How Agroforestry Helps Biodiversity: A Study of Our Work in Kentucky
Propagate recently contracted a third party to collect biodiversity data across 20 sample sites on 2 farms in Mason county, Kentucky. The sites were selected based on crop type and system age: chestnut-hay agroforestry systems at different maturity levels were benchmarked against a conventional soy baseline. These measurements will help us understand the impact of agroforestry practices on local ecology.
What did we learn? Our initial results found that the 2022-planted chestnut orchard had 40% more bird species richness and 103% more insect species richness than the soy plots.
We’ll frame the significance of these findings by sharing more on why we believe this work is critical, how the study was conducted, and what we’ve learned through the process.
Why Biodiversity Matters
Why should we care about bird and insect diversity? These species provide a number of ecosystem services such as seed dispersal, pollination, pest control and even the occasional sanitary services (thanks, scavengers). Farms with more biodiversity tend to have healthier soil ecosystems, and a more stable overall environment compared to farms with less diversity — making them more productive and more profitable in the long run.
Unfortunately, biodiversity is not trending in a great direction. Around 1 million species at risk of extinction globally, and many experts contend that a sixth mass extinction event is currently underway (UN, 2019; Ceballo et al 2015). This looming threat poses serious consequences to human health, food security, ecosystem service provision, and the global economy.
How Agriculture Affects Biodiversity
Agriculture is cited as the leading driver of biodiversity loss globally, impacting 86% of the at-risk species on the ICUN’s red list (Benton et al 2021). Agriculture is also the fourth largest sectoral driver of climate change, responsible for 10% of all U.S. GHG emissions (EPA). "Intensive" or "industrial agriculture" is the type of practice most commonly associated with these negative outcomes. This includes large-scale monoculture farming, heavy use of pesticides and fertilizers, and land clearing, which significantly disrupt natural ecosystems and reduce the variety of plant and animal species in a given area.
By contrast, the scaling of regenerative, organic, and agroecological practices on farms is a known solution to the terrestrial and aquatic biodiversity crises, though not all practices are equal in their delivery of co-benefits (Shin et al, 2022).
Agroforestry stands out among regenerative practices as a driver of biodiversity gains on farms, and is also carbon-negative (Nair et al, 2010, Jose 2009, Udawatta et al 2019). Agroforestry improves biodiversity by incorporating trees, shrubs, herbaceous plants, and livestock into the same land area, expanding the variety of floral resources and habitats available for birds, insects, soil microorganisms, and other wildlife. Aquatic biodiversity downstream also benefits from agroforestry practices like riparian forest buffers (Surasinghe and Baldwin, 2015), which can be planted with income-generating species for added benefits.
The effects of agroforestry on biodiversity vary depending on system components, design, and spatiotemporal variables (Bohada-Murillo et al, 2019), speaking to the need to examine outcomes on a system by system basis.
How to Measure Agricultural Biodiversity
Biodiversity is notoriously difficult to measure and define. It can be generally defined by the variability among living organisms from all sources; terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. This includes diversity within species, between species, and of ecosystems (Convention on Biological Diversity). Essentially, we are attempting to distill the vast array of life that exists across different levels of an ecosystem into a single metric. This challenge is compounded by variation and limitations in sampling methods, errors in species identification, and taxonomic biases.
So what does “good” biodiversity measurement look like? Agricultural biodiversity is best measured comparatively across space, across time, and as a relative contribution to regional, national, or global biodiversity (Duelli 1997). Additionally, it should group species to measure functional diversity (Clergue et al 2015). Examples of different “functional groups” of organisms include pollinators, predators, and decomposers, which contribute to both crop and agroecosystem health (Swift et al, 2004).
Our efforts to measure biodiversity in Kentucky are based on a set of common methods and measurements employed by experts in the field. We partnered with SACRA, an organization that specializes in biodiversity and carbon monitoring, to begin sampling efforts on the ground. Our team then compiled the data using a handful of established metrics in our analysis:
Species richness, defined as the number of different species present in a specific ecosystem, habitat, or geographic area
Abundance, referring to the number of individuals of a particular species within a given area or ecosystem
The Shannon-Weiner Index, which accounts for the number of species (richness) and how evenly the individuals are distributed among those species (evenness/abundance)
We also examined native diversity and functional diversity as auxiliary outcomes after the analysis
What this looks like in context of our project
Understanding the broader ecological and historical context of the landscape where our Maysville plantings are based is important in guiding the interpretation of our results. Mason county, KY falls within the “Outer Bluegrass” ecoregion (EPA). The natural vegetation cover in this area was historically composed of a mixture of forests, oak-hickory woodlands and prairie, where unique “barrens” (or bluestem prairies resembling savannas) were managed by indigenous peoples using prescribed fire, supporting a wide variety of now extinct or endangered species (Campbell, 2012). Currently, agriculture represents 64% of all land in Mason county, with hay, corn, soy, tobacco, and grains representing the dominant crops grown (2022 census).
