The need for full inventories of tree modes of disturbance to improve forest dynamics comprehension: An example from a semideciduous forest in Brazil

A study was carried out to characterize the general pattern of tree mortality and damage in an old-growth semideciduous seasonal forest in the Caetetus Ecological Station, southeastern Brazil, and to assess species-specific patterns of mode and frequency of disturbances. We counted all disturbance events promoted by trees or parts of them larger than 20 cm in diameter within a 10.24 ha plot and recorded their mode of disturbance, basal diameter, age class, presence of re-sprouts and, whenever possible, their species. A total of 743 disturbance events were recorded inside the studied plot. Of these events, 650 were occasioned by entire trees (33% uprooted, 28% dead-standing, 26.5% snapped, 10.5% inclined and 2% complex events) while 93 were due to parts of trees (60.2% branch-falls and 39.8% stem-fall from multi-stemmed trees). Dead-standing trees were predominant in the recent age class, while uprooted trees predominated in the oldest age class. Probably, a large fraction of the trees in this forest die standing and then fall, exposing their roots. We found that considering all modes of disturbance is quite important, otherwise forest disturbance rates might be underestimated by approximately 25%. Even when usually neglected modes of disturbance were excluded from the estimates, this forest revealed a high disturbance rate compared to other forests. Some species showed damage and death rates greater than expected by chance, while others species showed significantly lower rates. A high proportion of re-sprouting was observed in this forest and the species presenting the greatest re-sprouting proportion were also the most abundant in the study area, corroborating the idea that this ability can be important to increase their competitive potential, especially in forest with high disturbance rates.