Final Report for GS01-007
Increased concerns regarding the long-term sustainability of production systems have resulted from investigation and documentation of real and potential adverse environmental consequences associated with conventional, large-scale, highly specialized, chemical and capital-intensive farming systems. Changing public expectations, expressed through regulatory action, consumer pressure, and evolving priorities of legislation and government programs provide incentive to develop production systems that satisfy world demands for food and fiber while maintaining ecological function and integrity of agroecosystems. These priorities are illustrated in successively increasing conservation provisions of the 1985, 1990, 1996, and 2002 Food Security Acts (Farm Bill). Specific programmatic examples include the creation of the Environmental Quality Incentives Program (EQIP), Wildlife Habitat Incentives Program (WHIP), Wetlands Reserve Program, Grassland Reserve Program, and elevation of wildlife habitat to co-equal status with soil erosion, water quality, and commodity control in the new Conservation Reserve Program (CRP).
Practices encouraged under the United States Department of Agriculture-Natural Resource Conservation Service (USDA-NRCS) National Conservation Buffer Initiative, such as field borders, filter strips, and riparian buffers, meet many of the objectives of sustainable agriculture. While primarily removing marginal land from production, these practices have been demonstrated to control erosion (Dillaha et al. 1989), maintain the quality of surface and ground water through sediment, nutrient, and herbicide retention (Daniels and William 1996; Webster and Shaw 1996), and enhance wildlife habitat (Gillespie et al. 1995; Puckett et al. 1995). Noncrop vegetated strips integrated within a cropping system can also assist in controlling pest insects by providing suitable habitat for beneficial predatory insects (Sotherton 1995; Funderburk and Higley 1994).
Despite direct financial compensation (both cost-share and incentive payments) for enrollment, the Buffer Initiative has not gained widespread participation and the goal of 2 million miles (up to 7 million acres) of conservation buffers by the year 2002 was not met. USDA-NRCS has identified the need for evaluation of benefits associated with conservation buffer practices and perceived obstacles to producer adoption. Numerous conservation buffer practices are encouraged through cost-shares and incentives under several different USDA programs (CRP, WRP, WHIP, EQIP). However, practices most likely to be implemented are those that accrue the greatest environmental benefits while minimally impacting production. In order to guide the development of incentives, cost-shares, regulations and policies, information is needed on both the environmental effects (improved water quality, wildlife habitat, etc.) of these conservation buffers and the value of resulting environmental services to the community. Adoption of conservation practices by farmers is often determined by the level of knowledge the farmer has regarding environmental benefits, costs in terms of crop loss, and availability and enrollment procedures of conservation programs promoting the practices (Lant et al. 1995, Traore et al. 1998). Conservation buffer practices will only be implemented if constraints on producer participation such as concerns regarding lost opportunity and propagation of weeds and insects are identified and addressed and if producers are informed about the costs and benefits of field border practices.
Bromley (1998), in an unrelated, but similar SSARE funded project, demonstrated that field borders with their associated environmental benefits could be successfully integrated with wildlife management for grassland bird species in production systems in Virginia and North Carolina. Replication of this project in other production systems and locations and on a larger spatial scale is needed to determine regional applicability of results.
Non-crop plant communities adjacent to agricultural crops may be perceived by farmers as unacceptable because they may contain host plant species for pest arthropods and may serve as a seed source for agronomic weeds. Sustainable weed and pest management requires an integrated systems approach for providing economically and environmentally sound management practices for reducing weed and pest damage to crops. Biological monitoring of pest and beneficial organism density and distribution in relation to crop stage and condition are crucial to integrated pest management (IPM). However, knowledge requirements and sampling costs are often prohibitive (Bird et al. 1990; Fleischer et al. 1997). Information on weed density, species composition, and distribution is also critical to inform and monitor weed management strategies (Johnson et al. 1997).
Finally, acceptance of border management practices will depend on their impact on farm profitability and on public support. The extent to which field borders influence profit levels will depend on changes in input usage and yield output with and without field borders. In addition, estimates of the value that society places on environmental quality improvements gained via use of filter strips is necessary to provide information to policy makers for designing incentive programs. Goals of this project were to: 1) build upon work by Bromley (1998) by evaluating ecological and economic field border effects on producers and communities in rowcrop production systems in Mississippi, 2) provide producers, resource conservationists and policy makers with information and training to move farming toward sustainability.
Specific objectives were to:
1.) Assess opportunity costs of participation in field border management programs by yield mapping fields in relation to crop type, proximity to edge, buffer establishment and landscape context (adjacent plant community type).
2.) Quantify spatial distribution of weed species in relation to field border management, crop type, proximity to edge, and landscape context.
3.) Assess effects of field border management practices on wildlife habitat quality using diversity and abundance of ground nesting grassland bird species, population performance parameters of radio-marked northern bobwhite, and foraging efficiency of human-imprinted bobwhite chicks.
SPATIAL DISTRIBUTION OF WEEDS
We tested the effects of non-crop herbaceous field borders on infield weed density by installing experimental herbaceous field borders on randomly selected 200 m field margin segments of fields on 3 farms in the Black Prairie Physiographic Region of Mississippi (Lowndes and Clay Counties). We used GPS geo-referenced in-field sampling on 20 x 80 m grids positioned at the center of the 200 m segment to characterize the spatial distribution of weeds in relation to field border treatments and proximity to edge. We measured weed density during 2000, 2001, and 2002 growing seasons. The number of replicate fields and bordered segments varied among farms due to variation in number of fields, field size, and edge types. Because crop type (corn or soybean) varied among farms and over years, we treat each farm/year combination as an independent experiment with internal replication of randomly assigned field margin segments.
Site 1 – Lowndes County
This site represented establishment of field borders in fields with herbaceous plant communities outside the cropped field boundary. Within this site we selected 4, 200 m herbaceous bordered and unbordered field edge segments (8 total 200 m segments) in a paired design, with each pair having similar management, position on landscape and plant species composition. Within each 200 m section, a 20 m X 75 m grid with nodes at 5 m intervals (80 points/grid) was placed adjacent and perpendicular to the field edge section or border. Field border segments were selected so that we had at least 75 m and 175 m separation from side and opposite field edges, respectively (to minimize effects from other non-crop plant communities). Grids were geo-referenced using a Trimble Pro-XRS GPS unit. A gridded quadrat (30 cm x 30 cm in corn or 76 cm x 76 cm in soy beans) was placed at each node. Density and cover of weed species was recorded for each field after use of any post-emergent herbicides, but prior to canopy closure by soybean or corn crops.
