Cause–effect relationship among morphological adaptations,growth, and gas exchange response of pedunculate oak seedlings to waterlogging

Context

In response to waterlogging, pedunculate oak is known to develop adventitious roots and hypertrophied lenticels. However, to date, a link between these adaptations and the ability to maintain net CO₂ assimilation rates and growth has not been demonstrated.

Aims

The aim of this study was to explore the cause–effect relationship between the ability to form morphological adaptations (hypertrophied lenticels and adventitious roots) and the capacity to maintain high assimilation rate and growth.

Methods

The occurrence of morphological adaptations and the parameters of photosynthesis were monitored over 20 days of waterlogging in 5-week-old pedunculate oak seedlings presenting similar morphological development.

Results

Based on the development or not of morphological adaptations, the following three categories of responses were identified: development of hypertrophied lenticels and adventitious roots, development of hypertrophied lenticels alone, and the lack of development of adaptive structures. These categories, ranked in the order given, corresponded to decreasing levels of initial net CO₂ assimilation rate growth and photosynthesis parameters observed during waterlogging.

Conclusion

We observed a two-way cause–effect relationship between the capacity to form adaptive structures and the assimilation rate. Indeed, the initial assimilation rate determined the occurrence of hypertrophied lenticels and growth during stress, and then the development of morphological adaptations enhanced the ability to maintain assimilation levels during the stress.     

Impact of time lags on diurnal estimates of canopy transpiration and canopy conductance from sap-flow measurements of Populus cathayana in the Qinghai–Tibetan Plateau

Recently, canopy transpiration(Ec) has been often estimated by xylem sap-flow measurements. However, there is a significant time lag between sap flow measured at the base of the stem and canopy transpiration due to the capacitive exchange between the transpiration stream and stem water storage. Significant errors will be introduced in canopy conductance(gc) and canopy transpiration estimation if the time lag is neglected. In this study, a cross-correlation analysis was used to quantify the time lag, and the sap flowbased transpiration was measured to parameterize Jarvistype models of gcand thus to simulate Ecof Populus cathayana using the Penman–Monteith equation. The results indicate that solar radiation(Rs) and vapor pressure deficit(VPD) are not fully coincident with sap flow and have an obvious lag effect; the sap flow lags behind Rsand precedes VPD, and there is a 1-h time shift between Ecand sap flow in the 30-min interval data set. A parameterized Jarvis-type gc model is suitable to predict P. cathayana transpiration and explains more than 80% of the variation observed in gc, and the relative error was less than 25%, which shows a preferable simulation effect. The root mean square error(RMSEs)between the predicted and measured Ecwere 1.91 9 10-3(with the time lag) and 3.12 9 10-3cm h-1(without the time lag). More importantly, Ecsimulation precision that incorporates time lag is improved by 6% compared to the results without the time lag, with the mean relative error(MRE) of only 8.32% and the mean absolute error(MAE) of1.48 9 10-3cm h-1.     

Analysis of the forest fires in the Antalya region of Turkey using the Keetch–Byram drought index

We investigated the correlation of large fires([300 ha) from 1992 to 2013 within the borders of the Antalya Regional Directorate of Forestry using the Keetch–Byram drought index(KBDI). Daily KBDI values were calculated for each year, and values for the period before the year 2000 differed significantly from those after2000. After 2000(large fires occurred in 2004, 2006, 2007,2008, 2010, and 2013), when KBDI values increased, the KBDI, but not the number of fires, was inversely correlated with the natural log of the burned area(NLBA). While there were both high and low KBDI values when the NLBA was small, only high KBDI values were associated with high NLBA values. Particularly for logarithmic values of 4 and higher, KBDI values increased in parallel with increases in NLBA values. On the basis of a Mann–Whitney U test done in addition to a Pearson correlation test, we found that when the burned areas were grouped according to small and large areas, the KBDI could be used to distinguish the two groups. Using a conditional probability analysis, we found that 4th, 5th and 6th class KBDI values may lead to large fires at the 60 % possibility.Similarly, the possibility of large fires greater than the median burned area in any given 6 years was found to be48 %. In addition, while the mean value of KBDI is 390.51 for the period from May to September for these 6 years, it is 359.93 for the other years. Consequently, the area burned also increased as the KBDI classes(Class 0: 0–99, Class 1:100–199, Class 2: 200–299, Class 3: 300–399, Class 4:400–499, Class 5: 500–599, Class 6: 600–699, and Class 7:700–800) increase.     

