In order to be a good steward or educator within the context of land conservation, it is important to develop an understanding of several basic concepts. The concepts and definitions below are provided for this purpose, and they reflect local and regional nuance. We have purposefully given them a strong bent toward application and function in the broader world of education and conservation. The effective application of such words as “native” or “natural” is often skipped in deference to the use of generic and outdated versions. Our standard is to keep an ear to the ground of current ecological work and adopt the most recent iteration of these definitions, without the noise of political wind (for example, the overly broad and ecologically meaningless “native to Virginia”), and to adopt and adjust definitions so that, while they are theoretical, they are relevant, reliable, and empowering in application.
Click on a term to expand its definition.
The totality of genes, species, communities, and systems in a specific geographic region or location. The richness, diversity, distribution, and evenness (rarity and commonality) at these four scales play an important role in determining biodiversity. The conservation of biodiversity, through time and at all scales of ecological organization, is critical for the survival of life on Earth. Conserving biodiversity requires the identification of key variables so that goals and objectives may be set. Education related to biodiversity must be bottom-up, place-based, and inquiry-based so that the critical elements of local nuance and variability can be understood.
Natural Plant Communities vs. Ecological Communities, in the context of human disturbance
Natural Plant Communities are assemblages of interacting plant species that are uniquely associated with a specific landscape niche. The assemblage of species in that context has had time to develop stable and balanced relationships with the living and nonliving parts of the same niche. A natural plant community has either experienced minimal modern human disturbance or has recovered from that disturbance under mostly natural conditions.
The process of natural community investigation and identification presents a paradox and related challenges. While plants and ecosystems often exist as a seemingly continuous gradient across the land, they also occur in groupings that are somewhat predictable. Natural communities are relatively predictable units of measure that are very useful for education and conservation efforts because they form the matrix within which all terrestrial animals interact and reproduce. In fact, we argue that the survival of species in the Piedmont Region is entirely dependent upon the restoration and preservation of natural community diversity and associated natural disturbance regimes.
An Ecological Community is defined as an assemblage of co-existing, interacting species, considered together with the physical environment and associated ecological processes that usually recurs on the landscape. Our research covers both traditional categories of “natural” and “un-natural” ecological communities. Because humans are mammals, and part of nature, we treat all ecological communities as “natural”, despite the level of human disturbance, and consider them to be on a spectrum of recovery from human disturbance. Our work is as much an effort to define degrees of recovery as it is to determine the classification of the system.
No part of the Piedmont landscape has escaped the influence of humans. Human animals are a large, numerous, and ambitious bunch, defined in part as being cosmopolitan – that is, we are found in nearly every corner of the world as a single species. No other lifeform has moved so far, so fast, while leaving a trail of ever-growing progeny and proportional ecological destruction that compounds with each step forward. The cart is way out in front of the horse, so far that we can’t see it or understand the effects our actions will have on future generations.
We have been on the Virginia landscape for more than 15,000 years. However, the heaviest impact on the non-human life of our region has come in the last 500 years – since the first European colonizers reached Turtle Island (the Indigenous name for the continent. The label “North America” is a relic of colonialism). A sizable scattered collection of small, remnant, pre-colonial habitats do remain throughout the region – particularly grasslands of the wetland, prairie, savanna, and woodland types. Most of those are essentially unchanged from their condition prior to the colonial invasion and subsequent settlement, due to being far short of ideal for Euro-centric agricultural production (monocultured non-native plants and animals).
Some habitats in the region have had only a decade or so to recover from the oppressive behaviors of modern humans, and even those continue to be impacted by things like fire suppression. Other habitats are best described as being in a middle successional stages of recovery from agriculture, forest clearing, fire suppression, trail building, or other disturbance events. A few habitats in the region should be considered “old-growth” and nearly intact or fully recovered from post-Columbian disturbance.