Site 2 – Lowndes County
A second experiment utilizing a similar experimental design and procedures was established on an adjacent farm in Lowndes County to examine field border effects in fields with wooded plant communities outside the cropped field boundary. Within this site we selected 4, 200 m bordered and unbordered field edge segments (8 total 200 m segments) in a paired design, with each pair having similar management, position on landscape and plant species composition. Within each 200 m section, a 20 m X 75 m grid with nodes at 5 m intervals (80 points/grid) was placed adjacent and perpendicular to the field edge section or border. Field border segments were selected so that we had at least 75 m and 175 m separation from side and opposite field edges, respectively (to minimize effects from other non-crop plant communities). Grids were geo-referenced using a Trimble Pro-XRS GPS unit. A gridded quadrat (30 cm x 30 cm in corn or 76 cm x 76 cm in soybean) was placed at each node. Density and cover of weed species was recorded in each field after use of any post-emergent herbicides, but prior to canopy closure by soybean or corn crops
Site 3 – Clay County
In a third experiment, 3 fields, each with 2 similar adjacent plant community types (grassed road shoulder and herbaceous riparian buffer) were selected within the field-bordered area of the Clay County study site. For each of the 2 community types within each field, half of a field edge pair (each edge approximately 200 m long) was randomly selected to be planted with herbaceous borders with the remaining half left without borders. Within this site we characterized infield weed communities adjacent to 6 pairs of bordered and unbordered field edges (12 total 200 m segments) in a paired design, with each pair having similar management, position on landscape and plant species composition. Within each 200 m section, a 20 m X 75 m grid with nodes at 5 m intervals (80 points/grid) was placed adjacent and perpendicular to the field edge section or border. Field border segments were selected so that we had at least 75 m and 175 m separation from side and opposite field edges, respectively (to minimize effects from other non-crop plant communities). Grids were geo-referenced using a Trimble Pro-XRS GPS unit. A gridded quadrat (30 cm x 30 cm in corn or 76 cm x 76 cm in soybean) was placed at each node. Density and cover of weed species was recorded in each field after use of any post-emergent herbicides, but prior to canopy closure by soybean or corn crops.
Within each year and site combination we used a spatially repeated measures, mixed model ANOVA to test for main effects of treatment (bordered and unbordered) and distance from edge (5 m distance classes, 5-75 m from edge). We considered treatment a fixed effect, distance from edge a spatially repeated factor, and blocks (paired bordered and unbordered segments) as a random effect.
WILDLIFE HABITAT QUALITY
Diversity and abundance of grassland birds
We estimated density and diversity of overwintering and breeding season grassland birds relative to field border management practices using line-transect, distance sampling methods. Transects (200 m in length) were selected randomly from a population of available transects across 6 study sites (farms) in the Black Prairie Physiographic region of Northeast Mississippi. Transects were stratified by experimentally implemented field border treatment type (bordered, non-bordered). Because bird species vary relative to adjacent plant communities (Best 1983, Rodenhouse and Best 1983, Shalaway 1985, Best et al. 1990), transects were further stratified by adjacent plant community type (woody/herbaceous) and width (<30 meter/>30 meter). Approximately 10 transects were selected for each treatment combination (border/adjacent plant community/width). Transects located adjacent to roadways or subjected to producer disturbance were not included within the sampling frame.
Surveys were conducted during the 2002 and 2003 winter seasons, and 2002 breeding season. Each transect was surveyed twice within each year and season. Winter surveys were conducted in Feb – Mar and the breeding season survey was conducted in late Jun – early Jul. Transects were assigned randomly among observers (n = 3 over all seasons and years). Within each study site, transects were surveyed in non-random order to permit efficient time allocation. However, the within site transect order was reversed during the second repetition. Following completion of the first repetition, observers switched transect schedules. Transects for bordered fields were positioned along the field border-field margin interface, while transects for the non-bordered fields were positioned along the crop-field margin interface. Surveys were conducted from 0700 – 1100 hr with wind speeds <10 mph. Flagging was placed at the beginning, end, and at 20 meter intervals to allow observers to monitor their speed and relative location along the transect. Observers walked (at approximately 20 meters/min) along transects and recorded the number of individuals and species of birds seen or heard within 10 meters of either side of the centerline of the transect. For species which sufficient numbers of observations were recorded, we used distance sampling methodology in program DISTANCE to estimate bird densities (in birds/ha) between bordered and non-bordered transects. This approach incorporates species-specific detection probabilities to provide less-biased estimates of density. We used a 23 factorial arrangement of treatments in a completely randomized analysis of variance (ANOVA) in PROC GLM (SAS Institute, Inc 1990) to determine border, adjacent plant community, and adjacent plant community width effects on overall bird abundance, species richness, and species-specific bird densities. Furthermore, we calculated Partners In Flight Total Avian Conservation Values (TACV) for each species. TACV is a prioritization scoring process that reflects different degrees of need for conservation attention based on 7 parameters (Carter et al. 2000). These parameters include: breeding and non-breeding distribution, relative abundance, potential threats to breeding and non-breeding habitat, population trend, and a physiographic-specific area importance value (Carter et al. 2000). Factor levels were: Field Border: bordered/non-bordered; Adjacent Plant community: woods/grass; and width of adjacent plant community: strip/block. Because of unequal sample sizes, we used LSMEANS pair-wise multiple comparison procedure following a significant (P<0.05) model effect. Northern bobwhite population response We estimated fall density and relative abundance of northern bobwhites using covey counts from 3 500 m x 500 m randomly selected sampling blocks per study area. Sampling blocks were re-randomized each year. Covey counts were conducted during late October-early November from 1999-2002. However, call counts were not conducted for bordered and non-bordered areas of the Noxubee county study site in 1999 because treatment designations had not yet been made. One observer was stationed at midpoints along each side of a sampling block >0.5 hours before sunrise (CST) to monitor morning covey calls until 0.25 hours after sunrise. Observers recorded time, azimuth, duration, and number of covey calls per calling event for coveys within and outside the sampling block. We then triangulated covey locations based on observer azimuths plotted on1:10,000 scale geographic information system (GIS) cover type maps in relation to time of calling activity to determine the number of coveys within the sampling block.
