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Early-successional Species (early-successional + species)
Selected AbstractsAre forest birds categorised as "edge species" strictly associated with edges?ECOGRAPHY, Issue 4 2003Louis Imbeau In recent years, studies of bird-habitat relationships undertaken in the context of habitat fragmentation have led to the widespread use of species categorisation according to their response to edge alongside mature forest patches (edge species, interior species, interior-edge generalist species). In other research contexts, especially in less fragmented landscapes dominated by a forested land base in various age classes, bird-habitat relationships are often described in relation to their use of various successional stages (early-successional species, mature forest species, generalist species). A simple comparison of these two commonly-used classifications schemes in a close geographical range for 60 species in eastern North America as well as for 36 species in north-western Europe clearly reveals that in these two particular biomes the two classifications are not independent. We believe that this association is not only a semantic issue and has important ecological consequences. For example, almost all edge species are associated with early-successional habitats when a wide range of forest age-classes are found in a given area. Accordingly, we suggest that most species considered to prefer edge habitats in agricultural landscapes are in fact only early-successional species that could not find shrubland conditions apart from the exposed edges of mature forest fragments. To be considered a true edge species, a given species should require the simultaneous availability of more than one habitat type and consequently should be classified as a habitat generalist in its use of successional stages. However, 28 out of 30 recognised edge species were considered habitat specialists in terms of successional status. Based on these results, we conclude that "real edge species" are probably quite rare and that we should make a difference between true edge species and species which in some landscapes, happen to find their habitat requirements on edges. [source] Resource and non-resource root competition effects of grasses on early- versus late-successional treesJOURNAL OF ECOLOGY, Issue 3 2009Christian Messier Summary 1This study assessed the effects of resource (i.e. nutrients) and non-resource (i.e. interference for space) competition from fine roots of competing grasses on the growth, morphology and architecture of fine roots of four tree species of varying successional status: Populus deltoides ¥ P. balsamifera (a hybrid), Betula papyrifera, Acer saccharum and Fraxinus americana. We tested the general hypothesis that tree fine-roots are affected by both below-ground resource and non-resource competition from non-self plants, and the more specific hypothesis that this effect is stronger in early-successional tree species. 2The experiment was conducted in split-containers where half of the roots of tree seedlings experienced either below-ground resource competition or non-resource competition, or both, by grasses while the other half experienced no competition. 3The late-successional tree species A. saccharum and F. americana were mostly affected by resource competition, whereas the early-successional P. deltoides¥balsamifera and B. papyrifera were strongly affected by both resource and non-resource competition. Non-resource competition reduced fine-root growth, root branching over root length (a measure of root architecture) and specific root length (a measure of root morphology) of both early-successional species. 4Synthesis. This study suggests that early-successional tree species have been selected for root avoidance or segregation and late-successional tree species for root tolerance of competition as mechanisms to improve below-ground resource uptake in their particular environments. It also contradicts recent studies showing perennial and annual grasses tend to overproduce roots in the presence of non-self conspecific plants. Woody plants, required to grow and develop for long periods in the presence of other plants, may react differently to non-self root competition than perennial or annual grasses that have much shorter lives. [source] Effects of CO2 and light on tree phytochemistry and insect performanceOIKOS, Issue 2 2000Jep Agrell Direct and interactive effects of CO2 and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance of insect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides; paper birch, Betula papyrifera; sugar maple, Acer saccharum) were grown under ambient (387±8 ,L/L) and elevated (696±2 ,L/L) levels of atmospheric CO2, with low and high light availability (375 and 855 ,mol×m,2×s,1 at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white-marked tussock moth (Orgyia leucostigma) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage, and complementary short-term (fourth instar) feeding trials were conducted with insects fed detached leaves. Phytochemical analyses demonstrated strong effects of both CO2 and light on all foliar nutritional variables (water, starch and nitrogen). For all species, enriched CO2 decreased water content and increased starch content, especially under high light conditions. High CO2 availability reduced levels of foliar nitrogen, but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO2 and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotannins in maple responded to light and CO2, respectively. The long-term bioassays showed strong treatment effects on survival, development time, and pupal mass. In general, CO2 effects were pronounced in high light and decreased along the gradient aspen birch maple. For larvae reared on high light aspen, enriched CO2 resulted in 62% fewer survivors, with increased development time, and reduced pupal mass. For maple-fed insects, elevated CO2 levels had negative effects on survival and pupal mass in low light. For birch, the only negative CO2 effects were observed in high light, where female larvae showed prolonged development. Fourth instar feeding trials demonstrated that low food conversion efficiency reduced insect performance. Elevated levels of CO2 significantly reduced total consumption, especially by insects on high light aspen and low light maple. This research demonstrates that effects of CO2 on phytochemistry and insect performance can be strongly light-dependent, and that plant responses to these two environmental variables differ among species. Overall, increased CO2 availability appeared to increase the defensive capacity of early-successional species primarily under high light conditions, and of late-successional species under low light conditions. Due to the interactive effects of tree species, light, CO2, and herbivory, community composition of forests may change in the future. [source] Forest Succession in Tropical Hardwood Hammocks of the Florida Keys: Effects of Direct Mortality from Hurricane Andrew,BIOTROPICA, Issue 1 2001Michael S. Ross ABSTRACT A tree species replacement sequence for dry broadleaved forests (tropical hardwood hammocks) in the upper Florida Keys was inferred from species abundances in stands abandoned from agriculture or other anthropogenic acitivities at different times in the past. Stands were sampled soon after Hurricane Andrew, with live and hurricane-killed trees recorded separately; thus it was also possible to assess the immediate effect of Hurricane Andrew on stand successional status. We used weighted averaging regression to calculate successional age optima and tolerances for all species, based on the species composition of the pre-hurricane stands. Then we used weighted averaging calibration to calculate and compare inferred successional ages for stands based on (1) the species composition of the pre-hurricane stands and (2) the hurricane-killed species assemblages. Species characteristic of the earliest stages of post-agricultural stand development remains a significant component of the forest for many years, but are gradually replaced by taxa not present, even as seedlings, during the first few decades. This compositional sequence of a century or more is characterized by the replacement of deciduous by evergreen species, which is hypothesized to be driven by increasing moisture storage capacity in the young organic soils. Mortality from Hurricane Andrew was concentrated among early-successional species, thus tending to amplify the long-term trend in species composition. [source] | ||||||||||