Leaf and Soil Nitrogen Following Lymantria dispar Defoliation in Central Massachusetts 2018-2019

<para>In this study we investigated relationships between ecosystem nitrogen (N) cycling and tree defoliation during a recent 2015-2018 irruption of invasive Lymantria dispar caterpillars, which can cause tree stress and sometimes mortality following multiple years of defoliation. Nitrogen is a critical nutrient that limits the growth of caterpillars and plants in temperate forests. We assessed the associations between N concentrations, soil solution inorganic N availability, and defoliation intensity by L. dispar at the scale of individual trees in the Amherst, MA area and forest plots in the Quabbin Reservoir area. </para> </section> </abstract> <keywordSet> <keyword>defoliation</keyword> <keyword>leaves</keyword> <keyword>nitrogen</keyword> <keyword>oak</keyword> <keyword>soil chemistry</keyword> <keywordThesaurus>LTER controlled vocabulary</keywordThesaurus> </keywordSet> <keywordSet> <keyword>organic matter</keyword> <keyword>inorganic nutrients</keyword> <keyword>disturbance</keyword> <keywordThesaurus>LTER core area</keywordThesaurus> </keywordSet> <keywordSet> <keyword>Harvard Forest</keyword> <keyword>HFR</keyword> <keyword>LTER</keyword> <keyword>USA</keyword> <keywordThesaurus>HFR default</keywordThesaurus> </keywordSet> <intellectualRights> <section> <para>This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.</para> </section> </intellectualRights> <licensed> <licenseName>Creative Commons Zero v1.0 Universal</licenseName> <url>https://spdx.org/licenses/CC0-1.0.html</url> <identifier>CC0-1.0</identifier> </licensed> <distribution> <online> <url function="information">https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf344</url> </online> </distribution> <coverage> <geographicCoverage> <geographicDescription>Central Massachusetts. Coordinates based on WGS84 datum.</geographicDescription> <boundingCoordinates> <westBoundingCoordinate>-72.5308</westBoundingCoordinate> <eastBoundingCoordinate>-72.1676</eastBoundingCoordinate> <northBoundingCoordinate>+42.5313</northBoundingCoordinate> <southBoundingCoordinate>+42.3144</southBoundingCoordinate> <boundingAltitudes> <altitudeMinimum>90</altitudeMinimum> <altitudeMaximum>160</altitudeMaximum> <altitudeUnits>meter</altitudeUnits> </boundingAltitudes> </boundingCoordinates> </geographicCoverage> <temporalCoverage> <rangeOfDates> <beginDate> <calendarDate>2018</calendarDate> </beginDate> <endDate> <calendarDate>2019</calendarDate> </endDate> </rangeOfDates> </temporalCoverage> <taxonomicCoverage> <taxonomicClassification> <taxonRankName>genus</taxonRankName> <taxonRankValue>Lymantria</taxonRankValue> <taxonomicClassification> <taxonRankName>species</taxonRankName> <taxonRankValue>dispar</taxonRankValue> </taxonomicClassification> </taxonomicClassification> <taxonomicClassification> <taxonRankName>genus</taxonRankName> <taxonRankValue>Quercus</taxonRankValue> <taxonomicClassification> <taxonRankName>species</taxonRankName> <taxonRankValue>rubra</taxonRankValue> <commonName>red oak</commonName> </taxonomicClassification> </taxonomicClassification> </taxonomicCoverage> </coverage> <maintenance> <description> <para>complete</para> </description> </maintenance> <contact scope="document"> <positionName>Information Manager</positionName> <organizationName>Harvard Forest</organizationName> <address scope="document"> <deliveryPoint>324 North Main Street</deliveryPoint> <city>Petersham</city> <administrativeArea>MA</administrativeArea> <postalCode>01366</postalCode> <country>USA</country> </address> <phone phonetype="voice">(978) 724-3302</phone> <electronicMailAddress>hf-im@lists.fas.harvard.edu</electronicMailAddress> </contact> <publisher scope="document"> <organizationName>Harvard Forest</organizationName> <address scope="document"> <deliveryPoint>324 North Main Street</deliveryPoint> <city>Petersham</city> <administrativeArea>MA</administrativeArea> <postalCode>01366</postalCode> <country>USA</country> </address> <phone phonetype="voice">(978) 724-3302</phone> <phone phonetype="fax">(978) 724-3595</phone> <onlineUrl>https://harvardforest.fas.harvard.edu</onlineUrl> </publisher> <methods> <methodStep> <description> <section> <title>Measurements at Individual Trees We measured leaf and soil N concentrations at 12 individual Quercus rubra trees in the Amherst, MA area. Each tree was scored for overall visual defoliation in the field in October 2018. Herbivory measurements were also scored on 30 leaves collected from each tree within reach from the ground in October 2018, and these leaves from each tree were pooled and analyzed for leaf N concentration. Soil samples of the O-horizon were collected in three locations about 0.5 m away from each tree and up to 10 cm depth using a 5 cm diameter split PVC corer and a mallet. These soil samples were pooled for each tree and analyzed for soil N concentration.

Measurements at Forest Plots We also collected data at nine 90 x 90 m plots in Central MA, where each plot was subdivided into three 20 x 20 meter subplots. Within each 20 x 20 m subplot, four soil samples of the O-horizon were collected 5 m inward towards the center of the subplot from each of the four plot corners. The samples from each subplot were then homogenized into a composite sample and analyzed for percent nitrogen. At each plot we used data from a Landsat-derived forest condition assessment product (doi:10.5281/zenodo.1493407) to calculated plot-level cumulative defoliation. Using this data product we calculated the cumulative seasonal defoliation by calculating the mean annual values in a 45 m radius circle from each plot center and adding values from 2015, 2016, 2017, and 2018. We also used a categorical version of the Landsat-derived data product to classify each plot as defoliated or not in the 2015-2018 growing seasons. Plots were classified as defoliated in each year if the mean categorical value for defoliation was “moderate” or higher. Within each plot we measured the availability of inorganic N in soil solution during the growing season using resin bags buried beneath the soil. For each resin bag, 10 g of resin was added to a mesh stocking packet and buried 5-10 cm below the soil surface in the center of the first subplot within each larger plot on June 11-14, 2019. Each resin bag was collected after 75-78 days to quantify accumulation of soil solution inorganic N over this period. Nitrate (NO3-) and ammonium (NH4+) were extracted from the resin using 2M KCl and we measured the resulting KCl extracts for NO3- and NH4+ concentrations using colorimetric analysis. Each sample was run twice for replication and quality assurance. The resulting concentrations of NO3- and NH4+ in ppm were converted to mg per kg dry resin, the two replicates were averaged, and that value was divided by the number of days that the resin bag was deployed in order to get the average rates of NO3- and NH4+ availability in mg per kg dry resin per day. To calculate the total rate of inorganic N availability, we added the mean rates of NO3- and NH4+ for each resin bag.