By returning trees to the landscape, reducing soil disturbance, and establishing a permanent diverse groundcover, these plantings aim to restore rare and threatened species to the landscape and create habitat for diverse functional groups that in turn support crop production. Our work is ongoing across our Maysville sites, and this initial survey is intended to benchmark initial levels of biodiversity of a 2-year-old chestnut-hay agroforestry system against a conventional soy baseline.
Methods Used & Observations
Propagate team members reviewed the data collected from SACRA, and grouped the bird and insect observations by their ecological functions. We then analyzed species richness and Shannon values, comparing samples from chestnut & hay sites with soy sites. This is what we learned.
Bird diversity
To estimate bird diversity at our Maysville sites, we employed acoustic monitoring using a SwiftOne recorder, which captures the unique vocalizations of all birds present. An audio file for each sampling location was saved and processed through BirdNET, Cornell’s machine learning and bioacoustics software that distinguishes between species even when multiple calls may overlap. Only calls recorded and identified above 90% confidence were used in our analyses. Of the 394 species of birds observed in Kentucky, 284 species are native to the Bluegrass State, which ranks 10th in the nation for the percentage of bird species at risk (NatureServ).
Results
Our initial results found that the 2022-planted chestnut orchard was 40% more biodiverse than the soy plots in terms of bird species richness, while the Shannon value was 30% higher (significance of these results was not estimated due to limitations in our sample size). Although diversity of species in the chestnut system was greater, analysis of functional diversity in both systems revealed a relatively even distribution across functional groups. A total of 3 species listed as near-threatened on the IUCN Red List were observed in the chestnut plot, 2 of which were present in chestnuts but not in soy.
Insect diversity
There are over 10,000 species of insects present in Kentucky — each with distinct behaviors, mobility and movement patterns. That is why we opted to employ a variety of monitoring strategies to capture a wider swath of insect life.
Pitfall traps, known to catch ground-dwelling invertebrates such as beetles, ants, spiders, millipedes, etc. Pitfall trapping involves placing a bowl or other container into the soil, such that the top is flush with the soil surface and insects can fall into the bowl.
Sweep-netting, which involves using a long-handled net to roughly, rapidly sweep vegetation to capture insects for later identification. This method targets a wide range of species from order Orthoptera (grasshoppers, crickets, katydids), Homoptera (cicadas, leaf hoppers, aphids), Hemiptera (stinkbugs, aphid bugs, planthoppers, leafhoppers), Odonata (dragonflies, damselflies), Diptera (flies, mosquitoes, gnats), Coleoptera (beetles, weevils), Order Hymenoptera (ants, wasps, bees), Lepidoptera (butterflies, moths), and spiders.
Visual inspection around both the base of the tree and within the entire plot, respectively targeting ground-dwelling, trap-avoidant insects and more mobile insects, such as butterflies and moths.
Blacklight traps were deployed at night using a UV light and white backdrop, designed to capture nocturnal insects such as moths.
Results
We observed that the average species richness, Shannon-Wiener Index (H), abundance, and native and functional diversity were all greater in the 2-year old chestnut agroforestry system compared to the conventional soy baseline. The mean per-plot species richness and H value for the chestnut system (19.9 and 2.237) were significantly greater than the values observed in the soy plots (9.8 and 2.028), indicated by p-values < .05 (.0001 and .034).
In the 2022 chestnut planting, a diverse groundcover was used that included a mixture of grasses and forbes; we suspect that the diverse groundcover contributed to the higher levels of biodiversity observed, alongside decreased disturbance and agrochemical applications relative to the soy plot. Compared to values cited throughout the literature for orchard systems, species richness and the Shannon-Index were relatively lower (Shannon values ranging from 2-2.5 indicate moderate diversity, while values from 2.5-4 indicate healthy agro-ecosystems). We anticipate that as the system matures, the contribution of both chestnut catkins and floral resources from native woody species (a “biodiversity mixture” that represent 7-8% of each planting), alongside the expansion of the tree canopy, will lead to increases in biodiversity above the initial values observed, though only time (and continuous measurement) will tell.
What We’ve Learned from This Process
Biodiversity is challenging to measure well
There are limited samples of biodiversity data available today, and collecting more to build a basis for localized trajectory is a long and costly process. This is due in part to variation in indicators across bioregions and farms, inherent complexity caused by cost overlap between indicators, variation between sampled farms, and labor effort variability caused by differences between organizations performing the studies.
Other biodiversity monitoring challenges include (but are not limited to):
Human sampling bias
Lack of coordination or standardization across monitoring efforts
Taxonomic bias
Fortunately, novel monitoring solutions such as camera traps and acoustic monitoring have begun to solve challenges associated with sampling bias and data collection at scale, while their accessibility and compatibility with machine-learning assisted identification speaks to their potential for broad use (Oliver et al, 2023; Naqvi, 2021). As we expand our monitoring program in Maysville, we aim to integrate new technologies as they become available.
Costs are a barrier to data collection for farms
Transitioning several thousand acres of ag land into commercial chestnut-hay alley cropping is costly, but creates significant economic opportunities for farmers. It is generally understood that these projects come with ecological benefits, but verifying them can be costly which can hinder their adoption. Research estimates monitoring costs can range from $15-45 per acre (Targetti et al, 2014) — not a negligible amount. And who should pay for that?