We determined calling probability using calling activity of coveys containing >1 radio marked bird. We used calling activity information from radiomarked birds at 2 of the field border study sites and from a nearby state-owned management area (Black Prairie Wildlife Management Area, Brooksville, MS) to estimate calling probability. We defined calling probability as number of coveys which exhibited calling activity divided by total number of coveys observed during the sampling period (1 October-7 December). We located radio marked birds >0.5 hrs before sunrise (CST) and remained at the location until 0.25 hrs after sunrise to record calling activity. At the end of the observation period, we flushed the covey containing the radiomarked bird and counted number of birds to estimate mean covey size.
We used breeding season call counts (Bennett 1951) to index annual bobwhite breeding density during 2000-2002. Call counts were conducted in mid-June between 0545-0900 hours with average wind speeds <15mph (Hutto 1986). We recorded number of calling males heard during a 5 minute listening period at 102 stations (55 bordered, 47 non-bordered). All stations were geo-referenced and the same set of stations were used throughout the study. Stations were arranged in grid fashion with a 800 m spacing among stations. Counts were conducted twice at each station during a 4-day interval of each year. For measures of fall and breeding season abundance, we used a repeated measures ANOVA in a randomized complete block design in PROC MIXED (SAS Inc. 2002) to test the null hypothesis that abundance measures did not differ between bordered and non-bordered sites during the 3 years of study. Because subtle differences in landscape context and farming practices existed among the study areas (n=3), study area was used as a random block effect whereas year was used as the repeated time effect. We modeled within-subject covariance (i.e., the repeated year effect) using the autoregressive (order 1) covariance structure. Results of all test were considered significant at á=0.05. Northern bobwhite survival Wild northern bobwhite were captured in late winter (February – March) with baited walk-in funnel traps (Stoddard 1931) or by night netting (Truitt and Dailey 2000). Birds were sexed, aged (adult/sub-adult), weighed, banded with a #7 aluminum leg band, and fitted with a 5 – 6 g pendant style radio transmitter (American Wildlife Enterprises, Tallahassee, Florida, USA) and released at the capture site. Radio transmitters operated on 148.000 – 151.000 MHz band and were equipped with a motion sensitive 12 hr mortality switch. Capture, handling, tagging, and radiomarking procedures were consistent with the Mississippi State University Institutional Animal Care and Use Committee (IACUC permit no. #99-212) guidelines and the American Ornithologist’s Union Report of Committee on the Use of Wild Birds in Research (American Ornithological Union 1988). We used a programmable scanning receiver with a 3 element Yagi antennae to locate radiomarked birds. Wide ranging birds were located using fixed wing aircraft. Radiomarked birds were located >1/ week from 5 Feb to 15 Apr and >5 times/week during the breeding season (15 Apr – 15 Sept) by homing to <25 m and triangulating from positions referenced geographically with a Trimble Geo-Explorer II (Trimble 1999) hand-held global positioning system (GPS) unit. When a mortality signal was detected, we located the transmitter and determined fate of the radio-marked bird using evidence at the recovery site (bird remains, scat, tracks, whitewash) and transmitter damage (Dumke and Pils 1973). Intact birds for which no apparent cause of mortality could readily be determined were necropsied at the College of Veterinary Medicine, Diagnostic Lab, Mississippi State University. We used Cox’s partial likelihood regression (Cox 1975) in PROC PHREG (Allison 1995) to estimate survival probabilities and test hypotheses of no difference in proportional hazard among genders, ages, years, and treatment effect (bordered/non-bordered) during the breeding season interval. Breeding season survival was based on a 154-day interval (15 Apr – 15 Sept) beginning with covey breakup and initiation of reproduction (Burger et al. 1995). We assumed sex and age classes were sampled randomly, individual survival times were independent, censoring mechanism was random, and capturing, handling, and radiomarking did not affect survival (Pollock et al. 1989). Imprinted northern bobwhite chick foraging trials We used human-imprinted, ligatured, pen-strain northern bobwhite chicks to measure availability of arthropods within field borders and adjacent rowcrop plant communities as a function of distance from field edge and crop type. Three sampling locations (3.1 m, 6.1 m, and 30.5 m from the field edge) were used to measure spatial effects of field borders on arthropod availability. Crop types were corn and soybeans. Within bordered fields, the first sampling location was within a field border whereas in control fields the first sampling location was 3.1 m within the rowcrop field. Replicate foraging trials, 30 minutes in duration, were conducted for each of the 12 treatment combinations (bordered, non-bordered; 3 distance2 from field edge; 2 crop types). To minimize effects of individual variability associated with foraging behavior, we assigned randomly 4–6 chicks into a foraging “group” for each trial. Mean arthropod consumption (g/chick) of all chicks within a group was used as the response variable for a trial. A “set” of trials consisted of 3 independent trials, one at each of the 3 sampling locations within a field during each day. Trials within sets were assigned randomly to each distance class. Moreover, sets were assigned randomly to each treatment combination (bordered, non-bordered; crop type) and were conducted in random order to avoid confounding time-of-day effects with treatment effects. Furthermore, because ambient temperature is known to influence foraging activity (Palmer et al. 2001), all trials were conducted in the late afternoon between 1600–1900 hours when ambient temperatures and solar irradiance was lower. Chick rearing, imprinting, surgeries, handling, and euthanasia procedures were consistent with the Mississippi State University Institutional Animal Care and Use Committee (IACUC permit #00–045) guidelines and the American Ornithologist’s Union Report of Committee on the Use of Wild Birds in Research (American Ornithological Union 1988). We used a split-plot arrangement of treatments within a randomized incomplete block design to test the null hypotheses that mean arthropod consumption did not differ between bordered and non-bordered fields and distance from field edge within each crop type (bean or corn). Bordered and non-bordered field was the whole-plot factor while distance from the field edge was the split-plot factor. Because environmental conditions varied by day and across years and sampling was conducted only at 1 study site for any given day, each day-year-site combination was considered a random block effect. While there is inherent confounding between day, study site, and year, these effects were not of particular interest thus were not explicitly addressed. However, the block effect of day-year-site was modeled as a random variate, thereby increasing inferential space. Because several blocks were incomplete, we used the PROC MIXED procedure in SAS (SAS Inc. 2002) because of its flexible maximum likelihood method of estimating variance components and modeling covariance structures when incomplete blocks are present. We modeled the covariance structure within each set of trials (3.1 m, 6.1 m, and 30.5 m distances) using the REPEATED statement. Because distances from the field edge were unequally spaced, we used the spatial power law covariance structure.
