以生態設計觀點探討台大校園植栽配置

Abstract

都市中校園綠地為重要的綠化空間之一，也是一般大眾休閒或活動的場所，然目前於校園內仍有些綠化問題如：過度遮陰、植栽生長不良、使用植栽種類單一、色彩配置少等，並對於不同植栽配置類型所產生的生態效益相關研究顯少。因此本研究將針對臺大校園內九處人潮聚集或具景觀特色的地點(辛亥門入口、舟山路入口、羅斯福路入口、大學廣場、行政大樓、振興草坪、舟山路側、鹿鳴廣場及黑森林)，進行植栽配置類型、使用植栽種類、整體景觀效果與維護管理頻度的調查，並從環境條件(以光照和土壤條件為主)與植栽視覺效果周年變化的角度探討植栽生長不良之因，最後評估其對於環境中負離子濃度之影響(生態效益)。 臺大校園內九處調查地點基本概況方面，共分為32小區，花壇小區多位於入口處或人潮聚集處，為該區的視覺焦點；綠地類型之小區則多以喬木為主體，依功能而有不同的配置方法(人為活動區域或休閒空間)，景觀類型的應用皆符合一般規劃原則。整體景觀效果受植栽生長狀況影響，而植栽生長狀況則與維護管理頻度相關；於整體景觀效果評分可看出，校園內植栽配置類型以多層次或雙層配置為主，但於同種植栽間層次性的配置組合仍有改善空間；植栽種類數和選擇方面，大致均運用三種以上的植栽種類進行配置，並選擇不同觀賞特性的植栽如：落葉喬木、觀葉植物、彩葉植物或季節性草花增添景觀效果。各類型植栽使用率最高的物種分別為榕樹(Ficus microcarpa L. f.)、杜鵑花(Rhododendron mucronatum)、地毯草(Axonopus compressus (Sw.) P. Beauv)、紫花酢醬草(Oxalis corymbosa DC.)與新幾內亞鳳仙花(Impatiens hawkeri W. Bull)。 各調查小區土壤及光度條件和植栽視覺景觀效果方面，影響植栽生長不良的原因以光度、各別植物生長習性和維護管理方法為主；當透光率小於25%和土壤硬度大於20 mm時，即有地被生長不均的情況發生，主要受影響的植栽為地毯草Axonopus compressus (Sw.) P. Beauv，且生長不良的情形會隨著遮陰程度越高而越嚴重。多數調查地點之土壤硬度(10-20 mm)與土壤介質含水量(20-40%)為適合植物生長的範圍，而土壤含水量較低(<20%)的地點通常也具有土壤硬度較高的現象。但校園內土壤電導度(EC)皆偏低，屬於較貧瘠的狀態，因此可透過施肥改善土壤肥力；土壤酸鹼值(pH)皆屬於植物生長可接受範圍(pH 4.2-7.7)內，並無植栽有明顯遭受毒害或元素缺乏的症狀發生，除杜鵑花有缺鐵情形。另外於冬季期間會發生寒害症狀的植物有：黃金葉金露華Duranta repens ‘Golden leaves’、矮仙丹花Ixora x williamsii Hort.、黛粉葉Dieffenbachia seguine (Jacq.) Schott var. seguine、粗肋草Aglaonema spp.天南星科等植物，皆會影響植物外觀的表現；錦竹芋Ctenanthe oppenheimiana (E.Morren) K.Schum.種植於舟山路側較通風處，皆有葉片反捲的現象而影響視覺景觀效果，因此建議應於環境濕度較穩定的地點使用，才可維持良好景觀效果。 植栽配置對空氣負離子濃度影響方面，有植栽區域負離子濃度皆大於無植栽區域，其中以喬木－灌木－地被組合最佳，雙層或具喬木組合次之，單一植栽層較差；而空氣負離子濃度和調查地點之綠覆面積呈顯著正相關(r＝0.9362***)。同時空氣負離子濃度具有季節性與日變化，以夏季和上午10點左右為濃度最高時段；雖然本研究調查結果顯示，空氣負離子與溫度、相對濕度和光度皆無顯著相關性，但由季節變化與日變化的調查結果推測，可能與植物生長最適時期相關。 綜合上述研究，於臺大校園內大部分地點之整體景觀效果良好，評分較低區域，主要原因為層次性低及植栽生長狀況不佳所致，而維護管理頻度將影響植栽生長表現。目前調查區域之植栽配置偏向多層或雙層的類型，但植栽種類的使用以自生植物比例較高。雖然校園內土壤EC值低於建議值並屬於較貧瘠的狀態，但對於植栽生長並無明顯影響，造成生長狀況不佳的主要因子為光度、土壤硬度和植栽挑選或配置不當所致。最後以空氣負離子濃度作為評估植栽產生生態效益的標準，顯示適當的使用植栽對於提升環境之空氣負離子濃度具有一定效果。因此，進行植栽配置時，環境條件、植栽習性和其具備的生態效益皆為重要的參考原則。

