Conservation Bio Exam 3: Reserve Management

two scenarios of alternate stable states

1: community 1 and 2 branch off from initiating disturbance; 2: community 1 branches from initiating disturbance and community 2 branches off community 1

two alternate stable states for low elevation chihuahuan desert

state 1 historic: black grama grassland state 2 degraded: woody shrubland

alternate stable states

occur when an ecosystem can exist in 2 or more configurations under same environmental conditions

even with grazers removed from the community

does not return to desert grassland

why do we need to manage reserves example

kirtland’s warbler

kirtland’s warbler

rare; nests only in early successional jack pine forests

minumum dynamic area

smallest area large enough to encompass patches in different stages of succession following disturbance

first important question for managing disturbance regimes in reserves

how far back in time do we need to go to simulate a natural disturbance regime?

second important question for managing disturbance regimes in reserves

how can we determine the intensity, frequency and spatial extent of natural disturbances?

tree ring fire scar analysis

allows re-construction of historical fire regimes in forest, woodland, and savanna communities

historical record is limited by

tree lifespan

first potential conflicting goal of livestock raising vs grassland biodiversity conservation

dealing with disturbances in grasslands: fire and drought

second potential conflicting goal of livestock raising vs grassland biodiversity conservation

predator control/eradication

third potential conflicting goal of livestock raising vs grassland biodiversity conservation

maximizing livestock biomass production vs avoiding overgrazing

overgrazing

grazing at an intensity that causes undesirable changes in the species composition of the plant community and reduced productivity of the ecosystem

ice cream plant

first plants to experience population declines when a site is grazed; often legumes high N content

decreasers

plants that tend to decrease in abundance with greater grazing pressure; often tall perennial grasses and forbs

increasers

plants that tend to increase in abundance with greater grazing pressure; often short grasses and annuals

invaders

species do not establish in ungrazed areas, but do establish under heavy grazing; often chemically or mechanically defended against herbivores

will removal of grazing allow and overgrazed pasture to return to high species biodiversity and high productivity?

probably not but there may be alternate stable states

first way in which cattle grazing does not simulate effects of native grazing mammals, and can produce over-grazing

different needs for water-degredation of riparian zones

solution for different needs for water-degredation of riparian zones

raise native grazers, establish water tanks in uplands, fence livestock out of riparian zones

second way in which cattle grazing does not simulate effects of native grazing mammals, and can produce over-grazing

unusually high herbivore densities

solution to unusually high herbivore densities

maintain lower stocking densities

third way in which cattle grazing does not simulate effects of native grazing mammals, and can produce over-grazing

livestock not allowed to migrate

solution to livestock not being allowed to migrate

rotate livestock among pastures, ensure that the rotation avoids individual pastures always being grazed in the same season