As a Climate Action Corps Fellow working at the Audubon Center at Debs Park this summer, I was given the opportunity to pursue an independent research project, among my other restoration duties at the center. For my project, I sought to measure the success rate of newly-planted native plants in our summer restoration sites.
With this project, I ultimately wanted to foster my newly-developed interest in native plants, following my last semester at Occidental College as a Biology Major. After taking a course on the flora of Southern California with Dr. Gretchen North, I became increasingly invested in learning more about habitat restoration, in the context of plants native to Los Angeles. And with this newfound intrigue and in transitioning into this fellowship, I also wanted to further explore how well we were doing in our restoration work and maintenance, how far we could succeed in planting in the summer (which is not done at the Center), and what the Center can do better in the future.
Through the project, I wanted to ask, “What proportion of newly-planted native plants in restoration sites during the summer survive? And which species performs/grows the best during this time period?” In order to address these questions, I measured “success” in three ways: Survival Rate (proportion alive vs. dead), Growth Rate (average height in cm), and Evaluation of Foliage Health.
Given the nature of traditional plant growth in the summertime, I hypothesised that--while most of the plants should live--there should be little to no growth in most sites, however, woody shrubs could potentially grow. And with unprecedented temperatures and drought in Los Angeles, I expected this to be even more so. However, my research presented that this lack of growth may not be the case.
The first assumption was correct in that only two out of 89 plants died in the duration of the 4 week study, with 99.16% of our plant population still alive. However on average, almost every plant species grew, with the exception of Black Sage (Salvia mellifera).
Although when the growth rate was broken down by site, this “little to no growth” hypothesis was correct in our Driveway Restoration Site. In contrast, the other two sites demonstrated a great amount of growth in most species, with at least 2 cm growth on average. Most likely, this is because the Driveway Restoration is in full sun all day, which can cause more stress on the plant and limit its growth. On the other hand, the other two sites have some sort of shade for at least some time of the day--giving the plants somewhat of a break from the harsh sun.
The same was also seen in terms of foliage health, for the most amount of non-normal, stressed plants by the end of the study came from the Driveway Restoration SIte too. However overall, the foliage health for most of the plants was generally good (83.9%), accounting for normal plants or only slight indicators of stress (slight browning, slight wilting, or slight leaf discoloration).
While 83.9% on the last week’s evaluation does not seem super ideal compared to our expectation of 100% with good maintenance, this percentage is still the exact same as the percentage of “generally in good condition” plants from the first visit. Meaning, after only a week of waiting to measure from the initial outplant, the plants generally encountered no more stress than they did after 4 weeks of observation. Only 16.1% of plants were in definitely poor condition, and, in turn, this proportion stayed the same throughout the study as well.
Though, what do all of these measurements mean? We can conclude from this data that, as a whole, all three of our summer restoration sites succeeded and were maintained well! But how can we move forward with this information?
Firstly, in the future, the center should most likely water "Full Sun" restoration areas, like the Driveway Restoration Site, more frequently to limit plant stress--specifically in the summer and in sites that are newly outplanted in the summer. Secondly, to limit stress all together, it might be beneficial to plant certain sensitive plants not in summer, potentially in the spring when soil moisture is greater and sun intensity is less. However, planting in the summer has shown to not necessarily be unsuccessful in achieving our goals.
At the Audubon Center at Debs Park, we ultimately strive to restore natural lands in Los Angeles, in order to create a more ideal habitat for native birds. In evaluating the success of our sites, and to what extent, we can better ensure the lasting impact of our current and future habitat restoration efforts on the birds, on the overall ecosystems in Los Angeles, and on the many benefits this can provide for our community as well.