Lecture 4
Plant Growth, Biomass and
Productivity
Lecture 4 topics
1. How plants grow
2. Carbon allocation
3. Forest Biomass and
Forest Productivity
Week 2 Learning Objectives
You should be able to:
• Recognize characteristics and general distribution of biomes and what
factors influence their spatial coverage
• Describe difference between biome based on actual cover and
potentialcover (spatially and temporally)
• Describe various biome/life zone types (globally and locally) and their
productivity
• Understand spatial variation (gradients) in forest types (e.g., elevation,
latitude, disturbance, temperature, precipitation)
• Describe basic photosynthesis and plant productivity (gross primary
productivity, net primary productivity, differences in plant requirements)
• Understand the role of vegetation in carbon storage (sequestration)
• Think about spatial and temporal differences in ecosystems
1. How plants grow
.
a. MERISTEMS
In humans and other animals growth can occur in most parts of the
body.
Trees do not grow like this and only produce new cells in a very limited
number of places called meristems (zones of intense activity).
Trees grow in height as a result of apical meristems that are located at
their branch tips.
All buds that you see on a tree contain apical meristems
Roots also expand through the soil as a result of root-tip apical
meristems.
Trunk diameter growth occurs as a result of another meristem called
vascular cambium.
Apical meristems (primary); cambium (secondary)
• Unlike animals, plants continue to grow
throughout their life span (can’t move)
• They have meristems which correspond to
stem cells in animals (can differentiate into
any organ)
• Apical meristems on roots and shoots
• Respond to light, searching for soil resources,
responding to herbivory
Buds
Roots
Primary meristems
Secondary meristems cause it to grow
laterally (i.e., larger in diameter).
Vascular cambium, produces secondary
xylem and secondary phloem
Where plants grow and what they
need
• Species have different needs for many abiotic
factors including:
– Light
– Water (precipitation)
– Nutrients
– Soil types
– Temperature
Ages and dimensions of forest trees on better sites in the PNW
and shade tolerance
Species (conifers)
Age
(yrs)
Diam
(cm)
Ht
(m)
Tol
Thuja plicata (western red cedar)
Chamaecyparis nootkatensis
(Alaska yellow cedar)
Picea sitchensis (Sitka spruce)
Pseudotsuga menziesii Doug fir)
Larix occidentalis (W. larch)
Pinus ponderosa (ponderosa pine)
Picea engelmannii
(Engelmann spruce)
Abies amabilis (Pacific silver fir)
Abies procera (Noble fir)
Pinus monticola W. white pine)
Tsuga heterophylla (W. hemlock)
Tsuga mertensiana (Mt. hemlock)
Abies grandis (grand fir)
Abies lasiocarpa (subalpine fir)
Pinus contorta (lodgepole pine)
1000+
1000+
150-300
100-150
60+
30-40
TOL
TOL
800+
750+
700+
600+
500
180-230
150-220
140
75-125
100+
70-75
70-80
50
30-50
45-50
TOL
INTOL
INTOL
INTOL
TOL
400+
400+
400+
400+
400+
300+
250+
250+
90-100
100-150
110
90-120
75-100
75-125
50-60
50
45-50
45-70
60
50-65
25-35
40-60
25-35
25-35
VTOL
INTOL
INTER
VTOL
TOL
TOL
TOL
INTOL
Hardwoods
Species
Age Diam
(yrs) (cm)
Ht
(m)
Tol
Quercus garryana (Garry oak)
500
60-90
15-25
INTOL
Acer macropyhyllum
(Big leaf maple)
300+
50
15
TOL
Populus trichocarpa
(Cottonwood)
200+
75-90
25-35
INTOL
Alnus rubra (red alder)
100
55-75
30-40
INTOL
2. Carbon allocation
So where does the Carbon
come from?
Carbon dioxide via photosynthesis
PRODUCTIVITY
Photosynthesis
CO2 + H2O + light
C6H12O6 + O2 + H20
Respiration:
C6H12O6 + O2
CO2 + H2O + energy
Production – increase in biomass or volume on a given area
over a given time period (usually a year).
Gross Primary Production (GPP) = Photosynthesis
Net Primary Production (NPP) = Photosynthesis – Respiration
homestead-farm.net
Measures of Productivity
• Ecological production and production for energy –
biomass production - (kg per ha per year or g C /sq
m/year or Kcal/sq m/year)*
• Timber production (board feet per acre per year,
cubic feet per acre per year or cubic meters per
hectare per year)
• Energy – kcal per square meter per year
• Tree height at a given age for given species. e.g.,
Douglas-fir
*
1 g Carbon ~ 2.2 g organic matter ~ 8420 Kcal
microbewiki.kenyon.edu
How do plants partition biomass (carbon,
carbohydrates)?
