1. Introduction

The core role of vocabulary in second language learning was emphasized, and the importance of improving vocabulary proficiency in college English teaching was pointed out. At the same time, it pointed out the shortcomings of current research on vocabulary loss after college English learning, and emphasized the practical significance of such research. The chapter introduces the characteristics of second language learning from the perspective of dynamic systems theory, including its complexity, nonlinearity, and close relationships between subsystems. The aim of this study is to track the vocabulary fluency and richness of college English learners after completion using the framework of dynamic systems theory, in order to reveal the common patterns and individual differences of second language vocabulary system depletion.

2. Literature review

In depth exploration was conducted on the issue of vocabulary loss that Chinese university English learners may encounter in the process of vocabulary acquisition, emphasizing the dynamic and nonlinear characteristics of vocabulary loss. The literature review points out that vocabulary loss is commonly present in the process of language learning, and vocabulary is the earliest part to experience loss. Researchers focus on the loss representation and development status of vocabulary subsystems, especially vocabulary fluency and richness. The information forgetting hypothesis suggests that vocabulary loss first manifests as difficulty in extraction. The Vocabulary Fluency Test (VFT) is an important tool for evaluating vocabulary extraction efficiency and cognitive ability, often used to assess the degree of language loss. Vocabulary richness involves the combination of vocabulary elements, including three dimensions: vocabulary density, complexity, and diversity. Dynamic systems theory provides a new perspective for studying second language acquisition and loss, emphasizing the nonlinearity and variability in the process of language development. This study, based on the perspective of dynamic systems theory, conducted a 9-month tracking test on the vocabulary production of non English major college students, aiming to explore the vocabulary loss of learners after the end of college English teaching, especially the development and changes of vocabulary fluency and richness.

3. Research Design

A detailed description of the design of a study on the loss of vocabulary fluency and richness among Chinese university English learners. The research subjects are sophomore non English major students from a university in Shandong. After screening, 17 participants completed all the tests. The research tools include semantic fluency test and formal fluency test, as well as oral topic task and movie retelling task, aimed at measuring the participants' vocabulary fluency and richness. The research process includes a background questionnaire survey, vocabulary testing, and four oral output tests at different time points. The data analysis adopts statistical and analytical methods such as audio editing, transcription, proofreading, as well as vocabulary fluency and richness. The international universality of research methods helps to enhance the standardization, scientificity, and replicability of research.

4. Research results

The loss of vocabulary fluency and richness among Chinese university English learners was studied through repeated measures analysis of variance and multivariate analysis of variance. The study found that participants showed significant changes in vocabulary fluency, with a lower total number of form symbols in T2 stage compared to T1 stage, a significantly higher number in T3 stage compared to T2 stage, and no significant difference in T4 stage compared to T3 stage. In terms of vocabulary richness, there were significant differences in vocabulary density, proportion of high-frequency word forms, proportion of high-frequency part of speech symbols, and verb complexity among the four tests in the oral topic task, while there was no significant difference in these indicators in the movie retelling task. In addition, there were significant differences in the modified verb diversity of the oral topic task, the modified class/form ratio of the movie retelling task, and Uber value among the four tests. Overall, the participants showed certain dynamics and differences in vocabulary fluency and richness at different testing stages.

5. Discussion

This chapter analyzes the loss of fluency and richness of second language vocabulary among Chinese university English learners from the perspective of dynamic systems theory. The study found that the vocabulary fluency of the participants showed a trend of "slow decline gradually recovery again improvement" at different stages, reflecting the short-term difficulty of vocabulary extraction for learners after finishing college English learning. However, over time, the vocabulary extraction ability gradually recovered and improved. At the same time, there are differences in the development trends of individual participants, and the development of vocabulary fluency is uneven. In addition, in terms of vocabulary richness, no significant changes were found in vocabulary density, while vocabulary complexity and diversity exhibited loss characteristics in specific situations. The research results reveal the dynamic characteristics of second language vocabulary development, including universality and non-linear dynamic features. By observing the indicators of vocabulary fluency and richness, two typical development paths can be inferred: one is a trend of first decreasing and then increasing, and the other is a non-linear development trend. These findings provide a new perspective for understanding the process of second language vocabulary loss and offer insights for teaching and learning.

6. Conclusion

Emphasis was placed on the implications of the research results for second language vocabulary teaching, including the importance of developing long-term vocabulary retention strategies, lifelong learning concepts, and teachers designing task-based assignments to monitor students' vocabulary development. At the same time, the limitations of the study were pointed out, such as the number of participants, study period, and study scope. It is recommended that future studies recruit more participants, extend the study period, and broaden the research perspective.