Generally crop yields are reduced near field edges compared to field centers with woody field edges having a more pronounced effect on yield reduction than herbaceous edges (DeSnoo 1994; Semple et al. 1994, Bromley 1998, Sparkes et al. 1998). This reduction in yield has been attributed to soil compaction from machinery (turning tracks), less favorable crop site conditions (fertilizer and water regime), and weed infestation and competition from adjacent edge vegetation (DeSnoo 1994). Semple et al. (1994) found that adding a grass border did not affect grain yield or move the poorer yielding edge area into the center of the field. Preliminary results indicated adjacent field borders of early successional plant communities minimally affected corn and soybean yields in a Virginia and North Carolina study (Bromley 1998). However, these studies only report results for one year of study and weeds might not have had time to colonize from edge and cause yield reduction. Winter wheat yields were adversely affected by weeds in the crop margin 5 years after establishment of perennial ryegrass strips (Milsom et al. 1994). DeSnoo (1997) reported harvest losses of greater than 30% in sugar beets from weed infestations when field edge was not sprayed with herbicide.
SPATIAL DISTRIBUTION OF WEEDS
As expected, spatial patterns of weed infestation varied among weed species. Overall weed density exhibited an edge effect with greater weed density near field margins. However, grids adjacent to experimental herbaceous field borders did not exhibit greater weed density than control grids on any of the sites in any year. Over the 3 sites and 3 years, the most abundant weed species included Solanum carolinense, Sorghum halepense, Brachiaria platyphylla, Ipomoea lucunosa, Ipomoea hederacea, Senna obtusifolia, Digitaria ciliaris, Jaquemontia tamnifolia, Cyperus esculentus, and Cynodon dactylon.
2000 Growing season
The growing season of 2000 was extremely dry, thus, crops, field borders, and weed communities were poorly developed across all sites. Weed grids were sampled in June 2000.
Site 1 – Lowndes County
During the 2000 growing season, experimental fields on Site 1 were planted to soybeans. Mean total weed density was not different (P = 0.596) between bordered (1.05/0.57 m2 ) and unbordered segments (1.75/0.57 m2) stems/0.75 m². Neither did total weed density vary in relation to distance from field margin (P = 0.418). Density of individual weed species did not differ between bordered and unbordered segments (P < 0.05), however; select individual weed species did demonstrate an edge effect. Ipomoea lacunosa was more abundant (P = 0.003) at 5 m from the field margin than any greater distance. Similarly, Senna obtusifolia was most abundant at 5 m and 10 m from the field edge than at greater distances (P = 0.024). Site 2 – Lowndes County During the 2000 growing season, experimental fields on Site 2 were also planted to soybean. Mean total weed density did not differ (P = 0.391) between bordered (3.689/0.57 m2) and unbordered (10.85/0.57 m2) field segments. Total weed density did not differ among distance from edge classes (P = 0.594). Density of the 10 most common weed species did not differ between bordered and unbordered (P > 0.05) or among distance from edge classes (P > 0.168).
Site 3 – Clay County
During the 2000 growing season experimental fields on Site 3 were planted to corn.
Mean total weed density did not differ (P = 0.822) between bordered (1.565/0.09 m2) and unbordered (1.775/0.09 m2) field segments or among distance from edge classes (P = 0.234). No weed species differed between bordered and unbordered field segments (P > 0.207). Only Cynodon dactylon differed among distance from edge classes. Cynodon dactylon density was more abundant (P = 0.036) at 5 m from the field edge than at all greater distances.
2001 Growing season
Site 1 – Lowndes County
During the 2001 growing season experimental fields on Site 1 were planted to corn. Mean total weed density did not differ (P = 0.102) between bordered (2.069/0.09 m2) and unbordered (3.181/0.09 m2) field segments. Total weed density differed among distance from edge classes (P < 0.001) and exhibited a declining pattern as distance from edge increased, (5 m, mean = 13.425, SE = 0.781); 10 m, mean = 6.475, SE = 0.781; 15 m, mean = 2.850, SE = 0.781; 25 m, mean = 1.575, SE = 0.781; 35 m, mean = 2.350, SE = 0.781; 60 m, mean = 0.850, SE = 0.781; 65 m, mean = 2.075, SE = 0.781; 80 m, mean = 2.250, SE = 0.781). Brachiaria platyphylla (P < 0.001), Ipomoea hederacea (P < 0.001) Senna obtusifolia (P = 0.018), Solanum carolinense (P = 0.038), Sorghum halepense (P = <0.001) were more abundant at 5 m from the field edge than at greater distances. Site 2 – Lowndes County During the 2001 growing season experimental fields on Site 2 were planted to soybeans. Mean total weed density did not differ (P = 0.121) between bordered (19.894/0.57 m2) and unbordered (12.784/0.57 m2) field segments. Mean total weed density similarly did not differ among distance from edge classes (P = 0.591). Only Ipomoea lacunosa exhibited an edge effect (P < 0.001) and was more abundant at 5m (mean = 2.500, SE = 0.612) and 10 m (mean = 2.975, SE = 0.612) than at all greater distances. Site 3 – Clay County During the 2001 growing season experimental fields on Site 3 were planted to soybeans. Mean total weed density did not differ (P = 0.790) between bordered (34.775/0.57 m2) and unbordered (37.294/0.57 m2) field segments. Mean total weed density was greater (P < 0.001) at 5 m (mean = 88.533, SE = 9.512) from edge than all other distance classes. 2002 Growing season Site 1 – Lowndes County During the 2002 growing season experimental fields on Site 1 were planted to soybean. Mean total weed density did not differ between bordered (15.209/0.57 m2 ) and unbordered (25.169/0.57 m2 ) field segments (P = 0.768). Mean total weed density was greater (P = 0.008) at 5 m (mean = 90.125, SE = 20.850). Digitaria ciliaris (P = 0.013), Senna obtusifolia (P = 0.035), Solanum carolinense (P < 0.001), and Sorghum halepense (P < 0.001) exhibited declining density with distance from edge. Site 2 – Lowndes County During the 2002 growing season experimental fields on Site 2 were planted to corn. Mean total weed density did not differ between bordered (11.066/0.09 m2) and unbordered (5.519/0.09 m2) field segments (P = 0.138). Mean total weed density (P = 0.081) and density of individual weed species (P > 0.06) did not vary in relation to distance from edge.
