DEVELOPING AND PROMOTING WOODLAND PAWPAW PRODUCTION PRACTICES TO IMPROVE FRUIT YIELD AND QUALITY

Progress report for LNC21-452

Project Type: Research and Education
Funds awarded in 2021: $249,846.00
Projected End Date: 10/30/2024
Grant Recipient: The Ohio State University
Region: North Central
State: Ohio
Project Coordinator:
Dr. G. Matt Davies
The Ohio State University
Co-Coordinators:
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Project Information

Summary:

Pawpaw (Asmina triloba) is the largest endemic edible fruit in North America. Its significant cultural importance is recognized in its declaration as Ohio’s State Native Fruit. Pawpaw is on the precipice of becoming a significant specialty crop within the NCR-SARE region but the next ten years will be critical. Orchard acreage is increasing both nationally and internationally (e.g. South Korea, Japan, France, Italy and Romania) but pawpaw orchards take five to ten years to reach full production and will thus not address the short- to medium-term critical issue of limited supply. Traditionally, pawpaw has been foraged and harvested from wild patches within forests and farm woodlands and currently at least half the fruit on the market is derived from such sources. Wild harvesting plays a major role in current pulp production (critical for value-added industries) and provides important supplemental income for rural communities. The woodland pawpaw economy could be expanded but is hampered by low levels of productivity. Meanwhile, consumer demand for pawpaw fruit and derived value-added products is growing rapidly leading to shortages in several nodes across the value chain. 

 In cooperation with growers, our preliminary studies have suggested that a set of agronomical limitations and lack of technical knowledge and training could be overcome to improve production. Our preliminary data shows productivity of woodland trees is highly variable between years and sites. Growers tell us a complex of factors may play a role including: low pollination rates, self-unfruitfulness in genetically homogeneous patches, and competition among pawpaw and neighboring plants for light and nutrients. We will work closely with woodland pawpaw producers on research and extension activtities that span the social, environmental, and economic spheres of sustainability.  

Working closely with growers, we will enhance production knowledge and deliver it to woodlot operators via extension programs. By doing so, this project will enhance the resilience of economically challenged rural Appalachian communities that sell wild-grown pawpaw for living. The project will connect production practices to management of invasive plants and woodland restoration leading to direct benefits for ecosystem healthMarket insights will demonstrate how attributes of woodland pawpaw fruit can be used for promoting value-addition. To achieve this we will: (i) examine impediments to increased production and quality of woodland pawpaw, (ii) evaluate potential win-wins between pawpaw production and restoration of woodland ecosystem health, and (iii) generate opportunity for value aggregation in woodland pawpaw based on an analysis of consumers’ preferences. 

Project Objectives:
  1. Extension: Engage growers, consumers and woodland managers to incentivize uptake of new pawpaw products and management systems. Learning Outcome – Consumers perceive enhanced value for woodland pawpaw; growers implement techniques to provide consistent, high-quality pawpaw products.
  2. Research: Quantify impediments to woodland pawpaw production and quality associated with genetic homogeneity and wild genotypes. Learning Outcome – Growers improve cross-pollination and patch genetic quality to improve productivity.
  3. Research: Evaluate woodland management practices to improve productivity and sustainability in existing pawpaw patches and establish new ones. Learning Outcome – Growers manipulate light and competition to enhance patch productivity, fruit quality and forest health.
Introduction:

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Cooperators

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Research

Hypothesis:

1) Managing woodlands for production of pawpaw can provide an economic incentive for forest health restoration

2) Pawpaw production in woodlands in predominantly controlled by light availability

3) Low within-patch genetic diversity and self-infertility limits fruit production in wild stands

4) Production in wild patches can be increased by introducing improved fruit varieties

5) Patch establishment success is a function of introduction method (seeding v. planting), stock-type (bare-root v. container) and browsing management (use of tree guards)

6) Consumers are willing to pay a premium for woodland-grown pawpaw products

Materials and methods:

We identified seven critical questions with regards to enhancing the economic and ecological sustainability of woodland pawpaw production. We have developed a program of integrated research and extension, involving close collaboration with grower and woodland management stakeholders, to address each of these questions.

