Presentation on theme: "Rainforest Ecology If a tree falls in the rainforest and no one is around, does it make a sound? It makes a GAP!! Who Cares!!"— Presentation transcript:
Rainforest Ecology If a tree falls in the rainforest and no one is around, does it make a sound? It makes a GAP!! Who Cares!!
Rainforest Ecology forest gaps Gaps have a different environment More light, changes humidity and temp The range is gap size is widespread (3- 400m 2 ), but probably follow logarithmic Large trees, particularly emergents, can take out several others Lianas increase the likelihood of a multiple tree fall
Rainforest Ecology forest gaps When? –Tree falls peak around the middle of the rainy season (extremely wet with relatively strong winds) Landslides can create long swaths of openings How frequent? –4-6% of any forest may be comprised of recent forest gaps
Rainforest Ecology forest gaps Gaps are typically shaped like an inverted cone, where it is larger the higher you get into the canopy This adds a nice component to structural diversity (which is going to influence biodiversity) Rapid growth and reproduction
Rainforest Ecology forest gaps Measurements made at La Selva in Costa Rica indicate that gaps of ≈300m 2 experience 8.6-23.3% full sunlight, compared with interior forest understory, which receives only 0.4- 2.4% full sunlight (50x more), which is appropriate for photosynthesis
Rainforest Ecology forest gaps Of 105 canopy species studied as saplings at La Selva, about 75% are estimated to depend at least in part on gaps to complete their life cycle
Rainforest Ecology forest gaps Denslow (1980) suggested that rainforest trees fall roughly into 3 categories (with respect to gaps) –1) large-gap specialists whose seeds require high temps of gaps to germinate and seedlings are not shade tolerant –2) small-gap specialists whose seeds germinate in shade but whose seedlings require gaps to grow to mature size –3) understory specialists, don’t need gaps
Rainforest Ecology forest gaps In reality, species don’t fit into these 3 packages Many shade-tolerant tree species show no gap association but rather demonstrate high levels of growth plasticity growing in shade but accelerating growth in sunlight
Rainforest Ecology forest demographics How long do trees survive? How long does it take a seedling to reach the top of the canopy? Is growth even during the seasons? What is the impact of short-term climatic fluctuations? What factors influence tree survival?
Rainforest Ecology forest demographics To answer these questions, we need long-term, detailed studies tracking the fate of individuals trees La Selva and BCI
Rainforest Ecology forest demographics: La Selva Longevity-for any given tree (>10 cm), it can expect to live 118 ± 27 yrs; estimate of disturbance rate resulting in complete turnover of the forest (although this would be rare with an average much shorter) Another study suggests annual mortality of 2.03% for ‘large’ trees Other Amazon studies, 1.2%, 1.13%, 1.5%
Rainforest Ecology forest demographics: La Selva Remember, adults survive much better than seeds or seedlings For Dipteryx panamensis seedlings (7 to 59 mo) experienced 16% mortality from litter fall alone Study of 6 sp of seedlings survival ranged 3-19%/yr
Rainforest Ecology forest demographics: La Selva Because growth rate is so strongly influenced by sunlight, growth is not consistent throughout an individuals life Why do emergents emerge? –Sunlight –Escape other falling trees –They do have higher survival rates
Rainforest Ecology forest demographics: BCI 50 ha plot (1980) all plants >1cm surveyed, then again in ’82, ’85, & ’90 El Niño brought drought in ’83 From ’82-’85, >8cm plants had a mortality rate of 3.04% / yr 10.5% in shrubs, 18.6% in understory trees, 19.3% in subcanopy trees and 31.8% in canopy trees DBH > 16cm 50% mortality
Rainforest Ecology forest demographics: BCI Those that survived showed elevated growth rates (e.g. 60% faster than ’85- ’90)…why? Imagine all the gaps created… That was short lived as by 1991 the number of gaps returned to predrought estimates
Rainforest Ecology forest demographics: BCI Turnover…what is it?
