strain group.     

Regional patterns of fire recurrence effects on calcareous soils of Mediterranean Pinus halepensis communities

The effects of fire recurrence on soils were studied on calcareous sites of Mediterranean Pinus halepensis-dominated communities in Catalonia (NE Iberian Peninsula). Soil organic horizons and mineral soils of 15 sites consisting in two adjacent areas, one burnt only once (in 1994) and the other burnt twice (in the same 1994 fire but also once before, from 1975 to 1993) were surveyed 9 years after the last fire. Fire recurrence decreased the occurrence and dry mass of soil organic horizons. Total nitrogen concentration in L organic horizon was higher in less recurrently burnt areas. No other significant difference between once- and twice-burnt areas was found for any studied chemical parameter either in organic L and FH horizons or in mineral soils. The present study underlines the fact that fire effects on soil organic horizons are accumulated through consecutive fires.     

不同整地方式对人工更新红松的影响试验

红松是辽宁省主要用材树种，近几年绝大部分是在采伐迹地上更新红松，为探索不同整地方式对红松生长的影响，对不同整地方式的人工更新进行了试验。试验结果表明，穴状整地造林保存率以及树高、胸径生长明显优于其他整地方式。因此，建议在土层较薄、水肥条件差的迹地更新红松，最好在前1年进行穴状整地，保证一次成林。在土壤肥沃、立地条件好的迹地伐后可以不整地及时更新，不仅节省了整地费用，而且使林地尽快利用。     

Effects of pre-commercial thinning on growth and reproduction in post-fire regeneration of Pinus halepensis Mill

Context

Excessive recruitment in post-fire regeneration of Pinus halepensis can require pre-commercial thinning. The 1994 Moratalla fire (Spain) and the thinning applied there since 2004 provided good conditions for testing pre-commercial thinning effectiveness.

Aims

To analyse pre-commercial thinning effects on tree size, reproductive potential, stem biomass and annual growth in 15-year-old saplings.

Methods

Twenty nine circular plots (5 m radius) were established based on (1) years since thinning and (2) aspect. Non-thinned plots were included as controls. Sapling variables were measured and pine cones were counted and classified according to maturity. Three saplings per plot were felled, five sample disks were extracted from each and tree rings were analysed with Windendro® software.

Results

Sapling size, annual growth and stem biomass were higher in thinned plots than in control plots 2–4 years after thinning. Annual growth declined five years after thinning. Cone counts were higher 2–5 years after thinning, depending on the cone type. Aspect influenced some variables.

Conclusion

Thinning accelerated stand maturity but positive effects were indiscernible until 2–5 years later. Serotinous cones, which are fundamental to regeneration after fire, increased in number after 5 years. The effects of aspect were inconclusive due to interactions with years since thinning.     

Diversification of Pinus halepensis forests by sowing Quercus ilex and Quercus pubescens acorns: testing the effects of different vegetation and soil treatments

The goal of this study was to develop management strategies favouring establishment and survival of holm oak (Quercus ilex L.) and downy oak (Quercus pubescens Willd.)??two species co-occurring in Southern France??in mature Allepo pine forests (Pinus halepensis Mill subsp. halepensis). An experimental design was assessed in a partially cut mature stand of Aleppo pine in which five soil and vegetation treatments??chopping, chopping followed by scarification in one or two directions, prescribed burning, control??and two slash treatments (presence/absence) were applied. A total of 1,600 sowing points, each composed of 3 Q. ilex or Q. pubescens acorns, were installed in the different treatments in November of two consecutive years at 6 and 18 months, after the end of treatments. Survival was monitored 3 and 2 years after sowing, soil surface at the sowing points was characterized at different dates, and predawn leaf water potentials were measured during the dry season. High mortality occurred after the first summer, but survival after 1 year was 2.3?C5.2 higher in Q. ilex than in Q. pubescens, confirming that Q. ilex was better adapted to the drier parts of the Mediterranean area. Survival was significantly influenced by the treatments, but there was a variable response between the two sowing years under most of the treatments. Only intense fire proved the most beneficial treatment for seedling survival in both years. The micro-local soil cover conditions induced by the treatments played a major role in explaining oak survival. In particular, grass cover (mainly Brachypodium retusum) proved to be largely unfavourable to seedling survival and growth, and this detrimental effect was also confirmed by lower predawn leaf water potential values with increasing grass cover. Acorn introduction designed to diversify mature Aleppo pine forest after soil and vegetation treatments therefore has to be considered for treatments that most efficiently impair the pre-existing competing grass cover such as prescribed high-intensity fire treatment.     

