**4. Growth of planted seedlings**

Rapid restoration of longleaf pine forest requires that seedlings emerge from the grass stage and sustain a higher rate of height growth than adjacent competing vegetation (Fig. 3).

Fig. 3. Longleaf pine seedlings in grass stage (left) and emerged from grass stage (right). *Photo credit: David Combs, USDA Forest Service Southern Research Station, Athens, GA.*

Vegetative Response to Weed Control in Forest Restoration 371

Fig. 5. Proportion of longleaf pine seedlings emerged from grass stage in each herbicide spot size weed control treatment: herbicide applied once in year 1 (H1) and herbicide applied twice (H2), in small (0.65 m2), medium (2.5 m2), and large (10 m2) spots around each planted seedling. Sample size: n=302 (H1-S: n=49, H1-M: n=47, H1-L: n=49, H2-S: n=53, H2-M: n=52,

The height development of longleaf pine seedlings that had emerged from the grass stage was compared between mechanical and chemical weed control treatments, and between

Height growth of individual seedlings was variable within and between treatments (Fig. 6). Among seedlings that emerged from the grass stage within a year of the first treatments being applied, average height development was most rapid after repeat application of herbicide. Height growth was similar in plots receiving either mechanical treatment or a

Seedlings emerging at different times caused the average height to rise and fall; the average height of seedlings emerging early increased over time, while later emergence introduced new, shorter seedlings to the calculation of average height. This presented challenges for analysis and testing for differences between treatments. Isolating height data for seedlings that emerged between two consecutive re-measurements somewhat mitigated the problem, and allowed us to test for differences in periodic height increment (rate of growth over a specified period) among seedlings that emerged within the same time period. The periodic average height increment between the third and fourth growing seasons was significantly greater after repeat application of herbicide (78 cm/yr; p = 0.03). Periodic height growth was similar in plots receiving either mechanical treatment (64 cm/yr) or a single herbicide

treatment (63 cm/yr), and slowest on average in the un-treated control (48 cm/yr).

single herbicide treatment, and slowest in the un-treated control (Fig. 7).

H2-L: n=52).

**4.2 Planted seedling height growth** 

**4.2.1 Mechanical vs. chemical weed control** 

different herbicide spot sizes.

#### **4.1 Emergence from grass stage**

The number of seedlings emerging from the grass stage was compared between mechanical and chemical weed control treatments, and between different herbicide spot sizes.

#### **4.1.1 Mechanical vs. chemical weed control**

Longleaf pine seedlings treated with herbicide were more likely to emerge from the grass stage sooner than seedlings receiving mechanical weed control or no weed control. Over 60% of seedlings receiving a single herbicide treatment had emerged from the grass stage by the fourth growing season. The repeat application of herbicide in year two resulted in a modest enhancement in emergence with 75% of seedlings emerging by the time of assessment midway through the fourth growing season (Fig. 4). By this time, across the four study sites, the number of emerged seedlings in measurement plots equated to 468, 368, 284, and 236 stems/ha in the H2, H1, M, and C treatments, respectively. The highest frequency of emergence among seedlings occurred sometime between consecutive assessments of the experiment in the months of June in the second growing season and May in the third growing season.

Fig. 4. Proportion of longleaf pine seedlings emerged from grass stage in each weed control treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Sample size: n=627 (H2: n=157, H1: n=145, M: n=159, C: n=166).

#### **4.1.2 Herbicide spot size**

The number of seedlings emerging from the grass stage in the year after the initial herbicide treatment ranged from 11-23% and was not significantly affected by size of herbicide spot. The repeat application of herbicide appeared to promote a modest 'wave' of emergence from the grass stage, but without any apparent relation to herbicide spot size (Fig. 5).

