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Effects of ground cover on tree survival and growth in filter strips of the Cornbelt Region of the midwestern US
_Agriculture r~cosystems Environment
E LS E V I E R
Agriculture,Ecosystemsand Environment53 (1995) 263-270
Effects of ground cover on tree survival and growth in filter strips of the Cornbelt Region of the midwestern US A . R . G i l l e s p i e ~'*, B . K . M i l l e r ~, K . D . J o h n s o n b aDepartment of Forestryand Natural Resources, Purdue University, WestLafayette, IN 47907-1159, USA bAgronomy Department, Purdue University, WestLafayette. IN 47907-1159, USA
Accepted17 November1994
Abstract Growing concern for non-point source pollution in agricultural watersheds has generated alternative agronomic practices such as filter strips that minimize off-site movement of farm chemicals and sediment. Guidelines for establishment of filter strips in the Midwest region of the US are few with respect to the interplanting of fine hardwood tree species that can provide additional income to farm owners as well as site protection. This study was undertaken to discern the effects of different herbaceous cover types on tree growth and survival when interplanted. Ladino clover ( Trifolium repens L.) and orehardgrass (Dactylis glomerata L.) were sown and seedlings of three tree species, green ash (Fraxinus pennsylvanica Marsh.), black walnut (Juglans nigra L.), and red oak (Quercus rubra L.) were planted within each cover type to examine the performance of these integrated covertree systems. A series of plots containing the native mix of annual and perennial weed species was used as a control. Height and stem caliper of the trees were taken for 4 years. Additionally, habitat quality for bird species was assessed with respect to the corn (Zea mays L ) crop the filter strips replaced. Results indicated that cover type had little influence on tree growth and survivel when weed control adjacent to seedlings was effective. Compared with the native weed population, clover and grass covers allowed equal height growth of '.tees, providing no greater competition but higher management costs. For habitat quality, filter strips provided better habitat for birds when compared with corn. Thus, the construction of filter strips with tree species along streams or drainage ditches can take several forms that can serve to filter excess nutrients and sediment. Keywords:America.UnitedStatesof; Groundcover;Filterstrips
1. Introduction At the time o f settlement of the American upper Midwest in the early 1800s, pioneers found much o f the landscape to be a virtually impenetrable swamp. With the invention o f the steam-powered dredge and the mass production o f drainage tile, the landscape has been transformed into some of the most productive agricultural !and in the world. * Correspondingauthor. 0167-8809/95/$09.50 © 1995 ElsevierScienceB.V.All rightsreserved SSDIOI67-8809(94)OO577-X
The result is a large network of drainage ditches connecting hundreds of thousands of hectares o f agricultural lands to major watersheds of the Great Lakes and the Mississippi river. This cropland-drainage interface has become the focus of research in the iastdecade, primarily due to the importance o f the interface in controlling non-point source pollution (Lowrance et al., 1985). Pollution occurs in the form of cropland sediment runoff (Cooper et al., 1987; Kuen zler, i 989 ) and, in the Eastern Combelt Region, sediment is the predominant water pollutant from non-point sources
264
A.R. Gillespie et al. ~Agriculture, Ecosystems and Environment 53 ~1995) 263-270
Fig. I. Conditionof Indiana.USAfilterstripstudysite beforeplantingin 1990.Notepreviouscroppingup to ditchmarginat centerright. (Brichford et al., 1993). In addition to sediment, nutrients remain a pollution problem from agricultural operations. Nitrogen, particularly nitrate-nitrogen, and phosphorus often enter streams and drainage ditches, contributing m eutrophication of waterways (Jacobs and Gilliam, 1985; Cooper and Gilliam, 1987). Agricultural operations may also contribute animal wastes and pesticides to surrounding watersheds at the cropland-drainage interface (Briehford et al., ! 993 ). Researchers and professionals are examining ways m manipulate this interface to optimize system performance in removing poilutan,s. Management interventions include the planting of cover crops or trees, combining cover types, managing the width of this riparian area, restoring and managing native ecosystems adjacent to streams or ditches and a host of other management techniques. Planted trees or natural riparian forest can be effective in reducing sediment and nutrient loads (Peterjohn and Correll, 1984; Lowrance et al., 1984; Fail et al., 1987) as well as grass filter strips and associated ecosystems (Osborne and Kovacic, 1993). In the midwestem US, the planting of trecs on former crop fields is becoming more common under various state and federal agriculture and forestry support programs. Normally, herbaceous cover is almost eliminated at establishment to provide an optimal
growing envirenment for newly planted tree seedlings. Annual and perennial weeds slowly invade but foresters feel that such weed encroachment late in the season is of little consequence (Seifert, 1991). However, an established vegetative cover between rows of trees is required to meet USDA Soil Conservation Service vegetative filter strip standards. Our study was initiated to provide guidelines for establishing filter strips composed of both herbaceous cover types and trees. The objectives were to develop a system that would ( 1) use a common cover type that would not inhibit tree establishment and growth, (2) provide beneficial wildl~#e cover, (3) be acceptable to farmers in terms of familiar species and low maintenance, and (4) provide the necessary soil erosion control. Thus, a legume and grass cover crop, both having a low structure, were selected for testing with three fine hardwood species to determine tree growth and survival.
2. Methods This study was conducted in the state of Indiana at the Purdue University Throckmorton Ag-iculturai Center located in Tippecanoe County (40°17.5'N,
A.R. Gillespie et aL /Agriculture, Ecosystems and Environment 53 (1995) 263-270
Orchardgrass
Clover
Control
2.4 m
3mr
265
50 m
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f Measurement Plot
Drainage Ditch
O • Oak W • Walnut A • Ash
Fig. 2. One of three treatment blocks of the study design.