Site 3 – Clay County
During the 2002 growing season experimental fields on Site 2 were planted to corn. Mean total weed density did not differ (P = 0.235) between bordered (4.80/0.09 m2) and unbordered (6.048/0.09 m2) field segments. Mean total weed density (P = 0.081) and density of individual weed species (P > 0.06) did not vary in relation to distance from edge. Mean total weed density did vary among distance from edge classes (P < 0.001) with highest density occurring at 5 m (mean = 53.433, SE = 1.754) and 10 m (mean = 7.200, SE = 1.754). Cynodon dactylon , Digitaria ciliaris, Ipomoea hederacea, Ipomoea lacunosa, Sida spinosa , and Solanum carolinense were more abundant at 5 m or 5 m and 10 m than all other distance classes.
Studies in England, the Netherlands and Canada indicate that plant species distributions for cereal and soybean agricultural systems can be grouped into 4 categories: 1) limited to field edges and unable to survive in the crop; 2) primarily limited to the field, but capable of exploiting disturbed areas of the field edge and recolonizing the field; 3) originating in field edge vegetation but capable of spreading into the crop, and 4) a headland (crop edge) distribution (Marshall 1989, Joenje and Kleijn 1994, Boutin and Jobin 1998). Depending upon presence of species belonging to the second and third categories and types of border used, study results have been mixed regarding weed encroachment into crops from planted or natural field edges. Common weeds observed in crop fields during this study seemed to primarily exhibit field only (type 2) or headland distribution (type 4). Weed species such as Ipomoea lucunosa, Senna obtusifolia, Solanum carolinense, and Sorghum halopense often, but not always, were most abundant within 5-10 m of the field margin. Although disturbed field edges with weedy annual species can readily provide a weed seed source for recolonizing a field (Marshall 1989, Davies and Carnegie 1994, Theaker et al. 1995, DeSnoo 1997), over 3 sites and 3 years we observed no occurrence of herbaceous field borders increasing the density of in-crop weeds. Although several studies reported minimal weed encroachment for field borders planted with perennial grasses and perennial grass/wildlflower mixtures in cropping systems in Europe, weeds increased in abundance in the crop margins of winter wheat fields after advancing through planted broadleaf mixtures or Perennial ryegrass (Lolium perenne) strips (Milsom et al. 1994, Smith et al. 1994, 1999, Kiss et al. 1997, DeSnoo 1997).
Weed effects from field borders may be concentrated in the field edge. Primary dispersal of Bromus sterilis and Anthriscus sylvestris was within 3.5 m of the parent plant; and secondary dispersal (dispersal by agricultural equipment) of seeds from the field edge vegetation was negligible (Rew et al. 1996). Hume and Archibold (1986) reported that the majority of seeds from an adjacent weedy pasture fell within 7 m of a field edge despite the wide variety of dispersal mechanisms present for the different plant species. Species common to the pasture were not abundant in the field center; therefore, cultural practices may have restricted further encroachment into the field. However, traces of Solidago missouriensis and Stipa comata seeds were found 45 m and 100 m from the field edge, respectively; and even small amounts of weed seeds may cause significant problems (Hume and Archibold 1986). We did observe concentrations of weed effects near the field edge for several important weed species. However, the distribution of weed effects was similar between bordered and non-bordered field edges. As such, we do not believe the presence of our conservation borders increased weed management problems.
In some instances, field borders and conservation headlands (pesticide-excluded crop edges) have been used in Europe to protect rare arable weeds; but their utility as a protection for rare plant species depends upon the vegetation and seed bank present (Marshall and Arnold 1995,de Snoo 1997, Kleijn et al. 1998). However, even if rare species are not present, biomass and diversity of field edge plant communities increased adjacent to field borders and conservation headlands as a result of diminished herbicide exposure to the benefit of insect and bird species (de Snoo 1997; Kleijn et al. 1998). Adjacent land use explained 21% of the variation of species composition of field edge plant communities in three different sites in Europe (LeCouer, et al. 1997). More exotic and invasive weedy plants were found in edge habitats adjacent to fields with herbicide use than fields without herbicide use (Boutin and Jobin 1998). Field borders may provide protection from herbicides for native plant species in adjacent field edge communities and increase diversity and biomass; but this has not been studied in North America (Boutin and Jobin 1998).
WILDLIFE HABITAT QUALITY
Diversity and abundance of grassland birds
Fifty-three species (1,686 individuals) were recorded from 688 observations during the breeding season survey. Indigo Buntings (Passerina cyanea; 16.72%), Dickcissels (Spiza americana; 12.50%), Red Winged Blackbird (Agelaius phoeniceus; 12.06%), Northern Cardinal (Cardinalis cardinalis; 9.30%), and Morning Dove (Zenaida macroura; 5.09%) accounted for most observations.
Species richness differed between border (LSMEANS = 6.58 species/transect, SE = 0.377) and non-bordered (LSMEANS = 5.43 species/transect, SE = 0.399) transects (P = 0.038). Bordered transects had higher densities of Carolina Wrens (Thryothorus ludovicianus; border LSMEANS = 0.52 birds/transect, SE = 0.111; non-bordered LSMEANS = 0.14 birds/transect, SE = 0.118; P = 0.025), Dickcissels (border LSMEANS = 3.19 birds/transect, SE = 0.421; non-bordered LSMEANS = 1.56 birds/transect, SE = 0.446; P = 0.001), Indigo Buntings (border LSMEANS = 3.68 birds/transect, SE = 0.289; non-bordered LSMEANS = 1.77 birds/transect, SE = 0.307; P < 0.001), and Common Yellowthroats (Geothlpis trichas; border LSMEANS = 0.35 birds/transect, SE = 0.072; non-bordered LSMEANS = 0.03 birds/transect, SE = 0.076; P = 0.003). However, bordered and non-bordered transects did not differ with respect to the total number of individuals (border LSMEANS = 23.67 birds/transect, SE = 4.290; non-bordered LSMEANS = 20.69 birds/transect, SE = 4.545; P = 0.636), TACV (border LSMEANS = 362.00, SE = 56.401; non-bordered LSMEANS = 303.72, SE = 59.751; P = 0.481), or Shannon Weaver Diversity Index (border LSMEANS = 1.44, SE = 0.065; non-bordered LSMEANS = 1.35, SE = 0.069; P = 0.361).