The number of seedlings emerging from the grass stage was compared between mechanical

Longleaf pine seedlings treated with herbicide were more likely to emerge from the grass stage sooner than seedlings receiving mechanical weed control or no weed control. Over 60% of seedlings receiving a single herbicide treatment had emerged from the grass stage by the fourth growing season. The repeat application of herbicide in year two resulted in a modest enhancement in emergence with 75% of seedlings emerging by the time of assessment midway through the fourth growing season (Fig. 4). By this time, across the four study sites, the number of emerged seedlings in measurement plots equated to 468, 368, 284, and 236 stems/ha in the H2, H1, M, and C treatments, respectively. The highest frequency of emergence among seedlings occurred sometime between consecutive assessments of the experiment in the months of June in the second growing season and May in the third

Fig. 4. Proportion of longleaf pine seedlings emerged from grass stage in each weed control treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Sample size: n=627 (H2: n=157, H1: n=145,

The number of seedlings emerging from the grass stage in the year after the initial herbicide treatment ranged from 11-23% and was not significantly affected by size of herbicide spot. The repeat application of herbicide appeared to promote a modest 'wave' of emergence

from the grass stage, but without any apparent relation to herbicide spot size (Fig. 5).

and chemical weed control treatments, and between different herbicide spot sizes.

**4.1 Emergence from grass stage** 

growing season.

M: n=159, C: n=166).

**4.1.2 Herbicide spot size** 

**4.1.1 Mechanical vs. chemical weed control** 

Fig. 5. Proportion of longleaf pine seedlings emerged from grass stage in each herbicide spot size weed control treatment: herbicide applied once in year 1 (H1) and herbicide applied twice (H2), in small (0.65 m2), medium (2.5 m2), and large (10 m2) spots around each planted seedling. Sample size: n=302 (H1-S: n=49, H1-M: n=47, H1-L: n=49, H2-S: n=53, H2-M: n=52, H2-L: n=52).

#### **4.2 Planted seedling height growth**

The height development of longleaf pine seedlings that had emerged from the grass stage was compared between mechanical and chemical weed control treatments, and between different herbicide spot sizes.

#### **4.2.1 Mechanical vs. chemical weed control**

Height growth of individual seedlings was variable within and between treatments (Fig. 6). Among seedlings that emerged from the grass stage within a year of the first treatments being applied, average height development was most rapid after repeat application of herbicide. Height growth was similar in plots receiving either mechanical treatment or a single herbicide treatment, and slowest in the un-treated control (Fig. 7).

Seedlings emerging at different times caused the average height to rise and fall; the average height of seedlings emerging early increased over time, while later emergence introduced new, shorter seedlings to the calculation of average height. This presented challenges for analysis and testing for differences between treatments. Isolating height data for seedlings that emerged between two consecutive re-measurements somewhat mitigated the problem, and allowed us to test for differences in periodic height increment (rate of growth over a specified period) among seedlings that emerged within the same time period. The periodic average height increment between the third and fourth growing seasons was significantly greater after repeat application of herbicide (78 cm/yr; p = 0.03). Periodic height growth was similar in plots receiving either mechanical treatment (64 cm/yr) or a single herbicide treatment (63 cm/yr), and slowest on average in the un-treated control (48 cm/yr).

Vegetative Response to Weed Control in Forest Restoration 373

Average height development of longleaf pine seedlings that emerged within the year following application of herbicide treatments in year one was enhanced by the repeat application of herbicide. Among spot sizes tested, average height was greatest within large spots and lowest in medium-sized spots (Fig. 8). Part of these differences between treatments was likely caused by a random variable that we were not able to control for: variations in timing of emergence from the grass stage and initiation of height growth. This problem was mitigated by examining the rate of longleaf pine seedling height growth between the third and fourth growing seasons. This 'periodic' height increment was greater on average among seedlings receiving a repeat application of herbicide (Fig. 9). However, differences in height growth between the repeat herbicide applications in small, medium, and large spots were not significant (p = 0.43). These repeat treatments resulted in significantly greater seedling height growth than among seedlings treated once with the smallest size of herbicide spot (p = 0.03). The statistical significance of differences between spot size treatments was likely understated because: (i) our sample sizes decreased when we restricted the analysis to seedlings emerging within one year of the first herbicide, and (ii) due to variability in periodic height growth data among young longleaf pines in each

Fig. 8. Average height of longleaf pine seedlings receiving herbicide weed control treatment once (H1) and twice (H2) in small (0.65 m2), medium (2.5 m2), and large (10 m2) spots around each planted seedling. Height data represent average height of seedlings that emerged from grass stage within one year of the first herbicide application. Sample size:

n=51 (H1-S: n=7, H1-M: n=4, H1-L: n=8, H2-S: n=11, H2-M: n=10, H2-L: n=11).

