Fragmentation patterns and systematic transitions of the forested landscape in the upper Amazon region,Ecuador 1990–2008

The analysis of the systematic transitions in the forested landscape and the study of the forest fragmentation patterns allow us to deepen our understanding of the changes in the vegetation ground cover. The importance of knowing the intricate patterns of the land usage of the upper basin of the Amazon region is widely recognized. This zone is one of the most diverse biological areas in the world, is home to large areas of mature tropical cloud forest and demonstrates high probabilities of stable climatic conditions in light of global warming. The research quan- tiffed systematic transitions through the ＂loss＂ and ＂gain＂ of the different categories of landscape during the eighteen-year study period of the Ecuadorian Amazon Region （EAR）, the forest fragmentation patterns were also analyzed based on a set of indicators. Therefore, with respect to the entirety of the landscape, the results registered for the ground coverage in forested areas during the first period （1990-2000）, show a decrease of 6.99% and an increase of 0.68%; and during the second period （2000-2008）, show a decrease of 3.99% and an increase of 2.14%. It demonstrated that forest and agricultural areas tended to replace or be replaced by herbaceous vegetation faster than expected fortuitously. Finally, the indices of fragmentation signaled intense changes during the 1990-2000 period with a reduction during the period 2000-2008. Per- centages registered in the Largest Patch Index （LPI） were between 79.58%; 52.39% and 49.99% respectively; while the Patch Density （PD） varied between 0.04; 0.06 and 0.07. This suggests the propensity of for- est cover to remain intact. The results of this investigation suggest a tendency towards stability in Ecuador＇s Amazon landscape. Within the framework for development and management of this area, the tendency is natural regeneration. This permits a consolidation of the conservation, reforestation, forestation and agricultural forestry plans, programs and systems for the protected areas in EAR.     

Influence of tree size, reduced competition, and climate on the growth response of Pinus nigra Arn. salzmannii after fire

Context

After wildfire, surviving trees are of major ecological importance as they can help in the post-fire regeneration process. Although these trees may be damaged, they may also benefit from reduced fuel hazard and competition. However, little is known about the long-term growth response of surviving trees.

Aims

This study aims to explain short- to long-term variations in the postfire growth of surviving black pines in an area burnt in 1994, focusing on levels of fire severity and tree sizes.

Methods

Relative basal area increments were used to detect time-course variations in postfire radial tree growth depending on fire severity. Linear mixed-effects models were used to describe the factors affecting postfire ring growth.

Results

In the short term, fire caused stronger reduction in growth in small trees with increasing bole char height. However, as time since fire increased, a positive effect of fire on growth due to reduced competition counteracted the short-term fire impacts. Indeed, small surviving trees demonstrated a surge in growth 15 years after the fire.

Conclusion

It was concluded that reduced competition might offset the short-term negative effects of fire in surviving black pines.     

Short-term changes in the soil carbon stocks of young oil palm-based agroforestry systems in the eastern Amazon

The current expansion of the oil palm (Elaeis guineensis Jacq.) in the Brazilian Amazon has mainly occurred within smallholder agricultural and degraded areas. Under the social and environmental scenarios associated with these areas, oil palm-based agroforestry systems represent a potentially sustainable method of expanding the crop. The capacity of such systems to store carbon (C) in the soil is an important ecosystem service that is currently not well understood. Here, we quantified the spatial variation of soil C stocks in young (2.5-year-old) oil palm-based agroforestry systems with contrasting species diversity (high vs. low); both systems were compared with a ~10-year-old forest regrowth site and a 9-year-old traditional agroforestry system. The oil palm-based agroforestry system consisted of series of double rows of oil palm and strips of various herbaceous, shrub, and tree species. The mean (±standard error) soil C stocks at 0–50 cm depth were significantly higher in the low (91.8 ± 3.1 Mg C ha^?1) and high (87.6 ± 3.3 Mg C ha^?1) species diversity oil palm-based agroforestry systems than in the forest regrowth (71.0 ± 2.4 Mg C ha^?1) and traditional agroforestry (68.4 ± 4.9 Mg C ha^?1) sites. In general, no clear spatial pattern of soil C stocks could be identified in the oil palm-based agroforestry systems. The significant difference in soil carbon between the oil palm area (under oil palm: 12.7 ± 2.3 Mg C ha^?1 and between oil palm: 10.6 ± 0.5 Mg C ha^?1) and the strip area (17.0 ± 1.4 Mg C ha^?1) at 0–5 cm depth very likely reflects the high input of organic fertilizer in the strip area of the high species diversity oil palm-based agroforestry system treatment. Overall, our results indicate a high level of early net accumulation of soil C in the oil palm-based agroforestry systems (6.6–8.3 Mg C ha^?1 year^?1) that likely reflects the combination of fire-free land preparation, organic fertilization, and the input of plant residues from pruning and weeding.     

