Variations in water use by a mature mangrove of Avicennia germinans, French Guiana

? In the tropical intertidal zones, little is known on water uptake by mangroves. Transpiration rates are generally measured at leaf level, but few studies exist on water use at tree or stand levels.

? The objective of this study was to measure sap flow in trees of different sizes to appreciate the range of variation in water use that may exist in a site dominated by 80% mature Avicennia germinans.

? The results showed that from the dry to the wet season the mean water use increased from 3.2 to 5.3 dm³ d^?1 in small trees (DBH ～ 13 cm), from 11.5 to 30.8 dm³ d^?1 in medium trees (～24 cm) and from 40.8 to 64.1 dm³ d^?1 in large ones (～45 cm).

? Sapwood remained active up to a depth of 8 cm with radial variations within the stem. Weak correlations were obtained with VPD and net radiation.

? This study confirmed that transpiration was larger under low levels of salinity. Water use at stand level (～1900 living stems ha^?1) was estimated to be in the range of 5.8 to 11.8 m³ ha?1 d^?1 according to the season.

     

Tree diameter, height and stocking in even-aged forests

? Empirical observations suggest that in pure even-aged forests, the mean diameter of forest trees (D, diameter at breast height, 1.3 m above ground) tends to remain a constant proportion of stand height (H, average height of the largest trees in a stand) divided by the logarithm of stand density (N, number of trees per hectare): D = β(H ? 1.3)/ ln(N).

? Thinning causes a relatively small and temporary change in the slope β, the magnitude and duration of which depends on the nature of the thinning.

? This relationship may provide a robust predictor of growth in situations where scarce data and resources preclude more sophisticated modelling approaches.

     

Ten years of fluxes and stand growth in a young beech forest at Hesse, North-eastern France

? Water and carbon fluxes, as measured by eddy covariance, climate, soil water content, leaf area index, tree biomass, biomass increment (BI), litter fall and mortality were monitored for 10 successive years in a young beech stand in Hesse forest (north-eastern France) under contrasting climatic and management conditions.

? Large year-to-year variability of net carbon fluxes (NEE) and to a lesser extent, of tree growth was observed. The variability in NEE (coefficient of variation, CV = 44%) was related to both gross primary production (GPP) and to variations in total ecosystem respiration (TER), each term showing similar and lower interannual variability (CV = 14%) than NEE. Variation in the annual GPP was related to: (i) the water deficit duration and intensity cumulated over the growing season, and (ii) the growing season length, i.e. the period of carbon uptake by the stand. Two thinnings occurring during the observation period did not provoke a reduction in either GPP, water fluxes, or in tree growth. Interannual variation of TER could not be explained by any annual climatic variables, or LAI, and only water deficit duration showed a poor correlation. Annual biomass increment was well correlated to water shortage duration and was significantly influenced by drought in the previous year.

? The relationship between annual NEE and biomass increment (BI) was poor: in some years, the annual carbon uptake was much higher and in others much lower than tree growth. However this relationship was much stronger and linear (r ² = 0.93) on a weekly to monthly time-scale from budburst to the date of radial growth cessation, indicating a strong link between net carbon uptake and tree growth, while carbon losses by respiration occurring after this date upset this relationship.

? Despite the lack of correlation between annual data, the NEE and BI cumulated over the 10 years of observations were very close.

? On the annual time-scale, net primary productivity calculated from eddy fluxes and from biological measurements showed a good correlation.

     

Estimating sap flow from stem heat balances in Quercus robur L. seedlings in relation to light intensity: A comparison of two methods during the establishment phase

? Knowledge of whole tree seedling water fluxes is important in ecological and forestry research, especially under conditions with low transpiration, but no standard method has yet been established that provides reliable in situ measurements.

? The aims were: (1) to assess the performance of two methods for estimating sap-flows in oak seedlings following planting by correlating the data they provided with natural light intensities over a three-week period, and (2) to compare the estimates with transpiration data obtained by weighing pots.

