Selective control of weeds in an arable crop by mulches from some multipurpose trees in Southwestern Nigeria

The use of agroforestry systems in which pruning from trees is used to mulch the companion crops is an important area of research in the tropics. However, previous studies mostly evaluated the contribution of mulch to soil improvement and rarely examined the effect of mulch on weeds. Field experiments were conducted during the 1995 and 1996 growing seasons to investigate the effects of mulch from three woody fallow species on weed composition, biomass and maize grain yield. Treatments consisted of mulch from Leucaena leucocephala, Gliricidia sepium, and Senna siamea applied at rates of five and three tons dry matter ha^–1 at planting and three weeks after planting (WAP), respectively, an unmulched treatment that received 90 kg N ha^–1 of inorganic fertiliser, and an unmulched control plot that received no fertiliser. In both years and sampling dates, plots mulched with G. sepium and S. siamea had significantly lower weed density and biomass than the control plot in each of the sampling times and year of study. There was no significant difference in either weed density or biomass between the plot mulched with L. leucocephala and the unmulched plots. Mulches from G. sepium and S. siamea reduced weed density and weed biomass, while L. leucocephala was less effective in reducing weed biomass and weed density. Weed reduction by the mulches was in the order G. sepium S. siamea > L. leucocephala. Sedges were the dominant species in all the treatments except in G. sepium plots, where Talinum triangulare and other broadleaved species were dominant.This revised version was published online in November 2005 with corrections to the Cover Date.     

Role of weeds in the management of nitrogen in a young Pinus radiata plantation

Pinus radiata trees were grown on a podzolized sandy soil at a second rotation site under the following treatments: total weed control, total weed control plus ammonium nitrate, strip weed control and no weed control. During the first two summers after planting the differences in needle water potential between trees under no, strip or total weed control were very small. Despite similar rates of net N-mineralization in strip and total weed control treatments, which averaged 64 kg ha^–1 yr^–1 in the 0–15 cm soil depth, weeds in the strip weed control treatment reduced soil mineral-N concentrations by 50–80%, leaching of N by the end of the first growing season by 45%, foliar-N concentrations by 4–14% and stem biomass at 20 months after planting by 46%. Although N-uptake by above-ground vegetation (trees plus weeds) was 49% higher in the strip weed control treatment, the amount of N apportioned to trees during the first 20 months after planting was reduced from 15.5 to 9.0 kg ha^–1. These effects of weeds were even more pronounced in the no weed control treatment. Since weeds had little effect on the needle water potential of trees and the annual rates of N-mineralization, but adversely affected N-uptake by trees, results indicate that weeds directly competed with trees for N, and thereby aggravated N-deficiency in trees. Application of ammonium nitrate after complete weed control increased foliar-N concentrations, and N-uptake and growth of trees, but also induced severe stem deformation.     

The effects of sulfometuron on the root growth of loblolly pine

The effect of sulfometuron (Oust) on the root growth of loblolly pine (Pinus taeda L.) seedlings was studied in the field and in two soil types in the greenhouse. In the greenhouse study sulfometuron was applied to the foliage only, the soil only, and to both foliage and soil at the rates of 0.10, 0.21, and 0.42 kg ai/ha. Twenty-eight days after application root growth significantly decreased for all methods of application and with increasing rates e.g., 0.10, 0.21, and 0.42 kg ai/ha sulfometuron reduced new root length by 42%, 53%, and 64%, respectively. Application in the field at the rate of 0.30 kg ai/ha resulted in a 68% reduction in root growth. However, by the end of the growing season treated seedling root and shoot biomass were 115% and 64% greater, respectively. To ensure earlier season survival the rate of sulfometuron applied should be kept at a minimum level that will allow both weed control and adequate root growth. Low rates would be particularly important during a dry planting season.     