86°54'W). This region of the US Midwest is located at what was the transition zone of the tallgrass prairie and the eastern hardwood forest at the time of settlement. The planting trial was established adjacent to the main ditch draining the farm in a field that had been cropped in corn the previous year. This field had not been tilled subsequent to cropping, but was disked prior to our spring 1990 planting (Fig. I). The soil series in the trial area is a SIoan clay loam (fine-loamy, mixed, mesic, fluvaquentic haplaquoll) consisting of neutral alluvium that is dark grayish-brown with yellowishbrown mottles below 50 cm. Slope is 0-3%. Annual rainfall is 972 mm with average daily winter temperatures of - 2°(= and average daily summer temperatures of 23°C. Three valuable hardwood tree species were planted in the trial area parallel to the drainage ditch using 10 bare-root seedlings. The species included green ash ( Fraxinus pennsylvanica Marsh.), black walnut (Juglans nigra L.), and red oak (Quercus rubra L.). Three rows of each species were planted with the species requiring the wettest soils (ash) located adjacent to the ditch. Walnut, requiring moist sites but good drainage, w~-, planted next to the ash rows, and oak was planted farthest from the drainage ditch. Tree spacing in the
plots was 2.4 m between trees in a row and 3 m between rOWS.
Immediately following tree planting, a 1.3 m band of herbicide was applied centered on tree rows. The herbicide mixture included 2,24 kg ha- i Princep (simazine), 3.36 kg ha- ' Surflan (olTzalin), and 2.24 kg ha-i Roundup (glyphosate). Nine plots, 0.15 ha in size (30 m X 50 m ), were delineated over the tree planting and three ground cover treatments randomly sown with three replications. The cover treatments included a control (the mix of native weeds ), ladino clover (Trifolium repens L.) cover, and orchardgrass (Dactylis glomerata L.), This layout of treatments provided a 30 m wide filter strip divided into three replications in a randomized block design (Fig. 2). Weed growth was vigorous the first growing season and an additional banded herbicide application was applied in July of 1990 (Fig. 3). This application consisted of 2.24 kg ha- =simazine, !. 12 kg ha- ' atrazine, and 2.24 kg ha- i glyphosate. In subsequent years, herbicide was applied only once during the growing season in April, again in bands, at a rate of 4.48 kg ha-i simazine and 1.12 kg ha-I glyphosate. In the second and third growing seasons, the percent of bare ground and cover of different species in the treatment bands
266
A.R. GiUespie et al. ~Agriculture, Ecosystems and Environment 53 (1995) 263-270
Fig. 3. Weed growthin the filterstripsduringJuly of 1990._':'equiringa ,secondherbicideapplicationfor control. was evaluated monthly for herbicide effectiveness. In addition to herbicide treatment, mowi:~g was conducted once each August as recommendi~d by foresters in the region. At the end of each growing season, from 1990 to 1993, tree height was measured and recorded to determine cover type treatment effects on tree growth and survival. Stem caliper (diameter at ground level) was measured annually after rite initial growing season to determine stem diameter growth. For tree response to cover type treatments, only the center row o f each tree species planting was measured. Originally, ten measurement trees were delineated in the center row of each plot. However, tree damage due to mowing and deer browsing necessitated the measurement of the five tallest trees as a measure of treatment potential. To compare filter strip structure for wildlife habitat with that of corn row cropping, transects among both were conducted monthly in the summer o f 1991 and bird species counts were taken at six sample points at 50-m intervals with sight and bird song survey techniques (Overton, 1971 ). 3. Results a n d discussion
The pattern of herbicide effectiveness during 1991 and 1992 was similar for all cover types as evidenced
by the amount of bare ground (Table 1). Early season control o1 weeds adjacent to tree seedlings was successful. As the growing season progressed, weed pressure increased with the germination of warm season grasses such as foxtail ( S e t a r i a spp.) (Table 2). Repeated measures analysis of variance found no significant differences ( P > 0 . 0 5 ) in weed control adjacent to tree seedlings among cover types. In late July and August, when tree height growth is normally completed for the species used in this study (Kramer and Kozlowski, 1979), weed growth significantly increased ( P < 0 . 0 5 ) for all treatments with, presumably, little effect on tree growth and survival (Seifert, 1991). Analysis of variance was used to examine height growth, caliper increase, total height and caliper, and seedling survival for the three tree species. Differences among the three cover types were tested. No differences in survival were found among the cover treatments as survival was very high among all plots. In general, height increments increased in magnPude each year of the four growing seasons o f the study, with red oak having the smallest increments, as is typical for this slow-growing genus (Fig. 4). This was also the pattern for caliper increments in the third and fourth years (Table 3). The only significant difference ( P < 0.05) in height growth found was in the fourth growing sea-
A.R. Gillespie et al. ~Agriculture. Ecosystems and Environment 53 (1995) 263-270
267
Table I Mean proportion(and standarddeviation)of bare ground,due to herbicideapplicationsin three filterstripcover typesin Indiana,USA Covertype
Percentbareground 1991
Control (Weeds) Ladinoclover Orchardgrass
1992
June
July
August
June
July
August
78.9a (13.4) 62.1b (20.1) 64.2ab (14.3)
61.3a (9.7) 45.4a (25.7) 54.9a ( 15.I )
59Aa (9.5) 44.8a (25.1) 54.1a (16.7)
49.3a (13.8) 41.6a (24.2) 47.8a (16.9)
5.0b (5.6) 13.3ab (16.6) 17.8a (11.5)
10.6a (5.3) l,~,.4a (8.8) 15.0a (93)
For each date, valuesfollowedby differentleuer~.aresignificz.~,~'.lydiffe.,ent.(LSD test, P<0.5). son. Here, walnut height growth in control plots lagged behind growth in the other treatments due to some wind damage during the growing season. Thus, no real difference was found in height increment due to the different cover types. This is reflected in the height of trees at the end of 4 years growth (Fig. 4). Of significance is the similarity in clover and grass cover treatments with the control weed population. Additionally, total caliper is similar between the planted cover plots and the control for ash and oak. For walnut, the control plots had a significantly larger caliper (Table 3). These data support the observation by regional foresters that a native weed mix provides little competition to planted seedlings if weed control is applied only to the area adjacent to the seedling. This is also due to the heterogenous pattern of native weeds, with normal clumping reducing weed pressure on a given area o f
