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Vol. 51—1997 - NorthEastern Weed Science Society

Vol. 51—1997 - NorthEastern Weed Science Society

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66<br />

FALLIN SNOW ECOSYSTEM PROJECT: CANOPY STRUCTURE OF COMPETING<br />

VEGETATION<br />

PE<br />

R<br />

Vegetatio around 500 spruce seedlingswas characterized and quantified on 4 blocks. Each block<br />

contained e following treatments: untreated control, brushsaw, Silvana Selective, Vision" [a.i.<br />

glyphosat ], and Release" [a.i. triclopyrj). These were monitored 1 and 2 years post-treatment.<br />

In August of each year, canopy structure (leaf area index [LAI] and mean tip angles [MTA]) of<br />

the vege ion was measured at ground level using a LiCor LAI-2000 Plant Canopy Analyzer.<br />

Photosynt etic radiation (PAR) reaching the forest floor also was quantified. In separate surveys,<br />

vegetation resent in 480 (120/block) 4 m 2 circular sub-plots was categorized into 11 plant groups<br />

in both y rs. Cover and height of each category were estimated to the nearest 5 % and 10 em<br />

respectivel . A vegetation index (VI = cover x ht) was calculated for each category. All canopy<br />

structure d light measurements were analysed using ANOVA procedures.<br />

In 1994 1 year post-treatment), leaf areas of competing vegetation for all conifer release<br />

treatments were lower than that for the untreated control treatment, and correlated well ( - 60%)<br />

with calc lated VI values for the same treatments. The lowest mean LA! was for the Vision"<br />

treatment, and differed from all other release treatments. MTA did not differ among treatments.<br />

PAR on t e forest floor was lowest for the untreated control treatment, highest for the Vision"<br />

treatment, and intermediate for all other treatments.<br />

In 1995 (2 years post-treatment), leaf areas of the vegetation for the release treatments was again<br />

lower th that for the untreated control treatment. In addition, LAI values were lower (0.4 to 1.1<br />

m 2 rn") fo all treatments on all blocks. Vegetation indices were generally lower in 1995 than in<br />

1994 for erbs, ferns, grasses, sedges, and rushes. They were generally higher in 1995 than in<br />

1994 for c nifers, deciduous trees, and shrubs. In 1995, MTA were higher (5.0 to 18.0°) for all<br />

treatment on all blocks.<br />

Because 0 reduced soil moisture levels in 1995 (20.0% less rain in early summer), leaf elongation<br />

was likel reduced resulting in lower LAI values. This decrease was most likely caused by a<br />

reduction in leaf area for herbs, ferns, grasses, sedges, and rushes, as evidenced by lower VI<br />

values fo these plant categories. Plants growing in the forest shrub and tree layers (e.g., hazel<br />

and aspen were apparently less affected by this drought than those in the forest herbaceous layer,<br />

presumab y because of deeper rooting. During periods of drought, LAI has been observed to<br />

decrease rom levels normally observed when soil moisture is not limiting.

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