Establishing a sustainable harvest for canada yew (Taxus canadensis marsh.) in Ontario

2011 ◽  
Vol 87 (04) ◽  
pp. 529-536 ◽  
Author(s):  
Thomas Noland ◽  
Lesley Rich ◽  
Maara Packalen
Keyword(s):  
First Year ◽  
Sustainable Harvest ◽  
Low Light ◽  
Harvest Intensity ◽  
Taxus Canadensis ◽  
Light Levels ◽  
Commercial Harvest ◽  
Spring Harvest ◽  
Canada Yew ◽  
Similar Growth

In 2003, commercial harvest of Canada yew (Taxus canadensis Marsh.) in Ontario began—but without a sustainable harvest policy. In 2005, we began to determine the sustainability of three harvest intensity treatments at three sites in central Ontario. Harvest treatments were labelled control (no initial harvest), light (two-year-old shoots removed), moderate (three-year-old shoots removed), and severe (seven-year-old shoots removed). We also looked at effects of harvest season and light levels on shoot regrowth. After three and four years, severe-harvest plants yielded less than half the biomass of the initial harvest, while biomass from moderate-harvest plants was about equal to the initial. Biomass from light-harvest plants generally increased. Moderate light levels stimulated more first-year regrowth in all plants than low light levels did but increased only Year 2 regrowth in severe-harvest plants. Spring harvest reduced first-year regrowth only. Comparing biomass of moderate-harvest plants after three or four years with initial moderate-harvest biomass suggested similar growth rate across time periods. Our results concur with Canada Yew Association sustainable harvest guidelines: Moderately harvesting three-year-old shoots plus allowing four years of regrowth before reharvest ensures sustainable harvest, at least through one harvest cycle.

Growth ofPseudotsuga menziesiiandTsuga heterophyllaseedlings along a light gradient: resource allocation and morphological acclimation

1997 ◽  
Vol 75 (9) ◽  
pp. 1424-1435 ◽  
Author(s):  
D. Mailly ◽  
J. P. Kimmins
Keyword(s):  
Leaf Morphology ◽  
Biomass Accumulation ◽  
Tsuga Heterophylla ◽  
Douglas Fir ◽  
Western Hemlock ◽  
Low Light ◽  
Growing Seasons ◽  
Light Levels ◽  
Light Gradient ◽  
Relative Light Intensity

Silvicultural alternatives that differ in the degree of overstory removal may create shady environments that will be problematic for the regeneration of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Gradients of light in the field were used to compare mortality, growth, and leaf morphological acclimation of two conifer species of contrasting shade tolerances: Douglas-fir and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Results after two growing seasons indicated that Douglas-fir mortality occurred mainly at relative light intensity (RLI) below 20%, while western hemlock mortality was evenly distributed along the light gradient. Height, diameter, and biomass of the planted seedlings increased with increasing light for both species but at different rates, and maximum biomass accumulation always occurred in the open. Douglas-fir allocated more resources to stem biomass than western hemlock, which accumulated more foliage biomass. Increases in specific leaf area for Douglas-fir seedlings occurred at RLI ≤ 0.4 and red/far red (R/FR) ratio ≤ 0.6, which appear to be the minimal optimum light levels for growth. Conversely, western hemlock seedlings adjusted their leaf morphology in a more regular pattern, and changes were less pronounced at low light levels. These results, along with early mortality results for Douglas-fir, suggest that the most successful way to artificially regenerate this species may be by allowing at least 20% of RLI for ensuring survival and at least 40% RLI for optimum growth. Key words: light, light quality, leaf morphology, acclimation.

Photoinhibition of DCMU-Enhanced Fluorescence in Lake Ontario Phytoplankton

1987 ◽  
Vol 44 (12) ◽  
pp. 2144-2154 ◽  
Author(s):  
M. Putt ◽  
G. P. Harris ◽  
R. L. Cuhel
Keyword(s):  
Vertical Mixing ◽  
Natural Populations ◽  
Bright Light ◽  
Euphotic Zone ◽  
Lake Ontario ◽  
Enhanced Fluorescence ◽  
Low Light ◽  
Light Levels ◽  
Phosphorus Status

Measurement of 1-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) enhanced fluorescence (FDCMU) suggested that photoinhibition of photosynthesis was frequently an artifact of in situ bottle incubations in Lake Ontario phytoplankton. In a seasonal study, FDCMU of all populations was depressed by bright light in an incubator. However, when the euphotic zone did not exceed the depth of the mixed layer, vertical transport of phytoplankton into either low-light or dark regions apparently allowed reversal of photoinhibition of FDCMU. Advantages of FDCMU as a bioassay of vertical mixing include rapidity of response time, ease of measurement in the field, and insensitivity of this parameter to changes in phosphorus status of the population. Because of seasonal changes in the photoadaptive response of natural populations, the rate constants and threshold light levels required to cause the response must be determined at each use if the method is to be quantitative.

Image classification at low light levels

1986 ◽  
Vol 3 (12) ◽  
pp. 2179 ◽  
Author(s):  
Miles N. Wernick ◽  
G. Michael Morris
Keyword(s):  
Image Classification ◽  
Low Light ◽  
Light Levels
Sign in / Sign up

Export Citation Format

Share Document