Progress 04/23/04 to 03/31/05
OUTPUTS: This research examined gorse's ability to alter the soil ecosystem and biochemistry over time, including pH, organic matter content, nutrient mineralization/immobilization and soil and water chemistry. This study laid the groundwork for further research into the alteration and impact of invasives to both above and below ground ecosystems over time. The research was conducted on the coast of Washington state, where gorse is found growing on sand. In order to determine the age of gorse stands, the progression of invasion over time was documented with aerial photos. Populations were identified, and then study and control areas were selected. Foliage and soil samples were sent for lab analysis. Local observations were made. Also, the technique "dendrochronology," estimating plant age by counting annual plant rings, was used to accurately assess individual gorse plant age. An exploratory analysis, using multivariate techniques was also done to begin to understand how these free dune systems are being changed by the succession of invasive plants across them. PARTICIPANTS: Participants: 1. Sarah Reichard, Associate Professor, University of Washington School of Forest Resources. 2. Bronwyn Scott, Graduate Student, University of Washington School of Forest Resources. Training or Professional Development: Bronwyn Scott is working on her masters' thesis with regards to this research. She is planning on going on for a PhD in quantitative invasive species ecology with Professor Reichard. TARGET AUDIENCES: The target audience is land managers, noxious weed control agencies and other governmental or academic natural resources groups. These results will be part of the empirical evidence needed to evaluate the current status of ecological impact models. With improvements in impact models and better understanding of the alteration of ecosystem processes, recommendations can be made for more precise prediction, assessment and management of invasives as well as improved recovery of processes to facilitate easier restoration once invasives are removed. PROJECT MODIFICATIONS: Not relevant to this project.
The gorse grew in thick populations in the sand dunes. There was a definite line where the gorse stopped, and the broom and grass continued towards the beach. There was not any apparent reason for this. It tended to grow with many stems, either straight up or laterally along the ground, making a tangled weave. The study area was lined by wetlands on the east, and my personal observation was that the gorse tended to grow more matted and lower, the closer to the wetland. The gorse rarely had plants directly underneath, and if there were plants, they were usually small and unhealthy. The plants that could sometimes survive were the native rose, sword fern, and carex. The top 10 cms of soil varied from sand, to clay, all the way to a slightly mottled wetland soil. Despite using nested ANOVAs, there did not seem to be any significant effect on the gorse and what kind of soil it was growing in. The stems collected ranged in ages from 4 to 26, which is consistent with what is known of gorse's biology. The older samples tended to be closer to the beach. It is clear that there are interesting results from this experiment. Every part came up with significance. There are still many types of analysis that can be done to help clarify what the results might mean. One of the first noticeable results is that counting the rings of gorse in this particular area seemed to work as a way of judging time. Not only were the rings clear, but also reflect what is known about gorse's life cycle. It is not a technique that can necessarily be transferred to other areas or plants. Complicating issues might be: no clear seasons, fire history, extensive use of poisons, and age of infestation longer then plant age. There was a choice that had to be made about how to look at the soil. Because this experiment was tied to research done by Ruth Mitchell in England, we chose to look at the top 10 cm of soil, and not the top 10 cm of mineral soil. This looks at the changes of the top 10 cm, but does not look at soil nutrient pools. This could explain apparent discrepancies in the data, such as total N increasing in the top 10 cm, but not significant in the foliage. Gorse appears to be quickly creating OM that is high in N, but it is not necessarily getting to the new plant tissue. A cursory comparison with Professor Mitchell's results show that in her research, gorse is increasing pH in a very acidic environment. On the Washington coast, it is lowering pH. It appears that gorse may have an ideal pH level, and that it is capable of changing the soil pH to approach that level. There were some other odd results, like the highly significant increase of Pb in the top 10 cms of the soil. This seems to be happening only for that heavy metal, so the argument that maybe more things are just accumulating doesn't really work. This research was only part of what would have to be done to have a whole picture of what is happening both above and below ground when invasion happens. Two things that would need to be added are looking at the biota of the soil, and also documenting and testing different soil layers so that nutrient pools can be estimated.
- No publications reported this period