Droughts (lack of rainfall) are a “natural disturbance” and when paired with hot temperatures can create the conditions for fires that kill or wound many trees.
Fires pave the way for changes in forest ecosystems like “ecological succession”. Forest succession occurs when trees die, other trees and plants take advantage of openings in the canopy, and with more sunlight, grow quickly to become the green space in the sky.
In Southeast Texas, the hottest, and sometimes driest part of the year, is usually July through September. This is often our seasonal drought time and when more natural and human started fires occur. However, fires can occur any time during the year in Southeast Texas.
A natural characteristic of native forests is diversity or heterogeneity in vegetation type and growth on the landscape. Topography and soil type exert their will when fires occur and can increase or decrease the effects of fire as can relative humidity.
Upland forests in Southeast Texas are usually dominated by pine trees (Loblolly, Shortleaf, and Longleaf Pines) which are more drought and fire tolerant because they have thicker bark and other more fire tolerant characteristics. However, even on uplands, ridges, and other raised topographic areas there are places where less fire tolerant vegetation exists due to natural fire barriers or breaks.
Natural fire barriers or breaks are those features on the landscape that reduce or eliminate the effects of fire on vegetation. Natural fire barriers or breaks do not work 100% of the time, but do allow less fire intolerant vegetation to grow on the landscape. Below is a list of some of these natural fire barriers or breaks.
1) Mesic and Hydric Soils – Mesic soils are intermediate in moisture (neither dry nor wet) and Hydric soils (wet) slow down or stop many fires. These soils usually are found on mid to lower slopes or floodplains. Some mesic soils occur on uplands and grow more hardwood trees with more hardwood leaves and litter which generally burn less readily than pine needles.
2) Downed Wood – Downed wood can burn and be turned to ash by a severe fire. Usually, however, only part of a downed tree is burned in most fires. Often vegetation that is found behind downed wood does not burn or burns with less intensity because downed wood reduces fire intensity due to its’ moisture content and can turns the direction of a fire away from fire intolerant vegetation.
3) Bluffs and Rocky Areas – There are not many rocky areas in Southeast Texas but those that do exist, and bluffs, act as natural fire barriers and breaks due to a reduction in fuel (vegetation) to burn and the change in topography.
4) Stream and River Floodplains, Wetlands, Lakes, and Ponds – These water bodies are hydric (wet) and have high humidity. They burn infrequently or not at all unless there is a severe drought. Intermittent and perennial streams and their floodplains burn less often than ephemeral streams because they retain more water longer.
5) Mid to Lower Slopes – Topography makes a difference about where fire will burn. Mid to lower slopes usually have a higher moisture content, more mesic soils which reduce fire intensity and area burned, grow more hardwood trees, and have higher relative humidity so fire frequency and intensity is usually less.
6) Hardwood Leaves and Leaf Litter – Hardwood leaves and leaf litter generally contain less of flammable oils or other chemicals than pine needles and do not burn as readily.
7) Seepage Areas and Other Groundwater Affected Areas – Groundwater affected areas, like seepage areas (baygalls, seepage creeks, etc.) are wet and thus do not burn or burn less intensely than areas where there’s no groundwater effects.
8) Shaded areas – Areas like ravines, have greater shade coverage and time spent shaded, more moisture in soils, more hardwood trees, more hardwood leaves and leaf litter, less wind, higher relative humidity, and burn less frequently and intensely.
9) Xeric (dry) Vegetation – Although it may seem counterintuitive, very, dry, sandy, upland areas, where fires burn, may serve as natural fire barriers or breaks. This is because they have little vegetation, due to their naturally dry soils and the effects of drought, so fires do not easily burn downslope toward other less fire tolerant vegetation due to a lack of fuel (vegetation) continuity.
Author: Brandt Mannchen