The Appalachian Region of the USA is characterized by steep, complex terrain and high average annual precipitation (> 1.1 m yr -1). Most of the region is geologically old and soils are highly leached resulting in low pH and nutrient deficiencies for most agricultural production systems. The indigenous vegetation is dominated by species diverse forests. Within the soil a web of tree roots and fungi are very efficient at capturing nutrients from decaying vegetation and on many sites most of the nutrients in the system are contained in the vegetation itself.
Due to the hilly topography, agricultural acreage requiring tillage is restricted to a small percent of the total with forage-based animal production systems dominating. With the conversion of forest to pasture, additions of lime and fertilizer are required on a regular basis to maintain a high level of productivity. The microbiological populations in soils that evolve after conversion to pasture are more strongly dominated by bacteria and are much more nutrient-leaky than the forest soils they replace.
|Rows of black locust planted in a hilly pasture. Light varied by a factor of 5 between mid alley and under trees but forage yield was not significantly different 2 out of 3 years. (Photo courtesy of C.M. Feldhake, USDA-ARS.)|
The most prominent difference between traditional pasture forage production and silvopastures is the presence of trees which decrease solar radiation at the forage level and also modify microclimate. Understanding how forages respond to tree shading is critical in Appalachia since solar radiation is already cloud-attenuated roughly by half. Silvopasture research at the USDA, ARS, Appalachian Farming Systems Research Center initially focused on how system design and age influenced solar radiation partitioning and microclimate modification. It is now moving beyond that to the study of impacts on grazing animals, litter decomposition, and soil processes.
There are several experimental sites that have been developed since Appalachian silvopasture research was started in 1992. Most sites are located near Beaver, WV on a ridge top with shallow soils weathered from sandstone and shale. Two adjacent sites are located near Blacksburg, VA, in cooperation with VA Tech, on a deep alluvial soil. Sites studied so far include:
- A randomly variable density stand of conifers, mostly white pine and red spruce, about 40 years old with an understory of perennial ryegrass and white clover grazed by sheep.
- Thinned second growth hardwood stands, mostly oak and over 50 years old, with an established understory of orchardgrass, perennial ryegrass, and white clover grazed by sheep.
- Gaps created within second growth hardwood stands for studying spatial edge effects on pasture bordering forest. one is 100 ft wide and about 1300 feet long oriented east-west and two are 50 feet wide and 150 feet long. one of the 150 ft gaps was cut into a forest bordering a pasture on the east side and one on the west with both gaps oriented east-west.
- Black locust planted in 30 ft wide rows within a steep pasture watershed dominated by tall fescue. Rows were oriented northeast to southwest.
- Black walnut and honey locust, each planted in a tree density gradient on a hill side pasture dominated by tall fescue. Rows were oriented northeast to southwest. (Blacksburg, VA).
- Black walnut and honey locust planted in 40 wide rows on a hill side pasture dominated by tall fescue and grazed by sheep. Rows were oriented north to south (Blacksburg, VA).
Forages were clipped at all sites for analysis and animal performance was evaluated at sites 1, 2, and 6. Various soil and microclimate parameters were measured depending on the project objectives.
We found that under tree rows, forages received sun early and late in the day in addition to mottled sun during midday. This gave forages directly under rows an effectively longer day for photosynthesis than in mid alley where forages were shaded early and late in the day. There was very little spatial variation in forage yield in row silvopastures although there was less clover but more grass under trees. Under tree rows, during midday, the highest light levels were measured when the sky contained about 30% cloud cover. At this level the radiation from cloud reflection from the between-row direction exceeded the sporadic attenuation of sun fleck radiation by overhead clouds.
Under mature trees from silvopastures produced from existing forest, yield decreased with daily total photosynthetically active radiation (PAR) although less on a percentage basis. Under thinned forest, day length is decreased in addition to daily totals compared to open pasture since trees cast more shadow early and late in the day.
Agriculture's primary purpose is to harvest PAR for food and fiber so increasing this harvest is potentially valuable. The PAR use efficiency (PARUE), which is calculated as leaf mass production relative to PAR, is much higher for shaded grass than unshaded. Grass leaf mass production is very low in open fields relative to incident PAR so that total system harvesting of PAR is potentially higher in silvopastures than pastures.
|During a hot summer day at VA Tech's Kentland Farm, sheep preferred grazing in the shade of black walnut. The north-south oriented rows facilitated the shade moving across the paddock during the day. (Photo courtesy of C.M. Feldhake, USDA-ARS.)|
Surface soil temperature and forage canopy temperature was lower in silvopastures compared to open sites, particularly during drought. This is useful during Appalachian summers as well as in other regions which rely on cool season forages for the majority of forage production. The lower temperatures in shade on hot sunny days can also reduce animal stress which improves livestock health and performance. Soil moisture, however, showed no significant trend of being different in silvopastures compared to open pasture at any site.
