Disturbance

Definition

• A relative discrete event in time and space that alters the structure of populations, communities, and ecosystems.

• causes changes in resource availability or the physical environment.

– Pickett and White, 1985

• Disturbance is difficult to define

• Must be defined in the context of the normal range of environmental variation that an ecosystem experiences.

• Normal Range?

• The dividing line between disturbance and normal function is somewhat arbitrary.

Disturbance Properties

• Type

• Severity

• Intensity

• Frequency

• Size

• Timing

Scale 尺度

• 尺度是指在研究某一物體或現象的空間與時間單位

• 研究者的角度來定義尺度。

量測 , Measurement

• 尺度是量測時所用的空間與／或時間單位的大小。

Extent 輻度

Grain (resolution) 解析度

Extent

Grain (resolution)

• 當我們經由觀察（量測）來描述一個現象、事件或事物時，表示它具有其特徵尺度。

• 例如﹔颱風（空間 10 2 km ，時間 10 1 days ）

尺度亦指某一現象在空間和時間上所涉及的範圍 ( space ) 和發生的頻率 ( time ) －－ 現象或過程的特徵尺度。

在時間的尺度上，可以用發生的頻度來表示

時間

空間 過程的場域S

pace

(A

ffec

ted

Are

a)

Time (occurrence frequency)

覓食 求偶

播遷

• 層級理論 (Hierarchy Theory)– 描述一個由兩層或以上尺度 (scale) 的分离的功能

元素 (discrete functional elements) 所組成的系統運作的方式。

– 每一個元素都自成一個單元，各自具有其功能與限制 (constraints) 並呈顯其穩定性與變異。

– 生態系統是一個配套的層級系統 (nested hierarchy) ，每一層級均包含了其下的層級。

– 同一層級內的元素之間和不同層級間的元素都有物質或能量流相聯接。

– Urban. D.L., R.V. O’Neill and H.H. Shugart, Jr. 1987. Landscape Ecology. Bioscienc, 37(2)

Level (+1)

Level (0)

Level (-1) Level (-1) Level (-1) Level (-1)

constraints

filter

關係較強

關係較弱

Level (0)

空間尺度大時間尺度大 下一層

的制約

上一層的機制空間尺度小

時間尺度小

Time and spatial scales of the boreal forest

Disturbance Properties

• Type

• Severity

• Intensity

• Frequency

• Size

• Timing

經由尺度可以讓我們重新檢視生態系的一些基本性質例如：穩定性或平衡如果相對於我們所關切的系統 ( 現象、過程 ), 干擾是大而迅速的 ,則生態系將呈顯不穩定。對同一性質的干擾 , 若伸展所考慮的系統至更廣的尺度 , 則系統仍會呈顯穩定的反應。遭受干擾的森林中 , 個別的小區中的林木可能會消失 , 但是整個大區域的森林仍會呈顯相對的恆常。

Ecosystem interested

Disturbances

Domain of Scales

TIME SCALE

SP

AT

IAL

SC

ALE

TURN OVER RATE

Resilience of Tropical Wet and Dry Forests in Puerto Rico

福山 南仁山

develop a framework for exploring the resilience of tropical forest General principles that may explain the similarities and differences that exist among forests from different life zones

• Resilience

• rate of a forest stand recovers from large and infrequent disturbances (LIDs)

• slope of the relationship between any parameter of forest structure or function plotted over time after a LID event.

• Unit: % of recovery of unit time

• define levels of a hierarchy used as the basis for comparisons

• describing and comparing the structure and functioning of mature stages of the two forest types selected for the case studies, and summarizing results that illustrate how resilience issues might be approached

• discussing the interaction of disturbances with ecosystems

• describing disturbances and forest response to them• identifying generalized resilience mechanisms

five criteria of the framework

Resilience measurements

• Responses of individuals to their environments– sprouting ability– time to first reproduction

• System parameters– Belowground storage (organic matter and nutrients)– Fluxes of biomass, nutrients, populations– Biotic control of fluxes– Species richness– Metabolic activity when disturbances occurred– Species turnover rate at a scale of less than 1 hectare– Capacity of plant populations to form communities

with similar structure and function.

