Litter production in Holm oak trees subjected to different pruning intensities in Mediterranean dehesas

Litterfall is a key process in forests which is sensitive to climatic conditions like precipitation and temperature, and management practices. Therefore, knowledge about litterfall patterns and its associated variables is important for the conservation of Mediterranean ecosystems under conditions of climate change. We aimed to quantify the temporal pattern of litterfall and to investigate the influence of abiotic variables and pruning on litter production. Litterfall was collected at monthly intervals for 2 years in trees subjected to different pruning intensities in two locations. The effect of pruning, abiotic variables and tree size on litter production was analyzed using a mathematical model. Leaf fall was strongly seasonal with a peak occurring in the wettest month of the year in this area. The variability in leaf fall was mainly related to rainfall and soil water in 2 years and locations. Pruning reduced the amount of litter production during the first year following this practice, and might have negative effect on soil fertility and crop productivity in dehesas ecosystems.     

The bio-economy as an opportunity to tackle wildfires in Mediterranean forest ecosystems

Wildfires represent a threat to forests and society and the risk of wildfires is expected to increase with global change. How should wildfires be tackled in the future? A paradigm shift is needed from the current focus on fire suppression to the management of forests, accompanied by the improved understanding that forests are a valuable resource and provide many benefits to society. Through the development of high value-added products, materials, fuels and chemicals, a forest-based bio-economy could provide the necessary investments and incentives to ensure sustainable, integrated forest and fire management strategies and thereby reduce fuel loads and fuel continuity, while at the same time revealing that forests are a valuable resource and provide many benefits to society.     

Effects of forest management on the amount of deadwood in Mediterranean oak ecosystems

Context

Deadwood is an important habitat for vertebrate and invertebrate species, a key factor in the nutrient cycle and a valuable carbon pool. Difference in the deadwood C stock depends on many variables such as forest type, microclimate and forest management.

Aims

We investigated the relationship between C stock in deadwood and forest management in oak stands of southern Italy.

Methods

Deadwood C stock was quantified in 74 forest stands under intensive, extensive or multifunctional management. The relationship between management and C stock in deadwood was assessed taking into account the decay class and the type of deadwood (snags, stumps and logs).

Results

Intensively managed forests are characterized by significantly lower mean levels of deadwood C than the other forms of management. Multifunctional management resulted in the highest level of C, mainly in logs and snags, while extensive management resulted in high levels of C storage concentrated in snags.

Conclusion

Results of the research highlight that forest management practices greatly influence the quantitative and qualitative presence of deadwood in forests.     

Heavy thinning in hinoki plantations in Shikoku (southwestern Japan) has limited effects on recruitment of seedlings of other tree species

Heavy thinning may provide a feasible means to convert single-species coniferous plantations to broadleaved or mixed forests. To assess this possibility, we monitored tree seedling dynamics of other tree species, the understory microenvironment, and seed availability following heavy thinning (50 % by volume) in two hinoki (Chamaecyparis obtusa) plantations in Shikoku, southwestern Japan. Conventional (35 % by volume) and row thinning (50 % by volume) treatments were also applied at one of the sites. Diffuse transmittance in the understory dramatically increased after all thinning treatments then rapidly decreased, except after row thinning. Heavy thinning accelerated recruitment of small seedlings (with stems <30 cm high) at one of the sites. However, the densities of these seedlings declined sharply, and increases in the densities of larger seedlings recorded in subsequent surveys were very small. Furthermore, at the other site, recruitment of small seedlings under heavy thinning was equivalent to that under conventional thinning and lower than that under row thinning. Abundant species in the recruited seedlings were pioneer or subcanopy species found in the soil seed bank. Low seed rain density at both sites appeared to be responsible for the poor recruitment of canopy tree species. Our results suggest that heavy thinning had limited effects on the seedling recruitment of other tree species in these hinoki plantations due to insufficient seed rain and rapid canopy closure.     