**4.2.2 Herbicide spot size and height growth** 

treatment.

Fig. 6. Height development of individual longleaf pine seedlings that had emerged from grass stage between the time of planting and the middle of the second growing season in each weed control treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Sample size: n=83 (H2: n=37, H1: n=24, M: n=11, C: n=11).

Fig. 7. Average height of longleaf pine seedlings that had emerged from grass stage between the time of planting and the middle of the second growing season in each weed control treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Sample size: n=83 (H2: n=37, H1: n=24, M: n=11, C: n=11).

#### **4.2.2 Herbicide spot size and height growth**

372 Herbicides – Properties, Synthesis and Control of Weeds

Fig. 6. Height development of individual longleaf pine seedlings that had emerged from grass stage between the time of planting and the middle of the second growing season in each weed control treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Sample size: n=83 (H2:

Fig. 7. Average height of longleaf pine seedlings that had emerged from grass stage between the time of planting and the middle of the second growing season in each weed control treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Sample size: n=83 (H2: n=37, H1: n=24, M:

n=37, H1: n=24, M: n=11, C: n=11).

n=11, C: n=11).

Average height development of longleaf pine seedlings that emerged within the year following application of herbicide treatments in year one was enhanced by the repeat application of herbicide. Among spot sizes tested, average height was greatest within large spots and lowest in medium-sized spots (Fig. 8). Part of these differences between treatments was likely caused by a random variable that we were not able to control for: variations in timing of emergence from the grass stage and initiation of height growth. This problem was mitigated by examining the rate of longleaf pine seedling height growth between the third and fourth growing seasons. This 'periodic' height increment was greater on average among seedlings receiving a repeat application of herbicide (Fig. 9). However, differences in height growth between the repeat herbicide applications in small, medium, and large spots were not significant (p = 0.43). These repeat treatments resulted in significantly greater seedling height growth than among seedlings treated once with the smallest size of herbicide spot (p = 0.03). The statistical significance of differences between spot size treatments was likely understated because: (i) our sample sizes decreased when we restricted the analysis to seedlings emerging within one year of the first herbicide, and (ii) due to variability in periodic height growth data among young longleaf pines in each treatment.

Fig. 8. Average height of longleaf pine seedlings receiving herbicide weed control treatment once (H1) and twice (H2) in small (0.65 m2), medium (2.5 m2), and large (10 m2) spots around each planted seedling. Height data represent average height of seedlings that emerged from grass stage within one year of the first herbicide application. Sample size: n=51 (H1-S: n=7, H1-M: n=4, H1-L: n=8, H2-S: n=11, H2-M: n=10, H2-L: n=11).

Vegetative Response to Weed Control in Forest Restoration 375

Fig. 10. Weed coverage of ground around planted longleaf pine seedlings. Cover percent is the average cover of each type of competing vegetation in each treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and notreatment control (C). Sample size: n=627 (H2: n=157, H1: n=145, M: n=159, C: n=166).

Calculating the average of height data for the tallest competing vegetation adjacent to each longleaf pine seedling gave an approximation of the 'top height' or 'dominant height' of the vegetation canopy. The dominant height and percent cover of competing vegetation recovered from each treatment at similar rates, with one exception: mechanical treatment appeared to stimulate height growth of competing vegetation (Fig. 11). Calculating dominant height for different components of the competing vegetation gave separate estimates for woody vegetation and for herbaceous vegetation (grasses and forbs). The height of woody vegetation increased steadily, whereas the height of herbaceous vegetation appeared to attain its maximum within two years of treatment. The time taken for vegetation cover or height to return to pre-treatment levels – referred to as 'treatment persistence' – was shorter (rapid recovery; low treatment persistence) for herbaceous vegetation height than for woody vegetation height or total vegetation cover. The repeat application of herbicide doubled herbicide treatment persistence in terms of vegetation cover, and checked hardwood height development by approximately three years (Fig. 11).

**5.2 Weed height development** 

Fig. 9. Relationship between herbicide spot size, number of herbicide applications, and height growth of longleaf pine seedlings emerging from grass stage within one year of the first herbicide application. Height growth calculated as the periodic height increment between the third and fourth growing seasons. Sample size: n=51 (H1-S: n=7, H1-M: n=4, H1-L: n=8, H2-S: n=11, H2-M: n=10, H2-L: n=11).

