Download The rainforest and how it functions

Explanations of buttress formation:
(reviewed by Hartshorn 1983)
1. Adaptive responses to wind or gravity
stresses.
2. Negative geotropism.
3. Conduction shortcut.
4. Mechanical stimulation of strains caused by
winds.
Christensen-Dalsgaard, K. K., A. R. Ennos, and M.
Fournier. 2008. Are radial changes in vascular
anatomy mechanically induced or an ageing process?
Evidence from observations on buttressed tree root
systems. Trees-Structure and Function 22:543-550.
Clair, B., M. Fournier, M. F. Prevost, J. Beauchene,
and S. Bardet. 2003. Biomechanics of buttressed
trees: Bending strains and stresses. American Journal
of Botany 90:1349-1356.
Mattheck, C., W. Albrecht, F. Dietrich, and R.
Kriechbaum. 1994. The Biomechanics of Rays in
Trees. Allgemeine Forst und Jagdzeitung 165:143147.
Tang, Y., X. F. Yang, M. Cao, C. C. Baskin, and J. M.
Baskin. 2011. Buttress trees elevate soil heterogeneity
and regulate seedling diversity in a tropical rainforest.
Plant and Soil 338:301-309.
Young, T. P., and V. Perkocha. 1994. Treefalls, Crown
Asymmetry, and Buttresses. Journal of Ecology
82:319-324.
Elmqvist et al. 1994. Effects of Tropical
Cyclones Ofa and Val on the Structure of a
Samoan Lowland Rain Forest. Biotropica 26:
384-391.
The frequency of uprooted trees was 31
percent after Ofa, but only 16 percent
after Val. Uprooting was significantly
more frequent among species lacking
buttresses or stilt roots.
The results of our study support the windresistance hypothesis. However, in studies
following hurricane Hugo in Puerto Rico,
no clear difference in wind resistance between
trees with different morphology was found.
STILT ROOTS:
•adventitious roots
•common in mangroves
•common in palms
Avalos, G., and M. F. Otarola. 2010. Allometry and Stilt
Root Structure of the Neotropical Palm Euterpe
Precatoria (Arecaceae) Across Sites and Successional
Stages. American Journal of Botany 97:388-394.
Goldsmith, G. R., and R. A. Zahawi. 2007. The
function of stilt roots in the growth strategy of Socratea
exorrhiza (Arecaceae) at two neotropical sites. Revista
de Biologia Tropical 55:787-793.
Greig, N., and J. D. Mauseth. 1991. Structure and
Function of Dimorphic Prop Roots in Piper-Auritum l.
Bulletin of the Torrey Botanical Club 118:176-183.
Hanagata, N., T. Takemura, I. Karube, and Z.
Dubinsky. 1999. Salt water relationships in
mangroves. Israel Journal of Plant Sciences 47:63-76.
TROPICAL LEAVES
RAINFOREST LEAVES:
•usually mesophyll
•20-182 cm2 upper surf. area
•oval and unlobed
•smooth margins
•long-lived
•drip tips are common
Drip tips speed water runoff and
drying of the leaf surface
(Dean and Smith 1978).
BakerBrosh, K. F., and R. K. Peet. 1997. The
ecological significance of lobed and toothed
leaves in temperate forest trees. Ecology
78:1250-1255.
Burd, M. 2007. Adaptive function of drip tips: a
test of the epiphyll hypothesis in Psychotria
marginata and Faramea occidentalis
(Rubiaceae). Journal of Tropical Ecology 23:449455.
Ivey, C. T., and N. DeSilva. 2001. A test of the
function of drip tips. Biotropica 33:188-191.
Lucking, R., and A. Bernecker-Lucking. 2005.
Drip-tips do not impair the development of
epiphyllous rain-forest lichen communities.
Journal of Tropical Ecology 21:171-177.