During winter 2002, 50 species (3,827 individuals) were recorded from 733 observations. Most commonly recorded bird species were Song Sparrow (Melospiza melodia; 23.74%), Swamp Sparrow (Melospiza georgiana; 10.45%), Savannah Sparrow (Passerculus sandwichensis; 8.82%), Northern Cardinal (7.19%), and Yellow Rumped Warbler (Dendroica coronata; 4.48%). Bordered and non-bordered transects did not differ with respect to total number of individuals (border LSMEANS = 64.33 birds/transect, SE = 18.820; non-bordered LSMEANS = 30.42 birds/transect, SE = 19.803; P = 0.219), species richness (border LSMEANS = 5.03 species/transect, SE = 0.460; non-bordered LSMEANS = 5.49 species/transect, SE = 0.484; P = 0.492), Shannon Weaver Diversity Index (border LSMEANS = 1.04, SE = 0.091; non-bordered LSMEANS = 1.18, SE = 0.096; P = 0.282), or Total Avian Conservation Value (border LSMEANS = 1,037.25, SE = 284.807; non-bordered LSMEANS = 496.40, SE = 299.670; P = 0.195). Only Swamp Sparrow differed between bordered (LSMEANS = 6.88, SE = 1.465) and non-bordered (LSMEANS = 0.48, SE = 1.540) transects (P = 0.004).
During winter 2003, 49 species (2,255 individuals) were recorded from 581 observations. Most common species observed were Song Sparrow (21.34%), American Robin (Turdus migratorius; 14.80%), American Pipit (Anthus rubescens; 7.57%), Northern Cardinal (6.20%), and Morning Dove (5.16%). Bordered and non-bordered transects did not differ with respect to total number of individuals (border LSMEANS = 25.93 birds/transect, SE = 4.685; non-bordered LSMEANS = 31.30 birds/transect, SE = 4.879; P = 0.430), species richness (border LSMEANS = 5.08 species/transect, SE = 0.345; non-bordered LSMEANS = 4.94 species/transect, SE = 0.359; P = 0.793), Shannon Weaver Diversity Index (border LSMEANS = 1.12, SE = 0.071; non-bordered LSMEANS = 1.10, SE = 0.074; P = 0.820), or Total Avian Conservation Value (border LSMEANS = 401.78, SE = 54.622; non-bordered LSMEANS = 439.09, SE = 56.880; P = 0.638). Only Yellow Rumped Warbler differed between bordered (LSMEANS = 0.58, SE = 0.138) and non-bordered (LSMEANS = 0.075, SE = 0.143) transects (P = 0.014).
We computed detection probability-corrected estimates of density for song sparrow, savannah sparrow, and a composite estimate of density of all sparrow species (field, fox, song, savannah, swamp, white-throated) for the overwintering sampling period. Density of song sparrows was greater for bordered (mean = 18.46 birds/ha, SE = 4.048) than non-bordered (mean = 2.88 birds/ha, SE = 1.490) transects. Likewise, density of savannah sparrows was greater for bordered (mean = 5.42 birds/ha, SE = 2.450) than non-bordered (mean = 2.35 birds/ha, SE = 1.448) transects. Density of all sparrows was greater for bordered transects (bordered mean = 45.33 birds/ha, SE = 22.900; non-bordered mean = 4.26 birds/ha, SE = 1.903).
Grassland songbirds are one of the most sharply declining groups of birds in North America (Herkert 1995, Peterjohn and Sauer 1999). Brennan (1991) suggested the elimination of field border communities as a contributing factor to the decline of northern bobwhite and many other grassland birds inhabiting farmlands. We observed that field borders enhance species richness and abundance of select species of birds during overwinter and breeding seasons. During the breeding season, field borders did not increase overall avian abundance or diversity. However, species richness (number of species) was greater for bordered transects suggesting that field borders likely influence avian community composition more so than abundance or diversity. Species such as Carolina wrens, common yellowthroats, indigo buntings, and dickcissels were more abundant along bordered transects. These results are particularly encouraging given that common yellowthroats, indigo buntings, and dickcissels are currently experiencing range-wide declines. Whereas we conducted the breeding season survey during only 1 year, we believe that the magnitude of the treatment effect (field border) was sufficiently large (204-486%) to warrant our conclusions that field borders enhance the abundance of selected species of grassland/shrub birds during the breeding season.
Similarly, during the overwintering season, we observed a greater abundances of sparrows along field bordered than non-bordered transects. Weed seed are the primary energy source for most overwintering grassland birds. Given that field borders in our study were recently established and consisted primarily of early successional grasses and forbs, we speculate that most of the granivorous bird species were using field borders as foraging sites during the overwinter season. Furthermore, once crops were harvested field borders provided the only source of vertical vegetation structure for thermo-regulation and roosting. Collectively, field borders provided important habitat for many grassland birds due to their greater abundance of food (arthropods, weed seeds) and more complex vegetation structure for nesting substrate, song perches, and thermal/escape cover than adjacent row crop fields (Patterson and Best 1996, Koford and Best 1996). Practices encouraged the USDA National Conservation Buffer Initiative, such as field borders, filter strips, and riparian buffers, offer potential opportunities for restoring critical overwintering and breeding season habitat for numerous grassland birds throughout the United States.
Northern bobwhite population response
Fall density did not differ between bordered (mean = 0.1801, SE = 0.0669) and non-bordered (mean = 0.1086, SE = 0.0486) sites (F1,10 = 2.18, P = 0.171). Likewise, number of coveys detected did not differ between bordered (mean = 0.7130, SE = 0.2283) and non-bordered (mean = 0.4579, SE = 0.1492) sites (F1,10 = 3.34, P = 0.097). Furthermore, mean number of calling males did not differ between bordered (mean = 0.981, SE = 0.181) and non-bordered (mean = 0.795, SE = 0.268) areas (F1,10 = 0.44, P = 0.219).