? Estimates of sap flows obtained from data provided by constant power (Dayau-type) heat balance gauges under low light conditions (100–450 μmol m^?2 s^?1) were less variable than estimates from variable power (EMS-type) heat balance gauges. The EMS-type system yielded data with little between-gauge variation, but consistently underestimated transpiration on a daily basis, a systematic error that should be corrected by other methods. The Dayau-type gauges yielded data with substantial variations, and several gauges are probably needed in research to cover these variations. Further, both systems provide rather uncertain estimates of short-time (hour) transpiration rates.

? However, provided that these considerations are taken into account, we conclude that it should be possible to use either system in various research contexts.

     

A generic model of thinning and stand density effects on forest growth, mortality and net increment

? For assessing forest thinning effects at large (i.e. continental) scale, data scarcity and technical limitations prevent the application of localized or individual-based thinning models.

? Here we present a simple general framework to analyze and predict the effects of thinning on growth and mortality, including the following stand density development. The effects are modeled in relative terms so that the model can be parameterized based on any thinning experiment that includes an unthinned control, regardless of site conditions and stand age.

? The model was tested against observed thinning effects on growth and mortality from five temperate and boreal species (all species pooled r ² = 0.51). It predicted a maximum increase in net stem biomass increment of 16% and a reduction in density-related mortality of 75% compared to un-thinned conditions at stand densities of around 70% of the maximum (increment optimal density).

? A sensitivity analysis revealed overlapping ranges of near optimal density (net increment within 95% of optimal) among all tested species, suggesting that one thinning scenario can be used for many species. The simple and general formulation of thinning effects based on only five parameters allows easy integration with a wide range of generic forest growth models.

     

Tree-ring Δ13C reveals the impact of past forest management on water-use efficiency in a Mediterranean oak coppice in Tuscany (Italy)

? The effects of thinning and heavy stand density reduction was investigated in Turkey oak (Quercus cerris L.) forests of central Italy, to evaluate the physiological responses and the growth status of trees that survived a past coppice cut and thinning to convert the stand to high-forest.

? The working hypothesis was that a strong decrease in stand density would cause a decreasing in canopy-intrinsic water-use efficiency (measured as the ratio of CO₂ assimilation to stomatal conductance, A/g), thus an increase in tree-ring carbon isotopic discrimination (Δ¹³C).

? The tree-ring Δ¹³C of the remaining trees (“survivors”) was found to have significantly (P < 0.05) raised between year two and year seven since the coppice stand was thinned (high-forest conversion thinnings). This effect was mostly caused by a large decrease in tree-rings Δ¹³C at control site which was characterized by high density and competition by trees. An increase in survivors tree-rings Δ¹³C probably indicates an improved water availability, possibly induced by a decrease in competition and in stand density or a decrease in the precipitation intercepted by the canopy (i.e., a stronger increase in g over A since a decrease in A is highly unlikely). A change in foliar nitrogen, foliar Δ¹³C and content in chlorophylls was also recorded seven years after thinning.

? Thinnings carried out to convert old abandoned coppices into high-forest stands induce short-term stimulation of Turkey oak growth by increasing light and water availability. We were able to make a detailed reconstruction of the impact of past silvicultural treatment on the stand using a tree-ring wood Δ¹³C time-series.

     

Effect of the span length of Granier-type thermal dissipation probes on sap flux density measurements

? Granier-type thermal dissipation sensors measure sap flux density (u) by using the temperature difference between the heater and the reference probe. To detect u correctly, heat must not be transferred to the reference probe by thermal conduction. The distance across which heat can be transferred by conduction is important for the span length of a sensor and spacing of a number of sensors.

? To validate span lengths and spacing of sensors, we used numerical simulations to calculate the potential distance across which heat can be transferred by conduction. We compared measurements with an original and a modified sensor for a Japanese red pine (Pinus densiflora) from December 2004 to May 2005. The span length of the original and the modified sensor is 15 and 4 cm, respectively.