Fire-free natural regeneration in water limited Pinus halepensis forests: a silvicultural approach

We aimed to elucidate environmental and silvicultural factors that determine the extent of fire-free natural regeneration in east Mediterranean Pinus halepensis forests. The specific aims were to study the potential and identify bottlenecks for natural regeneration and examine the effects of overstory thinning and site preparation treatments. We integrated four experiments conducted in diverse ecoregions in Israel ranging from semiarid to subhumid. Seedling emergence and survival were traced for 2–4 years in Mishmar Ha’Emek Forest (MHF) with annual rainfall of 604 mm; Shaharia Forest (SF)—435 mm; and Yatir Forest (YF)—280 mm. Effects of thinning treatments: clearcut, 100 tree, 200 tree ha^?1 and control—310 tree ha^?1, were examined in MHF. Effects of site preparation treatments: soil scarification and herb clipping were examined in SF. Density of emerged seedlings varied among ecoregions and was linked to average annual rainfall. Within ecoregions, emerged seedling density was higher on north-facing slopes than on south-facing slopes and was strongly related to stand characteristics (e.g., stem basal area) and seed rain. Seedling survival rate of about 20 % was recorded in MHF while no seedling survival was observed in YF and SF during the study years. Thinning treatments reduced seed rain and emerging seedling density, but increased seedling survival and growth. Recruitment 4 years after thinning was highest in the 100 tree ha^?1 treatment and lowest in the control. In SF, seedling survival was limited mainly by herbaceous vegetation and was improved by soil scarification and herb clipping. Silvicultural implications are discussed.     

Effect of burnt wood removal on the natural regeneration of Pinus halepensis after fire in a pine forest in Tus valley (SE Spain)

To determine the effect of burnt tree removal on post-fire natural regeneration of Pinus halepensis, two 2 500 m² areas were selected six months after the fire in a totally destroyed mature (>70 years) pine forest. In one area, all the trees were cut down and removed 10 months after the fire and, in the other, all the trees were left standing (control). In each area, 20 permanent plots of 20 m² each were randomly placed, and all seedlings emerging within them labeled by individual numbered plastic tags. Emergence, mortality, density and growth (height) of 6649 P. halepensis seedlings were monitored during the first four post-fire years. Seedling emergence was concentrated in the first post-fire autumn–winter period. No positive effect on seedling emergence was detected as a consequence of burnt trunk dragging and subsequent turning over of soil. Wood removal produced an immediate average seedling mortality of 33%, and notably increased seedling mortality during the subsequent summer, probably due to increased exposure of seedlings to sunlight and the possible debilitation of many individuals by mechanical contact during burnt wood removal. A negative correlation of pine seedling mortality with height was detected, which increased significantly on wood removal in the third post-fire year. That is, short seedlings (<10 cm) in treated plots were the most likely to die during this period. In spite of the detrimental effect of wood removal on sapling survival, seedling density four years after fire in the cleared area was large (3.3 seedlings/m²). Wood removal treatment reduced seedling growth: seedling height was significantly higher in the control stand, and differences in seedling height growth rate became particularly noticeable in the fourth post-fire year. The results denote that traditional wood removal practices do not threaten natural post-fire P. halepensis re-establishment if initial seedling density is large enough. However, further studies focused on wood removal effects on the final tree development level and other ecological aspects are necessary to choose adequate post-fire forest management.     

