Positive shrub-tree interactions facilitate woody encroachment in boreal peatlands
Holmgren, M. ; Lin, C.Y. ; Murillo, J.E. ; Nieuwenhuis, A. ; Penninkhof, J.M. ; Sanders, N. ; Bart, T. van; Veen, H. van; Vasander, H. ; Vollebregt, M.E. ; Limpens, J. - \ 2015
Journal of Ecology 103 (2015). - ISSN 0022-0477 - p. 58 - 66.
scots pine - sphagnum - bogs - growth - mire - communities - recruitment - transitions - sylvestris - ecosystems
1. Boreal ecosystems are warming roughly twice as fast as the global average, resulting in woody expansion that could further speed up the climate warming. Boreal peatbogs are waterlogged systems that store more than 30% of the global soil carbon. Facilitative effects of shrubs and trees on the establishment of new individuals could increase tree cover with profound consequences for the structure and functioning of boreal peatbogs, carbon sequestration and climate. 2. We conducted two field experiments in boreal peatbogs to assess the mechanisms that explain tree seedling recruitment and to estimate the strength of positive feedbacks between shrubs and trees. We planted seeds and seedlings of Pinus sylvestris in microsites with contrasting water-tables and woody cover and manipulated both shrub canopy and root competition. We monitored seedling emergence, growth and survival for up to four growing seasons and assessed how seedling responses related to abiotic and biotic conditions. 3. We found that tree recruitment is more successful in drier topographical microsites with deeper water-tables. On these hummocks, shrubs have both positive and negative effects on tree seedling establishment. Shrub cover improved tree seedling condition, growth and survival during the warmest growing season. In turn, higher tree basal area correlates positively with soil nutrient availability, shrub biomass and abundance of tree juveniles. 4. Synthesis. Our results suggest that shrubs facilitate tree colonization of peatbogs which further increases shrub growth. These facilitative effects seem to be stronger under warmer conditions suggesting that a higher frequency of warmer and dry summers may lead to stronger positive interactions between shrubs and trees that could eventually facilitate a shift from moss to tree-dominated systems.
Growth adjustments of conifers to drought and to century-long irrigation
Feichtinger, L.M. ; Eilmann, B. ; Buchmann, N. ; Rigling, A. - \ 2014
Forest Ecology and Management 334 (2014). - ISSN 0378-1127 - p. 96 - 105.
scots pine stands - water availability - climate-change - terrestrial ecosystems - wood formation - radial growth - tree-growth - ring width - sylvestris - mortality
Our knowledge on tree responses to drought is mainly based on short-term manipulation experiments which do not capture any possible long-term adjustments in this response. Therefore, historical water channels in inner-Alpine dry valleys were used as century-long irrigation experiments to investigate adjustments in tree growth to contrasting water supply. This involved quantifying the tree-ring growth of irrigated and non-irrigated (control) Scots pine (Pinus sylvestris L.) in Valais (Switzerland), as well as European larch (Larix decidua Mill.) and black pine (Pinus nigra Arnold) in Vinschgau (Italy). Furthermore, the adjustments in radial growth of Scots pine and European larch to an abrupt stop in irrigation were analyzed. Irrigation promoted the radial growth of all tree species investigated compared to the control: (1) directly through increased soil water availability, and (2) indirectly through increased soil nutrients and humus contents in the irrigated plots. Irrigation led to a full elimination of growth responses to climate for European larch and black pine, but not for Scots pine, which might become more sensitive to drought with increasing tree size in Valais. For the control trees, the response of the latewood increment to water availability in July/August has decreased in recent decades for all species, but increased in May for Scots pine only. The sudden irrigation stop caused a drop in radial growth to a lower level for Scots pine or similar level for larch compared to the control for up to ten years. However, both tree species were then able to adjust to the new conditions and subsequently grew with similar (Scots pine) or even higher growth rates(larch) than the control. To estimate the impact of climate change on future forest development, the duration of manipulation experiments should be on longer time scales in order to capture adjustment processes and feedback mechanisms of forest ecosystems. (C) 2014 Published by Elsevier B.V.
The domestication and evolutionary ecology of apples
Cornille, A. ; Giraud, T. ; Smulders, M.J.M. ; Roldán-Ruiz, I. ; Gladieux, P. - \ 2014
Trends in Genetics 30 (2014)2. - ISSN 0168-9525 - p. 57 - 65.
wild malus-orientalis - genetic-structure - population-structure - venturia-inaequalis - crop domestication - cultivated apple - fruit - sylvestris - markers - mill.
The cultivated apple is a major fruit crop in temperate zones. Its wild relatives, distributed across temperate Eurasia and growing in diverse habitats, represent potentially useful sources of diversity for apple breeding. We review here the most recent findings on the genetics and ecology of apple domestication and its impact on wild apples. Genetic analyses have revealed a Central Asian origin for cultivated apple, together with an unexpectedly large secondary contribution from the European crabapple. Wild apple species display strong population structures and high levels of introgression from domesticated apple, and this may threaten their genetic integrity. Recent research has revealed a major role of hybridization in the domestication of the cultivated apple and has highlighted the value of apple as an ideal model for unraveling adaptive diversification processes in perennial fruit crops. We discuss the implications of this knowledge for apple breeding and for the conservation of wild apples.