land. Additionally, establishment costs are reduced as no cover crop would be required. This is the normal tree planting prescription in the region when erosion and sediment filtering are not a concern. However, in a filter strip design, the establishment o f a suitable cover is desirable and, at the time our trial was installed, the USDA Soil Conservation Service had a cover crop requirement. The parity of tree growth wi~in the different treatments, orconversely, the lackofdifferentialeovercoml~etition, provides a topic for some speculation. In addition to the lack of competition, no facilitation o f tree growth was seen with the nitrogen-fixing legume co,Ter. These two observations suggest that, in these filter strip systems, nutrient resources and likely water resc,urces, are not restricting. The same system comparison placed high on a sandy ridge would undoubb
Table 2 Exampleof weedcontrolsuccessin tree rows withJune 1991 distributionof weedcoverin three filterstrip covertypes in Indiana,USA Species
Bare ground Trifolium repens L. Dac~. lus glomerata L. Convolvulus arvensis L. Cirsium art,ense (L.) Scop. C.vperus esculentus L. Setaria spp. Rumex crispus L. Arr,aranthus retroflexus L. Abutilon theophrasti Medic.
Other minorspecies
Percentcover Control
Clover
Orchardgrass
79
62
64
0 0 3
5 0 4
0 0 4
I 6 7
I 10 II
I 16 9
0 2
I 3
0 2
I I
0 3
I 3
268
A.R. Gillespie et aL /Agriculture. Eco~'stems and Enriroranent 53 (1995) 263-270
Table 3 Third- and founh-yearcalipergrowthand total caliperat 4 yeats (and standard deviation) for three tree speciesinterplanted in three filterstrip covertypes in Indiana.USA Tree species
Green ash
Cover
Control Clover Orehardgrng~
Black walnut
Control Clover Orchardgr~ss
Red oak
Control Clover Orchardgr~ss
Caliper growth ( mm per year)
Total caliper (mm)
3rd year
4th year
18.Ia (6.0) 18.Ia (5.0) 18.2a (4.9)
22.5a (4.9) 22.9a (5.2) 24.8a (5.2)
66.0a (13.3) 62.6a (8.4) 65.2,1 (8.4)
15.6a (5.1) 14.9a (5.3) 12.3a (3.5)
17.3a (4.2) 13.2a (7.5) 12.9a (7.2)
54.7b (8.7) 47.lab (10.6) 42.5a (9.6)
4.6a (2.2) 6.3a (3.6) 5.5a (3.6)
9.9a (3.23 8.9a (3.6) I 1.6a (6.1)
25.3a (4.2) 25.3a (6.7) 30.Oa (8.2)
Values followedby different lev,'ersare significantlydifferent ( LSD test. P < 0.05). edly show differem results. Thus, the movement of drainage waters (and the nutrien,,z they hold) to these riparian areas low on the landscape presumably plays an important role in the adaptability of filter strip systems to different plant components and their integration. This element is critical in allowing system design to be tailored to farmer needs. Impacts of filter strip systems on environmental quality extc~d beyond water quality issues. "Ihese systems provide b,~th feeding and nesting habitat for a variety of animal and insect species. Wildlife studies within agricultural landscapes show that corridors with tree cover play a crucial role in animal movements between forest fragments (see e.g. Noss, 1987). For woodland birds, movement between wooded corridor areas and adjacent agricultural fields was seen to be greater than movement from woodlands to adjacent fields (Wegner and Merriam, 1979), underscoring the importance of systems such as filter strips with tree cover. In the present study, nests of several bird species were located in the herbaceous vegetative cover when the filter strip was surveyed monthly in 1991. Darling
June and July, five nests of four bird species were found in clover and five nests of three bird species were found in orchardgrass cover. Only one nest was found in the control treatment cover. The adjacent corn crop provided no such nesting habitat. When bird use of corn and filter strip habitat was compared on a monthly basis in 1991, 13 species with 118 individuals were found to use the filter strip and 11 species with 49 individuals were found in the corn planting over the growing season Table 4 Diversity of bird species and monthly use of corn and filter strip habitatsduring 1991, Indiana,USA Habitat
Month Numberof Numberof MargalefDiversity species individuals Index
Filter strip June II July 9 August 8
79 24 15
2.29 2.52 2.58
Corn
34 10 5
2.55 1.75 1.86
June 10 July 5 August 4
A.R. Gillespie et al. /Agriculture. Ecosystems and Environment 53 (1995) 263-270
GREEt~SH ~
A
i i/J[
. sL,~g
v~t.NTu
•
REDCU~K
A,~auat~ e a t aacw'r, ccwy,;
: ! |1" coma~
CLO~
In(no. of individuals) ]: Magurran, 1988) indicated that while both corn and filter strip systems were equally diverse in the early summer, the diversity of bird use in the latter part of the growing season declined in corn but remained diver.';e in the filter strip. The low, clumped sw.~c~e of the filter strip cover crops provided the necessary structure for nest building not found in the corn. Additionally, the stable perennial structure of trees also provide~ nes;.i~g e~portunities not found in corn. Thus, these mixed-species hirer strip systems can aid farmers seeking to diversify wildlife and wildlife habitat in this region of the US. 4. Conclusions
i! ~"/~i~~~~TOTAL HI~7|~) i! 1
269
Though tree planting without cover would be cheaper, the ability of these fine hardwood species to grow equally well with and without a cover crop allows the option of combining these components for alternative objectives. Our results suggest that such an integration would not slow tree growth in areas such as dralnageways where water and nutrients are not limiting. Thus, selection of the system of choice (e.g. cover crop alone, trees alone, mixed cover and trees, etc.) would be a function of the system's ability to meet farmer objectives such as generating additional income, reducing nutrient and sediment inputs to streams, site stabilization, or improving wildlife habitat among others. However, it remains to be seen whether the selection of a legume cover crop for management reasons might reduce the system's ability to filter nitrates or other nutrients from draining waters. These are the interactions of system design and function that remain as research tasks as farmers implement current recommendations.
