WFC198: 15: Climate Change in the Tropics

What are RCPs? What do larger number means?

(representative concentration pathways) Four different greenhouse gas trajectories representing different futures. larger numbers = bad and more severe climate change (Named for the amount of radiative forcing in 2100 relative pre-industrial values: +2.6, +4.5, +6.0, or +8.5 W/m2 We are (sadly) on track for RCP 8.5)

describe the current trends in temperature and precipitation.

- Temperature is uniformly increasing (and strongly) - Precipitation effects are not as strong. They are more variable across space increasing and decreasing in different places.

is phenology more complex in the tropics or temperates? why? give ex.

---Phenology is more complex in the tropics -No dormancy and continuous growth throughout the year -Trends in temperature, solar radiation, and rainfall do not necessarily coincide as they do in temperate areas -Different species respond to different cues Still, phenological changes are occurring.... (Left graph: As CO2 rises, plants are flowering for longer durations on Barro Colorado Island, Panama Right graphs: A 15 year record of fruiting in Kibale, Uganda. Shows that fruiting takes places primarily in response to solar radiance. Clouds block the sun and thus rainfall is associated with a decline in fruiting (in this system). Expected to get more wet with climate change. So less fruiting in the future? Demonstrates how complex tropical phenology can be...)

global changes: how does climate change work? (starting with what humans do)

1. Humans have severely increased greenhouse gases (e.g., CO2) by burning fossil fuels 2. These fossil fuels trap heat, radiate it back to Earth, and increase global mean temperatures 3. That's it on how climate change works for this course...

why would tropical forests would be accumulating carbon?

1. Succession. Forests are still recovering from past impacts and are growing. So are transitioning to older denser shade trees that hold more carbon 2. CO2 fertilization. Plants take up CO2 to make sugars (photosynthesis). Increased emissions may 'fertilize" plants and promote growth.

what's a better way to estimate global extinctions? What are problems with species distribution modeling? What's one rosy view?

A better way would be to explicitly model physiology and account for species interactions. problems with this model?: doesn't account for biotic interactions. ALso how do you assume how far species will move? what if ranges are not constrained now by climate but by interactions? Species interactions are complic and if one guy moves and another dep on it, we'll see extinction... rosy view: maybe some are not affected by temp but by interaction so they won't go extinct bc of climate

spatial movts: In the tropics, temperature is stable over vast distances making latitudinal range shifts less likely. Instead species may move altitudinally. What happens when species move upslope?

Biotic attrition: species move upslope, reducing the diversity of lowland areas Range-shift gaps: species may be unable to move if gaps exist between their current vs. projected ranges Mountaintop extinctions: Species on top of mountains cannot move any higher and may go extinct

what's a carbon sink, and are tropical forests carbon sinks?

Carbon sink: When an ecosystem takes up more CO2 than it emits (via respiration) Despite deforestation, studies indicate tropical forests may be accumulating carbon (acting as a sink) (- Found carbon accumulating in most places but not in the paleotropics (low sample size, only 18 sites) )

Which area has been called the most responsive tropical region to climate change, and why?

Central America this area has Extreme events (floods, hurricanes, etc.) and Droughts

? study on spatial movts?

Colwell et al. (2008) simulated a 3.2°C temperature increase (600m upslope shift) in Costa Rica Freeman & Class Freeman (2014) measured changes in birds' elevational ranges in New Guinea (Dotted lines are predicted (long dashed) and observed range (short dashed) shifts in left graphs. Crested Berrypecker is now restricted to immediate vicinity of Mt Karimui's summit! it was biotic attrition and elevation that caused more changes in comm???? lots of birds changed in elevation , shifting upslope; some species like berrypecker, might be candidate for mntntop extinction. So mntntop extinctions are def a thing and are occurring)

What determines whether forests are carbon sinks versus sources?

Deforestation. ~85% of tree carbon is released to the atmosphere following deforestation 17-20% of emissions globally in the 1990s can be attributed to deforestation Fire is another HUGE emitter. In 1997-1998, tropical fires released roughly the same amount of carbon as 40% of ALL fossil fuel use globally

What are the predicted trends for precipitation in the tropics?

Despite spatial variability, there are regions where models agree precipitation will increase/decline takeaway: central america and lots of amazon is going to dry whereas western part on other side of andes and india will get wetter and parts of Africa.

bc of narrow range of temp, some species that are more vulnerable are ___ because ___.

Deutsch paper: bc of narrow range of temp, some of species that are most vulnerable are ectotherms bc they need to thermoreg based on environment

What's HANPP? how much NPP do we use globally?

Estimates for how much productivity we use vary One paper (Krausmann et al 2013) estimated that we use ~25% of NPP globally

unlike temperate leaves, tropical leaves are...

