Long-term collapse in fruit availability threatens Central African forest megafauna

Afrotropical forests host much of the world’s remaining megafauna, although these animals are confined to areas where direct human influences are low. We used a rare long-term dataset of tree reproduction and a photographic database of forest elephants to assess food availability and body condition of an emblematic megafauna species at Lopé National Park, Gabon. Our analysis reveals an 81% decline in fruiting over a 32-year period (1986–2018) and an 11% decline in body condition of fruit-dependent forest elephants from 2008 to 2018. Fruit famine in one of the last strongholds for African forest elephants should raise concern about the ability of this species and other fruit-dependent megafauna to persist in the long term, with potential consequences for broader ecosystem and biosphere functioning.

Proposing the solar wind-energy-flux hypothesis as a driver of interannual variation in tropical tree reproductive effort tropical tree reproduction

A growing body of research documents how the El Niño Southern Oscillation (ENSO) results in short-term changes in terrestrial environmental conditions, with the potential to drive ecosystem processes as the duration and severity of ENSO events increases with anthropogenic climate change. An ENSO positive phase results in anomalous patterns of rainfall and temperature throughout the tropics that coincide with leaf flush and increased fruit production in tropical forests worldwide. However, our understanding of possible mechanisms underlying this natural phenomenon is limited. Furthermore, flowering in tropical trees anticipates ENSO development, motivating the continued search for a global phenological cue for tropical angiosperm reproduction. We propose the solar energy flux hypothesis: that a physical energy influx in the Earth’s upper atmosphere and magnetosphere generated by a positive anomaly in the solar wind preceding ENSO development, cues tropical trees to increase allocation of resources to reproduction. We show that from 1994-2013, the solar wind energy flux into the Earth’s magnetosphere (Ein) is more strongly correlated with the number of trees in fruit or flower in a Puerto Rican wet forest than the Niño 3.4 climate index, despite Niño 3.4 being a previously identified driver of interannual increases in reproduction. We discuss the idea that changes in the global magnetosphere and thermosphere conditions via solar wind-effects on global atmospheric circulation, principally a weaker Walker circulation, cue interannual increases tropical tree reproduction. This may be a mechanism that synchronizes the reproductive output of the tropical trees to changes in environmental conditions that coincide with ENSO. Thus, space weather patterns may help explain terrestrial biological phenomena that occur at quasi-decadal scales.

Forest edge effects on Quercus reproduction within naturally regenerated mixed broadleaf stands

This paper explores the influence of forest edge on the development of tree reproduction and the use of edge as a silvicultural tool for manipulating regeneration outcomes. Oak (Quercus spp.) reproduction was sampled 9 years following edge establishment along transects extending from 8 m into clearcut openings to 40 m into the adjacent intact forest. Trends showed that oak reproduction height in the intact forest was inversely related to distance from edge up to 20 m into the intact forest. Observed oak reproduction densities were greater within 20 m of edge than in distance intervals further into the intact forest. Tree-ring analysis of 106 seedlings was used to evaluate temporal responses associated with edge development. Cross-sectional analysis indicated a mean age of 13 years, 3 years prior to edge establishment. Increased growth was associated with edge establishment, and 10-year radial growth following edge creation showed a similar spatial pattern as height with oak seedlings within 20 m of the edge exhibiting significantly greater growth than those occurring furthest into the intact forest. This study suggests that forest edge can be used to provide environments useful in building reproductive capacity for species like oaks that require advance reproduction.

Do birds bias measurements of seed rain?

Accurate measurements of seed rain are important for understanding tree reproduction (Greene & Johnson 1994), forest regeneration (Cole et al. 2010, Cubiña & Aide 2001, Howe et al. 2010, Zahawi & Augspurger 2006), forest ecology (Muller-Landau et al. 2008, Terborgh et al. 2011) and maintenance of community diversity (Harms et al. 2000). Seed traps generally consist of a bucket or net of a fixed area suspended 0.3–1 m above the ground, and seeds are typically collected once or twice per month. An implicit assumption of all seed-rain studies is that traps do not influence seed dispersal. Should birds perch on and defecate seeds into seed traps, seed abundance will be overestimated. This behaviour could produce a directional bias if birds perch on seed traps in one habitat more than others. To our knowledge, no study has considered this potential bias.