#### **5. Control of competing vegetation**

The extent of competing vegetation cover and its composition were monitored over consecutive growing seasons. Assessment of 1m2 quadrats centred on each longleaf pine seedling gave estimates of the percent cover and type of vegetation adjacent to, and presumably competing with, the planted seedlings.

#### **5.1 Weed coverage and composition**

Competing vegetation developed quickly in the first growing season. Approximately half of the bare ground around planted seedlings was covered by grasses and forbs, vines, and woody vegetation by the time of the first treatments, three months after planting longleaf pine. The herbicide treatment removed competing vegetation cover in the vicinity of planted seedlings, but only temporarily. Competing vegetation re-occupied herbicide-treated spots at a slower rate than before treatment. Total vegetation cover at the end of the first growing season was only 20% after herbicide treatment, whereas it had attained over 60% cover in the absence of any treatment and following mechanical treatment. In the second growing season, competing vegetation expanded to cover approximately 90% of ground area surrounding planted seedlings in the no-treatment control area and after mechanical treatment. It only covered approximately 50% of ground area in plots receiving a single herbicide treatment by the end of year two, and approximately 25% of ground area in plots receiving a repeat herbicide application in the second growing season. Grasses increased in relative abundance following mechanical treatment. Vine cover increased at the same rate in the control and mechanical treatment areas. Woody vegetation increased in relative abundance, at the expense of grass cover, in the no-treatment control areas. Herbicide treatments had a lasting impact on the development of woody vegetation cover, especially after herbicide was re-applied in the second growing season (Fig. 10).

Fig. 9. Relationship between herbicide spot size, number of herbicide applications, and height growth of longleaf pine seedlings emerging from grass stage within one year of the first herbicide application. Height growth calculated as the periodic height increment between the third and fourth growing seasons. Sample size: n=51 (H1-S: n=7, H1-M: n=4,

The extent of competing vegetation cover and its composition were monitored over consecutive growing seasons. Assessment of 1m2 quadrats centred on each longleaf pine seedling gave estimates of the percent cover and type of vegetation adjacent to, and

Competing vegetation developed quickly in the first growing season. Approximately half of the bare ground around planted seedlings was covered by grasses and forbs, vines, and woody vegetation by the time of the first treatments, three months after planting longleaf pine. The herbicide treatment removed competing vegetation cover in the vicinity of planted seedlings, but only temporarily. Competing vegetation re-occupied herbicide-treated spots at a slower rate than before treatment. Total vegetation cover at the end of the first growing season was only 20% after herbicide treatment, whereas it had attained over 60% cover in the absence of any treatment and following mechanical treatment. In the second growing season, competing vegetation expanded to cover approximately 90% of ground area surrounding planted seedlings in the no-treatment control area and after mechanical treatment. It only covered approximately 50% of ground area in plots receiving a single herbicide treatment by the end of year two, and approximately 25% of ground area in plots receiving a repeat herbicide application in the second growing season. Grasses increased in relative abundance following mechanical treatment. Vine cover increased at the same rate in the control and mechanical treatment areas. Woody vegetation increased in relative abundance, at the expense of grass cover, in the no-treatment control areas. Herbicide treatments had a lasting impact on the development of woody vegetation cover, especially

H1-L: n=8, H2-S: n=11, H2-M: n=10, H2-L: n=11).

presumably competing with, the planted seedlings.

after herbicide was re-applied in the second growing season (Fig. 10).

**5. Control of competing vegetation** 

**5.1 Weed coverage and composition** 

Fig. 10. Weed coverage of ground around planted longleaf pine seedlings. Cover percent is the average cover of each type of competing vegetation in each treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and notreatment control (C). Sample size: n=627 (H2: n=157, H1: n=145, M: n=159, C: n=166).

