Laci M. Gerhart Barley

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Second Novus RCN Workshop: Rocky Mountain National Park

As part of my continued appointment with the Novus RCN, I attended the Novus II workshop earlier this month in the *beautiful* Rocky Mountain National Park. For this conference, twenty-five researchers from twenty-one different institutions spanning three countries met at the YMCA of the Rockies to hash out the spatial, temporal, biogeochemical, and biotic responses of ecosystems to disturbance events and changing disturbance regimes. We spent three days building conceptual diagrams, populating them with actual data or case study examples, sharing them with the group and integrating our ideas across time, space, and disturbance agents. I really enjoyed being part of the biotic group. My PhD work focused more on plant ecophysiology, while my recent post-doc work at K-State shifted my focus more towards ecosystem biogeochemical cycling. It was nice to ‘get back to my roots’ (botany joke!) with the organismal focus of the biotic group.

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It wasn’t all work and no play, though – local host and Novus steering committee member Phil Higuera took the group on a hike through RMNP to his field site (and one of my Continental N locations!) of Chickaree Lake.  I was excited to see Chickaree Lake, as I prefer to at least have some interaction with my field sites. That’s the only aspect of the continental N project that I dislike – it is impossible for me to sample all the locations myself, which means I must rely on others local knowledge of sites and systems rather than my own experience at the site. I was glad to at least have some direct knowledge of the knowledge of the Chickaree Lake area and its history.  Along the hike we saw evidence of the stand-replacing fire this section of the forest experienced in 1872. Even 140 years later, the bark of the trees shows scars from the fire. Additionally, this region has recently been hit with mountain bark beetle attacks, so we also saw evidence of the bore holes through the bark (complete with tree chemical defense oozes), and where the bark had stripped away we could see internal bore holes from both the egg-laying female, and the subsequent larva. I had a great time chatting with Ken Raffa, who studies bark beetle outbreaks and beetle biology. It’s a fascinating ecological system, incorporating complex ecological relationships between the trees, the mountain bark beetle, and the ips beetle which appears after the mountain bark beetle and attacks tree hosts weakened by the initial beetle assault. It was a beautiful and educational hike.

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On the way back from the hike, the group also stopped at the Rock Cut Tundra Overlook. It was windy and sleeting and so foggy we couldn’t see much of the panoramic view. I loved every frigid second of it 🙂 It was ethereal and beautiful, and made for some nice photos too!

The plan now that the workshop is over is to coalesce our ideas into a manuscript outlining the results of our discussions. Check back here, or over at the Novus blog for updates!

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Isotopes and Paleonvironments II: DendroGeeks Data!

The newly named DendroGeeks working group at the I&P workshop has now completed our data analysis! We sampled 2 Ulmus americana (American Elm) trees in each of three watersheds at Konza Prairie. The watersheds are all bison-grazed, but experience different burn regimes: every two years (N2B), every four years (N4C), and annual burns in the 90s, switching to every 20 years in 1993 (N20A). See this map for details of grazing and burn regimes at Konza.

Figure 1: raw ring width by year for trees at 2-year, 4-year and 20-year burn regimes.

We measured ring widths on all trees from 1990-2010, and ran nitrogen isotope analysis on years 2002-2006 (for N2B and N4C trees), and 1992-1993, 2002-2004 (for N20A).

As you can see in Figure 1, raw ring width decreased similarly with age for all trees in all watersheds, which is expected under normal growing conditions.

We then compared ring width and nitrogen isotopic signature (abbreviated δ15N) in burn years, one year immediately post burn, and any years beyond one year post burn (Figs 2 and 3). Ring width showed no significant trends, but saw a slight increase in years beyond burns (Fig 2). δ15N was significantly higher in burn years, and all groups showed depleted (less than 0) δ15N values (Fig 3). Higher δ15N in tree rings may reflect increased ammonia volatilization (the loss of nitrogen from the ecosystem in the form of NH3 gas) due to increased ground temperatures during burning, which results in higher δ15N of the remaining nitrogen pool, increasing tree ring δ15N values.

Figure 2: Mean ring width for years in which a burn occurred (burn), one year following a burn event (post), and any years more than one year beyond a burn event (beyond). Includes data from all three watersheds sampled.

Figure 2: Mean ring width for years in which a burn occurred (burn), one year following a burn event (post), and any years more than one year beyond a burn event (beyond). Includes data from all three watersheds sampled.

