槟榔林冠穿透雨空间格局的时间稳定性

槟榔林是热带地区广泛种植典型经济林,独特的树冠结构改变了穿透雨的空间格局,但针对穿透雨空间格局的时间稳定性研究很少,影响对穿透雨生态效应的认识与调控。以海南岛槟榔林为研究对象,基于33场降雨数据,研究了穿透雨的空间格局及时间特性,结果显示:(1)槟榔树冠内不同位置穿透雨差异极显著(P0.01),穿透雨率分别为:树干附近(85.6%)、冠幅中央(48.3%)、冠幅边缘(59.8%),穿透雨空间格局表现为向树干附近汇集的特点;不同方位的穿透雨率仅东面显著高于南面(P0.1),表明风向对穿透雨空间格局具有一定影响。(2)槟榔树冠下各位点穿透雨时间变异程度大(65.7%),但槟榔树冠幅中央穿透雨时间稳定性较好(55.6%),而树干旁边和冠幅边缘穿透雨时间稳定性较差(25%、19.4%),各方位穿透雨的时间稳定性相差不大(约1/3)。(3)距树干距离和降雨量影响穿透雨的时间稳定性,距树干不同距离平均叶片倾斜角度的差异是造成穿透雨在时间上不稳定的关键因素,平均叶片倾斜角度与穿透雨时间不稳定程度呈现显著正相关关系(P0.05);穿透雨时间稳定性在中等降雨条件下最差,随着降雨量增加,冠层对穿透雨的"屏蔽效应"减弱,"滴水效应"增加。揭示槟榔植株个体穿透雨的空间格局及时间稳定性,可为认识乔木个体尺度穿透雨时空特征提供参考,也可为解释林地小尺度土壤水分和土壤侵蚀的空间格局及时间动态提供依据。

Temporal stability of throughfall pattern in areca plantation

Areca plantation, as a typical economic forest, is widely distributed in the tropical areas. Its unique canopy structure alters the spatial pattern of throughfall, which further influences the hydrogeological processes and results to different ecological effects, such as soil erosion. However, available information is limited on how the areca plantation changes the spatial pattern and the temporal stability of throughfall. Here the spatiao-temporal variation of throughfall was observed under 33 rainfall events in areca plantation in Hainan Island. We found that throughfall changed significantly with locations under canopy of areca plantation (P < 0.01). The throughfall rate was different near the trunk (85.6%), in the center of canopy (48.3%), and at the edge of canopy (59.8%). The location near the trunk had the highest throughfall. The throughfall rate in the east of the trunk was significantly higher than that in the south (P < 0.1), indicating that wind also impacted the spatial pattern of throughfall. In addition, The throughfall of different locations under the canopy of areca plantation presented high variability over time (65.7%). However, the throughfall in the center of canopy was relatively stable over time (55.6%), while it had poor temporal stability near the trunk (25%) and at the edge of canopy (19.4%). Small differences (about 1/3) of temporal stability in throughfall among different directions were observed. The distance from the trunk and the rainfall were the main factors affecting the temporal stability of throughfall. Furthermore, the former influenced the temporal stability of throughfall mainly through leaf angle. The mean angles of leaves were negatively correlated with the temporal stability of throughfall (P < 0.05). The temporal stability of throughfall was the weakest under moderate rainfall. With the increase of rainfall, the "wetting effect" of the canopy decreased, and the "drying effect" increased. The above results improved our understanding how tree species impact the temporal and spatial patterns of throughfall, which could also help to explain the spatio-temporal dynamics of soil moisture and soil erosion at small scale in plantation ecosystems.