九份二山崩塌地之土壤性質與養分型態

Abstract

土壤性質、養分型態與森林生態受到崩塌影響甚大，土壤性質的改變不只受到崩塌過程 (堆積或崩落) 與規模的影響，亦會因崩塌後植生演替的差異，而造成崩塌後土壤性質在崩塌地區有著極大的空間異質性。本研究調查九份二山崩塌後，崩塌過程 (堆積或崩落) 與植生演替對土壤性質與養分型態的影響，並與鄰近的非崩塌地做比較。我們依崩塌過程的不同，先將樣區分為3處(土石移動、土石堆積與非崩塌樣區)，再依植生不同，總共區分為6個採樣樣區，包括 (1) 土石移動無草區 (2) 土石移動有草區 (3) 土石移動芒草區 (4) 次生林堆積區 (5) 人工林堆積區與 (6) 非崩塌樣區。 結果顯示土石移動無草區、土石移動有草區和土石移動芒草區的土壤性質與養分，較次生林堆積區、人工林堆積區與非崩塌樣區等，有較高的含石率、總體密度、pH值，較低的有機碳、總氮、氮礦化速率和CEC，其中又以土石移動無草區的測值呈現最高或最低，顯示該區域土壤化育明顯受崩塌干擾的影響。磷分層萃取的結果顯示土石移動處與堆積處總磷含量皆低於非崩塌樣區，而非崩塌樣區的可利用磷 (resin-P、NaHCO3-Pi和NaHCO3-Po) 含量也最多，土石移動處則以HCl-P佔總磷百分比最高，土石堆積處以Residual-P和NaOH-P比例最高，皆為植物不易吸收利用的磷型態。由苗圃施肥試驗，土石移動處與堆積處的土壤中，磷並非植物生長的限制因子，然而NP肥的施用可以促進苗木生長。另外，由現地水分勢能的監測得知，次生林堆積區與土石移動芒草區表層土壤的水分勢能在一年的觀測中皆能維持在- 1.5 MPa以上，而土石移動無草區與土石移動有草區在冬天枯水期時，水分勢能低於- 1.5 MPa，不適宜植物生長。綜觀實驗結果，土石移動無草區位於演替初期階段，土壤化育程度最低，其次為土石移動有草區與土石移動芒草區，次生林堆積區則因崩塌後有次生林生成，植物加速土壤化育，但部分的土壤性質與養分型態仍與非崩塌樣區呈顯著差異。因此崩塌造成的土壤性質與養分型態的改變，是影響土壤化育與植生生態的關鍵因子。

Landslides may exert immense impacts on soil properties, nutrient speciation and forest ecosystems. The impacts of landslides on soil properties not only vary with their movement type (deposition or removal) or scale but also the succeeding vegetation can have great contribution to spatial variation inside landslide. In this study, the effects of movement type (deposition or removal) and succeeding vegetation on soil properties and nutrient speciation inside the Chiufenershan landslide scar were evaluated. Landslide soil was also compared with the adjacent undisturbed soil. According to the movement type and vegetation, we divided soil samples into three main sites (removal, deposition and undisturbed sites). And then divided soil samples into six small sites, including (i) removal site without vegetation, REM-NG (ii) removal site with vegetation, REM-G1 (iii) removal site at a gentle slope with vegetation, REM-G2 (iv) deposition site with secondary forest, DEP-SEC (v) deposition site with plantation forest, DEP-PLA and (vi) Adjacent undisturbed sites, UND. Our results indicated that soil properties and nutrient at removal sites (REM-NG, REM-G1 and REM-G2) had higher bulk density, rock fragment content and pH value, but less soil organic carbon, total nitrogen, CEC and N-mineralization rate than both deposition (DEP-SEC and DEP-PLA) and undisturbed (UND) sites. The soil properties without vegetation (REM-NG) even showed the extreme end compared to the soils with grass vegetation. The removal and deposition sites had similar total phosphorus concentrations, but were significantly less than that at the undisturbed sites (p < 0.05). Most of the phosphorous were HCl-P in the removal sites, Residual-P and NaOH-P in the deposition sites. Although the main phosphorus speciation in the removal and deposition sites were biologically unavailable, our results did not showed that P was the limiting nutrient for soil. However, applying both N and P could improve seedling growth. In addition, the long-term field monitoring data of soil water potential showed the deposition site (DEP-SEC) and the lower removal site (REM-G2) had water potential maintained above -1.5 MPa throughout the whole year. While the removal site without vegetation (REM-NG) and removal site with vegetation (REM-G1) had soil water potential lower than -1.5 MPa in winter, indicating that the adverse effects for both sites. Overall, the soil in removal sites without vegetation (REM-NG) showed its early stage of succession, and the soil weathering was less severe than removal sites with vegetation (REM-G1 and REM-G2). By contrast, the deposition sites had more advanced soil weathering, but the soil properties and nutrient speciation were still different from the undisturbed sites. Therefore, the Chiufenershan landslide has changed the soil properties and nutrient speciation, and it is speculated that these changes played important roles on soil and ecosystem development.