Detecting Signatures of Forest Change in Nebraska's Niobrara Valley
I spent the summer conducting a seedling census in a long term forest monitoring plot at Nebraska's Niobrara Valley Preserve. This presentation is a compilation of my experience and research findings. If you like trees or are interested in forest ecology and conservation, have a listen!
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[00:00:01.474]Detecting signatures of forest change in Nebraska’s Niobrara Valley.
[00:00:05.529]Hey everyone! My name is Brittni.
[00:00:07.679]I spent my summer living in Sparks, NE doing a forest ecology research project.
[00:00:11.981]Today I’m going to share my experience and research findings with you!
[00:00:15.506]My project was set on the Niobrara Valley Preserve.
[00:00:18.995]While this land is currently owned and managed by the Nature Conservancy,
[00:00:22.301]it is important to acknowledge that the preserve resides on the traditional lands of the
[00:00:26.362]Pawnee, Lakota, and Comanche Peoples.
[00:00:30.225]The Niobrara Valley is home to one of the most biogeographically unique forests in the world.
[00:00:34.356]We see the convergence of three different forest types:
[00:00:37.469]northern boreal, eastern deciduous, and western coniferous — making the valley one of the only places
[00:00:43.088]to find trees like paper birch, ponderosa pine, and black walnuts co-occuring in the same forest!
[00:00:48.412]Many people don’t associate Nebraska with forests because the lack of water availability excludes them from most of our landscapes.
[00:00:54.950]But, the forest along the Niobrara is supported by a high water table and ground water seeps.
[00:01:00.129]This unique water source gives life to the forest, but in a very limited area.
[00:01:04.301]Within 500 meters of the river, the landscape transitions from forest to rolling prairie.
[00:01:09.559]Narrow forests like this are called Boundary Forests and are especially vulnerable to
[00:01:13.404]environmental changes and stressors like high intensity wildfire, drought, and climate change.
[00:01:18.210]In 2019, a long-term forest monitoring plot was established by Dr. Sabrina Russo and Forest GEO.
[00:01:25.241]Every sapling and adult tree in the plot has since been censused and mapped.
[00:01:29.369]The work done to establish this plot set the stage for my project this summer…
[00:01:33.302]Which was to establish and census 504 seedling monitoring plots.
[00:01:38.555]Seedlings are the future of the forest. When you look out into the forest and you see those big, adult Mother Trees
[00:01:45.884]those all used to be tiny little seedlings.
[00:01:48.472]While mortality rates are high for seedlings, they all have potential to become adults.
[00:01:53.825]So, when we conduct a seedling census, the goal is to gain insight on the future of the forest
[00:01:58.649]by understanding species-level recruitment strategies and community level responses to environmental changes.
[00:02:04.533]So, how do you do a seedling census?
[00:02:07.787]Well, first we would locate and establish a plot using a PVC 1m square.
[00:02:12.223]Then we tag and collect data on every seedling which included measurements
[00:02:16.502]like height, diameter, and leaf count. Then it’s off to the next plot to repeat these steps 504 times!
[00:02:25.740]Here is a time-lapse of me collecting data on one of our seedling plots.
[00:02:29.237]As I take measurements, I say them aloud and one of my partners documents the data using a special form on an iPad.
[00:02:35.064]The plots varied quite a bit, some had no seedlings and some had more than 60 seedlings.
[00:02:39.503]Some took 5 minutes some literally took 2 hours.
[00:02:42.640]Overall, we were able to complete the census in about 2 months.
[00:02:50.621]Now let’s get into the results!
[00:02:53.706]Here is the forest at a glance.
[00:02:55.607]We defined three size classes: Adults trees are above 5cm in diameter, Saplings are between 1 and 5, and seedlings are under 1cm in diameter.
[00:03:04.669]There are 27 different woody species
[00:03:07.107]and collectively the census has identified about 4700 adults, 3600 saplings, and 2200 seedlings.
[00:03:14.708]Keep in mind, the seedling census only covered 504 square meters of the plot.
[00:03:19.399]However, the area censused is representative of the plot as a whole.
[00:03:23.339]So by extrapolation, we estimate there are actually about 878,000 seedlings — which is crazy to think about!
[00:03:33.294]One way we visualize the data we’ve collected is plotting trees on topographic maps.
[00:03:38.017]There is about 75 meters in elevation difference between the lowest and highest point in the plot.
[00:03:43.650]I have labeled both a blank topographic map on the left and a topographic map overlaid on an aerial photo of the plot
[00:03:50.060]to help you get oriented with these models before I dive into the data analysis.