RESEARCH SITES

Research will be completed at eight different sites including four operated by collaborating growers (denoted by *):

  • *England’s Orchard, McKee Kentucky (37°31'17.5"N 084°06'15.8"W) - Collaborating farmer – Mature commercial nursery orchard.
  • *Integration Acres, Albany Ohio (39°11'51.5"N 082°07'08.2"W) - Collaborating farmer – Largest by volume commercial grower and processor of pawpaw pulp. Permaculture and agroforestry-based production within orchard and managed wild patches. Site includes existing regularly monitored wild pawpaw patches.
  • *FoxPaw Farm, Abredeen Ohio (38°39'18.7"N 083°41'57.1"W) - Collaborating farmer –Commercial orchard producing fruit, pulp seed and scion wood. Most diverse repository of pawpaw germplasm in North America. Site includes existing regularly monitored wild pawpaw patches.
  • *West View Pawpaw Farm, Wooster, Ohio (40°45'57.5"N 081°58'47.4"W) - Collaborating farmer – Commercial orchard producing fruit and engaged in agritourism and public/consumer education.
  • Secrest Arboretum, Wooster, Ohio (40°47'05.7"N 081°54'45.3"W) – Multiple wild pawpaw patches.
  • Waterman Farm, Columbus Ohio (40°01'03.8"N 083°02'42.5"W) - Hosts 1.3 acre orchard of 400 trees including seedlings and 12 select varietals. Site includes existing regularly monitored wild pawpaw patches.
  • OSU South Centers, Piketon, Ohio (39°02'51.8"N 082°59'23.8"W) – Replicate of Waterman orchard. Site includes existing regularly monitored wild pawpaw patches.
  • Pomerene Forest Laboratory, Coshocton, Ohio (40°18'29.2"N 081°50'05.3"W) Site has strong edaphic gradients in soil type and soil moisture, variable canopy cover and composition. Significant cover of invasive species which have been recently controlled in some areas.

Standard woodland monitoring protocol: Several of our questions utilize established or new long-term monitoring plots. All plots, other than where new pawpaw patches are being established, are centered on unique pawpaw patches. A unique patch is defined as an individual pawpaw patches demarcated by clear separation (i.e. no contiguous pawpaw stems) of at least 20m. All such plots are monitored based on the standardized FLN method [1]. Briefly, trees and large saplings are measured in a 20 m diameter plot with. Point intercept readings of shrub species presence, and canopy cover (latter via GRS densiometer) are recorded on two intersecting 20 m transects. Within a nested 23.5 ft diameter FLN plot we record density of all woody seedlings and saplings. Herbaceous species cover and composition is assessed in four quadrats around the outside of the FLN plot. A 10-F forest inventory prism is used to estimate basal area with readings taken from the center of the plot.

 

RESEARCH METHODS

Question 1 ~ Pollen and genetic incompatibility as limitations on production: We will compare fruit set in open pollinated and controlled hand pollinated flowers to assess the effect of pollen deposition.  Hand pollination will also address potential issues of self-incompatibility.  We will use five pollination treatments representing pollen from trees across a gradient of genetic dissimilarity: 1) flowers within the same tree; 2) flowers from different trees within the same patch; 3) flowers from different patches within the site; 4) flowers from different sites; and 5) flowers from three commercial varietals representing three distinct genetic groups [2]. Unpollinated flowers will serve as controls. Pollen will be collected on the day of pollination, stored under refrigeration and applied to recipient flowers using a camel-haired brush.

Working with our cooperator at West View, and at the Secrest, and Waterman site, we will establish three replicate woodland pawpaw plots (see above). As genetic variation between mother trees is likely to be a significant factor in fruit set and production, we will identify five trees in each plot to receive hand-pollination. Recipient flowers within a tree will be distributed throughout the canopy with five flowers per tree randomly assigned to each of the eight pollen treatments (40 pollinated flowers per tree + 5 unpollinated controls). To evaluate the effect of growing conditions and their interaction with pollen source we will monitor canopy and shrub-layer cover using the standard protocol.

To prevent natural pollination flowers will be isolated in pollination bags from the initial signs of petal expansion. Bags will be left in place after anthesis to retain any initially developing fruit that might abscise early. Flowers will be monitored regularly to quantify initial fruit set and abortion rates and timing. All fully-developed fruit will be harvested and fruit quality assessed (see below). Data will be analyzed using generalized liner mixed effects models (GLMMs) where fruit set, yield and quality metrics are analyzed as a function of pollen treatment with site and tree defined as nested random effects. Canopy and shrub-layer cover will be included as covariates.

