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Christian Smit - One of the best experts on this subject based on the ideXlab platform.
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coarse woody debris facilitates oak recruitment in bialowieza primeval forest poland
Forest Ecology and Management, 2012Co-Authors: Christian Smit, Dries P J Kuijper, David Prentice, M J Wassen, Joris P G M CromsigtAbstract:While oaks contribute to the ecology and economy of temperate lowland forests, recruitment into larger size classes is generally scarce. Ungulate herbivory is a limiting factor for tree recruitment, thus natural structures protecting against ungulates may be important for recruitment success. We studied oak recruitment in relation to coarse woody debris (CWD) in the Bialowieza National Park, Poland, one of the last remaining reference sites for undisturbed temperate lowland forests in Europe that contains the full natural assemblage of large ungulate species and their predators. We compared two contrasting management types: one that excludes all forestry activities (the strict reserve) and one where sanitary cutting and removal of bark-beetle infested Picea abies occurs to prevent further spread. We sampled 4 m wide transects (19 ha in total, of which 15.8 ha in the strict reserve) and recorded Sapling height and Sapling browsing, distance from, height of and CWD encirclement, distance to and diameter of mature oaks, tree composition, distance to and diameter of nearest trees, canopy openness and cover of herbs, mosses, bare soil and litter in an equal number of plots with and without Saplings. We found 161 oak Saplings (8.5/ha). CWD was predominantly formed by P. abies. Sapling plots contained more often CWD than plots without Saplings. Also, the distance to CWD was smaller and the CWD encirclement was higher in Sapling plots, while canopy cover did not differ. Sapling height increased and Sapling browsing decreased with increasing presence of CWD. Both CWD and recruitment beyond 50 cm were reduced in the managed zone. Our study shows that CWD plays an essential role for the recruitment of oaks in old-growth temperate forest systems, predominantly via protection against ungulate browsing. Sanitary cutting of infested trees, a common management practice in temperate forests, prevents the natural accumulation of CWD and so can be counter-productive for the recruitment of appreciated species.
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From protégé to nurse plant: establishment of thorny shrubs in grazed temperate woodlands
Journal of Vegetation Science, 2011Co-Authors: Christian Smit, Jasper L. RuifrokAbstract:Question Thorny shrubs play keystone roles in grazed ecosystems by defending non-protected plants against herbivores, but their establishment in grazed ecosystems is poorly understood. Which factors control establishment of recruits of thorny nurse shrubs in grazed temperate woodlands? Location Ancient grazed temperate woodlands (52 degrees 32'N, 6 degrees 36'E), The Netherlands. Methods We surveyed biotic and abiotic factors for Saplings of thorny nurse shrubs in plots with and without Saplings. To disentangle these factors, we performed a transplantation experiment over two growing seasons with nurse shrub Saplings (Prunus spinosa and Crataegus monogyna) planted in two dominant vegetation types - tall unpalatable swards and short grazed lawns - half of them protected from herbivory via exclosures. Results Plots with shrub Saplings had taller surrounding vegetation, higher soil pH and higher soil moisture than plots without Saplings. These plots predominantly contained unpalatable sward species, while plots without Saplings mainly contained palatable lawn species. After transplantation, Sapling survival was higher in exclosures than in the open, and higher in sward exclosures than in lawn exclosures. Sapling growth was higher in swards than in lawns, higher inside than outside exclosures, and higher for Prunus than Crataegus, while browsing on Saplings was higher in lawns. Conclusion Unpalatable swards form essential establishment niches for thorny shrubs in grazed temperate woodlands: they protect against herbivores before thorns fully develop in Saplings, and Sapling growth is better due to improved micro-environmental conditions. Once established and thorny, shrub Saplings grow out of the protective range of the swards and in turn facilitate tree seedlings, which are essential for long-term persistence of grazed temperate woodlands. This study shows that nurse plants may start as proteges before becoming facilitators for other plants in a later life stage. This may be common for nurse plants in various ecosystems. We argue that improved understanding of establishment of nurse plants and their constraining factors is crucial for effective conservation and restoration in various ecosystems.