~¢~amaAss Acknowledgement
• Fig. 4. Annual height growth and total height o f tree seedlings after
4 yearsin a filterstripstudy, Indiana.USA. (Table 4). The number of individuals recorded in the filter strip was always at least twice that recorded in the corn each month. Bird use varied by month, exhibiting a normal decline over time. Combining species richness and abundance in the Margalef Diversity Index ( [ Diversity -- (no. of species) /
Contribution from the Department of Forestry and Natural Resources and Department of Agronomy, Purdue University, West Lafayette, IN 47907, Agriculture Research Program Journal Paper No. 14289. Referenc~ Brichford, S.L.. Joem. B.C. and Whitford, F.. 1993. A ~ c u l t u m ' s
effectonenvironmentalquality:key managementis.ques.Purdue
270
A.R. Gillespie el al. /Agriculture, Ecosystems and Ern,ironment 53 (1995) 263-270
Cooperative Exzension Bulletin WQ-17, Purdue University, WeN Lafayeue. IN. 4 pp. Cooper.J.R. and Gilliam. J.W.. 1987. Phosphorus rudistribution from cultivated fields into riparian areas. Soil Sei. Soc. Am. J., 51: 1600-1604. Cooper. J.R.. Gill;.am. J.W.. Daniels, R.B. and Robarge, W.P., 1987. Riparian areas as filters for agricultural ~ i m e n l . Soil Sci. Soc. Arn. J.. 5 I: 4 !6-420. Fail. J.L.. Haines. B.L. and Todd. R.L.. 1987. Riparian forest cornmunities and Ihe~r role in nutrient conservation in an agricultural watershed. Am. J. Alternative Agric.. 2:114-120. Jacobs, T.C. and Gilliam. J.W.. 1985. Riparian loses of nitrute from agricultural drainage waters. J. Environ. Qual., 14: 472-478. Krnmer, P.J. and Kozlowski. T.T., 1979. Physiology of Woody Planls. Academic Press. New York. 811 pp. Kuenzler. EJ.. 1989. Value of forested watlands as filters for scdimenLs and nutrients. USDA For. Serv. Gco. Tech. Rep. SE-50, Asheville. NC. pp. 85-96. Lowrance. R., Todd. R., Fail, J.. Hendriekson. O.. Leonard. R. and Asmussen, L., 19~4. Riparian fnrnsls o,s nutrient filters in agricultural watersheds. BioScience. 34: 374-377.
Lowrance, R., Leonard, R. and Sheridan. J.. 1985. Managing riparian ecosystems to control nonpoint pollution. J. Soil Water Conserv., 40: 87-91. Magurtan, A.E., 1988. Ecological Diversity and its Measurement. Princeton University Press, Princeton, New Jer--~ey, 179 pp. Noss. R.F., 1987. Corridors in real landscapes: a reply to Simherloff and Cox. Conscrv. Biol., I." 159-164. Osborne. L.L. and Kovacie. D.A., Iq93. Riparian vegetated buffer strips m water-quality restor~on and stream management. Freshwater Biol.. 29: 243-258. Overton, S.W., ! 97 !. Estimating the numbers of animals in wildlife pqpulations, in: R.H. Giles (Editor), Wildlife Management Techniques. ~ Wildlife Society, Washington. DC. pp. 403456. Pezerjoho. W.T. and Cormll, D.L., 1984. Nutrient dynamics in an agricu!tural watershed: observations on the role of a riparian forest. Ecology, 65: 1466-1475. Seifert, J.R.o 1991. Growing Christmas Trees. Purdue Cooperative Extension Bulletin FNR- ! 18, Purdue University, West Lafayette, IN, 8 pp. Wegner, J.F. and Merriam, G., 1979. Movements by birds and small mammals between a wood and adjoining farmland habitats. J. Appl. Ecol., 16: 349-357.
