One thing someone might notice if you're a tree nerd like me is that the Northwestern United States is not very diverse in the number of plant species found here especially trees. Most forests consist of a handful of conifer tree species and that's about it. In the eastern U.S. there is a much higher diversity of native trees and one can easily find over 10 different species walking through a small woodlot. For example there is only one species of oak in Washington state, the Oregon white oak and none in Idaho. Where as in Ohio for example there are many different species just from the genus Quercus. After years of research on the topic one will probably find out that there actually used to be many more tree species in the northwest based on fossil evidence including many deciduous species like oaks, chestnuts, hickories and basswoods. But due to likely catastrophic events many of these species were wiped out and all that remained or at least those that were able to recolonize the area were hardy conifers such as pines, firs and cedars. That is why I basically see the Northwest as a recovering wasteland with a lot of ecological niches that have yet to be recolonized.
But what were the events that made this area relatively dead when it comes to plant species richness? The first and possibly the most catastrophic was the huge lava flows that covered much of the area a few million years ago. The columbian basin is almost completely made up of super thick basaltic lava flows that could have easily pushed many plant species to extinction. But there are more catastrophic events that could have led to species extinction. Another was the massive Missoula flood/floods that happened in the same region just a few thousand years ago. Supposedly a giant ice dam held back a glacial lake called lake Missoula in Montana and through possible multiple ice dam collapses released unheard of amounts of water through idaho Washington and Oregon and out through the Columbia river delta destroying everything in its path. Another more controversial explanation was that an asteroid or comet hit the ice cap in British Columbia during the ice age instantaneously melting the ice and sending catastrophic flooding and debris flows throughout the entire region as well as possible blast waves from the impact such as with an atomic bomb. Either way the Northwestern US has seen a lot of destruction and when compared to similar climates it is easy to tell from the lack of plant diversity that it is still in the process of recovering.
Another interesting aspect or consequence of this is that the lack of filled ecological niches means that invasive species can really take hold and dominate these landscapes. For example my property in idaho is almost completely dominated by invasive or naturalized species. The vast majority of the grass is nonnative perennial as well as annual grass species such as medusahead and meadow foxtail. Most of the perennial forbs are nonnative and most of the shrubs are nonnative roses. The only native tree is Ponderosa Pine, but I also have large sweet cherries and cherry hybrids that are part native bitter cherry and part nonnative sweet cherry. In my region there are also black locusts, common apple, common pear, cherry plum, american elm, silver maple, norway maple, black walnut, English walnut and many other tree species that are adding a huge amount of diversity to the local forests. Where as the only common native trees are Ponderosa Pine and Douglas Fir.
I've also noticed that this added plant diversity is speeding up plant succession. For example many areas of the Columbia basin area transitioning from desert scrub with little else but sagebrush and they are transitioning into grasslands dominated by cheatgrass and medusahead. These species are adapted for fire and they are increasing the fire frequency to a point that is killing off the desert plants and leaving only the grassland plants that are adapted to fire. I believe this will also over time build up the soil quicker adding a deep layer of organic matter and could eventually allow more moisture dependent species such as pines to grow in what was once just desert scrub. This could in theory change the climate of the region to one that is wetter because more moisture could be stored in the deep soils allowing for more trees and more transpiration and this could have a runaway effect that could turn the whole region into an area that could support forests. Obviously this would take a lot of time but that is the one major benefit I see from these invasive species is that they could improve the soil and climate to the point where forests could be grown even in the driest desert areas. I believe the real benefit though would be if deciduous trees such as Sweet Cherry and Norway Maple really took off and became a high percentage of the tree cover. That is because the soil under deciduous forests is much more fertile than that in conifer forests. In the area of Orofino, ID there is already a huge amount of sweet cherries and black locusts even on dry south facing slopes where the only native tree is Ponderosa Pine. This is pretty amazing to me and I imagine it will eventually lead to a mixed forest ecosystem that is more resilient to fires since the deciduous trees will better shade the ground than the pine and they generally will not burst into flames like most conifers do. This could change the fire regime leading to only infrequent understory fires which is generally the same fire regime across the eastern us. On my property I am planting many different deciduous trees, especially nut trees, with the hope that they will eventually shade out the grass and shrubs under a closed forest canopy creating somewhat of a protection against fires. Another thing about deciduous forests is that they generally only burn in late fall or early spring when the leaves are dead and dry, there is no snow on the ground and the leaves have yet to decay from the summer heat. That could work very well here considering the dry season is during summer and early fall. During this time the leaves on the trees would still be green and the leaves on the ground from the previous fall will likely already be decayed and turned into soil. At least in theory this could help prevent fires on my property and if mirrored throughout the entire northwest could significantly reduce the number and severity of fires. This may be a good strategy for fire prevention in urban areas and small towns is to surround the area with dense deciduous forests.