Northern bobwhite exhibit tremendous reproductive potential allowing for immediate response to favorable habitat conditions. Using breeding season call counts, Puckett et al. (2000) reported a 59.1% increase in northern bobwhite abundance on 1 of 2 sites where field borders were recently established. Abundance increases were consistent across both sites for the breeding season flush count (430%) and catch-per-effort (89.3%) indices. Similarly, Bromley et al. (2002) observed consistently more northern bobwhite coveys on farms with field borders than non-bordered farms. Whereas most of the field borders in Puckett et al. (2000) were located primarily along drainage ditches, field borders in our study were situated along edges of entire fields within a study site. Field borders in our study comprised only 0.8-1.3% of the land area of bordered sites whereas those in Puckett et al. (2000) comprised 4.9%-9.4%. No data was provided by Bromley et al. (2002) regarding percentage of their study sites in field borders. We defined our effective study site size by buffering all cropping units which received field borders by 800m (2x mean home range size of resident radiomarked northern bobwhites) which may differ from methods used in Puckett et al. (2000) for delineating study area boundaries, thus influencing percentage of land area in field borders. Field borders in Puckett et al. (2000) averaged 3.5m in width whereas field borders in our study were 6.01m in width. Clearly, based upon percentage of land area in field borders and field border width, the study area in Puckett et al. (2000) was more complex (i.e., greater edge density of field borders/ha) than in our study. Although the directional patterns in fall density, number of coveys detected, and breeding season call counts all suggested greater abundance in the field bordered landscapes, we did not observe strong field border effect on abundance parameters, given the sample size and observed variability. Given the magnitude of field border effects reported by Puckett et al. (2000) relative to the percentage of their sites in field borders, we expected similar population responses on our study sites. However, the relatively lower acreage of field borders established in our study may not have been sufficient to elicit an observable population response. Whereas some individual sites displayed favorable results, we did not detect an overall net effect of field borders on northern bobwhite abundance. Given our results in the context of those of Puckett et al. (2000), the proportion of the land base converted to field borders may be more important in eliciting a population response than field border width.
Northern bobwhite survival
During 2000-2002, 209 northern bobwhite were radiomarked. However, only 170 were alive during the breeding season (15 Apr – 15 Sept). Of these, 98 birds were right censored due to survival past the breeding season (n = 49), dispersal from the study site (n = 44), transmitter failure and accidental researcher induced mortality (n = 5). Primary sources of mortality included: avian (n = 6), mammalian (n = 20), unknown predator (n = 41), and unknown cause of death (n = 5). Unknown mortalities were events in which an intact bird was found but no identifiable source of mortality could be identified. All intact birds found had undergone decompositions to an extent to preclude necropsy.
Survival did not differ across years (2000 = 37.96, SE = 0.0845, 2001 = 30.71, SE = 0.065, 2002 = 50.04, SE = 0.090; X2 = 1.38, P = 0.241), sex (MALE = 41.95, SE = 0.057, FEMALE = 30.15, SE = 0.077; X2 = 1.23, P = 0.268), or age (ADULT = 29.62, SE = 0.088, JUV = 39.79, SE = 0.053; X2 = 1.58, P = 0.209). Furthermore, survival did not differ between bordered (S = 37.02, SE = 0.064) and non-bordered sites (S = 32.88, SE = 0.072; X2 = 0.001, P = 0.971). Overall survival was 33.04% (SE = 0.056).
Survival is a critical component governing northern bobwhite population growth. Northern bobwhites in our study experienced survival rates similar to those reported in other studies within agricultural landscapes (33%, Puckett et al. 1995; 33.2% Burger et al. 1995) but lesser survival than on intensively managed areas (43.8%, Burger et al. 1998; 46.9%, Smith 2001; 50.9%, Taylor et al. 2000). Management techniques (i.e., burning, disking) recommended by Stoddard (1931), Rosene (1969) and others are practiced today to elicit positive population responses. Undoubtedly, these responses stem from increases in population performance parameters (survival, reproduction) or rates of immigration as a result of the management practice. However, identifying and understanding the roles of population parameters relative to field border management practices is unclear. Whereas we collected information regarding reproductive performance, insufficient numbers of nest were available to obtain reliable estimates of reproductive success, thus precluding definitive statements regarding the role of reproduction in our results. Point estimates of survival for bordered areas suggested that northern bobwhite inhabiting field border areas may have experience greater survival, however, this difference was not sufficient enough to infer a treatment (field border) effect. The observed treatment effect size (~5%) is sufficient to produce differing population trajectories, and may account for the patterns in slightly greater abundance in bordered landscapes. Future research should focus on determining relative fitness consequences (i.e., increased survival, reproduction) associated with field border management practices using replicated studies with adequate sample sizes to estimate all population performance parameters with greater precision.
Imprinted northern bobwhite chick foraging trials
We used 117 groups (i.e., 4–6 chicks foraging as a unit) in soybean fields and 102 groups in corn fields to test differences in arthropod availability between bordered and non-bordered fields and distance from the crop edge. Within soybean fields, we had 15 complete and 9 incomplete blocks. Within corn fields, we had 14 complete and 6 incomplete blocks. Mean number of chicks per group was similar between soybean (mean = 4.051, SE = 0.070, range = 2–6, median = 4) and corn (mean = 4.098, SE = 0.090, range = 1–8, median = 4) foraging trials.
Within soybean fields, no treatment by distance interaction was observed (F2,74 = 0.39, P = 0.676). Arthropod consumption did not differ between bordered and non-bordered fields (F1,14 < 0.01, P = 0.975). However, arthropod consumption differed among distances from the field edge (3.1 m = 0.091, SE = 0.014; 6.1 m = 0.073, SE = 0.014; 30.5 m = 0.041, SE = 0.014; F2,74 = 6.86, P = 0.002). Arthropod consumption declined as distance from the field edge increased.
Within corn fields, no treatment by distance interaction was present (F2,64 = 1.07, P = 0.345). Arthropod consumption did not differ between bordered and non-bordered fields (F1,13 = 2.65, P = 0.128). Furthermore, arthropod consumption did not differ among distances from the field edge (3.1 m = 0.075, SE = 0.017; 6.1 m = 0.069, SE = 0.017; 30.5 m = 0.082, SE = 0.014; F2,64 = 0.22, P = 0.805).
