The biogeomorphic impacts of organisms may differ at different stages in the development of landforms, ecosystems, or the individual organisms. I was thinking about this recently here along the shoreline bluffs of the Neuse River estuary, North Carolina, where I have been both looking at some soil profiles and enjoying the coastline.

There are at least five distinctly different biogeomorphic roles trees play along this shoreline--many more if you wanted to get more specific within these categories. The specifics are probably of only limited applicability elsewhere, but the general principle--multiple effects, which vary at different stages of both landform and vegetation development--is widely valid.

Trees and other vegetation grow thick and fast in this moist subtropical climate.

Stage 1A Surface Bioprotection

Trees (including canopy, roots, and litter) protect the ground surface from erosion and add organic matter to soil.

Biogeomorphology considers the impacts of organisms on surface processes and landforms (e.g., biological weathering, effects of burrowing animals), and vice-versa (e.g., the role of landforms as habitat, effects of erosion on biota). We are particularly concerned these days, however, with reciprocal interactions, such as sediment trapping by vegetation, and the feedback effects of this deposition on plants and their habitat. We are also learning a lot about biogeomorphic ecosystem engineering (BEE), whereby biota modify the abiotic environment in ways that influence habitat or resources (positively or negatively) for themselves or other species, and biogeomorphic niche construction, where BEE effects influence selection pressures and biological evolution.

State-and-transition models in geomorphology, co-authored with Chris Van Dyke, has just been published in Catena. The abstract is below:

Imagine exploring and mapping a newly discovered cave opening. At this point, there is only one set of questions--how long, deep, tall, wide, etc. is the passage, and where does it go? But as you begin to map it, more often than not, other passages and fissures will be discovered (and many of them will lead to others, and so on). This opens up a whole new set of questions. Some of the passages can be mapped, assuming someone can get the time and resources. Others can't be no matter how skilled the spelunker; they are too small. But even these can possibly be explored later, perhaps with remote control or AI tiny robots or probes; or with imaging techniques that can see through rock.

This is a pretty good metaphor, I think, for research in general. The more you learn, the more you discover you don't know, and more potential pathways for research appear--some possible now, some awaiting new techniques.

A forest biogeomorphology two-fer, courtesy of my central European boyz, who have graciously allowed me to ride their coattails here in the twilight of my career. The first is one where Pavel Daněk took some of my ideas and methods on applying graph theory to soil geomorphology, and went places with them I never even imagined:

Daněk, P., Šamonil, P., Phillips, J.D., 2016. Geomorphic controls of soil spatial complexity in a primeval mountain forest in the Czech Republic. Geomorphology 273: 280-291.

The second is one  that arose when Pavel Samonil took me to one of his field sites, where I saw things I hadn't imagined:

Phillips, J.D., Šamonil, P., Pawlik, L., Trochta, J., Daněk, P., 2017.  Domination of Hillslope Denudation by Tree Uprooting in an Old-Growth Forest. Geomorphology 276: 27-36.

The abstracts are below.

Hurricane Matthew devastated Haiti and other Caribbean areas, and did tremendous damage in Florida and South Carolina (I rode out the storm in Myrtle Beach, SC with my son Nate, his wife Morgan, and my delightful 2-year-old granddaughter Caroline). By the time it got to North Carolina, winds were down to gale force, but rain was ferocious (15 to 40 cm) in much of eastern N.C. Where I am at the moment, in Croatan, there was "only" about 10 cm of rain, and only gale force winds. However, that was enough, as it usually is, to get some geomorphic work done in the forest.

Below are some photos of trees uprooted by the storm in Croatan National Forest in the Flanner Beach area. Uprooting not only does significant soil mixing, but the pit-mound topography left behind significantly influences hillslope and soil processes for decades (and occasionally longer) thereafter.

Another example from a cemetery near Maysville, N.C.

Many biogeomorphic ecosystem engineer organisms exert their biogeomorphic effects through intrinsic activities and behaviors that occur wherever the organism occurs. Ants, earthworms, sphagnum mosses, and marsh grasses, for example are going to have the same qualitative ecosystem engineering impacts wherever they occur. In other cases, however, biogeomorphic impacts may differ (or even occur) in different geomorphic settings or habitats. This can be called contingent ecosystem engineering, because the effects are contingent on the environmental setting. For example, beavers build dams to create suitable pond habitats, with attendant geomorphic effects on streams. However, where water is deep enough (that is, there is suitable habitat without damming a stream), they don’t bother building dams or lodges (though they do have different biogeomorphic impacts, via burrowing into banks for their lodges). Thus the ecosystem engineering impacts are contingent on the hydrophysical properties of the stream. An example of an organism where the existence (not just the nature or degree) of biogeomorphic effects is contingent is the sulfate reducing bacterium Desulfovibrio desulfuricans. This microbe is found in soil, water, and living organisms in a wide variety of settings.

Where soils are relatively shallow, tree roots penetrate into the underlying bedrock through joints and fractures and promote weathering by funneling water into the rock, and facilitating chemical weathering. In addition to these processes, mass displacement by tree growth and bedrock "mining" by tree uprooting help deepen soils and regoliths. While this ihas been demonstrated in several studies, it was unclear the extent to which these processes occur where the bedrock is flat-bedded sedimentary rocks, which offter fewer vertically oriented joints for root access. Soil deepening by trees and the effects of parent material addresses this question (yes, the same general processes do occur in horizontally-bedded rocks). The paper, just out in Geomorphology (vol. 269, p. 1-7) by (mostly) Michael Shouse and myself, also provides some heretofore unprecedented spatial resolution on the spatial variability of soil & regolith thickness attributable to effects of individual trees. The abstract is below. 

Just published in Earth-Science Reviews, and available via: http://www.sciencedirect.com/science/article/pii/S0012825216301143

I'm happy to have my name on this, and contributed enough to justfiy that, but this was not an equal contribution by all authors--Lukasz gets most of the credit!