Rainforest Ecology forest demographics: BCI Turnover Many species changed abundance 10 sp were lost and 9 were gained from ’82 to ’90 Overall, rather consistent E.g. 1982=301 sp, 4,032 ind, 1985=303 sp, 4,021 ind, 1990=300 sp, 4,107 ind Why? There are always winners and losers
Rainforest Ecology forest demographics: BCI Conclusions: –1) sort-term fluctuations can have relatively dramatic effects on forest composition and structure –2) there is long-term change in species composition (precipitation has declined dramatically over past 70 yrs…14%) 20-30 moisture-sensitive sp may be lost and rare sp were more (-) impacted
Rainforest Ecology forest demographics: BCI “the BCI forest suffered a sever drought, yet the overall structure of the forest bounced back. There is a regulating force at work here: remove a tree and a tree grows back. But this force only preserves the forest as a forest, not the diversity of tree species it contains” Condit et al. 1992
Rainforest Ecology disturbance and ecological succession In many places the forest is relatively open
Rainforest Ecology disturbance and ecological succession But in others, it can be extremely dense
Rainforest Ecology disturbance and ecological succession When the forest gets disturbed enough, it can properly be called ‘jungle’ Oxford: “land overgrown with tangled vegetation, especially in the tropics” Jungles are representative of disturbed rainforest (which is everywhere)
Rainforest Ecology disturbance and ecological succession Think of a forest being cleared After the land is abandoned, some things start to colonize (which ones can be random to predictable) Eventually, it will likely to likely come back to the pre-disturbance state (albeit with some changes) The speed at which this occurs resilience
Rainforest Ecology disturbance and ecological succession The sequence of events can also be predictable E.g. the first species are going to those that do well in light, temp variability, and have a fast growth rate Next sp that tolerate the shade better and may be stronger competitors eventually come in and displace the first set of pioneer sp
Rainforest Ecology disturbance and ecological succession Bare soil Sedges and grasses Herbs, shrubs and vines (epiphytes rare) Trees quickly appear (many which reproduce quickly) More shade tolerant sp compete for light
Rainforest Ecology disturbance and ecological succession Within Amazonia, a typical square meter of soil is estimated to contain 500-1000 seeds. This does not take into account the number of seeds deposited on the surface on a relatively regular basis The result is a crowded group of plants (e.g. vines, shrubs, and quick growing palms) all competing for sun
Rainforest Ecology disturbance and ecological succession Is the composition of early success plots very consistent? The ‘species pool’ is generally too large to predict which species will establish themselves, although we may be able to describe some of their general attributes
Rainforest Ecology disturbance and ecological succession Species appearing early (colonizers) grow rapidly and produce many seeded fruits In later succession, most plants tend to be larger, grow more slowly, and have fewer seeds per fruit (equilibrium sp)
Rainforest Ecology disturbance and ecological succession Depending upon the frequency of disturbance and the quality of soil, there may be significant changes E.g. on poor soil the repeated displacement, colonization of rapid growing plants, may result in a general long-term drain on minerals resulting in a shift from forest to savanna
Rainforest Ecology disturbance and ecological succession Successional forest can be relatively productive (biomass and LAI) often mimicking older forests, although composition is not similar –E.g. 11 mo after burning, one plot had a dense mixture of veg attaining 5m By 15 yrs, it may resemble a older, closed-canopy forest (again, not in composition)
Rainforest Ecology regeneration pathways The regeneration pathways are going to be dependent on the scale and intensity of the disturbance Some possible pathways include: –1) from seedlings and saplings already present in the forest understory (advance regeneration pathway)
Rainforest Ecology regeneration pathways Some possible pathways include: –2) from vegetative sprouting from stem bases and/or roots (which remain after trees are disturbed) –3) from recolonization by germination of seeds already present in soil (seed bank) –4) from the arrival of new seeds brought by wind or animal dispersal
Rainforest Ecology regeneration pathways On small scale disturbances (0.01 -10 ha), the advance regeneration pathway dominates –There is a huge storehouse of small saplings (10-20 per m 2 ) waiting their turn –They will represent >95% of all trees >1m tall 4 yrs after gap formation ‘sprouting’ is a common approach of some individual trees in small gaps
Rainforest Ecology regeneration pathways In large scale disturbances (1-100,000 km 2 ) death to the understory trees is common (e.g. fire, flooding) Regeneration is from a combination of vegetative sprouting plus germination of seeds in the soil, plus import of seeds by dispersal mechanisms
Rainforest Ecology disturbances Fires in Amazonia appear to relatively frequent in recent (6,000 yrs) time Probably occurred during dry periods
Rainforest Ecology disturbances Pastures abound in the tropics Relatively good evidence that much (light to moderately grazed) of converted rainforest can convert back from pasture into rainforest The speed of the resilience will depend upon the intensity of grazing The composition of reclaimed forest was very different than original forest
Rainforest Ecology regeneration pathways Tikal practiced intensive agriculture and had relatively extensive urbanization (i.e. deforestation) Having been abandoned, it was ‘reclaimed’ by the jungle Figs, palms, and mahoganys all sat on the main square Given enough time, most gaps can be closed!
Rainforest Successional Plants Heliconia: one of the most conspicuous early colonizers Sun loving 150 sp Hermit hummingbird Bloom sequentially Birds disperse seeds (28 sp)
Rainforest Successional Plants Piper is a common early successional plant (and understory) with 500 sp Most are shrubs Pollinated by many sp. of bees, beetles and fruit flies Fruit dispersal by Carollia bats
Rainforest Successional Plants Mimosas and Legumes (acacias) Probably most diverse family of tropical plants (everywhere in tropics)
Rainforest Successional Plants Cecropias are abundant and are readily found in gaps Seeds remain viable (2 yr) In Surinam 73/m 2 Grow rapidly (2.5 m/yr) Short-lived Moderate in size Easy to recognize
Rainforest Successional Plants Cecropias have separate sexes Female can producee 900,000 seeds 48 sp of animal use Cecropia obtusifolia 33 bird sp feed on its flowers & fruits Hollow stems (why?): biting ants (Azteca spp) live inside feeding on extrafloral nectaries
Ceiba, Silk Cotton, or Kapok Tree Very typical traits (e.g. flat crown, buttress, smooth bark) High light requirement, common rivers, edges, disturbed areas Rapid growth Lose leaves prior to flowers (why?)
Rainforest Successional Plants May flower once every 5 or 10 yrs 500-4,000 fruits with 200+ seeds per (thus 800,00 seeds per yr) Each seed is surrounded by silky, cottonlike fibers called ‘kapok’ May aid in seed dispersal Leaves not well protected, lots of insect damage. Is this a problem?
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