Silvopastures can also facilitate an extended grazing season during some years. Under northern conifers, forage canopy temperatures were up to 10 oC warmer under night time radiation frost conditions due to tree foliage blocking thermal radiation loss to the cold clear sky.
Other Research Programs
A. Dr. Dave Belesky, Research Agronomist, has been studying the response of forages to simultaneous defoliation and low light stress. His emphasis is on morphological and nutritive plasticity. Orchardgrass plants during the second growing season, after vernalization, had improved productivity, nutritive value, and persistence compared to the establishment year. Nutritive value was improved by modest amounts of shade (less than 50%) relative to plants growing in full sunlight.
B. Dr. Jim Burger, Professor of Forest Soils (VA Tech), has worked with best management practices for establishing trees in silvopastures. He is currently working on assessing differences in soil chemical and biological properties in pasture compared to 10 year old silvopastures. There is also work underway on how soil water is partitioned between trees and forages on a deep soil.
C. Dr. Jim Neel, Animal Scientist, has found that even though forage in shade is lower in energy and higher in protein, lambs grazing in silvopastures gained weight at the same rate as lambs in open pasture. Blood urea nitrogen is higher for lambs grazing in silvopastures where grass has elevated crude protein suggesting the enhanced protein is not being utilized but packaged for excretion.
D. Dr. John Fike, Assistant Professor Forage Agronomist (VA Tech), Has worked on forage yield and quality as a function of silvopasture tree density and landscape position on a deep soil. He is currently working on assessing animal performance and health on silvopasture of black walnut and honey locust compared to treeless pastures (also how to protect lambs from coyotes although this is not by choice).
E. Dr. Doug Boyer, Hydrologist, has characterized how much nitrate and fecal coliform is released from soil into streamflow from grazed pasture compared to forest and mixed forest-agriculture watersheds.
|Forage growing in a thinned second growth oak forest. Forage yield was half of an adjacent long-established pasture, however, the soils were inferior so light may not have been the limiting factor. (Photo courtesy of C.M. Feldhake, USDA-ARS.)|
F. Dr. Jay Halvorson, Ecologist, has found that tannins, which are abundant in deciduous tree leaves, added to soil reduce the amount of soluble nitrogen and soluble organic carbon that is leached by water. He is also studying forest litter decomposition rates along forest-silvopasture-pasture gradients.
G. Dr. Kathy O'Neill, Ecologist, has found that microinvertebrate populations in natural soil and orchardgrass litter bags are larger in forest than pasture systems. Using mesh sufficiently large to allow microarthropods access into litter bags resulted in greater decomposition rates than small mesh intended for measuring microbial decomposition. In a companion study, her research team documented a substantially larger presence of salamanders, normally found in forest, existing during spring and autumn in pasture than conventional wisdom predicted.
H. Dr. Tom Staley (recently retired) and Dr. Javier Gonzalez, Microbiologist and Soil Chemist respectively, found that soil chemical properties in forest converted to silvopasture are intermediate between pasture and forest soils except for being higher than both in organic phosphorus.
I. Dr. Rich Zobel, Plant Physiologist, is using mini-rhyzotrons to track root growth and found that tree roots begin growing a month before forage roots in the spring. This needs to be studied further for implications on how to manage nutrients. After grazing, orchardgrass roots die back and the initial regrowth in silvopastures is shorter than in conventional pasture. This may not be a problem since there is a lower evaporative demand in a shaded environment.
J. Dr. Aida Jimenez, Soil Microbial Ecologist, was hired in November of 2006 to study the structure and function of microbial populations in silvopasture systems compared to forest and pasture.
The silvopasture research program at the USDA-ARS Appalachian Farming Systems Research Center continues to expand in complexity. In addition to determining production potential for silvopasture systems, we are also looking at long term ecological implication of these management systems. The cooperation with VA Tech at Blacksburg, VA has been very useful since that site, while hilly, is on an old alluvial soil that is deep in contrast to the shallow soils weathered from shale and sandstone at Beaver, WV. The differences in sites should improve our ability to generalize management advice for release to producers in Appalachia.
The Appalachian region is 23% larger than the state of California. Improving and diversifying income from this largely rural area will benefit the economy and help stabilize small communities.
By Charles M. Feldhake
USDA-ARS Appalachian Farming Systems Research Center
Beaver, West Virginia, USA