Standards for valuing & incentivizing biodiversity improvements are still forming
A growing number of organizations have outlined some form of biodiversity strategy, and could potentially provide the capital needed. We applaud those rallying around commitments to halt and reverse biodiversity loss, but recognize that many cannot make actionable investments when the measures of impact vary, or the standards for quality are unclear. Fortunately, there are a growing number of crediting methodologies starting to be approved for use. Perhaps we’ll see a future where farming sustainably is incentivized as well as, or better than the commodity-based subsidy system?
Conclusion: Agroforestry Supports and Restores Biodiversity
Agroforestry is a multi-tool for ecosystem & climate recovery
Nature-based solutions like agroforestry offer a blend of environmental and economic benefits. Agroforestry improves biodiversity, sequesters carbon, and protects our watersheds — creating a valuable option for farms that fit a variety of contexts. The trick is finding the right trees, for the right places on a farm, that align with a farm’s holistic context & goals.
How to get started on your farm
Propagate is an agroforestry project developer that makes it easy to plant profitable, regenerative systems. We provide technical assistance to help you assess tree crop suitability, layout a farm plan, assess farm budgets, and enable farm management. Our farm services team can help translate your plan into a thriving system with site & soil prep, high-quality nursery supply, planting & protection, and management & monitoring.
We work with farms of different scales and with different goals to design, finance, plant and manage different agroforestry systems like alley cropping, silvopasture , and riparian forest buffers.
Contact us to learn what’s possible on your land.
References:
Benton, T. G., Bieg, C., Harwatt, H., Pudasaini, R., & Wellesley, L. (2021). Food system impacts on biodiversity loss: Three levers for food system transformation in support of nature [Research Paper]. Chatham House: Energy, Environment and Resources Programme. https://www.chathamhouse.org/sites/default/files/2021-02/2021-02-03-food-system-biodiversity-loss-benton-et-al_0.pdf Bohada-Murillo, M., Castaño-Villa, G. J., & Fontúrbel, F. E. (2019). The effects of forestry and agroforestry plantations on bird diversity: A global synthesis. Land Degradation & Development, 30(15), 1799–1808. https://doi.org/10.1002/ldr.3478Ceballos, G., Ehrlich, P. R., Barnosky, A. D., García, A., Pringle, R. M., & Palmer, T. M. (2015). Accelerated modern human–induced species losses: Entering the sixth mass extinction. Science Advances, 1(5), e1400253. https://doi.org/10.1126/sciadv.1400253Clergue, B., Amiaud, B., Pervanchon, F., & Lasserre-Joulin, F. (2005). Biodiversity: Function and assessment in agricultural areas: A review. Agronomie, 25(1). https://doi.org/10.1007/978-90-481-2666-8_21 Convention on Biological Diversity. (2006). Article 2. Use of Terms. https://www.cbd.int/convention/articles/default.shtml?a=cbd-02Duelli, P. (1997). Biodiversity evaluation in agricultural landscapes: An approach at two different scales. Agriculture, Ecosystems & Environment, 62(2-3), 81–91. doi:10.1016/s0167-8809(96)01143-7 Jose, S. (2009). Agroforestry for ecosystem services and environmental benefits: An overview. Agroforestry Systems, 76(1), 1–10. https://doi.org/10.1007/s10457-009-9229-7Nair, P. K. R., Nair, V. D., Kumar, B. M., & Showalter, J. M. (2010). Carbon sequestration in agroforestry systems. Advances in Agronomy, 108, 237-307. https://doi.org/10.1016/S0065-2113(10)08005-3 Oliver RY et al. (2023) Camera trapping expands the view into global biodiversity and its change. Phil. Trans. R. Soc. Shin, Y.-J., Midgley, G. F., Archer, E. R. M., Arneth, A., Barnes, D. K. A., Chan, L., Hashimoto, S., Hoegh-Guldberg, O., Insarov, G., Leadley, P., … (2022). Actions to halt biodiversity loss generally benefit the climate. Global Change Biology, 28(9), 2737-2754. https://doi.org/10.1111/gcb.16109Stein, B. A. (2002). States of the Union: Ranking America’s Biodiversity. NatureServe. https://www.natureserve.org/sites/default/files/stateofunions.pdf Surasinghe, T. D., & Baldwin, R. F. (2015). Importance of riparian forest buffers in conservation of stream biodiversity: Responses to land uses by stream-associated salamanders across two southeastern temperate ecoregions. Journal of Herpetology, 49(1), 83–94. https://doi.org/10.1670/14-003Udawatta, R. P., Rankoth, L., & Jose, S. (2019). Agroforestry and biodiversity. Sustainability, 11(10), 2879. https://doi.org/10.3390/su11102879United Nations. (2019). Biodiversity - Our strongest natural defense against climate change. Retrieved from https://www.un.org/en/climatechange/science/climate-issues/biodiversity#:~:text=Up%20to%20one%20million%20species,carbon%20sources%20due%20to%20deforestation