Wood density of three oak species in Tennessee, 1940–45 and 1970–75

Three oak species from East Tennessee were core-sampled to determine whether the density of wood produced in a pre-pollution period (1940–45) was different from that of a pollution period (1970–75) using gamma-densitometry. Component densities of average earlywood, average latewood, minimum earlywood, maximum latewood and average periodic density for Quercus alba L. and Quercus prinus L. were significantly greater for 1940–45 than for 1970–75. Differences between the two time periods for mean earlywood (P = 0.05), maximum latewood and mean periodic densities were found for Q. velutina.     

Shear strength development of the phenol–formaldehyde adhesive bond during cure

The development of the shear strength of the phenol–formaldehyde (PF) adhesive bond during curing was investigated. Five different PF adhesive mixtures and 1.1 mm thick peeled beech (Fagus sylvatica L.) veneer were used to produce lap-shear specimens, which were cured at a pressing temperature of 160°C. Dielectric analysis (DEA) and modified ABES (automated bonding evaluation system) were used to evaluate the physical–chemical and mechanical aspects of PF adhesive cure in a miniature hot-press. The degree of cure, which was calculated from conductivity data, was dependent on pressing time and the composition of the PF adhesive. An addition of rye flour to the PF adhesive significantly postponed the curing process as determined by DEA. It was found that the adhesive bond started to develop in the last stage of the curing (vitrification), by which time most of the physical–chemical conversion of the adhesive had been completed.     

A review of the development of Mediterranean pine–oak ecosystems after land abandonment and afforestation: are they novel ecosystems?

Context

Mediterranean landscapes are composed of different interacting vegetation patches. Pine and oak ecosystems form contiguous patches within these landscapes, in pure stands, or as mixed pine?Coak ecosystems. During the nineteenth century, pine forest distribution in the Mediterranean Basin increased dramatically as a result of large-scale re-forestation and spontaneous forest regeneration. At the same time, secondary succession of abandoned agricultural land allowed development of pine and oak ecosystems. Consequently, a pine?Coak mosaic has developed, which created opportunities for cross-colonization, i.e. species colonization from one ecosystem in the reciprocal system. Pines shed their wind-dispersed seeds and colonize Mediterranean oak vegetation. Oaks regenerate in different ecosystems, including pine forest understories.

Research question

This paper reviews fire-free landscape-scale dynamics of pine?Coak Mediterranean mosaics and analyze how landscape-scale interactions are leading to pine?Coak ecosystems by different processes.

Results

Published information from the Mediterranean Basin illustrates pathways of pine?Coak ecosystems formation. Using Mediterranean literature, I try to elucidate the factors that (1) control colonization potential and (2) modulate the resistance to colonization, in different habitats, land uses, and landscape settings.

Conclusion

Management implications for these mixed pine?Coak ecosystems are suggested. The question of whether they are novel ecosystems is discussed.     

Estimating the age–diameter relationship of oak species in Switzerland using nonlinear mixed-effects models

Tree growth plays a key role in forest dynamics, yet little attention has been paid to quantifying tree age–diameter relationships. Predicting diameter growth of oaks is especially important due to their role in nature conservation and adaptive forest management under climate change. Thus, we (1) identified environmental variables that shape age–diameter relationships of oaks and (2) quantified the accuracy of predictions based on these variables. We determined the age–diameter relationship of 243 oaks (Quercus spp.) growing in Switzerland by using tree-ring samples. Nonlinear mixed-effects models based on a modified Chapman-Richards equation were fitted with environmental variables included as covariates. The fixed effects elevation, slope and water-holding capacity were most important in shaping the age–diameter relationships. Lower elevations, steeper slopes, north-facing aspects, higher water-holding capacities and moister summers resulted in larger maximum diameters. For 75 % of the oaks, age–diameter relationships predicted by the fixed effects matched fairly well the observations (root mean square error between predictions and observations <6 cm); the inclusion of random effects reduced root mean square errors for 86 % of the trees. These results suggest that water runoff plays a key role for the age–diameter relationships, accompanied by limiting temperature effects at higher elevations. The fixed effects covered variability in site quality, whereas the random effects included tree-specific deviations from expected age–diameter relationships, potentially due to neighbourhood effects such as stand density and competition.     

