Remotely Sensed Estimates of Aboveground Net Primary Production of Cultivated Grasslands in a Suburbanizing LandscapeBy: Paul A. Pellissier, Scott V. Ollinger, Lucie C. Lepine

--Background--

--Methods----Grass is More Than Just

Green--

Components of Net Primary Production?• In many terrestrial ecosystems Nitrogen (N) is central to, and often limits, net primary production (NPP) of terrestrial plants.

• In cultivated grasslands N is often supplied, by way of fertilizer, to achieve management goals. This may lead to other limiting factors such as available water.

•Understanding how these systems function in terms of N cycling and carbon storage at the landscape level is important in quantifying their environmental impacts at the regional to global scale.

Site Description-- Lamprey River Watershed:• Fifth order river located in

southern New Hampshire• Area: 479 square kilometers• Encompasses nine towns • Population density ranges

from 0 to 630 people km-2,with an average of 129.

• 17.5% of land area is non-forested

• Surface waters currently impaired from excess N

Prepared by Paul A. Pellissier for the NSF EPSCoR National Conference, 4th November 2013

--Abstract--• The current study aims to determine

generalizable relationships between aboveground NPP and spectral reflectance in both turf and agricultural grasslands.

• Hyperspectral measurements of canopy reflectance collected over two growing seasons are correlated with foliar and environmental attributes.

• Relationships derived from ground-based canopy reflectance will be applied to watershed-scale airborne imagery.

Field Collection:Two summers, two aims: The goal of summer 2012 was to collect data critical to relating airborne and field-based spectra, whereas during summer 2013 efforts were focused on determining relationships between plant /environmental conditions and ground based spectra. Data 2012•Airborne imagery: approx. 500km2 , spatial resolution 5m2

•Eighteen field sites established •Ground-based canopy reflectance•Canopy height•Foliar biomass and N content

Data 2013• Intensive ground based reflectance, sub-meter spatial resolution•Canopy height•Foliar biomass and N content•Leaf water content•Soil moisture•Leaf mass per area•Photosynthetic capacity

Spectral Relationships:Attribute Spectral Prediction Important Regions

Figure 1: Site location within New Hampshire.

Lamprey River Watershed

Photo 1: UNH wants to cut my grass? Collecting biomass at one of our sites located in Deerfield, NH. (Photo by L. Lepine)

Photo 2: Collecting field measurements of hayfield canopy reflectance with a portable field spectrometer at the UNH Fairchild Dairy, Durham, NH. (Photo by L. Lepine)

Looking Forward:

Figure 2: Averaged spectral reflectance curves of grass canopies by management regime. Curves represent over 3500 individual spectra taken at 18 sites located within the Lamprey River watershed. Average spectral reflectance differs significantly (P<0.003) for several regions ( 750-920nm*, 920-1150nm, 1151-1350nm**)in the NIR plateau . *Hay fields and pasture P=0.0165. **Hay field and pasture P=0.6933.

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Visible Light Near Infrared Short-wave Infrared Future efforts will focus using the relationships shown here to predict NPP, scaling these predictions to the watershed scale, and interpreting any observed spatial patterns in NPP.

Foliar Water ContentPrediction and importance plots based on PLS regression of 5 extracted factors . Sample size, n=29; Root mean PRESS=1.02361. Regions of influence include the blue green transition zone, chlorophyll absorption well, red edge, and NIR plateau.

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f(x) = 0.489265460409941 x + 1.19375181028842R² = 0.489265460405842

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Dry BiomassPrediction and importance plots based on PLS regression of 4 extracted factors . Sample size, n=29; Root mean PRESS=0.93348. Importance plot shows the heavy influence throughout the visible wavelengths including blue, green and red edge regions.

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Foliar %NPrediction and importance plots based on Partial Least Squares (PLS) regression of 11 extracted factors . Sample size, n=27. Root mean PRESS= 0.73447. The Importance plot shows the heavy influence of chlorophyll absorption in the blue region and reflectance in the green region. The PLS analysis also values the red edge, and a possible water absorption feature near 1300nm. 300 500 700 900 1100130015001700190021002300

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f(x) = 0.942313750582443 x + 0.116649322974627R² = 0.942599729253785

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Photosynthetic Capacity Prediction and importance plots based on PLS regression of 2 extracted factors. Root mean PRESS=0.589011PLS regression was preformed using 8 modeled light response curves incorporating 80 instantaneous photosynthetic assimilation readings (plotted)Importance plot shows importance of short wave infrared, red edge, and green regions

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f(x) = 0.898108110047342 x + 2.04123767669116R² = 0.898108110053036

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