#### **5.2 Weed height development**

Calculating the average of height data for the tallest competing vegetation adjacent to each longleaf pine seedling gave an approximation of the 'top height' or 'dominant height' of the vegetation canopy. The dominant height and percent cover of competing vegetation recovered from each treatment at similar rates, with one exception: mechanical treatment appeared to stimulate height growth of competing vegetation (Fig. 11). Calculating dominant height for different components of the competing vegetation gave separate estimates for woody vegetation and for herbaceous vegetation (grasses and forbs). The height of woody vegetation increased steadily, whereas the height of herbaceous vegetation appeared to attain its maximum within two years of treatment. The time taken for vegetation cover or height to return to pre-treatment levels – referred to as 'treatment persistence' – was shorter (rapid recovery; low treatment persistence) for herbaceous vegetation height than for woody vegetation height or total vegetation cover. The repeat application of herbicide doubled herbicide treatment persistence in terms of vegetation cover, and checked hardwood height development by approximately three years (Fig. 11).

Vegetative Response to Weed Control in Forest Restoration 377

Fig. 12. Height development of the tallest 200 stems/ha longleaf pine seedlings and competing woody vegetation in each treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Height of competing vegetation represented by average height of the tallest woody vegetation in 1 m2 quadrat centred on each longleaf pine seedling. Sample size: n=200 longleaf pine seedlings (n=50 per treatment, representing 200 stems/ha), and n=454 quadrats containing woody vegetation (H2: n=113, H1: n=105, M: n=120, C: n=116).

Mechanical control of competing vegetation provided an early enhancement in survival and emergence of longleaf pine seedlings planted in beetle-killed areas, but the beneficial effects were short lived. Herbaceous vegetation exhibited the most aggressive early response to mechanical treatment. The mechanical treatment also appeared to stimulate height development of woody vegetation, resulting in low treatment persistence. Our data suggest that mechanical treatments may need to be repeated regularly if sufficient numbers of longleaf pine are to overtop the competing vegetation. Repeat application of herbicide provided lasting control of competing vegetation, enhanced survival and emergence from the grass stage, and promoted rapid height growth of longleaf pine seedlings planted on the

Seedlings emerging from the grass stage began their height growth at different times, providing challenges for summary and analysis of treatment effects on height growth. The

**7. Conclusion** 

four sites in the central Georgia Piedmont region.

Fig. 11. Development of competing vegetation cover and height in each treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Height of competing vegetation represented by average height of the tallest individual competitor (herbaceous or woody vegetation) in 1 m2 quadrat centred on each longleaf pine seedling. Sample size: n=627 (H2: n=157, H1: n=145, M: n=159, C: n=166).

#### **6. Comparing growth of crop trees and woody competitors**

The most vigorous individuals in any cohort of planted trees are of notable importance in forest restoration. The expectation is that these trees will dominate and form the main forest canopy. Woody vegetation could represent an ongoing threat to successful restoration of longleaf pine because, unlike herbaceous vegetation, it can sustain height growth and compete with the longleaf pines for light and growing space over the longer term. Longleaf pines that outsize their competitors by several meters should be able to maintain long live crowns, remain vigorous, and retain dominance over competing vegetation. We compared height growth of the tallest longleaf pine seedlings, in terms of average height of the tallest 200 stems/ha, with height growth of their major competitor: naturally-regenerating woody vegetation. The repeat application of herbicide in year two was the only treatment that allowed longleaf pine seedlings to gain a substantial height advantage over adjacent woody vegetation by the fourth growing season. The average height of the tallest 200 stems/ha of longleaf pine in the H2 treatment was 115 cm greater than the average height of competing woody vegetation. By the fourth growing season, the tallest 200 longleaf pine seedlings/ha in no-treatment control plots were an average of 45 cm shorter than the average height of competing woody vegetation in the absence of mechanical or herbicide treatment (Fig. 12).

Fig. 11. Development of competing vegetation cover and height in each treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Height of competing vegetation represented by average height of the tallest individual competitor (herbaceous or woody vegetation) in 1 m2 quadrat centred on each longleaf pine seedling. Sample size: n=627 (H2: n=157, H1: n=145, M: n=159, C: n=166).

