Quarantining the Sahara desert: growth and water-use efficiency of Aleppo pine in the Algerian Green Barrier

The Algerian Green Barrier, mainly composed of native and artificial Aleppo pine forests, spreads along the pre-Saharan steppes and is threatened by anthropogenic and natural disturbances, including climate change. We hypothesized that the ecophysiological functioning of this conifer has been substantially modified in reaction to recent warming and drought much beyond the expected effect of CO₂ fertilization. Our aim was to characterize the long-term performance (1925–2013) of native Aleppo pines thriving at their southernmost distribution. We used tree-ring width (TRW) and carbon isotope discrimination (Δ¹³C) to characterize basal area increment (BAI) and intrinsic water-use efficiency (WUEi) at three sites. BAI remained stable or slightly increased over time, with mean values ranging between 4.0 and 6.3 cm² year^?1. Conversely, site-Δ¹³C decreased from ?0.022 to ?0.014‰ year^?1 along time, which translated into WUEi increases of ca. 39%. This strong physiological reaction indicated that pines were responding simultaneously to rising CO₂ and drier conditions, inducing a progressively tighter stomatal control of water losses. However, WUEi increments were essentially unrelated to BAI and did not affect carbon reserves, which suggests a high resilience to climate change. This finding could be due to shifts in growing season towards earlier months in winter–spring, as suggested by temporal changes in climate factors underlying Δ¹³C and TRW. Our study highlights the substantial plasticity of Aleppo pine, but this species is unlikely to follow a similar pace of ecophysiological adjustments according to unprecedented low Δ¹³C records and lack of WUEi stimulation observed from 2000 onwards.     

Understanding patterns of tree adoption on farms in semi-arid and sub-humid Ethiopia

Trees on farms are a widespread feature of landscapes across a large part of Ethiopia with an important role in enhancing the resilience of smallholder livelihoods through the provision of ecosystem services. Despite their importance, little is known about what trees are planted or retained from natural regeneration by different types of farmers that results in the pattern of tree cover found in the region. We address this knowledge gap through analysis of household survey data from semi-arid and sub humid areas of Oromia regional state. A set of composite variables that represent distinctive patterns of tree cover on farms were derived from principal component analysis and Pearson correlation analysis. This revealed two major tree adoption strategies: farmer managed natural regeneration (FMNR) of trees to meet subsistence needs as well as contributing to other ecosystem services; and, high value agroforestry (HVAF) involving planted trees used largely to produce fruits, timber and fodder. Regression analysis further identified fine-scale variation in ecological and socio-economic factors that affect which of these two broad strategies are adopted by farmers. Favorable climatic conditions coupled with institutional arrangements to control free grazing were pre-conditions for HVAF, whereas poor biophysical potential and sloping land provided a positive incentive for farmers to adopt FMNR. Farmers with preferences for tree species with multiple utilities and locational flexibility favored FMNR while adoption of HVAF was more asset-driven. Our findings reveal that farmers integrate many native and exotic tree species on their farms to meet their variable farm conditions, needs and asset profiles in stark contrast to most tree promotion efforts that focus on a few, usually exotic, tree species. We recommend that future agroforestry promotion should embrace a diversity of tree species appropriate to matching the fine scale variation in ecological conditions and farmer circumstances encountered in the field.     

Individual leaf area estimations of a dioecious tropical tree species <Emphasis Type="Italic">Carpotroche brasiliensis</Emphasis> (Raddi) A. Gray,Achariaceae

Carpotroche brasiliensis is a dioecious tree species native of the Brazilian Atlantic rainforest. Due to medical and industrial use of the oil extracted from its seeds, C. brasiliensis has a great potential for cultivation as non-timber forest product in agroforestry systems. This study was conducted with the objective to analyze the leaf dimensions of male and female adult trees and seedlings of C. brasiliensis. Two hypotheses were tested: (a) leaf dimensions do not differ between male and female adult genotypes; and (b) it is possible to develop single regression models for predicting leaf area (LA) from dimensional variables encompassing male and female adult genotypes and seedlings. LA, leaf length (L) and maximum leaf width (W) were measured in leaves collected from seven male and seven female adult genotypes and three seedling lots. The feasibility of using a single model for leaves of males and females, and seedlings and adults, was tested by analysis of covariance (ANCOVA). The prediction errors (PE) for each of the regression models were calculated from the cross-validation method. The average values of L, W and LA were, respectively, 136, 142 and 457 % higher in adults than in seedlings, and the average values of leaf shapes (L:W) of seedlings were intermediate between the average values of L:W of adult males and females. The average values of L did not differ between adult males and females, but significant differences were observed between males and females for W, LA and L:W (both p < 0.01, nested ANOVA). The mean L:W values of adult males and females, and seedlings, indicate that leaf shape should be used as a criterion for sex differentiation in this species. It was not possible to develop single models encompassing adult males and females, and seedlings; but high accurate predictive models of LA from L × W measurements were developed for adult males (R² = 0.98, PE = 0.69, n = 350), adult females (R² = 0.98, PE = 0.01, n = 350), and seedlings (R² = 0.99, PE = 6.80, n = 150).     

