East/West, Moist/Arid

I’ve been thinking a lot on this trip about differences between the arid West and the moist temperate Northeast.  There’s a lot, it turns out, and they primarily reduce to climate, landform/topography, and land use history.

For example, the Rio Grande valley around Santa Fe is very dry – ~14 inches of rain a year.  And if you follow the valley 50 miles southwest and down-elevation to Albuquerque, it’s even drier, with juniper/pinon woodland giving way to grassland scrub on the edge of the Sonoran desert.  But all you need to do is go up in elevation to rapidly move through different landscape types.  Dry scrub moves to dry woodland moves to moister Ponderosa forest, to yet wetter spruce-fir forest, to very snowy subalpine forests, to alpine tundra, as you climb, like in this image from the Colorado Rockies.

And aspect makes a major difference as well, with different aspects being hotter or cooler and wetter or dryer with sun access and weather patterns.  And riparian corridors add major structural and species diversity everywhere they occur, both in the forested mountains and the dry basins.  So what this adds up to, from an ecosystem perspective, is that landscape-scale structural diversity is very high in much of the arid mountain West.  The number of structurally distinct plant communities accessible in two day’s walk, or an hour’s drive, from many places is staggering.  However, within many of those plant communities, species richness is very low both in general and compared to historical levels. This is both because of the arid climate (i.e. water as a major limiting factor), and because of a century and more of overgrazing, fire suppression, climate change, and widespread removal of native people and traditional land management practices.

In the moist temperate Northeast, annual rainfall is high enough that even third-or-fourth-growth forests, regrowing from overgrazed pasture land, contain quite a high level of species richness compared to arid Western forests*.  But, also unlike most of the West, landscape-scale structural diversity is very low throughout most of the Northeast.  It’s the land of urban and suburban landscapes, annual crops and pasture, 80-year-old full-canopy even-height forest, and very little else.

One reason for this is, again, climate and landform.  40-50+ inches of rain a year, plus heavy winter snows, means there’s more than enough water for closed-canopy forest to grow in all but the driest or thinnest soils.  And the Northeastern hills and mountains are old, low, eroded, and gentle enough that only the steepest cliffs, thinnest-soil rock faces, and very highest elevations have enough belowground competition or natural disturbance to limit tree growth.   But it’s also because of our particular land use history defined by: very early widespread removal of native people; multiple, protracted deforestation events; extirpation or extinction of apex predators and keystone herbivores; and pasture and farm abandonment throughout the region in the early 20th century leading to monotypical regrowth.  See Wessels and Cronon for more on this land history.

Early-succession environments, patches of meadows and shrublands in the forest, and open savannas and woodlands with larger trees are all very rare in the Northeast.  And that means that the species diversity associated with those landscape types is very rare.  And that means that it’s very hard to live off the land in the Northeast, because those mostly missing landscape types – like the oak savanna below – are the ones that have the most available niches for wild foods, medicines, fiber plants, and game animals!

More to come on regions other than the Northeast and the arid mountain West, and also on directions for land stewardship in these different regions based on this line of assessment.

*Although, herbaceous spring ephemerals and valuable slow-growing ethnobotanicals, (which are often one and the same) are underrepresented in current-day northeastern forests.  And, of course, many of the keystone animals.

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2 Responses to East/West, Moist/Arid

  1. Cara Michelle says:

    Thanks for sharing your well articulated ideas and observations, Connor. With a natural historical and personal relationship to the arid mountain west yet little restoration ecology knowledge, I am drawn to a big question that I’m not sure how to bring down to the ground in order to consider what land management could actually look like.

    With regard to humans always having managed land in some way…

    I am thinking about how physical and biochemical processes have a tremendously FAST impact on arid mountain landscapes. While the basement rocks of the Grand Canyon are 2000 million years old, the Canyon itself is at most 6 million years old! One reason that landforms like the Grand Canyon can form so fast is because of super speedy headward erosion – greater elevation change results in greater hydraulic force, cutting a canyon further and further back into a landscape. This means that in a region staggered with sharp elevation differentials, riparian landscapes, scrub zones, and cliff habitats are in a hugely dynamic flux over a much shorter time scale than more temperate and topographically mellow landscapes. And people have lived in these areas for millennia.

    I am also thinking about the dry sponge/wet sponge analogy to imagine how arid mountain landscape responds to some climatic events. Quickly pour a bucket of water vertically over a brittle sponge and it will absorb a small bit of water. Pour the same bucket of water at the same elevation over the sponge, only dampen it this time, and it will absorb significantly more water. Arid mountain landscapes work similarly. Flash floods can alter an arid western landscape in a way that floods cannot in moister regions where valleys, floodplains, and continental areas are better equipped to absorb water. Cycles of 20 year floods, 100 year floods, 1000 year floods, were common before massive damming, and integral in native land use practices. Such time scales are within the scope of humans and cultural memory.

    So I am trying to somehow align geologic time scales with human time scales and human land management. While for the mostpart geologic processes are beyond our scope to witness, has geologic memory passed on through oral story partly informed traditional land use practices? Since homo sapiens only date back some 200,000 years, is it even possible for geologic and human scales to interact this way? What landscape memory did early humans carry down with them from the trees through their instinctive behaviors that in turn came from earlier evolutionary memory, and earlier memory, and so on, ultimately inspiring diverse and culturally unique land use practices?

    Some British scientists have been positing for over a decade that we have entered (more accurately, prompted) an entirely new geologic epoch – the Anthropocene – in which the human footprint is so vast that there is as distinct a shift in ecology and surface earth and atmospheric processes as there was at the massive Cretacious extinction. If humans can visibly affect geological processes, can our relationship to geologic time really be as simple as, “Even the ‘young’ Grand Canyon formed millions of years before the first humans, so we cannot possibly remember such processes, let alone have shaped land use practices around them”? It’s a plausible argument that my scientific self cannot rebut yet my cosmic self can’t believe. The soil we are growing in and treading on is our direct line to these processes and our previous human relationships with them.

    So, bottomline – How can we use our understanding of geologic time and processes to understand modern and traditional land use practices? To what extent is this even a valuable perspective to consider?

    And when do I get to see you?

    With Earthy Blessings,

    Cara Michelle

  2. grousedrum says:

    hmm, I’m going to need to think about that! I’ll get back to you on this soon….

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