Grassland – Savanna complex without grazing, millions of acres in the Midwest landscape perpetuated in the catastrophic state:
These pictures were taken in a regional park within the Twin Cities, Minnesota. Both sites are southwest aspects on well drained Hawick gravel glacial moraine soils, perfect aspect and soils for mesic-dry and dry grassland-savannas. The current photo shows an afforested landscape, in other words, a landscape suddenly dominated by trees, that was never covered by trees before. This landscape is not a forest and never will be forest (Clements 1916). The dominate vegetation, wood nettles, woodbine, snake root, etc. is non-edible to toxic, nitrophilic, and non-provisional of ecosystem services, such as soil building, long-term carbon sequestration, and water purification to name but a few. In fact, the current conditions are highly corrosive of ecosystem services, as noted by eroding soils, off-gassing carbon, fouling waters, and providing no edible vegetation for invertebrates, birds and mammals. Even if we remove the non-native “invasive species” the site remains in the catastrophic state, and extremely vulnerable to re-invasion by nitrophilic (nitrogen loving) shade tolerant species, such as buckthorn and garlic mustard. This is so because of the open niche spaces, created by too many trees and excessive shade, and rapid decomposition, fueled by high inputs of labile tree-shed, higher humidity facilitated by closed canopies, and high inputs of nitrogen back into the abiotic, creating a positive feedback-loop that facilitates continual dominance by a nitrophilic vegetation, that come to dominate state dynamics. Tragically, and to the detriment of ecological integrity for millions of acres, many “afforested” landscapes are erroneously labeled by such terms such as “Oak Woods”, “Oak Forest”, “Forest”, and “Floodplain Forest”. These labels in turn constrain management in ways that actually perpetuates the catastrophic state. The only way to move beyond this state is via frameworks based on the concept of state transition models.
The historic grassland savanna biotic assemblage, the most diverse, functional, and provisional terrestrial ecosystem ever, was maintained and managed for thousands to millions of years by a diverse array of grazing animals, and later on, by humans using fire to maximize grazing. The historic biotic assemblage of this site was composed of >250 grassland-savanna plant species, building soils, sequestering carbon, locking up nitrogen, and feeding several thousand species of herbivores, including invertebrates (e.g. pollinators), avian, reptile, amphibians, and mammal species. The current afforested state is corrosive of soil building, liberating of nutrients, and non-edible, thus starving complex food-webs.
When the last grazing animals were removed from this site, 60 – 70 years ago, humans no longer had any reason to manage the land, and the amazing grassland-savannas died.
Symptoms of death include:
- Loss of ground layer vegetation due to a positive feedback loop I call Terrestrial Eutrophication and Afforestation (TEA), that over-tops and smothers historic vegetation, and creates an environment that favors non-edible, non-provisional (of ecosystem services) high nitrogen conditions, that in turn favors a faster, weedier, more competitive biotic assemblage, a classic positive feedback and downward spiral into the catastrophic state.
- Loss of oak regeneration and all other plant and animal species dependent upon sunlight, dependent upon herbivores. No oaks have regenerated here for 60 years. Aspen and hazel, both highly edible plants, once common to the sites, are completely extirpated.
- Trophic cascades and the collapses of highly evolved complex food-webs. The loss of keystone grazers ended a highly evolved nutrient cycling mechanism that was critical to ecological integrity. What would happen to you if your body lost its capacity to regulate chemical flows? Vegetation that was once consumed suddenly wasn’t, and instead decomposed nutrient loads back into the soils, which in turn facilitated a faster weedier vegetation that soon over-topped the graminoid based community, and eventually became afforested by a low quality, non-edible, nitrophilic vegetation.
- Extreme declines in biodiversity due to the sudden dominance by low-quality vegetation that is non-edible to toxic, entire foodwebs have collapsed. Likewise, the lack of herbivore signal, dung piles, structural-chemical heterogeneity, entire species guilds have been eliminated (e.g. grassland-savanna birds dependent upon invertebrate food pulses)
- Domination by low quality species, whether native or not isn’t the issue, but instead, species that come to dominate this radically disturbed landscape, (e.g. loss of keystone grazers), share a similar set of functional traits (Grime 2006) including:
a. Nitrogen Loving and Liberating
b. Non-edible to Toxic
c. Short Life-span
d. Labile (fast decomposing)
e. Non-provisional to Eroding of Ecosystem Services.>br />
- Loss of Ecosystem Services including the loss of soil building, carbon sequestration, water regulation and purification, and the production of edible structures that fuel complex foodwebs.
- Erosion of Natural Capital including the erosion of soils, off-gassing carbon into the atmosphere, regulation of nitrogen, and perpetuating declines in water quality, edible structures and biodiversity.
- Grazing (or some form of green biomass harvest) is essential to the maintenance of grassland savanna complexes.
- Grassland savanna complexes historically represent the dominate earth ecosystem.
- Grassland savanna complexes represent the most evolutionary advanced terrestrial ecosystems ever.
- When grazing animals were eliminated, grassland-savannas were replaced by a dysfunctional, non-provisional catastrophic afforested state.
- Invasive species are not invasive as much as they are symptomatic to the loss of keystone species and processes.
- The ultimate goal in ecological restoration is the restoration of the processes that reinforce desirable biotic configurations.
- Official vegetation labels, such as “oak woodlands”, “oak forests”, and “floodplain forest” actually facilitate the catastrophic state.