Performing Department
Entomology
Non Technical Summary
Black cherry is the highest value timber species in the Northeastern US, with significant production in the Allegheny National Forest (ANF) of Pennsylvania. PA grows the highest quality black cherry in the world, and sales of cherry lumber and products account for a significant portion of the value of timber sales in the state. However, seed production and regeneration have been declining since 2000 in the ANF, threatening this important industry. Since black cherry requires insect pollination to produce viable seeds, the observed reductions suggest that pollination in these regions may be compromised. Declines in wild pollinator species have been broadly documented in agricultural regions, but we have little understanding of pollinator communities within forested landscapes, which are necessary for production of flowering timber trees such as black cherry, and the habitats that support these pollinators. Many factors that impact pollinator species (changing climate, site conditions, and stand structure) will also impact tree health and productivity. Our goal is to understand the relationship between habitat factors that support a robust community of pollinators and production of abundant viable black cherry seeds for regeneration. Armed with this knowledge, we will offer recommendations to the PA Bureau of Forestry and the US Forest Service for increasing black cherry seed production, and in turn, improving regeneration of black cherry in PA forests.Our objectives are to: (1) comprehensively assess the pollinators of black cherry trees and identify the most important pollinators, and (2) examine the degree to which viable seed production in the ANF is determined by the presence and abundance of suitable pollinator species, and how pollinator species and viable seed production relate to important biotic and abiotic factors in the landscape.In Objective 1, we will identify the key pollinators of this important timber species through a series of detailed observational and sampling studies, using easily accessible trees in landscapes that support diverse pollinator communities. In Objective 2, we will conduct larger landscape scale studies in the ANF to determine if the presence of these pollinator species and/or overall pollinator community abundance and diversity influence fruit and seed production (yield). We will simultaneously assess other aspects of landscape quality, stand structure, and tree health. We expect that the percentage of successful fruit set will correlate with the abundance and diversity of key pollinator species, but we also expect these parameters and the density of flowers/tree will vary with a number of biotic and abiotic factors.The results of these studies will help forest managers develop methods for assessing the quality of pollinator communities and landscapes for supporting viable seed production of black cherry in the ANF. Our findings will also provide recommendations for practices to improve pollination, viable seed set, and regeneration. New information will allow forest managers to determine which sites are most likely to respond favorably to interventions, such as thinning or shelterwood cutting.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
Our goal is to understand the relationship between habitat factors that support a robust community of pollinators and production of abundant viable black cherry seeds for regeneration. Armed with this knowledge, we will offer recommendations to the PA Bureau of Forestry and the US Forest Service for increasing black cherry seed production, and in turn, improving regeneration of black cherry in PA forests.Our objectives are to: (1) comprehensively assess the pollinators of black cherry trees and identify the most important pollinators, and (2) examine the degree to which viable seed production in the Allegheny National Forest is determined by the presence and abundance of suitable pollinator species, and how pollinator species and viable seed production relate to important biotic and abiotic factors in the landscape.
Project Methods
Objective 1. Comprehensively assess the pollinators of black cherry trees and identify the most important pollinators. We will use 3 sites with at least 5 black cherry trees with accessible canopies (using a crawler lift) on a forest edge that showed significant fruit set in August/September 2018. Because forest edges have significant pollinator biodiversity, these sites represent trees that should be serviced by diverse and abundant pollinator communities. At each site, we will conduct the studies outlined below on each of 3 trees in spring of 2020.(a) Identify the insect community present in the canopy of flowering black cherry trees. For these studies, we will use two methods for passive sampling. As in 2019, we will use the standard sampling approach of hanging bowl traps on platforms near flowering racemes in the trees. The bowls will be hoisted into the tree canopy and placed next to the flowering racemes using two sets of bowls per tree. Bowls will be set out for 5 days before flowers begin to open, 5 days during peak flowering, and ~5 days after flowering has finished. We will collect trap contents and refill the bowls with fresh soapy water solution daily.Because our preliminary results indicated that the insects sampled by the bowl traps did not always correspond to the insects observed visiting the flowers, we will use colored sticky cards in addition to bowl traps. Sticky cards will be coated with Tanglefoot, and specimens removed by dissolving the adhesive in xylene for identification. All collected insects will be identified to species.