Green landscapes on school campuses are part of an important green space in an urban area, providing places for public recreational use. Some common problems on campus green space include excessive shading, poor plant growth, lack of plant diversity, and monotonous color configuration. Moreover, there were few studies about the ecological effects of different plant arrangement. This study aimed to analyze the plant arrangement, plant species used, overall landscape effects and maintenance frequency in nine crowded or attractive landscape locations on NTU campus (Xin-Hai entrance, Zhou-Shan Rd. entrance, Roosevelt Rd. entrance, College plaza, Administration Building, Zhen-Xing Lawn, alongside of Zhou-Shan Rd, LuMing Square and Dark Forest). In addition, we investigated the reasons for poor plant growth through observing the surrounding environment (specifically lighting and soil conditions) and annual changes in the visual appearances of the plants. Finally, we evaluated the ecological effects from landscaping by measuring NAI concentrations in the environment. Nine different survey locations on NTU campus were divided into 32 smaller areas. Flower beds are mostly located near entrances or where people gather and they form the visual focus for the area. Green-ground areas mainly consist of trees arranged based on different purposes (recreation or leisure). The application of landscaping types generally met planning guidelines. Maintenance frequency and the conditions of plant growth were associated with overall landscape effect. Plant growth was affected by maintenance frequency and this agreed with the result from overall landscape effect scoring. Plant arrangementies on campus are mostly multi-layered or bi-layered with much room for improvement for layering combinations of similar species. In terms of plant variety and selection, at least three plant varieties with different viewing attributes have been used in the allocation to increase viewing deciduous trees, foliage plants, color-leaf plants and seasonal floral plants. Species of different plant types with the highest usage rates include Ficus (Ficus microcarpa L. f.), Azalea (Rhododendron mucronatum), Tropical carpetgrass (Axonopus compressus (Sw.) P. Beauv), Lilac oxalis (Oxalis corymbosa DC.), New Guinea Impatiens (Impatiens hawkeri W. Bull). Soil and lighting conditions as well as visual effects of plants in each survey area revealed that poor plant growth was mostly the result of light intensity, individual plant growth habit and routine maintenance and management. When the rate of light penetration was smaller than 25% and soil hardness greater than 20 mm, inconsistent growth of ground coverings occurred. The plant affected the most was the tropical carpetgrass where growth worsened as shading increased. Soil hardness and soil moisture content in most survey areas were appropriate for plant growth. Locations with lower soil moisture generally exhibited higher soil hardness. Soil EC in general was lower on campus indicating poor soil structure, which may be improved with fertilization. Soil pH was within an acceptable range for plant growth (pH4.2-7.7) where most plants did not show symptoms of toxic injury or nutritional deficiency, except for Azalea which was iron-deficient. The plants that suffered from chilling injury during the winter included Golden dewdrop (Duranta repens ‘Golden leaves’), Ixora (Ixora x williamsii Hort.), Dumb canes (Dieffenbachia seguine (Jacq.) Schott var. seguine), and Aglaonema (Aglaonema spp.). Never-never plant (Ctenanthe oppenheimiana (E.Morren) K.Schum) grown alongside of Zhou-Shan Rd. with good air circulation resulted in leaf curl and negatively affected viewing aesthetics. We recommend using this plant in a location with more stable atmospheric humidity for better viewing results. Plant community also affected the NAI concentration. Areas with plants had higher NAI concentrations than those without. The highest NAI concentration was found near combinations of tree-shrub-ground covers, followed by the bi-layer combinations with trees. Single layers had the lowest NAI concentration. A significant positive correlation was found between NAI concentration and green coverings in survey areas (r＝0.9362***). Also, NAI concentration was seasonal and diurnal with summer and 10am having the highest concentration. Although this study did not find a significant correlation between NAI, temperature, relative humidity and light intensity, NAI concentration may be related to the optimal period for plant growth by observing the seasonal and diurnal variations.