[00:03:53.671]Feel free to pause and take a look before moving on!
[00:04:00.506]While I’d love to share the story of all 27 species in the plot,
[00:04:03.985]for times sake I have chosen to highlight a few species that I find have the most interesting stories to tell.
[00:04:09.801]First up, we have American Basswood!
[00:04:13.176]We censused 420 basswood seedlings (168,000 when extrapolated), 61 saplings, and 404 adults.
[00:04:22.694]So, what do these numbers tell us about the species?
[00:04:25.744]Well, basswood is a very prolific seeder and produces a lot of seedlings.
[00:04:29.485]But, we see a big drop off in the number of saplings which means most seedlings are not surviving.
[00:04:34.570]Now, does this mean there is something bad happening causing all of the seedlings to die?
[00:04:40.659]All species have recruitment strategies and we happen to know that generally basswoods
[00:04:45.324]produce a ton of seedlings with the hope that a few will survive to sapling and adulthood.
[00:04:50.064]Understanding the species recruitment strategy allows us to look at the data and
[00:04:55.343]know if something is out of the ordinary or just part of how a species is.
[00:05:00.026]What we just analyzed was the size distribution of basswood in the forest.
[00:05:04.279]We can also look at the spatial distribution and related environmental factors.
[00:05:08.471]Solar radiation was measured for each square meter of the entire plot —
[00:05:12.623]you think of this as the cumulative amount of sunlight a spot in the plot gets in an entire year.
[00:05:18.661]We can match the location of each tree with the solar radiation at that same location
[00:05:23.667]to know the intensity of sunlight the tree is experiencing.
[00:05:28.113]Now, the box plot on the left is showing us the range of solar intensities that basswood seedlings, saplings, and adults are experiencing.
[00:05:35.725]What’s interesting is the seedlings and adults are occupying locations with higher solar radiation than the saplings.
[00:05:43.173]We can also use the same box plot to visualize the ranges of elevation the different size classes are occupying.
[00:05:50.683]Looking at the figure on the right, they all seem to be living at about the same elevation.
[00:05:55.126]Finally, for what I find is the most interesting way to look at the data.
[00:05:59.666]Let’s move to the topographic map in the middle!
[00:06:01.311]Each blue dot is a sapling, each yellow dot is an adult, and each purple dot is a plot that has one or more seedlings in it.
[00:06:08.705]From this map, it looks like the adults are very spread out, living on the bench, upland slopes, and in the canyons —
[00:06:15.264]not really showing a preference for any one habitat. A similar story with the seedlings.
[00:06:19.884]But, it seems like the saplings are concentrated in the canyons only.
[00:06:24.662]So bringing all of this together, what sort of presence will basswood have in the future of the forest?
[00:06:29.856]The best answer is “we need more data and more time.”
[00:06:34.202]However, working with what we have I would say basswood does have a future in the forest —
[00:06:39.540]there are no big warning signs that make us worry about the recruitment of this species.
[00:06:43.500]But basswood’s spatial distribution may begin to shift more towards and exclusively along the canyons.
[00:06:50.986]So, now you know the story of American Basswood in the forest and how to look at the data.
[00:06:55.156]I’m limited on time so I can’t walk through the next two species with you in the video,
[00:06:59.196]but if you’re interested go ahead and press pause to check them out!
[00:07:03.771]Pause here to check out bur oak
[00:07:07.592]and pause here to check out hackberry.
[00:07:11.157]Looking forward, the adult and seedling census will continue for many years to come and as it does,
[00:07:16.485]our data set will get stronger and we will learn more about the forest.
[00:07:19.938]We’ll also begin looking at the seedling distribution data alongside microclimate data from the weather stations.
[00:07:25.383]Finally, I will be spending this fall taking a deeper dive into the data analysis to write my undergraduate thesis.
[00:07:32.458]In conclusion, climate change is effecting ecosystems worldwide.
[00:07:36.621]The only way to truly understand how ecosystems are responding, is to get out there and collect a bunch of data.
[00:07:42.808]The data allows us to identify signatures of forest change.
[00:07:46.246]We can then use that data to inform management plans to help conserve ecosystems and species we value.
[00:07:52.685]Data-informed management gives us our best shot at preserving special places like
[00:07:57.101]the Niobrara Valley in the face of climate change.
[00:08:00.792]To wrap things up I want to give a quick shoutout to UCARE and Cabela’s for funding this experience.
[00:08:05.687]And of course to Dr. Sabrina Russo, Bailey McNichol, and Susanna Moyers for your mentorship and contagious curiosity about forests!
[00:08:13.456]Thank you for listening!
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