VARIATION IN TROPICAL LEAVES:
•compound leaves more common
in lowlands
•leaf size declines with average
temperature of coolest month
•leaves are smaller on poorer
soils
Leigh 1999
EPIPHYTES:
•attach firmly to other plants
•trap soil particles for nutrients
•create unique ecosystems
•moist conditions are necessary
•most common in pre- and
lower montane rainforests
•arboreal mammals may prevent
extreme epiphyte abundance
on upper branches
•families include: Bromeliaceae,
Orchidaceae (1200 spp. In CR)
and Araceae
•abundance and species richness
is more pronounced in Neotropics
EPIPHYLLS:
•tiny epiphytes occurring on leaf surfaces
•include mosses, liverworts, lichens, and algae
•common in understory of lowland wet life zones
•usually detrimental
•drip tips enhance runoff, reducing epiphyll loads
•canopy lichens fix nitrogen
Dyer and Letourneau 2006. Determinants of Lichen
Diversity in a Rain Forest Understory. BIOTROPICA
39(4): 525–529 2007.
Epiphyll cover (mosses, liverworts, and lichens) was greater
on plants that had ant-mutualists and balanced resources. Lichen
species richness was greater for plants with balanced resources,
particularly for those with high light availability. In this system,
natural sources of variation were reliable determinants of lichen
diversity and both biotic and abiotic influences were
important.
VINES:
Climbers: vines (herbaceous) and lianas (woody)
Bignoniaceae the most common family
Lianas are more common in drier forests
Thick lianas indicate undisturbed forest (Hartshorn 1983)
Stranglers: Ficus (Moraceae) and Clusia (Guttiferae)
Start out as epiphytes, send down woody, clasping roots
Kill tree with dense monolayer of evergreen leaves on top
Tropical Rainforest Constants
Leaf area index (LAI):
LAI = L/A, where L = upper leaf area, A = area of
the forest (no dimensions). Traditionally
calculated via measuring the leaf area above a
square meter of forest floor, so that LAI = L, the
total leaf area (without dimensions).
BCI LAI = 8
Temperate forest LAI = 6
Tropical Rainforest constants:
•LAI is 7-8
•trees drop 6-8 tons dry wgt lvs/ha/yr
•death rates of trees >= 10cm dbh = 1-2%/yr
•basal area (total cross sectional area
at 1.3 m above ground of all trees >= 10cm
dbh) near 30m2/ha and above-ground
biomass near 300 tons dry wgt/ha
Bala ant Paraponera clavata
La Selva: 18
4.5 per hectare
Protect .04 tons wet-weight leaves
per hectare per year.
DISCUSSION OF LEIGH 2009
What are the roles of phenotypic plasticity versus
fixed adaptations in generating Leigh’s forest
constants?
What controls forest productivity?
What governs forest structure?
How do animals shape the botanical characteristics
of tropical forests?
Why are there so many species of tropical trees?
How has math helped answer these questions?
STRUCTURE OF A “RAINFOREST”
I. Structural complexity
II. Telling the trees from the forest
A. Buttresses and prop roots
B. Trunks and crowns
C. Leaves
D. Variation across life zones
III. Vines and epiphytes
IV. Flowers, fruits and seeds
V. Diversity revisited
VI. GAPS
HIGHER
GROUND
ADAPTING
TO LIFE IN
THE FOREST
CANOPY
EPIPHYTE DIVERSITY
• Over 20,000 species in total
• 10% of all vascular plants
• More than 80 families contain
epiphytes
– Monocots are dominant group in
epiphytes
– Ferns are roughly 1/3 number of
epiphytes
– Gymnosperms very rare:
• Seeds not dispersed easily
• Wind pollination inefficient for epiphytes
MAJOR FAMILIES
• POLYPODIACEAE
(ferns): most of 1100
• ORCHIDACEAE
(monocots):
13,000/19,000
• ARACEAE (monocots):
1350/2500
• BROMELIACEAE
(monocots): 1144/2500
• PIPERACEAE (dicots):
710/3100
• MELASTOMATACEAE
(dicots): 648/4770
EVOLUTIONARY HISTORY
• POLYPHYLETIC (in unrelated groups)
• RECENT development (Pliocene/Pleistocene)
– WHY? Animal dispersers evolved during late
Tertiary and early Quaternary
– EVIDENCE: Current high rates of genetic
evolution in certain groups;
– Highest diversity in geologically young
MONTANE habitats
GLOBAL RANGE
• Epiphytes are found in virtually all humid
tropical forests;
• Highest diversity in pre-montane and
montane forests with high air moisture
• Drier forests have lower diversity but may
have equal densities of stress-tolerant
epiphytes, as well as abundant vines and
lianas
WINTER
• FROST: Primary limiting
factor in latitudinal ranges
• Hardy epiphytes:
Tillandsia usneoides,
Polypodium polypodioides
(along SE coast)
• Mistletoe: Parasite
protected by host body
• Nonvascular epiphytes:
temperate rainforests have
large bryophyte and lichen
populations
NONVASCULAR
EPIPHYTES
• What is a LICHEN?
– SYMBIOSIS between a
fungus and photosynthetic
algae (or cyanobacteria)
• Dessication Strategy
– POIKILOHYDRY
– Nitrogen Fixation:
Decreases Water Need
• EPIPHYLLS
– Most primitive form of
epiphytism
How to classify
Arboreal Flora?
• POLYPHYLETIC
• No Unifying Characteristics
• Several Different Systems:
–
–
–
–
–
Relation with Host
Growth Habit
Light
Humidity
Substrate
DEFINITIONS
• VINE: herbaceous climber with soil contact
• LIANA: woody climber with constant soil
contact
• HEMIEPIPHYTES:
– PRIMARY: Germinate as epiphyte, form
soil contact
– SECONDARY: Germinate in soil, climb
into canopy
• HOLOEPHIPHYTES: True Epiphytes
BENEFITS for Epiphytes
• Higher levels of sunlight
• Lower levels of competition for light
resources
• Lower amounts of herbivory (especially
from large mammals)
• Lower investment in support structure
Partitioning Light Resources
Epiphytic Bromeliads
• Evolved from terrestrial ancestor from arid
habitat (well-suited for epiphytism)
• 3 Different Basic Forms
– Tank Bromeliads
– Atmospheric Bromeliads
– Ant-House Bromeliads
TANK BROMELIADS
Tank Bromeliad
Fauna
INTERACTIONS WITH HOST
• COMMENSALISM?
1. Epiphyte Load
2. Nutritional Piracy
a. Throughfall interception
b. Canopy roots
3. Parasitism
Ant-Plant Interactions
• Myrmecochory
• Pollination (quite rare)
• Leaf-cutter ants
Myrmecophily
• Ant-mediated protection
• Myrmecotrophy
Myrmecophytic Strategies
Protection-based
• Plants are defended
against herbivory and
competition
• Ants may receive
shelter and specialized
food bodies or
extrafloral nectar
Nutrition-based
• Plants obtain nutrients
from ants through
stems or root systems
• Ants receive nesting
sites or nest structural
support, as well as
food bodies or nectar
Epiphytes as Myrmecotrophs
• Epiphytes have greater requirements for both
water and nutrients
• Epiphytes experience less herbivory and
competition over light resources than terrestrial
species
• Many arboreal ant species are well-suited for
myrmecotroph association
• Myrmecotrophs tend to colonize exposed,
nutrient-poor areas where the ant-plant mutualism
provides necessary advantages
Ant-Garden vs. Ant-House
Myrmecotrophs
• Ant-garden epiphytes
obtain nutrients from
arboreal carton nests in
which ants plant their
seeds
• These plants offer food
bodies and nectar, as well
as support and drainage
(through transpiration) of
the arboreal nests
• Ant-house epiphytes
absorb nutrients through
stems or adventitious roots
from inhabitant ants
• These epiphytes provide
nesting sites within their
vegetative structures, and
offer limited rewards to
the ants
Ant-House Bromeliads
Transition from tank
morphology to anthouse myrmecotroph
Bromeliad trichomes
facilitated ant-house
adaptations
Bulbous waterproof
chambers formed by
leaf morphology
Ant-House
Orchids
Hollow pseudobulbs
with natural entrance
holes
Solutes absorbed by
adventitious roots
inside pseudobulbs
Extrafloral nectaries
may attract larger
ants that defend the
orchid more
successfully
Ant-House Ferns
Ant-House Rubiaceae
Chamber Morphology
Ant colonies use the
dry, smooth-walled
cavities for their
brood, and store
debris and prey items
in the “warted”
chambers, where the
plant can absorb
nutrients directly
from organic debris.
YANAYACU
• Premontane wet
tropical forest
• Highest diversity
of epiphyte
groups
• Lower diversity
of vines and
lianas
LA SELVA
• High diversity
of all groups
of arboreal
flora
(Epiphyte
diversity
higher in
premontane
wet forest)
BARRO COLORADO ISLAND
• Fairly rich flora of
epiphytes and arboreal
fauna
• Not as diverse in
arboreal flora as
tropical wet forest (La
Selva) or premontane
wet forest (Yanayacu)
ACG
• Shares under 5% of
epiphyte community
with La Selva
• Relatively low diversity
(High local densities of
vines and lianas)
SERENGETI
• Orchids and vines
only in riverine
forest habitat
(seasonal rains and
humid shade)
MILNE BAY
• Mangrove forests
often contain
halophytic plants
including hardy
epiphytes, lichens,
and parasitic plants
FLOWERS:
•flowering time is variable
•mass flowering can be common
•pollination syndromes and coevolution are common
•large, showy bracts are common
•asexual reproduction may be more important
for some species
•is self compatability more common in rainforests?
Sequential blooming and synchronous fruiting in 6 species of Shorea.
FRUITS AND SEEDS:
•fruit size and structure variable
•very large fruits are common
•seed dispersal is variable
(wind 31% at ACG, 8% at La Selva)
(La Selva 50% bird dispersed, 13% bats)
•seed predation is high
Gross Primary Productivity: The total amount of solar
radiation converted by plants into chemical energy (i.e.
sugars)
Net Primary productivity: Amount of carbon fixed in excess
of the respiratory needs of the plant.
Most biological metabolic activity takes place within the
range 0-50o C. The optimal temperatures for productivity
are 15-25o C.
The productivity of plants,
especially at the local scale,
can also be controlled
by the availability of nutrients.
“Nutrients are regenerated more
rapidly in tropical than in temperate
forests.”
Ultisols: well-weathered, acidic soils (nutrient-poor)
Inceptisols: young soils of recent origin, rich in minerals
near the surface, higher pH (but still acidic)
RESOURCE AVAILABILITY HYPOTHESIS:
plant species adapted to resource-limited
habitats have inherently slower relative
growth rates, contain higher levels of carbon
based defenses, and are less preferred by
herbivores (Janzen 1974, Coley et al. 1985).
WITHIN A HABITAT:
In resource-limited habitats within-species
allocation of nutrients to growth has highest
priority, and allocation to defenses increases
when resource-limiting conditions improve
(Bazzaz et al. 1987).
(predicts that at higher relative growth rates,
concentrations of defensive compounds will be
greater than at lower rgr)
Carbon/nutrient balance hypothesis:
A plant’s C:N ratio determines its
nutritive quality and palatability to
generalist herbivores and is an adaptive
response to herbivory that evolved
under constraints of availability of
resources in the environment (Bryant et
al. 1983).
predicts lower herbivory in nutrient stressed
plants (high C:N), and high rates in fertilized
plants (low C:N)
PLANT STRESS HYPOTHESIS
Insect herbivores preferentially attack
stressed plants because of breakdown
and mobilization of nitrogen-containing
compounds (White 1974).
Predicts outbreaks and increased herbivory
on nutrient stressed plants
PLANT VIGOR HYPOTHESIS
(concentrates on specialist, rather than
generalist herbivores): Vigorously growing
plants are more favorable to specialist
herbivores (Price 1991)
Feller, I.C. 1995. Effects of nutrient enrichment
on growth and herbivory of dwarf red mangrove
(Rhizophora mangle). Ecological Monographs
65:477-505.
Is nutrient limitation responsible for the slow growth and
characteristic physiognomy of dwarf red mangrove trees
in the interior of a mangrove island?
How does increased nutrient availability affect herbivory
in red mangrove?