Question 2 ~ Relative importance of growing conditions and genetic identity for production and quality. To determine if fruit production and quality is limited by inherent genetic characteristics, or primarily by growing conditions, we will investigate the performance of genetically-identical plant material in contrasting woodland and open-grown conditions. Research will used paired orchard and wild patches at the Waterman, Piketon and Fox Paw Farm sites.  Scion wood will be grafted reciprocally on to lateral branches of mature trees: i) from open-grown varietals to wild woodland trees; and ii) from the same wild woodland trees to the open-grown varietals. By grafting onto side branches of existing mature, productive trees we will maximize the potential for fruiting within the project time period. Varietals used will include a representative from three distinct genetic groups [2]. Three woodland plots will be used per site to represent a range of stand conditions and historic productivity. For all grafts we will analyze differences in graft survival, growth, flowering, fruit set, fruit production and fruit quality between genotypes and woodland versus open-grown settings. Plot structure and fruit quality will be assessed as per the project standard methods. Graft-level metrics will be analyzed using GLMMs as a function of the interaction between scion source and destination (wild/varietal) with site and tree defined as nested random effects. Canopy and shrub-layer cover will be included as covariates.

Question 3 ~ Light availability as a critical control of production and quality We will use a combination of monitoring and controlled experiments to determine thresholds in fruit production and quality in relation to light availability. We will:

  1. Survey our permanent monitoring plots to assess differences in photosynthetically active radiation (PAR) levels in relation to woodland canopy cover, composition and mid-story competition. This will include standard monitoring of our 30 permanent monitoring plots distributed across our growers’ (FoxPaw, Integration Acres) and OSU sites (Waterman and Piketon). All sites include three plots where we have previously manipulated light and competition through thinning and invasive control. PAR will be measured at noon during mid-April, June and September during cloud free conditions using an Apogee MQ-610 ePAR Meter (ten randomly-located measurements per plot). Each year we will record the total number of flowers, fruit clusters and final fruit produced. All fruit will be harvested and standard quality metrics assessed. Data will be analyzed using GLMMs where yield and quality metrics are analyzed as a function of treatment (managed/unmanaged) and PAR with site defined a random effect.
  2. Work with multiple growers (England’s Orchard and FoxPaw), we will utilize orchard experimental shade treatments to directly quantify light availability effects on tree performance in a controlled environment. Confounding factors associated with wild stand experimentation (e.g edaphic characteristics, plant genotype, age, competition) hampers our ability unequivocally recommend specific woodland thinning levels. We will construct shade enclosures around productive trees of similar ages and sizes. Enclosures will provide four levels of shading 0% (control), 20%, 50%, 90% of maximum shading (i.e., lowest PAR values) determined in woodland plots. At each site we will select one variety from each of three distinct genetic groups [2] with each variety replicated three times. Enclosures will be established at the start of the project with flowering and fruit production monitored in all years and fruit quality in year 1 and 2. Fruit yield and quality metrics will be analyzed using GLMMs with genetic group and shade treatment included as fixed effects and site as a random effect.

Question 4 ~ Management intervention effects on fruit quality. In all experiments relating to questions 1-3, fruit yield will be determined by number of fruit produced and pulp mass. Quality will be assessed by measuring Brix, color, hardness, pulp to seed ratio, seeds per unit fruit volume. Qualitative scores will be devised on a five-point likeability scale that we will develop with our growers to measure flavor profile. IRB clearance will be obtained prior to any research involving human subject surveys.

Question 5 ~ Efficacy and efficiency of patch establishment methods: Research will be completed at Pomerene where landscape-level variation in conditions have been well-characterized by previous projects. We will establish a network of ten patches split across areas with or without invasive control and gradients in light availability (understory shade - full sunlight) and environmental setting (riparian - upland). Plots will be monitored using our standard protocol. In each plot we will plant: three container-stock grafted trees from each of three varieties (representing three distinct genetic groups [2]), 50 bare-root seedling trees, and 400 pawpaw seeds (latter split evenly across four permanently marked 4m2 quadrats. All trees and emerging seedlings will be permanently tagged to track survival and growth which will be recorded every month during the first growing season and annually (end of growing season) thereafter. Economic efficiency of establishment will be calculated as dollars per surviving tree and dollars per unit length of surviving stem.

 Question 6 ~ Pawpaw patch management and forest health: In collaboration with growers (Fox Paw Farm, Integration Acres) and at our Waterman and OSU South Centers sites, half of our permanent pawpaw plots at were manipulated in 2021 to reduce competition, invasive species, and increase light availability. We will track flower and fruit production on all pawpaw trees in these plots for the duration of the study and evaluate management effects on key forest health parameters. Our standard plot protocol will allow us to assess changes in: i) invasive species cover; ii) density and species of regenerating tree seedlings and saplings; iii) the cover and diversity of ground flora including ephemeral spring wildflowers. Indicators of forest health will be analyzed using GLMMs to test for differences between treatments (managed/unmanaged) with site included as a random effect. Variation in woodland species composition between sites and treatments will be characterized using Non-metric Multidimensional Scaling.