E LS E V I E R
Agriculture,Ecosystemsand Environment53 (1995) 263-270
Effects of ground cover on tree survival and growth in filter strips of the Cornbelt Region of the midwestern US A . R . G i l l e s p i e ~'*, B . K . M i l l e r ~, K . D . J o h n s o n b aDepartment of Forestryand Natural Resources, Purdue University, WestLafayette, IN 47907-1159, USA bAgronomy Department, Purdue University, WestLafayette. IN 47907-1159, USA
Accepted17 November1994
Abstract Growing concern for non-point source pollution in agricultural watersheds has generated alternative agronomic practices such as filter strips that minimize off-site movement of farm chemicals and sediment. Guidelines for establishment of filter strips in the Midwest region of the US are few with respect to the interplanting of fine hardwood tree species that can provide additional income to farm owners as well as site protection. This study was undertaken to discern the effects of different herbaceous cover types on tree growth and survival when interplanted. Ladino clover ( Trifolium repens L.) and orehardgrass (Dactylis glomerata L.) were sown and seedlings of three tree species, green ash (Fraxinus pennsylvanica Marsh.), black walnut (Juglans nigra L.), and red oak (Quercus rubra L.) were planted within each cover type to examine the performance of these integrated covertree systems. A series of plots containing the native mix of annual and perennial weed species was used as a control. Height and stem caliper of the trees were taken for 4 years. Additionally, habitat quality for bird species was assessed with respect to the corn (Zea mays L ) crop the filter strips replaced. Results indicated that cover type had little influence on tree growth and survivel when weed control adjacent to seedlings was effective. Compared with the native weed population, clover and grass covers allowed equal height growth of '.tees, providing no greater competition but higher management costs. For habitat quality, filter strips provided better habitat for birds when compared with corn. Thus, the construction of filter strips with tree species along streams or drainage ditches can take several forms that can serve to filter excess nutrients and sediment. Keywords:America.UnitedStatesof; Groundcover;Filterstrips
1. Introduction At the time o f settlement of the American upper Midwest in the early 1800s, pioneers found much o f the landscape to be a virtually impenetrable swamp. With the invention o f the steam-powered dredge and the mass production o f drainage tile, the landscape has been transformed into some of the most productive agricultural !and in the world. * Correspondingauthor. 0167-8809/95/$09.50 © 1995 ElsevierScienceB.V.All rightsreserved SSDIOI67-8809(94)OO577-X
The result is a large network of drainage ditches connecting hundreds of thousands of hectares o f agricultural lands to major watersheds of the Great Lakes and the Mississippi river. This cropland-drainage interface has become the focus of research in the iastdecade, primarily due to the importance o f the interface in controlling non-point source pollution (Lowrance et al., 1985). Pollution occurs in the form of cropland sediment runoff (Cooper et al., 1987; Kuen zler, i 989 ) and, in the Eastern Combelt Region, sediment is the predominant water pollutant from non-point sources
264
A.R. Gillespie et al. ~Agriculture, Ecosystems and Environment 53 ~1995) 263-270
Fig. I. Conditionof Indiana.USAfilterstripstudysite beforeplantingin 1990.Notepreviouscroppingup to ditchmarginat centerright. (Brichford et al., 1993). In addition to sediment, nutrients remain a pollution problem from agricultural operations. Nitrogen, particularly nitrate-nitrogen, and phosphorus often enter streams and drainage ditches, contributing m eutrophication of waterways (Jacobs and Gilliam, 1985; Cooper and Gilliam, 1987). Agricultural operations may also contribute animal wastes and pesticides to surrounding watersheds at the cropland-drainage interface (Briehford et al., ! 993 ). Researchers and professionals are examining ways m manipulate this interface to optimize system performance in removing poilutan,s. Management interventions include the planting of cover crops or trees, combining cover types, managing the width of this riparian area, restoring and managing native ecosystems adjacent to streams or ditches and a host of other management techniques. Planted trees or natural riparian forest can be effective in reducing sediment and nutrient loads (Peterjohn and Correll, 1984; Lowrance et al., 1984; Fail et al., 1987) as well as grass filter strips and associated ecosystems (Osborne and Kovacic, 1993). In the midwestem US, the planting of trecs on former crop fields is becoming more common under various state and federal agriculture and forestry support programs. Normally, herbaceous cover is almost eliminated at establishment to provide an optimal
growing envirenment for newly planted tree seedlings. Annual and perennial weeds slowly invade but foresters feel that such weed encroachment late in the season is of little consequence (Seifert, 1991). However, an established vegetative cover between rows of trees is required to meet USDA Soil Conservation Service vegetative filter strip standards. Our study was initiated to provide guidelines for establishing filter strips composed of both herbaceous cover types and trees. The objectives were to develop a system that would ( 1) use a common cover type that would not inhibit tree establishment and growth, (2) provide beneficial wildl~#e cover, (3) be acceptable to farmers in terms of familiar species and low maintenance, and (4) provide the necessary soil erosion control. Thus, a legume and grass cover crop, both having a low structure, were selected for testing with three fine hardwood species to determine tree growth and survival.
2. Methods This study was conducted in the state of Indiana at the Purdue University Throckmorton Ag-iculturai Center located in Tippecanoe County (40°17.5'N,
A.R. Gillespie et aL /Agriculture, Ecosystems and Environment 53 (1995) 263-270
Orchardgrass
Clover
Control
2.4 m
3mr
265
50 m
oooooooooooooooo00o00o0oooooboo56-00ooo0~0~6o oooooo0006ooooooooo0ooooooooooooooo0o66001ooo ooobo6o0b0oooooooo0b00do0ooooooooob00b~6ooo WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
wwwwww~ww~wwwwwwwwwwwwwwwwwwwwwwwwwww~wwwww www~wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAA~AAAAAAAAAAAAAAAAAAiAAA
J
AAA'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
f Measurement Plot
Drainage Ditch
O • Oak W • Walnut A • Ash
Fig. 2. One of three treatment blocks of the study design.