Held throughout the year Thick, waxy, and weigh almost twice as much! (to reduce herbivory and bc they get inundated w/ water) so they store more carbon

is it more likely that tropical forests are accumulating carbon more because of succession or CO2 fertilization?

In Africa study, lighter-wood species (early succession) did NOT accumulate more carbon than denser wood species so here, idea of succession didn't work -More likely CO2 fertilization (negative feedback in climate change bc we put in more carbon into air and plants take up more carbon and grow more)

Effects of Drought on species distribution

In Panama, researchers studied plant distributions along a strong precipitation gradient. Plant study showed that species drought tolerance predicted whether they would show up on the Atlantic side of Panama (wetter) or the Pacific (drier) Also in Panama, researchers found dry season length is increasing, causing population declines in birds . In BCI, long term mist netting shows population decline (growth rate) with drought so species that exist in drier places are not so sensitive to drought. If you incr drought then it can affect which species are where

what's climate velocity?

It's how fast species need to move (shift ranges) to keep pace with climate changes. They can move to more temperate latitudes or higher elevations (where it is colder) (if you're in place w/ lots of topo and elevational change, prob don't need to move that far and that fast so it's easier to keep up w/ climate change. but if there are more rapid turnover as you move north, don't have to move so far vs if it was slower turnover??)

What did Janzen point out about how different species experience temperature variability?

Janzen (1967) pointed out tropical species experience less temperature variability than temperate species (pic is supposed to be a map of temp variabilities. so maybe they specialize on narrow temp bands and so are very vulnerable)

what's the long-term carbon trend int he Amazon, and why?

Long-term trend of decreasing carbon accumulation in the Amazon. Likely due to slowing tree growth (trees are already inundated w/ C so there's not as big an effect now) and increased mortality (e.g., from climate change induced droughts) Worse if you consider deforestation and fires...

define NPP. What's the productivity like in tropical forests? compare to coniferous forest and grassland

Net Primary Productivity: amount of CO2 taken up via photosynthesis minus CO2 released via respiration Tropical forests are very productive. Per unit area... -2x more than coniferous forest -5x more than grassland in temp areas, there are prod pulses in summer that fades in winter. More constant prod in tropics

why are coral reefs important for humans?

Reefs provide food for ~1 billion people Reefs protect the coast by dissipating wave energy and reducing wave height ~200 million people receive coastal protection benefits from coral reefs.

local extirpations: Very few studies identify the immediate cause of climate-induced population decline. How are sceloporous lizards (ectotherms) being affected by high temps?

Sceloporous lizards (ectotherms) are declining due to high temperatures restricting their daily activity But direct physiological impact of climate is rarely the cause... (reduction in food, spread in pathogens, might cause local extirpations)

describe ecosystem transformation in Amazon

Severe droughts may have large regional effects, especially in the eastern Amazon Complex feedbacks may elicit change from rainforest to savannah...

how could we estimate global extinctions? describe the process

Species distribution modeling: 1. Where you associate where a species is now with current climates. 2. Project future changes in climate. 3. Identify which areas will be suitable for species in the future. 4. Use changes in area and assumptions about how far species can move to estimate extinctions.

describe the earth's latitudinal trends in warming. What does this mean for the tropics specifically?

Temperate areas (especially in the Northern Hemisphere) are warming faster than the tropics. But temperature variability (and thus extreme events) are projected to increase in the tropics esp the north pole is warming a lot more than tropics. What's this mean for tropics? Might mean that climate change is not such big deal in tropics since warming is in the poles??? That's what a lot of people think BUT... there are other changes we need to worry about, see next

does temperature determine whether forests are carbon sinks versus sources? Why or why not?

Temperature Increases productivity but also increases decomposer activity. No overall impact. ---Transfer of carbon from the soil to vegetation (- In higher temperatures, more productivity in the plant than in the soil! as you incr temp, more carbon in plants vs in the soil. Plants grow more and have more carbon in them, and soil microbes act faster and break down carbon in soil so there's less soil carbon. Makes sense bc tropics are hotter than temp, there's more soil microbe activity and there are more plants)

Rship b/w species turnover an climate change?

