Establishing a Silvopasture Site for Long-term Research, Education, and Livelihood

This grant will allow us to maintain and secure establishment of the silvopasture, and obtain baseline and early data on environmental changes. The TAs plan on securing additional resources to conduct experiments, quantify effects on livestock, and track long-term changes to biodiversity, soil health, and carbon stocks. During 2022-2023 the site has been laid out, including the planting of trees and shrubs (See Supplemental Materials maps). Additional planting to compensate for first year mortality will be done in fall/winter 2023-24. 

The Confluence Farms property encompasses 112 acres, including 90 in farm fields and 17 in riparian forest along a mile of the Marys River. The farm has a mile long west to east axis and varies in width north to south from 700 to 1200 ft. It has a perimeter livestock fence and cross fences, and buried, well-fed, livestock water lines. An irrigation pump accesses the Marys River and buried mainline and risers distribute water to fields. Soils and slopes change from west to east, reflecting the geomorphology of historic Marys River overflow channels. Soils are primarily silty-clay loams suitable for high value crops, although seasonal flooding and slow drainage on Conser soil swales are a management challenge. 

We have installed the silvopasture on a 10 acre field with predominantly Conser soil. This field is centrally located and least valuable as cropland, making it ideal for this project. Based on tolerance to hydric soils, three main, canopy tree species have been planted: Black cottonwood (Populus trichocarpa), White alder (Alnus rhombifolia), and Pacific willow (Salix lasiandra). (Note: Oregon ash was not chosen because of the Emerald ash borer risk). In addition, a diversity of small trees and shrubby species are planted as an additional vegetation layer: Blue elderberry, Red elderberry, Pacific ninebark, Red-osier dogwood, Hooker's willow, Oregon crabapple  Lewis’ mockorange, Black hawthorn, Osoberry, Red-flowering currant, Black twinberry, Common snowberry, Douglas spirea, Salmonberry, Thimbleberry. 

In addition to practical information on ease of establishment and growth rates for each species, our goals are to both understand the characteristics of these single species plantings on some basic environmental and forage parameters, as well as uncover any differences from more diverse plantings in key metrics (e.g., carbon sequestration, biodiversity). Plantings are in a complete block design, with three blocks, meaning there are replicates of each planting combination within each block (3 single species tree X 3 replicates; 3 single species tree + diverse understory X 3 replicates) for 18 treatment rows. Because we have questions about the efficacy of carbon sequestration, animal health, and other environmental parameters there are control areas between blocks lacking tree cover. 

Objective 1: Maintain and secure establishment

The trees and shrubs need time to grow in the absence of browsing and we plan to keep livestock out of tree rows for at least five years. The trees were planted prior to sowing a pasture sward, but we may still need to mow vegetation as we develop grazing systems to allow for irrigation equipment (K-line) to be moved and ensure high survivorship, reduce competition, and promote rapid growth rates. Local arborists are dropping off wood chips, and these are being dumped at the base of trees to retain water and prevent weed growth. 

After a summer of mowing, grazing, and mulching with chips, we will till the area between rows of trees and shrubs and sow a new, permanent pasture. The pasture itself will be biodiverse, including forbes, clovers, and potentially native wetland plants. 

We have a data table that collects survivorship of each individual planted, after a few years we will also be able to infer and compare growth rates among species, and over time follow biomass accumulation.

Objective 2: Obtain baseline and early data on environmental changes

During the early years we will be collecting data on weather, soil health, and biodiversity. The initial weather station will allow for continual sampling of wind, precipitation, temperature, and humidity. We plan on having two stations eventually, one near a tree row and one in a control area. Additional funding will be sought for more fine-grained deployment of microclimate sensors, and expanded data on irradiance and soil moisture, as tree rows mature. 

Standard surface layer (0-8” depth) soil sampling will be conducted in control and treatment areas, and compare pasture vs tree rows. Soil health metrics include standard chemical analyses, as well as bulk density, aggregate stability, and infiltration. We plan to store soil samples at -80C for eventual environmental DNA tests (eDNA), which will likely pick up many macro-organisms too. We will seek additional funding to repeat these tests after the term of this grant, and also to perform non-standard soil sampling at deeper horizons that will help refine estimates of carbon dynamics.

For biodiversity surveys we are focusing on two taxa with strong area expertise, i.e., birds and bees. Both studies will enable us to understand changes in the silvopasture in the context of broader sampling on the farm and in the region. Monthly bird surveys using standard protocols at 14 sample points on the Confluence Farms property are already being done, including two within the silvopasture. These will allow us to gauge population changes in silvopasture relative to adjacent open farm fields and closed canopy riparian forest. Bee surveys using standard techniques developed by the Oregon Bee Atlas team, will allow for species richness, abundance, and relative population reproduction estimates each summer. 

These metrics have been chosen to understand how silvopasture alters microclimate, builds carbon above and below ground, and how the biological communities respond. We are facing atmospheric overloads of carbon, farmland loss of carbon, as well as regional declines in many bird and insect populations from intensive, industrial agriculture. Silvopastures incorporating native vegetation may help arrest these trends, and by demonstrating changes on the more marginal soils we might ease farmer acceptance and adoption.