Using digital camera images to analyse snowmelt and phenology of a subalpine grassland
Using digital camera images to analyse snowmelt and phenology of a subalpine grassland
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DOI：
10.1016/j.agrformet.2014.08.007
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发表时间：
2014-11-01
影响因子：
6.2
通讯作者：
Menzel, Annette
中科院分区：
文献类型：
--
作者：
Julitta, Tommaso;Cremonese, Edoardo;Menzel, Annette
植物物候学是气候变化对植被影响的常用且合适的指标。在山区，物候受气温、光周期和积雪等环境因素的影响。本研究利用亚高山草原3年（2009年、2010年和2011年）采集的数字图像，在空间和时间维度上研究融雪时间与生长季节开始之间的关系。对约150 m(2)的广阔区域进行图像分析，以表征草地物候的空间异质性。所研究的区域被划分为 855 个 10 x 10 像素单元，并且对于每个单元，每年的绿色色坐标 (gcc) 时间序列是根据每小时图像计算的。为了分析物候的空间模式，从 gcc 时间序列中提取每个单元的季节开始。基于相同的网格维度，获得了与每个单元中的积雪从地面消失的年份相对应的三张年融雪日期图。尽管该区域的完全融雪发生得很快，但最多在六天内，我们发现了几种不同的空间模式，凸区比凹区雪融发生得更早。出人意料的是，融雪日期的差异与生长季节的开始呈负相关。负相关性的解释是考虑到具有不同微地形特征的区域也具有不同的物种组成：在凹地区域，生长季节开始得更早，机会性物种在融雪后生长迅速，而典型的凸地区域草的物候发育可能需要更长的时间。这种行为在 2011 年尤为明显，其特点是极其令人期待的融雪。相反，本研究分析的三年间融雪时间与季节开始之间关系的分析强调了 2011 年生长季节开始的提前。然而，这仅适用于机会性物种丰富的地区，例如非草类植物，对于这些地区，积雪在决定物候发展的开始方面起着主要作用。本研究的结果支持使用重复数码摄影来分析亚高山和高山草原等复杂生态系统中植物物种组成对物候的作用的可能性。 (C) 2014 Elsevier B.V. 保留所有权利。
Plant phenology is a commonly used and suitable indicator of the impact of climate change on vegetation. In mountainous areas, phenology is governed by environmental drivers such as air temperature, photoperiod and the presence of snow. In this study, digital images collected over 3 years (2009, 2010 and 2011) in a subalpine grassland site were used to investigate the relationship between the timing of snowmelt and the beginning of the growing season in both the spatial and the temporal dimension.The image analysis was conducted for a wide area corresponding to approximately 150 m(2) to characterize the spatial heterogeneity of grassland phenology. The investigated area was divided into 855 10 x 10 pixel cells, and for each cell annual time series of green chromatic coordinates (gcc) were computed from hourly images. To analyse the spatial pattern of phenology, the beginning of the season for each cell was extracted from the gcc time series. Based on the same grid dimension, three maps of yearly snowmelt date corresponding to the day of the year in which the snow in each cell disappeared from the ground were obtained.Although complete snowmelt in the area occurred rapidly, within a maximum of six days, several distinct spatial patterns were identified with snowmelt occurring earlier in convex compared to concave areas. Differences in snowmelt dates were quite unexpectedly negatively related to the beginning of the growing season. The negative correlation was explained considering that areas characterized by different microtopography have also a different species composition: the growing season began earlier in concave areas preferred by opportunistic species with a fast development after snowmelt while phenological development of grass typical of convex areas can take longer. This behaviour was especially evident in 2011 characterized by an extremely anticipated snowmelt. On the contrary, the analysis of the relationship between the timing of snowmelt and the beginning of the season between the three years analysed in this study, highlighted an advancement of the beginning of the growing season in 2011. However, this is valid only in areas characterized by the abundance of opportunistic species such as forbs for which the snow cover plays a major role in determining the beginning of phenological development. The results presented in this study support the possibility of using repeat digital photography to analyse the role of plant species composition on phenology in complex ecosystems such as subalpine and alpine grasslands. (C) 2014 Elsevier B.V. All rights reserved.