Short-term effects of fire on soil nitrogen availability in Mediterranean grasslands and shrublands growing in old fields

In three different plant communities growing in Mediterranean old fields we studied the short-term changes in soil nitrogen availability that occur after the fire. Two of these communities were grasslands with great capacity of resprouting and contrasted N availability, one dominated by Brachypodium retusum, and the second one dominated by B. retusum and the N fixing shrub Genista scorpius. The third community was an obligate seeder community (shrubland) with low N availability and was dominated by Rosmarinus officinalis. We selected six plots for each type of vegetation and therefore performed 18 experimental fires. During fires we measured temperatures at the soil surface. Maximum temperature recorded during fire and time–temperature integral were used as indexes of fire severity. During the 6 months following fires we measured Net N mineralization and plant uptake by field incubations using the resin-core technique in paired burnt and control plots.Fire severity increased with plant biomass. In grasslands heating of the soil surface increased with plant biomass up to a limit of 1 kg m⁻² of above-ground biomass. For high biomass a large proportion of heat released during fire was probably transmitted to the atmosphere or to the deeper soil horizons. The increase of soil mineral N was larger in fires of greater severity. Most mineral nitrogen released to the soil during fire was ammonia. Increases of ammonia post-fire depends on the temperatures measured on the soil surface while increases of the less volatile N form (nitrate) were related to the amount of burnt biomass and were highly dependent on the type of vegetation.The amount of nitrogen released to soil during fire represented a small proportion of the N mineralized during the 6 months following fire and thus the amount of nitrogen mineralized per unit of N released during fire was very different across the different types of vegetation. In grasslands fire induced changes in N mineralization decreased as fire severity increased. In contrast, in shrublands we observed the opposite trend. Differences in potentially mineralizable and in net mineralization N between unburnt grasslands and shrublands could account for this fact. Despite the depression in nitrification that we observed in grasslands between 40 and 80 days after the fire, high nitrate concentration in the soil during that period increased N leaching in burnt plots. No plant uptake was detected at that time. In grasslands the onset of plant uptake in burnt plots was delayed as compared to control. Cumulative changes in N did not depend on the burnt biomass in grassland communities, but it did in the seeder community. On the contrary, soil temperatures measured during fires related to changes in N observed in grasslands but not in the seeder community. It appears therefore, that post-fire N mineralization and leaching in grasslands may have been driven by the changes induced by heating the soil surface while in shrublands it may have been driven by the quantity of ash deposited on the soil surface.     

Chemical characterization of Pinus halepensis sapwood and heartwood

ABSTRACT

This paper describes the chemical composition of sapwood (SW) and heartwood (HW) of Pinus halepensis Mill stem. Extractives were first isolated by accelerated solvent extraction and then analysed by gas chromatography-mass spectrometry (GC-MS). The cellulosic polysaccharide content present in the pre-extracted wood samples was determined with acid hydrolysis and GC. The hemicelluloses content was determined with acid methanolysis and GC. Free monomers were additionally analysed by GC. The amount of lignin was determined gravimetrically by the Klason lignin method and the acid-soluble lignin was determined by a UV method. Formic and acetic acids in wood were determined after alkaline hydrolysis and analysed by HP-SEC. It was found that lipophilic and hydrophilic extractives were more abundant in heartwood (1.6% and 2.5%) than in sapwood (1.1% and 1.8%). Celluloses content was higher in sapwood (42.5%) than in heartwood (39.7%), whereas lignin, hemicelluloses and sugar monomer contents were more abundant in heartwood (28.9%, 26.8% and 0.3%) than in sapwood (28.0%, 24.5% and 0.2%). The variation in acetic and formic acids and ash contents between sapwood (0.7%, 0.2% and 0.5%) and heartwood (0.6%, 0.1% and 0.4%) was small. The acetylation degrees were found to be slightly similar in sapwood (0.4) and heartwood (0.3).     

Canopy fuel characteristics and potential crown fire behavior in Aleppo pine (Pinus halepensis Mill.) forests

Canopy fuel characteristics that influence the initiation and spread of crown fires were measured in representative Aleppo pine (Pinus halepensis Mill.) stands in Greece. Vertical distribution profiles of canopy fuel load, canopy base height and canopy bulk density are presented. Aleppo pine canopy fuels are characterized by low canopy base height (3.0–6.5 m), while available canopy fuel load (0.96–1.80 kg/m²) and canopy bulk density (0.09–0.22 kg/m³) values are similar to other conifers worldwide. Crown fire behavior (probability of crown fire initiation, crown fire type, rate of spread, fireline intensity and flame length) in Aleppo pine stands with various understory fuel types was simulated with the most updated crown fire models. The probability of crown fire initiation was high even under moderate burning conditions, mainly due to the low canopy base height and the heavy surface fuel load. Passive crown fires resulted mostly in uneven aged stands, while even aged stands gave high intensity active crown fires. Assessment of canopy fuel characteristics and potential crown fire behavior can be useful in fuel management and fire suppression planning.     