(b) Identify insects actively visiting flowers in the canopy of black cherry trees. We will use protocols developed for orchard trees to identify insect species, and their relative abundance, which are directly visiting and interacting with black cherry flowers. Using a crawler lift, an observer will be placed in close proximity to the flowering branches. A 1 x 1 m2 plot within a sunny area of the canopy will be marked off; the insects on the flowers within this area will be observed for a 15 min period at 3 different time points during the day and the nature of their interaction recorded. After this initial observation period, a 15 min collection period will begin. The number of open flowers in this area will be recorded. All sampled insects will be identified to species. After fruit set, the number of fruit in each observed area will be counted as a measure of pollination services.(c) Determine the floral fidelity of different insect species moving black cherry pollen. In Obj. 1b, individual insects will be collected into different vials, allowing us to collect the pollen grains on each individual and evaluate the pollen species of origin. Each insect will be scored for the presence of black cherry pollen and relative frequency of "foreign" pollen. We will statistically compare results from the most abundant fly and bee species to determine which is the more efficient pollinator.Objective 2. Examine the degree to which viable seed production in the ANF is determined by the presence and abundance of suitable pollinator species, and how pollinator species and viable seed production relate to biotic and abiotic factors in the landscape. Obj. 1 will evaluate the diversity and efficiency of pollinators that are attracted to black cherry flowers at the forest edge. Pollinator diversity is particularly high at forest edges, due to the diversity of nesting habitats and flowering plant species near edges. However, even small forest clearings can still support diverse bee communities (Roberts et al. 2017). In Obj. 2, we will determine if these pollinator species are present within black cherry stands in landscapes typically used for timber production, and if their presence and abundance is correlated with fruit set and viable seed production in black cherry. We will also investigate the potential relationship between other biotic and abiotic landscape features outlined below.These studies will be conducted along 8 transects in the Kane Experimental Forest (KEF) in 2020 and 2021 (pre-scouted in 2019). Transects will be selected such that there are at least 5 black cherry trees per transect (focal trees) and include a distribution of stand structure, understory plant communities, and levels of open canopy. All of these factors can impact pollinator communities, tree health and potentially reproduction (see for example studies on black cherry tree mortality (Long 2017) and nutritional stress in sugar maple (St. Clair et al. 2008)).Insect species abundance and diversity. We will sample the insect populations in the canopies of focal trees during maximal bloom as for Obj. 1a. In 2020, we will use bowl traps and sticky traps, and transition to only sticky traps if our results from Obj 1 continue to suggest that these provide the best measure of the insects actually visiting the flowers.Quantities of viable fruit produced. After blooming is completed, for each focal tree, we will collect seeds every 2 weeks from June through November using seed trapping methods developed by Bob Long of the US Forest Service (2017). We will test seed viability, which is dependent on successful insect pollination, using tetrazolium staining based on protocols developed by Verma and Majee (2013); this method has worked well in our hands and is used by the USDA National Seed Lab. There are at least 3 major periods after drupe set begins that black cherry routinely drops developing seeds (Long 2017).Understory composition. We will characterize the understory plant composition using a 3-m fixed-radius circular plot centered at each focal tree. Within each plot, we will record the number and taxa of seedlings and saplings, as well as the estimated percent cover of understory shrubs and grasses. We will also record cover estimates for snags, leaf litter, exposed soil and rock.Tree health. Parameters for tree health will include live crown ratio, crown density, tree height, and dbh. Two increment cores per tree will also be taken and analyzed to determine tree age and vigor.Open canopy. We will also estimate the percentage of open vs. closed canopy surrounding our focal trees; we can obtain ultra-high resolution (gigapixel) photos from under the canopy and image side branches using GigaPan cameras. Climate. For each focal tree we will collect general weather conditions (rainfall, temperature, wind speed, humidity) from the weather station at KEF.Soil conditions. We will measure soil moisture near the root zone of each focal tree using a tensiometer. Two soil samples from each site will be tested by the Agricultural Analytical Laboratory at Penn State for soil pH, since black cherry prefers a slightly acidic soil for proper development. From the same samples, the test will also provide data on the levels of phosphorus, potassium, calcium, and magnesium.Using multivariate statistical approaches, we will evaluate the explanatory power of each measured biotic and abiotic factor, including weather (temperature, rainfall amounts and duration, growing degree days), canopy cover, tree health, age and size, pollinator community abundance and diversity, soil characteristics, and understory cover and composition on our response variables (amount of fruit set and amount of viable seed set). Fruit set and viable seed set will likely depend on pollinator community abundance and diversity, which may be most dependent on the abundance of the key pollinator species identified. However, we anticipate many of the other factors we measure will also be significantly correlated with the response variables. We also expect pollinator community diversity and abundance will be correlated with other features of the landscape (understory composition, proportion of open canopy and bare ground) and weather.