红壤丘陵区马尾松林和湿地松林物候特征的时空变异及影响因素

Temporal-Spatial Variation and Drivers of Phenology in Pinus massoniana and Pinus elliottii Forests in Hilly Regions with Red Soil

【目的】探究马尾松林和湿地松林物候期的时空变异及影响因素,为红壤丘陵区森林碳汇时空格局精准评估与预测提供理论支撑。【方法】基于2017—2021年的数码相机时间序列数据,提取29块样地(马尾松林18块,湿地松林11块)的有效叶面积指数(LAIe)时空动态。采用有效叶面积指数的广义双重逻辑斯蒂模型确定物候期指标(生长季开始时间,SOS;生长季结束时间,EOS;生长季长度,LOS)。利用变异系数表征物候期时空变异幅度。通过皮尔逊相关分析和线性混合模型,解析气候(干旱指数、空气温度、降水量、饱和水汽压差、光合有效辐射)、土壤(土壤温湿度、土层厚度、石砾含量)和生物因子(林分密度、林下植被丰富度)对物候期的驱动作用。【结果】1)马尾松林和湿地松林物候特征均为单峰曲线(但马尾松林无明显峰值)。与马尾松林相比,湿地松林的SOS较晚,但LAIe的季节变化幅度更大且值更高。2)马尾松林的物候期在时空尺度上不如湿地松林稳定。马尾松林的SOS、EOS、LOS在空间上的变异系数和SOS在时间上的变异系数均大于湿地松林。3)在年际尺度上,马尾松林的SOS和EOS分别与早春和旱季0~120 cm土层的土壤含水量呈负相关和正相关;湿地松林的EOS与旱季0~60 cm土层的土壤含水量呈正相关。4)在空间尺度上,马尾松林物候期受林分密度、草本层物种丰富度和0~60 cm土壤石砾含量影响。【结论】马尾松林和湿地松林的物候特征在曲线峰值、SOS、LAIe变化幅度和数值大小等方面存在明显差异。湿地松林的物候期在时空尺度上更稳定。种内、种间竞争强度和土壤资源异质性共同驱动了红壤丘陵区马尾松林物候的时空变异格局。

【Objective】The study aims to investigate the temporal-spatial variation and drivers of phenological periods in Pinus massoniana and Pinus elliottii forests,in order to provide a theoretical basis for understanding and predicting the temporal-spatial pattern of forest carbon sink in the red soil hilly region.【Method】The temporal and spatial dynamics of the effective leaf area index(LAIe)were extracted from a total of 29 plots(18 for P.massoniana and 11 for P.elliottii),based on digital camera time series data collected between 2017 and 2021.A generalized double logistic model of LAIe was used to determine the phenological periods(start time of growing season,SOS;end of growing season,EOS;length of growing season,LOS).The coefficient of variation was used to characterize the spatiotemporal variation amplitude of phenological periods.Pearson correlation analysis and linear mixed model were employed to investigate the driving effects of climate(aridity index,air temperature,precipitation,saturation vapor pressure deficit,photosynthetically active radiation),soil(soil temperature and humidity,soil thickness,soil gravel content)and biological(stand density,understory vegetation richness)factors on phenological periods.【Result】1)The phenological characteristics of P.massoniana and P.elliottii forests exhibited a unimodal curve,with the former lacking an obvious peak.Compared to P.massoniana forest,the P.elliottii forest had later SOS but higher LAIe with greater amplitude of seasonal variation.2)The phenological periods of P.massoniana forest exhibited greater variability than those of P.elliottii forest at both temporal and spatial scales.P.massoniana forest had greater spatial variation coefficients of SOS,EOS,and LOS and exhibited greate temporal variation coefficient of SOS than those in P.elliottii forest.3)On an interannual scale,SOS and EOS in P.massoniana forest showed negative and positive correlations with soil moisture at 0–120 cm depth in early spring and dry season,while EOS in P.elliottii forest was positively correlated with soil moisture at 0–60 cm depth in dry season.4)The spatial variation of phenological periods in P.massoniana forests was influenced by stand density,species richness in the herbaceous layer,and gravel content within the 0–60 cm soil layer.【Conclusion】There are significant differences in the phenological characteristics between P.massoniana and P.elliottii forests in terms of curve peak value,SOS,and LAIe amplitude and value.The phenological period in P.elliottii forests is more stable in temporal and spatial scale.The temporal and spatial variation patterns of phenology in P.massoniana forests within the red soil hilly region are jointly influenced by intraspecific and interspecific competition intensity,as well as soil resource heterogeneity.