Habitat-specific and annual variation in arthropod abundance has been shown to affect survival of gray partridge chicks, and subsequently population trajectories (Potts 1986). In some European countries, conservation headlands (i.e., field borders) within agricultural landscapes have been shown to provide essential, arthropod-rich habitat for chicks (Potts 1986, Sotherton 2000). Within the United States, conservation buffers such as field borders may provide similar benefits to northern bobwhite chicks. Palmer et al. (2001) demonstrated greater foraging rates by northern bobwhite chicks within no-till soybean fields, soybean field edges, and fallow communities than conventionally tilled fields suggesting that these conservation practices may ultimately impact local northern bobwhite populations through greater chick survival and recruitment. Other researchers (Blumberg and Crossley 1983, House and Stinner 1983, Palmer et al. 2001) have suggested that residual vegetation within no-till fields might provide habitat for many arthropods, thereby increasing foraging value for galliforms. During the first year of our study, field borders used in foraging trials were in their first growing season following establishment. As such, vegetation density was sparse and ground debris was minimal. Severe drought conditions during that initial season stunted vegetation growth within field borders, further contributing to minimal substrate for arthropods. However, chick foraging rates did not differ between field border and rowcrop habitats in subsequent years (2001 and 2002), even as the vegetation in the field border developed and ground debris accumulated. In soybean fields, we detected subtle differences in arthropod abundance in relation to distance from field edge. Similar “edge effects” in arthropod abundance within agricultural fields is well documented using conventional sampling devices (Duelli et al. 1990, Bedford and Usher 1994, White et al. 1995, Sorenson and Outward 1999). Although conservation headlands and field borders may supply abundant arthropods for chicks in some landscapes, during our study early successional (<3 years old) field borders did not provide more arthropods than rowcrops fields.
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Educational & Outreach Activities
To date, we have provided popular articles addressing benefits of field border practices and our current research to the following outlets: Alabama Wildlife Federation, Delta F.A.R.M., Delta Wildlife, and Mississippi Wildlife Issues. Additionally, in May 2001 we conducted a Buffer Short Course. This meeting, hosted by the Forest and Wildlife Research Center, MSU and sponsored by the USDA-NRCS Wildlife Habitat Management and Watershed Science Institutes featured scientists and policy experts from around the country presenting information on technical specifications for implementation of conservation buffers and findings of recent and ongoing research of the benefits of conservation buffers. Approximately 60 USDA-NRCS biologists, conservationists, and agronomists throughout the Southeast attended. The short course included both scientific presentations and a field tour of a private farm in Clay County, MS on which numerous buffer practices have been implemented. Additionally, results of this research have been or will be made available through the following professional outlets. Additional presentations and manuscripts are anticipated.
Burger, L.W., Jr. Conservation Buffers: Wildlife benefits in southeastern agricultural systems. Research Advances, Forest and Wildlife Research Center, Mississippi State University, Vol. 6, No. 2, April 2002.
Burger, L.W., Jr. Wildlife benefits of conservation buffers in southeastern agricultural systems. Alabama Wildlife Federation. Jan. 2002, Page 26-29.
Smith, M.D. Wildlife buffers for quail. Delta Wildlife. Vol. 9, No. 4, Page 28-29.
Smith, M.D. The bobwhite quail, buffers, borders, and water quality. The Delta Steward. Delta F.A.R.M. Vol. 3, No. 3. Fall 2001. Page 2-3.
Smith, M.D. Research Studies: Benefits of buffers for quail. Wildlife Issues. Mississippi Department of Wildlife, Fisheries, and Parks. Volume 1, Issue 2. Page 14.
Smith, M.D., P.J. Barbour, L.W. Burger, Jr., and S.J. Dinsmore. 2004. Density and diversity of overwintering birds in managed field borders in Mississippi. (In prep).
Smith, M.D., and L. Wes Burger, Jr. 2004. Use of imprinted northern bobwhite chicks to assess habitat-specific arthropod availability. Wildlife Society Bulletin (In review).
Smith, M.D., and L. Wes Burger, Jr. 2003. Multi-resolution approach to wildlife habitat modeling using remotely sensed imagery. Proceedings of the Society of Photo-Optical Instrumentation Engineers. 5153:34-43.
Smith, M.D., and L.W. Burger, Jr. Use of imprinted northern bobwhite chicks to assess habitat specific arthropod availability. September 2004, The Wildlife Society 11th Annual Conference, September 2004, Calgary, AB. (submitted)
Barbour, P.J., M.D. Smith, L.W. Burger, Jr. Grassland songbird and northern bobwhite population response to managed field borders in northeast Mississippi. September 2004, The Wildlife Society 11th Annual Conference, Calgary, AB. (accepted)
Barbour, P.J., M.D. Smith, L.W. Burger, Jr., and S.J. Dinsmore. Diversity and density of over-wintering birds in managed agricultural field borders in Mississippi. September 7, 2003, The Wildlife Society 10th Annual Conference, Burlington, VT.
Smith, M.D., and L.W. Burger, Jr. Multi-scale approach to wildlife habitat modeling using remotely sensed imagery. August 7, 2003, SPIE 48th Annual Meeting of the International Symposium on Optical Science and Technology, San Diego, CA.
Smith, M. D. and L. Wes Burger, Jr. Field borders and bobwhite foraging ecology. USDA-NRCS State Biologist Technical Training Shortcourse: Buffers and Wildlife in the Southeast. May 22, 2001, Mississippi State University, MS
Burger, L. W., Jr. Economic, agronomic, and ecological costs/benefits of field border management practices in agricultural systems of Mississippi. USDA-NRCS State Biologist Technical Training Shortcourse: Buffers and Wildlife in the Southeast. May 22, 2001, Mississippi State University, MS
Smith, M.D., and L. Wes Burger, Jr. Use of human imprinted northern bobwhite chicks to measure invertebrate availability. 9th Annual Meeting of the Southeast Quail Study Group, 25-28 August, 2003. Potosi, MO.
During our study, we provided farmers with an $83.00/acre/year rental payment for areas placed in experimental field borders. Despite this financial incentive, most farmers remained skeptical of the benefits of field border practices and only implemented them because of the economic incentive. However, as the study progressed and farmers were presented with study results (particularly yield data), their perceptions of field borders changed dramatically. With results of the yield monitoring portion of this study, one farmer was able to clearly see the costs (relative to the rental payment) associated with farming along non-bordered field edges due to consistently lower yields. This farmer was incurring a $75.00/acre/year net loss when farming along non-bordered field edges adjacent to wooded hedgerows. In contrast, the producer could receive an $83.00/acre/year conservation incentive payment yielding a net gain of $158.00/acre/year. In fact, this producer wished his field borders were 3 times wider than those used in this study! Another farmer was so impressed with the wildlife response to field borders that he established field borders on all of the remaining fields on his farm with no incentive payment. By the end of our study, all farmers elected to retain their field borders even though rental payments were no longer provided.