How did the characteristics of the growing season change during the past 100 years at a steep river basin in Japan?

The effects of climate change on plant phenological events such as flowering, leaf flush, and leaf fall may be greater in steep river basins than at the horizontal scale of countries and continents. This possibility is due to the effect of temperature on plant phenology and the difference between vertical and horizontal gradients in temperature sensitivities. We calculated the dates of the start (SGS) and end of the growing season (EGS) in a steep river basin located in a mountainous region of central Japan over a century timescale by using a degree-day phenological model based on long-term, continuous, in situ observations. We assessed the generality and representativeness of the modelled SGS and EGS dates by using phenological events, live camera images taken at multiple points in the basin, and satellite observations made at a fine spatial resolution. The sensitivity of the modelled SGS and EGS dates to elevation changed from 3.29 days (100 m)−1 (−5.48 days °C−1) and −2.89 days (100 m)−1 (4.81 days °C−1), respectively, in 1900 to 2.85 days (100 m)−1 (−4.75 days °C−1) and −2.84 day (100 m)−1 (4.73 day °C−1) in 2019. The long-term trend of the sensitivity of the modelled SGS date to elevation was −0.0037 day year−1 per 100 m, but the analogous trend in the case of the modelled EGS date was not significant. Despite the need for further studies to improve the generality and representativeness of the model, the development of degree-day phenology models in multiple, steep river basins will deepen our ecological understanding of the sensitivity of plant phenology to climate change.

Gall-forming aphids are protected (and benefit) from defoliating caterpillars: the role of plant-mediated mechanisms

Background Interspecific interactions among insect herbivores are common and important. Because they are surrounded by plant tissue (endophagy), the interactions between gall-formers and other herbivores are primarily plant-mediated. Gall-forming insects manipulate their host to gain a better nutrient supply, as well as physical and chemical protection form natural enemies and abiotic factors. Although often recognized, the protective role of the galls has rarely been tested. Results Using an experimental approach, we found that the aphid, Smynthurodes betae, that forms galls on Pistacia atlantica leaves, is fully protected from destruction by the folivorous processionary moth, Thaumetopoea solitaria. The moth can skeletonize entire leaves on the tree except for a narrow margin around the galls that remains intact (“trimmed galls”). The fitness of the aphids in trimmed galls is unharmed. Feeding trials revealed that the galls are unpalatable to the moth and reduce its growth. Surprisingly, S. betae benefits from the moth. The compensatory secondary leaf flush following moth defoliation provides new, young leaves suitable for further gall induction that increase overall gall density and reproduction of the aphid. Conclusions We provide experimental support for the gall defense hypothesis. The aphids in the galls are protracted by plant-mediated mechanisms that shape the interactions between insect herbivores which feed simultaneously on the same host. The moth increase gall demsity on re-growing defoliated shoots.

Diversity and structure preferences for ant-hemipteran mutualisms in cocoa trees (Theobroma cacao L., Sterculiaceae)

The aim of this study is to evaluate the diversity and specificity of ant-hemipteran mutualisms according to the different structures observed on cocoa trees. The experiment was carried out in two cocoa planting systems: cabruca and derruba total at Ilhéus, Brazil. We made observations and collected monthly over one year the mutualistic ants and hemipterans that occurred on Theobroma cacao L. trees. Observations were performed on cacao trees at three distinct sites of the plant: flowers, pods and leaf flush. We observed 932 ant-hemipteran associations, comprising 203 different mutualistic interactions. The assemblage was composed of 26 hemipteran species and 54 ant species. No differences were observed in the ant community, however, we found differences in the hemipteran community according to the different structure evaluated. We recorded a total of 404 trophobiosis events on pods, 394 on leaf flushes and 134 on flowers. Our results point out the diversity of ant-hemipteran trophobioses in the cocoa agrosystems resembles the diversity found in tropical forests and demonstrate that the location of interactions may result in ecological restrictions for some organisms involved in these trophobioses in cacao agrosystems.

Land Surface Temperature and Miombo forest canopy phenophases: what induces leaf fall and leaf flush?

