Climate change trends and impacts at Martin Van Buren National Historic Site: Focused condition assessment report

This assessment synthesizes information about current and projected climate and related impacts at Martin Van Buren National Historic Park (MAVA) in order to help park stewards understand, plan, and manage for climate change. Working with a group of park managers, scientists, and local stake-holders, six key park resources were identified for assessment herein: Climate, Water quantity, Phenology, Agriculture, Trees, and Cultural resources. Where data was available, this analysis assessed current condition and considered mid-century (2030–2060) and end-of-century (2100) impacts based on a range of projected future climate conditions, including reduced, low, high and highest emission pathways. Climate change stressors identified for MAVA include: Increased temperature, increased hot days, increased precipitation, increased extreme precipitation events, increased flooding and erosion, shifting ranges of both native species and pest, pathogen and weed species, and phenological shifts and mismatches.

Reproductive phenological shifts and other phylogenetic trait changes in the Arbutoideae (Ericaceae) in the context of drought, seed predation, and fire.

Phenology is an ecologically critical attribute that commonly is coordinated with other plant traits. Phenological shifts may be the result of evolutionary adjustments to persistently new conditions, or transitory, varying with annual flux in abiotic conditions. In summer-dry, fire-prone Mediterranean-climates, for example, many plant lineages have historically migrated from forests to more arid shrublands resulting in adaptive trait changes. These shifts in habitat abiotic conditions and biotic interactions influence morphology of flowers and fruits and will interact with phenological timing. The Arbutoideae (Ericaceae) is one lineage that illustrates such modifications, with fruit characters evolving among genera from fleshy to dry fruit, thin to stony endocarps, and bird to rodent dispersal, among other changes. We scored herbarium collections and used ancestral trait analysis to determine phenological shifts among the five Arbutoid genera found in semi-arid climates. Our objective was to determine if phenology shifts with the phylogenetic transition to different reproductive characters. Our results indicate that phenological shifts began with some traits, like the development of a stony endocarp or dry fruits, but not with all significant trait changes. We conclude that early phenological shifts correlating with some reproductive traits were permissive for the transition to other later character changes.

Climate causes shifts in grey seal phenology by modifying age structure

There are numerous examples of phenological shifts that are recognized both as indicators of climate change and drivers of ecosystem change. A pressing challenge is to understand the causal mechanisms by which climate affects phenology. We combined annual population census data and individual longitudinal data (1992–2018) on grey seals, Halicheorus grypus , to quantify the relationship between pupping season phenology and sea surface temperature. A temperature increase of 2°C was associated with a pupping season advance of approximately seven days at the population level. However, we found that maternal age, rather than sea temperature, accounted for changes in pupping date by individuals. Warmer years were associated with an older average age of mothers, allowing us to explain phenological observations in terms of a changing population age structure. Finally, we developed a matrix population model to test whether our observations were consistent with changes to the stable age distribution. This could not fully account for observed phenological shift, strongly suggesting transient modification of population age structure, for example owing to immigration. We demonstrate a novel mechanism for phenological shifts under climate change in long-lived, age- or stage-structured species with broad implications for dynamics and resilience, as well as population management.

Patterns of flower-visiting insects depend on flowering phenological shifts along an altitudinal gradient in subalpine moorland ecosystems

Alpine and subalpine moorland ecosystems contain unique plant communities, often with many endemic and threatened species, some of which depend on insect pollination. Although alpine and subalpine moorland ecosystems are vulnerable to climatic change, few studies have investigated flower-visiting insects in such ecosystems and examined the factors regulating plant-pollinator interactions along altitudinal gradients. Here, we explored how altitudinal patterns in flower visitors change according to altitudinal shifts in flowering phenology in subalpine moorland ecosystems in northern Japan. We surveyed flower-visiting insects and flowering plants at five sites differing in altitude in early July (soon after snowmelt) and mid-August (peak growing season). In July, we found a higher visiting frequency by more variable insect orders including Dipteran, Hymenopteran, Coleopteran, and Lepidopteran species at the higher altitude sites in association with the mass flowering of Geum pentapetalum and Nephrophyllidium crista-galli. In August, such altitudinal patterns were not observed, and Dipteran species dominated across the sites due to the flowering of Narthecium asiaticum and Drosera rotundifolia. Earlier snowmelt associated with recent climate change is expected to extend the growth period of moorland plants and modify flowering phenology in moorland ecosystems, leading to altered plant-pollinator interactions. Our study provides key baselines for the detection of endangered biotic interactions and extinction risks of moorland plants under ongoing climate change.

Does Climate Warming Favour Early Season Species?

