I mentioned on Twitter that more trees had failed to leaf out this spring, victims of the long drought which not only did not provide them enough water to survive, but prevented us from having any supplemental water to give them. Someone suggested what seemed reasonable–why not plant trees from the next climate zone (or two) to the south of us. I realized then that the traditional “planting zone/climate zone” concept had taken hold to such an extent that the complexity of keeping anything alive through a rapid change of climate wasn’t being talked about.
Let me go back 13 years, to our original plans for the 80 acres. Wildlife management, and prairie restoration on the overgrazed, juniper-invaded former grassland portion. Retention and enrichment, by interplanting natives, of the two natural woodlands–the riparian near the creek (which then flowed, and had flowed, every year) and the rock-ridge “dry woods” of native brush and some trees, up on the rocky knoll. The plan worked well for the first five or six years, including dry years. Reintroduction of native grasses, forbs, shrubs and trees seemed to be working; ground cover increased, as did the number of species of wildlife. We did include plantings leaning toward the land south and west of us by several hundred miles, knowing that it twas lkely to become dryer and hotter over time.
But between years six and eight, we realized that climate change was overtaking us faster than anticipated–and by year ten, we were dealing with a regression in progress. Natives to this region, some of which had survived the years of bad management without any help…were dying. The creek no longer flowed most of the year (it now does not flow at all…has not had normal flow (and only a couple of flash-flood pulses) for over two years.) Both native plants and native wildlife diminished–our joy in seeing increasing diversity in the first years of good management was gone, and the goals were no longer included “prairie restoration” since it became clear that the old natives could not survive. Our garden could not survive, as night-time temperatures climbed higher every summer (tomatoes, for example, will not set and mature when nighttime temps are too high.) The small town we live in has wells, but the wells aren’t producing as they should; we’ve been on water restriction now for several years. Reservoirs in the area are dropping, many below 50% of capacity. The population (and demand for water) continues to grow.
“Climate zones/planting zones” are based purely on the length of the frost-free growing season. That works for most (not all) garden plants, but it’s not the only determinant for native plant life. Every plant has a preferred habitat: maximum and minimum temperatures, amount and distribution of precipitation, humidity (impacts plant’s water management), maximum tolerable wind, soil type (including both the structure, from tight clay to gravel, and the pH–whether acidic or basic), soil depth, soil temperature (some seeds germinate only in hot soil; others only in cool soil), the presence or absence of specific soil nutrients and microbiota, a specific day-length cycle (great difference in daylength through the season, or less to no daylength change.)
Plants differ in how much leeway they can handle in each of these parameters. I remember my Native Plants prof fulminating against those who planted azaleas (acid-loving) as landscape plants in Central Texas…which has a basic soil over limestone. The university put them in raised beds and treated heavily with iron and soil acidifiers…but eventually the azaleas’ roots reached the limestone below….and they died, and had to be replaced. Some plants can handle moderately acidic soils to moderately alkaline, basic soils…they’re generalists. But not all.
In a small garden or yard, creating a fairly neutral environment suited to all the generalists and some of the pickier plants may be possible. If the gardener has access to supplements, to ample water, to climate altering enclosures (a greenhouse for some, shade cover for others.) We gardened very successfully in San Antonio (about 130 miles south of us) by digging out heavy black Houston Clay and making our own soil by mixing it with sharp sand, composted horse and chicken manure, bedding from horse stalls, leaves, etc. It was intensive gardening, and we grew several dozen varieties of vegetables.
But when dealing with open land, that’s not possible, especially in drought conditions. What, then, can we do, when the predictions for change outpace the possible interventions? When the change seems to be outpacing the predictions? Just picking plants from straight south of us won’t work, because of the soil differences. I grew up 400 miles south of where I live now; I know the original botany of that area well. The soil was a light sandy loam, very deep, alluvial in origin, from repeated floods of the Rio Grande. Native vegetation had two basic forms: along the resacas and the river itself, taller riparian woods; away from the permanent water, “brush” and grassy openings. The brush consisted of low woody trees, woody understory, cactus, and almost everything had thorns. As you moved away from water and onto higher ground, the brush lowered–sometimes less than waist high. It’s notable that it’s closer to the Gulf, and thus more likely to pick up both humid air and hurricane rains when hurricanes occur than here–several hundred miles inland. In northern Mexico, the same kind of semi-desert brush country (modified by ag, but that’s its nature) exists, with more forest (where it hasn’t been logged) at higher elevations in the mountains that start about there.
Here, the soil is thinner, with a higher pH (more alkaline) and was formed under prairie and over limestone: it’s a dense dark clay, where there is soil left. It’s a completely different soil from that 400-500 miles south. Its soil microbiota are different. Generalist brush plants (mesquite for instance, and huisache) will grow here, but neither is a shade tree in the usual sense, and both support a different kind of wildlife from the local live oak, cedar elm, ash, pecan trees, with the understory of viburnum, roughleaf dogwood, and other plants, all with a lot of berries both migratory and resident birds enjoy. Our upland brush is different too: Ashe juniper, cedar elm, occasional live oak, with elbowbush, Mexican buckeye, for understory woody plants. Wildlife here depends on these familiar plants for food and habitat.
Loss of frequent standing and running water on the land has already meant the loss of species that were previously increasing under our management of water conservation and relief from livestock grazing. This included fish, most amphibians (some still live in the large backyard water garden), and invertebrates such as crayfish. We had been increasing the number of species of odonates…now they’ve reduced, as the breeding habitat has disappeared. Despite having four wildlife watering stations, we have fewer birds (both in numbers and species) as habitat degrades with the death of favorite nest trees, and the gradual loss of species of food plants in every category, from lichens to trees.
We did attempt to bring in natives from a similar soil type but 100+ miles to the SW (southern part of the Edwards Plateau) but those trees, despite supplementing water as long as we could, finally died. Young trees are not as drought tolerant as older ones, up to a point. South of there…are no trees that will live here without adequate water we don’t have, or altitude and rainfall we don’t have.
We have quit planting trees. We are still seeding grass, but not planting root divisions of the taller grasses (in part because the “grass garden” in which we nurtured and propagated tall grasses native to this area and scavenged from construction sites is no longer producing enough; in part because the ones that had taken hold and seemed thriving are now dying back. Instead, we’re seeding only short-grass varieties and will be adding more. We’re looking at adding forbs from more western, dryer areas as well. We’ve increased the storage capacity at the rain barns for wildlife water–but there’s no way to collect enough rainwater to water everything. We hope to save a few of the household trees, simply for the cooling effect of the shade–but water restrictions are making that a very slim possibility.
It’s a brown spring around here. Looking out at the land, it might be winter, all grays and browns, but for a few trees leafing out, some grass in ditches where the soil stayed damp longer. And we’re fighting to keep anything alive, and water available for the spring migrant birds….and expecting the worst again this summer.