Parameter Fushan Puerto Rico Subtropical

Wet Dry

Mean annual rainfall, mm

4388 3537 860

Mean annual temp.

18 21-22* 21-22

Ratio of PE to Rainfall

0.2 0.33 1.4

Elevation 690-780 (plots)

150-500 125-145

*mean annual biotemperature: daily mean temperature = 0 when it > 30oC and < 0 oC

Structure Parameter Fushan Puerto Rico

Subtropical

Wet dry

Total tree species/ha 515 (total) 50 52

Tree density (tree/ha) 950-1500 1750 1170 to 2307

Canopy height (m) 9.4-11.6 20-30 6-9

Common dbh range (cm) 16.3-25.7 (trees only)

4-50 3-8

Above ground stemwood biomass (Mg/ha)

185 – 272 190 50

Epiphte biomass (Mg/ha) 0.015 – 0.5 0.5 0.14

Leaf biomass (Mg/ha) 4.8 – 7.9 7.9 4

Leaf Area Index 5.7 – 8.39 6 to 7 2 to 4

Loose litter (Mg/ha) 5.7 to 9.0 6 to 8 9 to 15

Leaf litter (Mg/ha) 2.3 to 3.6 5 to 6 7 to 12

Specific leaf area (cm2/g)

Not enough information to

calculate

127 92

Parameter Fushan Puerto Rico Subtropical

Wet Dry

Processes Litter fall (Mg/ha/yr) 5.5 (3.0-10.8) 8.6-9.7 2.9-5.5

Leaf fall (Mg/ha/yr) 3.8 (2.1-6.4) 4.9-5.5 2.5-4.4

Wood fall (Mg/ha/yr) 1.3(0.59-3.31) 1.4 0.4-0.8

Litterfall/loose litter mass (yr-1)

0.42 1.2 0.3

Leaf fall/leaf litter mass (yr-1)

1.05 0.5 0.14

Herbivory rate (Mg/ha/yr)

0.38 0.08

Stemwood biomass growth

2.5 2.1

Aboveground net primary productivity (Mg/ha/yr)

10.5 6.9

Nutrient use efficiency (Mass fall/Nutrients in mass fall

N 56 92 98

P 1087 2999 6057

Structure Parameter Fushan Puerto Rico

Wet

Tree density (tree/ha) 950-1500 1750

Canopy height (m) 9.4-11.6 20-30

Above ground stemwood biomass (Mg/ha)

185 – 272 190

Loose litter (Mg/ha) 5.7 to 9.0 6 to 8

Leaf litter (Mg/ha) 2.3 to 3.6 5 to 6

At FEF large gaps are rare and most trees survive from typhoon disturbance and are capable of taking up nutrients continuously. Slower foliage decomposition at FEF helps reduce the loss of nutrients in general allowing for greater plant uptake.

Processes Parameter Fushan Puerto Rico

Subtropical Wet

Litterfall/loose litter mass (yr-1)

0.42 1.2

Leaf fall/leaf litter mass (yr-1)

1.05 0.5

Nutrient use efficiency (Mass fall/Nutrients in mass fall)

N 56 92

P 1087 2999

Fushan: Nutrient concentrations of leaf fall are no different between months with and without typhoon

Puerto Rico: Nutrient concentrations (N & P) of leaf fall in the hurricane are 1.1 to 1.5 and 1.7 to 3.3 times than that without hurricane

NO3- Concentration in Streamwater

McDowell 2000 Wang et al., 1999

Before and after Hurricane Hugo Before and after typhoon Herb

losses of most nutrients decline to pre-disturbance levels in 1.5-2.5 years. The rapidity of this decline appeared to be associated with forest re-growth.