Use of soil solarization to improve growth of eucalyptus forest nursery seedlings in Argentina

Damping-off and root rot are major diseases affectingseedlings of Eucalyptus species in forestnurseries in temperate regions in Argentina. The mostcommon fungi associated with these diseases andaffecting the vigor of the root system are Fusarium and Pythium species. Two forestnursery experiments were conducted in the province ofBuenos Aires, Argentina, to determine the effect ofsoil solarization on growth of Eucalyptusviminalis seedlings and relate this effect to thepresence of pathogenic and native ectomycorrhizaepopulations in roots and nutrient availability insoil. Changes in populations of soilborne pathogenswere determined by a bioassay that relates theirpotential to induce disease. Changes in nativeectomycorrhizae were assesed by measuring colonizationlevels in roots. Nutrient availability was determinedby the amount of nitrates released by solarization.Solar heating decreased pathogenic and ectomycorrhizalinoculum potential and increased soil nitrates.Seedling growth in solarized seedbeds may be relatedto a low initial pathogenic population and/or toincreases in nitrate availability. Solarization mayinduce soil suppressiveness against re-establishmentof major seedling pathogens in treated soils.     

Growth versus storage: responses of Mediterranean oak seedlings to changes in nutrient and water availabilities

We compare dry mass (DM) and storage of starch (St) and nitrogen (N) in seedlings of three Mediterranean oaks, two evergreens (Quercus coccifera L. and Q. ilex L. subsp. ballota (Desf.) Samp) and one deciduous (Q. faginea Lam.), across different scenarios of nutrient and water availabilities. Three fertilization (5, 50 and 200 mg of N per plant and growing period) and watering (28–39, 55–71 and 70–85 g H₂O 100 g _soil ^?1 gravimetric soil water) treatments were applied to current-year seedlings between May and October 2002 in two independent experiments. The three species showed a similar response to fertilization, storing nitrogen instead of increasing biomass, in agreement with adaptations to nutrient-poor habitats. However, they differed in their responses to water, reflecting the different water requirements in the field: Q. coccifera, from arid zones, showed no response to water regarding DM and St; Q. faginea, from humid zones, required higher water availability to simultaneously increase growth and storage; while Q. ilex, spanning over most of the water availability range, exhibited a balanced increase of both functions when water increased moderately. In the two evergreen species, N concentration increased with water supply, whereas the reverse occurred in Q. faginea. The latter species favoured growth over storage at moderate water supply (according to its more competitive strategy), although it was the species which accumulated more St and N at the end of the experiments (autumn).     

Root volume as a grading criterion to improve field performance of Douglas-fir seedlings

Three seed sources of 2+0 Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings were graded into three root-volume categories (<9, 9–13, and >13 cm³) and outplanted to determine (i) differences in survival and growth after one and two growing seasons in the field, (ii) relationship(s) of seedling height after one and two seasons to preplanting nursery root volume, total fresh weight, root-collar diameter, and height, and (iii) differences in field performance due to fertilization at planting. Field survival was >90% among all root-volume categories. Seedlings in the largest category grew significantly better than those in the smaller two categories over two seasons. Apparently, a population of seedlings having a large proportion of high root volumes will outperform a population having a large proportion of low root volumes in the field. Fertilization at the time of planting had no effect on survival or growth because of shallow placement of the fertilizer pellet. The results suggest that targeting root volume, as well as height and diameter, is worthwhile where morphological quality must be maximized to improve field performance. Thus, root volume has potential for use as a criterion for grading seedlings.     

Ecophysiology of seedlings of three Mediterranean pine species in contrasting light regimes

Seasonal dynamics of net photosynthesis (Anet) in 2-year-old seedlings of Pinus brutia Ten., Pinus pinea L. and Pinus pinaster Ait. were investigated. Seedlings were grown in the field in two light regimes: sun (ambient light) and shade (25% of photosynthetically active radiation (PAR)). Repeated measures analyses over a 12-month period showed that Anet varied significantly among species and from season to season. Maximum Anet in sun-acclimated seedlings was low in winter (yet remained positive) and peaked during summer. Maximum Anet was observed in June in P. pinea (12 micromol m-2 s-1), July in P. pinaster (23 micromol m-2 s-1) and August in P. brutia (20 micromol m-2 s-1). Photosynthetic light response curves saturated at a PAR of 200-300 micromol m-2 s-1 in winter and in shade-acclimated seedlings in summer. Net photosynthesis in sun-acclimated seedlings did not saturate at PAR up to 1900 micromol m-2 s-1 in P. brutia and P. pinaster. Minimum air temperature of the preceding night was apparently one of the main factors controlling Anet during the day. In shade-acclimated seedlings, photosynthetic rates were reduced by 50% in P. brutia and P. pinaster and by 20% in P. pinea compared with those in sun-acclimated seedlings. Stomatal conductance was generally lower in shaded seedlings than in seedlings grown in the sun, except on days with a high vapor pressure deficit. Total chlorophyll concentration per unit leaf area, specific leaf area (SLA) and height significantly increased in P. pinea in response to shade, but not in P. pinaster or P. brutia. In response to shade, P. brutia showed a significant increase in total chlorophyll concentration but not SLA. Photosynthetic and growth data indicate that P. pinaster and P. brutia are more light-demanding than P. pinea.     

