Lecture 4b: species level climate change impacts: phenology

Question 1

Define phenology

Answer 1

Phenology is defined as: The timing of key events in an organism’s annual cycle of activities

For example:

In plants: bud burst, flowering, development of ‘autumn colour’ and leaf fall in deciduous species
In butterflies: egg hatching and adult emergence
In birds: migration and breeding

Timing matters – a mismatch in young birds hatching and the peak availability of insect larvae due to climate change impacts on migration can result in malnourished chicks and brood failure
(see simplified graph in notes)

Question 2

What triggers phenology events?

Answer 2

usually endogenous mechanisms sensitive to day length

Question 3

Photoperiodic trigerring

Answer 3

Higher plants

both long-day (respond to increasing day length) and short-day (respond to decreasing day length)
* Flowering
* Seed germination
* Bud break
* Leaf abscission

Animals

Short-day responses
* insects entering diapause
* migratory birds departing from the breeding area
* moult into winter plumage (e.g. Lagopus mutus – Ptarmigan) or pelage
(e.g. Lepus americanus – Snowshoe Hare)
* antler shedding (e.g. Cervus elaphus – Red Deer)

Question 4

Tracking phenology: Citizen science

Answer 4

e.g. iNaturalist
Butterfly Conservation
EBird (Cornell lab)

Question 5

Remote sensing

Answer 5

See Phenocam- seasonal vegetation tracker (Richardson 2023)

Remotely-sensed phenological data are useful for assessing crop conditions, drought severity, and wildfire risk as well as tracking invasive species, infectious diseases, and insect pests. Because phenological events are sensitive to climate variation, these data also represent a powerful tool for documenting phenological trends over time and detecting the impacts of climate change on
ecosystems at multiple scales. Remote sensing phenology studies use data gathered by satellite sensors
that measure wavelengths of light absorbed and reflected by green plants. Certain pigments in plant leaves strongly absorb wavelengths of visible (red) light.
The leaves themselves strongly reflect wavelengths of near-infrared (NIR) light, which is invisible to human eyes. As a plant canopy changes from early spring growth to late-season maturity and senescence, these reflectance properties also change.

Question 6

Tracking phenology: remote sensing: NDVI

Answer 6

Many sensors carried aboard satellites measure red and near-infrared (NIR) light waves reflected by land surfaces. Using mathematical formulas (algorithms), scientists transform raw satellite data about these light waves into vegetation indices.
NDVI (Normalised Difference Vegetation Index) – The foundation for remote sensing phenology:

NDVI=(NIR-Red)/(NIR+Red)

Values range from -1 (no vegetation) to +1 (healthy green vegetation)

See NASA NDVI: http://svs.gsfc.nasa.gov/search/Series/NDVI.html

Question 7

Phenology triggers

Answer 7

Events usually triggered through endogenous mechanisms sensitive to day length or seasonal climate - most often seasonal temperatures – hence why climate change is causing disruption

Question 8

Phenology response to climate change

Answer 8

See Huntley et al. (2010) figure 1:
Schematic representation of species’ responses to climatic changes. Species’ predominant response to climatic
changes depends upon the combination of the magnitude and the rate of those changes. Spatial responses, i.e. changes in
geographical distribution, predominate for relatively large magnitude and relatively rapid changes, such as those projected for the present century.

Question 9

Phenology responses to climate change: leaf out

Answer 9

• Northern hemisphere first leaf date indicates such phenological responses at least hemispheric, if not global, in scope.
• Comparison of phenological and temperature data indicates a strong correlation.
  o given the very large number of species with documented responses this almost certainly reflects a causal relationship

Question 10

Ecosystem services

Answer 10

Phenology of many species has shifted and continues to shift
^ expected initial response of many species to recent climatic changes

Do these responses have potential consequences for global biodiversity and/or for the ability of ecosystems to continue to provide vital ecosystem services?