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nurse plants tree Saplings and grazing pressure changes in facilitation along a biotic environmental gradient
Oecologia, 2007Co-Authors: Christian Smit, Charlotte Vandenberghe, Jan Den Ouden, Heinz MullerscharerAbstract:Current conceptual models predict that an increase in stress shifts interactions between plants from competitive to facilitative; hence, facilitation is expected to gain in ecological importance with increasing stress. Little is known about how facilitative interactions between plants change with increasing biotic stress, such as that incurred by consumer pressure or herbivory (i.e. disturbance sensu Grime). In grazed ecosystems, the presence of unpalatable plants is reported to protect tree Saplings against cattle grazing and enhance tree establishment. In accordance with current conceptual facilitation-stress models, we hypothesised a positive relationship between facilitation and grazing pressure. We tested this hypothesis in a field experiment in which tree Saplings of four different species (deciduous Fagus sylvatica, Acer pseudoplatanus and coniferous Abies alba, Picea abies) were planted either inside or outside of the canopy of the spiny nurse shrub Rosa rubiginosa in enclosures differing in grazing pressure (low and high) and in exclosures. During one grazing season we followed the survival of the different tree Saplings and the level of browsing on these; we also estimated browsing damage to the nurse shrubs. Shrub damage was highest at the higher grazing pressure. Correspondingly, browsing increased and survival decreased in Saplings located inside the canopy of the shrubs at the high grazing pressure compared to the low grazing pressure. Saplings of both deciduous species showed a higher survival than the evergreens, while Sapling browsing did not differ between species. The relative facilitation of Sapling browsing and Sapling survival – i.e. the difference between Saplings inside and outside the shrub canopy – decreased at high grazing pressure as the facilitative species became less protective. Interestingly, these findings do not agree with current conceptual facilitation-stress models predicting increasing facilitation with abiotic stress. We used our results to design a conceptual model of facilitation along a biotic environmental gradient. Empirical studies are needed to test the applicability of this model. In conclusion, we suggest that current conceptual facilitation models should at least consider the possibility of decreasing facilitation at high levels of stress.
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Unpalatable plants facilitate tree Sapling survival in wooded pastures
Journal of Applied Ecology, 2006Co-Authors: Christian Smit, Jan Den Ouden, Heinz Müller-schärerAbstract:Summary 1. In endangered wooded pasture ecosystems established tree Saplings are frequently found in spatial association with protective structures, suggesting nurse effects. This associational resistance is thought to be a driving force behind tree regeneration in wooded pastures. Experimental evidence for associational resistance is, however, scarce. We studied the effects of unpalatable plants on tree Sapling performance in a wooded pasture ecosystem in Switzerland and tested the associational resistance hypothesis experimentally. 2. We transplanted 600 Picea abies Saplings of two size classes (5 cm and 10 cm) in plots: (i) with unpalatable plants (either Gentiana lutea or Cirsium acaule, representing a chemically and mechanically defended species, respectively); (ii) with one of both unpalatable plants clipped to the ground; and (iii) without any unpalatable plants. Grazing intensity was measured once in each plot and tree Sapling performance was followed for 2 consecutive years. 3. Grazing intensity was significantly higher in plots without unpalatable plants, and significantly higher in plots with Cirsium than with Gentiana. Correspondingly, Sapling survival (21?5% and 10?6% after 1 and 2 grazing years, respectively) was significantly higher near unpalatable plants, and significantly higher in plots with Gentiana than with Cirsium . Large tree Saplings survived significantly better than small ones, and depended less on the unpalatable plants for survival. 4. Except for Saplings planted near Gentiana, Sapling removal by cows and horses was the major cause of death, the extent varying between unpalatable species and treatments. 5. The growth in height of the Saplings was unaffected by the treatments. 6. Synthesis and applications. This study shows that unpalatable plants can enhance tree regeneration in wooded pastures. Sapling survival was significantly higher near unpalatable plants where grazing intensity was significantly lower. Protection against cattle is particularly important for small Saplings. These results have important management implications for the endangered and disappearing wooded pastures in western Europe. Transplanting tree Saplings near unpalatable plants could be an alternative reforestation technique in intensively grazed wooded pastures. On the other hand, removal of unpalatable plants and shrubs might prevent or slow down undesired tree encroachment in less intensively grazed areas. Key-words: associational resistance, cattle, Cirsium acaule, Gentiana lutea, grazing, Picea abies, tree regeneration
Susanna Lehvavirta - One of the best experts on this subject based on the ideXlab platform.