There will be losers and winners with climate change, causing no-analog communities (unique comm that never existed in the past, aka novel) Other pressures may compound turnover (- Lawler modeled changes in ~3000 species of birds, mammals, and amphibians under 30 climate models. A1B projections. Note the biggest changes in Central America, the Andes, and the Tundra Up to 90% TURNOVER!!!! left pic: showed that abundance to response to agric strongly correl to response to drying. sme epecies are really good at occupying agric. a bird does fine w/ incr in agric and incr in forest. but barred antshek do poor in agric AND in drier areas so only persist in wet biomes. tells us that fi we seeclimate change happening and see more drying in this region, we'll see certain amt of turnover; and it's the same species that don't benefit from habitat loss.if there's both habitat loss and ? we'll see high turnover ?????/ lost me)

give some ex. of how tropical biomes are distributed across a range

Tropical forests often located in mountainous regions (low velocity) Mangroves can't shift upslope to avoid the heat (high velocity) (tropical forests often located in more mountainous regions so have slower climate velocities so are better to deal w/ climate change. vs mangrove which is on fringe of water, not much topo, bc tropics exist where across bands the temp is pretty constant, have to move fast to keep pace bc can't move upslope. from climate velocity perspective, some biomes are more vulnerable than others. It's not just climate and temp that we have to worry about, have to think about how fast species can move)

How much carbon do tropical forests store and where, vs how much of Earth's surface do they occupy?

Tropical forests store 40-50% of terrestrial carbon despite occupying only 7-10% of Earth's surface Most carbon is stored in wood (longer term storage)

describe ecosystem transformation in coral reefs

We already learned about how bleaching works... It is a big problem. In 2016, 35% of the Great Barrier Reef corals were dead or dying. Corals (and other animals) create calcium carbonate skeletons -Lay down layers of skeleton, building a reef over time -The specific carbonate mineral they use is aragonite -When we add carbon dioxide to the water, it reacts with water to form carbonic acid. This lowers the pH of the ocean. The extra H+ ions combine with carbonate to form bicarbonate. This is unusable for corals Reefs at low latitudes will be the first to exceed thermal bleaching thresholds Reefs at high latitudes will experience the most rapid reductions in aragonite

making stuff up... choose a 'fingerprint' of climate change. How could you test whether tropical v. temperate species are more sensitive? What is your hypothesis? What data would you need?

ex: incr var in precipitation -in tropical regions, problem would be drought so you could isolate tropical and temperate species and do various treatments with lots of heavy or med or less rainfall or drought; see who did better by measuring body test conditions; see how much their initial body composition changed over time. Hypothesis: temperate ones would do better bc are more used to variability data: their initial body condition, how much water is needed

What was Darwin's ideas about abiotic factors?and biotic

had idea that Abiotic factors (temperature, precipitation) should set species range limits in the temperate zones ---these huge swings in temperature make temperate areas stressful but Biotic factors (predation, competition) should set range limits in the tropics (so abiotic factors are not so imp??) ---The tropics are benign but full of competitors/predators (can predict dens of birds based on isocline of how cold it gets. shows that species range limits are set by harsher abiotic conditions in temperate zones)

Janzen: Do low and high tropical altitudes overlap in temperature? What can this lead to?

no, they don't overlap. May lead to species with narrower physiological tolerances (if you think of a mntn, in tropics not much temp var throuout yr so low altitude is nuniformly warm througout yr and higher is colder. in temp area, not what happens bc low alt has big change in temp, high alt is colder but also has big range of temp. broad range of overlap so species at low alt might xp lots of same temp that species at high alt would. so would need to evolve broad physiol tolerance w/ overlap basically idea is in tropics if you have narrow thermal bands, species can speiciliaze on narrow bands, and as you go up mntn, it's like the enviro is changing. you see tons of beta diversity in tropics. but in temperate species have broader range and don't need to specizliae as much climate implications: ones at top of mntn can't move to colder higher elev areas. can be worried about mntntop extinctions. And in general, tropical species might be more vulnerable bc have more narrow thermal tolerance. so lesser degree of warming might have more impact on tropical sepcies than in temperate)

Feeley et al. (2017) argues that tropical species are unrepresented in climate change analyses. Why is this a problem?

problem w/ underrepresentation bc tropics rep ⅓ of land surface; spatial rep is important. so many funds go into protecting the habitat but climate change needs to be considered too. Secondary mutualism, interspecific interactions, ldg is in tropics; socioeconomic value so many ppl in tropics rely on tropical resources, may play vital role in these ppl's lives so we have to gain undst of these species... these all are imp to consider

what is phenology? Why is it understudied in the tropics?

temporal 'movements'; Well documented pattern of shifting activities earlier in the year (breeding, flowering, egg-laying, migrating...) *** One reason is that tropics were considered aseasonal and thus not really studied from a phenological perspective before 1950 and rarely after that. Very few older studies as it is hard to maintain resources and identification is difficult lots of cases where species were moving earlier in the yr.

On to the Paleotropics (Africa)... how much of the world's tropical forest is there? How has carbon storage changed? What area is the effect similar to?

~1/3 of the world's tropical forest is in Africa Study of 79 plots in 10 African countries Carbon storage increased from 1968 - 2007 Similar to effect in Amazonia