86°54'W). This region of the US Midwest is located at what was the transition zone of the tallgrass prairie and the eastern hardwood forest at the time of settlement. The planting trial was established adjacent to the main ditch draining the farm in a field that had been cropped in corn the previous year. This field had not been tilled subsequent to cropping, but was disked prior to our spring 1990 planting (Fig. I). The soil series in the trial area is a SIoan clay loam (fine-loamy, mixed, mesic, fluvaquentic haplaquoll) consisting of neutral alluvium that is dark grayish-brown with yellowishbrown mottles below 50 cm. Slope is 0-3%. Annual rainfall is 972 mm with average daily winter temperatures of - 2°(= and average daily summer temperatures of 23°C. Three valuable hardwood tree species were planted in the trial area parallel to the drainage ditch using 10 bare-root seedlings. The species included green ash ( Fraxinus pennsylvanica Marsh.), black walnut (Juglans nigra L.), and red oak (Quercus rubra L.). Three rows of each species were planted with the species requiring the wettest soils (ash) located adjacent to the ditch. Walnut, requiring moist sites but good drainage, w~-, planted next to the ash rows, and oak was planted farthest from the drainage ditch. Tree spacing in the
plots was 2.4 m between trees in a row and 3 m between rOWS.
Immediately following tree planting, a 1.3 m band of herbicide was applied centered on tree rows. The herbicide mixture included 2,24 kg ha- i Princep (simazine), 3.36 kg ha- ' Surflan (olTzalin), and 2.24 kg ha-i Roundup (glyphosate). Nine plots, 0.15 ha in size (30 m X 50 m ), were delineated over the tree planting and three ground cover treatments randomly sown with three replications. The cover treatments included a control (the mix of native weeds ), ladino clover (Trifolium repens L.) cover, and orchardgrass (Dactylis glomerata L.), This layout of treatments provided a 30 m wide filter strip divided into three replications in a randomized block design (Fig. 2). Weed growth was vigorous the first growing season and an additional banded herbicide application was applied in July of 1990 (Fig. 3). This application consisted of 2.24 kg ha- =simazine, !. 12 kg ha- ' atrazine, and 2.24 kg ha- i glyphosate. In subsequent years, herbicide was applied only once during the growing season in April, again in bands, at a rate of 4.48 kg ha-i simazine and 1.12 kg ha-I glyphosate. In the second and third growing seasons, the percent of bare ground and cover of different species in the treatment bands
266
A.R. GiUespie et al. ~Agriculture, Ecosystems and Environment 53 (1995) 263-270
Fig. 3. Weed growthin the filterstripsduringJuly of 1990._':'equiringa ,secondherbicideapplicationfor control. was evaluated monthly for herbicide effectiveness. In addition to herbicide treatment, mowi:~g was conducted once each August as recommendi~d by foresters in the region. At the end of each growing season, from 1990 to 1993, tree height was measured and recorded to determine cover type treatment effects on tree growth and survival. Stem caliper (diameter at ground level) was measured annually after rite initial growing season to determine stem diameter growth. For tree response to cover type treatments, only the center row o f each tree species planting was measured. Originally, ten measurement trees were delineated in the center row of each plot. However, tree damage due to mowing and deer browsing necessitated the measurement of the five tallest trees as a measure of treatment potential. To compare filter strip structure for wildlife habitat with that of corn row cropping, transects among both were conducted monthly in the summer o f 1991 and bird species counts were taken at six sample points at 50-m intervals with sight and bird song survey techniques (Overton, 1971 ). 3. Results a n d discussion
The pattern of herbicide effectiveness during 1991 and 1992 was similar for all cover types as evidenced
by the amount of bare ground (Table 1). Early season control o1 weeds adjacent to tree seedlings was successful. As the growing season progressed, weed pressure increased with the germination of warm season grasses such as foxtail ( S e t a r i a spp.) (Table 2). Repeated measures analysis of variance found no significant differences ( P > 0 . 0 5 ) in weed control adjacent to tree seedlings among cover types. In late July and August, when tree height growth is normally completed for the species used in this study (Kramer and Kozlowski, 1979), weed growth significantly increased ( P < 0 . 0 5 ) for all treatments with, presumably, little effect on tree growth and survival (Seifert, 1991). Analysis of variance was used to examine height growth, caliper increase, total height and caliper, and seedling survival for the three tree species. Differences among the three cover types were tested. No differences in survival were found among the cover treatments as survival was very high among all plots. In general, height increments increased in magnPude each year of the four growing seasons o f the study, with red oak having the smallest increments, as is typical for this slow-growing genus (Fig. 4). This was also the pattern for caliper increments in the third and fourth years (Table 3). The only significant difference ( P < 0.05) in height growth found was in the fourth growing sea-