? Numerical simulations showed that span length and spacing of Granier sensors should be more than 10 cm for trees in which u ceases for a few hours before the predawn period. The modified sensor underestimated u by 18–46% in winter (December–March) because its reference temperature was increased by heat transferred by conduction. The modified sensor measured u correctly in warm seasons, and only underestimated the annual amount of transpiration by 6%.

     

Sap flow measurement by a single thermal dissipation probe: exploring the transient regime

? In thermal dissipation method the stationary regime is used to estimate sap flow density from the temperature difference between a heating probe and a non-heating one.

? A new approach, based on the non-stationary regime of a single heating probe, is investigated on an olive tree branch. Probe temperature is monitored for different flow densities and for heating and cooling modes. Measurement sequences of 10 min using 5 s time steps are made just after the heating is switched on or off.

? Results show that temperature variation has a quasi-exponential phase whose duration decreases for increasing flow densities. Thermal indices using temperature of the probe measured at initial, final, and intermediate times t _i were developed. Relationships between sap flow density and thermal indices were found to be linear for t_i = 10 s?60 s with better coefficients of determination in cooling mode (R ² = 0.94–0.96) than in heating (R ² = 0.83–0.93). Validation tests confirmed the robustness of the single probe method with lowest error obtained for t _i = 20 s.

? Single probe method seems to be a promising technique to measure tree sap flow. Its application could be considered under cooling mode using t _i = 20 s and relatively short measurement sequences e.g. 5–10 min.

     

Fecundity and larval development of Monochamus galloprovincialis (Coleoptera Cerambycidae) in experimental breeding

?The study aimed at clarifying basic life traits (fecundity, mortality and development) of Monochamus galloprovincialis, the vector of Bursaphelenchus xylophilus, the causative agent of the Pine Wilt Disease, in Portugal.

? Mating and oviposition experiments were conducted on P. sylvestris logs under laboratory conditions during two years. Larval development was followed outdoors.

? Fecundity was high, with 138.2 eggs per female.

? For the first time, the number of larval instars (4) in M. galloprovincialis was recognized and instars were described.

? Informations are provided on the shape and size of the larval galleries. Boring of galleries in sapwood and heartwood started at the third instar. All instars could overwinter but adults emerged simultaneously resulting in a univoltine life cycle for the majority of the individuals.

? An obligatory diapause in the forth instar was assumed. However, 8.1% of the insects had a two year development.

? Important differences in mortality were noted between the two experimental years, which could be explained by differences on the size of the breeding logs.

? There is a high biological proximity between M. galloprovincialis populations in France and those in Portugal and Northern Europe. However, a higher fecundity and longevity was observed in France, as well as a higher percentage of insects with a two year development, compared with portuguese populations.

     

Site preparation and competing vegetation control affect loblolly pine long-term productivity in the southern Piedmont/Upper Coastal Plain of the United States

? A site preparation study was established in 1986 to evaluate the effect of different site preparation treatments on growth and yield of loblolly pine (Pinus taeda L.) plantations on the Piedmont and Upper Coastal Plain regions of the southern United States. Site preparation treatments included: (1) burn only, (2) chop-burn, (3) shear-pile-disk, (4) chop-herbicide-burn, (5) herbicide-burn, and (6) herbicide-burn-herbicide.

? The data from the available 19 installations at age 21 were analyzed with separate analysis of variance and a multilevel nonlinear mixed-effects modeling approach.

? The herbicide-burn-herbicide treatment significantly increased average Dbh, height, basal area and volume per hectare compared to all other treatments. The burn only treatment consistently ranked worst and was followed by the chop-burn treatment. The shear-pile-disk and chop-herbicide-burn treatments had similar overall growth pattern, and will approach the same level of pine volume as the herbicide-burn treatment.

? Loblolly pine mean annual increment in volume (m³ ha^?1 y^?1) at age 21 by treatment were: herbicide-burn-herbicide (17.9), shear-pile-disk (16.1), herbicide-burn (15.9), chop-herbicide-burn (15.4), chop-burn (14.3), and burn (11.2).

