2006
Howard, Jeanette K.; Cuffey, Kurt M.
Factors controlling the age structure of Margaritifera falcata in 2 northern California streams Journal Article
In: Journal of the North American Benthological Society, vol. 25, no. 3, pp. 677-690, 2006.
Abstract | Links | BibTeX | Tags: age structure, annual rings, California, discharge, freshwater mussels, Margaritifera falcata, mortality, recruitment
@article{Howard2006b,
title = {Factors controlling the age structure of Margaritifera falcata in 2 northern California streams},
author = {Jeanette K. Howard and Kurt M. Cuffey},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Howard_2006_Bentho.pdf},
doi = {10.1899/0887-3593(2006)25[677:FCTASO]2.0.CO;2},
year = {2006},
date = {2006-01-01},
journal = {Journal of the North American Benthological Society},
volume = {25},
number = {3},
pages = {677-690},
abstract = {Freshwater mussels are long-lived and relatively stationary organisms that form annual rings, so they provide excellent opportunities for studying how population properties such as age structure relate to environmental influences on recruitment and mortality. We investigated population dynamics of the freshwater pearl mussel, Margaritifera falcata, in 2 northern California Coast Range rivers, the South Fork Eel and the Navarro. We used field observations and inverse theoretical modeling to assess age structures and identify factors that control population demographics. Distinctly different mortality rates for young (<20 y) and old (≥20 y) mussels were observed in the South Fork Eel, and recruitment and mortality both were related to river discharge regimes. Margaritifera falcata recruited more successfully during low-discharge than during high-discharge years, and a 2-fold increase in discharge caused a 60% decline in recruitment success. Active annual recruitment (˜1100–1800 ind./y) was observed in the South Fork Eel, whereas recruitment has been low or nonexistent during the past 30 y in the Navarro. This difference probably is a consequence of the influence of 2 non-mutually exclusive factors: landuse history and host-fish abundance. The Navarro watershed has extensive timber harvesting and orchard/vineyard agriculture and has had severe declines in fish populations, whereas large sections of the South Fork Eel pass through protected land and the river has retained its historical fish populations. Investigation of the factors that shape local M. falcata population age structures yielded insights into the influence of environmental variables and history on mortality and recruitment that will aid conservation of this endangered family.},
keywords = {age structure, annual rings, California, discharge, freshwater mussels, Margaritifera falcata, mortality, recruitment},
pubstate = {published},
tppubtype = {article}
}
Freshwater mussels are long-lived and relatively stationary organisms that form annual rings, so they provide excellent opportunities for studying how population properties such as age structure relate to environmental influences on recruitment and mortality. We investigated population dynamics of the freshwater pearl mussel, Margaritifera falcata, in 2 northern California Coast Range rivers, the South Fork Eel and the Navarro. We used field observations and inverse theoretical modeling to assess age structures and identify factors that control population demographics. Distinctly different mortality rates for young (<20 y) and old (≥20 y) mussels were observed in the South Fork Eel, and recruitment and mortality both were related to river discharge regimes. Margaritifera falcata recruited more successfully during low-discharge than during high-discharge years, and a 2-fold increase in discharge caused a 60% decline in recruitment success. Active annual recruitment (˜1100–1800 ind./y) was observed in the South Fork Eel, whereas recruitment has been low or nonexistent during the past 30 y in the Navarro. This difference probably is a consequence of the influence of 2 non-mutually exclusive factors: landuse history and host-fish abundance. The Navarro watershed has extensive timber harvesting and orchard/vineyard agriculture and has had severe declines in fish populations, whereas large sections of the South Fork Eel pass through protected land and the river has retained its historical fish populations. Investigation of the factors that shape local M. falcata population age structures yielded insights into the influence of environmental variables and history on mortality and recruitment that will aid conservation of this endangered family.
2001
Hunter, John C.; Barbour, Michael G.
Through-growth by Pseudotsuga menziesii: A mechanism for change in forest composition without canopy gaps Journal Article
In: Journal of Vegetation Science, vol. 12, no. 4, pp. 445-452, 2001, ISSN: 1100-9233.
Abstract | Links | BibTeX | Tags: acer-saccharum, competition, disturbance, light, morphology, northern California, patterns, recruitment, stands, trees
@article{Hunter2001,
title = {Through-growth by Pseudotsuga menziesii: A mechanism for change in forest composition without canopy gaps},
author = {John C. Hunter and Michael G. Barbour},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Through-Growth-by-Pseudotsuga-menziesii-A-Mechanism-for-Change-in-Forest-Composition-without-Canopy-Gaps_Hunter_Barbour_2001.pdf},
doi = {10.2307/3236996},
issn = {1100-9233},
year = {2001},
date = {2001-08-00},
journal = {Journal of Vegetation Science},
volume = {12},
number = {4},
pages = {445-452},
abstract = {exception. In California's Pseudotsuga-mixed hardwood forests, crowns of Pseudotsuga menziesii (Douglas fir) are within those of angiosperm trees (Arbutus menziesii and Quercus species). In the forests we examined, every Pseudotsuga was younger and all but one were growing more rapidly in girth than the Arbutus or Quercus whose crown it had penetrated. Furthermore, as saplings. the Pseudotsuga had grown at rates between those of suppressed saplings and canopy dominants, The recruitment of emergent Pseudotsuga substantially alters these canopies because of the large size Pseudotsuga attains. Given the density of Pseudotsuga growing in canopy crowns, such recruitment is likely. As a mechanism of recruitment, this through-growth differs from gap recruitment in that the turnover of canopy trees is determined by an understory species' growth rate rather than the overstory species' longevity, and community attributes may change rapidly by replacement of canopy dominants with a dissimilar species. Pseudotsuga could grow through the canopy because of its greater potential height (> 60m vs. 20-40m for the angio-perms). narrower crown and its branches suffering less mechanical damage than those of the angiosperms. In general, resource levels in the understory, canopy height, and interspecific differences in maximum height and crown architecture all influence the likelihood of through-growth. Therefore, for vegetation types whose dominants differ substantially in growth form, through-growth may be a mechanism for rapid ecosystem change.},
keywords = {acer-saccharum, competition, disturbance, light, morphology, northern California, patterns, recruitment, stands, trees},
pubstate = {published},
tppubtype = {article}
}
exception. In California’s Pseudotsuga-mixed hardwood forests, crowns of Pseudotsuga menziesii (Douglas fir) are within those of angiosperm trees (Arbutus menziesii and Quercus species). In the forests we examined, every Pseudotsuga was younger and all but one were growing more rapidly in girth than the Arbutus or Quercus whose crown it had penetrated. Furthermore, as saplings. the Pseudotsuga had grown at rates between those of suppressed saplings and canopy dominants, The recruitment of emergent Pseudotsuga substantially alters these canopies because of the large size Pseudotsuga attains. Given the density of Pseudotsuga growing in canopy crowns, such recruitment is likely. As a mechanism of recruitment, this through-growth differs from gap recruitment in that the turnover of canopy trees is determined by an understory species’ growth rate rather than the overstory species’ longevity, and community attributes may change rapidly by replacement of canopy dominants with a dissimilar species. Pseudotsuga could grow through the canopy because of its greater potential height (> 60m vs. 20-40m for the angio-perms). narrower crown and its branches suffering less mechanical damage than those of the angiosperms. In general, resource levels in the understory, canopy height, and interspecific differences in maximum height and crown architecture all influence the likelihood of through-growth. Therefore, for vegetation types whose dominants differ substantially in growth form, through-growth may be a mechanism for rapid ecosystem change.