CRUI Land Use Project - Herbaceous Stratum Sunfleck Regimes

Data

• hf140-01: sunfleck regimes

Overview

• Lead: Timothy Sipe, Richard Bowden, Charles McClaugherty
• Investigators: Kirsten Bixler
• Contact: Timothy Sipe
• Start date: 1998-06-01
• End date: 1998-08-31
• Location: Prospect Hill Tract (Harvard Forest)
• Latitude: +42.53 to +42.55
• Longitude: -72.20 to -72.17
• Elevation: 335 to 357 meters
• Taxa:
• Research topic: historical, plot, community
• Study type: short-term measurement
• LTER core area: disturbance
• Keywords: photosynthetic photon flux, sunfleck
• Release date: 2009
• EML version: knb-lter-hfr.140.3
• Revisions:
• Related links:
• CRUI Land Use Project - Litterfall, Biomass and Productivity
• CRUI Land Use Project - Tree Canopy Leaf Area Index
• CRUI Land Use Project - Canopy Sky Factors
• CRUI Land Use Project - Herbaceous Species
• CRUI Land Use Project - Mapped Trees
• CRUI Land Use Project - Microclimate
• CRUI Land Use Project - Photosynthetic Light Response Curves
• CRUI Land Use Project - Tree Seedlings
• CRUI Land Use Project - Herbaceous Community Composition
• CRUI Land Use Project - Soil Properties
• CRUI Land Use Project - Soil Respiration
• Abstract:

  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.

• Methods:

  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.

• Use:

  This dataset is released to the public and may be freely downloaded. Please keep the designated Contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement. For more information on LTER Network data access and use policies, please see: http://www.lternet.edu/data/netpolicy.html.

• Citation:

  Sipe T, Bowden R, McClaugherty C. 2009. CRUI Land Use Project - Herbaceous Stratum Sunfleck Regimes. Harvard Forest Data Archive: HF140.

Detailed Metadata

hf140-01: sunfleck regimes

1. Site: site
   • P1: Plow 1
   • P2: Plow 2
   • S1: Pasture 1
   • S2: Pasture 2
   • W1: Woodlot 1
   • W2: Woodlot 2
2. Statistic: statistic
   • Mean: mean
   • Minimum: minimum
   • Maximum: maximum
   • Std. Dev.: standard deviation
   • Std. Err.: standard error
   • C.V.: coefficient of variation
3. 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 )
4. 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 )
5. Fleck Duration: mean duration of sunfleck events (second )
6. Mean Fleck PPF: mean value of the average PPF recorded during individual sunfleck events (micromolesPerMeterSquaredPerSecond )
7. Peak Fleck PPF: pean value of the peak PPF recorded during individual sunfleck events (micromolesPerMeterSquaredPerSecond )