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  • 1
    Electronic Resource
    Electronic Resource
    The effects of the spatial pattern of defoliation on regrowth of a tussock grass (1990)
    Springer
    Oecologia 82 (1990), S. 12-17 
    Details
    ISSN: 1432-1939
    Keywords: Tussock grass ; Defoliation ; Canopy structure ; Light interception ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The spatial pattern of foliage removal from a tussock grass can influence regrowth through effects on daily carbon gain (CERd). This field study examined the extent to which tussock photosynthetic responses to different defoliation patterns were associated with changes in whole-canopy attributes (e.g., foliage age structure, canopy light microclimate). During the spring growing season, 60% of the green foliage area was removed from individual Agropyron desertorum tussocks with scissors in different spatial patterns. These patterns represented extremes of defoliation patterns that might be inflicted by natural herbivores. Tussock photosynthesis (per unit foliage area) at high light (2000 μmol photons m−2 s−1 between 400 and 700 nm; P2000) increased following clipping with all defoliation patterns. The increases in P2000 were greater when leaves were removed from low in the tussock (older leaves) than if leaves high in the canopy (younger leaves) were removed. These relative changes of P2000 among clipping patterns paralleled the responses of CERd and regrowth from an earlier study. Furthermore, the changes in P2000 corresponded with increases in the proportion of foliage within the tussocks that was directly illuminated at midday. The greater photosynthesis of tussocks after lower-leaf removal was directly related to a higher proportion of younger foliage and a smaller fraction of foliage shaded within the tussock. In a dense canopy, such as these grass tussocks, the influence of defoliation on whole-canopy attributes may be of primary importance to whole-plant photosynthetic responses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318527
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of the spatial pattern of defoliation on regrowth of a tussock grass (1989)
    Springer
    Oecologia 80 (1989), S. 289-296 
    Details
    ISSN: 1432-1939
    Keywords: Tussock grass ; Clipping ; Defoliation ; Spatial pattern ; Regrowth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effects of the spatial pattern of defoliation within a tussock grass, Agropyron desertorum, were investigated at a semiarid field site. In the middle of the spring growing season (mid-May), tussocks were clipped in repeatable defoliation patterns, and the regrowth of foliage was monitored. These clipping patterns involved removal of foliage from different locations within the tussock, but the total amount of foliage removed was held constant. Active meristems were left intact in all cases. The spatial pattern of defoliation affected both initial rates of tussock regrowth and total growing-season aboveground biomass production. When leaves were removed low in the tussock (older leaves), regrowth was greater than after removal of the same quantity of foliage high in the canopy (younger leaves). These differences in regrowth were due to differences in the rate of new tissue production rather than differences in the timing of senescence. The results were consistent over two years even though aboveground production differed considerably between years. The interaction of the spatial pattern and timing of defoliation was also studied by clipping additional plants in late May. The timing of defoliation affected the relative influence of different defoliation patterns on regrowth. In those defoliation patterns where active meristems were not removed in the late-May clipping, there were no differences in regrowth of tussocks which had either upper or lower foliage removed. However, because the grass culms had elongated by late May, active meristems were higher and were removed by one of the defoliation pattern treatments (a uniform clipping). This resulted in much less regrowth. Differences in the effects of clipping patterns applied in late May were associated with this removal of active meristems. Whereas, differences among clipping treatments following the earlier mid-May defoliation were probably a result of changes in factors which affected tussock carbon gain (e.g., light interception, foliage age structure). In either case, the spatial pattern of defoliation within a tussock grass clearly had significant effects on aboveground regrowth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379029
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  • 3
    Electronic Resource
    Electronic Resource
    The effects of the spatial pattern of defoliation on regrowth of a tussock grass (1989)
    Springer
    Oecologia 81 (1989), S. 437-442 
    Details
    ISSN: 1432-1939
    Keywords: Tussock grass ; Clipping ; Defoliation ; Gas exchange ; Regrowth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effect of different defoliation, patterns within a tussock grass on CO2 and water vapor exchange of entire tussocks was assessed and compared with differences in regrowth behavior. During rapid spring growth, 60% of the green foliage area was removed from Agropyron desertorum tussocks in different spatial patterns. Compensatory growth responses of defoliated tussocks corresponded well with increases in integrated daytime CO2 exchange rate of tussocks per unit foliage area (CERd) immediately following clipping. When leaves were removed from low in the tussock (older leaves), both regrowth and CERd were greater than after removal of foliage located high in the canopy (younger leaves). Water vapor conductance (gw) increased similarly for all clipped plants, regardless of defoliation pattern. Thus, the differential responses of CERd to the defoliation patterns could not be fully attributed to changes in gw. The increases in gw of all clipped plants resulted in large increses in tussock daytime water loss (Ed) and decreases in tussock water-use efficiency (CERd/Ed), even in the case where mostly older, shaded foliage was removed. Despite increases in CERd, whole-tussock CO2 fixation (net CO2 exchange per tussock) declined immediately after clipping because of the removal of considerable foliage. Whole-tussock CO2 uptake recovered more rapidly in tussocks which had lower leaf blades removed than in tussocks which had upper foliage removed because of differences in the rate of new foliage production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378949
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  • 4
    Electronic Resource
    Electronic Resource
    Characteristics of successful competitors: an evaluation of potential growth rate in two cold desert tussock grasses (1987)
    Springer
    Oecologia 71 (1987), S. 167-173 
    Details
    ISSN: 1432-1939
    Keywords: Agropyron ; Artemisia ; Relative growth rate ; Competition ; Tussock grass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Within the first few weeks after seedling emergence, Agropyron desertorum, a more competitive tussock grass, had a much higher mean relative growth rate (RGR) than Agropyron spicatum, a very similar, but less competitive species. However, beyond the early seedling stage, the two grasses had a remarkably similar whole-plant RGR in hydroponic culture and aboveground RGR in glasshouse soil, if root temperatures were above approximately 12°C. At soil temperatures between 5 and 12°C, A. desertorum exhibited a 66% greater aboveground RGR than A. spicatum (P〈0.05). Both species responded similarly to warming soil temperatures. In the field, however, tiller growth rates were generally similar. Neither species showed marked tiller elongation until a couple of weeks after snowmelt, by which time soil temperatures, at least to a depth of 10 cm, were above 12°C for a significant portion of the day. Aboveground biomass accumulation over a three-year period indicated that both grasses had similar potential growth rates whereas Artemisia tridentata ssp. vaseyana, a common neighbor planted in the same plots, had a much greater potential growth rate. The greater competitive ability of adult A. desertorum, as compared to A. spicatum, cannot be attributed to appreciable differences in potential growth rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377281
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