Fertilization,weed control,and pine litter influence loblolly pine stem productivity and root development

Following site preparation, three cultural treatments and three open-pollinated loblolly pine (Pinus taeda L.) families were studied on a gently sloping Beauregard silt loam in central Louisiana. The treatments were: (1) fertilization (either broadcast application of 177 kg N and 151 kg P/ha or none); (2) herbicide application (either broadcast application of herbicides during the first through third growing seasons, and felling of a few, scattered volunteer hardwood trees greater than 2.5 cm dbh during the third growing season or none); and (3) litter application (either broadcast application of 37 Mg/ha (oven-dried weight) of pine straw over the plots to form a 10 to 15 cm layer or none). The subplot treatment was planting stock, where in November 1988, 28-week-old container-grown loblolly pine seedlings from three open-pollinated families were randomly assigned to planting locations. Through five growing seasons, fertilization and weed control with herbicides resulted in the greatest loblolly pine productivity, but the use of herbicides severely reduced other vegetation. Applying litter, which was less effective than herbicides as a weed control treatment, increased the presence of blackberry (Rubus spp.) when herbicides were not applied. Applying litter resulted in a decrease and fertilization resulted in an increase in the number and length of live lateral roots. Soil temperature was reduced by litter application. Treatment responses were not influenced by loblolly pine family.     

Growth responses of six seed sources of Pinus brutia Ten. (Turkish red pine) to herbaceous weed competition

Herbaceous weeds present amajor obstacle to foresters in the earlyestablishment and growth of Turkish red pine (Pinus brutia Ten.), an important coniferof the semi-arid Mediterranean region. Greatgenetic variability of this pine species indrought resistance has already beenwell-studied. The existence of such variationwithin this species in relation to herbaceousweed competition is unknown. This studyinvestigated the effect of herbaceous weedcompetition on the growth of the seedlings ofTurkish red pine seed sources with differentmoisture regimes in their native sites, usingthe rapid screening technique. Two-month-oldTurkish red pine seedlings were grown inindividual pots in a glasshouse either with orwithout joint goose goat grass (Aegilopscylindrica L.). After two simulatedgrowing seasons, grass competitionsignificantly and progressively reduced pinegrowth. Although mean total pine biomass wasreduced by 71% due to weed competition,seedlings of different pine seed sourcesdisplayed significant differences in growthresponses to the weed treatments: dry site seedsource seedlings generally exhibitedsignificantly greater growth than moist siteseed source seedlings under weed competition. These results suggest that competition fromherbaceous weeds is an important factor inreducing the early growth of Turkish red pineseedlings, and that selection ofcompetition-tolerant seed sources can result insubstantial enhancement of the competitivestatus of this pine species against itsherbaceous competitors in early years.     

The effects of herbaceous and woody competition on planted white pine in a clearcut site

We investigated the effects of herbaceous and woody vegetation control on the survival and growth of planted eastern white pine (Pinus strobus L.) seedlings through six growing seasons. Herbaceous vegetation control involved the suppression of grasses, forbs, ferns, and low-shrubs, and was maintained for 0, 2, or 4 years after white pine seedlings were planted. Woody control involved the removal of all tall-shrub and deciduous trees, and was conducted at the time of planting, at the end of the second or fifth growing seasons, or not at all. Seedling height and basal diameter responded positively and proportionally to duration of herbaceous vegetation control. Gains associated with woody control were generally not significant unless some degree of herbaceous vegetation control was also conducted. Only herbaceous control increased pine crown closure and rate of crown closure. Herbaceous control and the presence of 5000–15,000 stems per ha of young overtopping aspen were associated with reduced weevil (Pissodes strobi Peck.) injury and increased pine height growth. The study suggests that white pine restoration strategies on clearcut sites should focus on the proactive, early management of understory vegetation and the gradual reduction of overtopping cover from woody vegetation to create a seedling light environment that supports acceptable growth with minimal weevil damage.     

