Wildland Resources Faculty Publications

Through use of repeat photography, archival research, and field observation to reconstruct landscape vegetation patterns and changes across a 120 year period in the upper Tintic Valley of central Utah, researchers found significant changes in landscape vegetation pattern over time, including change in pinyon-juniper woodland area. Previously reported massive woodland harvest associated with early mining, domestic and agricultural activities elsewhere in the Intermountain West also took place in Utah. The impact on woodland area of the agricultural "bull" fence alone was significant. More recent study area woodland expansion also occurred. Because intensive industrial activity associated with development of the Tintic Mining District occurred prior to the taking of the study's 1911 photographs, those photos failed to reflect presettlement, or even early settlement, vegetation conditions. Overall, results suggest that historical ecological studies must employ a range of overlapping methodologies to accurately interpret the nature and direction of landscape vegetation change. Such information is useful for managing regional ecosystems now and into the future.

The pre-Columbian mixed-growth form, composition, and structure of sagebrush steppes was mostly due to the highly variable semiarid climate and long fire-free intervals. The weak stability of this relatively complex vegetation was easily upset by excessive livestock grazing, especially in drought periods. After a few decades of uncontrolled livestock grazing, it was easy for introduced winter annuals, especially cheatgrass, to dominate the understory and alter the fire regime to larger, more frequent fires that occur earlier in the year. Accelerated soil erosion has caused many sites to lose the potential for management back toward native perennial dominance by controlling only livestock and fire. Major investments will probably be necessary to lengthen the current fire-free interval, as well as reduce the size of fires and their occurrence during late spring and early summer on large areas of cheatgrass dominance. Livestock could be used in some circumstances to help reverse the damage they did before grazing became regulated. Opportunities to apply genetic engineering to native plants and new herbicides to cheatgrass should also be explored before even more noxious biennials gain a major foothold.

A major goal in ecology is to make generalizable predictions of organism responses to environmental variation based on their traits. However, straightforward relationships between traits and fitness are rare and likely to vary with environmental context. Characterizing how traits mediate demographic responses to the environment may enhance the predictions of organism responses to global change. We synthesized 15 years of demographic data and species-level traits in a shortgrass steppe to determine whether the effects of leaf and root traits on growth and survival depended on seasonal water availability. We predicted that (1) species with drought-tolerant traits, such as lower leaf turgor loss point (TLP) and higher leaf and root dry matter content (LDMC and RDMC), would be more likely to survive and grow in drier years due to higher wilting resistance, (2) these traits would not predict fitness in wetter years, and (3) traits that more directly measure physiological mechanisms of water use such as TLP would best predict demographic responses. We found that graminoids with more negative TLP and higher LDMC and RDMC had higher survival rates in drier years. Forbs demonstrated similar yet more variable responses. Graminoids grew larger in wetter years, regardless of traits. However, in both wet and dry years, graminoids with more negative TLP and higher LDMC and RDMC grew larger than less negative TLP and low LDMC and RDMC species. Traits significantly mediated the impact of drought on survival, but not growth, suggesting that survival could be a stronger driver of species' drought response in this system. TLP predicted survival in drier years, but easier to measure LDMC and RDMC were equal or better predictors. These results advance our understanding of the mechanisms by which drought drives population dynamics, and show that abiotic context determines how traits drive fitness.

The savannas of the Kenya-Tanzania borderland cover >100,000 km2 and is one of the most important regions globally for biodiversity conservation, particularly large mammals. The region also supports >1 million pastoralists and their livestock. In these systems, resources for both large mammals and pastoralists are highly variable in space and time and thus require connected landscapes. However, ongoing fragmentation of (semi-)natural vegetation by smallholder fencing and expansion of agriculture threatens this social-ecological system. Spatial data on fences and agricultural expansion are localized and dispersed among data owners and databases. Here, we synthesized data from several research groups and conservation NGOs and present the first release of the Landscape Dynamics (landDX) spatial-temporal database, covering ~30,000 km2 of southern Kenya. The data includes 31,000 livestock enclosures, nearly 40,000 kilometres of fencing, and 1,500 km2 of agricultural land. We provide caveats and interpretation of the different methodologies used. These data are useful to answer fundamental ecological questions, to quantify the rate of change of ecosystem function and wildlife populations, for conservation and livestock management, and for local and governmental spatial planning.

Eutrophication is a widespread environmental change that usually reduces the stabilizing effect of plant diversity on productivity in local communities. Whether this effect is scale dependent remains to be elucidated. Here, we determine the relationship between plant diversity and temporal stability of productivity for 243 plant communities from 42 grasslands across the globe and quantify the effect of chronic fertilization on these relationships. Unfertilized local communities with more plant species exhibit greater asynchronous dynamics among species in response to natural environmental fluctuations, resulting in greater local stability (alpha stability). Moreover, neighborhood communities that have greater spatial variation in plant species composition within sites (higher beta diversity) have greater spatial asynchrony of productivity among communities, resulting in greater stability at the larger scale (gamma stability). Importantly, fertilization consistently weakens the contribution of plant diversity to both of these stabilizing mechanisms, thus diminishing the positive effect of biodiversity on stability at differing spatial scales. Our findings suggest that preserving grassland functional stability requires conservation of plant diversity within and among ecological communities.