Forest canopy gaps offer a window into the future: The case of subtropical coastal forests within an urban matrix in South Africa

Aim of study: Alien and indigenous species emergence patterns within canopy gaps in urban subtropical forests are poorly understood. This study compared canopy gap floristics in relation to abiotic and physical characteristics across three subtropical urban forests differing in disturbance history. Area of study: Three Northern Coastal Forests of varying disturbance histories located in coastal subtropical urban KwaZulu-Natal (KZN), South Africa (SA). Main results: Closed canopy (n = 15 quadrats per forest) and four gaps (n = 12 quadrats per forest) from three size classes ('small' < 25 m(2), 'medium' 25 - 45 m(2); 'large' > 45 m(2)) were surveyed for the primary least disturbed (PLD), primary highly disturbed (PHD) and transitional highly disturbed (THD) forests using classical vegetation sampling techniques. Soil moisture content and air temperature were measured within each gap. Research highlights: Cumulatively all forest gaps hosted 198 species. Equivalent number of species (Hill numbers from H = 0 to H = 2) were constantly higher in the PHD forest followed by the PLD forest and lowest in the THD forest. Alien and indigenous plant density were negatively correlated. Species richness was positively correlated with gap size and soil moisture content, and negatively correlated with air temperature.

Automated summary

This study compared the canopy gap floristics in three urban subtropical forests with different disturbance histories, revealing that alien and indigenous plant density were negatively correlated, species richness was positively correlated with gap size and soil moisture content, and negatively correlated with air temperature.