? An additional chop or herbicide treatment to the burn treatment significantly increased loblolly pine yield. Complete control of both herbaceous and woody completion enhanced long-term pine productivity.

     

Influence of several tree traits on rainfall partitioning in temperate and boreal forests: a review

? In forests, rainfall is partitioned into intercepted water (IW), throughfall (TF) and stemflow (SF). We reviewed the majority of published works comparing water flows among tree species in temperate and boreal forests to test the effect of several tree traits on water flows.

? We hypothesized that water flows differed between evergreen and deciduous species, and according to successional status and bark roughness. We also investigated that water flows would be explained by stand variables such as basal area.

? Linear mixed models fitted on reviewed data showed that evergreens had a lower TF than deciduous trees (decrease of 13.9% of total precipitation year-round and 8.4% over the growing period). Similar results were found for conifers compared to broadleaves. TF also declined with the successional status from pioneer to late-successional tree species. SF decreased with bark roughness from smoother to rougher bark. Evergreens had water flows that were dependent on age of the stand, especially for TF which increased by 15.6% of total precipitation from young to adult forests.

? The large scale of TF differences between tree genera together with specific transpiration amounts and rooting features highlighted in other studies should result in significant differences in soil water content among tree species. This may have consequences on stand fitness and growth, and understory vegetation.

     

Genetic variation in architectural seedling traits of Patagonian cypress natural populations from the extremes of a precipitation range

? Species distributed along wide environmental ranges are expected to be either plastic or adapted to local optima. The elucidation of which of these alternatives prevails, is crucial in planning breeding and conservation strategies for not yet domesticated species. Austrocedrus chilensis (Cupressaceae) is the most commercially important conifer of the temperate forests of Argentina and the target of a domestication program. A steep precipitation gradient characterizes its Argentinean range.

? Variation within and differentiation among four natural populations of this Patagonian cypress representative of two contrasting precipitation regimes (>1 300 and 330 mm per y) were assessed by analyzing several morpho/architectural traits in one-year-old seedlings grown in a greenhouse.

? Progenies from one of the two xeric populations did not differ from those corresponding to both humid-site populations. The two most variable populations in terms of additive genetic variance belonged to contrasting precipitation regimes. Differentiation among populations was low as measured by each and every variable (average Q _st = 0.088). Morphological traits related to the main axis size would have a dubious adaptive meaning.

? The results suggest that the Patagonian cypress would have not evolved genetic pools adapted to local optima, and thus it appears to be a phenotypically plastic species, at least regarding growth at juvenile age.

     

Which factors most influence heartwood distribution and radial growth in plantation teak?

? To investigate the effect of climate on radial growth in young plantation grown teak (Tectona grandis L.), growth ring width was measured in 105 trees and correlated to precipitation and temperature data.

? The social status of trees within the stand was also determined and cross-sectional area (CSA) for the trunk correlated to the proportion of heartwood (HW) within the tree. HW develops asymmetrically in leaning stems of some conifer species, but it is not known if this phenomenon also occurs in broadleaf species. Therefore, we measured HW proportion in leaning and straight stems, along with the number of growth rings in the HW.

? Annual ring width depended strongly on mean monthly temperature during the rainy season and the most significant relationships were found corresponding to the months of June and July. With regard to the weaker relationship between precipitation and radial growth, correlations were highest during the period of bud-break at the beginning of the rainy season.

? The very high stand density affected radial growth, particularly in suppressed trees, which responded little to thinning operations. HW formation was greatest in dominant trees, and was highly regressed with stem CSA.

? Therefore, rapid growth of young stands should be encouraged by reducing stand density. Asymmetric HW formation occurred in both leaning and straight trees, and was significantly greater along the upper sides of leaning stems. It is probable that this eccentric HW formation is linked to mechanical loading on the tree.