Effects of grazing exclusion and environmental conditions on the soil seed bank of a Mediterranean grazed oak wood pasture

Large seed banks in the soils of Mediterranean wood pastures can allow the composition of the understorey vegetation to adapt to changing conditions such as under-grazing, grazing exclusion and climate change. This three year study investigated the effect of grazing exclusion on the transient and persistent seed banks of 23 areas of a Mediterranean wood pasture of Quercus suber L., Q. ilex L. and Q. pubescens Willd. A canonical correspondence analysis was used to determine the effect of topo-climatic (elevation, aspect, slope, rainfall, temperature, tree coverage), soil (pH, soil texture, and soil nitrogen, phosphorus, lime and organic carbon content) and biodiversity (Shannon index, species richness index, and Pastoral Value) variables on the soil seed bank under grazed and ungrazed conditions. The size of the persistent seed bank increased with rainfall, grazing, and the available phosphorus content of the soil. Specific site by site grazing regimes could increase the abundance of legumes in the soil seed bank and the species richness and diversity of the understorey vegetation. These results can help guide the conservation management of this silvopastoral area.     

Acclimation of loblolly pine (Pinus taeda) seedlings to high temperatures

To determine the extent to which loblolly pine seedlings (Pinus taeda L.) acclimate to high temperatures, seedlings from three provenances-southeastern Texas (mean annual temperature 20.3 degrees C), southwestern Arkansas (mean annual temperature 16.2 degrees C) and Chesapeake, Maryland (mean annual temperature 12.8 degrees C)-were grown at constant temperatures of 25, 30, 35 or 40 degrees C in growth chambers. After two months, only 14% of the seedlings in the 40 degrees C treatment survived, so the treatment was dropped from the experiment. Provenance and family differences were not significant for most measured variables. Total biomass was similar in the 25 and 30 degrees C treatments, and less in the 35 degrees C treatment. Foliage biomass was higher, and root biomass lower, in the 30 degrees C treatment compared with the 25 degrees C treatment. Net photosynthesis and dark respiration of all seedlings were measured at 25, 30 and 35 degrees C. Both net photosynthesis and dark respiration exhibited acclimation to the temperature at which the seedlings were grown. For each temperature treatment, the highest rate of net photosynthesis was measured at the growth temperature. Dark respiration rates increased with increasing measurement temperature, but the basal rate of respiration, measured at 25 degrees C, decreased from 0.617 &mgr;mol m(-2) s(-1) in the 25 degrees C treatment to 0.348 &mgr;mol m(-2) s(-1) in the 35 degrees C treatment, resulting in less carbon loss in the higher temperature treatments than if the seedlings had not acclimated to the growth conditions. Temperature acclimation, particularly of dark respiration, may explain why total biomass of seedlings grown at 30 degrees C was similar to that of seedlings grown at 25 degrees C.     

Ecophysiological characteristics of Taiwan alder (Alnus formosana) seedlings adapted to the subtropical region

We investigated several ecophysiological characteristics of seedlings of a low-elevation (100-200 m) and a high-elevation (2000-2400 m) population of Taiwan alder (Alnus formosana Makino) from subtropical Taiwan. Both populations had a wide optimal temperature range for photosynthesis, and there was little difference in the optimal temperature range for photosynthesis between populations. Photosynthetic rate (P(N)) was near maximal from 20 to 35 degrees C when seedlings of both the low-elevation and the high-elevation populations were acclimated at a day/night temperature of 30/23 degrees C. When seedlings were acclimated at a day/night temperature of 20/10 degrees C, P(N) was near maximal over the range 15-35 degrees C in the low-elevation population and 15-30 degrees C in the high-elevation population. Compared with nine other tree species native to Taiwan, Taiwan alder had a high P(N) and stomatal conductance (g(s)) under well-watered conditions. Reflecting its higher transpiration rate, Taiwan alder had a significantly greater leaf-air temperature difference than camphor (Cinnamomum camphora (L.) J. Presl), a co-occurring lowland tree species with leaves similar in shape and size to those of Taiwan alder. Despite higher g(s), high root and shoot hydraulic conductances enabled Taiwan alder to maintain higher leaf water potentials than camphor under well-watered conditions. We conclude that both photosynthetic characteristics and water relations are important factors enabling Taiwan alder to adapt to a wide temperature range, thereby ensuring its success at both high and low elevations in subtropical Taiwan.     