A.R. Gillespie et al. ~Agriculture. Ecosystems and Environment 53 (1995) 263-270
267
Table I Mean proportion(and standarddeviation)of bare ground,due to herbicideapplicationsin three filterstripcover typesin Indiana,USA Covertype
Percentbareground 1991
Control (Weeds) Ladinoclover Orchardgrass
1992
June
July
August
June
July
August
78.9a (13.4) 62.1b (20.1) 64.2ab (14.3)
61.3a (9.7) 45.4a (25.7) 54.9a ( 15.I )
59Aa (9.5) 44.8a (25.1) 54.1a (16.7)
49.3a (13.8) 41.6a (24.2) 47.8a (16.9)
5.0b (5.6) 13.3ab (16.6) 17.8a (11.5)
10.6a (5.3) l,~,.4a (8.8) 15.0a (93)
For each date, valuesfollowedby differentleuer~.aresignificz.~,~'.lydiffe.,ent.(LSD test, P<0.5). son. Here, walnut height growth in control plots lagged behind growth in the other treatments due to some wind damage during the growing season. Thus, no real difference was found in height increment due to the different cover types. This is reflected in the height of trees at the end of 4 years growth (Fig. 4). Of significance is the similarity in clover and grass cover treatments with the control weed population. Additionally, total caliper is similar between the planted cover plots and the control for ash and oak. For walnut, the control plots had a significantly larger caliper (Table 3). These data support the observation by regional foresters that a native weed mix provides little competition to planted seedlings if weed control is applied only to the area adjacent to the seedling. This is also due to the heterogenous pattern of native weeds, with normal clumping reducing weed pressure on a given area o f
land. Additionally, establishment costs are reduced as no cover crop would be required. This is the normal tree planting prescription in the region when erosion and sediment filtering are not a concern. However, in a filter strip design, the establishment o f a suitable cover is desirable and, at the time our trial was installed, the USDA Soil Conservation Service had a cover crop requirement. The parity of tree growth wi~in the different treatments, orconversely, the lackofdifferentialeovercoml~etition, provides a topic for some speculation. In addition to the lack of competition, no facilitation o f tree growth was seen with the nitrogen-fixing legume co,Ter. These two observations suggest that, in these filter strip systems, nutrient resources and likely water resc,urces, are not restricting. The same system comparison placed high on a sandy ridge would undoubb
Table 2 Exampleof weedcontrolsuccessin tree rows withJune 1991 distributionof weedcoverin three filterstrip covertypes in Indiana,USA Species
Bare ground Trifolium repens L. Dac~. lus glomerata L. Convolvulus arvensis L. Cirsium art,ense (L.) Scop. C.vperus esculentus L. Setaria spp. Rumex crispus L. Arr,aranthus retroflexus L. Abutilon theophrasti Medic.
Other minorspecies
Percentcover Control
Clover
Orchardgrass
79
62
64
0 0 3
5 0 4
0 0 4
I 6 7
I 10 II
I 16 9
0 2
I 3
0 2
I I
0 3
I 3
268
A.R. Gillespie et aL /Agriculture. Eco~'stems and Enriroranent 53 (1995) 263-270
Table 3 Third- and founh-yearcalipergrowthand total caliperat 4 yeats (and standard deviation) for three tree speciesinterplanted in three filterstrip covertypes in Indiana.USA Tree species
Green ash
Cover
Control Clover Orehardgrng~
Black walnut
Control Clover Orchardgr~ss
Red oak
Control Clover Orchardgr~ss
Caliper growth ( mm per year)
Total caliper (mm)
3rd year
4th year
18.Ia (6.0) 18.Ia (5.0) 18.2a (4.9)
22.5a (4.9) 22.9a (5.2) 24.8a (5.2)
66.0a (13.3) 62.6a (8.4) 65.2,1 (8.4)
15.6a (5.1) 14.9a (5.3) 12.3a (3.5)
17.3a (4.2) 13.2a (7.5) 12.9a (7.2)
54.7b (8.7) 47.lab (10.6) 42.5a (9.6)
4.6a (2.2) 6.3a (3.6) 5.5a (3.6)
9.9a (3.23 8.9a (3.6) I 1.6a (6.1)
25.3a (4.2) 25.3a (6.7) 30.Oa (8.2)
Values followedby different lev,'ersare significantlydifferent ( LSD test. P < 0.05). edly show differem results. Thus, the movement of drainage waters (and the nutrien,,z they hold) to these riparian areas low on the landscape presumably plays an important role in the adaptability of filter strip systems to different plant components and their integration. This element is critical in allowing system design to be tailored to farmer needs. Impacts of filter strip systems on environmental quality extc~d beyond water quality issues. "Ihese systems provide b,~th feeding and nesting habitat for a variety of animal and insect species. Wildlife studies within agricultural landscapes show that corridors with tree cover play a crucial role in animal movements between forest fragments (see e.g. Noss, 1987). For woodland birds, movement between wooded corridor areas and adjacent agricultural fields was seen to be greater than movement from woodlands to adjacent fields (Wegner and Merriam, 1979), underscoring the importance of systems such as filter strips with tree cover. In the present study, nests of several bird species were located in the herbaceous vegetative cover when the filter strip was surveyed monthly in 1991. Darling
June and July, five nests of four bird species were found in clover and five nests of three bird species were found in orchardgrass cover. Only one nest was found in the control treatment cover. The adjacent corn crop provided no such nesting habitat. When bird use of corn and filter strip habitat was compared on a monthly basis in 1991, 13 species with 118 individuals were found to use the filter strip and 11 species with 49 individuals were found in the corn planting over the growing season Table 4 Diversity of bird species and monthly use of corn and filter strip habitatsduring 1991, Indiana,USA Habitat
