Lianas have a seasonal growth advantage over co‐occurring trees

Abstract

The seasonal growth advantage hypothesis posits that plant species that grow well during seasonal drought will increase in abundance in forests with increasing seasonality of rainfall both in absolute numbers and also relative to co‐occurring plant species that grow poorly during seasonal drought. That is, seasonal drought will give some plant species a growth advantage that they lack in aseasonal forests, thus allowing them attain higher abundance. For tropical forest plants, the seasonal growth advantage hypothesis may explain the distribution of drought‐adapted species across large‐scale gradients of rainfall and seasonality. We tested the seasonal growth advantage hypothesis with lianas and trees in a seasonal tropical forest in central Panama. We measured the dry‐season and wet‐season diameter growth of 1,117 canopy trees and 648 canopy lianas from 2011 to 2016. We also evaluated how lianas and trees responded to the 2015–2016 El Niño, which was the third strongest el Niño drought on record in Panama. We found that liana growth rate was considerably higher during the dry‐season months than the wet‐season months in each of the five years. Lianas achieved one‐half of their annual growth during the 4‐month dry season. By contrast, trees grew far more during the wet season; they realized only one‐quarter of their annual growth during the dry season. During the strong 2015–2016 El Niño dry season, trees essentially stopped growing, whereas lianas grew unimpeded and as well as during any of the previous four dry seasons. Our findings support the hypothesis that seasonal growth gives lianas a decided growth advantage over trees in seasonal forests compared to aseasonal forests, and may explain why lianas peak in both absolute and relative abundance in highly seasonal tropical forests. Furthermore, the ability of lianas to grow during a strong el Niño drought suggests that lianas will benefit from the predicted increasing drought severity, whereas trees will suffer, and thus lianas are predicted to increase in relative abundance in seasonal tropical forests.

Effects of dry‐season irrigation on leaf physiology and biomass allocation in tropical lianas and trees

“…) are consistent with Schnitzer (), who also found that lianas grew more than trees when water was limited. Similarly, in a recent study of >1,100 canopy trees and >800 canopy lianas in central Panama, Schnitzer and van der Heijden () reported that liana growth rate was higher during the dry season than the wet season in each of the five years of their study, and that lianas grew as much during the ~4‐month dry season as they did during the ~8‐month wet season. By contrast, they found that tree growth rate was far higher during the wet season, and that trees grew far more during the 8‐month wet season than the 4‐month dry season.…”

“…For example, in a seasonal forest in Panama, understory lianas were found to grow in height seven times more than understory trees during the dry season, but only two times more during the wet season (Schnitzer ). In a more recent and much larger study in Panama, canopy lianas had a far higher growth rate during the dry season than the wet season, whereas trees had the opposite pattern, with a higher growth rate during the wet season than the dry season (Schnitzer and van der Heijden ).…”

Effect of lianas on forest‐level tree carbon accumulation does not differ between seasons: Results from a liana removal experiment in Panama

“…Lianas may also sustain their water potential by either accessing deeper water (Andrade et al, ; Chen et al, ) or different water sources (De Deurwaerder et al, ) than trees or by exercising strong stomatal control under drought conditions. Lianas may therefore have the ability to remain photosynthetically active during periods of seasonal drought (Cai et al, ; Sánchez‐Azofeifa et al, ; Schnitzer, ), thereby taking advantage of the increase in irradiance as a result of reduced cloud cover during the dry season (Graham, Mulkey, Kitajima, Phillips, & Wright, ; Schnitzer, ) to vigorously grow (Schnitzer & van der Heijden, ). However, even though liana biomass increment during the dry season was greater than during the wet season in all 5 years (Figure ), the relative impact of lianas on tree biomass increment did not differ between the seasons (Figure ).…”

“…Rowland et al, ). We did not include a shrinkage correction for liana stems for two reasons: (a) liana stems were measured with diameter tapes which have an accuracy of 1 mm and shrinkage terms were therefore considerably inflated compared to shrinkage calculated from the tree dendrometer measurements, and (b) liana stems generally grew faster in the dry than in the wet season (Schnitzer & van der Heijden, ) and adding any shrinkage correction would amplify any differences in liana growth between the dry and the wet season. By not correcting liana diameter measurements for shrinkage effects, we therefore present a more conservative pattern in seasonal differences in liana biomass increment.…”

“…Lianas may have a competitive advantage over trees by maintaining their ability to grow during the dry season (Cai, Schnitzer, & Bongers, ; Sánchez‐Azofeifa et al, ; Schnitzer, ; Schnitzer & van der Heijden, ). Lianas differ from trees in foliar nutrients, hydraulic traits and allocation to defence, especially in tropical dry forests (Asner & Martin, ; Collins, Wright, & Wurzburger, ; Werden, Waring, Smith‐Martin, & Powers, ), which may augment carbon fixation during seasonal drought (Collins et al, ; Wyka, Oleksyn, Karolewski, & Schnitzer, ; Zhu & Cao, ).…”