Hydraulic adjustments underlying drought resistance of Pinus halepensis

Drought-induced tree mortality has increased over the last decades in forests around the globe. Our objective was to investigate under controlled conditions the hydraulic adjustments underlying the observed ability of Pinus halepensis to survive seasonal drought under semi-arid conditions. One hundred 18-month saplings were exposed in the greenhouse to 10 different drought treatments, simulating combinations of intensities (fraction of water supply relative to control) and durations (period with no water supply) for 30 weeks. Stomata closed at a leaf water potential (Ψ(l)) of -2.8 MPa, suggesting isohydric stomatal regulation. In trees under extreme drought treatments, stomatal closure reduced CO(2) uptake to -1 μmol m(-2) s(-1), indicating the development of carbon starvation. A narrow hydraulic safety margin of 0.3 MPa (from stomatal closure to 50% loss of hydraulic conductivity) was observed, indicating a strategy of maximization of CO2 uptake in trees otherwise adapted to water stress. A differential effect of drought intensity and duration was observed, and was explained by a strong dependence of the water stress effect on the ratio of transpiration to evapotranspiration T/ET and the larger partitioning to transpiration associated with larger irrigation doses. Under intense or prolonged drought, the root system became the main target for biomass accumulation, taking up to 100% of the added biomass, while the stem tissue biomass decreased, associated with up to 60% reduction in xylem volume.     

Mycorrhization, growth and nutrition of Pinus halepensis seedlings fertilized with different doses and sources of nitrogen

? Although fertilization is commonly used in nurseries, the effects of high level of nitrogen on Pinus halepensis mycorrhization are still unknown.

? The effect of fertilization at different N levels (low-LN: 35 mg/plant; medium-MN: 60 mg/plant; high-HN: 120 mg/plant), differing N sources (ammonium-(NH₄)₂SO₄; nitrate-HNO₃; ammonium+nitrate-NH₄NO₃) and inoculation with Pisolithus tinctorius and Lactarius deliciosus on the mycorrhization, growth and nutrient status of P. halepensis has been studied.

? P. tinctorius 3SR showed higher mycorrhizal ability (100% of mycorrhizal seedlings) than L. deliciosus (nearer to 50%). The application of increasing doses of N resulted in a significant reduction of mycorrhizal seedlings but no differences were observed between NH₄ and NO₃as N source at the 60 mg N/plant dose applied. The effects of fertilization on growth were mainly observed in uninoculated plants. The use of NH₄ increased growth in non-mycorrhized plants. Nutrient status was similar in all cases except for K concentration, which was higher in plants mycorrhized with P. tinctorius. Interactions between inoculation and fertilization were found, mycorrhizal effects appearing only at LN fertilization.

? It is advisable to avoid high doses of N fertilization in order to produce mycorrhizal P. halepensis seedlings.

     

不同经营模式对马尾松天然次生林土壤理化性质的影响

以慈利县二坊坪乡马尾松天然次生林为研究对象,比较其在不同经营模式下土壤理化性质的变化规律。结果表明:马尾松次生林经过1年的经营改造,Ⅱ处理(马尾松密度为900株/hm2)的土壤理化性质得到了改善,表现在土壤养分的提高,特别是土壤速效养分得到了较大的增加;而传统经营模式的土壤理化性质基本上所有指标均存在递减趋势。这说明合理的经营模式对马尾松次生林土壤肥力的维持和提高起到了积极作用,过大或过小的林分密度不利于土壤结构的改良和养分的循环与累积。     

Effects of light/darkness, thermal shocks and inhibitory components on germination of Pinus canariensis, Pinus halepensis and Pinus pinea

