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Oud-Heverlee, Belgium

Gareca E.E.,Catholic University of Leuven | Gareca E.E.,Higher University of San Simon | Vandelook F.,University of Marburg | Fernandez M.,Higher University of San Simon | And 2 more authors.
Seed Science Research

Seed germination is a crucial event in a plant's life cycle. Because temperature and water availability are important regulators of seed germination, this process will likely be influenced by global warming. Insight into the germination process under global warming is thus crucial, and requires the study of a wide range of water availability and temperature conditions. As hydrothermal time (HTT) models evaluate seed germination for any combination of water potential and temperature, they can be suitable to predict global warming effects on seed germination. We studied the germination characteristics of the high Andean endemic tree species Polylepis besseri (Rosaceae), using HTT models. We were especially interested in the potential effects of global warming on seed germination. Assembly of HTT models for P. besseri was fairly straightforward due to the lack of a seed dormancy mechanism. The models allowed prediction of Polylepis germination under constant and alternating temperatures. Initially, a global warming induced increase in the field minimum and mean temperature will increase P. besseri germination, but as maximum temperatures rise above the optimum temperature for the species, seed germination will become jeopardized. Effects of global warming on seed germination are currently considerably underexplored. HTT models prove to be useful tools to study a plant species' general germination characteristics, and how they may become affected under global warming. For the endemic mountain tree species P. besseri, we predict an increase, followed by a decrease of seed germination under global warming. © Copyright Cambridge University Press 2012. Source

Ampoorter E.,Ghent University | De Schrijver A.,Ghent University | Van Nevel L.,Ghent University | Hermy M.,Nature and Landscape Research | Verheyen K.,Ghent University
Annals of Forest Science

• Context Nowadays, harvest operations are predominantly performed fully mechanized using heavy tractors or forestry machines. The resulting soil compaction may negatively affect the soil ecosystem. • Aims We wanted to draw general conclusions concerning the impact of mechanized harvesting on forest soil bulk density and the influencing factors. • Method Therefore, we combined the data of several studies using a meta-analysis approach. • Results The impact decreased from the surface towards deeper soil layers. At 0-10 cm depth, the impact on clayey soils was highest although not significantly different from the impact on sandy soils. Higher initial bulk densities, i.e., on already compacted forest soils, generally led to smaller extra increases of bulk density after machine traffic. For sandy soils, the impact was also significantly smaller when machines were lighter. No significant relationship was observed between the compaction degree and traffic intensity. • Conclusions We observed clear compaction on both clayey and sandy soils, especially in case of low initial soil compaction degrees and heavy machines. The compacted initial state of many forest soils, the long recovery period, and the generally high impact of the first passes that is frequently mentioned in literature all count in favour of designated skid trails and an adjustment of the machine type to the job. © INRA/Springer-Verlag France 2012. Source

Ampoorter E.,Ghent University | Van Nevel L.,Ghent University | De Vos B.,Research Institute for Nature and Forest | Hermy M.,Nature and Landscape Research | Verheyen K.,Ghent University
Forest Ecology and Management

An extensive field trial was set up in eight forest stands to examine the influence of soil texture (two stands on sand, four on loam to silt loam, two on clay), machine mass (light, heavy) and traffic intensity (one and five skidding cycles) (i.e. pass back and forth on the skid trail) on soil compaction after mechanized harvesting. Dry bulk density (BD), penetration resistance (PR), micro-topography and soil carbon dioxide (CO2) concentration were applied as response variables for soil compaction. Significant effects on BD were nearly absent (<7% increase) and occurred occasionally for PR (60-70% increase, up to 150% on clay soils). Especially for loam to silt loam and clay soils, this was in contrast with the expectation. The negligible compaction degrees for loam to silt loam are attributed to high initial compaction levels that prevented further compaction, as was found by general linear modelling (GLM) for both BD and PR. For clay soils the small compaction degrees can be explained by the high water contents that result in plastic deformation instead of strong compaction degrees, as was confirmed by the micro-topographical measurements. GLM also revealed a significant impact of machine mass (BD) and soil water content (BD, PR) on the compaction degree. Soil texture, traffic intensity and position in relation to the wheel tracks generally turned out to have an insignificant influence. With regard to clear interactions the influence of traffic intensity depends on the position in relation to the wheel tracks and the machine that was used (PR).In contrast with BD and PR, soil CO2 concentration, measured in a forest stand on sand, showed significant increases within and between wheel tracks, even after one skidding cycle. Although soil compaction degrees were small to negligible, machine passes apparently had a strong negative impact on pore continuity. CO2 concentration seems to be a more sensitive and thus better indicator for soil compaction. © 2010 Elsevier B.V. Source

Ampoorter E.,Ghent University | De Schrijver A.,Ghent University | De Frenne P.,Ghent University | Hermy M.,Nature and Landscape Research | Verheyen K.,Ghent University
Ecological Engineering

It is ecologically undesirable to solve forest soil compaction due to mechanized harvesting at large spatial scales using agricultural mechanical soil loosening techniques. We therefore examined whether a stimulation of biological activity through litter manipulation, liming and/or inoculation of the anecic earthworm species Lumbricus terrestris could significantly contribute to the ecological restoration of compacted forest soils by comparing the impact of these treatments on the soil within and beside compacted wheel tracks. The replacement of native litter by litter with a better quality resulted in a faster litter decomposition. However, maximal decay rates were obtained only when litter manipulation, earthworm inoculation and liming were combined. Anecic earthworms were initially absent as soils were probably too acid. Liming as well as litter manipulation had a small positive influence on the numbers of retraced L. terrestris, inducing positive feedback mechanisms on soil pH and litter decomposition rates. None of the treatments, however, had a significant effect on the compaction degrees within or beside tracks within the small study period. L. terrestris realized only a small decrease of bulk density beside the tracks. Within the tracks a similar number of L. terrestris was retrieved, but effects on the compaction degree were negligible. Liming decreased penetration resistance, but only in the absence of anecic earthworms. Endogeic earthworms were overall more abundant than the anecics, especially within tracks where soil water contents and pH values were higher. However, endogeics only had a marginal effect on litter decomposition and although they positively influence soil structure, they could not realize a reduction of the compaction degree, quantified by bulk density and penetration resistance, due to different burrowing habits. Our results indicated that a positive impact of anecic earthworms on the structure of compacted forest soils can be obtained in the long-term, at least in case soil conditions (acidity, nutrient availability and moisture content) are favourable. This can be achieved by conversion of forests towards tree species with high quality litter. © 2011 Elsevier B.V. Source

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