Seasonal effects of prescribed burning and roller chopping on saw palmetto in flatwoods

Shrub encroachment has become a problem in many rangeland systems across the United States due to a reduction in the disturbances, primarily fire, which historically maintained them. The shrub saw palmetto (Serenoa repens) has become abundant in many habitats of the southeastern Coastal Plain, including Florida. When fire regimes are altered or fires are suppressed, this species can proliferate leading to significant changes in the ecosystem, particularly the herbaceous vegetation. Prescribed burning and roller chopping are management activities often used to control saw palmetto. However, little is known about the effects these treatments have on this shrub, particularly when applied in different seasons. We compared the seasonal effects of prescribed burning, roller chopping, and combinations of the two on saw palmetto. The effects of treatments on saw palmetto were assessed using a paired-sample approach, where saw palmetto height, cover, and density were compared between sampling locations randomly located within treated (e.g., burned) and untreated areas. Dormant season burning had no effect on saw palmetto density and height and only temporarily reduced cover, with rapid regrowth occurring the first year post-treatment. Growing season burning also had no effect on saw palmetto density. However, saw palmetto cover was lower on growing season burn compared to control sites the first year post-treatment and height the first and second year post-treatment. The combination of burning and roller chopping, despite having no effect on saw palmetto density, did result in lower saw palmetto height compared to controls the first and second year post-treatment. The effect of roller chopping/burning on saw palmetto cover depended on season and year. Saw palmetto cover and height were lower on dormant and growing season roller chop than control sites the first and second year post-treatment, but only growing season roller chopping had an effect on saw palmetto density. The single application of a dormant or growing season burn is not recommended for control of high-density saw palmetto, however, it may be suitable to maintain areas where saw palmetto levels are low and proliferation of the species is not a threat. Dormant and growing season roller chopping showed the greatest potential for rapid saw palmetto control. Growing season roller chopping is recommended if significant reductions in saw palmetto density are desired.     

Forage production and small ruminant grazing responses in Mediterranean shrublands as influenced by the reduction of shrub cover

Reduction of shrub cover in Mediterranean shrublands is considered as a method of optimising forage and animal production. In this study, forage production in grazed and protected plots and grazing responses of small ruminants in cleared (25% shrub cover), slashed (34% shrub cover) and not treated (control, 55% shrub cover) kermes oak (Quercus coccifera L.) shrublands were compared during the spring seasons of 1992, 1993 and 1994. The alterations in shrub density were done in October 1991 and pastures remained ungrazed until spring of 1992. Clearing and slashing of shrub vegetation resulted in higher amounts of available herbaceous forage and useable browse. At the end of the growing season, averaged across years, herbaceous biomass was generally two to three times higher in the treated shrublands than in the control; also, browse biomass was slightly less (1,078 vs 1,533 kg/ha) but easily accessible because of the open structure and the lower height of the sprouting shrubs. There were generally no grazing response differences between the cleared and slashed pastures. However, grazing animals (sheep and goats) had a higher bite rate (bites/min; P 0.05) in the treated pastures than in the control. Levels of crude protein in the forage selected by animals were higher (P 0.05) in the treated pastures than in the control. Animals in the improved pastures maintained diets that were significantly more digestible (53.5%) than those in the control pasture (48.5%). Neutral detergent fibre and lignin contents of animal diets were similar in the improved pastures but lower (P 0.05) than those of the control. It is concluded that removing of woody vegetation in Mediterranean shrublands results in increased forage production (available herbage and useable browse) and improved forage quality and availability for small ruminants.     

Plant community responses to a gradient of site preparation intensities in pine plantations in the Coastal Plain of North Carolina