Question 7 ~ Woodland pawpaw as a premium product: We will use a survey research method [3] to characterize preferences for pawpaw product attributes. The survey will lead to a discrete choice experiment in which consumers are invited to indicate preference for a set of alternative products. We will employ an econometric model to estimate willingness to pay (WTP) for pawpaw fruit and pawpaw ice cream attributes including: (i) production system (‘woodland patch’ or ‘orchard’); (ii) graded and standardized fruit (‘yes’ or ‘no’); (iii) grade entity (‘USDA’, ‘Pawpaw industry association’, ‘Not graded’); (iv) adoption of sustainability guidelines (‘yes’ or ‘no’); and (v) price. The survey will also collect social-demographic and consumption behavior data to properly characterize survey participants. We will distribute the survey during the 24th Annual Ohio Pawpaw Festival in 2022, and a week after the festival using the contact database of past attendees. The contact database is maintained and annually updated by the North American Pawpaw Growers Association, one of our collaborators in this proposal. We expect to access a random sample of 1,500 individuals and obtain a +15% response rate. Individuals will be presented with six choice scenarios yielding +675 observations. The survey instrument will be pretested in focus group meetings and investigators are committed to obtain IRB exemption before contacting study participants. Our subsequent outputs and outreach activities will integrate information on WTP on the basis that adoption of yield and quality enhancing practices are more likely to occur when growers understand the potential economic gains.

 

REFERENCES

[1] Fire Learning Network (FLN) (2013). https://www.conservationgateway.org/ConservationPractices/FireLandscapes/FireLearningNetwork/NetworkProducts/Documents/FLN_ForestStructureandCompositionMonitoring_Protocol_and_Datasheets_Standard_20131213.pdf; [2] Pomper et al. (2010). https://doi.org/10.21273/JASHS.135.2.143; [3] Fowler (2014). ISBN: 9781452259000

Research results and discussion:

The first year of our project was focused on establishing key experiments. The main period of data collection following our manipulations will commence in the spring of 2023

Question 1 ~ Pollen and genetic incompatibility as limitations on production

We piloted our reciprocal hand-pollination experiment at two separate sites in contrasting growing zones in Ohio. A third location will be added in 2023. Experiments revealed significantly enhanced pollination and fruit set where hand pollination was used. Importantly, for a tree long-thought to be self-sterile, we detected higher rates of fruit set in trees pollinated from other plants in their potentially clonal patch. We will investigate this more thoroughly in 2023 and explicitly investigate evidence for self-fertility. Additionally inspection of pawpaw flower morphology revealed significant differences in pistil numbers between wild and varietal pawpaws with the former having 1-3 pistils and the latter 3-many. This reveals an important constraint on the maximum number of fruit many wild trees can produce.

Question 2 ~ Relative importance of growing conditions and genetic identity for production and quality

To initiate this experiment we completed reciprocal grafting between orchard and wild trees at two different sites. Graft take was minimal at one site due to unusually stressful conditions but was close to 50% at the second site. We will be tracking the flowering and fruiting effort by the grafts in 2023 and completing a second round of grafting where there was initial failures.

Question 3 ~ Light availability as a critical control of production and quality

Shade enclosures were established around trees at two different orchards. Fruit yield did not differ significantly in 2022 but was not expected to. We will continue to track production in 2023 when, having experienced 18 months of enhanced shading, we anticipate differences in production will become noticeable. Our treatments did lead to substantial differences in ripening time for fruit under different levels of shade. We are thus investigating effects on phenology and are excited to have revealed a potential means for growers to extend the fruiting season.

Question 4 ~ Management intervention effects on fruit quality

Work on Question 4 will commence in 2023 once we have a first crop of fruit from trees manipulated in experiments 1-3

Question 5 ~ Efficacy and efficiency of patch establishment methods

We established ten new pawpaw patches in woodland currently lacking any known pawpaw populations. Plots were cleared of invasive species and thinned to reduce understory competition. We logged the time and resources required to impose the treatments. Thirty bare-root pawpaw seedlings were planted in each plot half with and half without tree guards. Three container-grown grafted varietals were planted in each plot. Grafted varietals showed significant mortality with most of this attributed to disturbance by racoons post-planting. Deer browsing pressure was high and counter-intuitively particularly damaging on trees with guards (guards were removed by the deer in many plots). Survival of seedlings was assessed in summer 2022 and will be monitored again in spring, summer and early fall 2023. Initial survival of the seedlings was good (80-90%) despite deer damage.