     

Leaf water status and stem xylem flux in relation to soil drought in five temperate broad-leaved tree species with contrasting water use strategies

? Five temperate broad-leaved tree species were compared with respect to their water consumption strategies under ample and restricted water supply. We measured synchronously leaf conductance (g _L) in the sun canopy, xylem sap flux (J _s) and leaf water potential (predawn, ψ_pd and noon, ψ_noon) in adult trees in a mixed stand and related them to the fluctuations in vapor pressure deficit (D) and soil moisture.

? Maximum g _L was particularly high in F. excelsior, C. betulus and T. cordata and revealed a higher D sensitivity. ψ_pd remained constantly high in A. pseudoplatanus, C. betulus and F. excelsior, but decreased in T. cordata and F. sylvatica with decreasing soil moisture.

? J _sddecreased linearly with decreasing soil matrix potential in all species except for F. excelsior. Apparent hydraulic conductance in the soil-to-leaf flow path (L _c) was higher in A. pseudoplatanus than in the other species.

? F. sylvatica maintained a low maximum g _L and reduced J _sd markedly upon drought, but faced severe decreases in ψ_pd and ψ_noon. F. excelsior represents an opposite strategy with high maximum g _L and stable ψ_pd.

? The species drought sensitivity increases in the sequence F. excelsior < C. betulus < T. cordata < A. pseudoplatanus < F. sylvatica.

     

Modelling site quality and individual-tree growth in pure and mixed Pinus brutia stands in north-east Greece

? Simulation tools, based on individual tree growth and mortality models can produce the most detailed predictions of forest stand development under different management schedules. These models allow the manager to predict the development of any type of stand (even- and uneven-aged, and pure and mixed stands).

? Different model approaches and predictors are required for pure even-aged or mixed uneven-aged forest stands. This study developed and compared two sets of models which enable tree-level simulation of the development of pure and mixed stands of Pinus brutia in north-east Greece. The first set of models for even-aged forestry consists of site index models, diameter growth models, tree height models, and mortality models. The second set, which is for uneven-aged forestry, uses a past growth index instead of a site index.

? The simulations and overall fitting statistics suggest that the two types of models provide realistic and accurate predictions of forest stand development and allow one to simulate the development of complex Pinus brutia stand structures in Dadia National Park forests.

? The advantages of the two approaches are discussed and it is suggested that the growth index is an effective predictor of site quality and the set of models which used such variable as predictor performed in a similar way as the models using site index, which require more information and a given stand structure (even-aged).

     

Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

? We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate.

? Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth.

? High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes.

? Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak.

     

Damage reduction and performance of mass trapping devices for forest protection against the spruce bark beetle, Ips typographus (Coleoptera Curculionidae Scolytinae)

? The spruce bark beetle, Ips typographus, is one of the main European forest pests, and mass trapping is probably the most common strategy applied to reduce its population density. However, the results concerning the effectiveness of this control system are often controversal, and many studies consider only the trapping performance with no attention to the damage reduction.

? During spring-summer 2005, a control program against I. typographus outbreaks was set up in NE Italy. Twenty-four spruce forests heavily infested by I. typographus were studied: six protected by pheromone slot-traps, six by horizontal trap-logs and six by standing trap-logs; six untreated stands were kept as controls. Trap-logs were baited with a pheromone specific to I. typographus and treated with insecticide. Each type of device was tested at high, medium and low density in relation to the number of trees infested during the previous year. New damage occurring in the investigated stands was later monitored for one year.

? Protected forests showed mean damage about 80% lower in 2005 than in 2004, with no statistical difference among traps, trap-logs or standing trap-logs. Instead, unprotected forests (controls) suffered damage to a similar extent in both years. Trapping devices showed no statistical differences among mean captures. Device densities showed similar results in damage reduction and insect trapping.

? The results support the hypothesis that intensive trapping performed at stand level may be useful for protecting forests against I. typographus, locally reducing population density and tree mortality.