Intensively managed loblolly pine (Pinus taeda) forests are common in the southeastern United States and offer opportunities for conservation of biologic diversity. Within intensively managed landscapes, stand establishment relies on combinations of mechanical and chemical site preparation and herbaceous weed control (HWC) to manage competing vegetation and increase pine production. However, few long-term studies have described relationships between intensity of stand establishment and effects on plant communities. Therefore, we examined effects of 6 treatments that varied in intensity via combinations of mechanical (wide spacing and strip shear or narrow spacing and roller chop) and chemical (application or no application) site preparation treatments with HWC (broadcast or banded) from 1 to 8 years after site preparation on plant communities in loblolly pine plantations (n = 6) in the Coastal Plain of North Carolina, USA. All treatments resulted in abundant and diverse plant communities. Chemical site preparation had short lived (?4 year) effects on the herbaceous community but long-term effects on woody plants and pine cover. Increasing management intensity by including broadcast HWC or roller chop/narrow spacing did not additively reduce woody vegetation cover or species richness. However, broadcast HWC reduced grass, vine, and forb cover in the first year post-treatment. Average Morista community similarity values ranged from 0.69 to 0.89 among treatments and plots receiving the same chemical site preparation contained the most similar plant communities. Banded HWC can be paired with wide spacing to maximize herbaceous plant growth important for many wildlife species, particularly in the first few years after site preparation. Site preparation techniques should be tailored to local site conditions, plant communities, and management objectives.     

Weed biomass dynamics in planted fallow systems in the humid forest zone of southern Cameroon

Interest in planted fallow systems has focused on soil fertility improvement, neglecting other potential benefits of such systems. It is important to quantify other processes responsible for crop yield increases under planted fallows, such as weed control. The suppressive potential on weeds of Flemingia macrophylla [(Willd.) Merrill] and Pueraria phaseoloides (Roxb.) Benth, planted fallows was evaluated in field trials in three villages in southern Cameroon. In each village, experiments were set up in 4–5 year-old bush fallow dominated by Chromolaena odorata (L.) R. M. King & H. Rob. and 20 year-old secondary forest. Total aboveground biomass production of P. phaseoloides was 7.45 Mg ha⁻¹, 4.2 times higher than F. macrophylla (1.78 Mg ha⁻¹ ; P < 0.05). The high biomass of P. phaseoloides resulted in a significantly greater reduction in total weed biomass compared to Flemingia macrophylla in both wet and dry seasons. In the wet season (11 and 18 MAP), there were significant fallow system × land use and fallow system × village interactions for total weeds and broadleaf weeds. P. phaseoloides in bush (0.55 Mg ha⁻¹), and P. phaseoloides at Ngoumou (0.09 Mg ha⁻¹) had the lowest total weeds in the wet seasons. After the dry season, the lowest total weed mass was consistently recorded in P. phaseoloides while the highest was in the natural regrowth. The population of grasses was always higher in the F. macrophylla system than in P. phaseoloides system throughout the wet and dry seasons. Grass biomass in the P. phaseoloides-forest LUS was the least (0.01 Mg ha⁻¹), 58 times lower than in F. macrophylla-bush (0.58 Mg ha⁻¹). Biomass production of P. phaseoloides was highly significantly correlated with total weed biomass (r = −0.64; P = 0.004) while no relationship was found between biomass production of F. macrophylla and total weed biomass (r = −0.08, P = 0.747). It was concluded that P. phaseoloides was a suitable leguminous species for weed control. But for F. macrophylla, its low biomass production coupled with a compact plant architecture compromised it as an appropriate species for weed control in a planted fallow system.     

Soil nitrogen mineralization at various levels of canopy cover in red pine (Pinus resinosa) plantations

The objective of this study was to determine the rate of nitrogen (N) mineralization in response to various levels of canopy cover in red pine (Pinus resinosa Ait.) stands. Experimental plots consisted of various levels of canopy cover,i.e., clearcut, 25% (50% during first sampling year), 75%, and uncut in red pine plantations in northern Lower Michigan, USA. Net N mineralization and nitrification in the top 15 cm of mineral soil were examined during the first two growing seasons (1991–1992) following the canopy cover manipulations, using anin situ buried bag technique. Mean net N mineralization over the course of both growing seasons (May–October) ranged from 26.9 kg ha⁻¹ per growing season in the clearcut treatment to 13.4 kg ha⁻¹ per growing season in the uncut stand. Net N mineralization and nitrification increased significantly in the clearcut treatment compared to the uncut treatment during the second growing season only. However, net N mineralization and nitrification did not differ significantly between the partial canopy cover treatments and the uncut stand. Increased N mineralization and nitrification in the clearcut during the second growing season may be associated with increased soil temperature and changes of organic matter quality with time since canopy removal. This study was supported in part by the USDA Forest Service and Michigan Technological University.     