Goal is to minimize resource limitation and maximize
resource capture and NPP
If water or nutrients are limiting: grow roots
utsa.edu
If light is limiting: grow shoots
article.wn.com
3. Biomass and Productivity
Biomass
• Biomass (the quantity of living plant material) is most
abundant in forests.
• Tropical forests account for 50% of Earth’s total plant biomass,
although they occur on only 13% of the ice-free land area;
• Other forests contribute an additional 30% of global biomass
(Chapin et al. 2002)
• Measured in various ways:
–
–
–
–
–
in-situ measurements,
national forest inventories,
administrative-level statistics,
model outputs and
regional satellite products.
Hoh Rainforest
Biomass (Old-growth forest – Hoh River Valley,WA) – Mg/ha
(western hemlock, Douglas-fir, western redcedar, Pacific silver fir,
Sitka spruce)
Total live tree
Shrubs and herbs
Standing dead trees
Logs
Dead shrubs and herbs
Forest floor
Soil
Roots
TOTAL
1044.1
0.7
171.0
92.3
0.5
89.8
360.3
-----1758.6
Terrestrial Production
• Carbon balance of vegetation governs productivity of the biosphere
• Enters the system as gross primary productivity (GPP) and
accumulates as biomass
• Returns to atmosphere via respiration or disturbance
• NPP (Net primary production) = GPP – respiration
• Plants lose carbon through other avenues besides respiration, e.g.,
• Litterfall
• Root exudations (secretions of soluble organic compounds)
• Carbon transfers to microbes
• To herbivores (being eaten)
Net Primary Production (NPP) – kg (g C, Kcal) per hectare
per year
NPP = Growth + Detritus (Litterfall, etc.) + Loss to Grazing
Average Net Primary Productivty (kcal/m2/year
Estuaries
Swamps/Marshes
Tropical rain forest
Temperate forest
Northern conifer
Savanna
Ag land
Woodland/shrubland
Temperate grassland
Lakes and streams
Continental shelf
Tundra
Open ocean
Desert scrub
Extreme desert
Open ocean
ropical rain forest
emperate forest
avanna
Northern conifer
ontinental shelf
Ag land
emperate grassland
Woodland/shrubland
stuaries
wamps and marshes
Desert scrub
akes and streams
undra
xtreme desert
Total global net productivity (billion kcal/year
Site Index
• Site index : measure of the productivity of a site based on
how tall trees will grow over a specified period of time.
• Indexes to a base age, usually 50 or 100.
• For example, a 50-year site index of 120 means that at age 50,
the dominant trees (of the given species) would be expected
to be 120 feet tall. T
• Higher the site index, signifies more productive a sites for a
given species
• Can get site class information from USDA
http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm.
Total height (ft)
Age at Breast Height - Years
theglobaleducationproject.org
Carbon sequestration
• the process through which carbon dioxide (CO2) from
the atmosphere is absorbed by trees, plants and
crops through photosynthesis, and stored as carbon
in biomass (tree trunks, branches, foliage and roots)
and soils.
• Forests and soils have a large influence on
atmospheric levels of carbon dioxide (CO2)
• Tropical deforestation is responsible for about 20% of
the world's annual CO2 emissions, these emissions
are more than offset by the uptake of atmospheric
CO2 by forests and agriculture.
Carbon sequestration
• Carbon sequestration rates vary by tree
species, soil type, regional climate,
topography and management practice.
• Carbon accumulation in forests and soils
eventually reaches a saturation point
• Economic considerations and end use of wood
product is important
Methods of sequestration in land
management
•
Management
Afforestation
Tonnes C/acre/year Time to
saturation
(yrs)
0.6- 2.6
90- 120
Reforestation
0.3- 2.1
90-120
Lengthening
rotations
0.2-0.8
15-20
Switch to
reduced tillage
0.2-0.3
15-50
Grazing changes
0.02- 0.5
25-50
Tonnes of carbon (C) per hectare
(total carbon Gt)
162
35
85
Central Am
175
75
105
How Can Forest Management Help with Carbon
Storage?
Best case scenario: On a global basis, forests could store up
to one-third of total carbon emissions.
Longer rotations; bigger effect on westside than eastside
Retain woody debris on site or utilize it for products
Extend the life cycle of wood products; encourage recycling,
re-use
Protect forests from crown fire (suppression, fuel
management)
Summary
• Photosynthesis drives the carbon cycle
• Plants allocate carbon to maximize resource
use
• Productivity is affected by a suite of ecological
conditions
• Management can play a role in carbon
sequestration