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Spatial distribution of Saplings in heavily worn urban forests: Implications for regeneration and management
Urban Forestry & Urban Greening, 2012Co-Authors: Kaisa Hauru, Aki Niemi, Susanna LehvavirtaAbstract:Abstract We studied the spatial distribution of Saplings in the vicinity of other Saplings and mature trees in heavily worn urban forests. Our aim was to identify favorable microsites for Saplings to regenerate under different levels of wear. We hypothesized that these safe microsites were situated close to tree trunks that might offer shelter from trampling caused by humans and their pet dogs. The distribution of Saplings was explored at 0.1–0.6 m to the nearest Sapling and 0.1–2 m to the nearest mature tree. Sorbus aucuparia was the most abundant Sapling species, followed by Populus tremula , Betula pubescens and Picea abies . These species all tended to cluster with their conspecific Saplings and were generally randomly distributed with respect to mature trees. Saplings of S. aucuparia and P. tremula favored growing close to mature P. abies (already at 0.4–0.8 up to 2 m from the trunk base, respectively) and S. aucuparia trees (at 0.2–0.4 m up to 2 m). Betula sp. and Acer platanoides grew close to Pinus sylvestris trees. Furthermore, with increased levels of wear, Saplings clustered more likely together and close to tree trunks. The results are contrary to the gap regeneration hypothesis known from rural unworn forests where Saplings often grow in canopy gaps. We suggest the idea of a ‘sheltering group’, i.e. tree groups and thickets of densely growing conspecific Saplings, for the maintenance of regeneration of Saplings and other vegetation in heavily worn recreational forests. Since urban forestry may strongly affect the existence and spatial location of a high variety of microhabitats, small-scale spatial exploration is needed to identify microsites that offer opportunities for natural regeneration under heavy recreational use. To maintain natural regeneration and the survival of Saplings in worn urban forests, we recommend microhabitat-level species-specific forest management.
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Barriers against wear affect the spatial distribution of tree Saplings in urban woodlands
Urban Forestry & Urban Greening, 2004Co-Authors: Susanna Lehvavirta, Hannu Rita, Matti KoivulaAbstract:Abstract In order to maintain indigenous, self-regenerating tree populations in urban woodlands, it is essential to identify factors affecting the survival of tree seedlings and Saplings. In densely populated areas, intensive recreational use may cause considerable wear of the vegetation and soil, and decrease the total number of Saplings. At the same time trees, high stones and other structural elements in a woodland patch can act as natural barriers and give shelter against wear. Hence, we hypothesised that with an increasing amount of wear, a greater proportion of tree Saplings survive, and is thus found, close to these natural barriers. We tested this hypothesis with observational data, and described the microhabitat associations of different Sapling species in detail to define the most favourable or unfavourable microhabitats. We recorded the microhabitats of Saplings and randomly chosen points in 30 medium-fertile Picea abies dominant woodlands in Helsinki and the surroundings, Finland. The description included location in relation to physical objects (stones, trees, topography, etc.), other Saplings, vegetation and canopy. We then compared the Sapling microhabitats to those available (the random points). Our results suggest that the microhabitat associations of Saplings change with increasing wear: Sorbus aucuparia , Populus tremula , Rhamnus frangula , Picea abies and Acer platanoides Saplings grew more often close to natural barriers (obstacles ⩾30 cm high excluding other Saplings), the first three showing a statistically significant response to wear in logistic regression models. The Saplings were able to grow in a variety of microhabitats, but the species also differed in their microhabitat associations. In general, Saplings grew in groups, and in worn sites the grouping was more pronounced. With increasing wear the Saplings associated more positively with trees, canopy cover and lush vegetation.
Matti Koivula - One of the best experts on this subject based on the ideXlab platform.