Ex situ genetic conservation potential of seeds of two high elevation white pines

Genetic variation in a plant species is a key to its ability to survive and evolve in the face of changing environmental pressures. Due to insect and disease impacts, changes in fire regimes, and a changing climate, many populations of high elevation white pine species continue to experience high mortality levels and potentially worrisome decreases in genetic variation. In recent years, some trees rated highly for resistance to the non-native white pine blister rust have been killed by fire or mountain pine beetle. Ex situ genetic conservation offers the possibility to conserve the genetic variation within a species before much of it is lost. For many conifer species, freezer storage of seed offers a relatively inexpensive, long-term method of storing germplasm for future use. However, there is uncertainty concerning how long seed of some conifers can be stored and retain viability. We report here on results of germination testing of the oldest known seedlots of whitebark pine (Pinus albicaulis Engelm.) and foxtail pine (P. balfouriana Grev. & Balf.), some of which had been in storage for several decades. The 52 whitebark pine seedlots averaged 47.7% germination (average seed age of 19.2 years), while the four foxtail pine seedlots had an average germination of 71.3% (average seed age of 15.3 years). Some seedlots of both species had greater than 90% germination. Refinements to the stratification procedure have since been developed which should enhance germination further. A follow-up study examining seedling vigor of long-stored whitebark pine seed is planned.     

Reproductive investment of <Emphasis Type="Italic">Pinus pseudostrobus</Emphasis> along an altitudinal gradient in Western Mexico: implications of climate change

Climate varies along altitudinal gradients and species performance may be affected in response to these variations. Climate change can modify these gradients and, at the lower limit of species distributions, individuals may become stressed and their general health and reproductive performance may decrease. Study and prediction of the effects of climate change on the distribution of species along these gradients is therefore necessary. Our model study species, Pinus pseudostrobus, is a widely distributed pine in Mexico, ranging from 1600 to 3200 masl in altitude. In order to explore changes in health condition and reproductive investment along an altitudinal gradient, ten reproductive trees were selected in each of four populations (at 2300, 2400, 2700 and 2900 masl). As a proxy of individual health, we conducted a rapid visual assessment for each tree, based on crown defoliation, dead branches and foliage discoloration. This stress condition index (SCI) ranges from zero to fifteen, and lower values indicate low stress and therefore better health conditions. We also evaluated reproductive (cone weight, number/weight of seeds) and progeny (germination/seedling growth) traits. In addition, the relationships between SCI and the reproductive/progeny traits were assessed. The lowest altitude population presented poor health, with higher values of SCI (mean ± SE = 6.3 ± 0.9) that reduced up to 4.8-fold in higher-altitude populations. Cone weight also differed among altitudes, with lighter cones in the lower population (mean ± SE = 38.2 ± 4.3 g), and 1.5-fold heavier cones found in the higher populations. In general, all of the reproductive/progeny traits differed among altitudes. The population of intermediate altitude (2700 masl) presented the highest values for all traits evaluated, indicating higher performance at this altitude. Finally, a negative relationship was found between stress condition and cone weight. Based on our results and climate change models and their predictions, an increase in physiological stress can be expected in individuals of low altitude populations. Furthermore, possible increases in pests and pathogens are likely to contribute to the decline of this population. It is therefore necessary to maintain efforts of stress condition assessment and population dynamics, as well as to permanently monitor the climate along altitudinal gradients.     

Communities of saprobic fungi on leaf litter of <Emphasis Type="Italic">Vismia guianensis</Emphasis> in remnants of the Brazilian Atlantic Forest

We examined the mycobiota associated with Vismia guianensis leaf litter in three Atlantic Forest remnants of Brazil’s semiarid region. Among the study sites, two remnants were protected forest reserves, whereas the third was influenced by major anthropogenic activities. Eighteen litter samples were collected in wet and dry seasons and were processed by particle filtration technique. A total of 4750 fungal isolates of 142 taxa were identified. Species richness was higher in litter samples collected during wet season. Nonmetric multidimensional scaling multivariate analysis showed differences in the composition of fungal communities among the sampling sites and the seasons. Analysis of similarity showed that the differences were statistically significant (R = 0.85; P = 0.0001). Our findings revealed that spatial and temporal heterogeneity, and human activities had significant impacts on the saprobic fungi of V. guianensis leaf litter.     

