Disturbance Dynamics in Foothills Riparian Zones

FRI ND Program Information SessionEdmonton, AlbertaDecember 9th, 2009

David Andison

Riparian Zones Are Unique Landscape Features

- higher moisture regimes- more toe slopes, valleys, steep slopes- more non-forested- more rich eco-sites- different stand composition- different stand structure- land-water interface- culturally important (recreation, fishing, water values, etc).

>> unique places

Assuming 25m buffers, riparian zones account for

5-10% of foothillslandscapes.

And they are everywhere.

Are Riparian Zones Deserving of Special Management Consideration?

Clearly, yes.

Can Natural Disturbance History Tell us Anything That Might be Valuable Towards

Sustainable Management of Riparian Zones?

Tree DBH Along TransectLittle Berland River

05

101520253035404550

0 150 300 450 600 750 900

Distance Along Transect (m)

Tree

DB

H (c

m)

UplandRiparian

Are there unique features of fire behaviour in riparian zones at

the stand scale?

Tree Age Along TransectTributary of Beaver Creek

0

20

40

60

80

100

120

0 100 200 300 400 500 600

Distance Along Transect (m)

Tree

Age

UplandRiparian

No.

Figure 3. Percent of Burnt Areas and Island Remnant Areas in Riparian Zones

0

5

10

15

20

25

5656 1451 1070 1060 1140 1073 1970 1119 843 1635 1216 1206

Fire Number

Perc

ent A

rea

in R

ipar

ian

Zone

Burnt Areas

Island Remnant AreasLower

FoothillsSubalpineUpper

Foothills

Are Island Remnants More Likely to Form in Riparian Zones?

No – although…

% of Pixels That are Fire Edges

Landscape Overall All Streams Large Streams

Sub-Landscape 1 2.4 2.4 3.5

Sub-Landscape 2 2.4 2.6 2.8

Sub-Landscape 3 4.0 4.8 n/a

Sub-Landscape 4 3.2 3.2 2.6

Sub-Landscape 5 2.8 3.2 3.6

Sub-Landscape 6 2.9 3.0 2.8

Sub-Landscape 7 2.9 3.0 3.5

Are Riparian Zones More Likely to be Associated with Fire Edges?

No.

% Older Forest

Landscape Overall All Streams Large Streams

Lower Foothills 24 16 27

Upper Foothills 21 24 26

Sub-alpine 40 43 39

Montane 30 28 23

Do Riparian Zones Have More Old Forest at Regional scales?

No.

All evidence of the interaction between riparian zones and fire behaviour was quite weak.

We found no evidence that riparian zones are refugia.

In other words, fire is

an active process in

riparian zones.

A fundamental shift in ecosystem dynamics:- Tree ingress (changes habitat)

- More old riparian habitat, less young.

- Fire, insect, disease risk may increase

- Old forest is no longer representative (BC)

- Old forest is linear – no “interior”

- Changes LWD dynamics

- Nutrient dynamics

- Changes in aquatic system dynamics

What happens if we significantly curtail the process of terrestrial disturbance in

riparian zones?

Is Harvesting a Sustainable Management Option in Riparian Zones?

Not necessarily.

Traditional tree harvesting in riparian zones potentially results in:

- compaction, - rutting, - erosion, - removal of biomass, woody debris,- destruction of aquatic habitat, and- deterioration of water quality.

Dominant Management Strategy

Protection (from disturbance)The reason being that they ARE unique components of the landscape, and more sensitive to environmental stress than other components of the landscape ecosystem.

Protection is intended as a conservative strategy.

But by protecting riparian zones....

we potentially create new risks.

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10 12 14 16 1810-year Time-steps

Proportion of "Old" Spruce

LFS Two-passLFS LRSYAHWP One-pass

Riparian Zone Protection Scaled up to the Landscape Over 200 Yrs

Historic Range (NRV)

20% of our samples were associated with ingress.

Workshop – June, 2002

The Dilemma: Harvesting in riparian zones creates some biological issues, and not disturbing riparian zones creates others.

The Question: Can we find some alternative management solutions that are (more) biologically sustainable?

Our Solution: See if the greater “natural model”can provide any further direction.

(Chisholm-Dogrib Research Initiative, FRI Fish and Watershed Program, FRI Natural Disturbance Program, Sundre Forest Products, Hinton Wood Products, ASRD Forest Management, ASRD Fish and Wildlife, DFO, University of Alberta,

Sunpine Forest Products).

• Type• Frequency• Size & Shape• Severity• Tendencies

• Seral-stage levels• Old forest patch sizes• Edge density• Coarse woody debris• Large woody debris• Suspended sediment & O2…

• Fire risk• MPB risk• Water quality• Caribou habitat• Grizzly bear habitat…

Disturbance Patterns

Landscape Condition

Biological Consequences

We understand these bits, but it provides no definitive management solutions.

Why don’t we try approaching this from the perspective of the conditions created by disturbance?

A wildfire runs through the riparian zone of a small stream

Dead trees fall down and create large woody debris (LWD) in and over the stream.

Healthy fish and invertebrate communities.

Changes in water flow, direction and velocity.

New LWD over the stream create bridges for small mammals.

Convoluted streams with LWD

act as buffers against flooding.

Structurally diverse aquatic ecosystems filter toxins in water.

Organic matter and sediment erodes

from the banks into the stream.

Summary

- Riparian zones are disturbed as often as any other part of the landscape.

- The disturbance regime was identified, but offered little specific guidance wrt best management practices.

- Our solution was to shift our focus on understanding NRV of (landscape condition) LWD attributes.

- Stay tuned for tomorrow morning’s session!