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Mesic Sites (mesic + site)
Selected AbstractsLeaf-level resource use for evergreen and deciduous conifers along a resource availability gradientFUNCTIONAL ECOLOGY, Issue 3 2000B. D. Kloeppel Abstract 1.,We compared leaf-level carbon, nitrogen and water use for a deciduous (Larix occidentalis Nutt.) and sympatric evergreen (Pseudotsuga menziesii, Beissn., Franco, or Pinus contorta Engelm.) conifer along a resource availability gradient spanning the natural range of L. occidentalis in western Montana, USA. 2.,We hypothesized that leaf photosynthesis (A), respiration (r), specific leaf area (SLA) and foliar nitrogen concentration (N) would be higher for deciduous than sympatric evergreen conifers in mixed stands, and that these interspecies differences would increase from high to low resource availability. We also hypothesized that leaf-level nitrogen and water-use efficiency would be higher for the co-occurring evergreen conifer than L. occidentalis. 3.,In general, mass-based photosynthesis (Am) was significantly higher for L. occidentalis than co-occurring evergreen conifers in the drier sites, but Am was similar for evergreen and deciduous conifers at the mesic site. 4.,Mass-based foliar nitrogen concentration (Nm) was positively correlated to SLA for all species combined across the gradient (R2 = 0·64), but the relationship was very weak (R2 = 0·08,0·34) for evergreen and deciduous species separately. Mass-based Am and rm were poorly correlated to Nm for all species combined across the gradient (R2 = 0·28 and 0·04, respectively). 5.,For each site-species combination, daily maximum Am was negatively correlated to vapour pressure deficit (VPD) (R2 = 0·36,0·59), but was poorly correlated to twig predawn water potential (R2 < 0·04). 6.,Instantaneous nitrogen-use efficiency (NUEi; Am divided by Nm) and water-use efficiency (,13C) increased significantly (P = 0·05) from high to low resource availability for both evergreen and deciduous conifers, except for NUEi in L. occidentalis. [source] Earlywood vessel size of oak as a potential proxy for spring precipitation in mesic sitesJOURNAL OF BIOGEOGRAPHY, Issue 12 2008Patrick Fonti Abstract Aim, In this study, we evaluate the importance of the mean earlywood vessel size of oaks as a potential proxy for climate in mesic areas. Location, The study was conducted in Switzerland at three forest sites dominated by oak (Quercus petraea and Q. pubescens). The three sites were in different climatic zones, varying mainly in terms of precipitation regime. Methods, Three 50-year-long site chronologies of mean earlywood vessel size and tree-ring widths were obtained at each site and related to monthly meteorological records in order to identify the main variables controlling growth. The responses of mean vessel size to climate were compared with those of the width variables to evaluate the potential climatic information recorded by the earlywood vessels. Results, The results show that the mean vessel size has a different and stronger response to climate than ring-width variables, although its common signal and year-to-year variability are lower. This response is better in particular at mesic sites, where it is linked to precipitation during spring, i.e. at the time of vessel formation, and is probably related to the occurrence of only a few processes controlling vessel growth, whereas radial increment is controlled by multiple and varying factors. Main conclusions, The mean earlywood vessel size of oak appears to be a promising proxy for future climate reconstructions of mesic sites, where radial growth is not controlled by a single limiting factor. [source] Ecological effects of changes in fire regimes in Pinus ponderosa ecosystems in the Colorado Front RangeJOURNAL OF VEGETATION SCIENCE, Issue 6 2006Rosemary L. Sherriff Abstract Question: What is the relative importance of low- and high-severity fires in shaping forest structure across the range of Pinus ponderosa in northern Colorado? Location: Colorado Front Range, USA. Methods: To assess severities of historic fires, 24 sites were sampled across an elevation range of 1800 to 2800 m for fire scars, tree establishment dates, tree mortality, and changes in tree-ring growth. Results: Below 1950 m, the high number of fire scars, scarcity of large post-fire cohorts, and lack of synchronous tree mortality or growth releases, indicate that historic fires were of low severity. In contrast, above 2200 m, fire severity was greater but frequency of widespread fires was substantially less. At 18 sites above 1950 m, 34 to 80% of the live trees date from establishment associated with the last moderate- to high-severity fire. In these 18 sites, only 2 to 52% of the living trees pre-date these fires suggesting that fire severities prior to any effects of fire suppression were sufficient to kill many trees. Conclusions: These findings for the P. ponderosa zone above ca. 2200 m (i.e. most of the zone) contradict the widespread perception that fire exclusion, at least at the stand scale of tens to hundreds of hectares, has resulted in unnaturally high stand densities or in an atypical abundance of shade-tolerant species. At relatively mesic sites (e.g. higher elevation, north-facing), the historic fire regime consisted of a variable-severity regime, but forest structure was shaped primarily by severe fires rather than by surface fires. [source] Rosette Recruitment of a Rare Endemic Forb (Gaura neomexicana Subsp. coloradensis) with Canopy Removal of Associated SpeciesRESTORATION ECOLOGY, Issue 1 2002Linda M. Munk Abstract Gaura neomexicana subsp. coloradensis Munz (Onagraceae), (Colorado butterfly plant), a short-lived perennial forb, became listed as a threatened species by the U.S. Fish and Wildlife Service in October 2000 because of its small global range and population size. This endemic subspecies consists of only 18 extant populations within southeastern Wyoming, southwestern Nebraska, and northeastern Colorado. Wyoming occurrences are on private land with the exception of three occurrences on F. E. Warren Air Force Base, near Cheyenne. Gaura neomexicana subsp. coloradensis may be displaced by many competitors, including Cirsium arvense (L.) Scop. (Canada thistle), an invasive, noxious weed. In June 1998, three G. neomexicana subsp. coloradensis populations were examined for rosette establishment in the presence of and after removal of associated species. The four study treatments removed: (1) Cirsium arvense, (2) grass and forb canopy and associated litter, (3) grass and forb canopy, litter, and C. arvense, and (4) no removal of associated plant species (control). Mature G. neomexicana subsp. coloradensis plants were evaluated for height, number of leaves, and capsule production. The mature plant characteristics monitored in 1998 were not good indicators of subsequent G. neomexicana subsp. coloradensis rosette densities in the following spring. Recruitment was assessed by counting new rosettes in the fall 1999. Although both G. neomexicana subsp. coloradensis and the exotic C. arvense have comparable habitat, removal of C. arvense did not increase G. neomexicana subsp. coloradensis vegetative growth, seed capsule production, or rosette density. Removal of other forbs, grass, and litter, however, increased G. neomexicana subsp. coloradensis rosette density in the following two years, indicating that canopy removal of associated species can enhance rosette establishment of this rare native. The accumulation of dense vegetative cover and litter associated with the absence of herbivory and fire may contribute to the decline of rare species in rich riparian habitats. Return of herbivory and fire in mesic sites to reduce standing biomass accumulations should be considered in restoring recruitment potential to rare monocarpic species. [source] | ||||||||||