<p>Miombo woodland is the most widespread tropical seasonal woodland and dry forest formation in Africa covering between 2.7 and 3.6 million km<sup>2</sup> in eleven countries. Leaf fall and leaf flush during the dry season is a major characteristic feature of the various Miombo species. However, the question on what induces the leaf fall process is by far inconclusive. Different studies indicate either moisture or temperature or both elements as inducers for leaf fall. Knowing what induces leaf fall is important for studying the consequence of e.g., climate change on the Miombo forest. To better understand the driver of leaf fall in Miombo forest we employed a simple remote sensing and statistical analysis approach using long term averages (2009 – 2018) of Land Surface Temperature (LST) of the Miombo forest, various vegetation indices (VI), actual evaporation (E<sub>a</sub>), and root zone soil moisture (SM). The vegetation indices (VI) included the Normalised Difference Water Index (NDWI) as indicator of vegetation water content and the Normalised Difference Vegetation Index (NDVI) as indicator of plant photosynthetic activities and leaf cover. Results showed that the NDWI, NDVI, E<sub>a</sub> and SM begun to decline immediately following the end of the rainy season in early April while the LST remained relatively constant before it began to decline in May when leaf fall in some Miombo species begins. Hysteresis graphs revealed that vegetation water content (i.e. NDWI) responded quicker to changes in both LST and SM. Furthermore, high rates of decrease in NDWI and NDVI values were observed between July and September the same period when LST increased. This is also the same period when leaf fall intensifies in Miombo forest. Correlation analysis revealed strong season-dependent LST relationship with VI and SM with the rainy season exhibiting strong negative linear correlations (R<sup>2</sup> = 0.77, 0.91, 0.88; for the NDWI, NDVI and SM respectively). In the dry season relatively weaker negative correlations (R<sup>2</sup> = 0.52, 0.60, 0.55; for NDWI, NDVI and SM respectively) were observed. On the other hand SM showed strong positive linear correlations (R<sup>2</sup> > 0.6) with NDWI and NDVI (for the rainy and dry seasons respectively). The correlations imply that in Miombo forest soil water content (i.e. SM), vegetation water content (i.e. NDWI) and the photosynthetic activities and leaf cover (i.e. NDVI) declines with increase in LST. These relationships show the possibility of land surface temperature being a major inducing element of leaf fall and changes in canopy structure in the Miombo woodland.</p>

Phenology of Sclerocarya birrea (A. Rich.) Hochst. Provenances

Phenology study was conducted to assess 22 genotypes of Sclerocarya birrea (A. Rich.) Hochst, collected from West, Eastern and Southern Africa. Assessments were done on time for bud onset, flower opening, leaf flush, fruit set, fruit maturity period and fruit production. Highly significant (P< 0.001) variations between provenances were obtained in all the phenological traits assessed including variations between sexes in time from flower bud set to anthesis. There was flowering overlaps and synchrony between provenances and sexes with males flowering earlier than females. So far two subpopulations have emerged within the trial referred to as early and late flowering genotypes. The early flowering included provenances from Mozambique, and Swaziland while the late flowering encompassed provenances from Malawi, Zimbabwe, Namibia, Tanzania and Zambia. Fruit maturity period ranged from 76±2 to 192±15days. The early flowering genotypes flowered, fruited and matured between August and January while the late genotypes flowered and fruited from September to May. There were highly significant (P≤0.001) variations in fruit yield of S. birrea provenances between 2016/2017 and 2017/2018 seasons with the former being more productive than the later confirming that S. birrea fruit yield is not constant across seasons due to seed mating effects. There were very strong positive relationship ranging r=0.81 to r=0.78 between leaf flush, bud set, flower opening and fruit set significant at (P<0.001). Some trees classified as females in the first year as based on flowers were found have male flowers which calls for more detailed investigations into this sex change behaviour.

Comparative phenology of mistletoes shows effect of different host species and temporal niche partitioning

The study of plant phenology deals with seasonal events and how these are influenced by environmental factors, including symbiotic interactions. Considering host–mistletoe associations, our goal was to analyze the potential effects of host tree deciduousness on the life cycle of a mistletoe. Thus, Struthanthus martianus Dettke & Waechter was analyzed while growing upon a deciduous host tree and upon an evergreen one. We also compared the phenology of S. martianus with that of a closely related and sympatric species, Struthanthus flexicaulis (Mart. ex Schult. f.) Mart., growing upon a different but also evergreen host. Reproductive and vegetative phenological events were recorded during a three year period following a semiquantitative method. Circular statistical analysis was employed to compare phenological patterns. The peak of leaf production in S. martianus was observed to depend on host deciduousness, as the population infesting a deciduous host showed significant leaf flush during host defoliation. When comparing S. martianus and S. flexicaulis, nearly opposite patterns of flowering and fruiting phenology were recorded. Based on these observations, we conclude that Struthanthus species show niche partitioning to avoid competition. Additionally, we observed that the relationship established with different hosts can alter the mistletoe phenology. This observation highlights the uniqueness of the each host–mistletoe relationship.

Phenology of two Ficus species in seasonal semi-deciduous forest in Southern Brazil

We analyzed the phenology of Ficus adhatodifolia Schott ex Spreng. (23 fig tree) and F. eximia Schott (12 fig tree) for 74 months in a remnant of seasonal semi-deciduous forest (23°27’S and 51°15’W), Southern Brazil and discussed their importance to frugivorous. Leaf drop, leaf flush, syconia production and dispersal were recorded. These phenophases occurred year-round, but seasonal peaks were recorded in both leaf phenophases for F. eximia and leaf flushing for F. adhatodifolia. Climatic variables analyzed were positively correlated with reproductive phenophases of F. adhatodifolia and negatively correlated with the vegetative phenophases of F. eximia. In despite of environmental seasonality, little seasonality in the phenology of two species was observed, especially in the reproductive phenology. Both species were important to frugivorous, but F. adhatodifolia can play a relevant role in the remnant.