Tree diversity promotes growth of late successional species despite increasing deer damage in a restored forest

Abstract

The role of tree diversity in restored forests and its impact on key ecological processes like growth and resistance to herbivory has become increasingly important. We analyzed height growth and white-tailed deer Odocoileus virginianus browsing damage to saplings of 16 broadleaved tree species in a large-scale (13 ha) reforestation experiment in Maryland, USA, where we manipulated tree diversity in 70 1,225-m 2 plots. After four growing seasons, higher plot-level tree richness led to increased deer browsing damage (i.e., associational susceptibility). Despite increased deer damage to saplings in mixed plots, tree richness had no overall effect on sapling height growth. However, diversity-height relationships were related to species functional traits. Light demanding species with large leaves and faster growth rates had reduced heights in mixtures, whereas shade-tolerant, slower-growing species generally had either increased or unchanged height growth in diverse tree communities, likely related to increased canopy closure in mixtures relative to monocultures. We show that tree diversity can improve growth of late successional species despite exacerbated mammalian herbivore damage. By facilitating the establishment of species with a range of life-history strategies, increased tree diversity may enhance ecosystem multi-functionality in the early stages of forest restoration.

Species richness, functional traits and climate interactively affect tree survival in a large forest biodiversity experiment

“…The manifold interactions between the effects of stand diversity and age, functional traits and identity of species and time‐dependent covariates on annual survival rates indicate that generalizations for this demographic variable are perhaps more difficult to be obtained than for ecosystem functions such as biomass production. Thus, even though the species traits affecting survival are suggestive for successional (Devaney et al, 2020; Tilman, 1988) or plant‐economic strategies (Wright et al, 2004), none of them seems to present a consistent advantage across environmental fluctuations between years. While the differential responses to temporal climatic fluctuations between years increase coexistence and community stability due to buffering and performance‐enhancing effects of biodiversity (Schnabel et al, 2021; Yachi & Loreau, 1999), reduced inter‐specific relative to intra‐specific competition in diverse stands may increase coexistence due to complementarity effects within years (Tilman et al, 2014).…”

Mixture effect on radial stem and shoot growth differs and varies with temperature

“…Thirdly, the effect of facilitation would depend on the stress tolerance of the species considered. Examples of facilitation under intermediate conditions exist in forest ecosystems, mostly on seedlings: positive effect of shading in seedlings in temperate forests (Devaney et al, 2020;Simard et al, 2012) and nurse shrubs and tree seedlings at intermediate drought stress (Callaway, 1992;Guignabert et al, 2020). More recently, a theoretical framework has been proposed linking complementary resource use and stress gradient (Forrester, 2014) suggesting that the positive effect of complementary use of light resources is only possible when the water or nutrient resource is sufficient.…”

Positive tree diversity effects on arboreal spider abundance are tied to canopy cover in a forest experiment

“…In 2013, the site was reforested from corn agriculture into a classic BEF design with 75 plots measuring 35 × 35 m (Figure 1A) planted with 255 trees each, spaced 2.5 m apart. Diversity manipulations of 1, 4, or 12 tree species were drawn from 16 common species native to Maryland (Figure 1B; for more site description, see Griffin et al, 2019 and Devaney et al, 2020). This is a young successional forest, with dynamic changes in tree size.…”

“…description, see Griffin et al, 2019 andDevaney et al, 2020). This is a young successional forest, with dynamic changes in tree size.…”