In response to queries from growers and collaborators we established two additional planting trials including - 1) invasive removal and underplanting in existing/mature black walnut plantations; 2) development of chestnut and black walnut / pawpaw interplanting trials. Pawpaw survival was strong in all of these experiments. Severe drought and browsing damage limited the survival of chestnut trees. All dead trees will be replaced in spring 2023.

 Question 6 ~ Pawpaw patch management and forest health

All pawpaw patches and planting sites were monitored for woodland structure and composition prior to the application of treatments. Evaluation of the effects of thinning and invasive control treatments will commence in summer 2023

Question 7 ~ Woodland pawpaw as a premium product

Questionnaires and surveys were distributed to consumers and growers at the Ohio Pawpaw Conference and the Ohio Pawpaw Festival to evaluate how pawpaw certification schemes and growing conditions (e.g. organic v. conventional) would affect consumers willingness to pay for the crop. This work will continue through 2023 focusing on preferences for woodland/wild versus orchard grown fruit.

Participation Summary
1 Farmers participating in research

Education

Educational approach:

The first year of the project has focused on the establishment of our various planting and management experiments and demonstration sites. In project Year 2 we anticipate hosting a number of field site visits and workshops. We have continued a vigorous program of education and outreach activities as part of our wider pawpaw research program. Members of the project team have presented at national grower conferences as well as the Ohio Pawpaw Festival which attracts > 6,000 visitors each year. We are in the process of analyzing initial data from our monitoring of pawpaw establishment and woodland management interventions and these will be used to generate Extension notes that will be shared publicly and with our project stakeholders.

Project Activities

Wondrous wild pawpaws: production and growth of native stands
Wondrous wild pawpaws: production and growth of native stands
Pawpaw 101
MORE OHIO PAWPAW – A multidisciplinary research and extension development program
Growing pawpaws in woodlands, orchards and gardens
Pawpaw fruit quality: Its components, determinants, and importance to growers, processors, and consumers
Consultations with pawpaw growers

Educational & Outreach Activities

20 Consultations
3 Online trainings
3 Webinars / talks / presentations
1 Other educational activities: Project website development

Participation Summary:

50 Farmers participated
50 Ag professionals participated
Education/outreach description:

The first year of our project was strongly focused on the establishment of our trials and experiments. This included multiple on-farm research projects with collaborating growers. We completed several on-line and in-person trainings with many of the former reaching >200 participants including growers, educators and members of the general public. This wider outreach beyond the core pawpaw community is vital for growing awareness and the economy of our crop.

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
100 Agricultural service providers reported changes in knowledge, skills, and/or attitudes as a result of their participation
Key areas taught:
  • Use of shading to modify pawpaw ripening and production
  • Forest management and woody invasive plant control
  • Patch thinning and pruning
  • Grafting of wild and domesticated trees
  • Outplanting and direct seeding

Project Outcomes

5 Farmers changed or adopted a practice
Key practices changed:
  • Growers introduced netting to facilitate harvesting of ripe pawpaw
    Growers introduced shade enclosures to evaluate effects on fruit production, quality and yield
    Growers manipulated existing pawpaw patches to control competing non-native vegetation and enhance light availability

3 New working collaborations
Success stories:

In our first year we established multiple on-farm research projects with our collaborators including

Shade enclosures to evaluate the effects of light availability on fruit production and quality. A key finding here was that shading slows the fruit ripening process revealing a potentially important means to extend the pawpaw fruiting season. The short season is presently a major constraint for producers

Hand pollination trials across gradients of genetic relatedness. A key finding was that hand pollination definitively improves fruit set in woodland settings. Detailed evaluation of the pollination process revealed that many woodland pawpaw flowers show a reduced number of pistils which will limit the number of fruit per cluster. This strengthens the logic for introducing improved varietals into woodlands

Pawpaw patch establishment trials revealed wildlife damage to be a significant constraint on establishment and survival allowing us to refine approaches to management of this problem. A key finding was that while deer normally avoid browsing pawpaw, in setting where they are naive to the trees (i.e. pawpaw were not previously present) they may selectively and severely browse them.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.