Impact of a severe frost event in 2014 on woody vegetation within the Nama-Karoo and semi-arid savanna biomes of South Africa

Understanding and predicting frost‐induced tropical tree mortality patterns

“…Additionally, elevation seems to be a key modulator of frost‐induced tree mortality, helping us to predict where trees will most likely die—or where we will most likely find frost‐killed trees—within the landscape. Lowland vegetation is in general more prone to freezing damage when advective frosts occur in agreement with recent studies in savannas in South Africa and Brazil (Hoffmann et al, ; Muller et al, ; Whitecross et al, ). This finding can be explained by the strong influence of elevation on temperature distribution at the regional and landscape level (Florinsky, Kulagina, & Meshalkina, ; Hummer‐Miller, ; Matusick, Ruthrof, Brouwers, & Hardy, ), driving the movement of cold air masses downhill during an advective frost (Kalma, Laughlin, Caprio, & Hamer, ; Lindkvist & Lindqvist, ).…”

“…These rare extreme cold events can have a long‐lasting effect on tropical forests dynamics because subzero temperatures are not usually expected at tropical latitudes. Recent studies suggest that recurrent frosts can reinforce boundaries between tropical savannas and forests in Brazil (Hoffmann et al, ) or between savannas and shrublands in South Africa (Muller, O'Connor, & Henschel, ). Extreme freezing events could be thus important for maintaining or reducing tropical and subtropical ecosystems sharp borders and range limits by inducing tree mortality in species with low frost resistance (e.g., Whitecross, Archibald, & Witkowski, ).…”

“…A severe advective frost (i.e., related to a cold wave) will most likely induce plant damage and extensive tree mortality at lower elevations. This occurs because the normal pattern of decreasing temperature with elevation temporary reverses, and consequently, lower elevations become colder as the heavier cold air masses sink (Bannister, ; Muller et al, ; Snyder & de Melo‐Abreu, ). For example, a severe frost in February 2011 linked to a historic cold wave that affected most of North America (NOAA, , ), penetrated into subtropical northwestern Mexico, and triggered extensive damage to lowland agricultural valleys (Val Noris, ).…”

Spatiotemporal Variation of Frost within Growing Periods

“…It is recommended that growers be aware of the frost climatology and other agroclimatological risks in their areas so that they can minimize damage to their crops by avoiding susceptible crop growth stages coinciding with the period of greatest risks [17,24,29]. There has been no estimate in South Africa of the monetary value of frost damage to crops but this could reach millions of South African Rand as there are widespread reports of frost damage countrywide every year [5,27,[30][31][32][33][34][35][36]. Annual frost losses to agricultural activities amount to over 120 million dollars in Australia [12] and frost damage exceeding 1 billion dollars annually was recorded in some years in the United States since 1980 to date [37].…”

“…Frost normally occurs when air temperature drops to or below 0 ∘ C resulting in ice formation on plant material and soil [4]. The rate of temperature reduction during the night is influenced by, among other factors, wind speed, atmospheric water vapour pressure, atmospheric stability, precipitation, sky temperature, cloud cover, and local topographical features [4,5].…”