Effect of tapping activity on the dynamics of radial growth of Hevea brasiliensis trees

Rubber tree (Hevea brasiliensis Müll. Arg.) radial growth dynamics were monitored with displacement sensors, together with latex production, to investigate three aspects of the dual production of latex and wood: (1) the usefulness of fine-scale dendrometric measurements as a physiological tool to detect water shortage through radial growth; (2) the dynamic aspects, both at the seasonal and at the multi-year scale, of the competition between latex and wood production; and (3) the spatial distribution of radial growth rates around the tapping cut. Radial growth of untapped control trees started with the onset of the rainy season and lasted until the onset of the dry season, ceasing completely during the driest period. Displacement sensors provided a sensitive means of detecting water shortage, with a clear correlation between diameter variations and changes in water availability (both daily evapotranspiration and monthly rainfall) over the whole annual cycle. However, the correlation was significantly disturbed in tapped trees. After resumption of tapping, the radial growth rate dropped sharply within two weeks and the effect persisted throughout the whole season, so that the cumulative growth of tapped trees was about half that of untapped trees, with the cumulative growth deficit reaching 80% for the period from mid-June to November. This long-known negative impact of tapping on growth was much stronger in the second year of tapping than in the first, whereas latex production increased significantly between the first and second year of tapping. The increased latex production, which could not be ascribed to climatic conditions, shows that the establishment of an artificial latex sink is a progressive, long-term process likely involving many aspects of metabolism. As expected, ethylene significantly increased latex production in both years; however, ethylene had no effect on the growth rates of tapped trees. Radial growth was differentially affected at different locations around the tapping cut, with growth rates significantly lower in the tapped panel than in the untapped panel, and higher above the cut than below the cut. Thus, caution is needed when deriving whole stem wood production from girth measurements at one location on the stem, especially from girth measurements made close to the tapping cut. This also provides new evidence for the location of the latex regeneration area in the tapped panel, below the cut.     

Aboveground biomass,transpiration and water use efficiency in eucalypt plantation fertilized with KCl,NaCl and phonolite rock powder

Potassium has important physiological functions in eucalypt plantations, increasing their productivity when applied to soil via mineral fertilizers. There is interest in identifying alternative sources to KCl owing to its high cost and limited reserves. The aim of the study was to test the effect of replacing KCl with NaCl and phonolite rock powder. Two comparisons were made: (1) application of 283 kg ha^?1 of KCl compared with that of 2125 kg ha^?1 of phonolite rock powder (equivalent to 170 kg ha^?1 of K₂O in both treatments); (2) application of 139 kg ha^?1 of NaCl compared with that of 183 kg ha^?1 of KCl (equivalent to 2.33 kmol Na and K, respectively). Radial growth, soil water content, leaf water potential (Ψ), accumulated transpiration, stem volume and biomass increment, as well as water use efficiency (WUE) were evaluated. In the first comparison, both fertilizations presented equal values for all characteristics evaluated. In the second, the accumulated transpiration in trees fertilized with KCl was 17% higher than that in plants fertilized with NaCl. In contrast, the WUE was 20% higher in the trees fertilized with NaCl than in those fertilized with KCl, reflecting the lower water consumption for the same increment in stem volume and biomass. We conclude that phonolite rock powder and NaCl are possible substitutes for conventional K fertilization performed with KCl.

     

Influence of waterlogging on carbon stock variability at hillslope scale in a beech forest (Fougères forest — West France)

The Kyoto protocol [39] directs the signatory countries including France to establish an inventory of carbon stocks in forests. Precise estimates of carbon stocks are hampered by local spatial variability, in particular in wetland areas [25]. The aims of this work are: (i) to estimate the spatial variability of carbon stocks on two hillslopes presenting respectively, a transition between a well-drained zone and a wetland area over a short-distance, and a very progressive transition; (ii) to correlate this variability with soil waterlogging and topographic variations and (iii) to evaluate carbon stock prediction by modelling waterlogging intensity as soil organic carbon (SOC) stocks increase significantly with waterlogging. However, SOC stocks in redoximorphic soils are highly variable, particularly in zones where carbon is redistributed due to erosion and sedimentation. In the litter and the vegetation, the age and density of the stand are the main explanatory factors of C variability. Topographic modelling of the waterlogging intensity could improve the spatial estimation of SOC stocks but not of the C stocks in the humus and vegetation.