Green Tree Retention (GTR) was evaluated for its potential to retain soil microbial
activity and nutrient availability after harvesting in the Coastal Western Hemlock
biogeoclimatic zone of B.C., Canada. Soil samples were collected from four sizes (5, 10,
20, and 40 m diameter) of GTR patch at the centre, edge, and along a northerly transect to
30 m beyond the groups of live trees prior to and a few months after harvest.
PRS™ Probes were used to determine the availability of nutrients; total nitrogen,
nitrate (NO₃ ̄), ammonium (NH₄⁺) and phosphate (PO₄³ ̄), encountered by plant roots
before and after harvest. Before harvest, total nitrogen, NO₃ ̄, and NH₄⁺ availability was
similar in the organic layer and mineral layers. Phosphate availability was significantly
higher in the organic layer than in the mineral layer before harvest. After harvest,
nitrogen levels increased in both soil layers with NO₃ ̄ levels significantly elevated in the
mineral layer and NH₄⁺ levels significantly elevated in the organic layer. There was no
significant change in PO₄³ ̄after harvest. Nutrient availabilities after harvest varied little
along the transects of the different sizes of retention patches. Increased availability of
total nitrogen, NH₄⁺, and PO₄³ ̄was more noticeable in the smallest (5 m in diameter )
patch size when compared to the larger patch sizes (10 m, 20 m, and 40 m in diameter)
after harvest.
The activities of five soil enzymes important in carbon, nitrogen and phosphorus
cycling - β-glucosidase, chitinase, phosphatase, phenol oxidase and peroxidase - were
measured using colorimetric or fluorimetric substrates and a microplate technique. Before
harvest, hydrolytic enzyme activity (β-glucosidase, chitinase, and phosphatase) was
higher in the organic layer than in the mineral layer. After harvest, hydrolytic enzyme activity was still higher in the organic layer than in the mineral layer, although
glucosidase activity decreased in the organic layer and increased in mineral soil after
harvest, and chitinase activity decreased in the organic layer after harvest. Changes in
glucosidase and chitinase activity (decrease in organic soil activity and increase in
mineral soil activity) were more noticeable in the smallest (5 m in diameter ) patch size
when compared to the larger patch sizes (10 m, 20 m, and 40 m in diameter) after harvest.
Phosphatase activity was significantly lower in the 5 m patch size after harvest and
showed a trend of declining activity with increasing distance from the GTR patches after
harvest in the larger retention patches. Before harvest, oxidative enzyme activity (phenol
oxidase and peroxidase) was higher in the mineral layer than in the organic layer. After
harvest, oxidative enzyme activity was still higher in the mineral layer than in the organic
layer, although phenol oxidase activity increased significantly in mineral soil after
harvest, and peroxidase activity increased significantly in both organic and mineral soil
after harvest. The stimulation of the lignin-degrading oxidative enzymes following
harvest may have been caused by lignin-rich woody substrate from slash left on site. The
increase in phenol oxidase and peroxidase activity after harvest was more noticeable in
the smallest (5 m in diameter ) patch size when compared to the larger patch sizes (10 m,
20 m, and 40 m in diameter) after harvest. The change in enzyme activity and nutrient
availability in response to harvest was greatest in 5 m retention patches for total nitrogen,
NH₄⁺, PO₄³ ̄,β-glucosidase, chitinase, phosphatase, phenol oxidase and peroxidase,
suggesting that a minimum diameter of 10 m for GTR plots may be useful to retain soil
microbial activity and nutrient availability after harvest. / Forestry, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/31430 |
| Date | January 2007 |
| Creators | Daradick, Shannon Pearl |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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