Pine growth response to management of the subterranean clover understory

Management of subterranean clover (Trifolium subterraneum L.) understory grown with loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) resulted in differences in both clover yield and pine diameter. Loblolly and slash pines were planted into a subterranean clover pasture in 1984. Suppression of warm season herbaceous vegetation by applying herbicides or disking the site in late summer resulted in significantly greater subterranean clover production than on the control site where no additional understory management was applied. Pine species had no effects on clover yield. The N content of the pine foliage on the blocks managed with herbicide application or disking generally was significantly greater than the control from the 5th through 7th growing seasons (1988–1990). The dbh of the pine trees in the disked and herbicide treatments was greater than the control after the 7th growing season (1990).     

Why do large,nitrogen rich seedlings better resist stressful transplanting conditions? A physiological analysis in two functionally contrasting Mediterranean forest species

We analysed the physiological bases that explain why large and high nitrogen (N) concentration seedlings frequently have improved survival and growth relative to small seedlings in Mediterranean woodland plantations. Large seedlings of Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.) with high N concentration (L+), and small seedlings with either high (S+) or low (S−) N concentration, were planted on two sites of different weed competition intensity that created contrasting stress conditions. Seedling survival, growth, gas exchange, N remobilization (N_R) and uptake (N_U), and water potential were assessed through the first growing season. Weeds reduced survival and growth, but seedling response to weed competition varied among phenotypes and between species. At the end of the first growing season, L+ Aleppo pine seedlings had higher survival than both small seedling types in presence of weeds but no differences were observed in absence of weeds. Mortality differences among phenotypes occurred in spring but not in summer. L+ Aleppo pines grew more than small Aleppo pines independently of weed competition. No holm oak seedling type survived in presence of weeds and no mortality differences among phenotypes where observed in absence of weeds, although L+ holm oak seedlings grew more than small seedlings. Mortality and growth differences in Aleppo pine were linked to marked physiological differences among phenotypes while physiological differences were small among holm oak phenotypes. L+ Aleppo pines had greater root growth, gas exchange, N_R, and N_U than small seedlings, irrespective of their N concentration. Seedling size in Aleppo pine had a greater role in the performance of transplanted seedlings than N concentration. The functional differences among oak phenotypes were small whereas they were large in pine seedlings, which led to smaller differences in transplanting performance in holm oak than in pine. This suggests that the nursery seedling quality improvement for planting in dry sites could depend on the species-specific phenotypic plasticity and functional strategy. Improved transplanting performance in large Aleppo pine seedlings relative to small seedlings was linked to greater gas exchange, root growth and N cycling.     

Establishing American sycamore seedlings on land irrigated with paper mill sludge

A study was established to evaluate several management practices for improving American sycamore (Platanus occidentalis L.) establishment on land subjected to daily paper-mill sludge spray irrigation, and where a dense herbaceous cover dominated by pokeweed (Phytolacca americana L.) was nearly 2 m tall. Treatments studied included: two sludge application treatments (spray vs no spray), five weed control treatments (control, hand-release, oxyfluorfen, glyphosate and atrazine, and sulfometuron methyl), and two tree shelter treatments (control vs tree shelter). Survival and growth of sycamore seedlings were evaluated after one growing season. Sludge application treatment had the greatest effect on tree survival; survival was greatest on plots that were not sprayed during the year of tree growth. Among the weed control treatments, the hand-release treatment resulted in best survival; survival was 100% when hand release was used on unsprayed plots. Tree shelters provided no benefit to tree establishment.     