Month Numberof Numberof MargalefDiversity species individuals Index
Filter strip June II July 9 August 8
79 24 15
2.29 2.52 2.58
Corn
34 10 5
2.55 1.75 1.86
June 10 July 5 August 4
A.R. Gillespie et al. /Agriculture. Ecosystems and Environment 53 (1995) 263-270
GREEt~SH ~
A
i i/J[
. sL,~g
v~t.NTu
•
REDCU~K
A,~auat~ e a t aacw'r, ccwy,;
: ! |1" coma~
CLO~
In(no. of individuals) ]: Magurran, 1988) indicated that while both corn and filter strip systems were equally diverse in the early summer, the diversity of bird use in the latter part of the growing season declined in corn but remained diver.';e in the filter strip. The low, clumped sw.~c~e of the filter strip cover crops provided the necessary structure for nest building not found in the corn. Additionally, the stable perennial structure of trees also provide~ nes;.i~g e~portunities not found in corn. Thus, these mixed-species hirer strip systems can aid farmers seeking to diversify wildlife and wildlife habitat in this region of the US. 4. Conclusions
i! ~"/~i~~~~TOTAL HI~7|~) i! 1
269
Though tree planting without cover would be cheaper, the ability of these fine hardwood species to grow equally well with and without a cover crop allows the option of combining these components for alternative objectives. Our results suggest that such an integration would not slow tree growth in areas such as dralnageways where water and nutrients are not limiting. Thus, selection of the system of choice (e.g. cover crop alone, trees alone, mixed cover and trees, etc.) would be a function of the system's ability to meet farmer objectives such as generating additional income, reducing nutrient and sediment inputs to streams, site stabilization, or improving wildlife habitat among others. However, it remains to be seen whether the selection of a legume cover crop for management reasons might reduce the system's ability to filter nitrates or other nutrients from draining waters. These are the interactions of system design and function that remain as research tasks as farmers implement current recommendations.
~¢~amaAss Acknowledgement
• Fig. 4. Annual height growth and total height o f tree seedlings after
4 yearsin a filterstripstudy, Indiana.USA. (Table 4). The number of individuals recorded in the filter strip was always at least twice that recorded in the corn each month. Bird use varied by month, exhibiting a normal decline over time. Combining species richness and abundance in the Margalef Diversity Index ( [ Diversity -- (no. of species) /
Contribution from the Department of Forestry and Natural Resources and Department of Agronomy, Purdue University, West Lafayette, IN 47907, Agriculture Research Program Journal Paper No. 14289. Referenc~ Brichford, S.L.. Joem. B.C. and Whitford, F.. 1993. A ~ c u l t u m ' s
effectonenvironmentalquality:key managementis.ques.Purdue
270
A.R. Gillespie el al. /Agriculture, Ecosystems and Ern,ironment 53 (1995) 263-270
Cooperative Exzension Bulletin WQ-17, Purdue University, WeN Lafayeue. IN. 4 pp. Cooper.J.R. and Gilliam. J.W.. 1987. Phosphorus rudistribution from cultivated fields into riparian areas. Soil Sei. Soc. Am. J., 51: 1600-1604. Cooper. J.R.. Gill;.am. J.W.. Daniels, R.B. and Robarge, W.P., 1987. Riparian areas as filters for agricultural ~ i m e n l . Soil Sci. Soc. Arn. J.. 5 I: 4 !6-420. Fail. J.L.. Haines. B.L. and Todd. R.L.. 1987. Riparian forest cornmunities and Ihe~r role in nutrient conservation in an agricultural watershed. Am. J. Alternative Agric.. 2:114-120. Jacobs, T.C. and Gilliam. J.W.. 1985. Riparian loses of nitrute from agricultural drainage waters. J. Environ. Qual., 14: 472-478. Krnmer, P.J. and Kozlowski. T.T., 1979. Physiology of Woody Planls. Academic Press. New York. 811 pp. Kuenzler. EJ.. 1989. Value of forested watlands as filters for scdimenLs and nutrients. USDA For. Serv. Gco. Tech. Rep. SE-50, Asheville. NC. pp. 85-96. Lowrance. R., Todd. R., Fail, J.. Hendriekson. O.. Leonard. R. and Asmussen, L., 19~4. Riparian fnrnsls o,s nutrient filters in agricultural watersheds. BioScience. 34: 374-377.
Lowrance, R., Leonard, R. and Sheridan. J.. 1985. Managing riparian ecosystems to control nonpoint pollution. J. Soil Water Conserv., 40: 87-91. Magurtan, A.E., 1988. Ecological Diversity and its Measurement. Princeton University Press, Princeton, New Jer--~ey, 179 pp. Noss. R.F., 1987. Corridors in real landscapes: a reply to Simherloff and Cox. Conscrv. Biol., I." 159-164. Osborne. L.L. and Kovacie. D.A., Iq93. Riparian vegetated buffer strips m water-quality restor~on and stream management. Freshwater Biol.. 29: 243-258. Overton, S.W., ! 97 !. Estimating the numbers of animals in wildlife pqpulations, in: R.H. Giles (Editor), Wildlife Management Techniques. ~ Wildlife Society, Washington. DC. pp. 403456. Pezerjoho. W.T. and Cormll, D.L., 1984. Nutrient dynamics in an agricu!tural watershed: observations on the role of a riparian forest. Ecology, 65: 1466-1475. Seifert, J.R.o 1991. Growing Christmas Trees. Purdue Cooperative Extension Bulletin FNR- ! 18, Purdue University, West Lafayette, IN, 8 pp. Wegner, J.F. and Merriam, G., 1979. Movements by birds and small mammals between a wood and adjoining farmland habitats. J. Appl. Ecol., 16: 349-357.