LANDSCAPE HETEROGENEITY MODULATES FOREST SENSITIVITY TO CLIMATE

I F O R I IC O N 5

COLLEGE OFFO R E ST R Y A N D CONSERVATIONWhere Ideas Take Flight

Zachary Hoylman and Kelsey JencsoCollege of Forestry and Conservation, University of Montana, Missoula, MX 59801

The University ofMontana ' he University ofMontana

Climate Change ^ - Studies

INTRODUCTIONAt higher elevations in the Rocky Mountains, snowmelt strongly influences the magnitude and timing of net ecosystem productivity. Throughout the western U.S., increased spring temperatures, declining snowpack, and earlier snowmelt have been observed over multiple decades. These trends have been correlated with decreased water availability and coniferous forest productivity and concurrent increases in forest wildfire activity and tree mortality. However, previous work has provided little insight into how topographic complexity may modulate plant available water and therefore forest productivity. We hypothesize that landscape scale lateral water redistribution patterns influence the persistence of soil water during the growing season and subsequently tree biomass accumulation.

SITE DESCRIPTIONNorth Fork of Elk Creek - Lubrecht Experimental Forest• Location - 25 miles NE of Missoula, MT• 4 primary tree species

• Pseudotsuga menziesii, Pinus ponderosa, Pinus contorta, Larix occidentalis

• Average Annual Precipitation 515mm• Mean Elevation 1570m• Snow dominated

r q nFigure 1 - This map shows the Topographic Wetness Index (TWI) for the North Fork of Elk Creek watershed as well as tree core sampling distribution (red dots) within the watershed

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• We derived the topographic wetness index (TWI) from a 1 m LiDAR derived DEM. The TWI represents moisture availability and the potential for lateral water

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Topographic Wetness Index redistribution.Figure 2 - This plot shows a histogram of the TWI frequency in the North Fork o f Elk Creek and a point cloud (red dots) showing the sampling frequency o f tree core TWI values.

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Figure 3 - 1 . Precipitation data retrieved by a NRCS SNOWTEL site in Elk Creek (top) and 2. the annual growth rate for multiple stems from Pinus Ponderosa and Pseudotsuga Menziesii species (middle and bottom respectively.

Figure 4 - A representative tree core (Pseudotsuga Menziesii)

PRECIPITATIONThese graphs display how precipitation and average annual growth for two species lack a clear relationship. This may change with an increase in data set size.

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TWI RELATIONSHIP Figure 5 - These scatter plots display average annual growth for two species, plotted against annual precipitation.

Initial comparisons of measured tree growth rates to the topographic wetness index suggest differential tree growth response as a function of landscape position. Generally, trees located in wetter landscape positions exhibited greater average growth rates.

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Figure 6 - These graphs show average growth rate plotted against the TWI value associated with each stem. (Eeft plot represents north aspect samples, right plot represents south aspect samples)

GROWTH/HjO vs. TWIInitial analysis of the slope produced by annual precipitation and annual growth, plotted against the stem’s associated TWI value, show a differential growth rate related to TWI.

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Figure 7 - These plots shows the relationship between TWI and the change in biomass per unit of precipitation for each tree.

WORK TO BE CONTINUEDTree Cores

• Continued data analysis of tree cores

NDVI• Explore TWI - NDVI relationship at the

catchment scale.

Seasonal Response to Transpiration• Data extraction from Sap-Flux sensors• Examine relationship of Sap-Flux, soil

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ACKNOWLEDGMENTSThis work was supported by:- USD A Mclntire Stennis grant awarded to Jencso- University of Montana Climate Change Studies grant awarded to Hoylman

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