Question 10

Phenology responses to climate change:

Answer 10

The following phenology events have been observed to be impacted by climate change:

In plants: Flowering, fruiting, leaf colour and leaf fall

In butterflies: Adult emergence

In birds: Migration and breeding

In amphibians: Breeding

Menzel et al. (2006), Parmesan & Yohe (2003)

see Parmesan et al 1999:
phenological records for 677 species over time periods of 16 – 132 years
* Woody plants, Herbaceous plants, Mixed plants, Birds, Insects, Amphibians and Fish
* 62% showed trends of advance in the date of spring phenological events
* overall mean trend of ca. 3 days per decade advance – differed by taxa

Question 11

Ecosystem services: Carbon storage

Answer 11

Earlier spring greening and later leaf fall (longer growing seasons) ought to result in increased photosynthetic uptake and hence slow the rate of increase of atmospheric CO2 concentration
… if warmer winters do not compensate by increasing respiration rates

During 1970s and 1980s, seasonal amplitude in the Mauna Loa CO2 curve increased, indicating that both photosynthetic and respiration rates were increased

recent work (Buerman et al. 2007) shows enhanced summer photosynthesis was principally in North America whereas enhanced winter respiration was principally in Eurasia

amplitude decline during the 1990s related to the effect of summer droughts on photosynthesis in North America
- amplitude increased sharply after return to more typical rainfall in 2004

signal is confounded by changes in predominant circulation patterns

• reduced transport of air masses from Eurasia in northern hemisphere spring also contributed to the reduction in amplitude during the 1990s

Question 12

Phenological mismatch

Answer 12

Phenological mismatch results when interacting species change the timing of regularly repeated phases in their life cycles at different rates.
Interacting species may respond to different phenological cues in spring, or respond at different rates
e.g. if Species A – responds to photoperiod but Species B – responds to accumulated warmth
* B advances spring phenology in response to warming, but A does not
* B feeds on A and its phenology initially was optimised to synchronise its emergence with the time when A was most abundant and/or most palatable and nutritious
* following warming, B emerges too early, before A is most abundant and/or most palatable/nutritious
* B suffers food shortage
* B may delay development and thus increase exposure to predation risk
* B may starve, and thus fail to survive, if food shortage is extreme

Question 13

Example of phenological mismatch:

Answer 13

Visser & Holleman (2001)

Evidence of increasing asynchrony between bud-burst in Quercus robur (Pedunculate Oak) and egg hatching in Operophtera brumata (Winter Moth)

synchronisation ensures larvae feed on newly expanding oak leaves
- which are soft, highly nutritious, palatable and low in tannins and other phenolics that protect mature foliage from herbivory (yet to be accumulated in the young foliage)

series of warm winters since 1975
-whereas egg hatching and bud-burst near synchronous in the 1980s, by 1999, eggs
hatching an average of more than 10 days earlier than bud-burst
- newly hatched larvae survive only 2-3 days without food (max. recorded is 10 days)
- asynchrony thus leads to death of a large proportion of the larvae
-negative consequences for O. brumata and wider community of the food web dependent on it

Higher trophic levels typically respond slowly to climate change. They rely on lower trophic levels for food which adapt more quickly so this impacts their survival and reproduction

Question 14

Impact on demography example: Roe Deer

Answer 14

See Plard et al 2014 PLOS biology
& Visser and Gienapp 2019

Question 15

Impact on demography example: Migratory birds

Answer 15

See Cotton 2003 PNAP
&
Burgess et al 2018 NEE

Question 16

Summary 1

Answer 16

1. The timing of key events in an organism’s annual cycle of activities are of critical
   importance for survival and reproduction of both plants and animals.
2. Photoperiod and/or seasonal climate triggers are important (with much evidence
   coming from ‘citizen science’ activities).
3. Earth observation methods offer many possibilities for a whole planet phenology
   assessment over time – as does citizen science
4. Different levels of coverage and spatial scale – choose which to use based upon
   the needs of the data/experiment.
5. Phenology of many species has shifted in response to climate change and continues to shift – typically behavioural responses come first.
6. Potential impacts on ecosystem services.

Question 18

Summary 2

Answer 18

1. Phenology of many species has shifted and continues to shift.
2. With climate change, phenological mis-matching is a growing concern in both plants, animals and plant-animal interactions as mismatch can impact survival and reproduction negatively
3. Migratory species may be most at risk – due to need to anticipate conditions from
   geographically disparate areas
4. Need to determine a species’ capacity for response in terms of both genotypic and/or
   phenotypic response capacity.
5. EO products are getting ever better, as is our ability to model likely impacts of facets of global warming upon phenology of organisms, the potential for mis-matching and, in turn, its potential impacts.