Time Consumption and Production Costs of Two Small-Scale Wood Harvesting Systems in Northern Greece

A field-based study was carried out to determine the productivity and production cost of the tree length (TL) and the wood assortment (WA) systems implemented under small-scale forestry conditions in two Scots pine stands in Northern Greece. Tree felling and processing productivity were estimated at 8.64 m³ per productive machine hour (PMH^?1) and 10.21 m³ PMH^?1, respectively. Wood felling and processing times were strongly dependent on dbh and total tree volume. However, when manual debarking was also considered the productivity rates decreased to 1.96 and 1.43 m³ PMH^?1, respectively. Skidding productivity was calculated to be 3.35 m³ PMH^?1 for TL and 7.17 m³ PMH^?1 for WA, respectively. Strong correlations have been found between the net skidding time and (a) the skidding distance and (b) the load per turn in both wood harvesting systems. Production costs varied greatly, from 19.38 € m^?3 up to 44.81 € m^?3 of roundwood depending on the harvesting system and the inclusion of debarking. The findings suggest that the WA system is more efficient in terms of productivity and production cost than TL, and that there is a substantial optimization potential. The optimization potential can be encoded in four suggestions: (a) opening up of more forest roads to reduce high skidding times, (b) replacement of manual debarking by mechanical debarking at the sawmill, (c) replacement of old pieces of equipment with newer ones and (d) training of the existing workforce.     

A Survey of Logging Contract Rates in the Southern European Alps

A survey of harvesting contracts was conducted in the Alpine regions of France and Italy. The main goal was to produce a benchmark for the harvesting contract rates in the area that may guide forest owners and logging contractors when making their harvesting decisions. The sample included 443 contracts, evenly distributed between France and Italy. The mean tract size was 9.17 ha, while the mean lot size was slightly larger than 500 m³ under bark (ub). Mean removal intensity varied from 70 to 120 m³ ub ha^?1, depending on country and harvesting technique (i.e. ground-based or cable-yarder based). Mean contract rate was 35€ m^?3 ub, but individual contract rates varied significantly between countries and for different harvest techniques. Regression analysis showed that contract rate was strongly affected by tree size, extraction distance and harvest technique. Contrary to expectation, neither tract size nor lot size had any effect on contract rate. This may be explained by the widespread use of mobile operations that are specifically designed for handling small lots and incur minimum relocation cost. The technical factors explored in the study could only explain 40 % of the variability in the dataset, and therefore at least part of the variability must derive from non-technical factors such as local market dynamics and national economics. The study did find significant differences between countries. In particular, ground-based operations were more cost efficient in France, and cable yarder-based operations in Italy.     

The effect of surface fire on tree ring growth of <Emphasis Type="Italic">Pinus radiata</Emphasis> trees

Key message

Pinus radiata trees showed significantly reduced basal area increments and increased latewood/earlywood ratios, when their stem was charred by surface fires even if no needle damage occurred. An interaction of fire damage and precipitation on growth was observed.

Context

Heat from forest fires is able to penetrate beyond the bark layer and damage or completely kill a tree’s cambium. Short-term growth reductions following surface fires have been reported for some species. However, most studies have in common that they describe a compound effect of stem and foliage damage.

Aims

This study investigated the impact of surface fires on the radial growth of Pinus radiata, where only the stem of trees was charred, while no needle damage was recorded.

Methods

Tree ring measurements were performed on cores obtained at breast height. Analysis of variance and tests, based on annual basal area increment values were calculated to quantify pre- and post-fire growth differences of tree ring width and latewood/earlywood ratios.

Results

The analysis revealed significant growth reductions following a surface fire on P. radiata in the year on which the fire occurred as well as in the following year. As a consequence of the fire, basal area increment and latewood/earlywood ratios were significantly reduced. An interaction of fire damage and precipitation on growth was observed.

Conclusion

The obtained results show how fires without crown damage can affect growth and tree ring structure of P. radiata trees and indicate that stem char could be associated with a significant decrease in ring width and latewood/earlywood ratio.

     

Xylem traits in European beech (Fagus sylvatica L.) display a large plasticity in response to canopy release

Key message

The position of trees in the canopy impacts xylem structure and its inter-annual variation. After canopy release, the increase in the hydraulic conductivity of growth rings was driven by an increase in radial growth in large trees, and by both an increase in radial growth and changes in xylem structure in saplings.

Context

Forest canopies are frequently subjected to disturbances that allow understory trees to access the upper canopy. The effect of canopy release on xylem anatomy has been assessed in juvenile trees and saplings, while the potential acclimation of larger trees remains poorly documented.

Aims

We estimated the potential hydraulic conductivity of growth rings in large understory trees compared to overstory trees, and evaluated the responses to canopy release in large trees and in saplings.

Methods

We recorded radial growth, wood density, and vessel structure in beech trees according to their position within the canopy and their size. Xylem traits were followed during 6 years after canopy release for large trees, and during 2 years for saplings. Vessel diameter and frequency as well as ring area were used to compute the potential annual ring hydraulic conductivity.

Results

Large understory trees displayed lower radial growth increments and lower potential annual ring hydraulic conductivity than overstory trees. After canopy release, potential annual ring hydraulic conductivity increased in large trees, due exclusively to increased radial growth without any change in specific hydraulic conductivity. It increased in saplings due to both increased radial growth and increased specific conductivity.

Conclusion

Tree size impacted xylem structure and resulted in plasticity of the potential hydraulic conductivity of the annual tree ring following canopy release.