Effects of sludge on germination and initial growth performance of Leucaena leucocephala seedlings in the nursery

A study was carried out to determine the influence of different types of sludges （municipal, industrial and residential） on field germination, growth and nodulation of L. leucocephala seedlings in the nursery. Before sowing of seeds, different combinations of sludges were incorporated with the nutrient deficient natural forest soils. Field germination, nodulation status and physical growth parameters of seedlings （shoot and root length, vigor index, collar diameter, leaf number, fresh and dry weight of shoot and root and total dry biomass increment） were recorded after three and six months of seed sowing. Field germination, nodulation status and growth parameters were varied significantly in the soil amended with sludges in comparison to control. The highest number of nodule was recorded from soil amended with residential sludge （ 1：1 ） and highest fresh and dry nodule weight was also found from the same combination in both three and six month old seedlings. In case of growth parameters, the highest growth was recorded from soil and residential sludge （ 1：1 ） combination compared to control. From the study, it can be recommended that soil amended with residential sludge （ 1：1 ） provide better field germination, growth and nodule formation of L. leucocephala in degraded soil.     

Development over time of the tree-related microhabitat profile: the case of lowland beech–oak coppice-with-standards set-aside stands in France

European forest managers are implementing set-aside measures in managed forests to restore key structures for forest biodiversity such as tree-related microhabitats (TreMs). However, the time required to regenerate these structures is little known. We assessed the patterns of thirteen TreM types on 282 plots in 24 lowland forests in southwestern France. We applied a synchronic sequence ranging from 1 to 80 years after the last harvest, a time frame which is considered long enough to observe significant changes in the TreM profile. We sampled lowland beech–oak coppice-with-standards stands representative of the different forest ownerships and management regimes occurring in France; our assessment included both public and private forests with or without formal management plans. We found that both TreM density and diversity just after harvesting were lower, though not significantly so, in private stands without any management plan than in the other management regimes. We observed both significantly higher TreM density and diversity in plots harvested 10–15 years ago than in plots harvested 1–5 years ago. The next marked difference did not occur until stands had been harvested 70–80 years ago. Globally, time since last harvest was the best explanatory variable for variations in both TreM density and diversity. We therefore recommend: (1) conserving more habitat trees in harvested areas, particularly cavity trees, since the densities we observed were much lower than the densities required by cavity-dwelling species, and (2) letting set-aside patches freely complete several full silvigenetic cycles. This latter practice would avoid the inefficacy (or possibly even negative effects) of a temporary conservation network, and would also simplify management of the network over time. Further research should assess TreM occurrences in a permanent reserve network. Diachronic observations would make it possible to highlight the drivers of TreM profile development.     

Assessing the effect of late-season fertilization on Holm oak plant quality: insights from morpho–nutritional characterizations and water relations parameters

Forest restoration projects with Holm oak (Quercus ilex) have had limited success, mostly due to water stress after planting and poor plant quality. Recent studies indicated that large and nutrient rich plants perform better in Mediterranean areas, suggesting that late-season fertilization may improve plant quality and field performance. The purpose of this study was to assess the effect of late-season fertilization on the quality of Holm oak seedlings, as determined by morphological, nutritional, and water relations analyses. We grew Holm oak nursery seedlings under 5 different late-season fertilization regimes and then analyzed morphological characteristics, nutritional status, and water relations parameters of the fertilization groups at the end of the nursery period. We also analyzed the effect of fertilization on nutritional status by use of vector nomograms. Our results indicated that late-season NPK fertilization improved shoot and root growth, and the overall nutritional status of seedlings. The lack of late-season fertilization leads to nutrient deficiency in plants, whilst the application of imbalanced fertilization treatments may trigger nutrient luxury consumption and nutrient dilution, pointing out the importance of NPK proportions in the fertilizer. Moreover, late-season fertilization with nitrogen might improve the drought resistance of seedling by enhancing their osmotic adjustment.     