Knowledge of the germination characteristics of Pinus species can help in the understanding, prediction and management of the regeneration of pine forests. In the Canary Islands, several exotic pines (Pinus halepensis L. and Pinus pinea L.) were planted with Pinus canariensis Chr. Sm. Ex DC, the only native pine species, and there is now an interest in controlling these exotic species to restore the original forest. The main objective of the present study is to determine the germination response of P. canariensis, P. halepensis and P. pinea to different light regimes (darkness and light/darkness), thermal shocks and the presence of inhibitory substances from the leaves and litter of P. canariensis. P. halepensis seeds showed the highest viability and germination rate. Darkness accelerated P. halepensis germination, while exudates accelerated P. canariensis germination. Only treatments of 200 °C for 5 min and 300 °C for 5 min significantly decreased the germination of all three pine species. In the absence of strong differences in germination among species after treatments, the key for fire management or prescribed burning in this case may be the sprouting ability of P. canariensis. A possible management strategy to control the two obligate seeder exotic species could be to use one intense prescribed fire followed by a low-intensity prescribed fire after seed bank germination in the field, so in this way, only P. canariensis could resprout after fire and it would eliminate only the exotic pines in a mixed stand.     

Effects of site preparation on soil properties and on morphology of Pinus sylvestris and Picea abies seedlings sown at different dates

The aims of the study are to find out the effects of site preparation on soil properties and on the morphology of three-year-old Pinus sylvestris L. and Picea abies (L.) Karst. seedlings sown at different dates along a slope with variation in soil texture, water, and fertility. Based on the hypothesis that soil texture affects soil water content, water retention capacity, and nutrient content, we studied site preparation of varying intensities: exposed C horizon, mounds (broken O/E/B horizons piled over undisturbed ground), and exposed E/B horizon. Though the growing time difference between sowings was about one month, after three growing seasons, spring-sown seedlings were larger than summer-sown seedlings. P. sylvestris seedlings were largest with mounds and smallest with exposed C horizon, but site preparation did not affect the morphology of P. abies seedlings.     

Long term effects of fire on ectomycorrhizas and soil properties in Nothofagus pumilio forests in Argentina

The forests of Nothofagus pumilio have historically been affected by forest fires. The effects of fire on certain above and belowground, biotic and abiotic components of these ecosystems have been previously documented, albeit belowground components have received much less attention. It has been suggested that the effects observed in the short-term after a fire usually differ from the longer-term effects. The long-term effects of fire (i.e. >5 years after burning) on belowground components in Nothofagus forests are currently unknown. In the present study we evaluated the long-term effect of fire on ectomycorrhiza (ECM) colonization and morphotype composition in N. pumilio roots, as well as soil chemical properties in temperate forests in Patagonia. Sampling was conducted in three mature monospecific forests. In each, nearby burned and unburned sites were selected. The time since the occurrence of fires differed between areas (i.e. 6-10 years). Within each site, 3 transects of 40 m were established randomly along which 5 samples of roots and soil were collected in spring and autumn. The main results were: (1) in comparison with the unburned site, ECM colonization was lower in the burned site in the area with the shorter time length since fire occurrence and no effects in the other two areas were observed; (2) richness and diversity were not significantly affected by fire but there was a significant effect of season for both parameters, being higher in spring; (3) ECM dominance was significantly higher in the unburned than in the burned site in Tronador, while in Challhuaco the opposite was observed, mainly in autumn; (4) in general carbon, nitrogen and phosphorous decreased while pH increased in the burned sites; (5) ECM colonization positively correlated with NH⁴⁺ and phosphorus and negatively with pH but was not significantly correlated with organic matter or any other soil variable. Altogether the results suggest that effects of fire on ectomycorrhiza and soil properties in N. pumilio forests are probably related to the time elapsed since fire occurrence combined with site characteristics. In addition, the direct and indirect effects of fire in these forest systems may persist for more than 10 years.     

Short-term effects of agroforestry systems on soil health in Southeastern Brazil

Agroforestry Systems - The Soil Management Assessment Framework (SMAF) has successfully been tested as an objective tool to quantify land use and management effects on soil health, including under...