The most vigorous individuals in any cohort of planted trees are of notable importance in forest restoration. The expectation is that these trees will dominate and form the main forest canopy. Woody vegetation could represent an ongoing threat to successful restoration of longleaf pine because, unlike herbaceous vegetation, it can sustain height growth and compete with the longleaf pines for light and growing space over the longer term. Longleaf pines that outsize their competitors by several meters should be able to maintain long live crowns, remain vigorous, and retain dominance over competing vegetation. We compared height growth of the tallest longleaf pine seedlings, in terms of average height of the tallest 200 stems/ha, with height growth of their major competitor: naturally-regenerating woody vegetation. The repeat application of herbicide in year two was the only treatment that allowed longleaf pine seedlings to gain a substantial height advantage over adjacent woody vegetation by the fourth growing season. The average height of the tallest 200 stems/ha of longleaf pine in the H2 treatment was 115 cm greater than the average height of competing woody vegetation. By the fourth growing season, the tallest 200 longleaf pine seedlings/ha in no-treatment control plots were an average of 45 cm shorter than the average height of competing woody vegetation in the absence of mechanical or herbicide treatment (Fig. 12).

**6. Comparing growth of crop trees and woody competitors** 

Fig. 12. Height development of the tallest 200 stems/ha longleaf pine seedlings and competing woody vegetation in each treatment: herbicide applied once in year 1 (H1), herbicide applied twice (H2), mechanical weed control (M), and no-treatment control (C). Height of competing vegetation represented by average height of the tallest woody vegetation in 1 m2 quadrat centred on each longleaf pine seedling. Sample size: n=200 longleaf pine seedlings (n=50 per treatment, representing 200 stems/ha), and n=454 quadrats containing woody vegetation (H2: n=113, H1: n=105, M: n=120, C: n=116).

#### **7. Conclusion**

Mechanical control of competing vegetation provided an early enhancement in survival and emergence of longleaf pine seedlings planted in beetle-killed areas, but the beneficial effects were short lived. Herbaceous vegetation exhibited the most aggressive early response to mechanical treatment. The mechanical treatment also appeared to stimulate height development of woody vegetation, resulting in low treatment persistence. Our data suggest that mechanical treatments may need to be repeated regularly if sufficient numbers of longleaf pine are to overtop the competing vegetation. Repeat application of herbicide provided lasting control of competing vegetation, enhanced survival and emergence from the grass stage, and promoted rapid height growth of longleaf pine seedlings planted on the four sites in the central Georgia Piedmont region.

Seedlings emerging from the grass stage began their height growth at different times, providing challenges for summary and analysis of treatment effects on height growth. The

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problem was not completely mitigated by examining a subset of data for seedlings that emerged during a single time period between consecutive re-measurements of the experiment; sample size was reduced and differences in timing of emergence still introduced variability in height growth estimates. More frequent re-measurements should overcome this problem by allowing for the study of subsets of seedlings emerging from the grass stage at similar times.

We found no evidence that treating larger areas around planted seedlings with herbicide would promote earlier emergence from the grass stage. Once emerged, the seedlings grew marginally more rapidly, on average, in larger spots. Height growth was significantly more rapid following the repeat application of herbicide in the second growing season than among seedlings receiving only one herbicide treatment in the smallest spot size. Therefore if only one treatment will be applied in future restoration projects, we recommend a larger size of herbicide spot treatment. However, total chemical usage is lower when implementing smaller spots, and more vegetation cover is maintained between the smaller spots. If repeat herbicide treatments are planned, then our results suggest that smaller spot sizes applied twice will provide adequate enhancement of survival, emergence, and growth among planted longleaf pine seedlings.

#### **8. Acknowledgement**

We are indebted to the late John Moore – manager of the Hitchiti Experimental Forest - for valuable advice and support for our research project, and for preparing the beetle-killed sites and planting longleaf pine seedlings. We gratefully acknowledge the support of the USDA Forest Service Southern Research Station at Athens, Georgia, and appreciate being involved in this collaboration between the Georgia Forestry Commission, Mac Callaham and his team at the Center for Forest Disturbance Science at the Southern Research Station, and Humboldt State University. David Combs of the Southern Research Station provided technical support and has spent considerable time in the field since the project was initiated in 2008. Rex Dagley has tirelessly volunteered field assistance since 2008. We also thank the Humboldt State University Sponsored Programs Foundation for supporting dissemination of original research results by covering page charges for this open-access publication.