Management of carob tree orchards in Mediterranean ecosystems: strategies for a carbon economy implementation

This paper offers a different framework for managing Mediterranean drought carob-tree orchard ecosystems. Two dry-farming systems were compared during two consecutive years: pure productive orchards and mixed orchards in a total of 360 mature trees distributed by 18 plots with areas of 0.55 and 0.30 ha per plot, respectively. Carob, fig, almond and olive trees compose mixed orchards. Trees of the mixed orchards were more productive than those of pure orchards. The main problem of both systems was the large variability and the low fruit production due to non-bearing trees, inducing unfavorable economic returns. Yield varied between 7.7 and 28.5 kg tree^?1 respectively in pure and mixed orchards. In this paper we propose to use carbon sequestration calculations as an added benefit to farmers. A carbon stocking model estimation was established, based on trunk diameters of different trees. We depicted two management scenarios based on fruits production and carbon sequestration incomes: a low value scenario, using mean fruit production, and a high valuable scenario based on the hypothesis that all trees reached its potential maximum. Since under dry-farming systems fruit production irregularity is still a pendent problem, mixed orchards may offer a potential higher revenue, while maintaining higher crop diversification and whole biodiversity. C sequestration benefit, as here we purpose, may represent 125–300 % of income, respectively under low or high valuable scenario. Thus, CO₂ equivalent is a novel ecological economic incentive that may potentiate a new income for farmers while assuring carob ecosystem services.     

森林生态系统重金属污染和富集研究进展(Ⅱ)--森林植物中重金属富集与污染及其生物效应

文章重点论述了重金属在森林植被中富集的特点以及植物遭受重金属污染后的生理变化及生长反应。     

Nutrient loading of forest tree seedlings to promote stress resistance and field performance: a Mediterranean perspective

The planting environment of Mediterranean areas is highly challenging as summer drought and winter frost jeopardize survival, and soil infertility limits establishment success. We review the potential for seedling nutrient loading to alleviate these post-planting stresses. A growing body of evidence indicates that nitrogen (N) rich seedlings have improved field performance in Mediterranean environments, due to their ability to grow new roots rapidly and out-compete weeds. In addition, frost resistance during hardening is crucial for relatively cold inland nurseries; recent research shows a positive relationship between N and shoot frost resistance though a knowledge gap exists regarding the influence of nutrition on root frost resistance. Some new evidence also implicates phosphorus as an important driver of seedling response in the Mediterranean due to its influence on root growth and physiology. Nutrient status influences other functional attributes critical to survival in Mediterranean areas, such as drought tolerance, root hydraulic conductivity, and mycorrhization. In light of the apparent benefits of high nutrient reserves for seedling performance in Mediterranean areas, we also review techniques for nursery nutrient loading. Exponential fertilization can be applied when species’ growth patterns match this application regime. However, many Mediterranean species exhibit episodic growth indicating that constant or fall fertilization could be more effective in reaching loading. In particular, late-season fertilization has shown good potential to avert nutrient dilution in the fall and increase frost resistance. Several needs for future research are identified, with special emphasis on the necessity to match fertilization regimes to species ecological traits and planting conditions.     

Soil surface properties in Mediterranean mountain ecosystems: Effects of environmental factors and implications of management

Understanding soil processes is fundamental to the success of forest restoration programs. We compared different types of soils in Mediterranean mountain forests with respect to their edaphic environments and influence of vegetation cover and lithology. We then used this information to determine the suitability of current forest restoration programs in these ecosystems.     

Response of oriental beech (Fagus orientalis Lipsky) seedlings to canopy gap size

The response of nursery seedlings and wildings of oriental beech(Fagus orientalis Lipsky) to canopy gap size was studied ina climax beech forest in northern Iran with respect to seedlingsurvival, shoot growth and vitality. These parameters were followedfor 2 years after planting in gaps of 50, 200 and 600 m², aswell as in the open field. Foliage coloration was used as acriterion for vitality. The survival rate of nursery seedlingsand wildings dropped rapidly with increasing gap size from 84per cent in 50-m² canopy openings to     

沙棘育苗技术(续)

沙棘种子可能混有沙棘病害的真菌、虫害的卵等，若不消毒播种，沙棘苗木易遭病虫侵害，为避免苗木被病虫害侵害，故要对种子进行消毒。