Carolina Reis de Brito

Tree seedlings play a key role in the conservation and regeneration of local diversity, are essential for the functioning of forest ecosystems and are more susceptible to environmental changes than adult trees due to their lower metabolic reserve and photosynthetic production capacity. To investigate the responses of young plants (seedlings, saplings, juveniles, and young) of different geographical origin to temperature increases, we conducted a systematic review and meta-analysis of experiments published until the last decade of temperature on young woody plants. We investigated the effects of rising temperatures on several leaf traits related to carbon balance, such as stomatal conductance, quantum efficiency of photosystem II, leaf mass per area, and others, in 62 species across 39 papers. Few studies have investigated internal and atmospheric carbon ratio , electron transport rate and maximum Rubisco carboxylation rate indicating a significant knowledge gap that necessitates additional data collection. There was a consistent pattern of acclimation in photosynthetic rate response to warming and an increase in dark respiration and photorespiration, disrupting the carbon balance and potentially affecting the growth and survival of young trees. Our results suggest that young plants exposed to warming may increase in photorespiration, as indicated by the rapid increase in the internal and atmospheric carbon ratio and the decline in maximum Rubisco carboxylation rate with increasing temperature. This evidence suggests that the increase in temperature could affect young plant growth and pose a challenge to forest regeneration in a warming world.

The Brazilian Atlantic Forest (AF) is recognized as one of the most threatened biodiversity hotspots by global climate change. Here, we examined the leaf traits (leaf mass area, leaf thickness, and chlorophyll content) and leaf thermotolerance (T₅₀ and T_Crit) of seedlings of nine species of AF trees grown experimentally in order to foresee how extreme heat events will affect the forest’s regeneration and diversity. Based on geographic range size, the species were classified into three groups, namely, species with a restricted-range distribution (endemic to the AF), species with an intermediate-range distribution (throughout the Brazilian tropical territory), and species with a wide-range distribution (Latin America). We found that the restricted-range group did not present lower thermotolerance compared to intermediate- and wide-range species groups. Surprisingly, leaf mass area had no effect on thermotolerance indices, while chlorophyll content and leaf thickness positively influenced T₅₀ and T_Crit. Some species-specific responses to high-temperature stress deserve attention for tropical tree conservation, as is the case of Arapatiella psylophylla, a vulnerable endemic species with a very restricted-range distribution. Our results suggest that the species-specific leaf thermotolerance is an important criterion to be considered for tropical tree forest conservation in the context of global climate change.

We conducted a scientometric review based on urban floristic inventories published in Brazilian scientific journals between 2000 and 2020 to determine the diversity and conservation status of trees used in urban forestry in Brazil. The floristic inventories were divided according to five Brazilian geographic regions. Tree species were divided into native and exotic species. We identified 71 floristic inventories of urban forestry, most of which were concentrated in the South and Southeast regions. In total, 473 species and 125 botanical families were identified. The largest number of species and families was found in the Southeast region, but most species/inventories were found in the North and Central-West regions. The ratio of native to exotic tree species was approximately 1:1; however, when the five most commonly used species were analyzed, the ratio of native to exotic species was less than 0.6, regardless of the geographic region. Regarding vulnerability, most of the species included in this study were not assessed for threat (86%), whereas only 1.7% of the species were vulnerable and 1% were endangered. We emphasize the urgent need to increase the number of tree species included in the IUCN Red List Categories and Criteria in urban forestry programs in Brazil.