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Barriers against wear affect the spatial distribution of tree Saplings in urban woodlands
Urban Forestry & Urban Greening, 2004Co-Authors: Susanna Lehvavirta, Hannu Rita, Matti KoivulaAbstract:Abstract In order to maintain indigenous, self-regenerating tree populations in urban woodlands, it is essential to identify factors affecting the survival of tree seedlings and Saplings. In densely populated areas, intensive recreational use may cause considerable wear of the vegetation and soil, and decrease the total number of Saplings. At the same time trees, high stones and other structural elements in a woodland patch can act as natural barriers and give shelter against wear. Hence, we hypothesised that with an increasing amount of wear, a greater proportion of tree Saplings survive, and is thus found, close to these natural barriers. We tested this hypothesis with observational data, and described the microhabitat associations of different Sapling species in detail to define the most favourable or unfavourable microhabitats. We recorded the microhabitats of Saplings and randomly chosen points in 30 medium-fertile Picea abies dominant woodlands in Helsinki and the surroundings, Finland. The description included location in relation to physical objects (stones, trees, topography, etc.), other Saplings, vegetation and canopy. We then compared the Sapling microhabitats to those available (the random points). Our results suggest that the microhabitat associations of Saplings change with increasing wear: Sorbus aucuparia , Populus tremula , Rhamnus frangula , Picea abies and Acer platanoides Saplings grew more often close to natural barriers (obstacles ⩾30 cm high excluding other Saplings), the first three showing a statistically significant response to wear in logistic regression models. The Saplings were able to grow in a variety of microhabitats, but the species also differed in their microhabitat associations. In general, Saplings grew in groups, and in worn sites the grouping was more pronounced. With increasing wear the Saplings associated more positively with trees, canopy cover and lush vegetation.
T. Curt - One of the best experts on this subject based on the ideXlab platform.
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Six-year time course of light-use efficiency, carbon gain and growth of beech Saplings (Fagus sylvatica) planted under a Scots pine (Pinus sylvestris) shelterwood
Tree Physiology, 2007Co-Authors: Philippe Balandier, Hervé Sinoquet, Ela Frak, R. Giuliani, Marc Vandame, S. Descamps, L. Coll, Boris Adam, Bernard Prévosto, T. CurtAbstract:Two-year-old Fagus sylvatica L. Saplings were planted under the cover of a Pinus sylvestris L. stand in the Massif Central (France). The stand was thinned to different degrees to obtain a gradient of transmitted PAR (0-0.35). Eighteen Fagus Saplings were sampled in this gradient and their growth (basal stem diameter increment) were recorded during six years. In the same time morphological parameters (leaf area, number and arrangement in space) were monitored using 3D-digitizing. Photosynthesis parameters (leaf nitrogen content, Vcmax, Jmax, Rd) were estimated with a portable gas-exchange analyser. Sapling photosynthesis was mainly linked to light availability while their morphology was more driven by Sapling size. Annual Sapling stem diameter increment was related to the amount of light-intercepting foliage (silhouette to total leaf area ratio (STAR) * total Sapling leaf area (LA)) and light availability above the Saplings (PARt). However, the light use efficiency, i.e. the slope of the relationship between STAR * LA * PARt and stem diameter increment, decreased over time. This decrease is due to a size effect, i.e. a relative decrease of the proportion of photosynthetic tissues in comparison with the total biomass of the Sapling.