#### **9. References**


problem was not completely mitigated by examining a subset of data for seedlings that emerged during a single time period between consecutive re-measurements of the experiment; sample size was reduced and differences in timing of emergence still introduced variability in height growth estimates. More frequent re-measurements should overcome this problem by allowing for the study of subsets of seedlings emerging from the

We found no evidence that treating larger areas around planted seedlings with herbicide would promote earlier emergence from the grass stage. Once emerged, the seedlings grew marginally more rapidly, on average, in larger spots. Height growth was significantly more rapid following the repeat application of herbicide in the second growing season than among seedlings receiving only one herbicide treatment in the smallest spot size. Therefore if only one treatment will be applied in future restoration projects, we recommend a larger size of herbicide spot treatment. However, total chemical usage is lower when implementing smaller spots, and more vegetation cover is maintained between the smaller spots. If repeat herbicide treatments are planned, then our results suggest that smaller spot sizes applied twice will provide adequate enhancement of survival, emergence, and growth

We are indebted to the late John Moore – manager of the Hitchiti Experimental Forest - for valuable advice and support for our research project, and for preparing the beetle-killed sites and planting longleaf pine seedlings. We gratefully acknowledge the support of the USDA Forest Service Southern Research Station at Athens, Georgia, and appreciate being involved in this collaboration between the Georgia Forestry Commission, Mac Callaham and his team at the Center for Forest Disturbance Science at the Southern Research Station, and Humboldt State University. David Combs of the Southern Research Station provided technical support and has spent considerable time in the field since the project was initiated in 2008. Rex Dagley has tirelessly volunteered field assistance since 2008. We also thank the Humboldt State University Sponsored Programs Foundation for supporting dissemination

of original research results by covering page charges for this open-access publication.

Amishev, D. Y. & Fox, T. R. (2006). The effect of weed control and fertilization on survival

Anon. (2000). *Piedmont*. The Columbia Gazetteer of North America. University of Columbia

Berrill, J-P.; Dagley, C.M. (2010). Assessing longleaf pine (*Pinus palustris*) restoration after

Boyer, W. D. (1990). Longleaf pine *Pinus palustris* Mill. In R. M. Burns, & B. H. Honkala

and growth of four pine species in the Virginia Piedmont. *Forest Ecology and* 

southern pine beetle kill using a compact experimental design. *Scandinavian Journal* 

(Eds.), *Silvics of North America*. *Agriculture Handbook 654, Vol. 1: Conifers* (pp. 405-

grass stage at similar times.

among planted longleaf pine seedlings.

*Management* 236: 93-101.

*of Forest Research* 25(8): 75-85.

412). USDA Forest Service. Washington, D.C.

Press. New York, NY.

**8. Acknowledgement** 

**9. References** 


**21** 

*Morocco* 

**Sugar Beet Weeds in Tadla Region (Morocco):** 

Sugar beet occupies each year about 65.000 hectares in Morocco which allows a production that approaches or exceeds three million tons of roots, with an average yield of 46 tonnes per ha (54% of national needs sugar consumption). Since its introduction in Morocco in 1962-1963, sugar beet yield increased significantly in quantity and quality. In Morocco, the sugar beet is a very important crop because of its products and by-products,


In Morocco, sugar beet is planted from September through June - July. Yield obtained by farmers, averaging 46T/ha, is significantly below the request potential that would be 90 to 100 T/ha. Many factors contribute to low sugar beet production. Poor stand establishment, inadequate weed control, inadequate insect control and inadequate nitrogen fertilization are

The sugar beet is an important strategic crop in the irrigated perimeter of Tadla. During these 5 last years, an annual surface of 12000 ha is emblaved by this crop representing 23% / of the national area. The average yield obtained in the region is approximately 45 to 50

Sanitary problems particularly weed management is a great constraint to sugar beet production and weeds may cause high yield losses (Rzozi et al., 1990). This paper presents the main results of investigations and experiments conducted in Tadla region to improve the weed management program by identifying mains weed species encountered in sugar beet field, studying the effect of weeds on sugar beet growth and estimating yield losses and

determining the critical period of weed control and evaluating herbicide treatments.


T/ha, which is very low compared to the potential yield.

the main causes of low tonnage and poor quality sugar beet in Morocco.

**1. Introduction** 

mainly:

made.

**Species Encountered, Interference** 

*1Centre Régional de la Recherche Agronomique de Tadla, Beni Mellal,* 

**and Chemical Control** 

Y. Baye1, A. Taleb2 and M. Bouhache3

*2,3Institut Agronomique et Vétérinaire Hassan ll, Rabat,* 