     

Influence of annual weather on growth of pedunculate oak in southern Sweden

? A network of oak (Quercus robur L.) chronologies containing 49 sites and 635 single trees was analysed to identify weather variables affecting annual tree-ring increment dynamics in southern Sweden during 1860–2000.

? We analysed (1) the growth response of oak to non-extreme weather, and (2) the temporal and spatial patterns of regional growth anomalies (pointer years) and associated climatic extremes resolved on a monthly scale.

? Growth was controlled by precipitation in the current (June–July) and the previous growing season (August) in 48% and 22% of all sites, respectively. Temperature during July of the current year and August of the previous year was negatively correlated with growth in 29% and 43% of the sites, respectively. Growth was positively correlated with temperature in October of the previous season in 72% of the sites. The most extensive growth anomaly occurred in 1965 and was probably caused by intrusion of cold Arctic air masses into the region at the end of March that year.

? During climatically non-extreme years, oak growth is driven mostly by the dynamics of summer precipitation. Many of the negative growth anomalies, however, were associated with temperature extremes. Southern Swedish oak pointer years tend not to coincide with the pan-European oak pointer years.

     

Properties of boundary-line release criteria in North American tree species

? Boundary line release criteria are increasingly applied to evaluate forest disturbance histories from tree-ring data. However, a number of important properties central to the technique have not been evaluated, including: (i) the ability of boundary line release criteria to standardize releases across various sites, species, and tree life stages (ii) the minimum sample sizes necessary for developing boundary lines, and (iii) the degree to which the criteria can resolve the degree of crown exposure following a disturbance event.

? In an analysis of eleven North American tree species, boundary line release criteria do not fully compensate for declines in release response a tree experiences with increasing age and size, with the exception Tsuga canadensis.

? A bootstrapping analysis indicates that approximately 50 000 ring width measurements are necessary to develop boundary line release criteria for a given species.

? In a Quercus prinus stand, boundary line release criteria better predict the degree of crown exposure following a disturbance than an earlier running mean technique.

? Despite certain limitations, boundary line release criteria have the potential to standardize release calculation across most life stages of a tree, and possibly among sites and species.

     

Hybridization between Quercus robur and Q. petraea in a mixed oak stand in Denmark

? Hybridization and mating pattern between Quercus robur and Q. petraea was studied in a 5.8 ha mixed forest stand in Jutland, Denmark which comprises in total 135 Quercus robur and 230 Q. petraea trees. Classification of the oak trees into species was performed using canonical discriminant analysis of a range of leaf morphological traits. Adult trees (365) and offspring (582) were genotyped with eight microsatellite markers. Seedlings were sampled in 2003 and acorns were collected in 2004.

? Mating patterns of Q. robur and Q. petraea are expected to be different in the northern range of the distribution area and a larger hybridization rate is expected. It is further expected, that pollination from outside sources will be relatively less in small fragmented forest management systems compared to large scale oak forest. The conclusions should be verified through repeated year to year analysis of the mating pattern.

? Phenological studies revealed that there was no difference in flowering time between species. Data for the adult trees revealed no significant departures from Hardy-Weinberg proportions and there was weak, but significant spatial genetic structure, which supports the idea that the stand is of natural origin. Spatial genetic structure in the first distance class is stronger for Q. petraea. The genetic composition of the offspring was remarkably consistent from year to year. Paternity analysis revealed that, on average, 85% pollination came from fathers within the stand. The direction of the pollen flow varied from year to year. Inter-specific hybridization was high and ranged from 15–17% and from 48–55% for Q. petraea and Q. robur mothers respectively. Paternity analysis revealed that the population was basically outcrossing and only 3.7% of the analysed progeny were the product of selfing. Over the two years of study, approximately 200 trees contributed to the paternity of the next generations.

? The study confirms earlier studies with a greater tendency for Q. robur mothers to produce hybrid seeds than Q. petraea mothers. The rate of hybridization is higher in this Danish stand than in comparable studies elsewhere in Europe. Gene flow from outside sources are relatively low.