uid=HFR,o=lter,dc=ecoinformatics,dc=org all public read doi:10.6073/pasta/2bd68676c8861ce85424f1ab92a60ca7 Timothy Sipe Richard Bowden Charles McClaugherty https://orcid.org/0000-0001-5884-0756 Kirsten Bixler Researcher 2023 English

Numerous variables related to land use disturbance and recovery processes can influence forest understory irradiance regimes. In addition to season-long measurements of herbaceous stratum microclimates (data archived separately), we explored the degree to which differences in forest community composition and structure generate differences in near-ground sunfleck regimes in our six land use sites (2 plowed, 2 pastured, 2 permanent woodlot). Considerable research has shown that photosynthetic responses to fluctuating irradiance cannot be predicted accurately from steady-state gas-exchange measurements, and that sunflecks may account for both a large fraction of total daily photon fluence and net carbon assimilation by plants in the herbaceous stratum of moist forests. We measured clear-day irradiance patterns to test predictions about how sunfleck frequency, duration, and brightness should vary across the three land-use legacies. We also wished to document sunfleck regimes as part of a companion study on photosynthetic responses by herb and tree species to sunflecks. Twenty-three quantum sensors (Li-190, Li-Cor, Inc., Lincoln, NE) were placed at regularly-spaced interior intersection points across the 30 m x 50 m permanent plot grid in each land use site. The sensors were mounted on stakes 50 cm above ground, leveled, and attached to a Campbell Scientific CR23X datalogger. Photosynthetic photon flux (PPF) values were recorded at all 23 microsites every 6 seconds for 3.5-4.5 hours in the morning (8:00-11:30+ a.m. EST) on one clear day per site in July and August 1998. Using custom software and a sunfleck definition threshold of 100 umol m-2 s-1, sunfleck events were extracted for each microsite across the sampling period and the following were calculated for each fleck event: number of fleck events per hour, sunfleck duration (sec), duration of the shade period prior to the sunfleck (sec), mean PPF across the sunfleck event, and peak PPF during the sunfleck. Descrtiptive statistics calculated across the 23 sample locations per site are reported in this archived data set.

herbs irradiance land use photosynthetically active radiation LTER controlled vocabulary disturbance human-environment LTER core area Harvard Forest HFR LTER USA HFR default

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.

Creative Commons Zero v1.0 Universal https://spdx.org/licenses/CC0-1.0.html CC0-1.0 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf140 Prospect Hill Tract (Harvard Forest). Coordinates based on WGS84 datum. -72.20 -72.17 +42.55 +42.53 335 357 meter 1998 1998 complete Information Manager Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 hf-im@lists.fas.harvard.edu Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu

Plot locations: Plow #1 Site: Prospect Hill Tract, Compartment # III, southern end. Plow #2 Site: Prospect Hill Tract, Compartment # III, southern end. Pasture #1 Site: Prospect Hill Tract, Compartment # I, southeastern edge. Pasture #2 Site: Prospect Hill Tract, Compartment # VIII, central edge. Woodlot #1 Site: Prospect Hill Tract, Compartment # VIII, northeastern edge. Woodlot #2 Site: Prospect Hill Tract, Compartment # VII, central.

Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu https://ror.org/059cpzx98 pointOfContact The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts. National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210. hf140-01-sunfleck.csv sunfleck regimes hf140-01-sunfleck.csv 1368 2b7f115971354ea5b32af0f322f70947 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p14/hf140/hf140-01-sunfleck.csv site site P1 Plow 1 P2 Plow 2 S1 Pasture 1 S2 Pasture 2 W1 Woodlot 1 W2 Woodlot 2 statistic statistic Mean mean Minimum minimum Maximum maximum Std. Dev. standard deviation Std. Err. standard error C.V. coefficient of variation events.hr number of sunfleck events recorded per hour, with the sunfleck PPF threshold of 100 µmol m-2 s-1 per hour. An “event” could last as little as one 6-second sampling interval. number 0.1 real NA missing value shade.duration mean duration of non-sunfleck shade (i.e., PPF < 100 µmol m-2 s-1) prior to each sunfleck event, averaged across all events second 0.1 real NA missing value fleck.duration mean duration of sunfleck events second 0.1 real NA missing value mean.fleck.ppf mean value of the average PPF recorded during individual sunfleck events micromolePerMeterSquaredPerSecond 0.1 real NA missing value peak.fleck.ppf pean value of the peak PPF recorded during individual sunfleck events micromolePerMeterSquaredPerSecond 0.1 real NA missing value 36 historical plot community short-term measurement https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf133 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf134 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf135 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf136 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf137 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf138 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf139 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf141 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf142 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf143 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf144