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從大肚臺地竹坑北坑的土壤種子庫組成特性探討其對森林復育影響

Composition of the Soil Seed Bank and its Effects on Forest Restoration in Beikeng, Zhukeng Area of Dadu Terrace, Taichung

摘要


大肚臺地竹坑北坑地區的植被形相為森林、疏林及草生地相鑲,經常發生火燒,森林有逐漸退化的跡象。本研究以種子發芽法調查大肚臺地竹坑北坑地區樟樹人工林、相思樹人工林、大黍-馬纓丹灌叢草生地和大黍草生地等4種植物社會的土壤種子庫組成特性,探討種子庫與地上植被組成之關係,並在火燒後之大黍草生地以土壤擾動方式進行相思樹種子發芽試驗。試驗區土壤種子庫共記錄899株幼苗,共24種種子植物,平均種子密度約1,816粒/m^2;種子儲量最豐富的前三科為菊科、茜草科與禾本科,出現最多種類的科為菊科(6種),種子儲量有92%為草本植物,以貓腥草、闊葉鴨舌癀舅和大黍等3種入侵性草本植物為優勢組成。歸化植物種數佔土壤種子庫種類41.7%,種子儲量佔總量的89.2%;土壤種子庫的原生木本植物僅6種,佔種子儲量5.8%,以相思樹比例最高。種子密度最高的植物社會為大黍草生地(3,363粒/m^2),其次依序為樟樹人工林(1,503粒/m^2)、相思樹人工林(1,500粒/m^2)及大黍-馬纓丹灌叢草生地(793粒/m^2),土壤種子庫中的種子主要集中在土壤表層,和地上植被的相似性偏低,最高者為大黍-馬纓丹灌叢草生地(32.3%),最低為相思樹人工林(13.8%)。火燒後大黍草生地去除大黍等草本植物並擾動土壤後,相思樹種子苗數明顯多於未處理的對照組。研究顯示歸化植物為研究區的土壤種子優勢組成,對潛在自然植群造成嚴重入侵污染,嚴重影響其森林自然恢復過程的物種多樣性。原生植物種類及種子儲量太少,即使減少火燒發生頻度,研究區亦難以恢復;人力適度介入植被更新,如鄉土樹種造林、原生植物種子或繁殖體引入,可以加速大肚臺地森林建立並增加物種多樣性。

並列摘要


The physiognomic vegetation of Beikeng, the Zhukeng area in Dadu terrace, is a mosaic of forests, savannas, and grasslands. The forest has gradually degraded due to the frequent occurrence of fires. A seed germination method was used to investigate the soil seed bank composition of four plant communities, namely Cinnamomum camphora plantation, Acacia confusa plantation, Panicum maximum-Lantana camara shrub-grassland, and Pa. maximum grassland. The composition relationship between the soil seed bank and aboveground vegetation was investigated, and the seed germination test of A. confusa was performed in the soil of Pa. maximum grassland that was disturbed after a fire. A total of 899 seedlings were recorded as belonging to 24 spermatophytes in the soil seed bank, and the average seed density was approximately 1,816 grains/m^2. Most of the seeds belonged to the three families, namely Compositae, Rubiaceae, and Gramineae, and Compositae (six species) had the highest number of species. Ninety-two percent of the seed abundance was from herbaceous plants. Among them, Praxelis clematidea, Spermacoce latifolia, and Pa. maximum, three invasive species were the most abundant compositions. The naturalized plants accounted for 41.7% of the species composition and 89.2% of the total seed abundance in the soil seed bank. The soil seed bank had only six native woody plant species, accounting for 5.8% of the total seed abundance, of which the highest level of abundance was of A. confusa. The highest seed density occurred in the Pa. maximum grassland (3,363 grains/m^2), followed by C. camphora plantation (1,503 grains/m^2), A. confusa plantation (1,500 grains/m^2), and Pa. maximum-L. camara (793 grains/m^2). The seeds of the soil seed bank were mainly concentrated in the soil surface. The composition similarity between the soil seed bank and the aboveground vegetation was low: the highest was Pa. maximum-L. camara shrub-grassland (32.3%) and the lowest was A. confusa plantation (13.8%). In the Pa. maximum grassland after a fire, the number of A. confusa seedlings was significantly higher in disturbed soil than in untreated control groups. Our results revealed that naturalized plants were the dominant species of soil seeds in the study area, and these species caused serious invasion of the potential natural vegetation, which would seriously affect the species diversity during the process of natural forest restoration. Because the composition and abundance of native species in the soil seed bank were considerably low, restoration of the study area to the native forest was difficult, even when the frequency of fire was decreased. Moderate involvement of humans in vegetation regeneration processes, such as in native tree afforestation, and the introduction of native plant seeds or propagules into the habitat can facilitate the establishment of forests and increase the diversity of species.

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