2,596 research outputs found
Impact of river management history on the community structure, species composition and nutrient status in the Rhine alluvial hardwood forest
The present-day Rhine alluvial hardwood forest (Querco-Ulmetum minoris, Issler 24) in the upper Rhine valley
(France/Germany) is comprised of three vegetation units, one still flooded by calm waters (F) and the two others
unflooded, one for 30 years (UF30) (after the river canalisation) and the other for about 130 years (UF130)
(after river straightening and embankment work in the middle nineteenth century). In the three stands, species
composition, structure and diversity of vegetation and nutrient content of mature leaf, leaf litter and soil have been
studied. Fungi (Macromycetae) were only studied in two stands (F and UF130). The intensity of nutrient recycling
was exemplified by comparing the chemical composition of rainwater, flood, throughfall, mature leaf, leaf litter,
soil and groundwater in two of these stands (F and UF30).
The elimination of floods has caused a change in floristic composition, tree density and plant diversity. Tree
density was higher in the two unflooded stands and was related to a large increase in sapling (< 6 cm dbh) density
more than to a change of stem (> 6 cm dbh) density. Sapling density increased 2 times and three times in the
UF30 and the UF130 respectively, whereas the stem density increased only 12% in the first stand and decreased
29% in the second one. The saprophytic macromycete communities have been supplemented with mycorrhizal
species
Impact of river management history on the community structure, species composition and nutrient status in the Rhine alluvial hardwood forest
The present-day Rhine alluvial hardwood forest (Querco-Ulmetum minoris, Issler 24) in the upper Rhine valley
(France/Germany) is comprised of three vegetation units, one still flooded by calm waters (F) and the two others
unflooded, one for 30 years (UF30) (after the river canalisation) and the other for about 130 years (UF130)
(after river straightening and embankment work in the middle nineteenth century). In the three stands, species
composition, structure and diversity of vegetation and nutrient content of mature leaf, leaf litter and soil have been
studied. Fungi (Macromycetae) were only studied in two stands (F and UF130). The intensity of nutrient recycling
was exemplified by comparing the chemical composition of rainwater, flood, throughfall, mature leaf, leaf litter,
soil and groundwater in two of these stands (F and UF30).
The elimination of floods has caused a change in floristic composition, tree density and plant diversity. Tree
density was higher in the two unflooded stands and was related to a large increase in sapling (< 6 cm dbh) density
more than to a change of stem (> 6 cm dbh) density. Sapling density increased 2 times and three times in the
UF30 and the UF130 respectively, whereas the stem density increased only 12% in the first stand and decreased
29% in the second one. The saprophytic macromycete communities have been supplemented with mycorrhizal
species
A Parallel Distributed Strategy for Arraying a Scattered Robot Swarm
We consider the problem of organizing a scattered group of robots in
two-dimensional space, with geometric maximum distance between robots. The
communication graph of the swarm is connected, but there is no central
authority for organizing it. We want to arrange them into a sorted and
equally-spaced array between the robots with lowest and highest label, while
maintaining a connected communication network.
In this paper, we describe a distributed method to accomplish these goals,
without using central control, while also keeping time, travel distance and
communication cost at a minimum. We proceed in a number of stages (leader
election, initial path construction, subtree contraction, geometric
straightening, and distributed sorting), none of which requires a central
authority, but still accomplishes best possible parallelization. The overall
arraying is performed in time, individual messages, and
travel distance. Implementation of the sorting and navigation use communication
messages of fixed size, and are a practical solution for large populations of
low-cost robots
Straightening the crooked: intraspecific divergence of stem posture control and associated trade-offs in a model conifer
Although the straightening capacity of the stem is key for light capture and mechanical stability in forest trees, little is known about its adaptive implications. Assuming that stem straightening is costly, trade-offs are expected with competing processes such as growth, maintenance, and defence. We established a manipulative experiment in a common garden of Pinus pinaster including provenances typically showing either straight-stemmed or crooked-stemmed phenotypes. We imposed a bending up to 35Âş on plants aged 9 years of both provenance groups and followed the straightening kinetics and shoot elongation after releasing. Eight months later, we destructively assessed biomass partitioning, reaction wood, wood microdensity, xylem reserve carbohydrates, and phloem secondary metabolites. The experimental bending and release caused significant, complex changes with a marked difference between straight- and crooked-type plants. The straight-type recovered verticality faster and to a higher degree and developed more compression wood, while displaying a transitory delay in shoot elongation, reducing resource allocation to defence and maintaining the levels of non-structural carbohydrates compared with the crooked type. This combination of responses indicates the existence of intraspecific divergence in the reaction to mechanical stresses that may be related to different adaptive phenotypic plasticity
Functional diversity in gravitropic reaction among tropical seedlings in relation to ecological and developmental traits
International audienceGravitropism is necessary for plants to control the orientation of their axes while they grow in height. In woody plants, stem re-orientations are costly because they are achieved through diameter growth. The functional diversity of gravitropism was studied to check if the mechanisms involved and their efficiency may contribute to the differentiation of height growth strategies between forest tree species at the seedling stage. Seedlings of eight tropical species were grown tilted in a greenhouse, and their up-righting movement and diameter growth were measured during three months. Morphological, anatomical and biomechanical traits were measured at the end of the survey. Curvature analysis was used to analyse the up-righting response along the stems. Variations in stem curvature depend on diameter growth, size effects, the increase in self-weight, and the efficiency of the gravitropic reaction. A biomechanical model was used to separate these contributions. Results showed that (1) gravitropic movements were based on a common mechanism associated to similar dynamic patterns, (2) clear differences in efficiency (defined as the change in curvature achieved during an elementary diameter increment for a given stem diameter) existed between species, (3) the equilibrium angle of the stem and the anatomical characters associated to the efficiency of the reaction also differed between species, (4) the differences in gravitropic reaction were related to the light requirements: heliophilic species, compared to more shade-tolerant species, had a larger efficiency and an equilibrium angle closer to vertical. This suggests that traits determining the gravitropic reaction are related to the strategy of light interception and may contribute to the differentiation of ecological strategies promoting the maintenance of biodiversity in tropical rain forests
Characteristics of coarse woody debris and its impact on urban streambed process and structure, North Buffalo Creek, Greensboro, USA
"Coarse woody debris is important in contemporary urban stream channel systems yet little is known about the dynamics and characteristics of CWD and its impact on streambed process and structure. Measurements of CWD pieces included length, diameter, volume, orientation to flow, and debris dam locations were surveyed. Wood sizes were a function of the frequency of debris dams, proportion of pools formed by wood, and variation of bankfull channel width. The frequency of debris dams increased downstream. The downstream increase of debris dams is a function of long-distance transport of CWD primarily by debris flow. Stream reaches intersecting partial wooded had longer woody debris pieces, more debris dams, and wood-formed pools compared to wooded and nonwooded reaches. The greater proportion of CWD pieces were parallel oriented to the stream channel. The proportion of pools formed by woody debris is low as compared to rural and forested streams. Changes in streambed processes and structure occurred in all debris dam locations and stable CWD sections. Channel widening associated with CWD was observed predominantly in the nonwooded site."--Abstract from author supplied metadata
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