In June 2017, wildfires burned 15 000 ha around the town of Knysna in the Western Cape, destroying > 800 buildings, > 5000 ha of forest plantations, and claiming the lives of seven people. We examined the factors that contributed to making this one of the worst fires on record in the region. One third of the area that burned was in natural vegetation (mainly fynbos shrublands), and more than half was in plantations of invasive alien (non-native) pine trees, or in natural vegetation invaded by alien trees. We used satellite imagery to assess burn severity in different land cover types by comparing pre- and post-fire images to estimate biomass consumed. We used daily weather data from two weather stations to calculate fire danger and drought indices over 70 years, and compared the fire weather conditions during the 2017 Knysna fires to the long-term weather record. The amount of biomass consumed was significantly higher in plantations of invasive alien trees, and in fynbos invaded by alien trees, than in uninvaded fynbos, providing support for the contention that invasion by alien trees increases the impact and difficulty of control of wildfires. Fire danger indices on the days of the fires were in the top 0.1 to 0.2% of days in the historic record, indicating that fire weather conditions were extreme but not unprecedented. The fires were preceded by a prolonged drought, and 18-month running means for two drought indices were the highest on record. The severity of the fires was exacerbated by very high fire danger conditions, preceded by an unprecedented drought, and further worsened by the conversion of natural fynbos vegetation to plantations, and invasion of vegetation by alien trees. Historical fire suppression also resulted in fuel buildups, further aggravating the problem of fire control, while residential development within and adjacent to fire-prone areas increased the risks faced by residents. Our results support calls to control invasive alien plants, reduce commercial planting of invasive alien trees, strictly regulate development in areas of high fire risk, and maintain awareness of the need for fire-wise practices. En junio de 2017, incendios de bosques quemaron 15 000 ha alrededor del pueblo de Knysna en la región del Cabo Occidental de Sudáfrica, destruyendo > 800 edificios, > 5000 ha de forestaciones y quitando la vida a siete personas. Examinamos en este trabajo los factores que contribuyeron a hacer de éste, uno de los peores incendios registrados en la región. Un tercio del área quemada estaba compuesta de vegetación natural (fundamentalmente de matorrales de “Fynbos”) y más de la mitad con plantaciones de pinos invasores (no nativos) o con vegetación natural invadida por árboles exóticos. Usamos imágenes satelitales para determinar la severidad del incendio en diferentes tipos de coberturas vegetales, mediante la comparación de imágenes pre- y post-incendio para estimar la biomasa consumida. Usamos datos meteorológicos diarios de dos estaciones meteorológicas para calcular el peligro de incendio, e índices de sequía de más de 70 años, y comparamos las condiciones meteorológicas que afectaron al fuego durante los incendios de Knysna de 2017 con aquellas correspondientes a registros históricos. La cantidad de biomasa consumida fue significativamente mayor en plantaciones de especies exóticas invasoras y en matorrales de Fynbos invadidos por árboles exóticos que en matorrales de Fynbos no invadidos, lo que apoya el argumento de que la invasión por árboles exóticos incrementan el impacto y la dificultad de controlar estos incendios. Los índices de peligro de los días de los incendios estuvieron entre el 0,1 y 0,2% más alto en el registro histórico, indicando que las condiciones meteorológicas eran extremas aunque no sin precedentes. Los incendios fueron precedidos por una sequía prolongada, y las medias de dieciocho meses para dos índices de sequía fueron las más altas que se tengan registros. La severidad de los incendios fue exacerbado por condiciones muy altas de peligro, antecedida por una sequía sin precedentes y también agravada por la conversión de los matorrales de Fynbos en plantaciones y la invasión de la vegetación nativa por árboles exóticos. La supresión histórica de incendios también resultó en incrementos de biomasa combustible, agravando luego el problema del control del fuego, mientras que el desarrollo residencial dentro y en las adyacencias a áreas proclives al fuego incrementó el riesgo afrontado por los residentes. Nuestros resultados apoyan el reclamo para controlar plantas invasoras, reducir las plantaciones comerciales de árboles exóticos invasores, regular estrictamente el desarrollo de áreas con alto riesgo de incendio, y mantener la concientización sobre la necesidad de llevar a cabo prácticas sensatas de manejo del fuego.

We characterised the historical fire regime (1900–2010) in eastern coastal fynbos shrublands, which occur in a poorly studied part of the Cape Floral Kingdom (CFK). Natural (lightning-ignited) fires dominated the fire regime. Fire seasonality decreased from west (Outeniqua region) to east (Tsitsikamma region) within the study area, and between the study area and further west in the CFK. This is consistent with a west–east climatic gradient in the CFK, where rainfall is concentrated in winter in the west, and evenly distributed across months in the east. Median fire return intervals (FRIs) (1980–2010) were broadly comparable to other fynbos areas but estimates varied widely depending on whether or not the data were censored (16–26 years with and 8–13 years without censoring). FRIs appeared to be shorter in the Tsitsikamma, where rainfall and plant growth rates are higher, than in the Outeniqua. The total area burnt annually has increased significantly since 1980, coinciding with an increase in weather conducive to fires, suggesting that fire regimes may be responding to climate change. Frequent recurrence of very large fires and the virtual absence of vegetation in older post-fire age classes are potential causes for concern in achieving fynbos conservation objectives.

Globe-LFMC is an extensive global database of live fuel moisture content (LFMC) measured from 1,383 sampling sites in 11 countries: Argentina, Australia, China, France, Italy, Senegal, Spain, South Africa, Tunisia, United Kingdom and the United States of America. The database contains 161,717 individual records based on in situ destructive samples used to measure LFMC, representing the amount of water in plant leaves per unit of dry matter. The primary goal of the database is to calibrate and validate remote sensing algorithms used to predict LFMC. However, this database is also relevant for the calibration and validation of dynamic global vegetation models, eco-physiological models of plant water stress as well as understanding the physiological drivers of spatiotemporal variation in LFMC at local, regional and global scales. Globe-LFMC should be useful for studying LFMC trends in response to environmental change and LFMC influence on wildfire occurrence, wildfire behavior, and overall vegetation health.