The European Forest Condition Monitor: Using Remotely Sensed Forest Greenness to Identify Hot Spots of Forest Decline

Forest decline, in course of climate change, has become a frequently observed phenomenon. Much of the observed decline has been associated with an increasing frequency of climate change induced hotter droughts while decline induced by flooding, late-frost, and storms also play an important role. As a consequence, tree mortality rates have increased across the globe. Despite numerous studies that have assessed forest decline and predisposing factors for tree mortality, we still lack an in-depth understanding of (I) underlying eco-physiological mechanisms, (II) the influence of varying environmental conditions related to soil, competition, and micro-climate, and (III) species-specific strategies to cope with prolonged environmental stress. To deepen our knowledge within this context, studying tree performance within larger networks seems a promising research avenue. Ideally such networks are already established during the actual period of environmental stress. One approach for identifying stressed forests suitable for such monitoring networks is to assess measures related to tree vitality in near real-time across large regions by means of satellite-borne remote sensing. Within this context, we introduce the European Forest Condition monitor (EFCM)—a remote-sensing based, freely available, interactive web information tool. The EFCM depicts forest greenness (as approximated using NDVI from MODIS at a spatial resolution of roughly 5.3 hectares) for the pixel-specific growing season across Europe and consequently allows for guiding research within the context of concurrent forest performance. To allow for inter-temporal comparability and account for pixel-specific features, all observations are set in relation to normalized difference vegetation index (NDVI) records over the monitoring period beginning in 2001. The EFCM provides both a quantile-based and a proportion-based product, thereby allowing for both relative and absolute comparison of forest greenness over the observational record. Based on six specific examples related to spring phenology, drought, late-frost, tree die-back on water-logged soils, an ice storm, and windthrow we exemplify how the EFCM may help identifying hotspots of extraordinary forest greenness. We discuss advantages and limitations when monitoring forest condition at large scales on the basis of moderate resolution remote sensing products to guide users toward an appropriate interpretation.

Severe frost but not shade could limit the future growing season of Erythronium americanum

Changes in climate are leading to modifications in the timing of seasonal events such as migrations and flowering. Erythronium americanum (trout lily) can break bud early in response to warming, but changes to its growing season may be limited by early shade from canopy trees and frost. I experimentally assessed the impact of shade and frost on senescence in E. americanum and descriptively monitored the response of E. americanum to vernal air and soil temperatures in a garden setting. Early shade did not affect the timing of senescence. Experimental exposure to frost resulted in increased leaf damage, earlier senescence, and greater corm death than in control plants. Despite ten days in which the air temperature dropped below freezing, there was no evidence of leaf damage in the field. These results suggest that early shade from canopy trees will not hasten the end of the future growing season for E. americanum, but that late frost could bring about early senescence if that frost is sufficiently hard.

A Practical Remote Sensing Monitoring Framework for Late Frost Damage in Wine Grapes Using Multi-Source Satellite Data

Late frost damage is one of the main meteorological disasters that affect the growth of wine grapes in spring, causing a decline in wine grapes quality and a reduction in yield in Northwest China. At present, remote sensing technology has been widely used in the field of crop meteorological disasters monitoring and loss assessments, but little research has been carried out on late frost damage in wine grapes. To monitor the impact of late frost in wine grapes accurately and quickly, in this research, we selected the Ningxia planting area as the study area. A practical framework of late frost damage on wine grapes by integrating visible, near-infrared, and thermal infrared satellite data is proposed. This framework includes: (1) Wine grape planting area extraction using Gaofen-1 (GF-1), Landsat-8, and Sentinel-2 based on optimal feature selection and Random Forest (RF) algorithm; (2) retrieval of the land surface temperature (LST) using Landsat-8 thermal infrared data; (3) data fusion using Landsat-8 LST and MODIS LST for a high spatiotemporal resolution of LST with the Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model (ESTARFM); (4) the estimation of daily minimum air temperature (Tmin) using downscaled LST and meteorological station data; (5) monitoring and evaluation of the degree of late frost damage in wine grapes in April 2020 by combining satellite-derived data and late frost indicators. The results show that the total area of wine grapes extracted in Ningxia was about 39,837 ha. The overall accuracy was 90.47%, the producer’s accuracy was 91.09%, and the user’s accuracy was 90.22%. The root mean square (RMSE) and the coefficient of determination (R2) of the Tmin estimation model were 1.67 ℃ and 0.91, respectively. About 41.12% of the vineyards suffered severe late frost damage, and the total affected area was about 16,381 ha during April 20–25, 2020. This suggests the satellite data can accurately monitor late frost damage in wine grapes by mapping the wine grape area and estimating Tmin. The results can help farmers to take remedial measures to reduce late frost damage in wine grapes, and provide an objective evaluation of late frost damage insurance claims for wine grapes. With the increasing weather extremes, this study has an important reference value for standardized global wine grape management and food security planning.

Application of a completely organic and bio-degradable sugar-based insulating coating to vine shoots, to prevent late frost damages

An innovative method against late frosts in vineyard has been developed at CIRIAF, University of Perugia. It consists of an organic coating made by cotton candy and straw to prevent the vine shoots freezing due to late frosts. This technique has already tested at lab-scale with very encouraging results. This paper aims to experiment the effect of the organic coating applied on young shoots of grapevine during artificially controlled frost events. A vine shoot covered by the organic coating was positioned in the climatic chamber and a thermocouple was rolled up to the vine shoot to control its temperature. Also, a vine shoot rolled up to the thermocouple and without organic coating was positioned inside the climatic chamber, used as a reference case. Results show that the temperature gap, gained with the adoption of the insulating layer was approximately in the range 0.2 – 3.2 °C, but the organic coating was not enough to maintain temperature above the ice-point able to prevent the vine shoot freezing in lab. Even thought, the experimental application of the present technique allowed to detect some crucial challenges which need to be solved before to test this technology in real situations.