Growth response of Scots pine with different crown transparency status to drought release
Eilmann, B. ; Dobbertin, M. ; Rigling, A. - \ 2013
Annals of Forest Science 70 (2013)7. - ISSN 1286-4560 - p. 685 - 693.
swiss rhone valley - pinning method - pubescent oak - xylem growth - mortality - sylvestris - forest - populations - dynamics - decline
Context - One short-term adjustment of trees to drought is the reduction of photosynthetic tissues via leaf shedding. But in conifers, it usually takes several years to fully restore needle mass and assimilation capacity. Aims - This study aims to evaluate whether leaf shedding sustainably damages conifers or if these trees still have the ability to recover from drought with respect to their foliage and wood formation. Methods - An irrigation experiment was established in a mature dry forest to test the growth reactions of Scots pine (Pinus sylvestris L.) differing in crown transparency (low, medium, high) to a drought release by irrigation in comparison with equivalent control trees growing under naturally dry conditions on the same site. Results - Drought and high crown transparency had a combined negative effect on radial tree growth: Control trees with medium to high crown transparencies showed a substantially shorter growth period and a long-lasting growth depression in response to the severe summer drought in 2003. However, all trees benefited from irrigation, irrespective of their crown status, and immediately increased growth in response to irrigation. Conclusion - The progressed drought-induced defoliation seemed to be a weakening factor for trees suffering from drought, but this can be reversed if the water supply is improved.
Origin matters! Difference in drought tolerance and productivity of coastal Douglas-fir (Pseudotsuga menziesii (Mirb.)) provenances
Eilmann, B. ; Vries, S.M.G. de; Ouden, J. den; Mohren, G.M.J. ; Sauren, P. ; Sass, U.G.W. - \ 2013
Forest Ecology and Management 302 (2013). - ISSN 0378-1127 - p. 133 - 143.
climate-change - scots pine - tree-growth - variability - seedlings - forest - photosynthesis - populations - sylvestris - adaptation
Forests of the future should be resistant to exacerbating climatic conditions, especially to increasing drought, but at the same time provide a sufficient amount and quality of timber. In this context coastal Douglas-fir (Pseudotsuga menziesii (Mirb.)) is a promising species since it remains productive even under chronic drought. By choosing suitable provenances within the range of Douglas-fir (P. menziesii (Mirb.)) for a given site we can further optimise tree fitness under dry conditions or even increase timber yield. Eighteen coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) var. menziesii) provenances were tested for seedling survival, yield, wood quality, and drought tolerance by taking advantage of a Dutch provenance trial, established in 1971 within the framework of the 1966/1967 IUFRO seed collection program. The site of the Dutch trial is representative for many sites in Central Europe and is characterised by a moderate precipitation and temperature regime. Measurements on height and diameter growth were combined with a dendrochronological study on growth response to drought years. We found a clear latitudinal trend indicating that Douglas-fir provenances from the northern part of the species-distribution range are generally more productive than provenances from the south. In contrast, drought tolerance increased towards the south. This suggests that it is impossible to identify provenances combining maximum productivity with lowest susceptibility towards drought. However, based on the results from the trial we can give recommendations on suitable provenances that are expected to perform best under future conditions in Central Europe. On sites where severe drought events are unlikely to occur in future, fast growing provenances from the north, like Nimkish, should be planted. These provenances respond plastically to drought years, but the strong reduction of tree growth in the drought year itself indicates that these provenances will be harmed by an increasing frequency of drought events. However, on sites where water availability is likely to decrease, provenances from the Olympic Peninsula like Forks and Matlock are very promising since they showed still relatively high yield in combination with a high potential to cope with drought. If summer drought increases in frequency and severity as expected, the latewood/earlywood ratio will be drastically reduced with negative consequences for wood quality and cavitation resistance. However, some provenances, like Marblemount or Matlock, might compensate for the negative effect of summer drought on latewood/earlywood ratio by the contribution of photosynthesis in winter to whole-year carbon stock.
Fuel load, humus consumption and humus moisture dynamics in Central European Scots pine stands
Hille, M.G. ; Ouden, J. den - \ 2005
International Journal of Wildland Fire 14 (2005)2. - ISSN 1049-8001 - p. 153 - 159.
douglas-fir stand - spatial-patterns - water-content - plot-scale - forest - soil - sylvestris - throughfall - severity - duff
Samples of Scots pine (Pinus sylvestris L.) humus were burned under different moisture and fuel load scenarios to model humus consumption. For moisture levels below 120% on a dry mass basis, a parabolic increase of humus remaining with increasing moisture content was observed while, for higher moisture levels up to 300%, humus was reduced by a constant 10¿15% on a dry mass basis. Both fuel load and humus moisture had a highly significant influence on humus consumption. Humus gross calorific value of Scots pine (19 509 KJ kg¿1) is lower than that of other pine species. We found a desorption time-lag for humus moisture of 85 h in this study. Field data show a steady accumulation of humus in Central European Scots pine stands (up to 45 t ha¿1 in 120-year-old stands). Amounts of litter remain constant over the different stand ages (~15 t ha¿1). This study provides important information to predict humus consumption in Scots pine stands. The results can be used to build a fire severity and post-fire succession model for Scots pine stands in Central Europe