Figure 3: Mean nitrogen isotopic signatures for years of burn events (burn), one year immediately following a burn event (post), and any years more than one year beyond a burn event (beyond). Includes data from all three watersheds.

Figure 3: Mean nitrogen isotopic signatures for years of burn events (burn), one year immediately following a burn event (post), and any years more than one year beyond a burn event (beyond). Includes data from all three watersheds.

Perhaps most interesting was the comparison between ring width and δ15N between burn, post, and beyond years (Figure 4). In this comparison, burn and post-burn years exhibit no relationship between ring width and δ15N, while rings more than two years beyond burn events showed a strong negative trend between ring width and δ15N. The group then looked more closely at the beyond-burn years, which included years from both 4-year and 20-year burn treatments, spanning two to ten years post burn event. Interestingly, 2-3 year post burn years (from watershed N4C) showed a slight increasing trend and were significantly higher than 10-12 year post burn years (from watershed N20A) which showed a slight decreasing trend. Unfortunately, our sampling strategy confounds the interpretation of these data: it could be that short-term post burn relationships differ significantly from longer-term post burn trends. It could also be that watershed N4C exhibits fundamentally different nitrogen cycling than watershed N20A. In order to tease apart these two issues, the group could (if time and budgets allowed…) sample rings 2-3 years post burn in the N20A watershed, and sample additional trees from other 4-year and 20-year burn regime watersheds at Konza.

These data show interesting trends between tree growth and nitrogen cycling between different disturbance regimes, and could form a solid basis for a longer-term and more intensive analysis of nitrogen cycling at Konza Prairie watersheds. Congrats DendroGeeks on a job well done!!

Figure 4: raw ring width by nitrogen isotopic signature split by year of burn event (blue), one year immediately post-burn (red) and years beyond one year post burn (green).

Figure 4: raw ring width by nitrogen isotopic signature split by year of burn event (blue), one year immediately post-burn (red) and years beyond one year post burn (green).

Figure 5: Ring width by nitrogen isotopic signature for years beyond immediately post-burn, split into 2-3 years post burn (blue) and 10-12 years post burn (red). Blue diamonds are trees from N4C, red squares are trees from N20A.

Figure 5: Ring width by nitrogen isotopic signature for years beyond immediately post-burn, split into 2-3 years post burn (blue) and 10-12 years post burn (red). Blue diamonds are trees from N4C, red squares are trees from N20A.

Isotopes and Paleoenvironments II Workshop

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Bison at Konza Biological Research Station

This week (May 27-31), Kansas State University is hosting 20 students from throughout the country who are interested in learning about stable isotope analysis and interpretation, particularly regarding paleo-environmental research. Instructors Jesse Nippert, Troy Ocheltree, Kendra McLauchlan, Joe Craine, and myself have outlined the use of nitrogen, carbon, and oxygen stable isotopes in ecosystem research on modern, decadal, and millennial time scales. Students are staying at the Konza Prairie Biological Station and have had the opportunity to design and implement sampling protocols for local vegetation, soil, and water. Samples are being run by the Stable Isotope and Mass Spectrometry lab at Kansas State, and students will present novel research at our seminar this Friday.

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In science, as in so many other aspects of life, women perform most of the duties while men give a solid thumbs-up 😀

I have been working with the drendrochronological group, made up of Kyleen Kelly (KSU), Ian Howard (KSU) and Mark Burhnam (WVU). We sampled two American Elm (Ulmus americana) trees in each of three watersheds with different fire regimes (burned every 2, 4, or 20 years). We then measured ring widths from 1990-2010 and chose individual rings for nitrogen isotope analysis (years 2002-2006 for 2- and 4-year watersheds, and years 1992, 1993, 2002-2004 for the 20-year burn). Once the analyses are run, the students can analyze ring width responses to fire events and regimes, as well as nitrogen response in each watershed through time.  Once the analyses and data interpretation are complete, I’ll post our impressive results here!

 

 

In addition, instructors Kendra McLauchlan and Joe Craine hosted a dinner for workshop participants. Following dinner, ice cream was planned for desert! Unfortunately, the Craine-McLauchlan household had recently sold their ice cream maker. What to do?! Never fear – scientists are nothing if not resourceful and ice cream was indeed produced via a ewer of liquid nitrogen and a mixer-bowl of cream and flavoring. Tasty and educational! Children at the event were notably impressed.

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