Plant Community Research

Key Findings in Plant Communities 2016–2018

In 2016, native plant species richness and non-compatible tree density was calculated within the wire zone area of research plots at SGL 33. Instead of examining these variables according to treatment type, we examined these variables in relation to the amount of herbicide used to treat the sites in 2012. In addition, we compared mechanical to chemical treatments in general. Like earlier studies, we found that herbicides significantly reduced the number of non-compatible tree species in the wire zone when compared to mechanical (mowing or handcutting) treatments. We also focused our analysis on compatible, native species of plants and found that species richness did not differ among plots that were mechanically or chemically treated. These recent findings further support the use of integrated vegetation management to control non-compatible tree species while maintaining native plant species richness in rights-of-way.

Pre-2016 Findings

When a transmission right-of-way is initially cleared, a short-term decrease in total vegetative cover occurs. Following tree canopy removal, plants that tolerate high levels of sunlight increase in dominance, and tree seeds present in the soil germinate and grow. Thus, follow-up management is necessary to maintain a low-growing plant community to optimize safe and reliable transmission of electricity.

Data collected from SGL33 and GLR&D sites indicate that herbicide treatments to remove incompatible species (e.g., tall-statured trees) produce a distinct change in the plant community. Post-treatment vegetative cover ranges from grasses, to herbicide-tolerant wildflowers, shrubs and small trees. These new plant communities are relatively stable and have diversity that equals or exceeds non-treated areas.

The data also shows that right-of-way vegetation managers can predict cover types and develop the kind of vegetation desired in a particular situation by prescribing appropriate maintenance. Management units that were treated with herbicides alone or in combination with mowing had fewer incompatible trees per acre within the wire zone compared to units with mowing alone or hand-cutting treatments Table 3. The diverse plant community created within the right-of-way as the result of vegetation management practices Table 1 produces a variety of native species important for wildlife food and cover Table 2 and Table 4.

Key Findings

  1. Plant communities can be changed with the use of an appropriate herbicide and application method. 23618202425262734
  2. Vegetation management practices that include the use of selective herbicides result in diverse vegetation that provides forage and habitat for wildlife on rights-of-way. 2141820
  3. Plant communities can be created that inhibit tree establishment, thereby reducing maintenance costs for utility companies and mitigating the potential for power outage. 5

Gallons of Herbicide Applied

Gallons of herbicide applied/acre (2012) and number of non-compatible trees/acre (less than 1 foot tall) in wire zones of 14 treatment units on the State Game Lands 33 Rights-of-Way Research and Demonstration Area in 2016. Dominant cover type (forb, grass, or shrub) for wire zone is also presented. Borders were all dominated by shrubs.

Gallons of herbicide applied/acre (2012 treatment cycle) Number of stems of non-compatible trees (per acre) in 2016 sampling effort Native species richness of compatible plant species Vegetation management approach* Herbicide [H] versus Mechanical [M] treatment** Herbicide application selective [backpack spray] or nonselective [broadcast spray] Cover type
0 600 7 Mowing M N/A Shrub
0 1100 9 Mowing M N/A Forb
.08 200 8 ULVF H Selective Grass
.08 300 8 ULVF H Selective Forb
.08 200 6 ULVF H Selective Forb
46.7 200 5 HVF H Broadcast Grass
.67 100 7 ULVF H Selective Forb
46.7 100 7 HVF H Broadcast Forb
25.8 200 10 HVF H Selective Shrub
3.42 300 10 LVB H Broadcast Shrub
18 0 19 HVF H Broadcast Forb
3.2 700 15 LVB H Broadcast Forb
0 4700 11 Handcutting M N/A Shrub
0 1400 25 Handcutting M N/A Shrub

*ULVF = Ultra-low volume foliar application. HVF = High volume foliar application. LVB = Low volume basal application.

**Significantly fewer non-compatible trees were present in herbicide versus mechanical-treated units (P = 0.0048, t = 3.07).

Table 2

Examples of vegetation compatible with wildlife within the wire zone and border zone of the electric transmission right of way in State Game Lands 33 Project Area.

TREES AND TALL SHRUBS (border zone) Witchhazel, Hammamelis virginiana; Bear oak, Quercus ilicifolia

LOW-GROWING SHRUBS (both zones) Sweet fern, Comptonia peregrina; Blueberry, Vaccinium spp; Blackberry, Rubus allegheniensis

FORBS AND GRASS (both zones) Rough goldenrod, Solidago rugosa; Narrow-leaf goldenrod, Euthamia graminifolia; Bracken fern, Pteridium aquilinum; Hay-scented fern,Dennstaedtia punctilobula; Whorled loosestrife, Lysimachia quadrifolia; Poverty grass, Danthonia spicata

Table 3

Number of incompatible trees remaining per acre under various integrated vegetation management practices on the State Game Lands 33 Project Area.

Treatment Number of Incompatible Trees
Mowing + Cut Stubble < 100
High-Volumne Foliar < 100
Ultra Low-Volume < 100
Low-Volume Basal Bark 300
Mowing 600
Hand Cutting 1,150

Table 4

Number of plant species present in the wire and border zones with various integrated vegetation management practices on the State Game Lands 33 Project Area.

Treatment Wire Zone Border Zone Both Zones
Mowing + Cut Stubble 39 40 54
High-Volume Foliar 41 40 39
Ultra Low-Volume 33 35 34
Low-Volume Basal Bark 34 28 46
Mowing 31 34 40
Hand Cutting 35 41 47
All Treatment Units Combined 95 110 125


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