A importância da luz na ocupação de árvores por lianas

Abstract

ResumoLianas interagem de forma negativa com as árvores, uma vez que aumentam suas taxas de mortalidade. Seria esperado, portanto, que árvores apresentassem possíveis caracteres que as defenderiam contra lianas. O objetivo desse estudo foi testar se os seguintes caracteres das árvores limitam sua infestação por lianas: 1) baixa altura; 2) tronco com ramificações altas (fuste alto); 3) casca lisa; 4) casca esfoliante, e 5) menor índice de iluminação da copa. O estudo foi realizado em um fragmento de Floresta Estacional Semidecídua no município de Alfenas (MG) no qual foi amostrado em 0,1 ha, todas as árvores com diâmetro na altura do peito maior do que 3 cm. Para cada árvore registrou-se os caracteres citados anteriormente, bem como foi estimada a porcentagem de cobertura de lianas na copa. Encontrou-se que quanto maior a altura e o índice de iluminação da copa, maior a sua ocupação por lianas. Essas árvores, apesar de atingirem o dossel da floresta e, portanto, adquirirem mais luz para crescimento e reprodução, estão também mais sujeitas à ocupação por lianas. Apesar disso, supõe-se que as árvores não investem em estruturas que poderiam diminuir a ocupação por lianas, provavelmente porque a competição com outras plantas da vizinhança pode ser também intensa. Palavras-chave: competição, comunidade vegetal, Floresta Estacional Semidecídua, trepadeira. AbstractLianas (woody climbers) interact negatively with trees, increasing their mortality rates. We expect, therefore, that trees have developed supposed traits that would defend them against lianas. The aim of this paper was test if these tree traits limit their liana occupation: 1) smaller height; 2) taller free bole height; 3) smooth bark; 4) exfoliating bark, and 5) low crown illumination. This study was carried out in a fragment of a seasonal semideciduous forest in Alfenas (Minas Gerais; Southeastern Brasil). We sampled in 0.1 ha all trees with diameter at breast height larger than 3 cm. For each tree we noted the traits previously cited, as well as we estimated the percentage of liana occupation on the tree crowns. We found that, for taller trees and trees with higher crown illumination, the probability of a tree to carry lianas was higher. These trees, in spite of reaching the forest canopy, and, therefore, acquire more light for reproduction and growth, they are also more prone to liana occupation. In spite of that, we suppose that the trees do not invest on traits that could decrease the liana occupation, probably because the competition with neighbor's plants may also be intense.

Species traits and abundance influence the organization of liana–tree antagonistic interaction

“…First, as one liana reaches the forest canopy, other liana can climb it. As the local features of rooting point of lianas can be important for their probability of interaction with trees in the neighbourhood (Nesheim & Økland 2007;Nogueira et al 2011), trees with more exposed canopies generally have more lianas (Sfair et al 2013(Sfair et al , 2016 and taller trees can contribute more to nestedness probably because lianas climb preferentially on them. Second, it is reasonable to consider that taller trees are generally older and have had more time to accumulate lianas (P erez-Salicrup et al 2001;Malizia & Grau 2006;Campanello et al 2007).…”

“…Lianas and trees interact antagonistically (Stewart & Schnitzer 2017) and compete mainly for nutrients and light (Dillenburg et al 1993;Schnitzer et al 2005;Cai et al 2009;Alvarez-Cansino et al 2015). In fact, lianas are very opportunistic and tend to climb closer (Roeder et al 2015) and taller trees (Sfair et al 2013(Sfair et al , 2016, and consequently, liana traits can play a minor role on tree species preference. In spite of these negative effects, our results showed that the lianas traits are less important in predicting their occupation on a tree species than their abundance and, consequently, their contribution to nestedness.…”

“…Taller trees are more prone to have lianas (Pinard & Putz 1994;P erez-Salicrup et al 2001;Malizia & Grau 2006;Campanello et al 2007;Sfair et al 2013Sfair et al , 2016, and we considered the maximum height of tree species (H max ) in the studied area as a trait that can influence liana climbing. Taller trees are more prone to have lianas (Pinard & Putz 1994;P erez-Salicrup et al 2001;Malizia & Grau 2006;Campanello et al 2007;Sfair et al 2013Sfair et al , 2016, and we considered the maximum height of tree species (H max ) in the studied area as a trait that can influence liana climbing.…”

“…For each individual tree, we recorded its height and the bark roughness, whereas for each individual liana, we recorded its diameter and climbing system. Taller trees are more prone to have lianas (Pinard & Putz 1994;P erez-Salicrup et al 2001;Malizia & Grau 2006;Campanello et al 2007;Sfair et al 2013Sfair et al , 2016, and we considered the maximum height of tree species (H max ) in the studied area as a trait that can influence liana climbing. Alternatively, we also considered the maximum diameter of liana species (D max ) in the studied area as a trait influencing liana-tree interaction; lianas tend to invest more on shoot growth than diameter (Schnitzer & Bongers 2002), and larger lianas tend to be older and occupy more trees (Dias & Sfair 2014).…”

“…On the other hand, lianas dispersed by wind, with latex and twining-climbing strategies, are more prone to climb a particular species of shrub (Garbin et al 2014). In spite of the importance of these traits, recent studies showed that light can be the main factor influencing liana occupancy (Sfair et al 2013(Sfair et al , 2016. Therefore, tree features related to light competition, such as maximum height (Poorter et al 2006) and crown illumination (Clark & Clark 1992), are better predictors of liana occupancy than other traits (Sfair et al 2013).…”