Impact of time lags on diurnal estimates of canopy transpiration and canopy conductance from sap-flow measurements of <Emphasis Type="Italic">Populus cathayana</Emphasis> in the Qinghai–Tibetan Plateau

Recently, canopy transpiration (E_c) has been often estimated by xylem sap-flow measurements. However, there is a significant time lag between sap flow measured at the base of the stem and canopy transpiration due to the capacitive exchange between the transpiration stream and stem water storage. Significant errors will be introduced in canopy conductance (g_c) and canopy transpiration estimation if the time lag is neglected. In this study, a cross-correlation analysis was used to quantify the time lag, and the sap flow-based transpiration was measured to parameterize Jarvis-type models of g_c and thus to simulate E_c of Populus cathayana using the Penman–Monteith equation. The results indicate that solar radiation (R_s) and vapor pressure deficit (VPD) are not fully coincident with sap flow and have an obvious lag effect; the sap flow lags behind R_s and precedes VPD, and there is a 1-h time shift between E_c and sap flow in the 30-min interval data set. A parameterized Jarvis-type g_c model is suitable to predict P. cathayana transpiration and explains more than 80% of the variation observed in g_c, and the relative error was less than 25%, which shows a preferable simulation effect. The root mean square error (RMSEs) between the predicted and measured E_c were 1.91 × 10^?3 (with the time lag) and 3.12 × 10^?3 cm h^?1 (without the time lag). More importantly, E_c simulation precision that incorporates time lag is improved by 6% compared to the results without the time lag, with the mean relative error (MRE) of only 8.32% and the mean absolute error (MAE) of 1.48 × 10^?3 cm h^?1.     

Effects of submergence in water on seed germination and vigor of the Copaifera lucens （Fabaceae） seedlings

We analyzed the tolerance of Copaifera lucens seeds to sub- mersion in water to assess the use of this species for direct seeding in riparian forest restoration programs. Seeds were submerged in water for 2, 4, 8, 16 and 32 days or not submerged （control = 0 days of submer- gence）. For the control and at the end of each period of submersion, germination and seedling vigor tests were carried out. For germination tests, seeds were sown in plastic pots containing sand and kept in labora- tory conditions. The percentage of seed germination, the germination rate and the average germination time were analyzed. For seedlings, total biomass, leaf area, leaf mass per area and leaf area ratio were analyzed. Submersion time drastically affected the dissolved oxygen content and seed germination. Between 4 and 8 days of submersion there was a de- crease from 83.8% to 15.6% in the germination percentage. No seed germination occurred after 16 days of submersion. Although there was a significant decrease in the percentage of seed germination between 4 and 8 days of submersion, seedling vigor was not affected. Seeds of this species were partially tolerant to submersion in water, suggesting that C. lucens is a promising species for direct seeding in riparian forest restora- tion projects.     

Influence of drought and salt stress on the growth of young Populus nigra ‘Italica’ plants and associated mycorrhizal fungi and non-mycorrhizal fungal endophytes

New Forests - Populus nigra ‘Italica’ (Lombardy poplar) is a breeding cultivar of black poplar, widely used as a street tree or windbreak, often exposed to salinity and limited water...     

Effects of shrub?grass patterns on soil detachment and hydraulic parameters of slope in the Pisha sandstone area of Inner Mongolia,China

The characteristics of soil holding capacity for different shrub-grass patterns are important to research the mechanisms regulating vegetation on slopes. The ob...     

Freezing temperatures in the root zone—effects on growth of containerized Pinus sylvestris and Picea abies seedlings

Roots of 1‐year‐old containerized seedlings of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) were experimentally frozen in December. The seedlings were then grown for 3 weeks in a growth chamber and evaluated with regard to root growth capacity (RGC) and shoot elongation. The subsequent RGC of Scots pine declined as root zone temperatures were lowered from ‐6°C to ‐11°C and from ‐11°C to ‐16°C. Almost no root growth was observed after exposure to ‐20°C. Shoot growth was also negatively affected by low root temperatures but less than root growth. Low root temperatures did not affect Norway spruce as much as Scots pine, although root and shoot growth of Norway spruce were reduced after exposure to the lowest test temperatures (‐16°C and ‐20°C). The length of exposure, ranging between 1 and 8 hours had no effect on subsequent growth.     