Plant species cover,frequency, and biomass: Early responses to clearcutting,burning, windrowing,discing, and bedding in Pinus elliottii flatwoods

Pinelands in a 49 ha naturally-regenerated, mature flatwoods forest in north Florida were clearcut harvested in the fall of 1978, site prepared by burning, shearing and piling, discing, and bedding, and planted to slash pine (Pinus elliottii) in 1979. Three vegetation surveys were conducted: one prior to harvest in the summers of 1977 and 1978, and two subsequent to planting in the summers of 1980 and 1981.Cover and frequency of all plant species encountered were assessed on permanent transects. Foliage biomass by species was assessed by destructive sampling of distinct subplots within permanent plots. The aim was to assess plant species cover, frequency, and biomass responses to the forest operations imposed.Pine was eliminated as a dominant genus by harvesting. Planted pines were a fast increasing, but not dominant, component of the vegetation at 2 years of age. Previously dominant shrubs were severely reduced — often by approximately two orders of magnitude. Indeed, woody species were severely reduced: woody cover from 151 to 12% of surface area at plantation age 2 years; woody biomass from 6223 to 521 kg/ha.Conversely, herbaceous species were substantially increased: herbaceous cover from 38 to 51% of surface area at 2 years; herbaceous biomass from 382 to 1439 kg/ha. Thus, a predominantly woody ecosystem was converted to a predominantly herbaceous one for 2 years following planting.There was little change in plant species richness as a result of forest operations. Plant diversity changes were mixed the 1st year but diversity substantially increased the 2nd year. Comparisons with a companion study (Conde et al., 1983) suggest that, while increases in diversity following maximum site preparation may lag increases following minimum site preparation, cover, frequency, and biomass diversity all converge to common values after 2 years despite disparity in treatments.     

The impact of timing and duration of grass control on growth of a young Eucalyptus globulus Labill. plantation

Interference by an introduced grass, Holcus lanatus L. (Yorkshire fog grass) in a young E. globulus (Tasmanian blue gum) plantation was investigated. The objectives were to determine (1) the critical period of competition, and (2) how the timing and duration of competition was related to the interaction between tree growth and resource availability. This was investigated during the first two years of establishment. Weed interference was severe with height and diameter growth of weedy trees being 52% and 40% of weed-free trees, respectively, at age two years. Most growth losses occurred during the first year. The critical period of weed interference was from planting to age 18 m and effective weed control was required for this period to maximise tree growth potential. The application of nitrogen to weedy trees promoted a significant growth response suggesting that competition for nitrogen was occurring. There was no significant response to level of irrigation. The use of critical period analysis is discussed.     

Pine growth response to different site-preparation methods with or without post-plant herbaceous weed control on North Florida's Lower Coastal Plain

A study was initiated in 1994 to evaluate the effects of bedding timing and frequency and pre-plant herbicide application, with and without post-plant herbaceous weed control, on growth of three slash pine (Pinus elliottii Engelm.) plantations and one loblolly pine (Pinus taeda L.) plantation on flatwoods sites. Site preparation treatments included early bedding alone, late bedding alone, double bedding, early bedding plus banded pre-plant herbicide, and early bedding plus broadcast pre-plant herbicide. Each site preparation treatment was tested with and without a first-year post-plant herbicide application for herbaceous weed control (HC). Results ranging from age 5 to 11 are reported, depending on installation. Pine growth following late bedding alone was similar or greater than that with early bedding alone. Double bedding did not consistently increase pine growth as compared with single bedding alone. Early bedding plus either broadcast or banded pre-plant herbicide application generally exhibited greater pine growth than did bedding alone treatments or bedding plus post-plant herbaceous weed control treatments. Broadcast pre-plant herbicide application resulted in similar or greater growth than banded pre-plant herbicide application. Post-plant herbaceous weed control improved loblolly pine growth across all site preparation regimes on the one test location. For slash pine plantations evaluated, post-plant herbaceous weed control resulted in significant growth increases on some but not all sites. The differences in growth response to bedding and pre- and post-plant herbicide applications are discussed in relation to treatment efficacy in controlling woody shrub and herbaceous competing vegetation. Effective bedding and chemical site preparation reduces the need for post-plant herbicide applications for slash pine on certain sites. Good site preparation, including the application of herbicides for competition control, is essential for fast growing slash and loblolly pine plantations in the flatwoods.     