It is important to understand that we include human disturbance as part of natural community development, and we aren’t alone. Most modern ecologists now recognize that it is about “how”, rather than “if”, when it comes to the positive or negative impacts of disturbance. It is important to differentiate between the disturbance activities of modern humans and those of Indigenous People. Natural community development does not occur unless humans allow for the natural disturbance regimes that shaped systems, plants, and animals through time. This includes the landscape management practices of Indigenous People, and in our region specifically, those of the Monacan, Mannahoac, Occaneechi, Sapon, and Catawba Indian Nations and their relatives.
Native organisms are those that have evolved in a specific ecological area for long enough to have developed thousands of obvious, and less apparent, complex and specialized relationships with other plants, animals, fungi, and communities of biota. The term “native” is most often prescribed to areas within political lines, but in fact it refers to groupings of plants that are natural to specific areas with unique physiographic and microclimatic conditions. Therefore, a plant that is native to one portion of a landscape may not be native, natural, or adapted to another part of it. This logic should be applied at multiple scales, from ecoregions to individual hills, fields, and boulders. This concept is very important for sustainable conservation practice, and for the support of locally adapted wildlife and the overall integrity of local and regional biodiversity. But, it is also critical for supporting the integrity of environmental education. Native, as a defining tool, should be used with local ecological specificity, and in a niche-based manner. Native species that volunteer in all phases of renewal and succession, are functional native plants… even if they emerge in a sidewalk crack or the gravel of an abandoned lot. Urban lots, suburban lawns, and old agricultural landscapes are teaming with native species, and they always spring forth if a bit of land is allowed to grow (albeit, in competition with non-native exotics that effectively suppress diversity).
Non-Native / Exotic / Invasive
We use these three terms interchangeably. They refer to any plant species that is introduced to the region, either purposefully or accidentally, outside its natural and normal ecological range in space and time. We do not use cultural divisions in time to define Nativism for plants, as we hold that the degree of nativism in flora has more to do with the development of complex relationships than it does the culture that moved the plant around. Given that climate oscillations have shaped and honed species and natural community movement and development through time, we hypothesize that nativism in a plant is closely tied to the minimum oscillation time-frame. That length of time is certainly greater than 1,000 years. Any plant shoved into new environments by humans in the last 1,000 years should be deemed as suspect, with respect to being a native plant. Non-native species that perpetuate in growing numbers have demonstrated the tendency to spread to a degree that causes damage to the environment, biological diversity, and often human economy and health. Non-native species are often invasive and aggressive, and compete directly with native species for moisture, sunlight, nutrients, and space. That said, other introduced species naturalize in a quiet manner, and will presumably graduate to the “native plant” status after deep time allows them to work out the multitude of environmental relationships required.
Non-native / Exotic species often invade landscapes that have experienced modern soil disturbance. In that context they face very few (if any) of the normal environmental checks and balances they evolved with, including weather variation, soil bacteria, fungi, and insect pests and diseases that keep them under control in their natural native range. The utter lack of natural enemies often leads to damaging and hard-to-control population eruptions. It is true that most seeds and vegetative materials of non-native species that are introduced purposefully or by accident, do not survive, but those that do tend to be voracious and beyond environmental control. Biodiversity is almost always lower in comparable proportion with the prevalence of exotic species.
Natural Community Trajectory
Natural community trajectory is a phrase we use to describe the often predictable vegetative potential of any landscape. If left to its own device, and given time, each bit of landscape has a general path of predicatable potentials. In fact, there are only a few types of natural communities that can regenerate without intervention on any given bit of landscape. Landcapes are quite selective and self limiting in that way. What’s more, most of the species that will occur in the emerging ecosystem are highly predictable. The reasons for this are complex, and long-debated and considered by ecologists, especially as it pertains to those generalist species that stretch the edges of predictability. The fact is, vegetative cover forms a continuum of growth across the land, and it changes along gradients that are both gradual and sudden. Because of this, and particularly upon the Eastern Temperate landscape, there are a pile of interesting correlations between different groupings of species and the landscape they gravitate toward. Because of these correlations and their relationships to climate and physiography, the remaining species in a natural community can be predicted with a high degree of confidence once the principle (indicator) species are confirmed. The primary factors that create the relative permanence and predictability are physiographic and climatic. That is, variables such as geologic chemistry, aspect, slope, elevation, land shape, land form, soil moisture and drainage, and geographic position combine to form a powerful selective force on vegetative composition. While individual species may be generalists, occurring across diverse sets of environmental conditions, groupings of plants are tied very strictly to local sets of conditions. There are complicating factors that make determining natural trajectory a challenge, such as history of human activity, relative abundance of non-native species, and the influence of natural succession on vegetation. But, all-in-all, the data proves with regularity that every bit of the Piedmont landscape has a normal, natural community potential, AND this potential is entirely predictable, albeit with ever-present variability existing in the details.