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Six-year time course of light-use efficiency, carbon gain and growth of beech Saplings (Fagus sylvatica) planted under a Scots pine (Pinus sylvestris) shelterwood
Tree Physiology, 2007Co-Authors: Philippe Balandier, Hervé Sinoquet, Ela Frak, R. Giuliani, Marc Vandame, S. Descamps, L. Coll, Boris Adam, Bernard Prévosto, T. CurtAbstract:Two-year-old Fagus sylvatica L. Saplings were planted under the cover of a Pinus sylvestris L. stand in the French Massif Central. The stand was differentially thinned to obtain a gradient of transmitted photosynthetically active radiation (PAR(t): 0-0.35). Eighteen Fagus Saplings were sampled in this gradient, and their growth (basal stem diameter increment) was recorded over six years. Over the same period, morphological parameters (leaf area, number and arrangement in space) were monitored by 3D-digitization. Photosynthetic parameters were estimated with a portable gas-exchange analyzer. Photosynthesis was mainly related to light availability, whereas Sapling morphology was mainly driven by Sapling size. Annual stein diameter increment was related to the amount of light-intercepting foliage (silhouette to total leaf area ratio (STAR) x total Sapling leaf area (LA)) and light availability above the Saplings (PAR(t)). However, light-use efficiency. i.e.. the slope of the relationship between STAR x LA x PAR, and stem diameter increment, decreased over time as a result of a relative decrease in the proportion of photosynthetic tissues to total Sapling biomass.
Alexandre Buttler - One of the best experts on this subject based on the ideXlab platform.
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the influence of competition from herbaceous vegetation and shade on simulated browsing tolerance of coniferous and deciduous Saplings
Oikos, 2008Co-Authors: Charlotte Vandenberghe, François Freléchoux, Alexandre ButtlerAbstract:The ability of Saplings to tolerate browsing (i.e. the ability to persist with reduced biomass and to compensate for biomass loss) is influenced by the level of stress and their growth strategies. Ultimately, insight into species-specific responses of Saplings to browsing, shade and competition from neighbours will help explain diversity, structure and function of grazed ecosystems such as the endangered wood-pasture systems. We measured the survival, whole-Sapling biomass and compensatory growth responses of two coniferous (Picea abies and Abies alba) and two deciduous (Acer pseudoplatanus and Fagus sylvatica) tree species to simulated summer browsing (one single clipping event), shade (installation of a shade cloth) and neighbour removal (mowing surrounding vegetation to ground level) treatments and the interactions between them after two-growing seasons. For all species, there were interacting effects on growth of browsing and environmental condition (shade and neighbours). Simulated browsing resulted in relatively smaller growth losses when plants were growing slowly due to competitive conditions related to herbaceous neighbours. Although none of the clipped Saplings could fully compensate for their biomass losses, the Saplings were closer to compensation under high competitive conditions than under low competitive conditions. Survival of the clipped Saplings remained relatively high and was only significantly reduced for Picea and Acer. Picea was least tolerant of competition and was the only species for which growth was not negatively affected by strong irradiance of a mountain pasture. Surprisingly, the tolerance of Saplings to herbivory as browsing tolerance was enhanced under conditions that negatively affected Sapling performance (i.e. survival and growth). Apparently, the relative impact of browsing at the early Sapling stage is linked to tree life history characteristics such as competition and shade tolerance and will be lower in situations with intense competitive interactions and/or strong irradiance.
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Short-Term Effects of Cattle Browsing on Tree Sapling Growth in Mountain Wooded Pastures
Plant Ecology, 2006Co-Authors: Charlotte Vandenberghe, François Freléchoux, Marie-agnès Moravie, Fawziah Gadallah, Alexandre ButtlerAbstract:Browsing by livestock has been identified as an important factor preventing tree regeneration in wooded pastures. Two field experiments were performed to investigate the effects of cattle browsing on tree Sapling growth in a mountainwooded pasture. Two size classes (ca. 12–17 cm and 41–59 cm) of each of 4 species (Picea abies, Abies alba, Acer pseudoplatanus and Fagus sylvatica) were exposed to zero, low and high grazing intensities. We measured the proportion of Saplings browsed and the effect of browsing on growth. A mowing treatment within the zero grazing intensity treatment showed no significant effect on Sapling growth. One percent of the large Saplings but 25% of the small Saplings escaped browsing. Saplings were better protected when surrounded by taller vegetation. The proportion of Saplings browsed was not significantly different among species although evergreen tree Saplings lost a larger proportion of biomass than deciduous species when browsed. Under grazing, average current-year shoot production and total aboveground biomass of all species were significantly reduced. Browsing effects tended to be smaller at the lower grazing intensity. Because the deciduous species were least reduced in aboveground growth, especially under the low grazing intensity, we conclude that at least in short-term, deciduous species are less affected by cattle browsing.
