We had a great showing at the SER 2013 World Conference in Madison, WI this past week! We had the opportunity to present on some great work from lab ranging from reference systems in restoration (Lauren), improving the likelihood of restoration success (Sara Jo), wetland restoration (Dylan), managing for resilience (Katie, Lauren) and tropical forest restoration (Fernando)!
by Erica N. Spotswood
The weed thresholds team just returned from a visit to SFREC to check on our plots. In October, we established 360 plots to which we added seeds of four species. On our last trip, everything was dry and the weather was hot! What was most remarkable on this trip is how quickly the landscape was transformed. Just a month later, last year’s grass has nearly disappeared, and new grass and forbs are germinating everywhere! The seed addition worked, and we found establishing seedlings in many of our plots. The weather was wet and foggy, following a big storm that dumped four inches in 24 hours. The next few months of cool wet weather should give a good start to the winter annual species characteristic of California grasslands. I can’t wait to see how much recruitment we will see next spring!
by Joanna Hsu
November 7, 2012
Iryna Dronova, a graduating PhD student in Peng Gong’s group, dazzled us at Friday’s lab meeting about how remote sensing might be useful in ecology and restoration. A fly-by review of her presentation:
1. The problem: field work takes time, money, and often painful logistics. Furthermore, measurements in the field may not be accurate or scale up to relevant scales.
For example, I have spent a good deal of time squinting at plots to estimate percent of vegetation cover. It is one of the places in life I second guess myself and others the most. I have no doubt that you can identify grasses to the subspecies based on a fragment of last year’s flowering stalk, but can you also get the percent cover in this plot right? (And by “right”, I mean “the same answer as me”?)
2. Enter remote sensing and image classification, which can extract useful information from satellite images because different land and vegetation covers have different spectral signatures.
3. However, classifying blindly based on the spectral signatures of pixels alone often hides meaningful entities.
4. Adding scale-dependent, object-based image analysis helps considerably. This image segmentation allows us to more easily separate interesting entities from similar-colored background.
5. A cool example from Iryna’s research: wetlands research at Poyang Lake, China. Swaths of land dominated by different plant functional types – C3 grasses, C3 forbs, C4 tall grasses, C4 short grasses – can largely be separated based on their spectral signatures if object-based image analysis is applied at the right scale (figure below from Dronova et al. 2012).
A species’ “functional type” or “functional group” refers to its role and function in an ecosystem, as opposed to its taxonomy. Ecologists often group species based on their contributions and responses to their ecosystems – it may be more ecologically meaningful that a species is a perennial shrub than that it belongs to the Ericaceae family, subfamily Diapensiaceae.
6. As for the hard-to-classify land areas, a field visit can clarify the ambiguity. Sometimes these areas are the most biodiverse, composed of several plant functional types. Or, we could also improve our classification success rate by defining new optically distinguishable plant functional types, as these authors suggest. (Thought: then does the term “functional” become more about being functional for ecologists as opposed to functional for ecosystems?)
7. There are lots of ways questions in ecology and restoration could be addressed using remotely sensed data. Iryna’s list is below:
Sara Jo will be giving a talk about seed bank limitation and management at the 21st Annual California Invasive Plant Council symposium, which is being held in October in Sonoma County. She will present results from a study of 131 restoration sites in Orange County, California.
“You don’t just go from artichoke thistle to coastal sage scrub.” -Sara Jo Dickens, talking about undesired restoration trajectories
Dark view from the seed bank
by Joanna Hsu
Prior to assuming the role of graduate student, I had the more glorious (and well-paid) job of being a champion weed fighter at Crystal Cove State Park in southern California. “Environmental services intern” was my real title, but in my mind I was so much more than that. I brought death to the artichoke thistle and stoked fear in the heart of invasive mustards. Exotic annual grasses didn’t stand a chance against me. In my more enthusiastic moments – when my passion for native ecosystems really flared – even non-invasive exotics were not spared. In my arsenal were chainsaws, weed whips, and gallons of Roundup.
On days I wasn’t battling weeds, I was working on a restoration project at an old sewage leach field site. I sowed native seeds by the fistful and put hundreds of sagebrush, buckwheat, orange monkeyflower, and other coastal sage scrub seedlings in the ground. I diligently hand-watered transplants, regularly removed weeds and things aspiring to be weeds, and rubbed the leaves of the few adult native shrubs on the site for good luck.
But as I worked, I wondered – was this enough? Do our weed killing projects and expensive, labor-intensive restoration efforts achieve their goals? What really makes an ecological restoration successful? Would I return to the leach field after my journey to the far-off land of grad school to find a thriving native coastal sage scrub community?
Well, it is now several years later and Sara Jo Dickens, a post-doc in my lab, is working on exactly these questions. She has evaluated outcomes from 131 restoration sites in Orange County, including Crystal Cove State Park. I got a preview of her results at our lab meeting this week. The take-home point was this: restoration needs to account for soil seed banks. Seeds can sit in the ground for months or years before germinating or dying, and this seed bank is important because it is a source of new vegetation at restoration sites. At restoration sites without planting or sowing, it is the main source of new individuals — so what’s in the seed bank matters.
Well, it turns out that Orange County seed banks are rich in exotic species but poor in native ones. By germinating seeds from soil samples at each site, Sara Jo found that on average, less than 1 out of every 100 seeds is from a native local species. Equally troublesome is the fact that less than half of native species are represented in the seed bank. These findings imply that removing invasive vegetation alone is not enough to restore native ecosystems. In the soil, weeds are still present en masse, waiting for the first winter rains to germinate. But this potential for natives is limited at many locations by depleted seedbanks. The lottery is strongly, strongly in favor of the weeds.
We don’t yet know why seed banks in Orange County are so depauperate in natives. Is it a reflection of the long history of exotic annual dominance in these ecosystems? Are native seeds preferentially munched on by animals? Are no seeds arriving from nearby sites with natives? These are all questions that need to be answered. But in the meantime, restoration plans need to account for the fact that our restoration sites are full of seeds that we never want to see grow into adults. Management of the seed bank will be an important strategy going forward. And not all restoration seeding techniques are equal. Sara Jo found that broadcasting and hydro-seeding are effective for herbaceous and woody native species. Native grasses, however, have higher probabilities of establishment with imprint seeding, which involves rolling over seeds with a large machine or tamping of soils post-seeding.
My weed-wacking days at Crystal Cove are over, but the interest in restoration success in Orange County continues. Orange County has lost nearly all native grasslands and a significant portion of the coastal sage scrub community to development and exotic plant invasion. Artichoke thistle alone had covered over 4000 acres of the Nature Reserve of Orange County before management efforts began in the early 1990’s. Sara Jo’s research will directly help land managers in southern California (and future generations of environmental services interns) achieve better restoration outcomes. In addition to looking at seed banks, Sara Jo also studied how other site-specific factors such as soil type, land use history, and management practices influenced restoration success. To learn more, come listen to Sara Jo give a talk at the Cal-IPC Symposium in Sonoma County later this week or read her paper when it comes out.