Tree spatial patterns of Abies alba and Fagus sylvatica in the Western Carpathians over 30 years

The decline of Abies alba (fir) in natural fir–beech forests in Europe has fascinated scientists for over a century. During this period, Fagus sylvatica (beech) became the dominant species in this forest type. We hypothesised that (1) the success of beech over fir is significantly connected with the fact that beech suffers less than fir from the presence of conspecific neighbours; that (2) shade tolerance is not a factor which favours beech over fir; and that (3) this is due to a significantly reduced proportion of litter treethrow mounds with suitable conditions for the successful regeneration of fir. We investigated these hypotheses by means of tree spatial pattern analysis. Eight rectangular plots (2–8 ha) were analysed in mountain fir–beech forests of the Outer Western Carpathians, Czech Republic. Various types of the pair correlation function and L function were used to describe the tree density variability of trees with DBH ≥10 cm. The analyses were carried out on datasets from the 1970s, 1990s and 2000s. Our results suggest that negative density dependence is not responsible for the current decline of fir. It seems that a higher shade tolerance of the advanced regeneration could be one of the factors which favour beech over fir. It is evident that fir trees have a markedly stronger positive association to mounds than beech trees.     

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity II: effect of the reference distribution database on the determination

A method of determining the Young’s modulus of timber using the stress wave propagation velocity without knowing the timber density was developed in our previous study. This method enables the estimation of Young’s modulus by Monte Carlo simulation using an existing database of the Young’s modulus versus density relationship as reference. Here, in Part II, we consider the effect of the reference distribution database on the accuracy of the estimated Young’s modulus by the developed method. Twelve different reference distribution databases were used in this study, containing Young’s modulus versus density data for more than 13 000 real-size timber specimens of ten different species. We obtained the following results: (1) the distribution of Young’s modulus estimated using an arbitrary stress wave propagation velocity depends on the reference distribution database employed, (2) the most important factor is not that the reference database has data on the same species as the timber in the test, but rather that the reference distribution database covers the foreseeable range of timber densities within the test, and (3) the estimation accuracy is higher than about 80% when the database covers many species and has wide ranges of densities and Young’s moduli. This estimation method was developed in order to measure the Young’s modulus of timber whose density cannot be measured. Considering that the quality of lumber has a large variation, such estimation accuracy will be useful for practical applications.     

Land-use impacts on the composition and diversity of the Baikiaea– Guibourtia–Pterocarpus woodlands of north-western Zimbabwe

Variation in floristic composition of recovering Baikiaea–Guibourtia–Pterocarpus woodlands was studied in different development stages (from early regrowth to mature woodland) under different land-use systems (protected areas, timber harvesting, pole and firewood collection, and abandoned crop fields), in the Gwayi and Tsholotsho areas in north-western Zimbabwe. A total of 150 nested circular plots were sampled representatively in four different development stages related to the land-use systems. The DBH (stem diameter at 1.3 m above ground level) and tree height were recorded by species for all stems of tree species with DBH ≥ 15 cm in a 30-m-radius plot (0.283 ha) and for trees with DBH 5.0–14.9 cm in a 11.3-m-radius plot (0.04 ha) (both centred around the same midpoint). Stems with DBH < 5 cm were counted by species in an inner sub-plot of 5.65 m (0.01 ha) radius. Tree data (stem DBH ≥ 5 cm) and regeneration data (stem DBH < 5 cm) by stem counts per species per plot, were used separately to run TWINSPAN (TWo-way INdicator SPecies ANalysis) classifications of species assemblages. Importance values were calculated for all tree species per community. Shannon–Wiener diversity indices were calculated for each community and tested for differences using one-way ANOVA in SPSS version 21. Detrended correspondence analysis (DCA) implemented in the CANOCO ordination software was used to determine the extent of variation amongst the identified communities. The classification identified 12 tree communities and 13 regeneration communities, clustering plots from different land uses together. Baikiaea plurijuga was the most important tree species in all tree communities, except where Combretum collinum, C. apiculatum, Commiphora mossambicensis and Pterocarpus angolensis were dominant. Pterocarpus angolensis showed low importance in most communities, except for communities from undisturbed sites (mostly mature trees) and abandoned fields (mostly young trees). Baikiaea plurijuga was most important in most regeneration communities, except in communities dominated by Baphia massaiensis, C. collinum, C. apiculatum and P. angolensis. Species diversity differed significantly (p < 0.05) amongst tree communities. The DCA ordination showed little variation amongst the communities. The cumulative contribution of environmental factors explaining variation in species composition was 22.6% for tree communities and 26.1% for regeneration communities, suggesting that recovery from disturbance after different land uses may explain more of such variation.