Land(scape) classification (continued)

•approaches

•applications

Land(scape) classification

climatic

physiographic

vegetative

ecosystematic

Climatic classification:

-climate naturally dictates the major vegetation zones

-useful at broad scales,but land units too broadfor local level uses

http://www.ec.gc.ca/soer-ree/English/vignettes/default.cfm

Physiographic classification:

-based on landform and soils

-based on relatively permanent features, so can be more long-lasting than e.g. vegetation classification alone

-lends itself to remote sensing

-of limited use for ecological purposes unless combined with vegetation

Vegetation classification:

-based on vegetation

physiognomy floristic composition

-integrates the total environment (vegetation is largely determined by climate and physiographic factors…)

-but, subject to change – vegetation form and composition also depends on time since last disturbance

Ecological Land Classification for Southern Ontario (new):

Based on physiognomy (e.g. coniferous forest, thicket swamp) at coarse level, floristic composition (e.g. sugar maple-white ash deciduous forest type) at finer level

Ecosystem classification:

-incorporates climate, vegetation, soils, landform

-usually focuses on vegetation-soil units

-more useful in changing landscapes

-more useful for ecosyste-based management

Land classification systems can be parametric (”bottom-up”)…

-classifies land units based on the value of selected parameters(e.g. soil nutrient levels, elevation, height of dominant plants, mean annual temperature)

-precise, objective approach….but, difficult to select appropriate attributes and the ‘cut-off’ values between classes

…or based on morphological appearance (“top-down”)

-uses observations of topography, vegetation to distinguish different land units

-can be more subjective…but more intuitive as it is based on obvious distinguishing features

Land classification systems can be hierarchical…

…or not

-Moss has suggested classifying landscapes based on rates of different ecological functions (e.g. productivity, decay)

-Land classification is done for a purpose, not as an end in itself

-choice of characteristics on which a classification system is based depends on the end use of the system

-too many characteristics = small classes (few land units in each class) = less useful for making generalizations

-too few characteristics = large classes = not specific enough

Choice of criteria should be based on:

1. Accessibility (easy to measure/observe)

2. Significance (how well does the characteristic distinguish one land unit from another?)

Applications of land classification systems based on ecosystem characteristics:

-forest management

-conservation

-forest fire control

-different classes of jack pine forest may be more or less susceptible to fire

-the Northwestern Ontario Forest Ecosystem Classification distinguishes between jack pine-dominated forests based on understory vegetation

-the type of understory vegetation partly determines the burn potential of a forest patch

-fire control personnel can better predict the behaviour of fire (potential for intensity, spread, etc.), and prioritize control efforts, using the FEC to map out jack pine forest types

-ecosystem classification can be used to plan habitat reserves in a managed landscape

-setting aside a representative amount of each land type can help to ensure the protection of different habitat types

-traditionally, reserves set aside on poor and/or inaccessible land

Landscapes – the spatial dimension

Categories of landscape elements: describing landscape structure

•matrix

•patch

•corridor

•mosaic

•network

•edge

•interior

•total habitat area

•patch area

•patch shape

•connectedness

•connectivity

•heterogeneity

•scale

Matrix:

-the dominant, all encompassing element in the landscape

Patch:

-relatively homogenous areas of contrasting habitat

matrix

patch

Carolinian Region: pre-European settlement

Carolinian Region: Mid-1990s

Both the quantity and quality of patches of a given type will affect the ecological functioning of the landscape (e.g. for wildlife habitat)

The habitat quality in a patch is related to its size and shape:

-large patches have a high ratio of interior to edge compared to small patches

Total area: large patch=2 km2

Total perimeter length=5 km

Total area: small patches=2 km2 (8 x 0.25 km2)

Total perimeter length=14 km !!

-for a given total area of a habitat type, fewer, larger patches will have less edge than numerous, small patches

-for a given patch area, a circular patch will have less edge than an elongated patch

Total area: circular patch=2 km2

Total perimeter length=5 km

Total area: long patch=2 km2

Total perimeter length=6.84

Why do we care how much ‘edge’ there is?

-different from interior-more influence from adjacent patches

In the case of forest patches in a fragmented landscape,edge habitat has:

-different microclimate, e.g. more light availability

-more ground vegetation

-different species…more ‘pioneers’, opportunistic species

The ‘edge effect’ – different microclimate near forest edge vs. interior

The ‘edge effect’ – different plant community composition near edge

The ‘edge effect’ – can result in more diversity at the forest edge vs. interior

forest old field

From a study of the effects of forest harvesting on landscape patterns in NB

Corridor:

-linear elements, may stand alone or link patches together

-not necessarily continuous…’stepping stones’ of habitat may also be considered corridors

Network: a set of corridors on the landscape

Function of corridors:

-provide connectivity between patches of habitat

-increase the permeability of the landscape

-(sometimes a distinction is made between connectivity and connectedness)

Function of corridors:

-why is more connectivity usually desirable in fragmented landscapes?

-is more connectivity always good?

From Tewksbury et al., 2002

Even in non-terrestrial ‘landscapes’…corridors aid dispersal between habitat patches

(this result was found in an estuary, with marine invertebrates moving through corridors and patches of seagrass)

The ‘patch/matrix’ view has largely given way to the ‘mosaic’ view

landscape is composed of patches of habitat within a ‘hostile’ matrix of non-habitat

landscape composed of a collection of patches

derived from ‘islands in ocean’ analogy

in the real world…the ‘matrix’ is just another habitat type

Landscape pattern:

-the spatial arrangement of the mosaic and networks

-the scale or grain with which you view or consider the landscape also influences the pattern you perceive

fine grain = lots of detail

cropland

forestold forestyoung forest

beans

wheat

corn

hay

coarse grain = little detail

-what constitutes a patch in this photo….forest cover in general, or each different type of forest cover?

-fine grain vs. coarse grain view depends on the question you are asking about the landscape, e.g. the organism you are concerned about

-what is continuous is also in the eye of the beholder…

-a corridor that is continuous on a coarse scale may be discontinuous on a fine scale

Landscape heterogeneity

-more heterogeneity = more variety = more “information” contained in the landscape (i.e. more difficult to describe)

What causes spatial heterogeneity in a landscape?

-environmental variability (e.g. soil texture, elevation)

-natural disturbances

-anthropogenic disturbances/land use

Landscape heterogeneity

Tree islands in everglades: ‘hotspots’ for nutrient capture and biodiversity

Positive feedbacks lead to island growth

Anthropogenic changes in hydrology leading to island loss = homogenization of landscape, loss of a habitat type

Landscapes – the temporal dimension

-movie-landscape change in Glacier Bay Park: primary succession

Tewksbury et al. 2002. Corridors affect plants, animals, and their interactions in fragmented landscapes. Proceedings of the National Academy of Sciences, 99(20): 12923-12926

Pickett and Cadenasso, 1995. Landscape ecology: spatial heterogeneity in ecological systems. Science 269(5222): 331-334

Mladenoff et al. 1993. Comparing spatial pattern in unaltered old-growth and disturbed forest landscapes. Ecological Applications 3(2): 294-306

This week’s readings…

(all are available online)