Plant species that start early in spring are generally more responsive to rising temperatures, raising concerns that climate warming may favour early season species and result in altered interspecific interactions and community structure and composition. This hypothesis is based on changes in spring phenology and therefore active growing season length, which would not be indicative of possible changes in growth as would changes in cumulative forcing temperatures (growing degree days/hours) in the Northern Hemisphere. In this study we analysed the effects of a moderate climate warming (2°C warmer than the 1981–2010 baseline) on the leaf-out of hypothetical species without chilling restriction and actual plant species with different chilling and forcing requirements in different parts of the globe. In both cases, early season species had larger phenological shifts due to low leaf-out temperatures, but accumulated fewer forcing gains (changes in cumulative forcing temperatures by warming) from those shifts because of their early spring phenology. Leaf-out time was closely associated with leaf-out temperatures and therefore plant phenological responses to climate warming. All plant species would be equally affected by climate warming in terms of total forcing gains added from higher temperatures when forcing gains occurring between early and late season species are included. Our findings will improve the understanding of possible mechanisms and consequences of differential responses in plant phenology to climate warming.

Disorder or a new order: how climate change affects phenological variability

Advancing spring phenology is a well-documented consequence of anthropogenic climate change, but it is not well understood how climate change will affect the variability of phenology year-to-year. Species' phenological timings reflect adaptation to a broad suite of abiotic needs (e.g. thermal energy) and biotic interactions (e.g. predation and pollination), and changes in patterns of variability may disrupt those adaptations and interactions. Here, we present a geographically and taxonomically broad analysis of phenological shifts, temperature sensitivity, and changes in inter-annual variance encompassing nearly 10,000 long-term phenology time-series representing over 1,000 species across much of the northern hemisphere. We show that early-season species in colder and less seasonal regions were the most sensitive to temperature change and had the least variable phenologies. The timings of leaf-out, flowering, insect first-occurrence, and bird arrival have all shifted earlier and tend to be less variable in warmer years. This has led leaf-out and flower phenology to become moderately but significantly less variable over time. These simultaneous changes in phenological averages and the variation around them have the potential to influence mismatches among interacting species that are difficult to anticipate if shifts in average are studied in isolation.

Plasticity in female timing may explain current shifts in breeding phenology of a North American songbird

Climate change has driven changes in breeding phenology. Identifying the magnitude of phenological shifts and whether selection in response to climate change drives these shifts is key for determining species’ reproductive success and persistence in a changing world.We investigated reproductive timing in a primarily sedentary population of the dark-eyed junco (Junco hyemalis) over 32 years. We predicted that juncos would breed earlier in warmer springs in response to selection favouring earlier breeding.To test this prediction, we compared the annual median date for reproductive onset (i.e., egg one date) to monthly spring temperatures and examined evidence for selection favouring earlier breeding and for plasticity in timing.Egg one dates occurred earlier over time, with the timing of breeding advancing up to 24 days over the 32-year period. Breeding timing also strongly covaried with maximum April temperature. We found significant overall selection favouring earlier breeding (i.e., higher relative fitness with earlier egg one dates) that became stronger over time, but strength of selection was not predicted by temperature. Lastly, individual females exhibited plastic responses to temperature across years.Our findings provide further evidence that phenotypic plasticity plays a crucial role in driving phenological shifts in response to climate change. For multi-brooded bird populations, a warming climate might extend the breeding season and provide more opportunities to re-nest rather than drive earlier breeding in response to potential phenological mismatches. However, as plasticity will likely be insufficient for long-term survival in the face of climate change, further research in understanding the mechanisms of female reproductive timing will be essential for forecasting the effects of climate change on population persistence.

TEMPERATURE AND NUTRIENT CONDITIONS MODIFY THE EFFECTS OF PHENOLOGICAL SHIFTS IN PREDATOR-PREY COMMUNITIES

While there is mounting evidence indicating that the relative timing of predator and prey phenologies shapes the outcome of trophic interactions, we still lack a comprehensive understanding of how important the environmental context (e.g. abiotic conditions) is for shaping this relationship. Environmental conditions not only frequently drive shifts in phenologies, but they can also affect the very same processes that mediate the effects of phenological shifts on species interactions. Thus, identifying how environmental conditions shape the effects of phenological shifts is key to predict community dynamics across a heterogenous landscape and how they will change with ongoing climate change in the future. Here I tested how environmental conditions shape effects of phenological shifts by experimentally manipulating temperature, nutrient availability, and relative phenologies in two predator-prey freshwater systems (mole salamander- bronze frog vs dragonfly larvae-leopard frog). This allowed me to (1) isolate the effect of phenological shifts and different environmental conditions, (2) determine how they interact, and (3) how consistent these patterns are across different species and environments. I found that delaying prey arrival dramatically increased predation rates, but these effects were contingent on environmental conditions and predator system. While both nutrient addition and warming significantly enhanced the effect of arrival time, their effect was qualitatively different: Nutrient addition enhanced the positive effect of early arrival while warming enhanced the negative effect of arriving late. Predator responses varied qualitatively across predator-prey systems. Only in the system with strong gape-limitation were predators (salamanders) significantly affected by prey arrival time and this effect varied with environmental context. Correlations between predator and prey demographic rates suggest that this was driven by shifts in initial predator-prey size ratios and a positive feedback between size-specific predation rates and predator growth rates. These results highlight the importance of accounting for temporal and spatial correlation of local environmental conditions and gape-limitation in predator-prey systems when predicting the effects of phenological shifts and climate change on predator-prey systems.