Department of Biology, Stanford University, Stanford, California 94305, USA.
Ecology. 2009 Nov;90(11):3074-86. doi: 10.1890/08-0813.1.
We compared forest canopy heights and nitrogen concentrations in long-term research sites and in 2 x 2 km landscapes surrounding these sites along a substrate age gradient in the Hawaiian Islands. Both remote airborne and ground-based measurements were used to characterize processes that control landscape-level variation in canopy properties. We integrated a waveform light detection and ranging (LiDAR) system, a high-resolution imaging spectrometer, and a global positioning system/inertial measurement unit to provide highly resolved images of ground topography, canopy heights, and canopy nitrogen concentrations (1) within a circle 50 m in radius focused on a long-term study site in the center of each landscape; (2) for the entire 2 x 2 km landscape regardless of land cover; and (3) after stratification, for our target cover class, native-dominated vegetation on constructional geomorphic surfaces throughout each landscape. Remote measurements at all scales yielded the same overall patterns as did ground-based measurements in the long-term sites. The two younger landscapes supported taller trees than did older landscapes, while the two intermediate-aged landscapes had higher canopy nitrogen (N) concentrations than did either young or old landscapes. However, aircraft-based analyses detected substantial variability in canopy characteristics on the landscape level, even within the target cover class. Canopy heights were more heterogeneous on the older landscapes, with coefficients of variation increasing from 23-41% to 69-78% with increasing substrate age. This increasing heterogeneity was associated with a larger patch size of canopy turnover and with dominance of most secondary successional stands by the mat-forming fern Dicranopteris linearis in the older landscapes.
我们比较了夏威夷群岛基质年龄梯度上的长期研究点以及这些点周围 2 x 2 公里景观中的林冠高度和氮浓度。远程航空和地面测量都用于描述控制林冠属性的景观水平变化的过程。我们整合了一个波形光探测和测距 (LiDAR) 系统、一个高分辨率成像光谱仪和一个全球定位系统/惯性测量单元，为每个景观中心的长期研究点周围 50 米半径的圆圈内的地面地形、林冠高度和林冠氮浓度提供了高度分辨率的图像 (1)；(2) 对于整个 2 x 2 公里的景观，无论土地覆盖如何；(3) 在分层后，针对我们的目标覆盖类，在每个景观的建筑地貌表面上，以原生为主的植被。所有尺度的远程测量都与长期站点的地面测量得出了相同的总体模式。两个较年轻的景观比较老的景观支撑着更高的树木，而两个中等年龄的景观的林冠氮（N）浓度比年轻或年老的景观都高。然而，即使在目标覆盖类中，飞机分析也检测到了景观水平上的林冠特征的大量变化。较老的景观中的林冠高度更为异质，变异系数从 23-41%增加到 69-78%，随着基质年龄的增加而增加。这种异质性的增加与林冠更替的斑块大小较大有关，并且在较老的景观中，大多数次生演替林由形成垫的蕨类植物 Dicranopteris linearis 主导。