Why is this important? The natural trajectory allows for conservation efforts to aim, with precision, at instigating the vegetative renewal that is natural and normal for a given landscape. Without an understanding of this trajectory at a site, restoration projects are wasteful, less successful, and tend to be artificial with very little net benefit for biodiversity (including animals). A great example of a common practice that has no regard for the natural community trajectory of a landscape is the planting of a “wildflower meadow”. Some call them “meadows-in-can”, and they rely upon showy, near-term aesthetic outcomes, and include performance species, generic mixes, and groupings of flora that have never co-occurred in the wild. For obvious reasons, they fail, and they fall extremely short of all goals related to biodiversity conservation, stewardship, and education.
Three additional definitions are integral to generating specific goals, objectives, and targets for restoration, and for tracking the overall ecological well-being of the land over time. These essential data points are: richness, diversity index, and exotic species importance index. A reasonable goal is to improve these three variables in all parts of the region, for the benefit of wildlife, for ecosystem function, and to enhance the natural aesthetic.
“Richness” refers to the total number of species within a given area. Many natural plant communities have naturally low species richness (such as the forested heath habitats in our region). In the Piedmont, forests tend to have fewer plant species than open-space grassland types such as prairies, savannas, and woodlands. There are a great number of reasons for this, but one worth noting here is that pre-Columbian native landscapes in the region were blanketed by as much grassland as forest. Enormous contiguous grasslands had thousands of years of robust, full sun, species development. One may surmise that the competition for space, nutrients, water, and light there-in resulted in enormous division of species within each Genera (in fact, this bears fruit in Solidago, Dichanthelium, Desmodium and many others). Time compounds this affect, and each taxa of plant fills every little niche of the grassland landscape, both spatially and temporally, with a well-suited species. Species richness is a very important data point for comparing natural communities across the land. In combination with abundance and seasonal change, one may use richness to begin to understand biological health and the potential of a site, regardless of the condition it is in.
“Diversity” is calculated by combining richness and abundance (% cover for each species), and is a reflection of variety in species, dominance, and evenness. The formula we use (see below) produces an index number that may be used to compare across different plant community types. This number has proven critical for tracking change during restoration projects, but also for comparing relative health in natural communities across the region. The “Diversity” number ranges from 0-5. The closer to 5 the number is, the more diverse the community is. Some communities have naturally low diversity. Tracking Diversity through time by repeating quantitative data collection at sample plot locations has tremendous benefit, as it sheds light on gradual changes that are happening that may go un-noticed in a qualitative view of things.
There are several popular ways to calculate Diversity. We have adopted a common calculation method in field ecology, as it has proven to have benefit for comparing restoration sites and natural communities of similar types and sizes across local landscapes:
Shannon-Weiner Diversity Index
Exotic Species Importance
We have adopted what is referred to as the “Exotic Species Importance Value (IV)”, as devised by Gary Fleming at the Virginia Department of Conservation and Recreation’s Division of Natural Heritage. This index number has proven valuable in creating goals, targets, and measures in restoration projects. It is a quantitative way of measuring and tracking non-native plant species impact across time. This formula combines non-native species richness (# of species) and abundance (% cover) and expresses each as a relative percentage of the total population (including native species). The final number is expressed as a value on a scale of 0-1, with “0” meaning a complete absence of non-native species, and “1” meaning 100% non-native species, and 100% non-native ground cover.
Exotic Species Importance Value Index (IV) = Relative Exotic Richness + Relative Exotic Abundance / 2