The present paper introduces a satellite-based approach to the detection of phenology events in beech forests across Slovakia (the Western Carpathians) using the MOD/MYD09 products. Normalized vegetation index (NDVI) was used for determining the onset of the phenophases in spring and autumn. Double logistic sigmoid function was applied in order to fit the NDVI profile during the year. The satellite-derived phenological metrics was based on calculating the extreme values of the sigmoid function and its derivatives. Between 2000 and 2015, a time-series analysis using the linear regressions models revealed that the onset of leaf unfolding shifted at a rate of 0.8 day per decade, the onset of leaf fall was delayed at a rate of 1.9 day per decade, and the growing season (GS) extended at a rate of 1.1 day per decade. However, at a regional level, the trends were not found to be statistically significant in either case. Leaf unfolding/fall was significantly non-linearly delayed/advanced with the increase of altitude (p<0.01). GS duration varied extensively within the region. Theil-Sen estimation of GS trend revealed the median shift of 1.8 days, the range of shift being from -7.0 to +12.1 days at the 5-95 % quantile for 2000-2015. A significant inverse correlation between GS shift and GS length (p<0.01) was observed. The GS shift was positive in the sites with shorter GS and negative in the sites with longer GS.

/pdf/phenology-of-the-beech-forests-in-the-western-carpathians-1zso9j3f5s.pdf

Phenology of the beech forests in the Western Carpathians from MODIS for 2000-2015

Analyses of climate change based on point observations indicate an extension of the plant growing season, which may have an impact on plant production and functioning of natural ecosystems. Analyses involving remote sensing methods, which have added more detail to results obtained in the traditional way, have been carried out only since the 1980s. The paper presents the results of a bibliometric analysis of papers related to the growing season published from 2000–2021 included in the Web of Science database. Through filtering, 285 publications were selected and subjected to statistical processing and analysis of their content. This resulted in the identification of author teams that mostly focused their research on vegetation growth and in the selection of the most common keywords describing the beginning, end, and duration of the growing season. It was found that most studies on the growing season were reported from Asia, Europe, and North America (i.e., 32%, 28%, and 28%, respectively). The analyzed articles show the advantage of satellite data over low-altitude and ground-based data in providing information on plant vegetation. Over three quarters of the analyzed publications focused on natural plant communities. In the case of crops, wheat and rice were the most frequently studied plants (i.e., they were analyzed in over 30% and over 20% of publications, respectively).

/pdf/remote-sensing-in-studies-of-the-growing-season-a-13366ca3.pdf

Remote Sensing in Studies of the Growing Season: A Bibliometric Analysis

In this study we analyzed the effect of selected biometeorological variables on the onset of phenophases in three beech stands in different climatic areas (warm, moderately warm and cold). We have focused on two phenophases – leaf unfolding and leaf colouring. Timing of both phenophases was identified visually and using series of MODIS satellite images. The data were collected during a 13-year period (2000–2012). For the spring period, we found a significant dependence between temperature and precipitation-based biometeorological variables and leaf unfolding in both datasets – those based on visual and remote sensing-based observations. The average air temperature in the period from February–April was the most significant factor which initiated the onset of beginning of leaf unfolding in all three investigated stands. The evapotranspiration-based biometeorological variables (climatic water balance, actual evapotranspiration, dryness index) had no effect on the onset of the beginning of leaf unfolding observed using both methods. The high precipitation totals in April caused the later onset of leaf unfolding in all stands. The relationship between the first autumn phenophase – leaf colouring and biometeorological variables was found significant in beech stand in the w arm climatic area only.

Effect of biometeorological variables on the onset of phenophases derived from MODIS data and visual observations Vplyv biometeorologických premenných na nástup fenofáz odvodených z MODISu a z vizuálnych pozorovaní

This study describes the methods and results of the validation of Regional Phenology Model based on NDVI (Normalized Difference Vegetation Index) from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite images for European beech (Fagus sylvatica L.). The time series of phenological observation of regional phenological observation sites of SHMI (Slovak Hydrometeorological Institute) for years from 2000 to 2009 and permanent monitoring plots of NFC (National Forest Centre) for 2002 – 2009 was used to validate the date of start of five main spring and autumn phenological events. The most accurately were derived the phenological events the first leaves, full leafing and the beginning of colouring of leaves. The resulting duration of full foliage was derived with an average error of ± 4.2 days (r = 0.84). Date of onset of phenophases bud break and full colouring of leaves, determining the duration of the entire growing season, were derived with a systematic negative (budbreak), respectively. positive error (full colouring) which increases with increasing altitude. It resulted in an overestimate of the duration of the growing season by an average of 26 days. Possible causes of the differences in the timing of the individual phenophases and their duration are discussed in this paper.

http://www.cbks.cz/SbornikBrno14/pavlendova.pdf

Using of long-term phenological observations of SHMI and NFC for validation of Regional Phenology Model for European beech

/pdf/effect-of-biometeorological-variables-on-the-onset-of-53embfkht4.pdf

Effect of biometeorological variables on the onset of phenophases derived from MODIS data and visual observations

Vegetation index NDVI derived from satellite data MODIS (product MOD09) was used for monitoring of phenological phases of beech stands. The effect of leaves of upper story and undergrowth trees, understory vegetation, bark of thin and thick branches, trunk, and litter on NDVI value was identified and quantified for determination of the onset of phenological phases in five beech stands. The phenological observations were carried out in the spring 2011. Phenological curves were modelled for each stand. Inputs were NDVIsat derived from MODIS. The NDVI value for each component was determined from spectral analyses, and its percentage was estimated. Consequently, NDVIₘₒdₑₗ values were calculated for each stand and compared with NDVIₛₐₜ. We found out that NDVIₛₐₜ values are systematically biased from NDVIₘₒdₑₗ values a quotient q was established to revise this biased NDVIₛₐₜ values. Possibilities for satellite long-term phenological monitoring resulted from the quantified effect of individual forest components on NDVI value. The 100% leaf onset is the most suitable phase for phenological monitoring of the canopy trees component. The 100% leaf budburst is suitable phenophase for monitoring of forest stands phenology.

Vplyv prízemnej vegetácie a podrastu na priebeh fenologickej krivky bukových porastov odvodenej z údajov MODIS / Effect of understory vegetation and undergrowth on course of phenological curve of beech forests derived from MODIS

Veronika Brandýsová

Papers

Vplyv prízemnej vegetácie a podrastu na priebeh fenologickej krivky bukových porastov odvodenej z údajov MODIS / Effect of understory vegetation and undergrowth on course of phenological curve of beech forests derived from MODIS