II. Phenology and Trophic Mismatch

http://arboreality.blogspot.com/2009/05/of-rain-and-bud-burst.html

Generally, increasing temperature will mean earlier spring and possibly changes in photoperiod (day length) as well. Many terrestrial forest species are sensitive to both cues, temperature and photoperiod, that takes part in phenology, which is the study of the timing of biological events. Since the cues are projected to shift, organisms will need to undergo phenological shifts to maintain high performance and fitness. One potential problem arising from the change is all individual species respond to a different extent. Different life history events that can accelerate with warming, varying mean seasonal timing in microhabitats, other driving factors that cause phenological shift that don't involve temperature change are all the things that could affect variability in direction and magnitude of phenological trends.(Thackeray et al. 2010) Some species are more tolerant and/or flexible to changes than others. This introduces imbalance among trophic levels and therefore, creating trophic mismatch. There are other ways to respond to climate change like range shifts, which will be discussed on the next page.

Bud burst is the first significant signs of the beginning of spring. (Figure on the left is a budburst of White Pine in the Pacific Northwest) Being located at the lowest trophic level as the primary producer, bud burst of trees will display the most direct effect of warming. In the article The Future of Spring Bud Burst: Looking at Possibilities, it explains that the scientists at Pacific Northwest Research Station found that bud burst requires an"intricate interplay" between chilling temperature and warmth exposure to initiate the growth cycle. The scientists further predicted that moderately warmer winters will result in earlier spring bud bursts, but as the the winters get even warmer, the trend will change direction and trigger later bud burst or even no bud burst, as soil moisture continues to deplete and limit bud burst growth.

Both et al. 2009 
[Y-axis clarification: Caterpillars-budburst(top),
 Passerines-caterpillars(middle),
 sparrowhawks-passerines(bottom)]

Although not much research has been done on full-scale trophic mismatch occurring in the Pacific Northwest forests, Both et al. 2009 illustrates a clear trophic mismatch due to uneven phenological shifts across trophic levels of northwest European deciduous forests. In this paper, scientists examined the impact of warming on four different kinds of species for increasing trophic levels focusing on the following: tree bud bursts (primary producer), peak biomass of herbivorous caterpillars (primary consumer), breeding phenology of insectivorous birds called passerines (secondary consumer), and sparrowhawks (tertiary consumers) on the top of the trophic level. Experiment results showed that there was no significant advance in budburst and sparrowhawk hatching dates but the caterpillar peak biomass and passerine hatching dates showed considerable advancement. They concluded that there was increasing asynchrony over time, assuming in response to climate change, in all three interactions. It was hypothesized that the varying degree of phenological response for each level could be a result of limitations in adapting sufficiently or adaptation to escape predation from higher trophic levels. Refer to the figure with three graphs on the right to visualize their data, which illustrate the varying slopes of phenological response between predator-prey interactions among trophic levels.