White spruce establishment: initial fertilization,weed control,and irrigation evaluated after three decades

Outplantings of white spruce (Picea glauca [Moench] Voss) in a factorial experiment in 1962 (P62) and 1963 (P63), near Ottawa, Ontario, addressed the problem of prolonged unsatisfactory growth of outplanted white spruce, a condition commonly termed check. Applied in the first 2 growing seasons, the treatments (3 levels of nitrogenous fertilization ×± weed control ×± irrigation) subjected the trees to differential fertility and soil moisture on each of three soils (clay, loam, and sand). There were 5 (P62) and 6 (P63) replications of 9-tree plots. The P62 Loam planting was destroyed by fire in 1966. Initial survival in the P63 Clay was too low to warrant long-term monitoring. Monitoring of the P62 Clay planting was discontinued after 20 years when it was clear that site factors unrelated to the experimental treatments were controlling stand development. After 30 growing seasons in the P62 Sand and 29 growing seasons in the P63 Sand and P63 Loam plantings, neither initial nitrogenous fertilization nor initial irrigation was influencing performance, but on all three sites the positive effect of initial weed control remained significant (P<0.001).     

Durability of selected mulches,their ability to control weeds,and influence growth of loblolly pine seedlings

Several mulches of natural, synthetic, or blends of natural and synthetic fibers were tested around newly planted loblolly pine (Pinus taeda L.) seedlings on a sheared and windrowed site in central Louisiana, USA. The vegetation was primarily winter annuals, some residual grasses and forbs, and sparse woody regrowth. Study 1 was rotary mowed just prior to planting in March 1992, and 35 mulches and an untreated check were established. In Study 2, 15 mulches and an untreated check were established in a 1-year-old rough in March 1993. In both studies, a single loblolly pine seedling formed each plot established in a randomized complete block design, with 10 blocks as replicates. Each block was planted with a separate open-pollinated loblolly pine family.Nearly all mulches had deteriorated to some extent after three growing seasons. Synthetic mulches were generally more durable than the natural or natural/synthetic mulches. Mulching eliminated the established vegetation and germinants, and vegetation did not readily reestablish following the deterioration of a mulch. The soil seed bank apparently was not sufficient to regenerate areas that were once covered with mulch and many of the natural materials deteriorated into a fibrous cover that acted like a natural litter layer. Both of these residual weed control effects -- insufficient soil seed bank and formation of a fibrous cover -- were important in stopping vegetation from reestablishing after a mulch had deteriorated. After three growing seasons, the loblolly pine seedlings generally grew better if mulches were used.     

Growth responses to planting density and management intensity in loblolly pine plantations in the southeastern USA Lower Coastal Plain

? Background

A culture/density study was established in 1995 in the Lower Coastal Plain of the southeastern USA to evaluate the effects of intensive silviculture and current operational practices on the growth and yield of loblolly pine plantations across a wide range of planting densities (741–4,448 trees/ha). The operational regime consisted of bedding and herbicide application in site preparation and fertilizer applications at planting and in the eighth and 12th growing seasons. The intensive management regime had additional complete competition control, tip moths control, and more repeated fertilization treatments.

? Methods

The data from 14 locations from this split-plot experiment design with repeated measurements were analyzed with a mixed-effects model approach in terms of average DBH, average height, average dominant height, survival, stand basal area, and stand volume.

? Results

In the first few years after planting, there were no significant effects of management intensity and planting density. In later years, both management intensity and planting density significantly impacted response variables, and their interaction was only significant for average diameter at breast height (DBH). Responses to intensive management in DBH were greatest at the lowest planting densities. Intensive management resulted in larger average DBH, average height, dominant height, stand basal area, and volume. Intensively managed plots had more mortality at age 12. There were negative average DBH, average height, dominant height, and survival responses but positive stand basal area and volume responses to increasing planting density. However, there were no significant differences for planting densities above 2,224 trees/ha.

? Conclusions

The results demonstrate that both management intensity and planting density significantly affect loblolly pine productivity in the Lower Coastal Plain, and their effects are additive in nature due to the general lack of interactions.