Ecosystem-Level characteristics that result in resilience

• Larger accumulation of nutrients and carbon below ground than above ground

• Rapid fluxes of nutrients, mass, and rates of growth – replacement time (total biomass/NPP = 13 yrs (wet), 23 yrs (dry)

• Biotic Control of fluxes:– Fungal and its extensive hyphal network and large te

mporary nutrient storage capacity, – high rate of translocations, – high nutrient use efficiency (Fushan seems very low, but may capa

ble to have high immobilization rates at low nutrient use-efficiency as typhoon occurs)

Nutrient Retention Mechanisms at Puerto Rico

• Secondary succession occurring at large blown down gaps after hurricane disturbance contributed to the retention of nutrients in the soil profile and help the recovery of stream water chemistry to pre-hurricane levels at Puerto Rico.

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

1994/4/27

1994/9/27

1994/12/9

1995/1/20

1995/3/4

1995/4/21

1995/6/7

1995/7/19

1995/9/26

1995/11/24

1996/1/17

1996/2/29

1996/5/12

1996/7/15

1996/10/31

1997/1/13

1997/4/7

1997/7/24

1997/11/9

1998/7/9

1998/11/4

1999/4/9

2000/8/30

2001/3/10

2001/10/10

2002/0712

2003/8/15

Typhoon strong　 medium light

LA

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% o

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TIME

100

0

recovery rate

0.00

0.050.10

0.150.20

0.25

0.300.35

0.40

Jul.96

Aug.96

Sep.96

Nov.96

Jan.97

Apr.97

Jul.97

Sep.97

Nov.97

prop

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East ridge

West ridge

Strong typhoonMedium typhoon

Frequent canopy defoliation maintains high understory light levels, allowing for the establishment of pioneer and late successional species, thereby maintaining species diversity in the absence of large canopy gaps

Understory Light Availability

Five levels of biotic interfaces• Individual’s response to their environment• Cumulative effect of how different species react

to their respective environments• Effect of legacies after an event, ex., surviving

seedlings or root systems• Consequence of inputs from, or effects of,

processes from other levels in the hierarchy under consideration

• Inherent characteristics of ecological systems, such as the negative feedback function of storage

• Negative feedbacks occur at all levels of biotic interaction– Storage function of nutrients in litter, soil, and

wood– Feeding loops among vertebrates and inverte

brates that control and stabilize populations in forests exposed to LIDs. ? Outbreaks of invertebrates?

• High species turnover after disturbance

Ecosystem-Level characteristics that result in resilience

• 福山的颱風每年都有，但是是否應該定義一下 LIDs ?

• Amount of litter fall correlates with strong typhoon, but not with medium and light ones.

Relative effectiveness of Hurricane

另外的想法？

Ecological Resilience of a system corresponds to the width of a stability domain.

Engineering Resilience is a local measure and is determined by the slope of the stability curve (its shape is determined by controlling variables of the system)

Basin of Attraction (attractor)

External conditions changes,The basin can shrink.

A ‘catastrohpic transition’ (regime shift) to another attractor can occur.

Scheffer and Carpenter. 2003

Alternative state models

If environmental conditions are shifted above E2, the system collapses to S2 (the ‘white’ state).

A shift in environmental conditions below E2 will always result in the system returning to the ‘green’ ecosystem state S1.

At environmental conditions between E1 and E2, thesystem could return to either the green S1 or the white S2 state depending on the initial conditions (whether at S1 orS2).

At environmental conditions between E1 and E2, thesystem could return to either the green S1 or the white S2 state depending on the initial conditions (whether at S1 orS2).

If environmental conditions are shifted above E2, the system collapses to S2 (the‘white’ state).

A shift in environmental conditions below E2 will always result in the system returning to the ‘green’ ecosystem state S1.

Figure 1. Species richness of aquatic insects in streams

Aquatic insect richness is directly influenced by water chemistry, which is governed by land cover, soil characteristics, and the chemistry of precipitation in the watershed.

A, acidic streams (never limed); L, limed streams; P, prelimed streams (acidic streams before liming), N, natural streams.

calcium (Ca2+) concentration in streamwater, mg/l

stable ecosystem states

unstable ecosystem states

Aq

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