Tuesday, December 3, 2013

After the storm: a tree census at Parks Loop South

By Glenn Juday, professor of forest ecology

On Nov. 13-14, central Alaska experienced a powerful snow and windstorm. Winter started late this year, but from Nov. 5-10, a good snowpack accumulated. Then, between Nov. 12-13, temperatures warmed from one below zero F to 44 above at Fairbanks. The average temperature on Nov. 14 was an amazing 31 degrees F above normal. Of course, in order to experience temperatures that warm only a few weeks from the winter solstice, Alaska has to import warm air from the south. The import came in the form of a very strong chinook (warm southerly subsidence wind off the Alaska Range).

The powerful, widespread winds on Nov. 12 snapped and toppled trees (Figure 1) across the Fairbanks North Star Borough. Many trees fell across electric transmission lines, which cut off power to a substantial share of the outlying homes in the Fairbanks area. But if a tree falls in the forest … will anyone notice? Yes.

Dashiell Feierabend, research technician, stands by an uprooted (“rootsprung”) tree in the Parks Loop South forest reference stand at Bonanza Creek Experimental Forest, Nov. 18. (Photo by Ryan Jess)

Among the research plots and installations in the Bonanza Creek Experimental Forest (20 miles west southwest of Fairbanks off the Parks highway) is a network of six hectare-scale (2.5 acre) forest reference stands. The reference stands were established by SNRAS Professor of Forest Ecology Glenn Juday in the late 1980s to conduct intensive long term monitoring of forest change. The forest types selected for reference stands include aspen-dominated, birch-dominated and white spruce-dominated types both in the old growth condition (three stands) and burned in the 1983 Rosie Creek Fire (three stands). The old-growth white spruce reference stand is called Parks Loop South. 
Aerial view of the first and second hectare reference stands in old-growth white spruce at Bonanza Creek Experimental Forest, May 2009. Red squares delineate 100m by 100m (1.0 ha), solid yellow lines are 50m by 50m (0.25 ha), and dashed yellow lines are 25m by 25m sixteenth hectare subplots.(Photo by Glenn Juday)

On Nov. 18 SNRAS research technicians Ryan Jess and Dashiell Feierabend walked through Parks Loop South and conducted a census of trees damaged or blown down by the storm. The Parks Loop South reference stand contains two mapped hectares, 1PLS near the top of the slope and 2PLS contiguous to the south (Figure 2). In 1PLS one tree experienced a broken top, 3 trees were heavily tilted and standing only because they were leaning into another tree (Figure 3), and one tree was snapped and shattered at the base. In 2PLS one tree had a broken top, two trees were heavily tilted and leaning on nearby trees, and 2 trees were uprooted and toppled (Figure 1). Several trees just outside the 1PLS and 2PLS reference stands fell into or close to the hectare boundaries. At least six previously standing dead trees were toppled too.

Parks Loop South reference stand in Bonanza Creek Experimental Forest, Nov. 18, 2013. The large white spruce in the center of this view has been partially uprooted and is leaning against the spruce that originates from the lower right corner. Trees in this condition either die immediately or are severely weakened and become susceptible to engraver beetles.(Photo by Ryan Jess)

So, this was an easy call, right? The crew could have waited until the spring and done the count in more pleasant weather, right? Well, maybe not. In late September a couple of trees fell near the UP3A instrument site in the 1PLS hectare (Figure 4). A survey after the fact, typically in spring once the snow has melted, likely would have incorrectly inferred that the November storm brought those trees down. So, if a tree falls in the forest, somebody needs to monitor it if we want to understand correctly the life and death of the forest. 

Two toppled trees at the UP3A instrument station in the Parks Loop South reference stand in Bonanza Creek Experimental Forest, Sept. 25, 2013. Note the well-decayed condition of the wood as indicated by the reddish color. Without frequent monitoring of the long-term study sites these trees might have been detected after the Nov. 14 storm and their death mistakenly attributed to it.(Photo by Ryan Jess)

In recent decades, life has not been easy for the old growth white spruce forest at Parks Loop South. In the winter of 1988-89 a heavy snowfall snapped the tops of many trees. In their weakened state these injured trees attracted attacks by engraver beetles. The tally from that round of tree death was about 20 percent of the stand. The record snowfall of the winter of 1990-91 snapped and toppled many more trees, and the beetle outbreak was sustained and increased in intensity. The result of that episode was the death of nearly another 1/3rd of the trees that were alive at the start of monitoring in 1986. Two events in the space of a few years resulted in the death of nearly half of the trees in a 200- year-old stand. The wood of the trees that were toppled in September 2013 had been weakened for years following the introduction of decay fungi on the back of wood-boring beetles.

As usual, there is always some actor in nature that is adapted to benefit when something changes or dies. During the post-storm survey a Black Backed Woodpecker (Figure 5), a large-bodied, year-round resident bird species, was busy in the understory. The Black Backed Woodpecker is a specialist feeder on wood-boring beetles, especially the white spotted sawyer and cerambycid beetles. Next spring and summer, homeowners and land managers around Interior Alaska may start to notice their white spruce trees that were injured in the November storm with red needles that fall off, and holes in the trunk that ooze sap as the beetles move in to finish them off. They may even notice the rhythmic thump of a Black Backed Woodpecker drilling in to feed. The events of the storm will be with us for a while longer.

A Black Backed Woodpecker is pictured at the Parks Loop South Reference stand. This bird was stripping the bark from a sapling Alaska birch. Next spring the dead and dying trees produced by the November 2013 storm will host beetles that will become the prey of this species.(Photo by Ryan Jess)

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