Think Globally; Act Locally

The above bumper sticker offers some good advise for everyday living but can it be applied to an ecological reserve? Everyone expects an ecological reserve to follow management programs for enhancing native species and ecosystems but what about bigger questions involving watersheds and global warming? We are not going to solve these problems on a few thousand acres but we can contribute some small amount and exemplify good stewardship.

Watersheds

Stream discharge, particularly in California, fluctuates, with huge storm flows in the wet season and minimal flow during the dry, hot season when water is most needed. Many human activities have exacerbated this trend by speeding runoff. What can an ecological reserve do to store more water? Dams retard flow but also generally disrupt ecosystems by destroying habitat, blocking migrations, and increasing evaporation. We need to work with nature to reduce runoff (increase temporary storage).The basic principle is to get as much rainfall as possible into the ground instead of into streams. Two things we can influence are soil compaction and ephemeral stream drainage. Within the ground, water travels much more slowly than it does on the surface (feet per day as opposed to feet per second).Traditional land use in our area involved pasturing cattle (and other livestock) as long as there was forage (often well into the dry season). Heavy bodies on small hooves compacted the soil, creating a “cow-pan” that retarded root penetration and forced water to drain over the surface, greatly speeding its journey to streams. We can reverse this by completely removing the livestock or by changing the grazing regime to more closely approximate natural migration patterns (flash grazing). Without the compaction, burrowing organisms and decomposing roots form tiny channels through the soil that water can follow.

In addition to compacting soil, livestock remove instream vegetation and crush streambanks, resulting in downcutting by small streams and rills. Swales became gullies that provide little habitat for the dense wetland vegetation that naturally follows drainages. Consequently runoff is carried efficiently to larger streams. Excluding livestock will help reverse this trend but adding cut brush or small check dams will speed the healing even more. The goal is to force water to flow around many small obstacles, slowing the flow so silt settles out. Wetland plants will establish themselves in that silt and further impede the flow. As the gullies fill, the runoff water is slowed and spread out giving it more contact time to soak into the ground. Less runoff reaches the main stream during rains and more is stored in the ground to recharge aquifers and enhance dry-season streamflow.

Traditionally ranch roads were formed simply by driving where possible and cutting roads to connect drivable areas. If any thought was given to drainage it was merely to get water off the road. Water followed tire tracks and road cuts, turning roads into tributaries, conveying rain that fell on their surfaces as well as intercepted ground water directly to streams. In addition to speeding transport of water to streams, roads became major contributors of silt both from their surfaces and from rapid down-cutting in rills whose flow was increased by road drainage.

Roads can be redesigned so that, rather than following the road, water flows off onto adjacent land where it can safely deposit silt as it spreads out and sinks into the ground. Roads must be diverted from fall lines and out-sloped. On unpaved roads, waterbars or rolling dips are needed at frequent intervals to prevent water from following tire tracks (see the HANDBOOK FOR FOREST AND RANCH ROADS).

 

Global Warming

What can be done locally to increase long-term carbon storage? In most grassland areas of California non-native annual grasses and forbs have replaced native, perennial grasses. These annuals grow rapidly during the wet season, producing mostly above-ground structures. They tie up carbon for a season then die to decompose and release the stored carbon back to the atmosphere. In contrast, perennial grasses tend to grow more slowly, producing large root masses that enable them to remain active far into the dry season. Even if the above-ground structures die back seasonally, the large root mass lives and stores carbon for many years. Roots that die contribute to soil humus, continuing to tie up carbon. Obviously we can increase carbon storage by restoring the native perennial grasses in grassland areas. This, however, has proved difficult. Established natives thrive and compete very effectively against the annual invaders but, because perennials tend to germinate and grow more slowly than annuals, they are difficult to establish. Starting seeds in a greenhouse and transplanting plants early in the wet season works well but is very time consuming. Burning an area then seeding it sometimes works; a fall burn after the annuals have sprouted seems most effective.

Wildfires release large amounts of CO2. Trees that are killed but not burned continue to release carbon as they decompose. However, in our fire-prone climate, fire prevention leads to fuel accumulation and eventually to hotter fires that kill more of the vegetation. Since large trees store more carbon than many smaller ones, a fire management plan that reduces fire intensity, preserving most large trees, provides the best carbon storage for wooded areas. Periodic controlled burns can, paradoxically, result in more carbon storage than produced by fire prevention.