Assessing the invasive potential of commercial Eucalyptus species in Brazil: Germination and early establishment

Abstract

The invasive potential of a species is related to the interaction between genetic and environmental characteristics, as climatic conditions and native vegetation, reflecting the species adaptation to local conditions. An ecologically-adapted alien species can alter diversity and structure of forest ecosystems. This study assessed the invasiveness potential of eight commercially important Eucalyptus species in the germination and early establishment phases in southeastern Brazil. The first experiment evaluated seed germination under controlled temperature and air humidity conditions testing six substrate water potentials. The second experiment was conducted in pots to evaluate seed germination and seedling mortality under rainfed and irrigated regimes. Nine field trials were set up in the third experiment in six locations. In each trial, 80 plots of 1 m 2 were installed with half the plots undisturbed and half where preexisting plants and litter were removed. In the first experiment, Eucalyptus taxa differed significantly in seed germination for substrate water potential PÀ0.6 MPa. No germination was found for any taxa at À0.8 MPa substrate water potential. In the second experiment, differences in germination between species and water treatments were observed 21 days after sowing. No mortality was found in the irrigated treatments. No seedling mortality was observed in the rainfed treatments when the relative air humidity was higher than 85%, even during a dry period of 45 days. By contrast, seedling mortality was observed for all taxa in all the rainfed treatments when relative air humidity fell under 80%. In the third experiment, germination and seedling establishment of Eucalyptus species was always very low. The non-Eucalyptus species showed differences in germination between trials and soil exposures. Our results showed that soil and air moisture were major drivers of eucalypt germination and initial establishment in controlled conditions. However, under field conditions additional factors such as competition of non-Eucalyptus species and seedlings predation drastically limited eucalypt establishment suggesting low ecological adaptation of Eucalyptus sp. as an invasive species.

Selection of Eucalyptus grandis families across contrasting environmental conditions

“…As a pure species or as parent of hybrid varieties, E. grandis can reach high productivity in suitable sites and produce timber with amenable properties to a wide range of uses (Denison andKietzka 1993, Silva et al 2013). E. grandis is among the group of "big nine" related species of subgenus Symphyomyrtus identified by Harwood (2011) that, along with its interspecific hybrids, account for around 90% of the world's eucalypt plantation resources across 90 countries (Silva et al 2016a).…”

Spontaneous regeneration of eucalypts from seed production areas

“…In older stands, which had a greater number of seed production cycles, the possibility of seed production under favourable environmental conditions increases; which in turn allows for some seed germination and seedling establishment. In an old area such as in this study, an important factor is the lack of intensive management such as weeding, which could favour seedling establishment (Silva et al 2016). Additionally, leaf-cutting ant controls performed systematically in both experimental stations improve the possibility of eucalypt establishment.…”

“…Even when some eucalypt seeds are able to germinate due to favorable environmental conditions, high mortality usually occurs during the initial phases of seedling development (Booth et al 2015). In southeastern Brazil, where climatic conditions are slightly different from those of the origin of the eucalypts species (Silva et al 2016), Brazilian native species have an advantage in adaptation and regenerate where eucalypt regeneration is not expected. In our study some specific conditions allowed for the establishment of some individuals.…”

“…However, eucalypt invasiveness is observed in some sites, such as E. globulus in some regions of California-United States (Ritter and Yost 2009), E. camaldulensis in a riparian vegetation in Western Cape and E. grandis in Mpumalanga-South Africa (Tererai et al 2013;Forsyth et al 2004). The spontaneous dispersion of eucalypt varies between regions and possibly increases with plantation age, in sites with exposed soil, disturbed by burning and without drought occurrence during germination time and establishment of seedlings (Lamcorbe et al 2013;Silva et al 2016). However there is a lack of information under field conditions where eucalypts have been established for a long time (Godfree et al 2004;Flory et al 2012).…”

Sobrevivência e crescimento inicial de espécies de eucalipto em diferentes condições climáticas

“…torelliana apresentou a melhor classificação na análise conjunta de sobrevivência, sendo a menor sobrevivência observada em Telêmaco Borba está relacionada ao veranico durante o mês de janeiro e fevereiro de 2017 que proporcionou umidade do ar abaixo de 80%, por pelo menos duas semanas durante a fase de estabelecimento das mudas no experimento. Silva et al (2016a), discutem que a umidade do ar abaixo de 80% por um período de vários dias consecutivos gera a mortalidade se não houver irrigação durante a fase de estabelecimento do eucalipto.…”